Control of water pollution from cropland

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Control of
WATER POLLUTION
from cropland

Volurnel- An overview

COASTAL 2ONE

INFORMATION CENM

TD
223
.A1
C6
197 6
V-2

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Control of

WATER POLLUTION
from crop-land

Volume][[ -An overview

Authored by a Committee of Scientists of Agricultural Research Service, USDA.

B. A. Stewart, Bushland, Texas ..................................... Coordinator
D. A. Woolhiser, Fort Collins, Colorado ........................... Hydrology
W. H. Wischmeier, Lafayette, Indiana ............................. Erosion
J. H. Caro, Beltsville, Maryland .................................. Pesticides
M. H. Frere, Chickasha, Oklahoma ............................... Nutrients

Appendix C prepared by K. F. Alt, Economic Research Service, USDA.
Prepared under an Interagency Agreement with the Office of Research and Development,
EPA. Project Officers were L. A. Mulkey, ORD, EPA, and C. W. Carlson, ARS, USDA.

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JUNE 1976

Office of Research and Development
Agricultural Research Service
U.S. Department of Agriculture Environmental Protection Agency

CONTENTS

chap,eE. Page

1. INTRODUCTION
B. A. Stewart and D. A. Woolhiser .......................................... 1

2. HYDROL%f,'OGIC ASPECTS OF NONPOINT POLLUTION
D. A. Woolhiser ....................................................... 7
Fundamentals of Hydrology ............................................ 7
Components of the Hydrologic Cycle ...................................... 10
Agricultural Chemical and Sediment Transport Models ........................... 17
Agricultural Practices to Control Direct Runoff ............................... 18
Research Needs ..................................................... 23
Literature Cited ..................................................... 24

3. CROPLAND EROSION AND SEDIMENTATION
W. H. Wischmeier ..................................................... 31
Sediment Sources and Quantities ......................................... 31
Cropland Erosion ................................................... 33
Erosion Factors .................................................... 36
Erosion Control Methods .............................................. 41
Sediment Delivery Ratios .............................................. 47
Tolerance Limits .................................................... 48
Research Needs ..................................................... 50
Literature Cited .................................................... 53

4. NUTRIENT ASPECTS OF POLLUTION FROM CROPLAND
M. H. Frere ......................................................... 59
The Problems ...................................................... 59
Sources of Nutrients ................................................. 61
transport from Cropland .................................. 68
Effect of Control Practices ............................................. 73
Research Needs .................................................... 81
Literature Cited ..................................................... 82

5. PEST:CIDES IN AGRICULTURAL RUNOFF
J. H. Caro .......................................................... 91
Extent and Trends in Use of Agricultural Pesticides ............................. 92
Dissipation of Pesticides from Treated Lands ................................. 94
Persistence and Fate of Pesticide Residues in the Aquatic Environment ................ 97
Characteristic Levels of Pesticides in the Aquatic Ecosystem ....................... 98
Impact of Pesticides on the Aquatic Environment .............................. 103
Removal of Pesticides from the Aquatic Environment ........................... 105
Practices for Reducing Entry of Pesticides into the Aquatic Environment ............... 106
Research Needs .................................................... 106
Literature Cited .................................................... 112

Page

6. INTERDISCIPLINARY RESEARCH NEEDS
B. A. Stewart ........................................................ 121

Appendix

A. SIMULATION OF DAILY POTENTIAL DIRECT RUNOFF ............................. 123
B. SIMULATION OF POTENTIAL PERCOLATION AND NITRATE LEACHING ................ 149
C. ECONOMIC ANALYSIS METHODOLOGY ........................................ 177

Control of

WATER POLLUTION
from cropland

Volume 11--An overview

CHAPTER I

INTRODUCTION

B. A. Stewart and D. A. Woolhiser

Agricultural technology is one of the real strengths of ing the nature and extent of nonpoint sources of
the United States. Although the population has in- pollutants. 'Ibis two-volume document on control of
creased steadily, food and fiber production has met the potential water pollutants from cropland was written by
domestic needs and has also provided substantial scientists of the U.S. Department of Agriculture in
amounts for export, which is so important to the U.S. response to this provision of the Act and at the request
trade balance. Fertilizers and pesticides have played a of the Environmental Protection Agency. Volume I is a
major role in this accomplishment because the acreage of User's Manual for guideline development. Here in Vol-
cropland has changed little in the last 45 years-agricul- ume 11 we will review some of the basic principles on
tural chemicals and other technological inputs have been which control of specific pollutants is founded, provide
substituted for land. supplementary information, and present some of the
The marvels of agricultural technology have not gone documentation used in Volume 1.
unchallenged. Much of the blame for polluted streams Management decisions relating to the control of
and lakes is often placed on agricultural activities. Some pollution from cropland involve a careful weighing of
groups and individuals have even called for a total ban potential costs and benefits. Some of the factors
on the use of agricultural chemicals. At the other affecting these decisions can be visualized by considering
extreme, there are those who claim that the use of the schematic drawing of an agricultural system in
chemicals has not had any adverse effect on the Figure 1. The system itself is arbitrary and could consist
environment and that there should be no restrictions on of a field, a state, or a river basin. Inputs to and outputs
or control of their use. from the system can be identified and inputs can be
The ultimate decision as to whether agriculture is classified as controlled or uncontrolled. Precipitation
contributing to pollution of particular water bodies to and solar radiation are uncontrolled and contribute to
such an extent that active control measures are required the stochastic nature of the outputs. The farmer has the
rests with State or local authorities. To assist these ultimate control over the controllable inputs, subject to
officials in reaching this decision and in choosing physical and legal constraints. The outputs can be
appropriate controls, the Federal Water Pollution Con- changed by varying the inputs or the system itself within
trol Act Amendments of 1972, Public Law No. 92-500, certain constraints imposed by physical laws.
specify that the Administrator of the Environmental Most people would agree that the system should be so
Protection Agency shall, in cooperation with other modified and that the inputs to the system should be
agencies, provide guidelines for identifying and evaluat- controlled at a level that maximizes the net benefits to

society attributable to the system. Obviously the modifi- costs include those normally borne by the farmer. The
cations and controls chosen depend strongly on the benefit from the sale of the crop will vary annually as a
concept of social welfare and must include many costs result of yield variability and the demand of society for
and benefits not normally accounted for by a land the particular crop, expressed as the price. Conceptually
manager. the management decision problem is not difficult, but
The costs and benefits of the agricultural use of land practically it is formidable. First there is the question of
depend on the weather and other elements that may be uncertainty-we do not know the long-term effects of
considered as stochastic processes; therefore, the costs low, intermittent concentrations of many chemicals on
and benefits associated with the agricultural use of the living organisms, including man. Therefore, we cannot
land may themselves be considered as stochastic estimate the cost attributable to the specific transport of
processes. Consider the four sample functions shown in a given chemical. Since this, among many other uncer-
Figure 2. X1(t) represents the amount of daily precipi- tainties, prevents the selection of control practices and
tation; C, (t) represents the amount of a chemical applied institutional mechanisms that maximize net social bene-
to a field and is a stochastic process because the time of fits, we may wish to state the objective in physical
application depends on precipitation, stage of crop terms. As an example, one could select those control
growth and other factors associated with the particular practices which maintained the average chemical concen-
chemical; Y, (t) symbolizes daily surface runoff which tration below some threshold value for a given percent
may transport the chemical to a stream or lake; Y2 (t) of the time. If social costs associated with the presence
represents the amount of chemical transported to of this chemical in a stream exceeded the benefits
surface water; and B(t) represents the benefit process attributable to it, this procedure would at least lead to
(costs are negative benefits). Social costs include those an improved situation. However, as will be shown in
incurred when surface runoff occurs shortly after a subsequent chapters, our technology in predicting the
chemical is applied and those due to sediment. Other effects of changes in inputs and in the system itself on

Uncontrolled Inputs Controlled Inputs

Precipitation Seed
Solar Radiation Ferti I izer
Energy
Pesticides
Management
Capital
System Labor
(Field, Region)

Outputs

Crop Production
Water
Sediment
Nutrients
Pesticides

Figure l.-Agricultural production system.

Precipitation

t
Chemical
Appl ica tion

Surface
>7 Runoff

Chemical Transport
>Ell to Stream

Benefits and Costs

b b d

a c

Figure 2.-Sample functions of hydrologic processes and social costs and returns for agricultural system.
a: planting cost to farmer; b: cost of applying chemical; c: social cost when chemical is transported to
stream; d: harvest cost; e: return from sale of crop.

concentrations of potential pollutants in surface waters Table 1. Predominant land use for nonfederal rural land in the
is not developed well enough to make this approach contiguous 48 states (USDA Statistical Bulletin No. 46 1)
feasible. As a last resort, we can use direct runoff,
percolation and erosion as surrogate variables with the A cres
assumption that a change in any of these variables will CROPLAND:
affect water quality. It must be recognized that reduc- Row crops ....................... 160,041,000
Close-grown crops and fallo%N ............ 132,620.000
tion of direct runoff or deep percolation may adversely Forage crops ...................... 77,629,000
affect water quality in some instances and, therefore Conservation use ................... 39,026,000
Temporary idle .................... 11,235,000
may create water quality and quantity problems for Orchards, vineyards, and bush fruits ...... 5,060,000
downstream water users who depend on runoff from Open land formerly cropped ........... 11,592,000
agricultural lands as a water supply. 437,203,000
Before dealing with specific potential pollutants, it is PASTURE AND RANGE:
important to know something about the land resources Pastureland ...................... 101,061,000
of the U.S. because this has a significant bearing on the Rangeland ....................... 379,929,000
use of agricultural chemicals. Only the land in the _T 8 0.9 9-0, 0 0 0
contiguous 48 states will be discussed, since there is so FOREST LAND:
little cropland in Alaska and Hawaii. Commercial ...................... 396,078,000
The contiguous 48 states contain 1,899,322,000 acres Noncommercial .................... 62,860,000
of land. The nonfederal rural land comprises 458.938,000
1,43 1,930,000 acres, or 75 percent of the total. Tile use OTHER LAND:
of this rural land is nearly equally divided between In faTIIIS ........................ 27,779,000
cropland, pasture and range, and forest land (Table 1). A Not in farms ...................... 27,020,000
land capability classification system' has been developed 54,799,000
by the U.S. Department of Agriculture and a summary
of the amounts of various classes of soils and their use is
given in Figure 3. Class I soils are nearly level, have a low Soils in Classes V, VI, VII, and Vill are limited in
erosion hazard, and are suited to a wide range of plants. their use and are generally considered unsuitable for
They are deep, have high permeability and water-holding cultivation. Class V soils have little or no erosion hazard
capacity, are well drained, and are fairly well supplied but have other limitations that are impractical to
with plant nutrients or are highly responsive to fertili- remove. Examples are bottorn lands subject to frequent
zers. Soils in Class It have some limitations that reduce overflow, stony soils, and ponded soils where drainage is
the choice of plants or require moderate conservation unfeasible. Class VI soils are usually limited to pasture,
practices. They often require special soil-conserving range, forest, or wildlife habitat. However, some Class VI
cropping systems, soil conservation practices, water- sods can be used for common crops with careful
control devices, or tillage methods when used for management. Some of the soils are also adapted to
cultivated crops. Class 11 soils usually have gentle slopes special crops such as sodded orchards, blueberries, and
and are moderately susceptible to wind and water similar crops. Class VII soils are not suited for cropland,
erosion. and Class Vill soils are not only unsuited for cropland,
Class III soils are usually found on moderately steep but have limitations so severe that they are restricted
slopes and are more susceptible to water and wind primarily to recreation, wildlife habitat, water supply,
erosion than soils in Class 11. They can be used for and esthetic uses.
cultivated crops but require highly effective conservation The erosion hazard of cropland increases sharply
practices that may be difficult to apply and maintain if from Class I through Class IV soils. Therefore, the larger
erosion is controlled. Class IV soils are also suited for the cropland acreage on Class III and IV soils, the greater
cropland, but they require careful management and are the hazard of erosion. Also, since sediment is a principal
often well suited for only two or three common crops. transport mechanism for agricultural chemicals, tile
They are usually found on steep slopes and are highly potential for their loss is much greater on these soils. For
susceptible to wind and water erosion. example, it is estimated that from one-third to one-half
of America's agricultural production depends on fertil-
izer use. Therefore, if fertilizer use were eliminated,
'National Inventory of Soil and Water Conservation Needs, cropland acreage would have to be greatly expanded.
1967. U.S. Department of Agriculture Statistical Bulletin No. Figure 3 shows that any large increase in cropland would
46 1, January 197 1. have to come from Class III and IV soils. These soils are

300 CROPLAND

PASTURE
& RANGE
250'

FOREST
fli

Z 200,r OTHER
0

X-

150

V
V V V"@ VM
A ND CLASS

Figure 3.-Use of various classes of land in the 48 contiguous states (based on data from USDA Statistical Bulletin No. 461).

less desirable, not only because they are more erodible, ever, it is possible to use them safely on these soils if a
but because they are lower in fertility and yield higher level of management is practiced to control
considerably less than Class I and K soils, particularly sediment and associated chemical losses. The treatments
when fertilizers are not used. necessary to reduce losses are given in Volume 1.
Unless sediment is controlled at a given level, the loss How much agricultural chemicals are affecting the
of agricultural chemicals from equal treatments will environment is certainly noi clear. However, it appears
usually increase as the soil class number increases. 7his that sediment, nutrient, and pesticide losses can be
suggests that one approach to control water pollution controlled at an acceptable level by the selection of
from cropland is to concentrate crops to the fullest proper management systems. The challenge, therefore, is
extent possible on Class : and 11 soils. These soils are to develop appropriate assessment techniques and insti-
naturally more productive, more responsive to fertilizers tutional mechanisms so that controls are used only when
because of higher water-holding capacities, and easier to needed. Also, recommending control practices for a large
control with respect to sediment losses. in all likelihood, area is extremely difficult because the practices are often
therefore, a high level of food and fiber production with site-specific. The concepts presented in Volume I and
the least impact on the environment would result from the material presented in the following chapters must,
7 7

using fertilizers and pesticides on the better lands where therefore, be considered only as general aids to the
their effectiveness is high and their loss is small. The use decision-making process. Control recommendations for
of chemicals on the more erosive soils presents a specific sites must be developed by specialists within the
substantially greater threat to the environment. :How- area.

CC":il APT E R 2

ASPHO'L'S OF NONPOINT POLLUTION

D. A. Woolhiser

Water, running over the land surface or percolating Only those aspects of the hydrologic cycle that are
through the soil mantle to eventually appear as ground- important in nonpoint pollution will be emphasized in
water runoff, is a potential carrier of pesticides, nutri- this report. Readers interested in a more comprehensive
ents and sediment to streams and lakes. Any discussion discussion of hydrology are referred to several texts (23,
of nonpoint water pollution from agricultural sources 32, 64, 115). Although results of experimental investi-
necessarily involves hydrology because water is the gations of the effects of land use and treatment on
primary transport medium. runoff from agricultural lands in the Urdted States were
In this chapter we will consider some hydrologic reported as early as 1927 (84), only recent experimental
fundamentals, including basic physical principles and a work will be considered here because dramatic changes
brief discussion of the stochastic nature of hydrologic in agricultural practices have introduced time trends in
processes. An understanding of the stochastic nature of the amount of direct runoff from cropland (114).
hydrologic processes is important because it affects the To understand how nonpoint pollutants move from
interpretation of experimental data. Components of the fields to surface waters, we must first consider the
hydrologic cycle will be described to illustrate the physical form and placement of agricultural chemicals,
physical basis for modifying surface runoff by agro- including nutrients and manures. Then we must consider
nomic and engineering practices. These components have the various paths they must follow and the conditions
been aggregated into fairly general mathematical models (such as temperature, oxygen status, biological activity)
with the objective of describing agricultural chemical they may encounter from field to stream or lake. Form
transport. Finally, documentation is provided for most and placement of the potential pollutants are considered
of the 18 direct runoff control practices presented in in subsequent chapters; in this chapter, we will concen-
Section 4.2 of Volume 1. trate on the pathways.

OF HYDROLOGY

3@," J@-Vn@-Z'@av If we consider the sector labeled "surface disposition
of precipitation -all forms" in Figure 1, applied to an
Two basic physical principles governing the amount arbitrary volume of soil with surface area, A, and depth,
and distribution of water on the earth are those of mass d, as shown in Figure 2, we can write the conservation
conservation and energy conservation. These principles, equation for some arbitrary period of time, z_\t:
along with several empirical relationships, form the basis
for most mathematical descriptions of hydrologic phe- P+W=Q s + QB + z@,D +,nS + U + E , (1)
nomena.
The principle of mass conservation is frequently where:
illustrated by the hydrologic cycle or by the water P = precipitation received on the area, A
budget for an arbitrary volume of soil. Horton's (52) W = water imported as a result of man's activities
qualitative representation of the hydrologic cycle, Figure QS = net surface runoff (surface runoff leaving A
1, is useful for introducing some hydrologic terms and less surface runoff entering A)
expressing the concept that the mass of water on earth is QB = net lateral outflow (may include ground
assumed to be constant. water flow or unsaturated flow)

Atomospheric Moisture in Transportation and Storage, clouds, Atmospheric vapor
Precipitation, Rain, Hail,Sleet, Snow Dew and frost Evaporation of Precipitation
Precipitation Intercepted and Evaporated from Trees and Vegetation Evaporation from the Ocean
Soils Precipitation Reaching Ground Surface,, Temporarily Stored onSurface Surface Runoff into Streams
Outflow from Streams Ocean Storage
Transpiration Evaporation
Groundwater Supply to Vegetation
Surface Disposition of Precipitation- All Forms

Figure l.-The hydrologic cycle-a qualitative representation [Horton (52)].

increase in surface storage (depression stor- where:
age and detention storage) R s = flux density of total short-wave radiation at
= increase in soil water storage the ground surface
U = net vertical outflow through soil or rock p = albedo of the ground surface (fraction of
E = evaporation including evaporation from incoming short-wave radiation that is re-
plants (transpiration). flected)
R L = net flux density of long-wave radiation
All dimensions are in appropriate depth units. The G = heat flux density into the ground
total water yield for this area, both surface and H = sensible heat transfer into the atmosphere
subsurface, is the difference between the total input of L = latent heat of vaporization of water
precipitation and imported water, and evaporation, E = evaporation rate
assuming changes in storage are insignificant. Each of
these components will be discussed in more detail in the Changes in heat storage in the vegetation and the heat
next section. used in photosynthesis have been ignored in Equation
The amount of evaporation is controlled by the (2). They would be about 1% of R The terms in
amount of energy available at the layer of soil and air in
which plants grow. A conservation of energy equation Equation (2) are in units of heat energy per unit area per
may be written at this interface, expressing the relation: unit time. The magnitude of the terms in Equation (2)
Net rate of incoming energy per unit area = net rate may vary substantially. If the soil surface is wet or
of outgoing energy per unit area covered by actively transpiring vegetation, most of the
available solar energy may be used to evaporate water. If
Rs(l - p) = R L +G + H + LE (2) the soil surface is dry, most of the incoming energy may
be used to heat the air.

Equations (1) and (2) are linked by the evaporation cannot predict with certainty how much rain will fall
term, E. The magnitude of E in Equation (1) is tomorrow. These series can be viewed as sample func-
effectively limited by the amount of heat energy tions of stochastic processes. A stochastic process may
delivered to the surface A. be informally defined as a process developing in time in
a manner controlled by probabilistic laws (81). Many
chance mechanisms are important in agriculture. Precip-
Stochastic Nature of Hydrologic Processes itation is perhaps the most important, but plowing,
planting and harvesting dates, and fertilizer and pesticide
A set of daily precipitation amounts on a particular application dates are certainly not deterministic.
field, arranged chronologically, is an example of a time To analyze a time series, one must first assume a
series. Other examples include the daily direct runoff mathematical model for the stochastic process which is
from a field, the daily amount of water percolating completely specified except for parameter values that
below the depth d, or any of the terms in Equations (1) can be estimated on the basis of an observed sample.
or (2) for an arbitrary period of time. An essential When the parameter values have been estimated, one can
feature of these time series or processes is that they are obtain certain probability expressions that may be
unpredictable in a deterministic sense. That is, we valuable in decision making. For example, what is the

P E

Z@ D A _QS

6S Q13
A

Figure 2.-Control volume for water balance.

probability that the concentration of some substance in Another important concept is that of stationarity. A
runoff from a field will exceed a certain level for 24 stationary process is one where the chance mechanism
hours or more? In an ideal situation, our stochastic does not change with time. If we consider the process of
models would be constructed in accordance with Equa- surface runoff from a field in continuous corn, we can
tions (1) and (2) so that one might see how a change in see that it is not stationary. Not only are there periodic
land management could affect the probability statement. changes within a year caused by seasonal phenomena but
We cannot construct such ideal models. However, the also there are long-term trends introduced by changes in
stochastic nature of hydrologic phenomena must be agricultural technology such as new tillage implements,
appreciated because, if a substance is applied on the new crop varieties and increased fertilizer use. Therefore,
land, we cannot guarantee that it will never be trans- one cannot use long time series to estimate parameters
ported to a stream. The probability of such transport because the parameters are changing with time.
happening in a particular year may become infinitesi-
mally small, however.

COMPONENTS OF THE HYDROLOGIC CYCLE

In this section we will describe individual components Although several have attempted to develop a mathe-
of the hydrologic cycle and review some of the matical description of interception based on physical
mathematical models that have been proposed or used to reasoning (51, 63), the models have been rather crude.
describe these elements. The discussions will not be Many mathematical watershed models do not include an
comprehensive but will consider those aspects deemed explicit component for interception (27, 50). Crawford
most significant for chemical transport or for reducing and Linsley (26) combine interception and depression
surface runoff. storage into a single lumped storage with depletion by
evaporation and transfer to a lower zone storage.
Interception Boughton's model (10) and the Tennessee Valley Au-
thority model (110) assume that precipitation will
When rain begins, drops strike plant leaves and stems accumulate in interception storage until a threshold or
and are retained on these surfaces by the forces of capacity value is reached. The TVA model uses capa-
adhesion and cohesion until a sufficiently thick film of cities for forested watersheds of 0.05 inch in winter and
water accumulates that gravitation overcomes these 0.25 inch in summer. Saxton et al. (95) used a storage
forces. If rain continues, the storage on an individual leaf amount of 0.10 inch for agricultural crops and showed
will become nearly constant, with as much water falling that evaporation from this source can be several inches
from the leaf as falls upon it. Water will also be lost from per year in a semi-humid climate.
the film on vegetation by evaporation. There is some Zinke (119) concluded:
disagreement as to whether this evaporation is a net loss "A survey of the data in the literature indicates
insofar as the water balance of a volume of soil is interception storage amounts for rain of from 0.25 mm
concerned (119). If transpiration is limited by the to 9.14 mm (0.01 to 0.36 in.) and a similar range for
energy available, evaporation from the water stored on snow, 0.25 mm to 7.62 mm (0.01 to 0.30 in.).
leaves is essentially equal to the amount of water that The storages indicate that one would not be greatly in
would be lost by transpiration unless the albedo of wet error to estimate about 1.3 mm (0.05 in.) storage
vegetation is less than that for dry vegetation. If capacities for rain for most grasses, shrubs and trees; and
transpiration were limited by soil water content, how- 3.8 mm (0. 15 in.) for snow for trees."
ever, the evaporation from a water film would be greater Jones (58) concluded that "a consistent difference in
and part of it could be considered as a net loss. Water storage capacity for trees, crops, and grass of various
evaporated from mulch, dead leaves, stems or trunks heights was not evident."
could be considered a net loss if energy were not From this brief review, interception does not appear
limiting. Rain intercepted by the canopy may subse- to have an important influence on runoff or deep
quently reach the ground by dripping from the leaves or percolation from fields. However, an increase in inter-
flowing down the stem. If sternflow is significant, it can ception is partly responsible for the reduction in runoff
produce substantial differences in soil-water content caused by conversion from clean-tilled crops to pasture
over rather small distances (65). or meadow.

Depression Storage dom roughness"of soil surface microtopography de-
scribed by Burwell and others (15, 16) might be an
After interception storage has been filled and the adaptable measure of the depression storage.
infiltration capacity of the soil is exceeded so that all or Although manipulation of depression storage is an
part of the soil surface is saturated, water will accumu- obvious method of affecting surface runoff, the amounts
late in surface depressions. Water stored in depressions of change can be deduced only indirectly by analysis of
either evaporates or infiltrates into the soil-none of it rainfall and runoff. The curve numbers for contoured
runs off the surface. and contoured and terraced areas for the Soil Conserva-
Depression storage can be increased by agronomic or tion Service method of estimating direct runoff shown in
engineering practices and, therefore, can be important in Appendix A reflect some empirical data mixed with
reducing direct runoff from fields. For example, under judgment. Mathematical models that include depression
ideal circumstances, as much as 2.5 inches may be stored storage explicitly could be used to predict changes.
in contour furrows constructed with a range furrowin However, transciency of depression storage and its
g dependence on precipitation, runoff, and erosion make
machine commonly used in the west (77). Level bench prediction difficult.
terraces with a capacity of over 2 inches have been
installed in the deep loess soils of western Iowa (96).
Doty and Wiersma (28) found that the maximum Infiltration
potential depression storage capacity for conventional
contouring and for bedding and listing practices ranged As snow melts or rain falls on the soil surface or drips
from approximately I inch for contouring to as much as from the vegetation, the phenomenon of infiltration
3 inches for listing and bedding. The potential surface governs the amount of water that will enter the soil and
water storage decreases as land slope increases and is thereby greatly affects the amount of surface runoff,
approximately half as great for a 7 percent slope as for a Some of the physical, chemical and biological charac-
I percent slope. teristics of soil that affect infiltration can be manipu-
Agronomic and engineering practices to increase lated by man through agronomic and engineering prac-
depression storage have a transient effect. With annual tices. Therefore, changing the infiltration characteristics
cropping systems, storage capacity usually is maximum of soils can profoundly affect the amount of surface
in the planting to first cultivation period, which is runoff as well as the amount of water stored in the soil
frequently the most important for reducing losses of for plant use.
agricultural chemicals by surface runoff. The storage Characteristics of both the porous medium and the
capacity then decreases and reaches a minimum during fluid affect infiltration.. The porosity, pore-size distribu-
the harvest to plowing period (28). Contour furrows in tion and tortuosity of soil pores all substantially affect
range and pasture have maximum storage immediately infiltration rates. Sands have higher infiltration rates
after installation. Erosion and trampling by livestock than silts or clays, which have a higher porosity but
gradually reduce this storage capacity. For example, much smaller pores. Soil compaction by the trampling of
contour furrows in eastern Montana had only half their livestock reduces infiltration capacity and increases
original storage capacity after 6-10 years, and the surface runoff (85). From this evidence it can be
average effective life (storage > .05 inch) was about 25 inferred that compaction by machinery would also
years (77). decrease infiltration rates and that practices that reduce
Mathematical descriptions of depression storage machine traffic on a field should reduce surface runoff.
usually represent it as a volumetric threshold that must Raindrop impact on bare soil breaks up soil aggre-
be exceeded before surface runoff occurs (10, 50). The gates into their component particles or much smaller
Stanford model (26) lumps depression storage with aggregates. These particles or small aggregates can be
interception but does not assume a fixed threshold carried into larger pores by water and form a thin
value. This approach can partially account for the spatial surface layer that has low hydraulic conductivity. This
variability of surface detention over the watershed. The surface layer may then control the infiltration rate (33,
parameters in these models are usually found by trial 47). Vegetation or mulches protect the soil surface from
and error or by optimization techniques. Very little raindrop impact and can prevent crust formation.
information is available that could serve as a guide in Dense vegetation with massive root systems and
choosing values for depression storage based on physical farming systems that leave substantial amounts of plant
measurements in the field. The work of Doty and residues near the surface maintain high soil organic
Wiersma (28) is one exception for fairly simple geo- matter content and promote aggregate stability, thus
metric shapes. Boughton (10) suggested that the "ran- maintaining high infiltration rates. Vegetation also has a

I I

higher evapotranspiration rate between rains than evapo- and Holtan (76) reviewed much of the data available
ration from bare soil, thus the soil water content is before 1964. Holtan and his associates attempted to
reduced at the beginning of the next rain which increases develop techniques for estimating parameters in the
the rate and amount of infiltration. Holtan equation by using information available in soil
Tillage can increase the volume of large pores near the surveys (34) or by estimating parameters for various
soil surface and thereby increase infiltration rates. The land-use or cover factors (49).
effect is transient, however. Of the hydrologic models considered, none includes
Frozen soil usually has a lower infiltration rate than an infiltration component based on the numerical
unfrozen soil. If the soil is frozen while wet, a dense, solution of unsaturated flow or two-phase flow in
nearly impermeable mass may result. However, if frozen porous media. The USDAHL model (50) utilizes
while dry, some soils will show little change in infiltra- Holtan's equation. The Boughton model, the TVA
tion rate (76). The effect of increased viscosity of the model and the Stanford model utilize empirical lumped
water is apparently compensated for by the structural storage infiltration components, although the Stanford
change caused by freezing. Frost usually penetrates model attempts to account for spatial variability by
deeper if the soil is bare than if it is snow covered. assuming an invariant statistical distribution of infiltra-
Therefore, practices that prevent snow from blowing tion capacity. The USGS model (27) utilizes an adapta-
away tend to lessen frost penetration but the additional tion of the Green and Ampt equation.
snow deposited may increase runoff.
Modern infiltration theory based on the theory of Soil Water and Groundwater
unsaturated flow or two-phase flow in porous media has
provided a basis for understanding infiltration behavior. Water stored in the soil and rock is frequently
This theory has been presented in several recent texts or separated into two components: the saturated or
reviews dealing with theoretical aspects of infiltration (8, groundwater zone and the unsaturated zone between the
38, 46, 75, 83). groundwater and the surface. Water moves within the
unsaturated zone in response to gravitational and capil-
Although infiltration theory is useful in explaining lary potential gradients. It may move generally down-
observed infiltration phenomena, it has just begun to be ward during rainfall or snowmelt and generally upward
used in quantitatively estimating the effects of agro- after a long, dry period, or it may move upward near the
nomic or engineering practices on infiltration and surface and downward in the lower part of the profile
surface runoff. The partial differential equations describ- simultaneously. In general, water movement in the
ing infiltration must be solved by numerical methods-a unsaturated zone will be predominantly vertical.
time consuming and costly task if one wishes to find In some soils, a rather permeable topsoil is underlain
long-term average effects or distribution functions of by a slowly permeable clay layer. If infiltration is rapid
surface runoff. Also, this approach, with its strong enough, the surface soil may become saturated, resulting
physical basis, requires costly and difficult measure- in flow which is predominantly in a lateral downslope
ments of soil conductivity and diffusivity (109). direction and is known as interflow. This water may
Because of these difficulties, several infiltration equa- reappear on the surface some distance downslope or at
tions, either entirely empirical or based on simplifi- the foot of the slope. Hydrologists generally agree that a
cations of the more general formulations, have been flow mechanism such as interflow exists; however, there
used. Equations presented by Horton (53) and Holtan is some argument about its importance. Dunne (31)
(48) are examples of the former. Green and Ampt (39) ' concluded from his measurements of subsurface storm
Philip (82, 83), Smith (104), Mein and Larsen (69), and flow in Vermont that interflow (subsurface storm flow
Brustkern and Morel-Seytoux (14) used either simplifi- in his terminology) did not contribute significantly to
cations of the basic equations or algebraic approxi- flood hydrographs. This does not mean, however, that
mations of numerical solutions of the basic equations. interflow is unimportant to water quality in some
The first three of these apply only to infiltration from a regions. Minshall and Jamison (71) presented data
ponded surface rather than to rainfall conditions. suggesting that interflow can exist on Midwest claypan
Although solution of these equations is simpler and less soils.
costly than solution of the more rigorous partial An interflow runoff component is included in the
differential equations, the question of parameter esti- Stanford model, the TVA model and the USDAHL,70
mation remains. Usually they are estimated for different model. However, the volume of interflow runoff has not
soil and cover conditions from infiltrometer experiments been compared with field measurements because of the
on small plots or data from small watersheds. Musgrave difficulty in making such measurements. Therefore, it is

difficult to ascertain if computed volumes are realistic or continually shifting. The medium shown in this sketch is
are merely a result of curve-fitting procedures. isotropic so the streamlines are perpendicular to the
As Amerman (3) has pointed out, the separation equipotential lines. In an anisotropic porous medium
between the saturated zone and the unsaturated zone is that contained a relatively impervious layer, for ex-
unnecessary from the physical point of view and is ample, this would not be true.
possibly misleading. Figure 3(a) shows a hypothetical Figure 3 fflustrates some important points about
transverse cross section through a valley during a transport of dissolved chernicals. Suppose that in Figure
relatively dry period and Figure 3(b) shows a similar 3(b) the soil surface from point A to point B was within
section during a wet period. Under steady-state condi- a single field. If we assume a steady state, the path line
tions, the streamlines would represent the path lines of from A to the stream is much shorter than that from B
water molecules or dissolved materials. However, hydrol- to the stream. Therefore, a soluble chemical that leached
ogic systems are usually unsteady so the streamlines are below the root zone on a particular day would take

I @WATER
TABLE

REAMLINE

EQUIPOTENTIAL
LINE

BEDROCK
Figure 3 (a). -Cross section of hypothetical hydrological system during a relatively dry period.

@WATER
TABLE

SEEP AREA

STREAMLINE

EQUIPOTENTIAL
-L- LINE

Figure 3(b).-Section of hypothetical hydrologic system during a wet period. From Amerman, (3)]

much longer to reach the stream from point B than from through a zone where chemical or biological reactions
point A. Hydrodynamic dispersion will also affect the may reduce its concentration to harmless levels before it
arrival time at a stream but has a relatively small effect reaches a stream. The same situation holds for the
compared with that of macroscopic flow (78). How contaminant moving from field B. Enclaves will change
much delay time might be involved between the arrival in areal extent and in shape as the water table changes its
times of chemical constituents at the stream? This time, configuration naturally or by pumping of wells.
of course, depends on the path length and velocity. Robbins and Kriz (92) presented a comprehensive
Some numerical models can answer this question if the review of groundwater pollution caused by point and
system geometry and hydraulic characteristics of the nonpoint agricultural sources. Their concern was pri-
medium are known (12, 86, 100). As a crude approxi- marily with measurements of water quality within the
mation we might use the results of Carlston (20), who enclaves of groundwater contamination, not with the
found that the mean residence time of groundwater effects on water quality in streams and lakes. For an
recharge in a Wisconsin drainage basin was about 45 excellent review of mathematical models describing
days. If we assume that the time of travel for a particle movement of chemicals in soils, see Boast (9).
following the streamline originating between A and B is The subsurface transport of agricultural chemicals
equal to the mean residence time and that the path from a field to water bodies is obviously very compli-
length of A is half the mean and the path length of B is cated. Although we have a qualitative understanding of
1.5 times the mean, the arrival of a slug of chemical such transport, much uncertainty is involved in predict-
distributed uniformly over the field extending from A to ing when and how much of a chemical may reach a
B might appear at the stream over an interval of 45 days. stream or lake, or how much the amount can be reduced
Of course, the physical, chemical and biological by control practices.
processes that affect the particular constituent during its We can, however, identify certain goals of subsurface
travels through the porous medium must also be water management on agricultural land. Maintaining
considered. For example, if we are concerned with adequate water in the root zone and encouraging a
nitrate transport, some zones along the flow path may vigorous crop are advantageous from both the crop
be anaerobic and contain carbon. Under these circum- production and water quality standpoints. Deep percola-
stances, bacteria may convert the nitrate to harniless N tion will occur in most humid and sub-humid climates.
gas. Such conditions might well exist in the seep area Variations in soil characteristics will lead to substantial
shown in Figure 3(b). differences in annual percolation, as shown in Figure 12,
Legrand (62) discussed the patterns of contaminated Vol. 1, and in Appendix B of this volume. In those areas
zones of water in the ground. Although he considered with substantial deep percolation, soluble agricultural
contamination sources of small areal extent (point chemicals must be applied with more care.
sources), his concepts can be readily applied to nonpoint
sources. He noted that when contaminants move Evapotranspiration
through the unsaturated zone and reach the water table,
"enclaves" of contaminated water extend from the The sum of evaporation from the soil surface and
source in the direction of groundwater movement, as transpiration from plants is called "evapotranspiration"
shown in Figure 4. If the contaminant is not adsorbed or and represents the transport of water from the earth to
chemically or biologically transformed, the enclave will the atmosphere. It is important in agriculture because it
terminate at a stream (Field A, Fig. 4) and may cause is required for crop growth. It is important in the loss of
pollution. Because of additional water entering the potential pollutants from cropland because it affects the
stream, the contaminant may be diluted to a harniless volume of direct runoff and the amount of soil water
level at a point C downstream. that percolates to the saturated zone. Evapotranspiration
The boundary of the enclave shown in Figure 4 is obviously a major component in the hydrologic
assumes a constant inflow of the chemical uniformly cycle-it transports about 70 percent of the water that
distributed over the field. As a rule, inputs will be falls on the conterminous United States back to the
intermittent; therefore, the pattern may consist of a atmosphere. This percentage can vary from 100 in and
series of smaller enclaves moving toward the stream regions to about 50 or less in some mountainous areas of
completely surrounded by uncontaminated water. The the U. S.
dashed line emanating from the lower boundary of field Three physical requirements must be met for evapora-
A terminates before reaching the stream, illustrating the tion from a surface to continue: 1) There must be a
situation in which some of the chemical may pass supply of heat to convert liquid water to vapor, 2) the

Direction of Ground
Water Concentration

Pumped
Well

C Downstream Limit of Harmful Concentration)

Figure 4. -Plan view of water-table aquifer showing enclaves of groundwater with high concentrations of a soluble material added to
fields A and B.

vapor pressure of the air must be less than that of the At most locations in the United States, soil water is
evaporating surface, and 3) water must be continually limiting some time during the year, so the actual
available. Evapotranspiration, through the latent heat evapotranspiration will be less than the potential even if
term, is a component of the energy balance, Equation the ground is fully covered by a crop. With annual row
(2), as well as the hydrologic water balance, Equation crops, the ground will not be covered by a transpiring
(1). crop canopy for a substantial period of time, so
When water is not limiting, the evapotranspiration evapotranspiration will be less than from grasses and the
rate is limited by the radiant energy and advected energy total runoff will be greater. This is one reason why
available. Therefore, a lower limit exists for total conversion from row crops to meadow or pasture usually
runoff-the difference between precipitation and poten- reduces runoff.
tial evapotranspiration. Potential evapotranspiration is The physics of evaporation and evapotranspiration is
defined as the hypothetical rate of water loss from a discussed in several texts (19, 93, 108). Here, we will
We I @11

large, homogeneous area of continuous green crop, briefly outline the approaches that have been used to
under the given meteorological conditions, when there is estimate actual evapotranspiration from cropland. In
no resistance to water supply at the evaporating surface general, the models used consist of a continuity relation-
(112). ship, a means of computing potential evapotranspiration,

E0, which serves as the upper limit of the actual Surface runoff begins when the rainfall (or snowmelt)
evapotranspiration rate, a method of computing actual rate exceeds the infiltration rate of the soil and
evapotranspiration, E, as a function of soil water content depression storage is filled. Surface runoff is classified
when it is below some critical level, and a means to somewhat arbitrarily as either overland flow or channel
modify E if the ground is not fully covered by a crop flow. Overland flow is sometimes considered to be thin
canopy. sheet flow over a relatively smooth surface. However, a
Potential evapotranspiration can be computed by the more general and realistic definition would be the flow
energy budget method, the aerodynamic method, or a that is outside of the well-defined channel system. The
combination of the two (113). It can also be estimated mean velocity of overland flow is directly related to the
empirically from evaporation pan data. The equation slope (laminar flow) or the square root of the slope
frequently used is: (turbulent flow) and is inversely related to the hydraulic
resistance of the surface. The hydraulic resistance varies
Eo=KEp widely, depending on the surface characteristics, from a
where K is a "pan coefficient" and E is the evaporation Mannings resistance coefficient of 0.02 for bare soil to
p 0.4 for a dense turf (118). Such differences in hydraulic
from a standard pan. Saxton et al. (94) found that daily resistance would result in water being about six times
evapotranspiration computed by adjusted pan evapora- deeper on the turf than on the bare soil for the same
tion was highly correlated (R' = 0.87) with Eo calcu- discharge. The velocity, of course, would be only
lated by the combination method. one-sixth of that on the bare soil. The greater depth on
It now seems to be accepted that actual evapotrans- the dense sod would allow much more time for
piration can be less than potential at soil water contents infiltration after the rainfall stopped, resulting in less
above the wilting point. Baier (4) presented a compre- runoff even if the infiltration characteristics of the soils
hensive review of this subject. The procedure used in the were the same. The decreased shear stress on the soil
simulations of potential percolation in Volume I and with a sod cover would also result in a much lower
documented in Appendix B of this volume uses a erosion potential.
relationship between E/Eo and available water that is Bailey, Swank and Nicholson (5) described the modes
similar to those presented in the literature. When of pesticide transport into and within the moving liquid
evapotranspiration estimates are needed for different boundary during rainfall. The same processes would also
stages of crop development, the evaporation rate can be apply to nutrient transport by surface runoff. This
corrected by using a crop coefficient, Kp, that varies
according to the stage of growth of the crop (57), or the transport process consists of four mechanisms, as shown
ratio E/Eo may be related to the leaf area index, LAI in Figure 5: 1) diffusion and turbulent transport of the
(41, 90). The methods used for the simulations pre- dissolved chemical from the soil water into the overland
sented in Volume I are described in more detail in flow film, 2) desorption of the chemical from soil
Appendix B. For the extensive simulation study of particles into or toward the moving film, 3) dissolution
percolation and nitrate leaching in Volume 1, a phys- of stationary particulate matter trapped at the bound-
ically more realistic but more complex model such as ary, and 4) scouring of particulate matter and its
presented by Richardson and Ritchie (89) or Saxton et subsequent dissolution.
al. (95) would have been difficult to use with existing From a consideration of these processes, one could
time constraints. infer that practices that reduce runoff velocities and
prevent scour of particulate matter might reduce chem-
Surface Runoff ical transport even if the total volume of runoff were not
reduced. However, the most effective practices would be
As the transport medium for dissolved chemicals and those that increased infiltration rates so that more
for sediments with their adsorbed chemicals, Surface chemicals could be carried into the soil by bulk-flow
runoff is an important link between fields and streams or transport. An increase in depression storage would have
lakes. a similar effect.

Moving Liquid Boundary
(Film Thickness Increasing
Down Slope

P P Z_- Ps Ps Soil Surface
r/W a fie r
Movement

D) Moving (C) Stationary B) Pesticide A) Liquid-Liquid
Dissolution Dissolution Desorption into or Diffusion Interchange
Pp= Pesticide Particulate Ps - Pesticide in towards Moving (Mass Transfer of
in Motion Solution in Motion Liquid Boundary Pesticide )

El Pesticide Particle C)Pesticide Adsorbed on Soil Particle
0 Soil Particle /// Soil Solution Containing Pesticide

Figure 5.- Modes of pesticide transport into and within the moving liquid boundary during a rainfall event. [From Bailey, Swank and
Nicholson (5)]

AGRICULTURAL CHEMICAL AND SEDIMENT TRANSPORT MODELS

Models of agricultural chemical and sediment trans- quite general models are in the development and testing
port (which may be interpreted to include predictions stage (13, 25, 37).
made by them) represent our descriptions of how water, The model developers usually started with a hydrol-
sediment, and chemicals move on fields or watersheds ogic model that was developed for some other purpose
under existing or proposed conditions. The models and added components for chemical transport. The
should not violate the basic physical principles of structure of the hydrologic model used thus served as a
hydrology and should incorporate principles of chem- constraint on the transport model, imposing all of its
istry and biochemistry needed to describe chemical constraints and shortcomings. When these models have
behavior in a biological system. They will also include a been tested more thoroughly, many of the shortcomings
number of empirical relationships. may be shown to be in the structure of the hydrologic
Oomprehensive models of the transport of water model.
(hydrologic models) have been used for about 10 years. These detailed models may be quite useful in an
Several of them have been discussed in previous sections intensive study of a particular field or watershed, but
of this paper. Although special purpose water quality they are far too complex for the extensive scope of this
models were developed as early as 192S (107), general report. Field data available for cahbrating or testing
transport models were not developed until 1967 (54, these models is also limited. Because of the present lack
55). of knowledge in modeling movement of agricultural
Development of agricultural chemical transport chemicals, we used potential direct runoff and potential
models started around 1970. There have been several percolation as surrogate variables in Volume 1. We
reviews of the "state of the art" and the philosophy of implicitly assumed that if surface runoff were reduced,
modeling chemical transport (1, 24, 37, 59, 61, 116, the transport of chemicals would also be reduced. The
117). models used to estimate potential direct runoff and
Bailey et al. (5) have developed a conceptual model potential percolation are described in Appendices A and
of pesticide runoff from agricultural lands, and several B, respectively.

AGRICULTURAL PRACTICES TO CONTROL DIRECT RUNOFF

Eighteen practices for controlling direct runoff, desig- Most of the research cited in Table I was completed
nated as RI though R18, are presented in Volume I within the last 15 years. Earlier work is not cited
(Table 14 and Section 4.2). Practices that reduce erosion because of possible nonstationarity caused by changes in
will usually reduce direct runoff, although to a lesser agricultural practices. The percentage reductions in
extent. Therefore, the first 16 runoff control measures runoff are shown without any indication of statistical
have been assigned the same reference numbers as the significance. However, the decreases reported are consist-
identical erosion control measures; only the alphabetical ent with the physical basis of hydrology discussed in
prefixes differ. These agronomic or engineering practices previous sections. Ranges in response for individual
constitute means whereby direct runoff may be reduced practices are usually attributable to soil and climatic
as compared to direct runoff from an index crop- differences and to sampling variability.
summer row crop (corn) with straight rows. These Additional documentation of land use and treatment
practices are discussed in Volume I without supporting is given in the reports of the Cooperative Water Yield
documentation. Table I contains citations of articles Procedures Study Project (101, 102) and in several re-
supporting statements made in Volume I and of articles cent reviews (11, 61, 74).
containing closely related information that may be
helpful in evaluating individual practices.

Table 1. Bibliography on practices to control direct runoff (Volume I, Section 4.2)

Runoff Control Practice

Page No. Citations Significant Subjects
No. in Description
Vol. 1.

R1 71 No-till Plant in Residues Harrold, Triplett and Comparison of runoff and soil loss from
of Previous Crop Youker (42) no-till and conventional tillage corn at
Coshocton, Ohio.

Harrold and Edwards (LS) Single-storm runoff from a no-till field of
corn on a 2 1 11o slope was less than that from
straight-row corn field on a 6.6% slope but
slightly greater than that from contoured
corn on the 6.6% slope.

Harrold, Triplett and Comparison of 3 years of runoff and soil
Youker (43) loss data from no-till and conventional
tillage corn at Coshocton, Ohio.

Harrold, Triplett and Five-year average May-Sept. runoff was 0.44
Youker (44) inch for conventional and 0.04 inch for
no-till corn at Coshocton, Ohio.

Smith and Whitaker (103) In a 3-year period at McCredie, Mo., runoff
ftom corn with conventional tillage
averaged 5 in; runoff from no-till fields was
6.7 in.

R2 71 Conservation Tillage Allis (2) Over a 9-year period direct runoff from a
subtilled field in a corn-oats-wheat
rotation was 19% less than from straight-row
fields in the same rotation.

Free and Bay (L6) Runoff from a field of corn with mulch
tillage was greater than runoff from
conventional tillage.

Mannering and Burwell Review runoff and erosion data from
(L6 various mulch tillage practices.

Table 1. (continued)

T_
RunoffControl Practice
No. in 0. Citations Significant Subjects
Description
Vol. I.

Moldenhauer et al (L2) Runoff from a till-plant field was slightly
less than from a conventionally-tilled field
for rainfall applied with a rainfall simulator
in early June.

Onstad (79) Till-plant tillage up and down the slopes
reduced runoff 42% over a 6-year period as
compared to conventional tillage.

R3 72 Sod-Based Rotations Jamison, Smith and Review of experiments at McCredie, Mo..
Thornton (LO

Epstein and Grant (35) Comparison of runoff and erosion from
continuous potatoes and potatoes-sod-oats
rotation at Presque Isle, Me.

Barnett (2) Rotation studies at Watkinsville, Ga.

Burwell and Holt (17) Compares runoff from corn-oats-hay
rotation with runoff from continuous corn
in west-central Minnesota,

Carter, Doty and Carroll Runoff from Berm udagriss-corn rotation
(22) compared with continuous corn at Holly
Springs, Miss.

Mannering, Meyer and Evaluated effect of sod-based rotation on
Johnson (67) soil loss and infiltration using a rainfall
simulator.

Moldenhauer, Wischmeier Runoff measured from corn-oats-meadow
and Parker (73) rotation and from continuous corn.

Saxton and Whitaker (L8) Runoff measured from corn, small grain,
meadow rotation and from continuous
row crops.

Sod Conservation Service Runoff curve numbers established for
(105) rotation meadow and row crops in
rotation.

R4 72 Meadowless Rotations Jamison, Smith and Review of crop rotation experiments at
Thornton (56) McCredie, Mo.

Richardson (88) Measurements of runoff ftorn cotton, corn,
oats rotation and oats, clover, cotton and
grain sorghum rotation at Riesel, Tex.

R5 73 Winter Cover Crop Mannering and Burwell No runoff reduction for corn interseeded
(66) with legumes at LaCrosse, Wis.

Smith and Whitaker (103) A small grain cover crop planted after
corn was removed for silage reduced runoff
substantially (5.5 in. vs. 11.5 in.)

R6 73 Improved Soil Fertility Jamison, Smith and Average annual runoff from plots at
Thornton (56) McCredie Mo. ranged from 6.8 to 11.7
inches during 1941-50. Lowest runoff was
for well fertilized pasture; highest runoff
was for unfertilized corn-oats rotation.

Table 1. (continued)

Runoff Control Practice

Page No. Citations Significant Subjects
No. in Description
Vol. 1.

Carter, Dendy and Doty Average runoff was 9.01 inches from
WI improved fertilized pastures and 17.9 from
unfertilized pastures for a 6-year period.
Experiment was at Holly Springs, Miss.

Moldenhauer, Wischmeier For a I 0-y car period at Clarinda, Iowa,
and Parker (73) runoff from continuous corn receiving
nitrogen fertilizer was 25% less than runoff
from unfertilized corn.

Saxton and Whitaker (L8) Average annual runoff from row crops with
fall fertilization was 1.10 inches as
compared with 2.16 inches from row crops
receiving only starter fertilizer.

Wischmeier (114) The ratio of runoff from corn land to
runoff from adjacent fallow decreases with
increases in corn vield. Much of the
increase in corn yield is caused @by higher
fertilizer use.

R7 73 Timing of Field Operations None

R8 73 Plow-Plant Systems Free and Bay (M) Average growing season runoff for plow-
plant corn was less than runoff from con-
ventional corn at Marcellus, N.Y.

Mannering and Burwell Runoff from simulated rainfall on plow-
(66) plant corn was less than that from con-
ventional corn.

Wischmeier (114) Reports three studies that show reduced
runoff for plow-plant corn.

R9 73 Contouring Harrold and Edwards (45) Runoff from a 5-inch rain was 2.30 inches
from a contoured corn field and 4.40 inches
from a conventional straight-row field.

Allis (2) Over a 9-year period direct runoff from a
contoured field in a corn-oats-wheat
rotation was 32% less than from straight-row
fields in the same rotation.

Carter, Doty and Example of 45% runoff reduction by
Carroll (22) contouring in northern Mississippi.

Onstad (79) Contouring in addition to till-planting is
more effective in reducing runoft'than till
plant alone.

Wischmeier (114) Refers to three reports showing runoff
reduction by contouring.

Ritter et al (9 1 Demonstrates that pesticide losses were
greater from contoured fields than from
ridged fields (R-14).

Burwell et al 0 8) Examples of comparative nutrient losses
from terraced and contoured fields.

able (continued)

Runoff Control Practice

Page No. Citations Significant Subjects
No. in Description
Vol. 1.

Onstad and Olson (80) Runoff from contoured and conservation
tillage fields in corn.

Sportier, Heinemann and Compares runoff from contoured corn with
Piest (06) level terraced corn and with meadow.

Soil Conservation Service Runoff curve numbers established for con-
(105) toured row crops.
RIO 73 Graded Rows Moldenhauer et al (72 Graded rows on slopes of 3.4 to 9% did not
reduce runoff.
Rll 73 Contour Strip Cropping None Effects inferred from runoff reduction by
meadow.

R12 73 Terraces Baird and Richardson Terracing alone on heavy clay soils of
Texas Blacklands had little effect on runoff
volume.

Richardson (88) Effects of conservation practices including
terracing on runoff.

Spomer, Heinemann and Level terraces drastically reduced surface
Piest (LOO runoff in western Iowa but groundwater flow
increased.

Burwell et al (18) Level terraces reduced discharge of water,
sediment, nitrogen and phosphorus.

Saxton and Sportier (96) Fourteen percent of water yield from level
terraced watershed was surface runoff.
Sixty-four percent of water yield from
contour watershed was surface runoff.

Saxton, Spomer and Effects of level terracing on runoff and
Kramer (97) erosion.

Soil Conservation Service Runoff curve numbers established for
(105) graded terraces.
R13 74 Grassed Outlets None No data available on effects of grassed
outlets on surface runoff.
R14 74 Ridge Planting Mannering and Burwell Ridge planting on contour reduced direct
(66) runoff.

Moldenhauer et al (7 2) Ridge planting on graded rows did not
reduce direct runoff from a simulated rain.

Ritter et al (9 1) Ridge planting reduced pesticide runoff.
RIS 74 Contour Listing Mannering and Burwell Cite Iowa study where annual direct
(6-6) runoff from contour-listed corn was 55% less
than that from straight-row planting up and
down the slope.
R16 76 Change in Land Use Jamison, Smith and Direct runoff from pasture and meadow was
Thornton (56) lower than that from corn in central
Missouri.

Table 1. (continued)

Runoff Control Practice

Page No. Citations Significant Subject's
No. in Description
Vol. 1.

Dragoun (29) At Hastings, Nebr. average annual direct
runoff was 0.20 inch from watershed in
grass and 5.24 inches from cultivated fields
in row crops.

McGuinness and Harrold Water yield decreased when watershed was
(68) reforested.

Rice and Dragoun (L7) Reseeding cropland with perennial prairie
grasses reduced runoff by 94%, in a 2-year
period.

Saxton and Whitaker (98) Comparison of direct runoff from pasture
and meadow.

Spomer, Heinemann and Comparison of direct runoff from perennial
Piest (106) grass, contoured corn and level-terraccd corn.

Thomas, Carter, Bermudagrass meadow reduced runoff.
and Carreker (LI 1)

Wischmeier (114) For nearly 5000 plot-years of data analyzed,
runoff from row crops averaged 12% of
total rainfall, while that from meadow
averaged 7%.

Hanson et al (40) Effects of grazing intensity on direct
runoff from rangeland -

Soil Conservation Service Runoff curve numbers established for
(105) pasture and meadow.

R17 76 Other Practices Dragoun and Kuhlman Contour furrowing reduced runoff from
(30) pastures.

Mickelson (70) Storing runoff in leveled areas for crop
production.

Neff (77) Storage capacity of contour furrows in
rangeland.

Schwab and Fouss (99) Surface runoff and tile flow from fields
with corn and grass cover.

R18 76 Construction of Ponds Langbein, Hains and Hydrology of ponds and stock-water
Culler (60) reservoirs.

RESEARCH NEEDS

.,esearch on the effect of land management practices probability structure of discharge of chemicals to a
on hydrology has usually involved three steps: I) stream and the quantity of water in the stream.
intensive experimental measurements on plots and A second generation of agricultural chemical trans-
watersheds, 2) analysis of the data using some type of a port models should be developed after the first gene-
mathematical model, and 3) generalization of results for ration models have been tested and their strengths and
more extensive application. weaknesses identified. Material models, systems which
Measurements made in the first step are frequently retain many of the important characteristics of real
governed by the model that is to be used in the second watersheds but are easier to manipulate and control,
step. For example, in most of the experimental work may play an important part in model testing and in
examined, only rainfall and runoff were measured. nmis understanding the significance of parameters. 7-hese
was adequate when the only question was "Will treat- models, which would be less than an acre in size but
ment A reduce surface runoff?" and when the study much larger and more complex than a soil column or a
could be maintained for enough time to obtain statis- lysimeter, would allow deliberate departures from homo-
tically significant results. Unfortunately, we can no geneity. The sensitivity of model parameters to such
longer afford this luxury of time. ?olicy decisions must variations could then be established under controlled
often be made quickly and by the time we have conditions.
statistical significance, the practice may be obsolete. The third aspect of past research, generalization of
.he alternative is to develop more detailed models to results for more extensive application, needs much more
use as a framework in analyzing the data and to obtain emphasis. The SCS curve number procedure for estimat-
more intensive measurements in a shorter time. The ing direct runoff and the Universal Soil Loss Equation
experimental data can be used to estimate model are examples. These techniques were developed before
parameters and techniques must be developed for the advent of, or during the infancy of high-speed
predicting parameters from readily obtainable physical computers and the models used were accordingly simple.
measurements. Simulation can then be used to evaluate This constraint has been relaxed considerably so it
the stochastic properties of the system and to examine appears that significant improvements could be made.
long-term effects. For example, the direct runoff estimation procedure
Stochastic models of point and areal precipitation could be improved by incorporating a simple soil
must be developed and the parameters regionalized by moisture accounting instead of the antecedent rainfall
mapping or other techniques. As plant growth models index. The functional form of the equation could be
and other biological processes are included in hydrologic changed to more closely approximate results predicted
models, the stochastic inputs must be expanded to by modem infiltration theory. -Results from complex
include temperature and radiation. Obviously, the joint hydrologic models should be used along with experi-
probability structure of precipitation, radiation and mental results to develop a new procedure for estimating
temperature must be maintained. direct runoff.
?rediction of runoff from complex areas is still Et should be emphasized that no single model will
difficult and needs a great deal of work from the meet all needs. We need a set of models, involving
standpoint of water quality. :f concentrations of the increasing abstraction, and an objective procedure for
chemical are important we must estimate the joint selecting the appropriate one for the job at hand.

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Col.: 485-508.

CHAPTER 3

CROPLAND EROSION AND SEDIMENTATION

W. H. Wischmeier

Erosion is the wearing away of the land surface by erosion control is cited (12, 60, 61, 99, 100). Observed
water, wind, ice, or other geological agents. Sediment is quantities of sediment from geological erosion and from
defined as solid material, both mineral and organic, that nonagricultural sources are cited to help portray crop-
has been moved from its original source by these agents land sediment in its proper perspective, and land
and is being transported or has come to rest on the classifications pertinent to large-area appraisals of crop-
earth's surface (66). Sediment impairs the quality of the land sediment potential are reviewed. Brief overviews of
water resources in which it is entrained and often (a) existing erosion research data, (b) the mechanics of
degrades the location where it is deposited. It may carry the soil-erosion process, and (c) progressive improve-
pesticides, toxic metals, and plant nutrients absorbed on ments in prediction equations, provide pertinent back-
the soil particles (25, 69). ground information for erosion-control technology. The
This chapter documents technical background and Universal Soil Loss Equation, soil loss tolerances, and
methodology for estimating and controlling cropland sediment delivery ratios are reviewed as potential tools
sediment production. It supplements the material given for pollution-control planning. The major emphasis is on
in Volume 1, Sections 3.3 and 4.1. Only sediment from discussions of erosion factors and important features of
cropland erosion by water was considered pertinent to erosion-control practices.
the purposes of this manual, but literature on wind

SEDIMENT SOURCES AND QUANTITIES

Sediment concentrations in rivers of the United where the mean annual rainfall is between 10 and 15
States range from 200 to 50,000 ppm, with an occa- inches. Under higher rainfall rates, improved vegetation
sional concentration as high as 600,000 ppm (21). The inhibits erosion; under rates of less than 10 inches
amount of sediment moved by flowing water has been se di men t-en training runoff becomes more rare (29).
reported to average at least 4 billion tons a year, with Natural erosion over long geologic periods can be quite
about one billion tons reaching major streams (19). dramatic, as evidenced by the wearing away of moun-
Estimates ascribe about 30% of this country's total tains and building up of flood plains.
sediment to geological erosion and about half of it to The more rapid erosion that is primarily a result of
erosion of agricultural lands (77). activities of man is called accelerated erosion (66).
Sediment produced by accelerated erosion comes from
Geological Erosion many sources.

The erosion that occurs under natural environmental Nonagricultural Sources
conditions of climate and vegetation, undisturbed by
man, is called geological, natural, or normal erosion (66). Some major nonagricultural sources of sediment are:
Estimates of annual rates of geologic deposition in the erosion from construction activities, roadside erosion,
United States range from less than 0.30 to 0.74 ton per stream channel and streambank erosion, scouring of
acre (38, 65). Even at such relatively low rates, a large flood-plain land by floodflow, mining and industrial
drainage area will produce large quantities of sediment. wastes dumped into streams or left in positions suscepti-
The Missouri River's name attests to the turbidity of its ble to erosion, and mass wasting from landslides.
waters before it was discovered by Europeans. The rate In some watersheds, the sediment that originates
of erosion under natural vegetation reaches a maximum from these sources may far exceed that from cropland.

A 1969 report by the Secretary of Agriculture and the watershed or land resource area. All except climate often
Office of Science and Technology (19) gave the follow- vary appreciably even among different fields on a single
ing statistics: During road construction in Scott Run farm. Therefore, soil-loss estimation and control plan-
Watershed, Fairfax County, Virginia, sediment at the ning are most effective on a local basis, by procedures
rate of about 140 tons per acre was produced at the given in Volume 1.
source, and about half of this amount was measured at a On a large-area basis, the cropland contribution to
downstream gaging station. Erosion losses at rates of 42 sediment in strearnflow is influenced by: the amount of
to 289 tons per acre per year were measured on bare sediment produced on the cropland (gross erosion), the
roadside cuts near Carterville, Georgia, and comparable density of cropland in the drainage area, and the portion
rates were measured on 35 road cuts in the Baltimore of the eroded soil that actually reaches a continuous
area. As much as 2,000 cubic yards of sediment per strearn system (sediment delivery ratio).
square mile of access road has been measured in
mountainous country. Sediment from construction ac- Gross Erosion
tivities in urbanizing areas near Lake Barcroft, Virginia,
was reported equivalent to 39 tons per acre annually. The erosion potential on a relatively homogeneous
Studies in southeastern Kentucky showed that sediment drainage area can be estimated by using representative
yields from strip-mined coal land can be 1,000 times soil, cover, and topographic features to evaluate the
that from forested land; there are about 2.3 million acres factors in the Universal Soil Loss Equation. Published
of strip-mined lands in the United States. Erosion is a maps and standard land classifications also provide
serious problem on at least 300,000 miles of stream- helpful information for appraisals of cropland sediment
ban k. hazard on a large-area basis.
The map given in Volume I as Figure 9 shows
Cropland Sediment relative potential contributions of cropland in the
conterminous United States by major land resource
Cropland does not produce the greatest arnount of areas.
sediment per unit of area, but because of the large area Soil survey maps are the best sources of information
involved, our 437 million acres of cropland as a whole on soil characteristics and associated land features. These
produce more sediment than any other source. Annual maps generally include classifications of erosion and land
soil loss from cropland ranges from about one ton to slope. The mapped erosion class is primarily an indica-
more than 100 tons per acre, depending on the crop tion of the extent of prior erosion; quantitative erosion
system, management practices, rainfall, soil characteris- rates are not mapped because of their local nature. The
tics, and topographic features. A 1967 Conservation slope class indicates whether the land is nearly level,
Needs Inventory by the USDA (15, 71) showed that gently sloping, moderately sloping, strongly sloping,
about half of our country's cropland averages between 3 steep, or very steep, but it does not provide infon-nation
and 8 tons of soil loss per acre per year, 30% averages on the slope shapes and lengths.
less than 3 tons, and 20% averages more than 8 tons. Land resource units are geographic areas of land,
Individual states have published the adjusted inventory usually several thousand acres in extent, that are
data, and the reports are available from state offices of characterized by particular patterns of soil (including
the Soil Conservation Service, USDA (15). slope and erosion), climate, water resources, land use,
and type of farming (73).
Major land resource areas consist of geographically
Large-Area Estimates of Cropland associated land resource units. The 156 major land
Sediment Hazards resource areas of the 48 conterminous states were
selected as the basis for mapping hydrologic and
In 1940, Baver (7) listed the major erosion factors as erosion-potential data in Volume 1. Major characteristics
climate, topography, vegetation, soils, and the human of the 156 individual areas are given in Agriculture
factor. The principal influence of climate is the type, Handbook No. 296 (73).
amount, and temporal distribution of the rainfall. The Capability classes (27) are interpretive soil groupings
human factor includes such items as crop sequence, soil made primarily for agricultural purposes. The classifica-
and crop management, and conservation practices. Each tion begins with the individual soil mapping unit. A
of these factors often varies widely within a single capability unit is a grouping of soils that are suited to

11-1
the same kinds of cultivated crops and pasture plants @Irorjiand 'Density
and have about the same responses to systems of Acreage data for land in each subclass of each of the
management. A capability subclass is a grouping of eight capability classes, by states and several land-use
capability units having similar kinds of limitations or classifications can be obtained from the Conservation
hazards. Four kinds of limitations or hazards are Needs Inventory (15). These data were used in the
recognized: erosion, wetness, root-zone limitation, and development of Figures 6 through 9, Volume 1. Wind-
climate. In the broadest category of capability classifica-
tion all the soils are grouped in eight classes. erosion limitations were included in the capability
subclass data used for Figure 7. The other tables and
The eight capability classes were briefly described in charts in the erosion sections of Volume I are for water
Chapter 1. A more detailed description is given in erosion only.
Appendix Il of USDA Statistical Bulletin No. 461 (71).
Generally, erosion hazards increase as the capability-class &d!m8nZ Delivery 'Ratic
number increases 'except Class V), but it is important to
recognize that for some areas the higher classifications This is the factor that adjusts the gross sediment
are due to wetness, root-zone limitations, or climatic estimate to compensate for deposition along the path
limitations rather than erosion. The class and subclass traveled by the runoff as it moves from a field slope to a
designations, together, provide information about both continuous stream system. The delivery ratio will be
the degree and the kind of limitation. discussed in more detail at the last of this chapter.

Rase-E@c`- CE-r@E new erosion control concepts and practices. This equip-
ment can simulate the drop sizes and terminal velocities
Measurements of runoff and soil loss from field plots of natural rain at common intensities, apply simulated
in the United States began about 1917, in Missouri (64). rainfall on several 75-foot plots simultaneously, and
Between 1929 and 1933 the U. S. Department of apply identical storms to plots on physically separated
Agriculture established ten Federal-State erosion re- soils and topographies (43).
search stations, in regions where the problem had
become most critical. in the next 25 years, erosion plot 7h.- Erosior Process
studies were established at 32 more locations. Precise
measurements of precipitation, runoff, soil loss, and Soil erosion is a process of detachment and transpor-
related field conditions at the 42 stations in 23 states tation of soil materials by erosive agents (16). It is a
were continuous for periods of 5 to 30 years (85). In mechanical process that requires energy. Much of this
1960, studies were underway on 18 soils. Fundamental energy is supplied by falling raindrops. The dead weight
studies of erosion mechanics were conducted concur- of the water failing in 30 minutes of a Alidwest
rently and have received increased emphasis since about thunderstorm may exceed 100 tons per acre. The
1960. billions of drops which comprise this I 00-ton volume of
In 1954, the Agricultural Research Service established water strike the soil, if unprotected, at an average
a national runoff and soil-loss data center at Purdue velocity of nearly 20 miles an hour. The impact energy
University. The basic data from more than 10,000 during the 30 minutes may exceed 1,000 foot-tons per
plot-years of erosion studies at 42 research stations were acre (93).
assembled, standarized in units, and transferred to When raindrops strike bare soil at a high velocity,
punched cards for summarization and overall statistical they shatter soil granules and clods and detach particles
analyses (79). Data from continuing studies were added from the soil mass. Splash action and shallow overland
annually for analysis with the previously assembled data. flow transport some of the detached particles directly
The plot studies and fundamental investigations down the slope and others to implement marks and
identified the major erosion factors and provided a other small channels, where the more concentrated
wealth of information on erosion mechanics and control. runoff provides transportation for them. This soil
Inherent limitations of the plot data will be pointed out movement is called sheet erosion (6), or interrill erosion
in the discussion of soil loss equations. (40). This type of erosion occurs rather uniformly over
Field-plot rainfall simulators are now used to expe- the slope and may go unnoticed until much of the
dite filling voids in existing plot data and Field testing of productive topsoil has been removed. In sheet erosion,

nearly all of the soil-particle detachment is by raindrop soil properties, topographic features, and numerous
impact (32, 36, 101). management details occurred at different levels and in
The erosive potential of flowing water depends on its different combinations in the various studies.
velocity, depth, turbulence, and type and amount of Plot data predict specific-field soil losses only if tile
material it transports (17). Water moving down the slope influence of each of the major contributing parameters
follows the path of least resistance and concentrates in can be isolated and evaluated relative to the level at
tillage marks, eroded flow channels, and depressions in which the paranieter was present in the study, so that
the natural land surface, where it gains in depth and the various influences can be combined in different
velocity. Erosion in these flow concentrations is directly proportions to simulate other Situations. However, ef-
related to the hydraulics of the concentrated flow (40). fects of rainfall characteristics and soil properties cannot
The concentrated runoff may remove enough soil to be isolated in a one-location study. where rainfall and
form small but well defined channels, or rills. Rills are soil are either constant for tile plot series or vary ill
often the first readily apparent evidence of erosion, but unison. Also, many relevant secondary variables cannot
tillage usually obliterates them. be controlled in plot studies. Some of' these vary
Rill erosion has been defined as an erosion process in randomly over time. Some differ with seasons, and
which numerous channels only several inches deep are otherg, such as rainfall distribution and storin character-
formed (66), and as the erosion occurring in flow istics, show long-term trends at a given location but
channels (40). In rill erosion, soil particles are detached fluctuate unpredictably for short time periods. The
by the shearing action of water flowing over the soil uncontrolled variables interact with controlled variables,
surface and by slumping of undercut sidewalls and small and these interactions call substantially bias brief-period
headcuts. The detached particles are transported by a research results. Assembling all the available erosion
combination of rolling, saltation, and suspension. Parti- research data at one location for overall statistical
cles transported by suspension may travel long distances analyses (79) counteracted many of' these limitations. It
before being deposited on the land surface. The capabil- enabled combining basic data from various locations ill
ity of runoff to detach soil material is proportional to analysis designs capable of providinginformation oil the
the sheer stress raised to a power of approximately two major factor effects individually and on some of' the
(17). Consequently, rill erosion increases rapidly as most important interaction effects. It also helped rilini-
steeper or longer slopes increase runoff flow depth. nlize bias of results by random variables.
Under continued rainfall, sheet erosion continues be- Mathematical relationships were derived whose basic
tween the rills. Field soil losses are usually a coinbina- and theoretical validity has been substantiated by
tion of sheet and rill erosion, and their relative contribu- subsequent fundamental research. When these factor
tions to total soil loss differ with soils and surface relationships are combined in a general soil loss equa-
conditions. tion, planners can determine what tile average annual
When water accumulates in narrow channels and, over soil loss rate and the potential Soil loss reductions fl-0111
short periods, removes the soil from this narrow area to various alternative crop and management systems are
depths of I to 2 feet, or more, the process is called gultv likely to be at specific locations other than that of a plot
erosion (66). Gully erosion produces large amounts of study.
sediment but can usually be prevented on cropland. The most accurate soil loss equation that is now
A soil's inherent ability to resist erosion by rainfall field-operational is the Universal Soil Loss Equation.
and runoff depends on its physical and chemical This equation has been used as ail crosion-control
properties. Erosion control is accomplished by reducing planning tool for more than a decade in tile 37 states
the mechanical forces of the water acting on the soil east of the Rocky Mountains and is now used to a more
particles or by increasing the soil's resistivity to erosion, limited extent also in the Western States, Hawaii. and
or both. several foreign countries. However. tile following brief
overviews of four soil loss equations are pertinent to tile
Soil Loss Equations subsequent discussion of erosion factors.

The literature of the past 40 years includes inany The Slope-Practices Equation
reports of local erosion studies. These reports may
appear to a casual reader as inconsistent, and sometimes This initial soil loss equation was developed gradually
incompatible, because of wide differences in the re- in tile early 1940's. Zingg (102) developed factors for
ported results. However, most of these differences can the effects of length and steepness of slope. Sinith (62)
be accounted for by the fact that the rainfall pattern, added crop and conservation practice factors and the

concept of a limiting annual soil loss. Browning and The Universal Soil Loss Equation (USLE)
coworkers (10) proposed soil-erodibility and manage-
ment factors for Iowa, but their work was not published The Universal Soil Loss Equation (80, 94, 95),
until 1947. With the cooperation of program leaders in developed in 1958, overcame many of the deficiencies of
the North Central Region of the Soil Conservation its predecessors. Its form is similar to that of the
Service, these initial developments were combined in the Musgrave Equation, but the concepts, relationships and
Slope-Practice Equation for use throughout the Corn procedures underlying the definitions and evaluations of
Bet t. the erosion factors are distinctly different (see section
This equation used several dimensionless factors to on Erosion Factors). The major improvements (84)
adjust an initial basic soil loss to specific field condi- included:
tions. Its basic soil loss was the average annual loss from 1. More complete separation of factor effects so that
corn-oats-meadow rotations on research plots in the results of a change in the level of one or several
North Central States. Factors for other crop systems factors can be more accurately predicted.
were estimated relative to this rotation. The equation 2. An erosion index that provides a good estimate of
had no rainfall factor, and its soil factor was expressed the erosive potential of rainfall and its associated
relative to 1.0 for Marshall silty clay loam. Zingg's slope runoff.
length and steepness exponents (0.6 and 1.4) were used 3. A quantitative soil-erodibility factor that is evalu-
to adjust the soil-loss computations to field slope ated directly from research data without refer-
dimensions. ence to any common benchmark.
4. An equation and nomograph capable of comput-
The Musgrave Equation ing the erodibility factor for numerous soils from
soil-survey data.
In 1946, a national committee, with G. W. Musgrave 5. A method of including effects of interactions
as chairman, was assembled in Ohio to reappraise the between cropping and management parameters.
factors in the Slope-Practice Equation and add a rainfall 6. A method of incorporating effects of local rainfall
factor. The modified model became known as the pattern and specific crop cultural conditions in
Musgrave Equation (48). A graphical solution of the the cover and management factor.
equation was published in 1952 for the Northeastern The Universal Soil Loss Equation computes average
States (3-5). annual soil loss as the product of two quantitative
The 1.75 power of the 2-year, 30-minute rainfall was factors (soil-erodibility and rainfall-erosivity) and four
adopted as the rainfall factor, and Zingg's slope-length qualitative factors (96). The equation is:
and percent-slope exponents were lowered to 0.35 and
1.35, respectively. Annual cover factors were estimated A=RKLSCP
relative to a value of 1.0 for either continuous fallow or
continuous rowcrop. A quantitative soil factor was where A is the average soil loss, in tons per acre, for the
derived by adjusting annual soil losses for effects of time period used for factor R (usually average annual).
rainfall, slope and cover. Subsequent research did not R is the rainfall and runoff erosivity index.
confirm the adequacy of 2-year, 30-minute rainfall as an K, the soil erodibility factor, is the average soil loss in
index of local differences in rainfall erosivity. The tons per acre per unit of R, for a Oven soil on a
lowered slope-length factor was compatible with some 11 unit plot" which is defined as 72.6 feet long,
early sets of data but too low for others. Numerous plot with 9% slope, continuously fallowed, and tilled
studies showed that continuous fallow and continuous parallel to the land slope.
rowcrop are not interchangeable and that the cover L, the slope-length factor, is the ratio of soil loss
effect of continuous rowcrops is highly variable. from a given length of slope to that from a
The Musgrave Equation has been widely used for 72.6-foot length with all other conditions identi-
estimating gross erosion from large heterogeneous water- cal.
sheds. Its highly generalized factor values are more easily S, the slope-steepness factor, is the ratio of soil loss
assigned to broad areas than are factors based on more from a given percent-slope to that from a 9% slope
specific descriptions of the erosion-influencing parame- with all other conditions identical. (In practice,
ters. However, erosion hazards are highly localized. For factors L and S are usually combined in a single
resource-conservation and pollution-control planning, topographic factor denoted by LS.)
soil loss equations need to reflect local conditions as C, the cover and management factor, is the ratio of
accurately as possible. the soil loss with specified cover and agronomic

practices to that from the fallow condition on variables, they will enhance analyses of erosion systems
which factor K is evaluated. and control practices. These models have not become
P, the practice factor, is the ratio of soil loss with field operational because additional research is needed to
supporting practices such as contouring or strip- bridge certain information gaps. However, they have
cropping to that with straight-row farming up and already improved the understanding of erosion proc-
down the slope. esses, helped explain some of the seeming inconsistencies
The concepts and relationships underlying the evalua- in the field-plot data, and improved the accuracy of
tions of these factors are reviewed in the discussion of some of the factor evaluations for the USLE.
Erosion Factors. The initial basic models have added several important
new concepts. One is the treatment of soil detachment
Basic Erosion Models by rainfall, detachment by runoff, and transport by
runoff, as individual subprocesses that bear substantially
Basic mathematical models are being developed that different relationships to the erosion factors and that
combine fundamental principles, concepts and relation- occur in widely differing combinations (39, 44). Either
ships of erosion mechanics, hydrology, hydraulics, soil detachment capacity or transport capacity can limit
science, and meteorology to simulate the erosion and erosion at a given site. Another new concept is the
sedimentation processes. Substantial progress has been separation of rill erosion from interrill erosion (17, 40).
made in developing static and dynamic models capable This distinction will help clarify unexplained differences
of predicting spatial and temporal variations in erosion in the erodibilities of soils and effectiveness of crop
and sedimentation (14, 17, 40, 52). To the extent that canopies. Some soils allow very substantial sheet erosion
these simulation models reflect direct and interacting without rilling; others are much more susceptible to
effects of more of the uncontrolled and secondary rilling.

EROSION FACTORS

The climatic, soil, topographic, and management benchmark because most of the erosion research plots
parameters that largely determine erosion rates have since 1930 were of this length. It is sufficient for
wide ranges of possible values, or levels, that can occur measurement of runoff effect as well as raindrop-impact
in any of an extremely large number of possible effect. Slope steepness of 9% was the most representa-
combinations. The six major erosion factors discussed in tive for the existing plot data. Straight-row farming up
this section estimate the effects of different levels of and down the slope represents complete absence of
these parameters on soil erosion by water. In a soil loss support practices. The "unit plot" on which the quanti-
equation, each factor must be represented by a number tative soil factor is measured has these benchmark
that reflects the specific local conditions, and all the conditions and factors L, S, C, and P have values of 1.0.
numbers must be relative to the same, clearly defined, The values of factors R, K, L, and S are essentially
benchmarks. The benchmark conditions for the Uni- firm for a particular location and, together, determine
versal Soil Loss Equation are free of geographic bounds the location's characteristic erosion potential. The
and are defined as follows. farmer or planner has no control over rainfall pattern or
The benchmark management condition is continuous steepness of the slope. The effective slope length can be
fallow that receives primary and secondary tillage each reduced by use of terraces or diversions, but this
spring and is periodically tilled during the summer to reduction can be classified as a practice effect. Manage-
prevent vegetation and serious crusting. The tillage ment systems that gradually improve soil structure and
operations are up and down the slope. This condition increase its organic-matter content can affect its erodi-
was selected because: (a) continuous fallow is the only bility, but an appreciable change in the soil factor would
condition under which soil effect could be evaluated require many years. Factors C and P, on the other hand,
independently of cover, management, and residual ef- are highly responsive to executed management decisions.
fects, and (b) it is a more constant condition than would Good management and erosion control practices reduce
exist with any type of cropping. The fact that this sediment production primarily through their effects on
condition rarely exists in practice is immaterial because these two factors. The following discussions of the six
the soil loss computed by the equation as a whole does major erosion factors include the concepts and relation-
reflect existing field conditions. ships underlying their definition and evaluation for the
The slope length of 72.6 feet was selected as a USLE.

Rainfall and Runoff Erosivity (Factor R) the storm. Therefore, the erosive potential of a rain-
storm is a function of its kinetic energy, maximum
Most cropland erosion by water is directly associated prolonged intensity, and their interaction, all three of
with rain events and is influenced both by the rain which are reflected in the El parameter.
intensities and by the amount and rate of runoff. The ne published rainfall energy -intensity table (84, 93)
function of factor R is to quantify these interrelated applied the equation given above to intensities up to 10
erosive forces. The parameter used to evaluate R must be in/hr. Two recent studies showed that median drop size
predictable on a probability basis from meteorological does not continue to increase when intensities exceed
data. It must be definable for specific storms and for about 3 in/hr (11, 26). Therefore, the energy given in
specific time periods other than annual, and its seasonal the table for a 3 in/hr intensity should be used for all
or annual evaluation must be influenced by all signifi- higher intensities as well. This change does not signifi-
cant rains rather than only by annual maxima. cantly affect El computation in the United States
because prolonged intensities greater than 3 in/hr are too
The Rainfall- Erosion Index, EI rare to have much effect on average annual El values.
For computation of average annual El values, contin-
The assembled plot data showed that when all factors uous records of from 20 to 22 years are desirable in
other than rainfall are constant, storm soil losses from a order to avoid bias by cyclical variations in rainfall
cultivated field are directly proportional to an inter- pattern (49). Erosion index values were computed for
action term, which is the product of the rainfall energy about 2,000 locations fairly uniformly distributed over
and the maximum 30-minute intensity. This product is the 37 states east of the Rocky Mountains. By interpo-
the El parameter ,(80, 93). The relation of soil loss to El lating between the computed point values, lines of equal
is linear, therefore, individual-storm values of El can be value (iso-erodents) were plotted on a map that included
summed to obtain seasonal or annual values of the county lines as references (82, 96). 7he mapped values
represent 22-year rainfall records (1937-1958). At sta-
parameter. Frequency distributions of annual, seasonal, tions where 40-year records were available, the 40-year
or annual-maximum-storm El values follow the log- average annual rain amounts generally coincided very
normal type of curve that is typical of many hydrologic closely with the corresponding averages for the 22 years
data(80). used in development of the iso-erodent map.
Median raindrop size increases as rain intensity The computed annual El values are reasonably well
increases, to about 3 in/hr, and terminal velocities of correlated with the 2-yr, 6-hr rainfall probabilities
free-falling waterdrops increase with increased drop size published by the Weather Bureau (74). The relationship
(22, 33). Since the kinetic energy of a given mass in is expressed by El = 27.38p2.17, where P = the 2-yr,
motion is proportional to velocity squared, rainfall 6-hr rainfall (87). The El values given in Figure 10a,
energy is directly related to rain intensity. Analyzing Volume 1, for the I I Western States were estimated by
published dropsize and terminal-velocity data, this equation. Those for the other 37 states were taken
!Xischmeier and Smith (93) derived the equation E = 916 from the original iso-erodent map (82.1.
+ 33 1 log I 0i, where E is the kinetic energy in foot-tons
per acre-inch of rain, and i is intensity in inches per Factor R in the USLE usually equals the pertinent El
hour. The energy of a rainstorm can be computed from value. For prediction of average annual soil loss, it is the
recording-raingage data. The storm is divided into annual-El value available from Figure 10a; for short
successive increments of essentially uniform intensity, specific time periods, it is the actual local El for that
and a rainfall energy-intensity table (93) derived from period. However, there are two conditions for which the
the above formula is used to compute the energy of each computed El must be modified to evaluate factor R.
increment. Thus, the energy of a rainstorm is a function 1. Where snowmelt runoff on moderate to steep
of all its component intensities and rain amount. slopes is significant, the El value must be adjusted
In exploratory analyses of data from bare fallow upward to add the erosive effects of this runoff to
plots, rainfall energy was the best single predictor of the R value. The Palouse Region of the Northwest
associated runoff, but was not a good predictor of soil exemplifies this condition. Numerical evaluation
loss. For sheet erosion, sod detachment is primarily by of the erosivity of runoff that is not an immediate
raindrop impact on the surface, but the capacity of the consequence of rainfall is an area of needed
associated runoff to detach and transport soil material is research. Only tentative estimates of the adjust-
directly related to its depth and velocity. These are ment factor for the Palouse Region are presently
directly related to the maximum prolonged intensity of available.

2. Experience has shown that on the Coastal Plains Soil Erodibility (Factor K)
of the Southeast, factor R is less than the El
values computed by the standard procedure. This The susceptibility of a given land area to erosion is a
discrepancy may be due to the combination of function of all the factors in the soil loss equation, but
hurricane- associated storms and flat slopes. The some soils erode more readily than others even when
hurricane storms compute very high El values, rainfall, topography, cover and management are identi-
but the gentle slopes are soon largely covered by cal. Soil erodibility refers to a soil's inherent suscepti-
very slowly moving runoff that shields the soil bility to erosion by rainfall and runoff. This is a function
surface from raindrop impact. In a study on a of complex interactions of soil physical and chemical
similar soil and slope in the Maumee Basin of properties. Numerous researchers have measured differ-
Northeastern Indiana, using a rainfall simulator ences in the erodibilities of a few soils, and some have
and inflow at the upper end of the plot, drop related erodibility to specific soil properties (5, 10, 34,
impact on the soil surface was needed to obtain 46, 50, 51, 55, 76, 91). Water infiltration into soils was
significant soil loss from a 35-foot plot (36). A reviewed by Parr and Bertrand (54).
maximum of 350 for El values in the Southeast The relation of soil loss to El is linear, and the
was recently adopted as a temporary measure
until research can provide "effective El" values average increase in soil loss for each additional unit of El
for these conditions. differs for different soils (93). The average soil loss per
unit of El, measured under the previously defined "unit
plot" conditions, is the numerical soil-erodibility factor
Runoff of the USLE. For 23 benchmark soils for which K was
measured in long-term plot studies under natural rain, its
Surface runoff is not a separate factor in the value ranged from 0.03 to 0.69 (50, 96).
Universal Soil Loss Equation or its predecessors because: Rainfall simulators were used in the Corn Belt, the
(a) no satisfactory prediction equation for cropland Southeastern States, and Hawaii to evaluate other soils
runoff existed, and (b) the respective roles of rainfall and obtain soil loss data for study of the relationships of
and runoff in the erosion process had not been separated various soil properties to erodibility (5, 89, 91). In a
in erosion research. Runoff data alone do not predict Corn Belt study of about 60 soils selected to include a
soil loss. The sediment content of an acre-inch of runoff broad range in soil properties, 24 primary and inter-
can range from a mere trace to many tons. For soil loss action terms were statistically significant in multiple
prediction, the factors in the USLE would need to be regression analysis of the data (91). This illustrates the
combined with the runoff factor, and the runoff would complexity of the problem, but for practical purposes
first need to be predicted as a function of essentially the many of these terms can be neglected either because of
same parameters. Therefore, it was advantageous to relatively small effect or because they are closely related
relate the factors directly to soil loss in an equation for to particle-size distribution, organic-matter content, soil
widespread field use. The El parameter combines esti- structure or permeability.
mates of runoff amount and rate with the potential of Two recent findings were particularly helpful for
the rainfall to detach soil material by drop impact and simplifying the prediction of inherent soil erodibility:
splash action. (a) that from the viewpoint of erodibility, very fine sand
Researchers have recently made good progress in (0.05 - 0.10 mm) would be more properly classified as
separating rain fall-in duce d (interrill) erosion from run- silt than as sand (91), and (b) that percentages of sand,
off-induced (rill) erosion (17, 40). With this separation, a silt and clay must be considered in relation to each
runoff factor added to the soil loss equation should have other, because of strong interaction between particle
substantial potential for improved accuracy. An equa- sizes. The most informative particle-size parameter in the
tion that predicts the two types of erosion as separate Corn Belt study was M = % silt(100 - % clay), where the
components of the total soil loss could largely solve the very fine sand is included in the silt fraction. When this
aforementioned problems with factor R in the North- parameter was included with organic-matter content, a
west and Southeast. Also, some erosion-control practices soil structure index, and the profile permeability class,
greatly reduce soil loss without appreciable effect on prediction of the erodibility factor was well within the
runoff. Onstad and Foster (52) obtained good results accuracy needed for field use (89). The equation is:
from adding a runoff factor to the USLE when using the
equation to route sediment through a watershed. How- OM)MIA 4
ever, more research is needed to make this approach K = (2.1 x 10 --6) (12 + 0.0325(S - 2)
field operational. + 0.025(P - 3),

where Om = percent organic matter, M = the particle-size (83). Neither is soil detachment per unit area by
parameter presented above, S = structure index, and P = raindrop impact greater on long slopes. The effect of
permeability class 02). Permeability is a profile para- slope length is, therefore, primarily due to greater
meter; the other three pertain to the upper few inches of accumulation and more channelization of runoff on the
soil. longer slopes. This increases the capability of the runoff
1he soil-erodibility nomograph presented in Volume to detach and transport soil material.
1, Figure 11, provides a quick graphic solution to this Factor L in the USLE is dimensionless. For slopes
equation. However, the relationship changes when the steeper than 4% it is generally computed by the formula
silt fraction exceeds 70%. This change is reflected in the L = (A/72.6)' -', where A = slope length in feet and 72.6
nomograph by the bend in the percent-sand curves, but feet is the benchmark length. The exponent of 0.5 is the
is not reflected in the above equation. The structure- average of values obtained in 10 independent studies in
index and permeability-class codings are defined on the which the observed values ranged from 0.3 to 0.9 (97).
nomograph (89). Field observations indicate that the exponent is prob-
For a few special conditions, the nomograph Solution ably about 0.3 for slopes of less than 3%, and 0.4 for 411o
may be modified to improve K-value accuracy: (1) slopes. Increasing the exponent to 0.6 when slopes
Fragipans and claypans reduce permeability in wet exceed 10%, as suggested in Agriculture Handbook No.
seasons, but do not greatly reduce it for thunderstorms 282, is of questionable validity. The higher exponents
that occur when soil is relatively dry. Separate erodi- observed in the length-effect studies were associated
bilities can be computed for dry and wet seasons by with plowed-out bluegrass sod or abnormally severe rain
using different permeability ratings in the nomograph events, on slopes that did not exceed 10%. Both L and S
formula. (2) The mulching effects of stone, gravel, or are believed to be influenced by density of cover, soil
shale on the surface are not accounted for in the erodibility, and rainstorm characteristics, but existing
nornograph equation. if used on such soils, it would be data are inadequate for mathematical evaluations of
applied to mechanical-analysis data for the soil exclusive these interaction effects.
of the large fragments, and the indicated K value would There have been field indications that the slope-
then be reduced by treating the large fragments as partial length exponent becomes smaller for extremely long
mulch cover. 1.3) The nomograph lacks sensitivity to slopes. This is logical because slopes approaching a
differences in erodibilities of desurfaced high-clay sub- thousand feet in length would rarely have a constant
soils, because other chemical properties become impor- slope steepness along their entire length, and upslope
tant under those conditions. Recent studies showed free depositional areas would be likely.
iron and aluminum oxides were important for high-clay Slope steepness affects both runoff and soil loss. In
subsoils but not for most topsoils (58). the assembled plot data, runoff from small grain tended
Standard texture classes are too broad to be accurate to increase linearly with increases in slope. For row
indicators of erodibility. Therefore, the K values listed in crops the increase was curvilinear, increasing at an
Table 2a of Volume I are only first approximations. increasing rate (83). Soil loss increases more rapidly than
Nomograph solutions will show a broad range of runoff as slopes steepen.
crodibilities within a texture class. The combined effects of length and steepness for
uniform slopes were shown in Table 3, Volume 1. The
j OPC9:.FPh1`C Vea@u-!as (Factors L and S) table was derived by the formula

Soil loss per unit area increases as slopes become
longer or steeper. The USLE denotes effects of slope IS = [ A ]' 430 sin 2 0 + 30 sin 0 + 0.431
length by L and effects of steepness by S. Both are 72.6 L 6.574
dimensionless and expressed relative to the "unit plot"
dimensions defined for factor K. In practice, the two are
combined in a single topographic factor denoted by LS. where m = 0.5 if the slope is steeper than 4%, 0.4 for 41yo
Slope length is the distance from the point of origin slopes, and 0.3 for slopes of 3% or less; and 0 = the angle
of overland flow to the point where either the slope of slope.
decreases enough that deposition begins, or the runoff The last quantity in this equation is an unpublished
water enters a well-defined channel (63). The effect of conversion of an earlier formula (96) to an expression in
slope length on runoff per unit area is generally not of terms of the sine of the angle of slope. Within the range
practical significance, although there have been instances of the research data, the two forms are equally accurate,
of statistically significant direct and inverse relationships but an expression in terms of sin 0 is more logical and

computes more realistic values when extrapolated to estimated in cornbination, because of many interrelated
steeper slopes. variables. Nearly any crop can be grown continuously or
The research data used to derive relationships of slope in any one of numerous rotations. The sequence within a
length and steepness to soil loss were from plots not system can be varied. Crop productivity can be low, or it
longer than 270 feet and slopes not steeper than 18 can be high. Crop residues can be removed, left on the
percent. The extrapolated values shown in Table 3 of surface, incorporated near the surface, or plowed under.
Volume I for slopes that exceed these dimensions, The amount of residues can vary from scattered. pieces
although speculative, are the best estimates presently to complete surface cover. The crop can be planted in a
available. Soil loss estimates for slopes steeper than pulverized and smoothed seedbed, in a rough and cloddy
about 30% are potentially subject to considerable error. seedbed, or with extremely little soil disturbance. It can
Research on steep slopes is a major need. be intertilled after emergence, or the weeds can be
Shape of the slope is also important. V,,hen a slope controlled with chemicals. The effectiveness of crop-
steepens or flattens significantly toward the lower end, residue management will depend on the amount of
or is composed of a series of convex and concave available residue. This, in turn, depends on the rainfall
segments, its overall average gradient and length do not distribution, the fertility level, and various management
correctly indicate the topographic effect on soil loss. An decisions made by the farnier. Also, the residual effect
irregular slope can be viewed as a series of segments such of meadow sod depends on the type and quality of
that the gradient within each segment can, for practical meadow, on how the succeeding seedbed was prepared,
purposes, be considered uniform. The segments cannot and on the length of time elapsed since the sod was
be evaluated as independent slopes when runoff flows turned under. The erosion-reducing effectiveness of a
from one segment to the next. However, the amount of crop system depends on how the levels of all these
soil detached on each segment can be computed by a variables, and others, are combined on the field.
recently published formula (18) and surnmed for the Factor C in the Universal Soil Loss Equation is the
entire slope length. For each segment, the effective slope ratio of soil loss from land cropped under specified
length is the distance from the top of the overall slope to conditions to the corresponding loss from clean-tilled,
the foot of the particular segment. continuous fallow (96) and therefore includes the effects
If the segments are selected so that they are also of of all these variables. If the actual soil loss equals the
equal length, the slope-effect table for uniform slopes potential loss predicted by the product of factors R, K,
can be used with appropriate adjustment factors for L, and S, factor C=I. This would be clean-tilled
position of the segment on the overall slope. For most continuous fallow or land where mechanical desurfacing
Field slopes, three segments should be sufficient. The has removed all of the surface vegetation and most of
procedure is as follows (8 7): the root zone. Where there is any vegetative cover, where
Ascertain the percent slope for each segment. Enter the upper layer of soil contains significant amounts of
the slope-effect chart or table with the total slope length roots or plant residues, or where cultural practices
and read the LS value corresponding to the steepness of increase infiltration and reduce velocity, soil loss is less
each of the three segments. Multiply the chart LS value than the product RKLS. Factor C brings this reduction
for the upper segment by 0.58, the middle-segment value into the soil loss computation. On cropped land, C
by 1.06, and the lower-segment value by 1.37. The ranges from about 0.60 downward to less than 0.01.
average of the three products is a good estimate of the This great flexibility in the value of C is extremely
effective LS value for that slope. The three products also important to erosion-control planners. If C is reduced,
indicate the relative magnitudes of soil loss on the three soil loss is reduced by the same percentage.
slope segments. (If two segments are sufficient, use tile The canopy protection of crops varies widely for
multiples: 0.71 and 1.29. For four segments: 0.50, 0.91 different weeks or months in the crop year. The overall
erosion-reducing effectiveness of a crop depends on how
1.18, and 1.40. For five segments: 0.45, 0.82, 1.06, much of the erosive rain falls while the crop provides the
1.25, and 1.42.) (87). least protection. The correspondence of periods of
Cover and Management (Factor C) highly erosive rainfall with periods of good or poor
vegetative cover differs appreciably between geographic
The ability of a soil to resist the erosive forces of regions. Therefore the C value for a particular crop
rainfall and runoff is profoundly influenced by the system will not be the same in all parts of the country. A
direct and residual effects of vegetation, crop sequence, field-tested routine is available for computing site
management, and agronomic erosion-control practices. C-values that reflect the net effect of the interrelated
The effects of cropping and management must be crop and management variables in whatever combination

they occur at the site and in relation to the local rainfall rainfall records used to develop the iso-erodent (R-value)
pattern. map (82.) Corresponding data for the I I Western States
The entire rotation cycle is divided into a series of and "awaii are presently available only as tentative
cropstage periods so defined that cover and management estimates.
may be considered approximately constant within each The soil-loss-ratio table (96) was derived from analy-
period. The five cropstage periods are defined as follows, sis of more than 10,000 plot-years of erosion data. The
for each crop-year in the system (81, 96): data in this table are percentages of soil loss frorn the
Period F - Rough fallow. Turn plowing to final indicated combinations of cover and management to
seedbeed preparation. (No-plow systems ornit this corresponding losses from continuous fallow. The table
period.) has limitations that need to be recognized. The "mini-
Period I - Seedling. Seedbed preparation to I month inum tillage" classification applies only to plow-based
after seeding. systems in which disking and smoothing are omitted. A
Period 2 - Establishment. The second month after partial list of ratios for no-plow systems that retain some
spring or summer seeding. For fall-seeded grain, or all of the residues on the surface was published in
this period extends to about May I in the 1973 (86). The ratios for corn in cropstage 4, residues
Northern States, April 15 in the Central States, left, are for stalk cover as left by the picker. Shredding
and April I in the Southern States. the stalks provides more complete cover and reduces the
Period 3 - Developing and maturing crop. End of soil-loss ratio. Some of the crop systems in the Western
period 2 to harvest. States and Hawaii are not represented, but approximate
Period 4 - Residue or stubble. Crop harvest to values for these systems are now available from the Soil
plowing or new seeding. (When meadow is seeded Conservation Service, Western Technical Center, Port-
with small grain, period 4 ends about 2 months land, Oregon. Approximate C-values for range, wood-
after grain harvest. The vegetation is then classified land, and idle land were published in 1974 (87).
as established meadow.) Practices that depend on small rates of residue and/or
Probable calendar dates for the events that begin the tillage-induced surface roughness for erosion-control
successive periods are selected on the basis of local effectiveness will be ineffective if slopes are excessively
climate and farm practice. The fraction of the annual El long. The precise length limits for various mulch rates,
that normally occurs in that locality during each slope steepnesses, kinds of soil, and rainfall patterns have
cropstage for each of the crops in the rotation is not been determined. Investigations by the Agricultural
determined from the applicable Ef-Distribution Curve in Research Service are underway to improve or verify the
Agriculture Handbook No. 282. These fractions are approximate limits given in Table 13, Volume 1.
multiplied by the corresponding soil loss ratios from
Table 2 in the same handbook. The sum of the products
obtained for the cropstage periods in any one year is the Supporting PrecVces (Fa=F P)
C-value for that particular crop in that system. The
crop-systern C-value is the sum of all the partial This factor is similar to C except that P accounts for
products, divided by the number of years in the system. additional effects of practices that are superimposed on
This procedure has been used by the Soil Conservation the cultural practices, such as contouring, terracing,
Service to develop local C-value tables that are available diversion, and contour stripcropping. Approximate
from their state offices. The illustrative C values given in values of P, related only to slope steepness, were listed in
Table 4 of Volume I were also derived by this procedure, Table 5, Volume 1. These values are based on rather
but the seeding and harvest dates and the El-distribution limited field data, but factor P has a narrower range of
data were generalized and are not precise for any possible values than the other five factors. Influences of
particular location. type of vegetation, residue management, rainstorm
The 33 regional EI-distribution curves in Agriculture characteristics, and soil properties on the value of P have
Handbook No. 282 were derived from the 22-year not been evaluated to the point of predictability.

EROSION CONTROL METHODS

Specific types of erosion-control practices were dis- tions, and variability of each type of practice. The
cussed in Section 4.1 of Volume 1. These discussions indicated percentages of reduction in soil loss were based
included general information on the advantages, limita- on C values estimated from all the available data rather

than on results of any specific local experiment. This from prolonged rains. In 542 plot-years of convention-
section discusses principles and relationships that deter- ally planted corn, the average runoff per thousand
mine the effectiveness of erosion-control practices. foot-tons of computed rainfall energy was only about 15
If surface runoff can be eliminated, movement of percent less in cropstage 3 than before canopy had
sediment from a field will. be insignificant. Breakdown of developed (90). But soil loss per El unit from a field of
soil aggregates by raindrop impact, rearrangement of soil clean-tilled 90-bushel corn is about 60 percent less in
particles, and surface sealing can occur before runoff cropstage 3 than in cropstage 1 (96, Soil Loss Ratio
begins, but very little sediment will leave the field unless Table), primarily as a result of raindrop interception by
surface runoff is available to transport it. Land treat- the canopy. Water drops from canopy may regain
ments that result in a deep, fertile topsoil, a high level of appreciable velocity, but usually not the terminal veloci-
organic matter, good tilth, and good vegetative cover ties of free-falling raindrops. Therefore, canopy reduces
increase infiltration and reduce runoff. These conditions rainfall erosivity by reducing its impact energy at the soil
may completely eliminate surface runoff from moderate surface. The amount of reduction depends on its height
rainstorms on some areas. Generally, however, where the and density. Canopy effect can be viewed as a reduction
rainfall is adequate for crop production some of it falls in the "effective" El of the rainstorms and as such can
at intensities greater than the soil can infiltrate even be directly computed for specific situations.
when well managed, and runoff occurs. Figure I shows the ratios of effective El's computed
Land treatments that increase infiltration and the for several drop fall heights to the El of unintercepted
capacity of the soil to store water will reduce small- rainfall (88). Percent cover was defined as the percentage
watershed flooding that results from short, intense rains of the total ground area that could not be hit by
during the growing season. However, when the soil vertically falling raindrops because of the canopy. Soil
becomes saturated to a considerable depth, as is often loss reductions due to canopy over a bare soil should be
the case in major flood periods, cultural practices have approximately proportional to the reductions in effec-
much less effect on runoff. Erosi on- control practices tive El. Figure I assumes a median dropsize of 2.5 mm
must also reduce the shear stress and transport capacity for both the rain and the droplets formed on the
of the runoff. This means reducing runoff amounts, canopy. Where rainfall is characteristically of low inten-
velocities, and depths and dissipating the flow energies sity and small drops, canopy effect would be less.
on plant residues rather than on the soil surface. All crops develop some canopy, but this may require
Erosion-control practices rely primarily on five means several months, and most or A of it may be lost with
of reducing erosion: 1) vegetation, 2) plant residues, 3) the crop harvest. Good soil-fertility management and
improved tillage methods, 4) residual effects of crops in narrow row spacing hasten the development of a
rotation, particularly systems that include grass and protective canopy. Crop sequences can be selected that
legume meadow, and 5) mechanical supporting practices. substantially reduce the length of time between succes-
A sixth potential approach would be use of chemical soil sive plant covers, and early seeded winter cover crops
stabilizers, but they have not yet become economically can provide interim cover.
feasible for field use.

Vegetation Vegetation At The Soil Surface
Vegetation (a) intercepts rainfall and thereby reduces Stands of grass or small grain are much more effective
runoff and soil-particle detachment by drop impact, (b) than a raised canopy. Much of the rain that such
increases the soil's water-storage capacity through tran- vegetation intercepts moves down the blades and stems
spiration, (c) retards erosion by decreasing runoff to a point so near the ground that the droplets regain no
velocity, (d) physically restrains soil movement, (e) appreciable energy. The dense vegetation at the soil
improves aggregation and porosity of the soil, and (f@ surface also reduces runoff amount and velocity and
increases biological activity in the soil (59). physically restrains soil movement. For about 5,000
plot-years of data, runoff from small grain averaged 9
percent of total precipitation, in contrast to 12 percent
Crop Canopies for row crops (83). Meadow averaged 7 percent. The
soil-loss-ratio table shows that soil loss from established
Leaves and branches that are not in contact with the small grain averages less than half of that under a canopy
soil reduce runoff from small rains but have relatively of conventionally planted corn. Sod loss from a good
little influence on the amount and velocity of runoff quality grass and legume meadow is generally negligible.

1.00

.80 4

LL_
LLJ
4'
.60

T-7
f

T
cr_
C)
LL. 3
.40 tit
C)
4
*Average fall he4ght of
drops from canopy f e e t i
.20

4tjlt
0
0 20 40 60 80 100

PERCENT GROUND COVER BY CANOPY

Figure I.-Effect of crop canopy on effective EL

Piant Residues in narrow slots opened through the residue by a fluted
coulter or other device, without tillage. No-till planting
With one-crop systems, crop residues can supply very for corn has been very highly effective in chemically
effective cover during the approximately 8 months from killed meadow or small grain, in grain stubble, in
harvest until the next crop develops full cover. Stalky chopped rowcrop residues, and in winter-cover crops.
residues such as corn and grain sorghum provide more However, the practice is not adaptable to all fields (see
effective cover when shredded than when left partially Section 4.1, Volume 1).
standing. Complete residue cover at the soil surface Reductions in soil loss by various rates of straw
virtually eliminates raindrop impact on the soil, greatly mulch tested under simulated rain have varied with soil
reduces the detachment capability and transport capac- type and surface conditions (1, 4, 9, 28, 37, 42, 45, 70).
ity of runoff, and usually increases infiltration. Runoff Figure 2 shows the average relation of soil loss with
i- 4r-

through or over a complete cover of residue mulch is various rates of mulch to corresponding losses with no
very low in sediment content. mulch, as observed on 35-foot cropland slopes subjected
For rowcrop production, high residue rates are most to 5 inches of simulated rain in two I -hour storms (86).
fully utilized in the no-till systems. The seeds are planted I-low much the slope length or steepness could be

increased before unanchored mulch would be undercut reduction with similar planting after disking (86). The
or transported by the flowing water has, however, not amount that soil-loss is increased by shallow tillage will
been fully determined. Mulch applied on plowed and vary in relation to initial amount of residue and how
disked surfaces of silt loam soils with slopes of 3 to 5 much is covered by the tillage.
percent substantially reduced runoff, but mulch on a Moldboard plowing inverts the upper 6 to 8 inches of
15% slope of untilled loam from which oat stubble had soil and usually covers virtually all of the residue. The
been removed with a scraper had no significant effect on surface is then quite susceptible to erosion. However,
amount of runoff. Under both conditions, however, one even with annual turnplowing, leaving the residues on
ton of straw per acre reduced the velocity of the runoff the field is far better than removing them. Regular
by about 60 percent (4.5). incorporation of crop residues by plowing gradually
Partial incorporation of the residues by shallow increases the amount of organic materials in the soil and
tillage, such as disking, reduces the percentage of surface improves water intake and soil structure. For 82
cover and loosens some of the soil for easy detachment. plot-years of continuous corn with residues removed
The residues are then less effective than equal quantities each fall, runoff during the seedling and establishment
left undisturbed on the surface. In a test under 5 inches months averaged 83% of corresponding losses from
of simulated rain, no-till planting without prior disking fallow-, for 50 plot-years in which the residues were
reduced soil loss 83 percent in contrast to a 73 percent plowed down each year, runoff in those months aver-

1.0

CL8

X
0
0.6

0.4 --- N_\

0.2

01
0 20 40 60 80 100

% OF SURFACE COVERED BY MULCH

Figure 2-Effect of plant-residue mulch on soil loss.

aged 5 1 % of that from fallow (90). Annual soil loss was Conventional tillage includes primary and secondary
about 20% less where residues were incorporated than tillage operations normally performed in preparing a
where they were removed. seedbed for a given crop grown in a given geographic
area. Where the term is used in this manual as a basis for
Improved Tillage Methods comparisons, it includes moldboard plowing and several
disking and smoothing operations.
That influence of a tillage practice on the disposition Minimum tillage is the minimum soil manipulation
of crop residues is extremely important for erosion and necessary for crop production under existing soil and
sediment control is evident from the preceding discus- climatic conditions. The term is often loosely applied to
sion. The surface microtopography and condition of the any system with fewer operations than a conventional
soil after tillage also strongly influence the amount of system, but it is most accurate when applied to
soil erosion. Roughness of the soil surface and porosity plow-plant and wheeltrack-plant systems, in which the
of the tilled layer are important parameters in describing field is plowed but secondary tillage is omitted. These
the structure of a tilled soil (31). Rough surfaces detain systems are most effective for erosion control when the
considerable quantities of water in mic rode pressions rowcrop follows one or more years of meadow, and
until they can enter the soil, and the porous soil layer before the clods disintegrate.
offers a channel system to funnel water throughout the Conservation tillage includes tillage systems that
tilled layer. Random roughness reduces runoff velocity, create as good an environment as possible for the
and the water that is temporarily ponded in the growing crop and that optimize conservation of the soil
depressional areas shields portions of the soil surface and water resources, consistent with sound economic
from particle detachment by raindrop impact. Also, practices. Conservation tillage includes maximum or
some of the sediment detached by raindrop impact on optimum retention of residues on the soil surface and
the exposed surfaces is deposited on the ponded use of herbicides to control weeds (98)
surfaces. Porosity and roughness are influenced by the No-till is a system whereby a crop is planted directly
type of tillage and by the water content of the soil at the into a seedbed untilled since harvest of the previous
time of tillage. Pulverizing the soil increases erosion by crop.
increasing the soil's detachability and increasing the
amount and rates of runoff. Residual Effects of Previous Crops
When soil dries after a rain that has broken down its
surface structure and washed fines into soil voids, crusts The benefits of crop rotations for minimizing periods
develop that are strong enough to reduce seedling 0
emergence (20, 47). Surface seals and crusts reduce of little or no vegetative cover were pointed out earlier,
water intake by the soil and substantially increase but crops and management practices also have residual
erosion (41, 78). Rough soil surfaces tend to concentrate effects that influence soil erodibility under succeeding
the dispersed material in the microdepressions and leave crops.
the peaks more porous, but mulches are more effective
for preventing surface seal. Sod-based Rotations
Soil compaction by heavy equipment can hamper
root and plant development and thereby increase soil The greatest residual effects are derived from grass
erosion. Conservation tillage practices generally require and legume meadows. In data assembled from conven-
less use of heavy equipment on the field. Aspects of soil tional seeding and tillage practices, soil losses frorn corn
compaction were recently summarized,by the American following meadow ranged from 14 to 68 percent of
Society of Agricultural Engineers (2). corresponding losses from corn on adjacent plots in
Larson (30) points out that the secondary soil meadowless systems. Grass and legume mixtures were
aggregates around the seed and seedling roots inust be more effective than legumes alone. The erosion-control
small enough to prevent undue drying of the soil, must effectiveness of rotation meadows tumplowed before
provide sufficient soil-seed or soil-root contact for corn planting was, in general, directly proportional to
moisture transfer, must provide adequate aeration, and the quality of the meadow, as measured by hay yields.
must not be so finely divided as to encourage surface Erosion reduction was greatest during the fallow and
crusting or mechanical impedance when dry. However, corn-seeding periods and decreased gradually for about 2
the area between the rows, which he designates as the years. The effects of well-managed long-term meadows
water management zone, may be rough and cloddy or were still apparent in the third year. When second-year
may be left untilled under a residue mulch. hay yield exceeded the first, 2-year meadows were more

effective than one-year meadows, but when allowed to ness of contouring is also impaired by decreased infiltra-
deteriorate in the second year they were less effective tion capacity due to surface sealing, and by reduction in
(81). depression storage after tillage operations cease and the
soil settles (59).
Meadowless Systems
Crops that are not sod forming also have beneficial Graded Rows
residual effects on soil erodibility, but they are muc Graded rows are land-formed to a precise gradient.
less pronounced than those of grass and legume mead- This improves surface drainage and decreases the likeli-
ows. Corn generally leaves the soil less erodible than hood of row breakovers.
soybeans but more erodible than good quality small
grain. All crop systems have beneficial residual effects
relative to continuous fallow; brief periods of fallow in a Contour Stripcropping
rotation are not as erodible as continuous fallow.
Removal of the crop residues year after year gradually Alternating contoured strips of sod with strips of row
reduces soil organic matter and adversely affects Sol crops is more effective than contouring alone. The sod
tilth. One-time incorporation of residues by moldboard strips serve as filters when rows break, and much of the
plowing had little effect on infiltration or erosion, but soil washed from a cultivated strip is filtered out of the
repeated incorporation year after year had very substan- runoff as it spreads within the first several feet of the
tial effects (90). sod strip (64). In the Mormon Coulee near LaCrosse,
Wisconsin, some fields are reported to have been
Mechanical Support Practices cropped in strips for more than 70 years. Where the
strips were on the contour, or nearly so, erosion control
These are mechanical erosion-control practices used was good. Where the strips were sufficiently off-contour
when slopes are too long or too steep for agronomic to give row slopes of 5 percent or more, soil losses from
practices alone to control erosion. flow of runoff down the rows were high (8).
Systems with alternate contoured strips in meadow
Contouring reduce soil loss to about half of that from the same
rotation with contouring alone. Three-year rotations of
Furrows made by plowing, planting, and cultivating sod, small grain, and row crop were slightly less
form natural channels in which runoff accumulates. if effective. Alternate strips of fall-seeded grain and row
the tillage is up and down slope, the shear stress of the crop have effected some reduction in soil loss, but
alternate strips of spring-seeded grain and corn on
runoff increases as the slope of the furrows increases, moderate to steep slopes have not proved more effective
and erosion may be serious. than contouring alone (64).
In contouring, tillage operations are carried out as Buffer stripcropping is a practice in which strips of
nearly as practical on the contour. The general rule is to grass are laid out between contour strips of crops in the
lay out guidelines which assure that all tillage is within a regular rotations. The grass strips may be irregular in
gradient limit of I to 2 percent (59). On gently sloping width and may be placed on critical slope areas in the
land, contouring will reduce the velocity of overland field (5 9).
flow by channeling it around the slope. Contoured ridge
or lister planting substantially increases the storage
capacity of the furrows and permits storage of large Terracing
volumes of water. When contouring is used alone on
steep slopes or under high rainfall intensities and soil Terracing with contour farming is more effective for
erodibility, the hazard of gullying is increased because erosion control than stripcropping, because it divides the
row breakovers may release the stored water. Breakovers slope into segments with lengths equal to the terrace
cause cumulative damage as the volume of water spacing. With stripcropping or contouring, the entire
increases with each succeeding row. If the contour lines field slope length is the effective length. With striperop-
are not carefully laid out and rows are allowed to cross ping, the saved soil is largely that deposited in the sod
natural depressions at gradients much greater than 2 strips; with terracing the deposition is in the terrace
percent, adverse results of breakovers may completely channels and may be as much as 80 percent (96) of the
offset the beneficial effects of contouring. The effective- soil moved to the channel. Erosion control between

terraces depends on the crop system and other manage- across the slope of rolling land. They may be either
merit practices; with stripcropping, an effective sod- channel type or ridge type. The primary purpose of the
based rotation is built into the system. graded or channel-type terrace is to remove excess water
If a control level is desired that will maintain soil in such a way as to minimize erosion. The primary
movement between the terraces within the soil-loss purpose of the level or ridge-type terrace is moisture
tolerance limit, the P factor for terracing should equal conservation; erosion control is a secondary objective.
the ? factor for contouring. However, if the soil loss The channel is level and is sometimes closed at both ends
equation is used to compute gross erosion for watershed- to assure maximum water retention. The Zingg conserva-
sediment estimation, a terracing P factor equal to 20 tion bench terrace is designed for use in semiarid regions
percent of the contour factor is warranted (96). Since for moisture conservation. It consists of an earthen
terracing shortens the slope length, it also reduces the embankment and a very broad flat channel that re-
between-terrace soil loss by decreasing the topographic sembles a land bench.
factor. Dividing a slope that is steeper than 4% into n The steep-backslope terrace is constructed with a
equal segments divides the value of factor L by Jn. In backslope of 50% or steeper, which is kept in grass (8).
the table of P values given in Volume 1, this reduction It may be either a graded or a level terrace. Parallel
was included in the Pt factor for convenience. grass-backslope terraces with subsurface drains are now
7he two major types of terraces are the bench terrace gaining popularity. They release the excessive water
and the broadbase terrace 1,59). Broadbase terraces are slowly and are also better adapted to use of large farm
broad-surface channels or embankments constructed implements than graded or level terraces.

SEDiMEM7 DELWE RY RA7@GS

The sediment delivery ratio is the parameter that Delivery Ratios for Dealing with Ooiftmstream
bridges the gap between upslope erosion data and Sediment Problems
drainage-area sediment yield. The sum of the soil-loss
estimates for the individual tracts constituting a drainage For this purpose, the delivery ratio is defined as the
area approximates the quantity of soil moved from its ' ratio of sediment delivered at a given point in the stream
original general position. 70 compute drainage-area system to the gross erosion from all sources in the
sediment yield, this estimate must be adjusted down- watershed above that point. Guides for estimating this
ward to compensate for deposition in terrace channels, ratio were given in Volume 1, section 3.3c. The source of
in sod waterways, in field boundaries, at the toe of field most of the information presented there was the
slopes, in depressional areas, and along the path traveled Sedimentation Section of the National Engineering
by the runoff as it moves from the field to a continuous Handbook developed by the Soil Conservation Service
stream system or lake 196). Sediment additions from (72). The approximate delivery ratios that were listed
sources along this path must also be taken into account. relative to watershed size were obtained from the
Further changes in sediment content of runoff water will relationship curve derived from published and unpub-
occur during the stream transport phase, The Universal lished data assembled by L. C. Gottschalk, G. M. Brune,
Soil Loss Equation computes gross sheet and rill erosion, J. W. Roehl, R. Woodburn, S. 3. Maner, L. H. Barnes,
but it does not compute deposition. Nor does it and L. M. Glymph and presented in the Engineering
compute sediment from gully, streambank, and channel Handbook. This curve relates the delivery ratio to the
erosion. The sediment delivery ratio provides a method negative 0.2 power of drainage-area size. There have
of accounting for the sediment losses and gains that been indications that the 0.1 power would be more
occur below the areas where the USLE is applied. accurate for large drainage areas (3).
The delivery ratio is usually estimated from natural Analyzing data from 14 Texas Blackland Prairie
drainage-area parameters and therefore does not account drainage areas that ranged from 0.42 to 97.4 square
for deposition in terrace channels or in constructed miles, Renfro (57) computed delivery ratios ranging
settling basins or traps. The amount of sediment from 0.62 for a drainage area of 0.5 square mile to 0.28
deposited in these man-made devices near the sediment for an area of 100 square miles. These are significantly
source is subtracted from the computed field erosion to larger than would have been estimated from the SCS
obtain the gross-erosion estimate to which the delivery general relationship curve, and emphasize the need to
ratio is applied. 7WO methods of defining the delivery consider the other factors listed in Volume I as well as
ratio will be discussed. watershed size. Several other relevant publications are

listed in the literature citations (3, 13, 23, 24, 53, 56, Anything that reduces runoff velocity (reduction in
07). slope steepness, physical obstructions such as ridges or
Delivery ratios derived on this basis are more appro- living or dormant vegetation, ponded water, etc.) re-
priate for dealing with downstream sedimentation prob- duces its capacity to transport sediment. When the
lenis than for estimating the arnount and composition of sediment load exceeds the transport capacity of the
cropland sediment that reaches a continuous stream runoff, deposition occurs. The observed sediment reduc-
system. However, they are presently more directly tions by terracing or contour stripcropping, are examples
available than those discussed below and can be helpful of the potential magnitude of upslope deposition. More
also for the latter purpose. than 80% of the soil eroded between terraces may be
deposited in the terrace channels because of the large
Delivery Ratios for Purposes of this Manual reduction in runoff velocity due to the terraces. Most of
For evaluation of cropland contributions to sediment the soil eroded from cultivated strips has been observed
in stream systems, the delivery ratio should be defined as to be deposited in the sod strips when contoured strips
the ratio of sediment delivered at the place where the of sod were alternated with equal-width strips in
runoffenters a continuous stream system or lake to the cultivated crops.
gross erosion in tile drainage area above that point. It Relative to the sediment-source area, the delivery
will then not be biased by sediment-content changes that ratio will generally be directly related to amount of
occur during the stream transport phase. Where this ratio runoff and inversely related to soil particle size. Relative
is known or can be closely approximated from drainage- to the land between the source area and the stream
area parameters, multiplying it by the computed gross system, the ratio will be directly related to slope
erosion will estimate the amount of sediment delivered steepness and amount of channel-type erosion, and
to the stream systern. inversely related to: distance of the source area from the
No general equation for sediment delivery ratios as a strearn system or lake; density of vegetation at ground
function of drainage-area parameters is presently avail- level@ and number of flow obstructions such as field
able. A generally applicable upslope-deposition equation boundaries, culverts, etc.
is a major research need. However, guides for approxi- The delivery ratio for a given drainage area will not be
inating the average delivery ratio for a particular constant for all runoff events, because the depth and
drainage area are available. The ratio can approach a velocity of runoff will differ with storm size and
Value of 1.0 for a particular field if the runoff drains antecedent surface conditions. These differences will not
directly into a lake or stream system, with no obstruc- only affect transport efficiency: a major runoff event
tions and no flattening of the land slope. On the other may also pick up some of the sediment deposited
hand, a wide expanse of forest duff or dense vegetation enroute to the stream or lake in prior events. The
below the eroding area may filter out essentially all of average delivery ratio for a drainage area can be
the sediment except some of tile colloidal material. estimated more closely and should suffice for estimates
These are the extremes. of long-term average sediment yields.

TOLERANCE LIMITS

This section discusses merits and tiniitations of several Tolerances for Preservation of Cropland
alternative methods of defining soil loss or sediment Productivity
limits, as background information for those who may be
involved in developing state sediment control standards. Tolerance limits on average annual soil loss have been
Soil loss limits used to illustrate points are not intended used in this country for a quarter century to guide soil
as specific recommendations. conservation planning. Limits ranging from 2 to 5 tons
Optimum soil-loss limits for preservation of cropland per acre are applied to individual field slopes. Experience
productivity may differ substantially from optimum has shown these limits to be feasible and generally
sediment standards for control of runoff pollution from adequate for preservation of high productivity levels.
nonpoint sources. The underlying considerations are The 2 to 5 ton tolerances represent the collective
quite different, and specific differences must be recog- judgment of soil scientists in the Soil Conservation
nized. Standards will be most beneficial when they Service, Agricultural Research Service, and State agricul-
achieve both objectives with the least possible adverse tural experiment stations in the 1950's. Factors consid-
effect on production of food and fiber. ered in defining these limits were published by the Soil

Conservation Service in reports of five regional soil loss include: upslope deposition, composition of the sedi-
prediction workshops held from 1960 to 1962. ment, the protection needs, and fluctuations in sediment
One of the major considerations was longtime mainte- loads.
nance of adequate soil depth for good plant growth. The
rate of natural soil renewal for mature soils has been Upslope Deposition
hypothesized to balance the rate of erosion under
natural conditions, without influences of man (65). For control of water pollution from nonpoint sources,
Since erosion in excess of renewal rates reduces soil soil material eroded from a field slope but deposited in
depth, shallow soils were assigned lower tolerance limits terrace channels, field boundaries, or elsewhere along the
than those for deep soils with subsoil characteristics path followed by the runoff enroute to the stream
favorable for plant growth. Prior erosion was a factor system is irrelevant. The fractions of sediments eroded
because of its effect on the soil profile. Other considera- from upslope areas that are delivered to a continuous
tions included the prevention of Field gullying, sedimen- strearn system or lake range from less than 10% to nearly
tation problems, seeding losses, soil organic matter 100%. Uniform limits on erosion rates will allow a wide
reduction, and plant nutrient losses. Research directed range in quantities of delivered sediments. Estimating
to precise definition of soil loss tolerances (65, 68) has sediment delivery ratios was discussed in the preceding
been extremely limited. section. Low sediment delivery ratios are of little
relevance to preservation of the eroding cropland, but
they are highly important for water quality control.
Tolerances for Sediment Control Basing sediment standards on gross erosion ininus the
estimated upslope deposition would achieve more uni-
Sediment-control standards that coincide with the form control of sediment quantity and allow greater
tolerances established for purposes of soil conservation cropping flexibility. This would be a great improvement,
have the distinct advantage that a farmer is in compli- but sediment quantity is not the only important
ance if he follows a conservation plan approved by the criterion.
SWCD. These plans include a safety factor in that they
are generally designed to protect the most erodible
portion of the Field. Since field slope gradients are Composition Of The Sediment
seldom uniform, the average soil loss for the entire field
is usually less than that on the slope the plan is designed Sediment traps or settling basins trap primarily the
to protect. coarse material. Clay, fine silt, and light soil aggregates
Uniformly applied sediment-control standards based remain in suspension much longer than the coarse
on average annual soil losses are perhaps the most material and are the greatest concern as a source of
feasible starting point, because of their simplicity and turbidity and carrier of chemical compounds. There is
because knowledge of precisely how much upslope soil some particle-size selectivity in erosion, but generally the
movement can be tolerated is inadequate. But if the composition of washoff material as it leaves the field is
initial standards fail to attain the desired level of water closely related to that of the soil from which it is
quality control, the next step should be a range in derived. There is substantial size selectivity in the
standards to suit the requirements of various local transport and deposition phases, but the composition of
conditions rather than successive lowerings of uniform the sediment as it leaves the field will deten-nine the
limits. Uniformly lowering soil loss limits to attain proportion of Fine material available for transport in
higher water-quality goals would unnecessarily remove suspension. Thus, for pollution control, variability in
substantial acreages from grain production. soil-loss limits should be related to soil texture.
Before quantifying gross-erosion limits for cropland,
specific objectives of the limits should be defined. Protection Needs
Uniform soil loss tolerances reduce the total quantity of
sediment produced. This is important for reduction of Sediment standards could also be selective in relation
direct damage by deposition on upslopc areas, on flood to the needs of the particular body of water being
plains, and in lakes or drainage ditches. But for control protected. For example, controls need to be more
of water pollution from nonpoint sources, other aspects intensive for land draining into recreational waters and
of the problem may be more important than the amount urban water supplies than for land draining into major
of soil eroded frorn a particular field slope. These river channels.

Fluctuations In Sediment Loads Limits prescribed on a crop-year basis would reduce
the frequency of very high single-year or single-event soil
Short-time high sediment yields are much more losses. In the preceding example, a 5-ton limit on the
relevant for pollution control than for preservation of design loss in any year of the cropping system would
the land resource. The average annual soil loss from a require the use of good residue management for the
particular crop system on a given field is the mean of second-year corn and no-till planting in shredded-corn-
yearly losses that may differ tenfold, or even a hundred- stalk mulch for the third corn year. If the soil and
fold, due to differences in the cover and management climate were not compatible with no-till planting in
effects of the crops in the system, fluctuations in rainfall residue cover, the third-year corn would need to be
erosivity, and intermittent crop failures. omitted from the cropping system.
The soil loss equation shows that under conditions However, crop-year soil loss limits would need to be
where a 6-year rotation of corn-com-com-wheat- higher or more flexible than the present rotation -average
meadow-meadow would average 5 tons of soil loss per tolerances. If not, they would prevent production of
acre per year with conventional planting and tillage, the corn, soybeans, or other rowcrops on numerous fields
first-year corn would average about 4 tons, second-year where these crops can be grown in rotation with
corn 9 tons, third-year corn 14 tons, wheat 2.7 tons, and meadow and small grain, and they could also eliminate
meadow 0.2 ton. On the average, at least half of the soil the acceptability of periodic clean plowing for weed and
loss from the corn would occur during the first month pest control on fields that are usually no-till planted.
after preparation of the clean-tilled seedbed. Appendix The reason for this is that crop-year limits would allow
tables in Agricultural Handbook No. 282 (96) show that no credit for much more drastic reductions in soil loss
about one year in ten the rainfall-erosivity factor is during other years in the crop system.
likely to exceed its local average value by 50 percent,
and one year in twenty by 75 percent. If a 20-year Modified Sediment Standards
rainfall occurred in the third corn year, the predicted
soil loss for that year on this field would be 1.75 times A possible alternative would be to continue the
14 tons, or nearly 25 tons, even though the longtime present crop -system -average tolerances and superimpose
crop-system average would not exceed the 5-ton limit, limits on the maximum design loss for any one year in
Soil loss variability due to fluctuations in rainfall or the system. The first limit would allow credit for
occasional seeding failures cannot be prevented, and meadows and other low-erosion crops in a system
yearly or seasonal rainfall differences can be predicted designed to preserve the productive capacity of the land.
only on a probability basis. Because these differences The second limit could be sufficiently higher to avoid
interact with other erosion factors, specific-storm soil unnecessary restrictions on land use and yet guard
losses can presently not be accurately predicted. How- against frequent occurrence of very high single-year
ever, for each crop in the system, the effects of sediment yields.
fluctuations in rainfall tend to average-out over long The second limit would take into account such
time periods, and the differences in cover and manage- factors as the intermittent more erodible conditions that
ment effects of the crops in a particular system are cannot be avoided, upslope deposition, soil texture, and
reasonably well known. Therefore, the average annual specific control needs for the location. Upslope deposi-
soil loss for each year in a crop sequence can be tion could be increased by requiring use of sediment
predicted by use of the Universal Soil Loss Equation traps or filter strips of grass or small grain across the
with about the same accuracy as crop-system averages. lower end of a field in the years when it is plowed. The
This is done by deriving factor C on a yearly basis by the same requirement could apply to the second and third
method illustrated in Agriculture Handbook No. 282. corn years in sod-based rotations.

RESEARCH NEEDS

The past 40 years have brought great progress in on many millions of acres of productive cropland. Urger
erosion control, but serious erosion and sediment dam- fields generally mean longer continuous slopes. Exten-
ages are still far too frequent. Population pressures, sive monoculture sacrifices the potential residual effects
increased export demands for agricultural products, and of sod-based systems. Large equipment greatly increases
more substitution of large machines for manpower production per man-hour but is not compatible with
changed the erosion problems and intensified the hazard following the field contours on much of the cropland.

Furthermore, soil conservation and sediment control are mentation and to predict specific events more accu-
two individual goals and do not have the same require- rately. However, some of the basic relationships assumed
merits. Personnel and resources available for erosion for these initial models need research testing, and the
research in recent years have been insufficient to keep parameters need to be defined for a wide range of field
pace with the changing needs. Research is particularly conditions. Relationships describing erosion and deposi-
needed in the following general areas. This research will tion in channels and gullies also need to be derived.
involve many preliminary and secondary investigations These models are generally complex and difficult to
that are not listed. use in the field. A relatively simple model that computes
in divi dual -storm soil losses more accurately than the
Sediment DeEvery to Stream.. Systerris Universal Soil Loss Equation is needed. Such a model
can use the basic format of the USLE, but it will need
Average annual erosion rates on cropland can be separate erosivity factors for rill erosion and interrill
predicted with reasonable accuracy, but the percentage erosion, and their relationships to the other factors in
of this eroded soil that reaches a continuous stream the equation will need to be determined. Use ofvolume
system cannot. Sediment delivery ratios as usually and peak rate of runoff to predict rill erosion shows
defined by geologists for dealing with downstream promise, but it requires derivation of a cropland-runoff
sediment problems are influenced too much by stream prediction equation.
transport efficiency and sediment accretions frorn non- Improvement of the basic models, and research to
agricultural sources to provide the information needed deterniine the needed parameter relationships, should be
for control of water pollution from nonpoint cropland emphasized. Such models can provide more dependable
sources. If the sediment delivery ratio is used for this interpretation and extrapolation of field-plot data, and
purpose, it should be defined as the ratio of sediment the predictions of spatial and temporal variations in
delivered at the place where the runoff wvter enters a erosion and deposition are needed for both conservation
continuous stream system to the gross erosion from the and pollution-control planning.
drainage area above that point.
The sediment delivery ratio, by either definition, Residue Management
represents an attempt to reflect deposition and sediment
accretions in a single factor. The net effect of the two Residue managernent is one of the major tools for
processes would be difficult to relate to drainage-area erosion control. In the densely populated countries, few
parameters in a regression equation because large residues are usually available for erosion-control use
amounts of deposition and large sediment accretions can because they are needed for other purposes. We may
occur in the same drainage area and balance each other. soon have similar problems in this country if crop
Prediction equations for deposition and for sediment residues become economically profitable sources of
accretions from runoff-induced erosion below the field energy, concentrated feeds, or building materials. Re-
areas need to be separately derived, each as a function of search must determine the optimum treatment and
the drainage-area parameters pertinent to that process. placement of very limited residues and the optimum
Such equations will facilitate estimating the effects of amount and type of associated tillage required to
cropland erosion control not only on the amount of minimize erosion in the absence of what we now
sediment delivered to the stream system but also on the consider adequate cover.
cornposition of sediment yields farther downstream. Neither has the optimum amount and placement of
Development of a better understanding of the basic residues where they are abundantly available been
sedimentation and erosion processes involved between determined. Optimum placement of a portion of the
the time when runoff leaves a Field area and when it residue may permit incorporation of the remainder into
reaches a continuous stream system is one of the greatest the topsoil. This may reduce soil-temperature and
erosion and sediment research needs. wetness problems without decreasing the erosion con-
trol.
Mave-mat'ca] ModsHng
Critical Slope-Length Limits for Practice
Recent progress in development of mathematical Effectiveness
models for simulating the erosion and sedimentation
processes on field-size areas and on watersheds has Critical slope-length limits for effectiveness of partial
demonstrated the potential of such models to predict mulch covers and favorable micro topographies provided
temporal and spatial distribution of erosion and sedi- by conservation tillage practices need to be determined.

If limits can be defined in terms of depth and velocity of the topographic factor can be predicted. This is impor-
runoff, they can then be related to soil, topography, and tant both for soil conservation planning and for pollu-
rainfall characteristics for guidance in field application. tion control guides.
Clear definition of critical slope-length and drainage-area Topographic effect also needs to be determined for
limits is needed for improved terrace spacing design and steep roadbank and construction slopes and for long
to prevent unexpected failures of some agronomic watershed slopes. Existing slope-length and steepness
practices. The investigations should include evaluation of formulas were derived from data on slopes not steeper
anchored versus loose mulches and of different types of than 18% and, with only one exception, not longer than
residues. 270 feet. Extrapolation of the formulas to slopes that
Slope-length limits for effective contouring need to far exceed these dimensions is quite speculative.
be more accurately def"med in relation to permeability,
soil stability, crop cover, and other factors. Successive Soil Erodibility
row breakovers can result in rill erosion that more than
offsets the reduction in sheet erosion effected by the The soil-erodibility nomograph needs to be aug-
contouring. mented for greater accuracy on high-clay subsoils and on
sandy loams. Effects of soil chemistry on erodibility
Erosion Index for Special Conditions need further investigation and quantification. Suscepti-
bilities of soils to sheet erosion and to rill erosion should
The El parameter is a good indicator of the erosive be evaluated separately, and influences of montmoril-
potential of the rainfall and runoff in most of this linitic clays need further study. Stripmine areas and
country, but there are a few conditions for which spoilbanks need specific research attention.
further investigation of this factor is urgently needed. Particle size sorting in erosion and sedimentation is
The erosivity of surface runoff that is not directly important for pollution control and has not been.
associated with drop impact needs to be evaluated, such adequately investigated.
as runoff from thaw and snowmelt. This item is
particularly important in the Palouse Region of the Runoff Equation
Northwest. The effects of soil-surface shielding by
ponded or very slowly moving runoff also need to be A cropland runoff equation designed for general field
identified and evaluated. These effects may account for use would be a valuable asset in pollution control
the difficulties experienced with the El parameter on the planning. It could also provide an additional factor for
Coastal Plains of the Southeast. the Universal Soil Loss Equation that would improve its
accuracy, particularly for moderate storms.
Topographic Factor
Sediment Traps
The topographic factor needs further research, both
with reference to factor interactions and with reference Vegetated filter strips, settling basins, and sediment
to long or steep slopes. The effects of slope length and traps can be used to cause sediments to deposit near the
steepness on soil erosion are known to be more variable point of origin, but more needs to be learned regarding
than indicated by existing formulas. There is evidence their design for optimum trapping efficiency and their
that they are significantly influenced by mutual inter- particle size selectivity. Also, extreme runoff events may
action and by interactions with cover, soil texture, and pick up substantial amounts of sediment from the traps.
rainstorm characteristics (or runoff rate). These inter- The probabilities of such occurrences and methods of
action effects need to be quantified so that variations in minimizing them need to be investigated.

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simulator for runoff plots. Agr. Engin. 39:644-648.
33. Laws, J. 0. 1941. Measurements of fall velocity of
water drops and rain drops. Trans. Amer. Geophys. 44. Meyer, L. D., and Wischmeier, W. H. 1969. Mathe-
Union 22:709-721. matical simulation of the process of soil erosion by
water. Trans. Amer. Soc. Agr. Engin. 12:754-758,
M. Lelland, J. H., Rogers, H. T., and Elson, J. 1941. 762.
Effect of slope, character of soil, rainfall, and
cropping treatments on erosion losses from Dun- 45. Meyer, L. D., Wischmeier, W. H., and Foster, G. R.
more silt loam. Va. Polytech. Inst. Tech. Bul. No. 1970. Mulch rates required for erosion control on
72, 31 p. steep slopes. Soil Sci. Soc. Amer. Proc. 34:928-931.

46. Middleton, 14. E., Slater, C. S., and Byers, H. G. 58. Roth, C. B., Nelson, D. W., and Ronikens, M. J. M1.
1932-1934. Physical and chemical characteristics of 1974. Prediction of subsoil crodibility using chem-
the soils from the erosion experiment stations. ical, mineralogical and physical parameters. Rep.
7ech. Bul. No. 316 and No. 430, U. S. Dept. Agr., EPA-660/2-74-043, I I I p. U.S. Govt. Printing Off.,
Washington, D.C. Washington, D. C.
47. Morton, C. T., and Buchele, W. F. 1960. Emergence 59. Schwab, G. 0., Frevert, R. K., Edminster, T. W.,
energy of plant seedlings. Agr. Engin. 41:428-431, and Barnes, K. K. 1966. Soil and water conservation
453-455. engineering, Second Ed. John Wiley & Sons, Inc,,
48. Musgrave, G. W. 1947. The quantitative evaluation New York.
of factors in water erosion, a first approximation. 60. Skidmore, E. L., Fisher, P. S., and Woodruff, N. P.
Jour. Soil and Water Conserv. 2:133-138. 1970. Wind erosion equation: computer solution
and application. Soil Sci. Soc. Amer. Proc.
49. Newman, J. E. 1970. Climate in the 1970's. Crops 34:931-935.
and Soils 22(4):9-12.
50. Olson, T. C., and Wischmeier, W. H. 1963. Soil 61. Skidmore, E. L., and Woodruff, N. P. 1968. Wind
erodibility evaluations for soils on the runoff and erosion forces in the U. S. and their use in
erosion stations. Soil Sci. Soc. Amer. Proc. predicting soil loss. U.S. Dept. Agr., Agr. Handbook
27:590-592. No. 346. U. S. Govt. Printing Off., Washington, D.
C., 42 p.
51. O'Neal, A. MI. 1952. A key for evaluating soil 62. Smith, D. D. 1941. Interpretation of soil conserva-
permeability by means of certain field clues. Soil tion data for field use. Agr. Engin. 22:173-175.
Sci. Soc. Amer. Proc. 16:312-315.

52. Onstad, C. A., and Foster, G. R. 1975. Erosion 63. Smith, D. D., and Wischineier, W. H. 1957. Factors
modeling on a watershed. Trans. Amer. Soc. Agr. affecting sheet and rill erosion. Trans. Amer. Geo-
Engin. 18:288-292. phys. Union 38:889-896.
53. Pacific Southwest Inter-Agency Committee. 1974. 64. Smith, D. D., and Wischmeier, W. H. 1962. Rainfall
Report of water management subcommittee, ero- erosion. In Advan. in Agron. XIV:109-148. Aca-
sion and sediment yield methods, 45 p. demic Press, Inc., New York.
54. Parr, j. F., and Bertrand, A. R. 1960. Water 65. Smith, R. M., and Stamey, W. L. 1965. Determining
infiltration into soils. In Advan. in Agron. XII: the range of tolerable erosion. Soil Sci.
311-363. Academic Press, Inc., New York. 100:414424.
55. Pecle, T. C., Latham, E. E., and Beale, 0. W. 1945. 66. Soil Conservation Society of America. 1970. Re-
Relation of the physical properties of different soil source conservation glossary. 52 p,
types to crodibility. South Carolina Agr. Expt. Sta.
Bul. No. 357. 67. Stall, J. B., and Bartelli, L. J'. 1959. Correlation of
reservoir sedimentation and watershed factors. 111.
56. ?iest, R. F. and Bowie, A. J. 1974. Gully and State Water Survey Rep. No. 37.
streambank erosion. Proc. 29th Ann. Mtg., Soil
Conserv. Soc. Amer.: 189-196, 68. Stamey, W. L., and Smith, R. M. 1964. A conserva-
tion definition of erosion tolerance. Soil Sci.
57. Renfro, G. W. 1972. Use of erosion equations and 97:183-186.
sediment delivery ratios for predicting sediment
yield. Proc. Sediment Yield Workshop, Oxford, 69. Stanford, G., England, C. B., and Taylor, A. W.
Miss. In press, U. S. Govt. Printing Off., Washington, 1970. Fertilizer use and water quality. ARS 41-168,
D. C. U.S. Dept. Agr., Washington, D. C., 19 p.

70. Swanson, N. P., Dedrick, A. R., Weakly, H. E., and 82. Wischmeier, W. H. 1962. Rainfall erosion potential -
Haise, H. R. 1965. Evaluation of mulches for geographic and locational differences of distribu-
water-erosion control. Trans. Amer. Soc. Agr. tion. Agr. Engin. 43:212-215.
Engin. 8:438440.
83. Wischmeier, W. H. 1966. Relation of field-plot
71. U. S. Department of Agriculture. 1971. Basic runoffto management and physical factors. Soil Sci.
statist ics--na tional inventory of soil and water con- Soc. Amer. Proc. 30:272-277.
servation needs. Statis. Bul. No. 461. Washington,
D. C. 84. Wischmeier, W. H. 1972. Upslope erosion analysis.
Chap. 15 in Environmental impact on rivers. Water
72. U. S. Department of Agriculture. Soil Conservation Resour. Publications, Fort Collins, Col.
Service. 197 1. Sediment sources, yields and delivery
ratios. In National engineering handbook, Sect. 3. 85. Wischmeier, W. H. 1972. Erosion and sediment
Washington, D. C. research in the United States. Proc. Second Allerton
Conf. on Environmental Quality and Agriculture.
C
73. U. S. Department of Agriculture. Soil Conservation Spec. Pub. No. 25, College Agr., Univ. lll.:21-23.
Service. 1972. Land resource regions and major land
resource areas. Agr. Handbook No. 296. U. S. Govt. 86. Wischmeier, W. H. 1973. Conservation tillage to
Printing Off., Washington, D. C. control water erosion. Proc. Nat]. Conserv. Tillage
Conf., Soil Conserv. Soc. Amer.: 133-141.
74. U. S. Weather Bureau. 1958. Rainfall intensity-
frequency regime. Tech. Paper No. 29, 5 parts. 87. Wischmeier, W. H. 1974. New developments in
estimating water erosion. Proc. 29th Ann. Mtg., Soil
75. Van Doren. C. A., and Bartelli, L. J., 1956. A Conserv. Soc. Amer.: 179-186.
method of forecasting soil losses. Agr. Engin.
37:335-341. 88. Wischmeier, W. H. 1975. Estimating the soil loss
equation's cover and management factor for undis-
76. Voznesensky, A. S., and Artsruui, A. B. 1940. A turbed areas. In Present and prospective technology
laboratory method for determining the anti-erosion for predicting sediment yields and sources: 118-124.
ARS-S-40, U.S. Dept. Aar., Washington. D.C.
stability of soils. Soils and Fert., Commonwealth 0 C,
Bur. Soils 10:289. 89. Wischmeier, W. H., Johnson, C. B., and Cross, B. V.
1971. A soil erodibility nomograph for farmland
77. Wadleigh, C. H. 1968. Wastes in relation to agricul- and construction sites. Jour. Soil and Water Con-
ture and forestry. Misc. Pub. No. 1065, U. S. Dept. serv. 26:189-193.
Agr., Washington, D. C., 112 p.
90. Wischmeier, W. H., and Mannering-, J. V. 1975.
78. Whitaker, F. D., Heinemann, H. G., and Wischmeier, Effect of organic matter content of the soil on
W. H. 1973. Chen-tical weed controls affect runoff, infiltration. Jour. Soil and Water Conserv.
erosion, and corn yields. Jour. Soil and Water 20:150-152.
Conserv. 73:174-176.
91. Wischmeier, W. H., and Mannering, J. V. 1969.
79. Wischmeier, W. H. 1955. Punched cards record Relation of soil properties to its crodibility. Soil Sci.
runoff and soil-loss data. Agr. Engin. 36:664-666. Soc. Amer. Proc. 33:131-137.
80. Wischmeier, W. H. 1959. A rainfall erosion index for 92. Wischmeier, W. H., and Meyer, L. D. 1973. Soil
a universal soil-loss equation. Soil Sci. Soc. Amer. crodibility on construction areas. Highway Res.
Proc. 23:246-249. Board, Nat. Acad. Sci. Spec. Rep. 135:20-29.

81. Wischmeier, W. H. 1960. Cropping-management 93. Wischmeier, W. H., and Smith, D. D. 1958. Rainfall
factor evaluations for a universal soil-loss equation. energy and its relationship to soil loss. Trans. Amer.
Soil Sci. Soc. Amer. Proc. 24:322-326. Geophys. Union 39:285-291.

94. Wischmeier, W. H., and Smith, D. D. 1961. A 98. Witmuss, H. D., Triplett, G. B. Jr., and Greb, B. W.
universal soil-loss estimating, equation to guide 1973. Concepts of conservation tillage systems using
conservation fann planning. Trans. 7th Cong. Inter- surface mulches. Proc. Nat]. Conserv. Tillage Conf,
natl. Soil Sci. Soc. 1:418-425. Soil Conserv. Soc. Amer.: 5-12.

95. Wischmeier, W. H., and Smith, D. D. 1962. Soil-loss 99. Woodruff, N. P. 1966. Wind erosion mechanics and
estimation as a tool in soil and water management control. Proc. First Pan Amer. Soil Conserv. Cong.
planning. Pub. No. 59, Intematl. Assoc. Sci. Hy- Brazfl:253-262.
drol.: 148-159.
100. Woodruff, N. P., and Siddoway, F. H. 1965. A
96. Wischmeier, W. H., and Smith, D. D. 1965. Predict- wind erosion equation. Soil Sci. Soc. Amer. Proc.
ing rainfall -erosion losses from cropland east of the 29:602-608.
Rocky Mountains--Guide for selection of practices
for soil and water conservation. Agr. Handbook No. 101. Young, R. A., and Wiersma, J. L. 1973. The role of
282, U. S. Govt. Printing Off., Washington, D. C., rainfall impact in soil detachment and transport.
47 p. Water Resour. Res. 9:1629-1636.

97. Wischmeier, W. H., Smith, D. D., and Uhland, R. E. 102. Zingg, A. W. 1960. Degree and length of land slope
1958. Evaluation of factors in the soil loss equation. as it affects soil loss in runoff. Agr. Engin.
Agr. Engin. 39:458-462, 474. 21:59-64.

CHAPTER 4

NUTRIENT ASPECTS OF POLLUTION FROM CROPLAND

M. H. Frere

Nutrients are naturally occurring chemicals essential emphasis of this chapter is on the practices that can
for plant growth. Sixteen elements are essential for the control nutrient losses and the background necessary to
growth and reproduction of most plants. Most soils are use these practices effectively. This chapter reviews the
lacking in adequate amounts of nitrogen, phosphorus, literature and summarizes the data for nitrogen and
and potassium. Hence, fertilizers containing these nutri- phosphorus leaving cropland by runoff, erosion, and
ents are essential to maintain the current level of leaching. The material covered is limited to precipita-
agricultural production. The other nutrient elements tion-induced transport of the nutrients from cropland
may be added as impurities in the fertilizer or to treat and improved pastures. Beyond the scope of this
specific nutritional problems. Present evidence indicates overview are the very important problems of irrigation
that nitrogen and phosphorus are the principal nutrient return flow, wind erosion, and losses from waste disposal
pollutants and, therefore, only these nutrients are are as.
considered in this chapter. It must be emphasized at the beginning that the
A major source of nutrients reaching water bodies in dynamic system under consideration is very complex.
thds country is sewage, both from municipal treatment The wide variety of climates and landscapes provides
plants and nonsewered residences. These are point such a wide range of results that there is no typical case.
sources of pollution and extensive efforts are underway Complications are introduced by difficulties in chemical
to limit their contributions. Runoff from rural land is analysis for nutrients in water samples. Numerous
another major source. Unlike point sources, runoff procedures have been followed for chemical analysis.
integrates the contribution of nutrients and water from a Changes in nutrient form can occur between the time
wide variety of landscapes that are continuously chang- the sample is taken and when it is analyzed. Some of the
ing with time. It must be recognized that nutrients leak nutrient reported as soluble could have been associated
from the system even when fertilizer is not applied and with colloidal material not removed. The practical
while we cannot eliminate nutrient losses, it is desirable significance of these complications is unknown, but they
to minimize them. are noted at this time to warn the reader of the
While a number of review papers have been written limitations of the data associated with nutrient pollu-
about nutrient losses (47, 76, 89, 98, 145, 167) the tion.

THE PROBLEMS
Two problems are associated with nutrients in the water. The nitrite forrn of nitrogen, which is the most
aquatic environment: the water may be toxic to humans, toxic, interacts with components in the blood to
animals, or fish when the concentration of certain interfere with oxygen transport. Methemoglobinemia,
nutrient forms exceeds a critical level; and eutrophica- the technical name given to this illness, is often called
tion may be accelerated. "the blue baby syndrome" because infants are very
susceptible. Most of the problems with drinking water
have been associated with farm wells with faulty well
Toxicity casings and located close to manure concentrations such
as barnyards.
Case (28), Lee (92), and Winton (181) reviewed the Nitrate is 5 to 10 times less toxic than nitrite and
problems associated with nitrates and nitrites inarifiking healthy mature animals with single stomachs are able to

excrete nitrate in the urine. Cattle, young animals, and exceeds about 0.015 ppm. These concentrations of the
children convert some of the nitrate to nitrite in their inorganic forms of nutrients are maintained by microbial
stomachs and can develop methemoglobinemia. Since conversion of organic forms so the total input of
food also contains nitrite and nitrate, the response to nitrogen and phosphorus per unit area of the lake
nitrate in drinking water could be quite variable. The U. (loading rate) is important (57). Current international
S. Public Health Service Drinking Water Standards of guidelines for eutrophication control are 1.8 to 4.5 lbs.
1962 set the limit for nitrate at 10 mg N per liter (45 of P and 45 to 90 lbs. of N per surface acre of lake per
ppm nitrate). Armitage (5) reported the Recommended year (169).
Drinking Water Standards of the World Health Organi- The various roles of nitrogen in eutrophication have
zation to be: 0-50 pprn nitrate = recommended, 50-100 been recently reviewed (24, 53). Aquatic organisms
ppm. nitrate = acceptable. There is some concern, assimilate nitrate and ammonium. Ammonia and amino
however, that even nontoxic nitrate levels (chronic acids are excreted by live organisms and released by
conditions) may lower resistance to environmental decaying organisms. Fungi and bacteria can convert the
stresses and interfere with normal metabolism. organic nitrogen in dead plant material and sediment to
Dissolved ammonia is another form of nitrogen that ammonia and nitrate. Whenever the environment be-
can occur at levels toxic to fish. Microorganisms can comes anaerobic, in the presence of decomposable
generate free ammonia from organic matter in lake organic matter, nitrates are denitrified to gaseous nitro-
bottoms during summer stagnation periods (164). Trout gen compounds. Bouldin (20) estimates that the daily
are sensitive to 1-2 ppm ammonia (35) while goldfish loss of the nitrate in the bottom sediments can be 7 to
appear to be less sensitive (48). 15 percent by microbiological denitrification and 2 to
28 percent of the ammonia by volatilization.
Some additional inputs of nutrients are often over-
Eutrophication looked, such as aquatic birds, leaves, dust, and pollen.
Another source is the fixation of atmospheric nitrogen
Eutrophication is the enrichment of waters by nutri- into organic nitrogen by a number of organisms such as
ents and the ensuing luxuriant growth of plants. Much the blue-green algae. This process is considered to be
has been written about this subject in the last few years adaptive in that it occurs when other sources of nitrogen
(100, 111, 153, 169). Rapid growth of algae is the are depleted.
greatest and most widespread eutrophication problem in Kramer et al. (86) and Lee (93) reviewed the role of
most states (2). Algae can create obnoxious conditions various phosphorus compounds in eutrophication. Sol-
in ponded waters, increase water treatment costs by uble orthophosphate is usually regarded as completely
clogging screens and requiring more chemicals, and cause available for algal growth. Soluble organic phosphates
serious taste and odor problems (17). When a large mass and polyphosphates are probably not too available, but
of algae dies and begins to decay, the oxygen dissolved are readily converted to orthophosphate. Finally, phos-
in the water decreases and certain 'toxins are produced, phate in particulate organic matter and adsorbed to
both of which kill fish (49). The complexities of the mineral sediments is usually only slowly released. The
ecosystem are illustrated by the observation that the adsorption capacity of the sediment for phosphate
nutritional status of a species of algae can vary from lake ranges from low for quartz sand to very high for certain
to lake or even from different areas and depths of the silicate clays.
same lake on the same day (39). Streams, however, do Sediment low in phosphate will usually remove
not age in the same sense as lakes, but their biological phosphate from solution as it settles out (63, 64, 80, 93,
productivity can be increased by added nutrients (69). 179). When the sediments have high P contents and the
For example, phosphate from farm land was a very environment around the clay is electrochemically re-
beneficial and important factor in the high production duced, then some of the phosphate can be released to
of brook trout in Canadian streams (137). the solution (86). This released phosphate may form the
Aquatic plants require a number of nutrients for mineral ap atite, which is relatively insoluble (179), or if
growth, but nitrogen and phosphorus appear to be the there is a mixing process, such as caused by wind, the
ones accounting for most of the excessive growth. phosphate is redistributed through the lake (63, 178).
Sawyer (128) concluded that eutrophication becomes a Because a lake's ecological system is so complex,
problem when the concentration of inorganic nitrogen Shannon and Brezonik (132) devised an index of seven
exceeds about 0.3 ppm and inorganic phosphorus parameters to quantitatively characterize the trophic

state of a lake. For 55 lakes in Florida, the relation was statistically the more important. An additive form
between this index and the loading rates of nitrogen and of the loadings accounted for 60 percent of the
phosphorus showed that an increased phosphate loading variability in the index.

SOURCES OF NUTRIENTS

Fertilizers are well known as a source of nutrients on Nutrient Cycles,
cropland, but they are not the only source and some-
times are not the most important source. Fertile Nitrogen
cropland soil is a pool of nutrients with different degrees
of availability to the crop and to the transport processes Volumes have been written about nitrogen behavior.
of runoff, erosion, and leaching. Precipitation and 7wo comprehensive reviews are: "Soil Nitrogen" (10)
animal wastes are other sources. M addition, legume and "Soil Organic Matter and its Role in Crop Produc-
crops, with the assistance of microorganisms, can biolog- tion" (3). Figure 1, adapted from Stevenson (149),
ically convert atmospheric nitrogen into organic nitro- illustrates the numerous compartments and pathways of
gen. nitrogen.
The relative importance of each of these sources Most of the reactions in the soil portion of the cycle
depends on a number of factors, such as the geographical are microbial and thus the rates are sensitive to
location with its relation to climate and soils and the temperature and moisture. Warm (900 F) and moist
-crop management practices previously and presently (water in 80 percent of the voids) are optimum
used. Table I shows the estimated 1969 national conditions for cycling within the soil. The conversion of
nitrogen inputs (119) and estimates for several water- organic nitrogen to nitrate (ammonification and nitrifi-
sheds in Wisconsin (13). 7he national input for phos- cation) is often called niineralization. A study of 39 soils
phorus in fertilizer is for 1973 (79), the manure input is from across the United States showed that the rate of
from Table 3, and the inputs from plant residues and mineralization was proportional to the pool of mineral-
precipitation were calculated from the N inputs and N/P izable nitrogen. The size of this pool was not highly
ratios of 7.5 (Table 17, Vol.1) and 100 (Fig. 3), correlated with the total organic matter or total nitrogen
respectively. (148). Thus, some forms of organic matter are readily
On the national level, fertilizer is a major input and converted to mineral forms whereas other organic forms
manure is a relatively small input. The relative contribu- are not. Part of the stable forms may exist as metal-
tion of these sources can be reversed for a specific organic and organic-clay complexes.
geographic location, as shown by the data for Wisconsin Soils contain 0.075 to 0.3 percent total nitrogen or
watersheds. 1,500 to 6,000 lbs. per acre in the top 6 inches (5). Soils

Tab.le 1. Sources of railtogen and phosphozus on a naLonal and a watershed scale
Source National Wisconsin watersheds
Nitrogen Phosphorus Nitrogen Phosphorus

Million tons Percent Million tons Percent lbslacre Percent lbslacre Percent
Fertilizer ............... 6.8 45.9 2.2 76 10 8.5 8 32
Fixation ............... 3.0 20.3 0 0 12 10.3 0 0
Manure ............... 1.0 6.8 0.4 14 42 35.9 12 48
Plant residues .......... 2.5 16.9 0.3 10 45 38.5 5 20
Precipitation ............ 1.5 10.1 0.01 0 8 6.8 0 0
Total ............ 14.8 2.9 117 25

N)
AIR
N? NH3 DUST

m HARVEST ADSORPTION
z
-no PRODUCTS

0 60
3> Z>

VOLATILIZATION

-n
m

RESIDUES
FR_U -NO F-F
m
m I EROSION
Cn

N03 IMMOBILIZATION SOIL ORGANIC AMMONIFICATION NH4
MATTER IMMOBILIZATION CLAY AND
ORGANIC COMPLEXES

LEACHING NITRIFICATION

Figure 1. -The nitrogen cycle in agriculture.

cultivated for 100 years can still release 30 to 60 Pounds Most of the estimates have been based on nitrogen
of nitrogen per acre per year and have drainage waters budgets where all unaccounted-for nitrogen is assigned
with 5 to 10 ppm nitrate nitrogen. Fertile soils in tile to denitrification. The nitrogen gases produced are very
Corn Belt are estimated to release 120 lbs. of N per acre difficult to measure under field conditions.
Average losses have been estimated at 10 to 30
,VI. In the semiarid west, some fields are fallowed (kept
free of vegetation) every other year to accumulate percent of the total yearly inineral nitrogen input (26).
moisture. The increased moisture also prornotes mineral- When excessive rates of nitrogen are applied, as much as
ization of 20 to 50 lbs. of N/acre (37). 50 percent can be lost (99).
VvIien amillonia (a gaseous form of nitrogen) reacts The inputs of fertilizer, biological fixation, aninial
with the water it forms positively charged ammonium wastes, and precipitation: and the losses by leaching,
ions. These ions are hold by the negative charge of the runoff and erosion, and plant uptake (avoiding excessive
clays as exchangeable cations. Some of the ammonium fertilizer use) will be covered in subsequent sections.
ions can be trapped or fixed between clay platelets. Phosphorus
Ammonia absorption by the soil has not been
considered in the past as a major path of nitrogen input. The phosphorus Cycle shown in Figure 2 is a lot less
However, in areas of high ammonia concentrations, such -
complicated than the nitrogen cycle, altliou-h it has
as downwind of industries or feedlots, the soil, lakes, t,
and plants have absorbed from 20 to 70 pounds of some of the same paths. Before considering the similar
N/acre/yr (55, 67, 68, 138). paths, we will examine those reactions in the soil which
are unique for phosphorus. Black (15), Olson and
Immobilization, the reverse of mine ralization, is tile Flowerday (115) and Ryden et al. (125) have prepared
part of the N cycle that converts nitrate and arnmonium comprehensive reviews of the subject.
into organic forms. It occurs under aerobic or anaerobic The phosphate concentration in the soil solution is
conditions and basically involves the uptake of the low, usually 0.01 to 0.1 ppm P, although the total P in
mineral forms by microorganisms in the synthesis of cell the soil ranges from 100 to 1,300 ppin (13). The mineral
tissue. Whenever organic residues low in nitrogen are forms of phosphorus-calcium, iron, and a]Llllli]IUIII
being decomposed, mineral nitrogen must be used phosphates-have very low solubilities and the phosphate
because the carbon-to-nitrogen ratio of microbial tissue is highly adsorbed to clay minerals. The organic forms of
is on the order of 5-10:1. Dead microbial tissue then phosphate have not been studied as extensively as have
becomes part of the organic matter pool that can be the inorganic forms. However, the organic part of the
mineralized. A major problern in quantifying tile inimo- total phosphorus can range from 3 to 75 percent.
bilization process is that it is impossible, without Because of the low solution concentrations and high
nitrogen tracers, to measure the small amount of tile degree of adsorption, phosphate tends not to ]each.
product in the large organic-matter pool. After 286 lbs. of P had been applied in I I years, the
0
Denitrification is not well understood but appears to plant "available" level had increased only 18 lbs. and
be a very important part of the nitrogen cycle affecting very little had moved below 12 inches (32). After 82
environmental quality. Denitrification is the use of years of fertilization, the total P had been doubled, but
nitrate by anaerobic microbes for oxygen and results in no added P was found below 54 inches (10). The
the production of nitrogen and nitrogen oxide gases. Tile availability of phosphate in tile soil decreases exponen-
necessary anaerobic conditions are most prevalent when tially with time. However, soils vary greatly in their
the water content of the soil is high, which is the same conversion of added P to insoluble forms (90). Recent
condition needed for leaching. Another requirement is a work (52) indicates that chemical reactions immobilize
supply of carbon for all energy source. Lack of useable more than 50 percent of added soluble phosphate in a
carbon may be the factor that prevents all the nitrate in few hours and an additional 10 percent in a month or so.
the leachate from being denitrified. Carbon is usually The amount of biological immobilization into organic
not very mobile and, therefore, once the nitrate passes phosphates that occurs simultaneously with the chemical
below the root zone, the opportunity for denitrification reactions depends upon the amount of biological activ-
is limited "1141. Complete waterlogging is not essential i ty.
for denitrification. Since the soil contains a wide range
of pore sizes, an unsaturated soil can have areas where Precipitation
the water contents and microbial activity are sufficient
to produce an anaerobic environment and denitrifica- The amounts of nitrogen and phosphorus added in
tion. Quantification of this process has been limited. precipitation are generally low and, for cropland, they

DUST

HARVEST
PRODUCTS

I ANIMALS

PLANT

FERTILIZERS RESIDUES RUNOFF
EROSION.
MINING
ADSORPTION IMMOBILIZATION

MINERALS PO SOIL ORGANIC
4 MATTER
DESORPTION MINERALIZATION

Figure 2-The phosphorus cycte in agriculture-
WOBILIZ@ATION

are negligible in comparison to other inputs. On forests, years ago. Yields from field tests started at England's
unimproved pasture arid rangeland, and lakes, the input Rothamsted Experiment Station in 1840 have been
of nutrients added by precipitation can be significant. maintained near maximum by the use of manure and
The concentrations of nitrogen and phosphorus in rain fertilizer while those from unfertilized plots have de-
and snow vary not only across the country, but within creased to an uneconomic level.
short distances and during a storm. Organic forms of nitrogen were the cheapest sources
Uttormark et a]. (166) list 40 factors that can of nitrogen until about 1900 (70). Before the 1950's,
influence the concentration of nutrients in precipitation. sodium nitrate and ammonium sulfate were the principal
Feedlots, industrial urban centers, power plants, disposal nitrogen sources. Then ammonium nitrate became the
sites, etc., are all relatively local sources that can increase leading source, only to be surpassed by anhydrous
the general regional level of nutrients. They prepared a ammonia and urea in the 1960's. Phosphate fertilizers
map of the United States delineating areas of different also changed in the 1950's from normal superphosphate
nitrogen contribution in rainfall. The Lake States had to concentrated super phosphates. These are trends to-
the highest contribution, about 2 to 3 lbs. of N/acre/yr., wards the use of more concentrated forms, thus reducing
whereas the Western States had less than I lb. of shipping charges per pound of nutrient. The source of
N/acre/yr. Dry fallout was not included. the nutrient makes no difference to the plant because of
Seasonal maps of ammonium and nitrate in rain the extensive cycling in the soil. Some sources, such as
across the United States (73) show that the highest ammonium sulfate, can increase the soil acidity if used
concentrations are in the spring and summer. It appeared for extended periods.
that the rainfall concentrations might be related to the Table 2 shows how fertilizer use on four major crops
soil because the Southeast acidic soils are the lowest. has changed over a 10-year period. The acreage of corn,
Ammonium concentrations may change as much as wheat, and cotton harvested has remained relatively
10-fold during the year, but nitrate changes much less. constant except in 1974 when acreage controls were
When rainfall samples are taken at different times removed. The acreage of soybeans has steadily increased.
during a storm, the nitrogen concentrations are often Except for cotton, the percentage of acres fertilized has
slightly higher during the first part (24, 50). This could consistently increased over the years. Note also that the
be due to evaporation from the drops into dry air or the yield per acre has tended to increase. Fertilizer rate has
washout of dust. increased except for nitrogen in 1974 when short
The phosphate input in most places may be associ- supplies and increased costs because of the energy crisis
ated with dust, either as dry fallout between storms or caused many farmers to reduce their application rate.
washed out of the atmosphere with rain. Dust or dry The relative plateau of fertilizer use on cotton deserves
fallout is a very important component associated with some comment. Cotton is relatively sensitive to nitrogen
the precipitation input of nutrients. It has been esti- and excess nitrogen can reduce yields. Cotton has been
mated 4,166) that in and regions 70 percent of the fertilized intensively for a long time and the optimum
nitrogen in uncovered rain gages is from dust. Storms rates have evidently been found. Pests, such as insects,
blowing in from oceans are quite low in phosphorus. weeds, and disease, are probably limiting yield more
Phosphorus can also be associated with ash and smoke, than fertility.
as indicated in concentrations of 0.24 ppm phosphate in Speculation on future fertilizer use is fraught with
rain at Cincinnati compared to threefold less at a rural uncertainties. The problem is basically economics. How
location near Coshocton, Ohio (174). A yearly input of much fertilizer should the farmer apply to maximize his
0.2 to 0.6 lb. P/acre/yr has been estimated (24, 110). profits? The yield response to fertilizer is less for each
One problem associated with evaluating the importance subsequent increment of fertilizer and as the yield
of dust is the absence of a measure of the loss by dust increases some other costs also increase. In the 1960's,
into the atmosphere. There is no evidence that snow has farmers received $2.50 for each dollar invested in
any different concentrations of nutrients than rain fertilizer and so they substituted an investment in
would at the same time of year. fertilizer for additional land or labor (62). Real estate
costs and wages increased over 250 percent since 1950
FertHizers while plant nutrient costs decreased (38). While the
energy crisis will tend to increase fertilizer costs faster
Fertilizer use to improve crop yields dates from than other costs, it will probably be sometime before
antiquity. Sanskrit writings of 3,000 years ago note the they reach the level of other farm costs. Thus, farmers
value of dung for fertilizer (103). Guano and Chilean will probably continue to fertilize, but will carefully
-nitrate were available in Europe as a fertilizer over 100 appraise the size of the applications and eliminate

Table 2. The change in fertilizer use on four crops in the past 10 years
Crop Year Acres Area fertilized 2 Fertilizer rate 2 Yield'
harvested N P N P

Millions Percen t lbs.lac. bu. lac.
Corn ........................... 1964 55.4 82 75 45 18 63
1966 56.9 91 85 83 24 73
1968 55.9 92 88 102 28 80
1970 57.2 94 90 112 31 72
1972 57.4 96 90 115 29 97
1974 63.7 94 87 103 27 -

Wheat . . . . . . . . . . . . . . . . . . . . . . . . 1964 49.8 47 36 28 12 26
1966 49.9 49 38 32 14 26
1968 55.3 56 43 37 14 28
1970 44.1 61 44 39 13 31
1972 47.3 62 44 46 16 33
1974 64.1 66 46 46 17 -

Soybeans . . . . . . . . . . . . . . . . . . . . . . 1964 30.8 6 10 13 11 23
1966 36.5 17 24 14 15 25
t968 41.1 21 27 12 17 27
1970 42.1 21 27 14 16 27
1972 45.7 22 29 14 18 28
1974 52.5 22 28 15 18 -

lbs.lac.
Cotton . . . . . . . . . . . . . . . . . . . . . . 1964 14.1 75 56 69 21 517
1966 9.6 75 58 77 23 480
1968 10.2 73 55 71 23 516
1970 11.2 72 48 75 24 438
1972 13.0 77 55 75 24 507
1 1974 13.1 79 58 78 23

United States Department of Agriculture, "Agricultural Statistics", Years 1964 to 1974.
21964-1970 data from "Cropping Practices" SRS-17, Statistical Reporting Service, USDA.
1972-1974 data from "Fertilizer Situation", FS-5, Economic Research Service, USDA.

excessive use. A food crisis that increases the price of and amount of water consumed. In addition, the amount
farm products relative to fertilizer costs would stimulate of bedding used to absorb the urine or presence of
fertilizer use. Fertilizer use in the United States will superphosphate to react with the ammonia, the method
increase 5 percent per year because of rising populations, of storage, and the duration of storage influence the
improved diets, and increased exports, according to a nutrient content of manure being applied to the soil.
recent estimate (78). Fresh manure contains 50 to 90 percent moisture, 0.2
to 6 percent total nitrogen, and 0.06 to 2.5 percent total
Animal Wastes phosphorus, on a dry weight basis. The old rule of
thumb was that the typical ton of moist cow manure
Before commercial fertilizers came into common use, contained about 10 lbs. of total nitrogen and I lb. of
animal manure supplied most of the nutrients added to total phosphorus when it was applied to the field.
the soil. In the 1960's it was more expensive to load, Present methods of confinement, feeding, and manure
haul manure several miles, and spread it than it was to handling vary enough that this rule of thumb is no
purchase and apply commercial fertilizer. In addition to longer adequate.
the economics, the convenience of commercial fertilizer Yeck et al (183) recently estimated that 5.8 million
caused animal wastes to become a disposal problem tons of nitrogen are excreted annually by livestock in
rather than a nutrient source. the United States. The percentage that can be collected
The following discussion is based on information varies from zero for cattle on the range to nearly 100 for
from several references (29, 30, 96, 170, 180). caged poultry. The work of a number of investigators
Manure is the excrement of animals that contains the indicates that about half the nitrogen collected is lost
undigested food and the urine. The nutrient content of, during storage, handling, and spreading before it can be
manure is different for different animals, type of feed, incorporated into the soil. Thus, of the 2.4 million tons

of nitrogen that they estimate can be collected, only 1.2 3V,ogicawl Fixation of Nitrogen
million tons are available as a substitute for fertilizer and
a large part of this is already being applied. One of the most recent reviews of the biological
The pollution potential isn't a result of animals per fixation of nitrogen is by Allison (3). Another good
se, but of the manure they produce. Since there are source of information is three chapters in "Soil Nitro-
maps showing the geographical distribution of animals gen" (10). Nonsymbiotic (free-living) organisms prob-
(Figs. 20-24, Vol. 1), we needed a method for conversion ably -fix about 10 lbs. of N per acre annually. This
to manure and its nitrogen and phosphorus contents. amount is of little practical importance in the nitrogen
From the collectible nitrogen previously described for balance of a cultivated field, but since it is comparable
each class of livestock, a 50 percent loss before to the precipitation contribution, it is important in
incorporation was assumed. This can then be geographi- nonfertilized grass sods.
cally distributed with the animals. To calculate the Nitrogen-fixing bacteria in a symbiotic relation with
amount of manure associated with nitrogen one must roots of certain plants, principally legumes, can fix
assume some percentage of N in the manure being sufficient nitrogen to support a grass-legume pasture.
spread. The amount of phosphorus can likewise be With low soil nitrogen, the amount of nitrogen fixed in
calculated from the percent phosphorus.,These percent- effective legurne nodules correlates closely with the dry
ages of N and P in the manure were estimated for the weight of the legume tissue produced. Generally, the
different kinds of animals from data of various re- fixed nitrogen is produced only as the plant needs it and,
searchers. These calculations are summarized in Table 3. therefore, plants with poor growth will not fix much
Not all of the nitrogen in manure is immediately nitrogen. Similarly, high soil nitrogen levels, such as
available. Most of the nitrogen left in manure when it is from fertilization, will reduce the amount of nitrogen
incorporated into the soil is in organic compounds. Like fixed because it is not needed for plant growth. There is
soil organic matter, microbes must mineralize the or- some indication (12) that fresh organic matter from
ganic nitrogen into ammonium and nitrate, which are previously fertilized crops stimulates N fixation. Biggar
taken up by the plant. About 40 or 50 percent of the and Corey (13) report 200 lbs of N per acre per year as
organic nitrogen is mineralized during the first cropping being fixed in legume systems. Allison (3) cites several
0
season (172). Additional amounts are released in subse- references where 150 to 300 lbs. are common and as
quent years so that yearly applications can build up the much as 600 lbs. of N/acre/year was observed. He
nitrogen -supplying capacity of the soil. Of course this concludes that a grass-legume mixture may fix more N
11 slow release" of nitrogen also rneans that some of it can per acre than legurnes alone because the grass will
be released when plants are not rapidly growing (fall and continually remove any nitrogen mineralized from the
spring) and thus be available for leaching. soil or plant material.

Table 3. Estimates of nitrogen and phosphorus in manure that is available for application to cropland
Vol. 1. 1 2 N coment3 AvailabO P contenI3
Animals Figure Collectible N Available N in nianUrc manure iit nianUre Available P
No.

Thousand tons 7housand tons Percclit Million tolls Percent 7housand tons
Beef cattle . . . . . . . . 21 650 330 2.S 13 0.9 100

Dairy cattle . . . . . . . . 22 670 330 2.0 17 0.6 100

Swine . . . . . . . . . . . . 23 600 300 2.8 11 1.0 110

Laying hens . . . . . . . . 24 250 125 4.5 2.8 1.7 50

Broilers . . . . . . . . . . 25 240 120 3.8 3.2 1.3 40

Totals . . . . . . . . 1 2,410 1,205 47.0 400
1Estimated amounts ot'nitrogen that can be collected (183).
2Available after application assurning 50'7, losses duringhi@tndling,, storage, and spreading.
3Estimated contents based on data from various authors.
4 Calculated fTom available N and N content.
5Calculated from available manure and P content.

TRANSPORT FROM CROPLAND

Water pollution by nutrients from cropland involves must be saturated before drainage will occur. This
one of three transport processes: leaching, runoff, and saturated zone can provide an opportunity for denitrifi-
erosion. In nature the results of these processes are not cation and dilution. Some lysimeters do not contain
easily distinguishable. Water may infiltrate into the soil undisturbed profiles while others are very shallow. Both
and thus cause leaching, but a few feet or yards conditions limit their usefulness for field interpretation.
downslope the water with its dissolved nutrients may Lysimeters have provided some valuable information
come to the surface and join the overland flow or about leaching. Kolenbrander (85) found that as the clay
runoff. Similarly, the distinction between runoff and content of the soil increased from 10 to 50 percent, the
erosion may be quite difficult when nutrients in the nitrogen loss decreased from 40 lbs. N/acre/year at 18
runoff are adsorbed on or released from the eroded ppm to 4 lbs. N/acre/year at 2 ppm. Wild (177) found
sediment that the runoff water is carrying. The larger the that nitrogen mineralized in the soil didn't leach quickly
drainage area of the stream sampled, the more mixed are in fine soil with cracks, but Kissel et al. (80) found that
the three transport processes. Some cases where these applied fertilizer, simulated by chloride, did move
processes operated independently will be examined so quickly through the cracks of a clay soil. Kolenbrander
that the system can be better understood. (85) reported phosphorus losses of 0.2 lb. P/acre/year at
The usual range of values is presented in Figures 3 0.08 ppm for both cropped and grass lysimeters, with
and 4. Occasionally, more extreme values will be and without fertilizer.
observed because the system is highly variable. Concen-
trations are not provided for sediment transport because Tile Drains
the concentrations of sediment vary so much. Soils
contain 0.075 to 0.3 percent nitrogen and 0.01 to 0.13 Tile drains have recently provided most of the
percent phosphorus and deposition of coarse material measurements of nutrient leaching. While tile drains
during transport can increase the concentrations in the sample a much larger area and thus provide a more
transported sediment by 2- to 6-fold. integrated value, they may not accurately reflect the
nutrient content and water volume leaving the field. One
Leaching problem is to define the boundaries of the drainage field
so that losses can be calculated on an area basis. Another
Leaching is the process whereby soluble chemicals are is that the tiles short-circuit the drain paths with aerated
dissolved and removed from the soil in water that is conditions reducing the time and opportunity for
percolating through the soil. Nitrate is the principal denitrification (15 7). As an illustration of this condition,
nutrient form found in drainage waters because it is Thomas and Barfield (157) monitored an area where
seldom adsorbed to the soil minerals. Some red subsoils one-third of the water flow was from tile lines with
in the southeast are an exception (156). Organic forms nitrate levels of 15 ppm N while the rest of the seepage
of nitrogen and phosphorus and the orthophosphate ion had only 3 ppm N. At lower flows, the seepage
are seldom found to any extent in drainage water accounted for nearly 90 percent of the flow with nearly
because they are held by the soil. zero nitrate while tile lines had 10 percent of the flow
Three principal ways of evaluating leaching are by with concentrations of 9 ppm N.
lysimeter studies, monitoring tile drains, and taking core Many studies have been reported concerning the
samples. Each method has some limitations and it is concentration and the average annual loss per unit area
important to recognize these limitations when interpret- of nutrients in drainage waters (83, 96, 125, 166). The
ing the data. first feature to be recognized is the extreme variability in
the data, both the loss per unit area and the concentra-
Lysimeters tion. Thus, an average value has little utility. One of the
major factors causing the variability in the loss data is
Drainage lysimeters are columns of soil in the field that the water flow, and thus the load of nutrients
isolated by impermeable cylinders with facilities for transported, varies greatly between dry years and wet
collecting the water that drains out of them. Cylinder years. The type of crop grown is another major factor.
walls at or above the surface can prevent or reduce Nutrient concentrations are consistently lower in the
runoff and, therefore, increase the amount of leaching. drain water from grasslands and woodlands than in that
Also, if suction is not applied, the bottom of the column from cropland. Grasslands and woodlands have a longer

CONCENTRATION -ppm

0.01 0.1 1.0 10.0 100.0

IP PRECIPITATI-ON

CROPLAND RUNOFF P =N

P N NON -CROPLAND RUNOFF

P1 DRAINAGE V/ 47 Z 171 7777=N

Figure 3. -Range of nitrogen and phosphorus concentrations in different watcrs.

SPATIAL RATE - lbs./acre/year

0.01 0.1 1.0 10.0 100.0

PRECIPITATION P N

Pr-- CROPLAND RUNOFF

77 77777=///// IN
NON-CROPLAND RUNOFF
P

P DRAINAGE 177777 77 7 77=N

N
CROPLAND SEDIMENT

NON-CROPLAND
SEDIMENT 177 77 77777777=7 7777-= N
P1 - -1

Figure 4. --Range of spatial rates of nitrogen and phosphorus in waters and sediments.

growing season in which to remove nutrients and reduce application and runoff, the greater is the chance for light
water flow. Also, even though they are located on soils rains to leach the fertilizer into the soil and even for
of lower fertility, these lands are seldom fertilized water from the moist soil to dissolve the fertilizer so that
because the economic return is insufficient. Generally it can be leached into the soil.
then, the fertile land that is cropped will have the As a result of the factors just discussed, it is not
highest concentrations in the drain water and the most unexpected that the concentration of nutrients in runoff
drain water. Fertilizer applied to these lands.tends to varies from field to field and front storm to storm. The
increase the concentration of nitrogen in the drain nutrient concentrations in runoff from small watersheds
water, but seldom that of phosphorus. and fields remain relatively constant during a storm (41,
129) but these concentrations are usually higher than
the base flow of streams in larger watersheds and thus
so'] (core's the impact of storm runoff can be detected in streani-
now (51).
%-ores of soil can be taken from plots and fields, then Bradford (23) observed that the total N in runoff
separated into segments and analyzed. This provides a Irom fertilized plots was 60 percent higher when the rain
means to follow the movement of the nutrients down occurred 3 days after application than when it Occurred
through the soil profile. In most soils, the distance the 3 months later. Rogers (123) reported 9 percent of tile
band of applied nitrate moves down through the soil is fertilizer was lost in the first rain and 4 percent in the
proportional to the amount of water in excess of that second rain after phosphate was applied to pasture. Oil a
required to raise the water content to field capacity (84, watershed basis, Kilmer et al. (79) found less than 0.5
94). Water in excess of crop needs and soil properties percent of tile phosphate fertilizer was lost in a storin
such as texture and structure are important factors in right after application. Dunigan et al. (36) found that
determining the rate of leaching. In Wisconsin, Olsen et more fertilizer was lost from top dressing (surface
al. (114) estimated the annual percolation below the application) in 1972 with less rain than in 1973, because
root zone to be 6 inches. A silt loam soil has a water the first few rains in 1973 did not produce runoff but
capacity of 30 to 50 percent, thus nitrate could move 12 Moved the fertilizer into the soil.
to 18 inches per year under these conditions and it
would take at least 20 years to reach a water table at 30 Nitrate, being very soluble, is usually leached into the
feet. soil by infiltration during the first part of the storm.
In the semiarid Great Plains, leaching is not a hazard Thus, the more infiltration there is before ruiloff, the
except when additional water is added by irrigation or lower the nitrate content of the runoff water. However,
fallow land prevents normal transpiration by plants. if tile infiltrating water moves laterally and returns to
North Dakota soils wetted to 6 feet only occasionally in the surface (interflow), its nitrate load is added to the
40 years (121), but in Colorado, nitrate accumulated overland flow. This return flow is more likely to occur as
below the root zone in a wheat-fallow system (150). The the size of the watershed above the sampling point
average nitrate content in a 20-foot profile was 260 lbs increases. Barnett et al. (8) observed this phenomenon
N/acre for cultivated dryland compared to 90 lbs N/acre with one of three soils in Puerto Rico. Oil two soils, the
in native grass. Since very little fertilizer is applied to runoff contained 0.3 percent of tile fertilizer, but oil tile
dryland crops in eastern Colorado, the difference be- third, where most of the water infiltrated and then
tween these averages is probably a result of nitrate moved laterally through the soil, 7 percent of the
production and leaching under cultivation and fallowing. applied fertilizer was lost. Sievers et al. (133) observed
that most of the nitrate leached into a silt loarn and a
Runoff sandy loarn soil gave a runoff concentration of' 5 to 7
ppin N. Conversely, a silty clay loarn soil with poor
Runoff occurs when the rate of precipitation exceeds drainage produced more runoff with a concentration of
the rate of infiltration. A heavy inulch apparently acts as 44 pprn N.
a sponge to hold water as do the numerous small surface Usually the most fertile lands are cropped and,
depressions. Surface-applied fertilizers can dissolve into therefore, it should be expected that the water leaving
this water held in the depressions and by the mulch. cropland contains more nutrients than water leaving land
When this water becomes runoff it carries a load of in other uses. Losses from pastures, rangelands, and
nutrients. This is why the highest concentrations in woodlands are usually much lower because the natural
runoff occur when there is runoff soon after surface fertility of tile soils is usually lower, fertilizer is applied
fertilizer application. The longer the time between less often if at all, and the amount of runoff is often less

because there is more plant cover more of the time. lost. Doty and Carter (34) found that when the sediment
Overgrazed lands have higher nutrient losses because of concentration was highest at peak flow, the chemical
increased runoff and erosion. Concentrations of nutri- and physical composition of the sediment was similar to
ents will also be high occasionally if animals have direct that of the soil. At lower flows, the sediment concentra-
access to a stream, if animals are fed near streams, or if tion was lower, the percentage of clay in the sediment
fertilizers and manures are surface applied. Phosphate increased, and the enrichment ratio increased.
concentrations in runoff may be higher from grasslands The loss of total N and P in sediment from cropland
than from adjacent cropland after harvest because ranges from I to 50 or 100 lbs. per acre per year. Two
freezing and drying cause a release of nutrients from the factors can contribute to the high loss from cropland:
vegetation (163, 176). Timber harvesting also causes a the soil is fertile and contains a lot of nutrients per
sudden release of nutrients to runoff waters from the pound of soil, and tillage operations often leave the soil
decay of the trimmed foliage (18). The reduced water very susceptible in the most erosive part of the year.
consumption after harvest also increases the annual Noncropland areas often have a lower nutrient content
nutrient loss. Uttormark et al. (166) and Brezonik (24) than the cropland and also lower erosion rates because
provide a summary of losses from land in various uses. of more vegetative cover. An exception is the large
Ryden et al. (125) provide a recent review of phos- amounts of sediment produced by gullies that are often
phorus losses. prevalent in noncropland.

Sediment Nutrient Losses from Large Watersheds
Sediment is the major transport vehicle for phos- As indicated at the beginning of this section, the
phorus and organic nitrogen. Raindrop splash and nutrient composition of a stream reflects a mixture of
overland flow of water detach soil particles containing the three basic transport mechanisms. The composition
adsorbed phosphorus and associated organic matter. The of streams changes with amount of flow, season of the
flowing water transports the particles off the field. year, and distance down the stream as new material is
Transport capacity depends primarily on the volume and added from tributaries, seepage, and outfalls.
velocity of water flow. Whenever the velocity is reduced, The Environmental Protection Agency (165) is under-
such as by a flatter slope, the transport capacity is taking a national eutrophication study, but at present
reduced and any sediment in excess of the reduced only a preliminary analysis is available. The data indicate
capacity settles out. Since the larger and heavier particles less variability in total nitrogen loss than in total
settle out first, the remaining sediment contains a larger phosphorus loss, and increases in the concentrations of
percentage of the finer particles. The finer particles have nutrients in the water are correlated with increased
a higher capacity per unit of sediment to adsorb density of animals in the watershed. A recent summary
phosphorus and, also, organic matter is lighter and tends of the spatial loss for streams (166) reports a range of 1
to be associated with the fine particles. Thus, the
transported sediment is richer in phosphorus and nitro- to 13 lbs. N/acre/year and 0.03 to 2 lbs. P/acre/year,
gen than the original soil (59). with averages of 5 and 0.4. Both studies indicate that
Bedell et al. (11) found that 98 percent of the forest land yields less nutrients than agricultural land
sediment samples from 2- to 4-acre watersheds contained and that the Midwestern states have higher losses than
as much or more organic matter, phosphorus, and other states.
nitrogen than the soil. The degree of enrichment has Most perennial streams have a number of outfalls for
often been described by an enrichment ratio, the ratio of municipal and industrial wastes, which complicates any
the nutrient concentration in the sediment to its budgeting of sources. For example, agricultural land is
concentration in the soil of the watershed. Recently, estimated to have contributed all of the inorganic N, 49
enrichment ratios of 2 to 6 have been found for percent of the total N, and 13 percent of the total P to
phosphorus (130, 155). Barrows and Kilmer (9) reported the Potomac River in 1966 (71). The figures for the
an average enrichment ratio of 2.7 for nitrogen and 3.4 agricultural contribution to the Hudson River were 37
for "available" phosphorus. Available means that frac- percent of the total N and 27 percent of the total P.
tion by chemical extraction that is expected to be Streams are dynamic systems with living organisms
available to plants. assimilating the nutrients and particulate matter ad-
Massey et al. (104, 105) found that the enrichment sorbing or releasing the nutrients. Some of the nutrients
ratio was inversely related to the concentration of removed from solution may go undetected in the debris
sediment in the runoff and the total amount of sediment moving along the bottom of the stream or floating on

the surface. Phosphate-deficient sediments will remove studies on two rivers where the overall loss from solution
phosphate from the solution (154). Thus, the concentra- was logarithmically related to the distance of strearnflow
tion of phosphate in a strearn changes as soil is added below a point source of phosphorus. The coefficient was
from noncropland and stream banks (88, 173) or gullies 0.01 to 0.02 per mile; that is, 14 to 30 miles for a 25
(130). Keup (75) provides a good discussion of the perceni reduction.
behavior of phosphorus in flowing streams. He cites

EFFECT OF CONTROL PRACTICES

There is every reason to believe that nutrient loss methods of control (140). Data on the effectiveness of
from cropland can be controlled at an acceptable level if these practices for controlling nutrient losses are ade-
proper management practices are used. As pointed out quate for only qualitative predictions. Generally, a
by Klingebiel (82), soil surveys are an important basis reduction in sediment loss provides less of a reduction in
for planning the optimum use of each field. By intensive nutrient loss.
use of fields with high crop production potential and
low hazards from runoff, erosion, and leaching, the use Residue Management
of marginal land with higher hazards can often be
reduced. The greater the amount of residue left on a field, the
The effectiveness of management practices for the greater the reduction in erosion. Zwerman et al. (184)
control of' nutrient losses has not been quantitatively reported that leaving the crop residues instead of
evaluated to the same degree as have the impacts on removing thern decreased runoff 50 percent and did not
runoff and erosion. Only in recent years have adequate change the nutrient content of the runoff water. Thus,
data on nutrients been collected. losses of nutrients in runoff were reduced 50 percent.
The possibility of creating another problem by Losses of nutrients with sediment were also reduced.
solving one problem should be the concern of all who Romkens et al. (124) used simulated rain and observed
make recommendations. The nitrate contarnination of that several conservation tillage systems reduced sedi-
ground water in Runnels County, Texas (87) can be used ment loss but increased the loss of soluble nitrogen in
as an example of this possibility. This land, which had the runoff. Ketcheson and Onderdonk (74) found that
been dryland farmed since 1900, had nitrate formed and covering broadcast fertilizer with a chopped cornstalk
leached below the root zone but not down to the water mulch reduced soil phosphorus losses 65 percent and
table. Extensive terracing after the drought in the early fertilizer losses 97 percent.
I 950's increased water retention and leached the nitrate No-till or zero tillage (7) is one of the most effective
on down to the water table. Thus, a nitrate leaching practices for reducing erosion. The effect of these
problem was created by the terracing done to solve a practices on the amount of runoff is variable; sometimes
problem of limited moisture. While hindsight is much runoff is increased and sometimes it is decreased. Smith
clearer than foresight, we should learn from previous et al. (136) reported that nitrogen in runoff was not
experiences and examine our recommendations for greatly affected by the no-till practice, whereas phos-
secondary effects. phorus increased 5- to 8-fold, probably from leaching of
residues. Since runoff is sometimes decreased, nitrate
Erosion and Runoff Control Practices leaching can be increased (158). Schwab et al. (131)
found little difference in the nitrogen and phosphorus
Sediment is a major pollutant in itself. That it also content of tile drainage from conventional and no-tillage
carries nutrients and pesticides means that the first goal plots.
in controlling pollution from cropland should be to
control erosion. For example, more than 97 percent of Cropping
the N and P lost from some watersheds was associated
with sediment lost primarily in the 2 months after Sod reduces runoff and permits very little erosion.
planting (27). Therefore, on an average annual basis, the rotations with
Soil conservation practices have been stressed for over sod should show a reduced nutrient loss. Results from
40 years and sufficient data have been collected to corn-wheat-clover plots (102, 134) indicate that the
permit fair predictions of average annual soil loss. Old rotation reduces the total N and P loss 3- to 6-fold
principles are continually being used to create new compared to continuous corn or wheat. Schuman et al

(129, 130) reported that a sod pasture lost about I 0-fold Eliminating Excessive Fertilization
less nitrogen than continuous' corn. The phosphorus
losses from the pasture were lower by a factor of two, For preventing nitrate leaching, Olson (116) sug-
even though the concentration in the runoff and on the gested that only enough nitrogen be applied to satisfy
sediment was higher. A higher concentration of phos- the crop needs, that the soil's capacity for producing
phorus in the runoff, particularly snowmelt, from nitrate be accounted for, that the nitrate already present
pasture or hay lands has been reported by several in the root zone be taken into account, and that
workers (27, 161, 176). adequate levels of other nutrients be supplied so that
When little or no residues are left on a field, as when there is maximum efficiency. These suggestions can be
corn is harvested for silage, then planting a cover crop reduced to a single concept of eliminating excessive use
such as a small grain will protect the soil during the of fertilizer.
winter. Smith et at. (136) recorded a 50 percent Nitrate builds up in the soil when excessive levels of
reduction in runoff and a 40-fold reduction in losses of nitrogen fertilizers are used (150). But when only
sediment, total nitrogen, and total phosphorus when adequate arnounts are used at the proper tiple, little of
corn was planted into a,ryegrass cover crop. They found the nitrogen is left after harvest (95, 99, 114, 135).
little effect on the soluble nutrients lost in runoff, which The greatest difficulty in preventing excessive fertili-
were already low. zation is in predicting what levels of fertilizer should be
Supporting Practices applied so that the resulting level in the soil is adequate.
The first requirement is to predict the potential yield of
Several erosion control practices such as contouring the crop and thus the nutrient requirements. Then, the
and terraces are physical rather than agronomic. They soil's ability to meet these requirements must be
can be used by themselves with regular cultivation or in evaluated. Finally, the efficiency of the applied fertilizer
conjunction with reduced tillage systems to achieve even in meeting the remaining nutrient requirements must be
greater reductions. Bedell et a]. (11) reported that considered.
contouring a corn-wheat-meadow rotation reduced sedi- This difficulty in accurately predicting fertilizer needs
ment, nitrogen, and phosphorus losses from 3- to 5-fold and low nitrogen costs has led some growers to
on all crops of the rotation. Schuman et al. (129, 130) overfertilize so that lack of nutrients would not limit
found terraces reduced water, sediment, and total yields. Recommendations based simply on "mainte-
nitrogen losses a little over 10-fold and phosphorus nance" or "balance" approaches to replace nutrients
losses a little less than 10-fold compared with contour removed by the crop should be discouraged (120). They
tillage. The enrichment ratio doubled from 2 to 4 and fail to account for either the nutrient supplied by the
the phosphorus concentration in solution doubled. soil or the losses of applied fertilizers.
Farm ponds are constructed for a variety of reasons The yield of any crop and its response to applied
such as stock watering, recreation, etc. They are also an fertilizer depends upon many different soil, plant,
effective trap for sediment and nutrients (1] 7). In some climatic, and cultural factors (159). For example,
soils, the ponds are difficult to seat and a local seepage experiment station reports from Maryland and Michigan
problem can be created. show the yield of corn can vary 2-fold across a single
state. Both climate and soil properties can be involved.
Nutrient Management Practices As the precipitation during the growing season decreases,
the water stored in the soil when the plant starts to grow
Erosion control practices wflI probably solve most of becomes the major yield determinant.
the phosphate pollution problems and many of the Stanford (141, 143) has published extensively on
nitrogen pollution problems. These practices will have estimating nitrogen fertilizer requirements. He argues
less effect on controlling nutrients dissolved in runoff persuasively that there is an internal nitrogen require-
than in sediment. They have no effect and may even ment of the crop for the expected yield. To adequately
aggravate a nitrate leaching problem. In these cases, it is estimate this requirement requires considerable field
necessary to use alternative or additional practices to work. A first approximation can be made by considering
achieve the desired degree of control. These practices the expected yields and nutrient contents (Table 17,
involve changing the use of nutrients. Table 4 contains a Vol. 1). Good farmers in fertile farming areas will
list of these practices and some of the references used in probably produce higher yields but it is anticipated that
the following discussion. the nutrient content of the crops will be proportionately

Table 4. Bibliography for nutrient management przctices (Volume 1, Section 4.3).

NUIrient management practice
Page No. Citations Si,,mficant suhiccts
No. in Description
Vol. 1.

General

NI 76 Eliminating Fxcessive Fertili- Herron cl al (60) Nitrate already in soil
zation

Linville and Smith (95) Little left with adequate an-tount,

Petersen and Sander ( 120) Discourages niaintertance and halanccd
approaches

St anford ( 14 3) Lstimating N tcrtili/er requirement

Stewart ( 15 0) BUild-up vvith e\ccssive use

Thornas and Hanway ( 159) Response to fertilizer

I homas and Peasice ( 160) Phosphorus reconinicridation,

Victs ( 168) Implication ot'hannin.L, all fertili7er

Leaching Control

N2 78 Timing Fertilizer Application Aldrich ( I ) Conditions for fall fertilization

Bouldin, Reid, and Ar,-unnent for sunnner sidedressinv,
Latim ell (22)

Lathwell, BOLddin, and Period Of 111,1XIML1111 Use
Reid (9 1 )
N3 79 Using Crop Rotations Bezdicek, Mulford, and Soybeans don't need ferifli/er N
Ma,L@cc ( 12)

Olsen ( 113) Profile N proportional to aniount applicd
Ste\% art, Victs, and Alfalfa removes dccl) N
Hutchinson (152)
N4 79 Using Animal Wastes for Ashraf(6) Cost of storage
I@ertilizcr
Uttormark, Chapin. and N and P lost in sno\%melt
Green ( 166)

Zwernian (q al (185) Manure increases imiltraflon
N5 80 PlOWing-Under Green L.Mflfle Lyon, Buckman, and Reference., for M11OLml of fis,ation
Crops Bradv (97)
N6 83 Usinv, Winter Cover Crops Frink (46) Reduced leaching bY cover crops

Thomas ( 15 6) Recommended plantirn@, tinie
N7 83 Controlling Fertilizer Release Anonymous (4) Cost estimate
or Transformation
Boswell and Anderson (19) Field c\periment with inhibitors

Broadbent (25) Poor 1,11111re prospects

Ilatick and Koshino (58) Advantaues ot'slow release

Table 4 (continued)

Nutrient management practice
Page No. Citations Significant subjects
No. in Description
Vol. 1.

Control of Nutrients in Runoff

N8 83 Incorporating Surface Appli- Timmons, Burwell, and Plow-down reduces fertilizer loss
cations Holt (162)

N9 83 Controlling Surface Appli- Wagner and Jones (17 1) Less-frequent P and K applications needed on
cations fertile soils

NIO 83 Using Legumes in Haylands and Allison (3) Grass uses N from legumes
Pastures

Control of Nutrient Loss by Erosion

Nll 83 Timing Fertilizer Plow-down None

higher. More accurate data for the area under con- can be reduced to some extent by applying the fertilizer
sideration are usually available from the State experi- when the plant is growing.
ment station. The behavior of nitrogen is quite complex and several
Given a yield estimate and a crop requirement, the estimates are required to predict the amount of fertilizer
next step is to estimate the amount of nitrogen the soil needed. A simpler, but often less accurate approach, is
will supply without fertilizer. There are several factors to presently used in most cases. This approach relies on the
be considered. One is the capacity of the soil to produce results of previous experiments in the area where
nitrate by mineralizing organic nitrogen in the soil. An different rates of nitrogen were applied to the crop.
incubation method would appear to give a reliable Figure 5 is a summary of such an experiment (66). In
estimate of the potential (144, 148) which is adjusted this particular case, the soil and residues supplied enough
for temperature and moisture effects (146, 147). How- nitrogen for a yield of 65 bu/acre. Applying nitrogen
ever, the time required for the incubation prohibits soil fertilizer at the rate of 120 lbs/acre produced 141
testing laboratories from using it (33). A hot water or bu/acre, which was close to the maximum yield observed
steam extraction of the soil sample may provide an (147 bu/acre). Such information would be the basis for
adequate estimate of the potential mineralizable nitro- recommending that 120 pounds of nitrogen be applied
gen (139, 142). to corn under similar conditions.
Also to be considered is the amount of nitrate already The phosphorus cycle is less complicated than the
in the soil (60, 61). In the more humid regions, any nitrogen cycle and the phosphorus fertilizer recom-
nitrate remaining in the soil after harvest will be leached mendations are also much easier to make (160). While
out of the root zone before the crop can use it the less than 20 percent of the applied phosphate is usually
following season. But in the more and areas such as the taken up because of the reactions with the soil, there are
Great Plains, this leaching doesn't occur regularly. A essentially no losses by leaching or volatilization. In
final factor that needs to be considered for the soil addition, soil tests have been extensively correlated with
supply is the amount of nitrogen that is available from yield responses so that the fertilizer requirement is more
residues and/or cover crops. readily predicted from soil tests.
The final step is to estimate the fraction of the Reducing fertilizer application to a less-than-adequate
fertilizer that the crop will use. Many field experiments level doesn't always decrease pollution and may in fact
show that the plant takes up less than 70 percent and increase it. Inadequate fertilization decreases growth and
often less than 50 percent of the applied nitrogen can increase runoff, erosion, and leaching. Smith (134)
fertilizer (91, 96, 116). Some of the fertilizer is reports a 9-fold increase in nitrate loss from inade-
immobilized into organic matter, some is denitrified, and quately fertilized corn. Viets (16 7) discusses the implica-
some can be leached out of the root zone. These changes tions of banning the use of all fertilizer. The effect

would range from very little with soybeans in Iowa to Timing Fertilizer Application
over a 90 percent reduction in per acre yield of
grapefruit in Florida. Acreage would need to be in- The time of the fertilizer application can be an
creased 20 to 30 percent for the major crops of corn, important tool for increasing the efficiency of fertilizer
wheat, and cotton in the first year while there was still use and reducing fertilizer loss. Fertilizer nitrogen use is
some residual fertility. In addition, the added acreage maximized when fertilizer is applied near' the time of
would be of lower fertility and more erodible, thereby maximum vegetative growth (21, 91). Most crops grow
creating additional problems. the fastest several weeks after the plant emerges, as
Mayer and Hargrove (106)used an economic model to illustrated by corn in Figure 33 of Volume 1 (56). The
examine the impact of restricting fertilization to certain application of nitrogen fertilizers several weeks after the
levels nationally and only in Iowa. Reduced use through- plant has started to grow is commonly called summer
out the country would eliminate foreign exports, in- sidedressing. Bouldin et al. (22) provide a number of
crease cropland acreage, and increase prices of farm arguments for the summer sidedressing of corn based on
products. If only a single state such as Iowa restricted experiments in New York. Since the fertilizer is used
fertilizer, the impact on the farmer would be very great, more efficiently, less fertilizer is needed and the lower
since his yield per acre would be reduced but the price fertilizer cost offsets the added cost of application. They
for his product would not go up because of supplies argue that if the field is too wet for sidedressing, then
from adjacent states. previously applied fertilizer will probably be lost by

175

150-

125-

100-

Zi
M 75-
2F 40
it
0

50 -

25-

0 40 80 120 160 200 240 280 320 360

APPLIED NITROGEN, lbs./acre

Figure 5.- An example of the yield response of corn to applied nitrogen (66).

leaching or denitrification. Conversely, if it is too dry to a poor year. The last application is not large enough to
move the nitrate down to the roots, then the growth will cause toxicity problems that sometimes occur and it
be retarded by lack of water anyway. provides an opportunity to adjust for favorable weather,
If leaching is not a problem, then applying fertilizers increased plant population, and optimum planting dates.
preplant in the spring or even in the fall (except on
sandy soils) may be acceptable. For fall fertilization it is
Using Crop Rotations
usually recommended that an ammonium type fertilizer
be applied after the soil cools below 500 F (1). This Crop rotations can be used to reduce the average
recommendation is based on the facts that while nitrate amount of nitrogen fertilizer required. High nitrogen-
is mobile, ammonium is relatively immobile and is requiring crops such as corn, cotton, and sorghum can be
converted to nitrate very slowly below 50' F (40, 126, rotated with crops requiring less nitrogen, such as small
182). grains, or legumes which require only small amounts of
Nelson and Uhland (112) were among the first to starter fertilizer, such as soybeans or alfalfa. Olsen (113)
show regional variation in leaching. Using Thorn- found the amount of nitrogen in the profile was
thwaite's calculations with a constant 4 inches of proportional to the amount of nitrogen applied during
water-holding capacity and implicitly accounting for the the rotation. Thus, the average nitrogen content in
temperature effects on nitrification, they divided the drainage from a watershed with diversified crops should
area east of the Rocky Mountains into four regions of be lower than if the watershed were completely in crops
different leaching potential (Fig. 20, Appendix B). like corn.
We have attempted to provide a more detailed Alfalfa is particularly useful because its deep root
mapping by combining a nitrification model with a system can remove some nitrate from deeper depths
percolation model. These models are described in detail than most crops can (152). Soybeans are high cash value
in Appendix B. The results of the simulations are also legumes that don't require nitrogen fertilization but
presented in Appendix B as maps of percentage loss for appear to respond to high levels of soil nitrogen from
various soil groups. These maps can be used to estimate previous crops (12, 175). The major limitations in crop
average leaching losses for an area if the hydrologic rotation are the loss of cash income and/or the cost of
characteristics of the soils are similar to one of the additional equipment.
groups modeled. Losses of fall-applied and spring-applied
ammonia (Figs. 34 and 35, Vol. 1) by nitrate leaching
were prepared from these maps by selecting the appro- Using Animal Wastes for Fertilizer
priate loss for the predominant soil group in each Land
Resource Area. Animal wastes, or manure, have been used as a source
These results still represent coarse approximations in of plant nutrients for thousands of years. A previous
spite of the numerous factors that were incorporated section discussed many of the properties of manure.
into the model. Only a few combinations of soil Zwerman et a]. (184, 185) report the increased infiltra-
characteristics were modeled. Another limitation was the tion and reduced runoff from long periods of manure
relation used for the ammonium -nitrate conversion. use. This section will be concerned with the problems
Other factors such as moisture and pH could modify the associated with using manure as a substitute for fertil-
actual conversion rate for a particular soil. Also, immobi- izer.
lization and denitrification could remove some of the The most serious problem from a water quality
nitrate produced, and the leaching process may not be standpoint is the loss of nutrients in runoff. Animal
exactly plug flow. The model assumes little transpiration manure produced during the winter must be either
and no uptake during the winter, which would tend to stored or applied when the crops are not growing and
overestimate leaching in southern states where there chances of loss are greater. Since equipment can't enter
could be plant growth. Thus, these maps can serve only fields that are wet with fall or spring rains, farmers with
as first approximations and more detailed information little or no storage capacity are forced to spread the
on locally important variations must be obtained from manure on frozen or snow-covered fields. The resulting
the Soil Conservation Service, State experiment stations, runoff from rains or snowmelt can carry 10 to 20
and extension staffs for each area. percent of the nitrogen and phosphorus in the manure
Split applications, applying part of the nitrogen in the (109, 166). The losses from a manure application
fall or spring and the rest as a summer sidedressing, containing 100 pounds of N per acre are 10 to 20
combines some of the features of each time of applica- pounds of N per acre and 3 to 10 pounds of P per acre
tion. The first application provides enough fertilizer for (107).

Plowing-down manure soon after application is the of information are older soil science books (97, 108).
most appropriate method of controlling losses from The practice is based on the symbiotic relation between
broadcast applications. This method also prevents nitro- some types of microorganisms and legurne plants in
gen loss as volatile ammonia. However, meadows and which nitrogen frorn the atmosphere is converted into
haylands can't be plowed, nor can frozen croplands. For plant protein. From 40 to 60 pounds of N call be
these cases, the State of Maine guidelines (101) recom- supplied per ton of' dry forage. Part of the nitrogen in
mend that only upland fields with less than 3 percent the plant comes from mineralized soil nitrogen, but this
slope be used for manure spreading when frozen or snow is probably balanced by not considering the nitrogen in
covered. They also recommend against spreading on any the plant roots. Obviously, the greatest limitation of this
fields with slopes greater than 25 percent or within 100 practice is loss of any return from this crop. If the forage
feet of wells, springs, ponds, or lakes, or when there is a is harvested, then the net gain in soil nitrogen is small.
high possibility of runoff.
While most manure is in a relatively solid form, some Us@ng Winter Cover Crops
stored wastes are in a slurry form. Slurries, principally
from dairy and swine operations, can be injected directly Although winter cover crops are recommended foi
into the soil, thus almost eliminating runoff losses. A control of soil erosion during the fall and winter (see
large part of the nutrients are in solution and can move Erosion Control Practices), thev can also reduce nitrate
into the soil even if surface applied. Storage of manure is leaching through plant uptake of nitrate and reduce
a large added expense with little economic return. The percolation by drying the soil out. An oat crop reduced
investment needed for manure storage on a dairy farm nitrate leaching 4-fold on one soil and eliminated it on
has been estimated as three to five times the cost of another. Vetch, however, reduced leaching only slightly
daily spreading (6). and because it is a legume, added nitrogen (14). Cover
A second problem of substituting manure for fertil- crops of oats, timothy, and rye reduced leaching 40 to
izer is determining how much nitrogen is being applied. 60 percent (46). Thomas (156) recommends that the
Not only does the nutrient content of manurc change cover crop be planted by October for the most effective
with different animals, but also with their feed and control of leaching.
environmental conditions. If bedding is used, this pro- The major expense of this practice is planting the
vides added bulk with no added nutrients, but it absorbs crop. Some economic return can be obtained by using
liquids and prevents nutrient loss. Tile largest losses are the crop for winter grazing. Also, in some areas it is
probably by volatilization of nitrogen during storage, possible to double crop; that is, grow a winter grain such
spreading, and before incorporation. As much as 40 as wheat and then plant a short season crop Such as
percent of the nutrient value can be lost by delaying soybeans. A serious lirnitation of cover crops is that they
incorporation for 4 days (127). Ammonia gas is con- can remove so much of the soil water that the main
tinually being lost, while denitrification of nitrate and suminer crop suffers, particularly in a dry year.
nitrite occurs in anaerobic storage.
Other problems include the fact that not all the
nitrogen is available during the first growing season. Controlling Ferfilizer Release or
Organic nitrogen compounds are similar to the soil 7ransformation
organic matter in that some are more easily mineralized
by microbes than others. This is not too serious since Many researchers have explored the possibility of
repeated yearly applications will build the organic controlling fertilizer release or availability. Recently the
nitrogen up so that the total mineralized is equivalent to interest has been very great and over 50 papers were
the amount added. The nutrients may not be in the presented at the 1974 Annual Meeting of the American
proper ratio for a particular crop on that field. However, Society of Agronomy dealing with this sub ect. Two
this can easily be corrected by adding nutrients to the basic approaches are being used: a slow release fertilizer
field or to the manure in storage. and a nitrification inhibitor.
Slow release fertilizers offer three advantages: i)
Green Logume Crops reduction in nutrient loss by leaching and runoff, ii)
reduction in immobilization before plant uptake, and iii)
This practice was frequently used to supply nitrogen reduction in losses by denitrification and volatilization
before the development of commercial fertilizers, but (58, 77, 119, 122). Three processes are used to slow the
little research has been done on it since commercial release of the fertilizer from the granule: i) controlling
fertilizers became available. Thus, the principal sources dissolution by a physical barrier, ii) using compounds of

limited water solubility, and iii) using a barrier that would reduce runoff losses. Pasture and haylands usually
decomposes. Of the 13 different slow release fertilizers require surface application of fertilizers and thus runoff
developed, sulfur-coated urea seems to be the most losses could be a problem, Wagner and Jones (171)
promising. Most of the commercial production is being report that if a high level of fertility is maintained, then
used on turf. The present cost is 25 to 40 percent more timing of phosphorus and potassium fertilizer applica-
than uncoated urea (4). The greatest problem is to tions is not critical. In fact, on slightly deficient soils
control the release so that the fertilizer is available when enough P and K can be plowed under when the forage is
the plant needs it. If the release doesn't occur in a short planted to last 4 or 5 years. Since nitrogen is so mobile,
period of time for row crops, then the remaining N is the greatest efficiency is obtained by applying it shortly
susceptible for leaching after harvest. The future looks before or during the growing season. Cool season forages
promising, but more research is needed before large scale such as the brome and blue grasses make their growth in
recom mend ations can be made. the spring and fall, whereas warm season grasses such as
Nitrification inhibitors are chemicals that prevent the Bermudagrasses make their best growth during the
microbes from converting ammonium to nitrate. Five summer.
chemicals offer possibilities. The most widely tested are: Spraying a fluid fertilizer on the surface might have
2-chloro-6-(trichloromethyl) pyridine, sold as lower losses in runoff than broadcasting granular ferti-
N-SERVE by Dow Chemical; 2-amino-4-chloro-6- lizers even though there is no published research on the
methyl pyridine, sold as AM by Mitsui-Toatsu Industries; subject. Fluid fertilizers are liquids or suspensions of
and sodium azide. Experiments with soil in plastic bags micro crystals and therefore should come in quicker
in the field from November to April show that most of contact with the soil than granules that must dissolve.
the conversion was prevented by N-SERVE (19). One of Ammonia cannot be used because it volatilizes too
the greatest difficulties has been to keep the inhibitor easily. Urea is also subject to some losses because it is
near the ammonium; usually percolating water separates converted to ammonium.
them. Broadbent (25) doesn't consider the prospects of
developing a practical method to be very good. Using Legumes in Haylands and Pastures
Incorporating Surface Applications Legumes can be planted with grass in pastures and
haylands to supply much of the nitrogen requirement
Immediate incorporation of surface-applied fertilizers and thus reduce the need to fertilize with nitrogen. The
and manure can prevent significant losses of nutrients. A legumes can be very effective in this situation because
number of studies have shown that the losses are greatest the grass receives nitrogen in leakage from the legumes as
when the runoff occurs soon after application (see the well as the mineralized soil nitrogen (3). As pointed out
section on runoff losses). Timmons et al. (162) report by Kilmer (76), leaching losses will be higher from
that deep incorporation of the fertilizer by plowing legumes than from grasses. However, if leaching is not a
down and subsequent disking reduced the nutrient losses problem and runoff losses are, then legumes can be used
to levels similar to those in runoff from unfertilized effectively. A major problem is that competition for
plots. Broadcasting on a plowed surface is adequate if no other nutrients, water, and sunlight causes the grass to
additional tillage is performed because the infiltration crowd out the legume in a few years.
is very high. Disking instead of plowing broadcasted
fertilizer was not effective. Up to 30 tons/acre of
manure have been incorporated into the soil with little Timing Fertilizer Plow-Down
increase in the nitrate and ammonium contents of the
tail water from irrigation (151). When nutrients are being lost by sediment transport,
erosion control practices are the obvious answer in most
cases. An additional procedure that can be recom-
Controlling Surface Applications mended is plowing during the least erosive period and
leaving the field in the least erosive condition. For
The time of application and the type of fertilizer can example, if erosion is less in the fall than in the spring,
be controlled to some extent. Fertilizer should not be phosphorus and potassium fertilizer might be plowed
applied during periods of expected runoff. Fall-seeded under in the fall using stubble mulching techniques or
grains are often top-dressed with fertilizer in the spring. followed by a cover crop so that an erosive period in the
If leaching is not a problem, then fertilization at planting spring can be avoided.

Mathematical Models nutrients on a storm-by-storm basis for a farm-sized
The soil-plant system is very complex and dynamic watershed. The hydrology model has been tested in a
and therefore the impact of various management prac- number of locations. The erosion model is being tested
tices can vary considerably. One of the most efficient and improved with Corn Belt watersheds, but the
ways of' testing alternatives on complex and dynamic chemical model is essentially untested.
systems is to describe the system with a mathematical Hagin and Amberger (54) developed a model for the
model. 11' the model adequately represents the behavior N and P loads in water and have tested only a few of the
of the system for known responses and is based on various relations used. Kling (81) developed a model for
sound fundamental relations, then its responses for sediment and phosphorus movement that was tested at
various alternatives can be quickly tested with modern locations in New York and Pennsylvania. Johnson and
computer equipment. Straub (72) developed more of an accounting system
A number of programs have been started in recent than a model for a 23-square-mile watershed in Minne-
years to develop models for sediment and chemical sota. EPA is developing a pesticide transport model (31)
transport from watersheds. Most of these efforts are still and a nutrient transport model.
in the development stage and have yet to be adequately As these and other models (43) are developed further,
tested against field results. they will provide increased understanding of the system.
ACTMO, an agricultural chemical transport model When they are completed, a tool will be available to
(44, 45) linked together a hydrology model (65), an better evaluate the alternatives for controlling pollution
erosion model (118), and a chernical model (42) to from nonpoint sources. Until then, we are left with the
predict the concentration and amount of pesticides and less exact recommendations discussed in this report.

RESEARCH NEEDS

The most immediate need is to measure and evaluate nutrients needed by various plants, but also when they
the impact of presently used conservation practices on are needed. We must be able to predict the rate of
chemical losses. It is anticipated that in most cases the nutrient release from the soil as well as the total amount.
needed control can be achieved by practices already In order to improve fertilizer efficiency we need a better
developed. The other cases will require a better under- understanding of the effects of placement and timing.
standing of the system to develop adequate control Now fertilizer materials need to be evaluated in terms
practices. Many of the conservation practices were of leaching and runoff characteristics as well as crop
developed for the older farming systems. They are now yield and cost, Continued development is needed on
being modified and adapted to the current large-scale chemical regulators such as nitrification inhibitors that
farming systems. The evaluation process for these can provide additional management control.
modified practices should include quantitative measure- The demand for low cost meat should increase the
ments of chemical transport as well as the traditional need for more forage of higher quality. The use of
variables such as erosion, crop yield, etc. commerical fertilizers, animal wastes, and legumes in
All forms of fertilizer research received less than achieving improved forage must be evaluated in terms of
adequate support in the previous decade. Now the environmental quality as well as costs. The possibility of
combined effects of environmental concern, increased improving nitrogen fixation by legumes should be
fertilizer costs, and increased food needs dictate that we pursued. Finally, the possibility of incorporating nitro-
improve our knowlege of the soil -plan t-wate r system. gen fixation into nonlegumes, while remote at this time,
Not only do we need to know the total amount of could be so useful that it should not be neglected.

LITERATURE CITED

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Proc. Twelfth Sanitary Engin. Conf., Univ. Illinois, nodulation, nitrogen fixation, and yield of soy-
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163, Timmons, D. R., Holt, R. F., and Latterell, J. J.
153. Stewart, K. M., and Rohlich, G. A. 1967. Eutro- 1970. Leaching of crop residues as a source of
phication-a review, Calif. State Water Qual. Con- nutrients in surface runoff water. Water Resour.
t rol Board, Sacranien to, No. 34, 188 pp. Res. 6(5): 1367-1375.

154. Taylor, A. W., and Kunishi, H. M. 197 1. Phosphate 164. U S. Environmental Protection Agency. 1973.
equilibria on streani sediment and soil in a water- Measures for the restoration and enhancement of
shed draining an agricultural region. Jour. Agr. quality of freshwater lakes. EPA-430/9-73-005. U.
Food Chern. 19: 827-83 1. S. Govt. Printing Off., Washington, D. C.

155. Thomas, A. W., Carreker, J. R., and Carter, R. L. 165. U. S. Environmental Protection Agency. 1974.
1969, Water, soil, and nutrient losses on Tifton Relationships between drainage area characteristics
loarny sand. Univ. Georgia, College of Agr. Expt. and nonpoint source nutrients in streams. Working
Sta. Res. Bul. 64. Paper No. 25, Pacific Northwest Environ. Res.
Lab., Corvallis, Ore.
156. Thomas, G. W. 1970. Soil and climatic factors
which affect nutrient mobility. In Orvis P. Engel- 166. Uttormark, P. D., Chapin, J. D., and Green, K. M.
stad, ed. Nutrient mobility in soils: accumulation 1974. Estimating nutrient loadings of lakes from
and losses: 1-20. Soil Sci. Soc. Amer., Inc., non-point sources. EPA-660/3-74-020. U. S. Govt.
Madison, Wis. Printing Off., Washington, D. C.

167. Victs, F. G., Jr. 197 1. Fertilizer use in relation to 178. Wildung, R. E., Schmidt, R. L., and Gahler, A. R.
surface and ground water pollution. In R. A. 1974. The phosphorus status of eutrophic lake
Olson, T. J. Army, J. J. Hanway, and V. J. Kilmer, sediments as related to changes in limnological
eds. Fertilizer technology and use: 517-532. Soil conditions - total inorganic and organic phos-
Sci. Soc. Amer., Inc., Madison, Wis. phorus. Jour. Environ. Qual. 3(2): 133-138.

168. Viets, F. G., Jr. 197 1. Water quality in relation to 179. Williams, J. D. H., and Mayer, T. 1972. Effects of
farm use of fertilizer. BioScience 21: 460-467. sediment diagenesis and regeneration of phos-
phorus with special reference to Lakes Erie and
169. Vollenweider, R. A. 1971. Scientific fundamentals Ontario. In H. E. Allen and J. R. Kramer, eds.
of the eutrophication of lakes and flowing waters, Nutrients in natural waters: 281-315. John Wiley
with particular reference to nitrogen and phos- and Sons, New York.
phorus as factors in eutrophication. Organ. for
Econ. Coop. and Devlpmt., Paris. 180. Willrich, T. L. and Smith, E. G. 1970. Agricultural
170. Wadleigh, C. H. 1968. Wastes in relation to practices and water quality. Iowa State Univ. Press,
Ames.
agriculture and forestry. Misc. Pub. No. 1065. U.S.
Dept. Agr., Washington, D. C. 181. Winton, E. F. 1970. The health effects of nitrates
171. Wagner, R. E., and Jones, M. B. 1968. Fertilization in water. In Nitrate and water supply: source and
of high yielding forage crops. In L. B. Nelson, M. control. Proc. Twelfth Sanitary Engin. Conf.,
H. McVickar, R. D. Munson, L. F. Seatz, S. L. Urbana,lll.
Tisdale, and W. C. White, eds. Changing patterns in
fertilizer use: 297. Soil Sci. Soc. Amer., Inc., 182. Yaalon, D. H. 1965. Downward movement and
Madison, Wis. distribution of anions in soil profiles with limited
wetting. In Experimental pedology: 157-164.
172. Walsh, L. M. 1973. Soil and applied nitrogen. Fact William Cloves and Sons, Ltd., London.
Sheet No. A2519, Univ. Wisconsin - Extension.
183. Yeck, R. G., Smith, L. W., and Calvert, C. C. 1975.
173. Wang, Wun-Cheng. 1974. Adsorption of phosphate Recovery of nutrients from animal wastes - an
by river particulate matter. Water Res. Bul. 10(4): overview of existing options and potentials for use
662-671. in feed. Proc. Internatl. Symp. on Livestock
Wastes, Univ. Illinois, Urbana.
174. Weibel, S: R., Weidner, R. B., Cohen, J. M., and
Christianson, A. G. 1966. Pesticides and other 184. Zwerman, P. J., Bouldin, D. R., Grewelding, T. E.,
contaminants in rainfall and runoff. Jour. Amer. Klausner, S. D., Lathwell, D. J., and Wilson, D. 0.
Water Works Assoc. 58(8):1075-1084. 1971. Management of nutrients on agricultural
175. Welch, L. F. 1974. Nitrogen on soybeans. Crops land for improved water quality. Project No.
and Soils 26(9): 9-10. 13020 DPB, Cornell University, New York. Rep.
No. P13209-858, Natl. Tech. Inform. Serv., Spring-
176. White, E. M. 1973. Water-leachable nutrients from field, Va.
frozen or dried prairie vegetation. Jour. Environ.
Qual. 2(l): 104-107. 185. Zwerman, P. J., Klausner, S. D., Bouldin, D. R.,
and Ellis, D. 1972. Surface runoff nutrient losses
177. Wild, A. 1972. Nitrate leaching under bare fallow from various land disposal systems for dairy
at a site in northern Nigeria. Jour. Soil Sci. 23(3): manure. In Waste management research: 495-502.
315-324. Cornell Univ., Ithaca, N. Y.

CHAPTER 5

PESTIMIES,"N AGR@ICUL7URAL RUNOFF

J. H. Caro

7he use of chemical pesticides has resulted in With respect to chronic effects, the true significance of
enormous benefits to mankind, chiefly in the areas of low residue levels of most pesticides in the general
public health and agricultural production. in public environment resultin 'a from long-term use of the chern-
health, insect control programs have saved millions of icals is still not well understood. In any event, it is
lives by combatting such diseases as malaria, yellow widely expected that the use of chemical pesticides will
fever, and typhus. In India, for example, the use of DDT remain all integral part of agricultural technology for
has been credited with increasing the average life many years and will in fact increase at least through the
expectancy from 32 to 47 years of age. In Sri Lanka, next decade. Consequently, information oil the path-
annual malaria cases dropped from 2 million in 1950 to ways by which pesticides leave the site of application
17 in 1963; when use of DDT was then discontinued, and distribute throughout the environment will continue
the number of cases immediately rose and again reached to be actively sought so that appropriate controls can be
I million in 1968 (45). Agricultural benefits are many: instituted.
pesticide chemicals have prornoted higher crop yields One such pathway is tile movement of pesticides
and improved quality of produce; aided the nlechani- away from treated fields in runoff water and oil
zation of agricultural production, with substantial reduc. sediment carried along in the water. In Volume 1, we
tion in labor requirements; and have helped to improve presented guidelines for identifying areas of potential
the utilization and management of land. Use of agricul- pollution problems arising from this movement and also
tural pesticides also has resulted in important economic described appropriate pesticide management practices
benefits to both the farmer and the consumer of food that would alleviate the problems. In this chapter, we
and fiber. Insecticides are widely estimated to return $5 will provide documentation to support the reconi-
to the farmer for every $1 expended (127), which often mended practices. We will also indicate the size of the
tips the scales to economic profit from a crop rather potential problem by showing the extent of agricultural
L
than economic loss. Agricultural products would prob- use of pesticides, and we will examine tile state of
ably cost the consumer two or three times more than at knowledge concerning pesticide transport in runoff.
present if the use of chemicals were eliminated (150). Related areas to be covered include (1) information on
Despite all the far-reaching benefits, the use Of pesticide persistence in soil, which affects the relation-
pesticides has brought about a conflict of interest ship between amounts of residues moved in runoff and
because of the possibility of harmful impact on environ- the tirne elapsed since application of the pesticide to the
mental quality. Conservationists have often indicted field; (2) characteristic levels of pesticides found in the
pesticide residues as being responsible for a variety of aquatic ecosystem; and (3) the impact of pesticides on
injurious effects, including fish kills, reproductive fail- aquatic organisms, which will perinit some assessment by
ures in birds, and acute illnesses in man and animals. the reader of potential hazards of tile reported levels. In
Agricultural applications have just as often been charged addition, we will summarize information on methods for
with being primary sources from which the chemicals removing pesticide residues from the aquatic environ-
dissipate into the environment. Although acute adverse nient, and we will show tile areas within the broad
occurrences have indeed taken place, the sources of the Subject of pesticides in runoff that clearly require
damaging pesticides have been a matter of some dispute. additional research.

EXTENT AND TRENDS IN USE OF AGRICULTURAL PESTICIDES

Because of the demands of our increasing population The number of specific chemicals is impressive. The
for space for cities, roadways, and recreational areas, and current domestic market for pesticides includes more
because economic trends have made smaller and less than 1800 biologically active compounds sold in over
efficient farm units unprofitable, the amount of crop- 32,000 different formulations. In 1971, 833 million
land that supports each of us has, until very recent pounds of the compounds were used in the United
times, declined steadily since the 1920's (Figure 1). The States, of which almost 60% were accounted for by use
same pressures have favored ever more intensive farming on farms (Table 2). Of all pesticides used on farms,
of the acreage still cultivated. An important component herbicides comprised 52%, insecticides 39%, and chemi-
of this modem, high-efficiency agriculture is the use of cals for control of plant diseases 9%.
chemicals to combat the pests and blights that attack The extent and distribution of pesticide use on major
our crops and agricultural products. The insects, weeds, crops in 1971 is shown in Table 3. Three crops-corn,
and plant diseases that cause significant agricultural soybeans, and cotton -accounted for almost W/o of all
damage are many and varied. In the United States alone, herbicide use on farms; two crops-cotton and corn-
for example, there are an estimated 10,000 species of accounted for nearly 70% of insecticide use; and fruit,
damaging insects and mites, about 600 of which are nut, and vegetable crops accounted for 85% of fungicide
serious pests that require control every year (114). use. The most extensively treated crop was peanuts,
The chemicals employed to control these pests have whereas only small percentages of alfalfa acreage were
been highly effective. The general impact of pesticide treated. The pests of most concern in specific crops are
use on crop yields is indicated in Table 1, which shows shown clearly in the table. Weeds, for example, are a
an apparent relationship between rates of pesticide severe problem in soybeans, but insect damage is limited.
application and crop yields in major geographic areas. Conversely, tobacco generally requires protection from
Al though yields may be increased by any of a number of insects but not from weeds.
improved agricultural practices, the importance of pesti- The geographic distribution of cropland treated with
cide use is undeniable. pesticides is shown in Table 4. Although the table shows

400- A 200
Population

C
0

cn
350- -150 '-E

.0
0
Cn Acres
C
.2 30
100 0
CL

2501 1 1 1 1 1 150
c r e >slt@"@@

19 10 1920 1930 1940 1950 1960 1970
Year

Figure I.-Land in crops and population in the United States. From Barrons (L7).

Table i. Rates of pesticide application and yields of major Table 3. Acres of crops grown and percenta
I ge treated with
crops in countries and geographic areas pesticides, United States, '9711
Pesticide Yields of Million Percentage of total acres
Country or Area application in aj or Crop acres treated with pesticides for
rates crops grown control of
OunceslA IbIA Weeds Insects Diseases
Japan . . . . . . . . . . . . . . . . . 154.0 4,890
Europe . . . . . . . . . . . . . . . . 26.7 3,060 Alfalfa . . . . . . . . . 27.5 1 8 < 0.5
United States . . . . . . . . . . . . . 21.3 2,320 Corn . . . . . . . . . 74.0 79 35 1
Latin America . . . . . . . . . . . . 3.1 1,760 Cotton . . . . . . . 12.4 82 61 < 0.5
Oceania . . . . . . . . . . . . . . . . 2.8 1,400 Fruit crops . . . . . 4.0 28 81 53
India . . . . . . . . . . . . . . . . . 2.1 730 Peanuts . . . . . . . 1.5 92 87 85
Africa . . . . . . . . . . . . . . . . . 1.8 1,080 Rice . . . . . . . . . 1.8 95 35 -
Small grains . . . . . . 91.7 37 5 < I
From Ennis et al (61 Sorghum . . . . . . . 20.8 46 39 < 0.5
Soybeans . . . . . . . 43.5 68 8 2
Sugarbeels . . . . . 1.4 75 30 13
Table 2. Use of pesticides and percentage used by farmers, Tobacco . . . . . . . 0.8 7 77 7
United States, 197 It Vegcta ble crops . . . 4.8 43 62 27

I Adapted from Andrilenas (5).
Type of pesticide Million pounds Percentage used 2 Includes wheat, oats, barley, rye, and mixed grains.
used 2 by farmers

Table 4. Cropland acreage treated with pesticides, by
Herbicides . . . . . . . . . 359 63 geographic region, 19691
Insecticides . . . . . . . . . 319 53
Fungicides . . . . . . . . . 155 27
2 Cropland acreage treated for
Total . . . . . . . . . . . . . 833 59 Region control of
From Andrilenas (5). Weeds Insects3
Active ingredients.

1000 acres 1000 acres
New England . . . . . . . . . . . . 260 245
data for 1969, the relative distribution has probably not Middle Atlantic . . . . . . . . . . 1645 675
changed significantly in succeeding years. By far the East North Central . . . . . . . . 20060 7890
West North Central . . . . . . . . 33375 10885
largest acreage treated is in the two North Central South Atlantic . . . . . . . . . . 4030 4210
regions, which basically comprise the Corn Belt and East South Central . . . . . . . . 4265 2670
much of the Wheat Belt. These 12 states contain 63% of West South Central . . . . . . . . 9990 7545
Mountain . . . . . . . . . . . . . 5655 1985
the cropland receiving herbicides and 47% of that Pacific . . . . . . . . . . . . . . . . 5635 3780
receiving insecticides. The treated area is lowest in the United States . . . . . . . . . . . . 84915 39880
Northeast (New England and Middle Atlantic regions).
In the United States, the use of pesticides has From U.S. Bureau of the Census (154).
continued to increase. Total annual sales for domestic States in the regions are:
use exceeded one billion pounds in 1973 (6), as NE: ME, NH, VT, MA, RI, CT
MA: NY, NJ, PA
contrasted with 833 million pounds in 1971 (Table 2), ENC: OH, IN, IL, MI, W1
and much of the increase is undoubtedly attributable to WNC: MN, IA, MO, ND, SD, NB, KS
expansion in agricultural demand. There are two main SA: DE, MD, VA, WV, NC, SC, GA, FL
ESC: KY,TN,AL,MS
reasons for this. Within the past year or two, farm prices WSC: AR, LA, OK, TX
have risen, so that the crop is worth more to the farmer MT: MT, ID, WY, CO, NM, AZ, UT, NV
and he will tend to apply pesticides at a lower level of 3PA: WA, OR, CA, AK, HI
infestation to protect it. Second, and also as a result of Not including land for hay crops.
changing farm economics, land is once more being
converted to cropland after a long period in the reverse and more than 8 million additional acres of wheat, of
direction (Figure 1). T he U.S. Department of Agricul- which about 2.5 million acres will need herbicide
ture has projected an annual increase in cropland within treatment.
the near future of approximately 4%. This corresponds Some economists estimate that the use of chemical
to over 3.5 million additional acres of corn, of which pesticides Will increase up to IS% annually over the next
about 57% will require herbicides and 33% insecticides, few years (45) because of the economic situation and

potential fuel shortages. To save fuel, fanners may well crops (corn, soybeans). Between 1961 and 1973, row
replace band treatment with broadcast applications, with crops increased from 58 to 80 million acres, whereas
a resultant increase in pesticide applied per acre. Within extensive crops fell from 49 million to 34 million (141).
the growing market, the patterns of use of specific Weed populations will change because the varieties that
chemicals will differ from the present because of shifts are more easily controlled will be selectively removed.
in cropping patterns and pest populations and the Despite the difficulties in moving chemicals through the
buildup of resistance in target species of pests. In the registration process, new pesticides will continue to be
North Central States, for example, there has been a introduced into the marketplace to combat stubborn
marked movement away from production of extensive weeds and to counteract pest resistance to older chem-
crops (wheat, oats, barley, rye, flax) and toward row icals.

DISSIPATION OF PESTICIDES FROM TREATED LANDS
During application to soil or foliage, pesticides may eroding sediment or leaches down into the soil-is
be lost in spray drift or by volatilization; after applica- governed by sorption and solution equilibria that depend
tion, they disappear from the site of application by primarily on the water solubility of the chemical, the
various pathways. The chemicals may undergo biological degree and strength of its adsorption on soil, and on the
or chemical degradation; on foliage or the soil surface, interaction of both soil and pesticide with water (144).
they may degrade under the action of sunlight or they Generally, compounds that are more water-soluble will
may evaporate; they may be taken up into the plant and move primarily in runoff water and those more strongly
removed in the harvested crop; they may be adsorbed adsorbed will move mostly on sediment. An inverse
onto soil particles and moved off the treated area in relationship exists between solubility and extent of
eroded material; or they may dissolve in rainwater (or adsorption, but only within families of compounds.
irrigation water) and move away in surface runoff or Some pesticides, such as paraquat and diquat, are very
down through the soil in the soil solution, perhaps later water-soluble but will move only on the sediment
to reappear in surface runoff or groundwater. The rates because of strong, irreversible adsorption; others have
of disappearance and the fractions moving by each low water solubility but will nevertheless move in the
pathway depend primarily on the properties and formu- water except when applied to a rather adsorptive sod
lation of the pesticide; the type, microbial population, (153).
moisture level, and type of management of the soil; the Soil characteristics are clearly very important in
extent and intensity of rainfall; and the soil and air determining the degree of adsorption, as illustrated by
temperatures. the fact that adsorptivity of a pesticide can vary by as
The movement in runoff water, eroded sediment, and much as 15-fold over a range of soil types. The most
subsurface water is of direct concern here and will be important soil property that influences the way a
examined in detail. A number of excellent reviews are pesticide partitions between soil and water, as deter-
available that deal with the other pathways: Kaufman mined by a number of investigators, is the organic
(98) on microbial degradation of pesticides, Crosby (54) matter content, which usually gives a good direct
and Armstrong and Konrad (9) on nonbiological degra- correlation with the degree of adsorption. Other prop-
dation, Spencer (145) and Guenzi and Beard (76) on erties that may be important are the acidity, cation
pesticide volatilization, Caro (33) and Nash (120) on exchange capacity, moisture content, temperature, and
uptake of insecticides by plants, and Foy et al (71) on clay mineral content. With some pesticides such as the
uptake of herbicides by plants. triazine and triazole herbicides, adsorption depends
primarily on soil acidity: in acid soils, they associate
Factors Influencing Pathway of Movement into with free hydrogen ions to form cations that adsorb
Water Courses strongly to the negatively charged soil; in neutral or
alkaline soils, they are in molecular form and are held
much more weakly by the soil (163). The acid herbi-
Adsorption and Solubility cides, such as 2,4-D and picloram, also adsorb more
strongly in acid soils. Bailey and White (13) showed
The pathway that a pesticide takes in its movement correlation coefficients for a number of soil properties
away from the site of application through the action of and adsorption as part of a comprehensive review of the
water-that is, whether it moves in runoff water or adsorption and desorption of pesticides in soil.

Water in the soil competes with pesticides for however, continuously move downward, except in very
adsorption sites on soil particles, so that as the moisture high rainfall areas. Evaporation at the surface causes
level in the soil decreases, the fraction of the chemical upward movement of' subsurface water and its coniple-
adsorbed increases @82, p. 100). Rain falling on a dry soil nient of dissolved pesticides, which then concentrate at
will therefore desorb a portion of the pesticide, which the surface (10 7, p. 429). Pesticides in the water can also
would then move with the water in any ensuing runoff. move laterally when they encounter a zone of water
Generally, adsorption decreases as soil temperature saturation or when they reach the boundary between
increases, and the response to changes in temperature two areas of different soil moisture, since water will
becomes less as the adsorption bonds weaken (82, p. move laterally into the drier soil (89). It' the laterally
97). moving water intercepts the sloping surface of the land,
?csticides adsorb preferentially on smaller sod par- the dissolved pesticide will join the overland flow and
ticles because of the high surface area per unit weight of appear in surface runoff.
these particles. When runoff occurs, the small particles Despite occasional reports of low-level groundwater
are transported greater distances than coarser material. contamination by pesticides, measurements have not in
Since rill and shect erosion primarily involve surface soil, general shown that groundwater pollution by leaching of
such erosion will tend to favor movement of the more pesticides through soil is extensive or significant. Much
strongly adsorbed pesticides 1,107, p. 431). Higher excess water must be applied even to a relatively mobile
pesticide concentrations in eroded material do not chemical to move it deeply into the profile. Many
necessarily mean that gross losses will be greater in the reported findings in experiments with piclorain, a
sediment than in runoff water; the reverse sometimes is relatively leachable herbicide, are in agreement: except
true because the amounts of water moved are so much in sandy soils, piclorarn does not ]each below the 2-foot
greater (134, 166). depth (107, p. 430). For a more strongly adsorbed
pesticide such as dieldrin, several hundred years would
be required for the chemical to be transported in
solution at a residual concentration of 20 ppb to a depth
Pesticides in the soil or on its surface may move down of I foot in neutral soils (67). The groundwater
through the soil profile dissolved in water. The principal contamination that does occur may be caused by
factors affecting the movement are the same as those pesticides being carried on soil particles washed down
controlling overland movement -adsorption and solubi- into deep cracks in the soil in drought-breaking rainfalls
lity-because a pesticide is partitioned between soil and (125, 169).
water in leaching as well as in runoff. Other parameters
influencing leaching are water flow rate and amount, and Formu@at@on
the formulation, concentration, and rate of degradation The formulation in which a pesticide is applied also
of' the pesticide (89). The correlation of solubility and may affect the pathway of' movement. especially if
adsorption with pesticide movement through soil sug- runoff occurs shortly after application, before the
gests that solubility may be important in the initial chemical has equilibrated with the soil. For example,
movement from the point of application, whereas ester formulations of the herbicide 2,4-D applied to a
adsorption may be the deterinilling process in later sandy loam soil in a set of experiments (16) were far
movement. Therefore, adsorption will, in general, be a more susceptible to washoff than an arnine salt formula-
better indicator of overall potential movement than will tion. The ainine formed a true solution with water and
solubility (21). As examples of this, prometryne (48 leached into the soil, whereas the relatively insoluble
ppm water solubility) moves less in soil than simazine (5 esters were adsorbed and moved on the eroded sediment.
ppin), because it is more strongly adsorbed, and monuron
"230 ppm" moves about the same as atrazine (33 ppin) Facton Influencing Amoun2s of Pest@cides
k I
for the same reason (85). Moved into Water (Ccurses
-lie pesticide moves downward through the profile
either by mass flow of water from impacting rainfall or The quantity of a pesticide moving into a water
b
by molecular diffusion in the soil solution. Diffusion, course from a treated area in any given runoff occur-
which is influenced by bulk density and temperature in rence depends on a number of associated factors. Its
addition to soil moisture, is slow in comparison with relationship to topography, intensity and duration of
I
mass flow and is important only over short distances rainfall, soil erodibility, and land management and
(21), so that mass flow is the primary means of cropping practices are discussed in the chapters on
0
movement under most conditions. Water does not, erosion and runoff. Obviously, the amount moved will

increase with the amount of pesticide initially applied to among others the weather; cultural practices; and type,
the area. It also depends on the following parameters. temperature, moisture level, and acidity of the soil.
Pesticides that are subject to microbial degradation will
Time After Application have reduced persistence when applied to an area that
had received an earlier application of the same chemical
Characteristically, pesticide losses are highest in the becau .se of growth in populations of active micro-
first runoff occurring after application of the chemical, organisms after the first treatment (99). If, as is often
and the magnitude of the loss generally decreases as time the case, more than one pesticide is applied, interactions
between the chemicals may also markedly alter the
between application and runoff increases. The effect of persistence of the individual compounds in both sod and
elapsed time is particularly noticeable with short-lived aquatic environments (97).
pesticides and with pesticides that are not incorporated
into the soil. Concentrations of the chemical in subse-
quent runoff events decrease at a rate that depends Antecedent Soil Moisture
largely on the persistence of the pesticide in the soil.
Field experiments with the carbarnate insecticides car- Some pesticides will have greater losses in runoff if
baryl and carbofuran showed that pesticide concentra- applied to wet soil than if applied to dry soil, partic-
tions in both runoff water and sediments in the third ularly if runoff occurs soon after application. Experi-
runoff, which occurred within I or 2 months after ments showing this have been reported for 2,4-D (16)
application, were less than 5% of the concentrations in and for fluometuron (15). The effect is probably related
the first runoff (35, 36). By contrast, concentrations of to the competition of water with the pesticide for
the persistent insecticide dieldrin in the third runoff, 3 adsorption sites on the soil particles.
or 4 months after application, were about 15% (water)
and over 30% (sediment) of those in the first runoff Proximity to Water Course
(34). The pattern of relatively high concentrations in the
first runoff, decreasing with time to eventually negligible Sloping cropland rarely abuts continuous streams.
concentrations in succeeding runoffs, has been noted in
experiments with many pesticides. Quantitative ex- Consequently, pesticide -containing runoff usually must
amples are illustrated below in the section on pesticide traverse some untreated land before reaching the water.
levels in runoff. This intervening area can trap some of the pesticide,
resulting in lowered contamination of the stream. Large
Persistence in Soil decreases can be obtained. In one set of measurements,
flow over only 5 feet of untreated soil with slopes of 3%
As mentioned, the persistence of a pesticide in soil or 8% reduced piclorarn losses in runoff from small field
affects the change with time in amounts lost in runoff. plots more than 50% (151); in another case, dieldrin
However, many factors influence the persistence of an applied at 10 to 20 times normal levels to strips of land
individual pesticide and, consequently, it can be quite 12 to 15 feet away from the edges of ponds, vAth
variable. Picloram, for example, has been reported in shallow to steep slopes intervening, did not appear in the
specific instances to effectively disappear ftom the soil pond water or bottom mud, except for very low (0.3
in as little as 50 days (110) or as long as 6 years (30) ' ppm) contamination of the mud when the pesticide was
but its persistence under moderate conditions is gen- left on the surface of the soil (58).
erally about 1.5 years.
A pesticide applied to the soil is subject to a sequence Placement of the Pesticide
of overlapping loss processes-application losses, volati-
lization, sorption, leaching, and eventually chemical and The most important effect of pesticide placement
biological degradation (92). As a result, the loss rate with respect to environmental contamination is that
changes rapidly during the early period when the soil-in corporate d pesticides will not be lost in runoff to
chemical is distributing and equilibrating in the soil, then as great an extent as those applied and left on the
becomes nearly constant over a relatively longer time. surface or sprayed on foliage. The subject is discussed in
This later rate is dictated by many conditions, including more detail in section 4.4 of Volume 1.

PERSISTENCE AND FATE OF PESTICIDE RESIDUES IN THE
AQUATIC ENVIRONMENT
Distribution of Pesticides on Entering inflow, desorption of acidic compounds (such as 2,4-D,
Water Bodies 2,4,5-T, or picloram) or weakly basic compounds (such
as the triazine or urea herbicides) will be favored, and
A pesticide carried in agricultural runoff entering a the reverse will be true if the pH of the body is lower
receiving water body-strearri, pond, or lake-will dis- than that of the inflow. Salinity in the take will favor
tribute within the aquatic system in a manner and at a adsorption of acidic pesticides and desorption of basic
rate that depends primarily on whether the chemical is pesticides, but the effect is generally minor. A lower
initially dissolved in the water or adsorbed on particles temperature in the water body will increase pesticide
of eroded soil suspended in the water. adsorptivity, but this too is a minor effect under field
A dissolved pesticide will be diluted in the larger conditions (126). If there is any oil pollution in the
volume of water and will be subject to processes that water, adsorbed oil will significantly concentrate the
dissipate it. In a flowing stream, it will simply be pesticides on the sediment (87).
transported away from the point of entry, later to
undergo degradation or removal from the water. In a Post-Distribution Processes
pond or lake, it may sorb or concentrate in algae and
aquatic vegetation or it may attach to suspended Pesticides never reach true equilibrium in water
sediment and other particulates in the water such as bodies because the systems are dynan-tic, with many
bacteria] flocs, diatoms, and general organic or inorganic processes continually operating to remove the chemicals
fragmentary material. In either case, it is eventually from the system at rates that change as conditions
deposited on the bottom of the lake unless it is change. Pesticides sorbed on bottom muds may be
chemically or biologically degraded before it reaches the churned up and carried along with sediment during
bottom or is taken up by living organisms. The sorption periods of turbulent flow or they may remain where
processes appear to be generally quite rapid and effi- originally deposited. Since sorption on particulate
cient, as shown in measurements of organochlorine matter is generally reversible, the bottom muds provide a
insecticide sorption on algae (91) and bacterial flocs continuous supply of desorbed pesticides to the over-
(106). Highly soluble pesticides that are only weakly lying water. In the water, the pesticides may be
adsorbed may be hydrolyzed or biologically degraded in chemically or biologically degraded, they may reach the
solution at a rate that depends on the types and numbers surface and volatilize, or they may be decomposed near
of microorganisms in the water. the surface by the action of sunlight. (Sunlight energy is,
The fate of pesticides entering water bodies adsorbed however, probably too weak to induce much photode-
on sediment has been discussed in detail by Pionke and gradation in natural waters.) At the surface of the
Chesters (126). The pesticide will distribute first with bottom muds, pesticide degradation is extensive. Be-
the carrying sediment, then will equilibrate with the cause organic matter accumulates there, it is an area of
remainder of the aquatic system. Sediments entering high microbial activity. The microbial populations may
water bodies will segregate on a particle-size basis: in a consume so much oxygen that the environment becomes
stream, the fractionation will depend on stream velocity; anaerobic, a condition that favors the degradation of
in a lake, the particles will settle on the bed in decreasing many pesticides. For example, most chlorinated hydro-
order of particle size. The finer particles containing the carbon insecticides, although normally highly persistent,
highest concentrations of pesticides will be transported will degrade at an appreciable rate under anaerobic
farthest and will be localized in a stream; in a lake, these conditions when the temperature is 200 C or higher (91).
particles will settle last and remain at the water-sediment
interface. In large, thermally stratified lakes, density Pesticide Persistence in Aquatic Environments
currents may control the movement and mixing of
incoming sediments and settling may be very slow. Measurements have been made of the persistence in
Conditions in the water body may affect the adsorp- aquatic systems of a large number of specific pesticides,
tion and desorption of the pesticide on the sediment. If as summarized by Pionke and Chesters (126), Paris and
the pH of the lake or stream is higher than that of the Lewis (123), and Eichelberger and Lichtenberg (60),

among others. Information of a more general nature is through the action of microorganisms. The degradation,
presented here. which generally involves a simple dechlorination of the
molecule, may require up to several months for comple-
Organophosphorus Insecticides tion in natural systems. There is, however, some varia-
tion among the individual members of the class, persist-
As a class, organ ophosph orus insecticides are among ence increasing in the following order: lindane,
the less hazardous pesticides in the aquatic system heptachlor, endrin, DDT, DDD, aldrin, heptachlor
because they hydrolyze rapidly. Within the pH range epoxide, dieldrin (90, 91).
6.0-8.5, which covers most systems, most organophos-
phorus compounds hydrolyze within 8 to 12 days, with Other Pesticides
hydrolysis occurring both in water and on sediments
(118, 126). Parathion is an exception, being somewhat The carbarnate insecticides have been shown to
resistant to chemical hydrolysis. It is, however, readily degrade in slightly alkaline river water in less than 4
susceptible to microbial degradation in both aerobic and weeks (60), but since the stability of these compounds is
anaerobic environments. In the absence of an active pH-dependent, appreciably longer persistence would be
microbial population, parathion remains in the aquatic expected in a more acid environment.
environment for several months; in the presence of an The decomposition of many herbicides is primarily
active population, it is degraded in a matter of weeks biological. In aerobic lake water, for example, 2,4-D
(75). persisted for up to 120 days, whereas in lake muds, it
was substantially decomposed in 24 hours once the
microbial populations had adapted to the chemical (2).
Organochlorine Insecticides The herbicide dicamba also dissipates from water most
rapidly under nonsterile conditions. The rate of disap-
As noted earlier, these compounds will degrade very pearance depends greatly on the temperature, especially
slowly, if at all, in aerobic aquatic systems, but will in the presence of sediments containing active microbial
decompose more rapidly in anaerobic environments populations (139).

CHARACTERISTIC LEVELS OF PESTICIDES IN THE AQUATIC ECOSYSTEM

When pesticide-containing runoff occurs from agricul- water (Table 5). An obvious goal of pesticide control
tural land, the chemicals are quickly diluted in the water programs is to assure that the natural waters of the
bodies receiving the runoff and are also partitioned country are sufficiently pesticide-free to drink without
among the various components of the environment- purification.
water, bottom sediments, and living organisms-so that
each component eventually bears a concentration of the Pesticide Levels in Runoff
pesticide. The magnitudes involved have been measured
by many investigators under a variety of conditions and Concentrations of pesticides leaving treated fields in
are summarized here, including levels in the runoff itself runoff water and entrained sediments during the crop
and in drainage streams, farm ponds, lakes, and oceans, season following application are almost always measur-
so that some appreciation may be gained of the impact able, so that there is little doubt that agriculture does
of agricultural activities on water quality. contribute to the pesticide residues found in the general
The importance of maintaining a constant surveil- aquatic ecosystem, Both concentrations and gross
lance of the aquatic system in the United States has been amounts lost depend on numerous factors, including
recognized by the Federal government. Comprehensive among others the intensity of rainfall, the time after
programs for continuous monitoring of pesticides in fish, pesticide application that runoff occurs, and the mode
estuarine shellfish, water, and bottom sediments, among of application. Concentrations of a given pesticide may
other components of the general environment, are therefore differ substantially in runoff occurrences at
conducted by various agencies to establish baseline levels separate locations under different sets of conditions.
and to signal significant trends. The overall program is Nevertheless, it is useful to examine the results of
coordinated by an interagency committee (122). With specific measurements reported in the literature, not
respect to the quality of our waters, standards have been only because an understanding may be gained of the
set for acceptable limits of certain pesticides in drinking orders of magnitude involved, but also because some

Table 5. Recommended limits for pesticides in drinking water' that the gross loss over the course of the year following
Pesticide Recommended application will represent only a small percentage of the
Limit amount of chemical that had been applied to the
cropland. Results of watershed and field-plot experi-
Organochlorine Insecticides ments reported in the literature 117able 7) show the wide
k-
ppb applicability of the relationship. Except for one experi-
Aldrin . . . . . . . . . . . . . . . . . . . . . I ment with atrazine in which a heavy rain occurred one
Chlordane .................... 3 week after application, total amounts lost in runoff
DDT ...................... 50 water and sediment were always 5 percent or less of the
Dieldrin .................... I
Endrin .................... lication. is appears to hold true irrespective of the
0.5(0.2)2 app
Heptachlor .................. 0.1 soil type or degree of incorporation of the pesticide into
Heptachlor epoxide .............. 0.1 the soil, and applies even on relatively steep slopes.
Lindane . . . . . . . . . . . . . . . . . . . . 5(4)2
Methoxychlor . . . . . . . . . . . . . . . . 1000(100)2 imulated rainfall experiments, in which the amount and
Toxaphene .................. 5 intensity of water falling onto a small sloping plot can be
Phenoxy Herbicides controlled, show that rainfalls of the size and intensity
that might be expected to occur every year produce only
2, 4-D ...................... 20(10 2 small percentage losses of pesticides in runoff, but that
Silvex ...................... 30(10)?@ heavier "10-year" rains may cause larger losses (11,
2, 4, 5-T .................... 2 166).
1 From Environmental Protection Agency (62).
2 Numbers in parentheses indicate limits proposed by the
Environmental Protection Agency to take effect in December LOUSIS @n D!a",raq,3 Streams
1976.

Almost all the measurements that have been made of
pesticide concentrations in flowing streams draining
informative general conclusions may be drawn. Table 6 treated areas indicate that, as might be expected,
lists a number of such measurements made on water- concentrations are substantially lower than in direct
sheds under normal agricultural conditions. runoff. With many herbicides, residues were always
The figures in the table show that pesticide concen- below detectable limits in waters a few hundred yards
trations in runoff are generally, but not always, highest below sprayed areas (66, 78). Even where detected,
in the first runoff occurrence following application of levels of such herbicides as 2,4-D, 2,4,5-T, dicamba, and
the chemical. Presumably, small flows can occasionally piclorarn were well below median tolerance limits for
produce higher concentrations than more intensive flows trout. in onL instance, the herbicide fenuron was applied
preceding them. Concentrations are always lower in at a high rate of 23 lb/A along stream channels. Only
runoffs occurring later in the season, irrespective of 2.4% of the application was lost in the stream water over
which pesticide is applied, and the reduction is generally a 27-month period, with a maximum concentration of
greater for water-borne pesticides than for those carried 430 ppb following a heavy rain (56). Results for
on sediment. The table also shows that the organochlo-' insecticides were much the same as those for herbicides.
rine insecticides, as is well known, adsorb to a great ?hosphorus insecticides were just at detection levels in
extent onto sediments, leaving only very low concentra- drainage streams in California (14' . Chlorinated insecti-
tions in water. Control of erosion will therefore reduce cides were generally at low but measurable levels. In
the movement of these chemicals substantially. Atrazine, streams draining sugarcane fields, waters contained a
on the other hand, moves with both water and sediment. maximum of 820 ppt (parts per trillion) of endrin over a
M general, the concentrations of pesticides in runoff are 4-year period, generally decreasing to 30 to 40 ppt 3
considerably above drinking water standards (Table 5) months after treatment. Streambed material averaged
and must be diluted substantially in drainage streams to 100 ppb, with levels decreasing as the season progressed.
avoid acute harmful effects on aquatic organisms in the Dieldrin, 311C, and DDT were also found in the waters
streams. Finally, the table shows, particularly in the in the parts-per-trillion range (104). @7n drainage streams
cases of carbaryl and picloram, how widely runoff from a commercial orchard that had received substantial
concentration of a pesticide may vary under different applications of organochlorine insecticides, no residues
conditions. were found in the water, but detectable levels of DDT
Though amounts of a pesticide lost in runoff may compounds, dieldrin, and endrin appeared in the silt,
vary among specific treatments, it is almost always true organic debris, and bottom organisms 017).

Table 6. Characteristic concentrations of pesticides in runoff: maxima and rates of decrease

Runoff occurrence giving Maximum concentration Runoff occurrence giving Reduced concentration
Pesticide Application maximum concentration reduced concentration Citation
rate Number after Days after In water In sediment Number after Days after In water In sediment
application application application application

IbIA ppb ppb ppb ppb
Chlorinated
Insecticides
DDT . . . . . . . . . . . 1.5 70.0 1 30,000 1.0 1 10,000 Haan (77)
DDT . . . . . . . . . . . 0.65 1 st 1 83.0 5th 46 7.0 Epstein and Grant (63)
Dieldrin . . . . . . . . . 1.5 70.0 30,000 1.0 30,000 Haan (77)
Dieldrin . . . . . . . . . 5.0 Ist 13 20.0 3rd 18 6.7 Caro et al (L4)
Dieldrin . . . . . . . . . 5.0 Ist 13 1 14,200 10th 82 1 5,000 Caro et al (LO
Endosulfan . . . . . . . 0.31 2nd 4 19.0 3rd 14 2.0 Epstein and Grant (63)
Endrin . . . . . . . . . . . 0.3 1 st 2 2.73 3rd 27 0.53 Willis and Hamilton TIM-)
Endrin . . . . . . . . . . . 0.3 1 st 6 5.02 3rd 23 2.88 Willis and Hamilton (169)
Endrin . . . . . . . . . . . 0.25 1 st 1 49.01 8.0 1 Epstein and Grant (63)
Methoxychlor . . . . . . 20.0 2nd 18 8.8 4th 3*3 1.0 Edwards and Glass (L9)

Other
Insecticides
Carbaryl . . . . . . . . . 4.5 1 st 17 248 12,200 3rd 29 8.4 80.0 Caro, Freeman, and Turner
(36)
Carbaryl . . . . . . . . . 1.5 1220 Fa-hey (68)
Phorate . . . . . . . . . 0.67 19.0 Fahey (68)

Herbicides
Atrazine . . . . . . . . 8.0 lst 24 4600 6,200 2nd 35 980 3,300 Hall, Pawlus, and Higgins (8 1)
Atrazine . . . . . . . . . 1.0 1 st 24 700 950 2nd 35 180 550 Hall, Pawlus, and Higgins (W-1)
Fluometuron . . . . . . . 4.0 1 st 870 Wiese (167)
Picloram . . . . . . . . . 3.0 3rd 86 19.0 4th 197 9.0 Bovey et al (L6)
Picloram . . . . . . . . . 2.0 1 st 30 14.4 3rd 98 < 1.0 Baur, Bovey, and Merkle (19)
Picloram . . . . . . . . . 1.0 3rd 6 89.7 8th 30 1.0 Baur, Bovey, and Merkle (L9)
Picloram . . . . . . . . . 0.25 1 st 10 17.0 2nd 20 < 1.0 Baut, Bovey, and Merkle (L9)
2,4, 5-T . . . . . . . . . 3.0 3rd 86 287 4th 197 6.0 Bovey et al (26)
2,4,5-T . . . . . . . . . 1.2 3rd 22 380 5th 38 50 Edwards and Glass (59)

Water-sediment mixture.

7able 7. Percentages of applied pesticides lost in runoff I in field experiments

Incorpo- Pesticide
Pesticide rated depth Soil texture Slope in runoff Citation

In. of app1n.
Atrazine . . . . . . . . . . . . . . 0 Silty clay loam 14 4.8-5.0 Hall (80)
Atrazine . . . . . . . . . . . . . . 0 Silty clay loam 14 2.6 Hall, Pawlus, and Higgins (8 1)
Atrazine . . . . . . . . . . . . . . 0 Silt loam 10-15 2.5-15.9 Ritter et al (134)
Carbaryl . . . . . . . . . . . . . . 2 Silt loam 10 0.1 Caro, Freeman-, and Turner (36)
Carbofuran . . . . . . . . . . . . 3 Silt loam 9 0.9 Caro et al (35)
Carbofuran . . . . . . . . . . . . 2 Silt loam 10 1.9 Caro et al (T5)
DDT . . . . . . . . . . . . . . . . 0 Loamy sand 24 1.0-2.8 Bradley, Sheets, and Jackson (27)
DDT . . . . . . . . . . . . . . . . 0 Gravelly loam 8 0.7 Epstein and Grant (63)
Dieldrin . . . . . . . . . . . . . . 3 Silt loam 14 2.3 Caro et al (34)
Dieldrin . . . . . . . . . . . . . . 3 Silt loam 10 0.02 Caro et al (34)
Endosulfan . . . . . . . . . . . . 0 Gravelly loam 8 0.25-0.35 Epstein and-Grant (63)
Endrin . . . . . . . . . . . . . . . . 0 Gravelly loam 8 0.01-1.0 Epstein and Grant (63)
Endrin . . . . . . . . . . . . . . . 0 Silty clay loam 0.2 0.1 Willis and Hamilton Tl 69)
Fluometuron . . . . . . . . . . . . 0 Various 0.14 < 3.0 Wiese (167)
Methyl parathion . . . . . . . . 0 Loamy sand 4 0.01-0.02 Sheets, iiradley, and Jackson (142)
Methyl parathion . . . . . . . . 0 Sandy loam 2 0.13-0.25 Sheets, Bradley, and Jackson (142)
Propachlor . . . . . . . . . . . . 0 Silt loam 10-15 M Ritter et al (134)
Toxaphene . . . . . . . . . . . . 0 Loamy sand 24 0.4-0.6 Bradley, Sheets, and Jackson (L7)
Trilluralin . . . . . . . . . . . . . . 6 Loamy sand 4 0.3-0.5 Sheets, Bradley, and Jackson (142)
Trifluralin . . . . . . . . . . . . . . 6 Sandy loam 2 0.5-0.8 Sheets, Bradley, and Jackson (142)

Both water and sediment.

Pesticide Levels in Farm Ponds (162). In another set of measurements, the waters of a
farm pond near a 5-lb/A treatment with carbaryl
Concentrations of pesticides in the waters of farm contained no detectable residues throughout the crop
ponds adjacent to treated areas are clearly sensitive to season, and a pond near a 0.67 lb/A treatment with
the amount of pesticide applied in the area and the phorate showed a maximum of only 4 ppb, becoming
length of time between application and the first heavy undetectable later in the season (68). Of course, ponds
rain. In a pond near cotton plots, for example, DDT and or any water body can receive relatively heavy doses of
toxaphene concentrations in the water were always pesticides by drift or inadvertent direct spray from aerial
significant after application and were especially high applications.
when intense rain closely followed the application.
Concentrations ranged from 0.4 to 13.4 ppb for DDT Pesticide Levels in Rivers
and from 2.9 to 65.2 ppb for toxaphene (142).
Similarly, in measurements of the herbicide picloram in Virtually no published information is available on
ponds at several locations in Texas, concentrations in the pesticide residues in river waters of the United States
water ranged from S5 to 184 ppb if the first rainfall showing concentrations occurring later than about 1970.
occurred within 2 weeks after application, but were only Nevertheless, the pattern is clear: contamination of the
2 to 29 ppb if the first rainfall was delayed for 6 weeks. streams peaked about 1966 (Figure 2) and then de-
Concentrations in all cases dropped to I ppb or less creased steadily, probably right up to the present, with
within 6 months (78). decline in domestic use of the most significant contami-
The few measurements that have been made indicate nants, the organochlorine insecticides. Concentrations
that farm ponds are not always contaminated despite have always been low and are often at trace levels, which
proximity to treated areas. In Virginia in 1966, when use are less than about I to 5 ppt for most of the chemicals.
of organochlorine insecticides was high, heptachlor was The national situation is perhaps best summarized by
found in the water of only 10 of 35 ponds examined, at examining the results of a few broad-scale monitoring
levels up to 5 ppb. In the bottom muds, the conversion studies. Lichtenberg et al (108) combined five annual
product heptachlor epoxide was found in 14 of the synoptic surveys of U.S. rivers for 1964 through 1968.
ponds at levels of 1 to 60 ppb. As is evident, the Except for dieldrin in 1964, no pesticide appeared in
majority of the ponds contained no detectable residues more than 40% of the samples, and the frequency of

101

occurrences; corresponding figures in 1970-71 were 53
50- Dieldrin and 54. Maximum concentrations found were 0.46 ppb
25- DDT and 0.99 ppb 2,4-D. In sum, contamination of river
F////// M WA FA waters by pesticides is at low levels, sporadic, and
0 decreasing. Even at worst, residues were well below
25 Endrin acceptable limits for drinking water (Table 5).
OVA F1,717A FA Pesticide residues in riverbed sediments are also
relatively low. In the Mississippi River, high concentra-
25 DDT tions were found only in sediments located just below
0 HA FA FA F/2720 pesticide manufacturing and formulating plants (18).
Large amounts of organochlorine insecticides applied to
25 DDE crops in the Mississippi River Delta did not contaminate
OFm r,@ r77= r777= streambed sediments widely (112). Dieldrin and endrin
25 DDD occurred in only 18 to 2Cr/o of the sediments taken from
a Louisiana estuary in 1968-69; maximum levels were 4
FZ= or 5 ppb (136). In Rhode Island streams, measurements
made about 1970 showed that DDT and its metabolites
C3 25 Aldrin
occurred in almost all sediments at concentrations
0
enerally below 500 ppb. Chlordane and dieldrin were
9
25 Heptachlor also found, but not as often and usually at less than 50
F ppb (133). The reported results suggest that riverbed
surfaces of streams draining extensive row-crop farmland
25 no Heptachlor could be contaminated by locally used pesticides at low
0 1 data Epoxide part-per-million levels.
25 Undone & BHC
or F//-/A F/m Pesticide Levels in Lakes
25 no no Chlordone
0 [data data - - Pesticide concentrations are generally lower in large
1964 1965 1966 1967 1968 lakes than in rivers. Water samples from Lake Erie in
Figure 2-Percent positive occurrences of ten organochlorine 1971-72 mostly showed no measurable residues. In the
insecticides in river waters of the United States, 1964-68. few positive samples obtained, low levels of diazinon,
From Lichtenberg et al (108). dieldrin, atrazine, and simazine were found. It was
concluded that the contribution by agricultural sources
to pesticide pollution of the lake was negligible and
insignificant (156). In 1967-68 in Lake Poinsett, the
positive occurrences declined sharply after 1966 (Figure largest natural lake in South Dakota, DDT and its
2). Maximum cont:entrations found during the 5-year metabolites predominated, averaging 80 ppt in the
period for the 10 compounds shown in the figure ranged water, with lesser amounts of other organochlorine
from 0.84 ppb for DDD to 0.048 ppb for heptachlor. An insecticides appearing in most of the samples (83). The
intensive examination of Mississippi and Missouri River waters in Lake Michigan contained only 2 or 3 ppt of
drinking water samples during the same period (137) organochlorine insecticides, chiefly the DDT family, in
showed frequencies of occurrence similar to those of the 1969-70. Upper sediment layers contained median con-
broader surveys: over 4CP/o of the samples were positive centrations of 18.5 ppb total DDT and 2.0 ppb dieldrin,
for dieldrin, over 30% for endrin and total DDT, and with traces of heptachlor epoxide and lindane (105).
200/o for chlordane. Little or no aldrin, heptachlor, Being large, diverse impoundments, lakes provide
toxaphene, or methoxychlor was found. For the later excellent environments for measurement of the process
period from 1968 through 1971, measurements of of biological magnification of pesticides through food
organochlorine insecticides and three herbicides (2,4-D, chains. Two studies clearly illustrate the effect. In one,
2,4,5-T, silvex) in waters taken from 20 stations in DDT in Lake Michigan appeared at levels of about 2 ppt
Western U.S. rivers (138) showed the characteristic in the water, 14 ppb in the bottom muds, 410 ppb in
decline in positive insecticide occurrences. In 1967-68, sand fleas, 3 to 6 ppm in fish, and as much as 99 ppm in
there were 165 insecticide occurrences and 70 herbicide herring gulls, which are near the top of the chain (114).

102

:n the second study, in which organochlorine insecti- other components of the ocean environment have
cides in Lake Poinsett were measured, the effect was probably also declined. Where they occur, concentra-
considerably smaller. Residues found were in the ratio: tions are highest in surface slicks; in 1968, coastal slicks
water 1, bottom sediments 18, crayfish 18, zooplankton contained up to 13 ppb of the organochlorine insecti-
37, algae 37, and fish 790 (83). Whatever the magnitude, cides, whereas the underlying waters were at low ppt
biological magnification must be considered when evalu- levels (140). Whole seawater off the Pacific Coast in
ating the significance of very low concentrations of 1970 also contained DDT, but only at a maximum of
persistent pesticides in waters and bottom sediments. less than 6 ppt (50).
I 's n Oceans The pattern of decreasing DDT concentration with
L I
_eva. distance from shore and with depth was confirmed in a
"Oesticides in the marine environment originate from more recent investigation of Pacific Ocean waters (168).
many sources and it is clearly not possible to define the DDT concentrations in surface film samples taken in
contribution from agricultural runoff. Taken together, 1971 and 1972 were I 1 -15 ppt in coastal waters, 0.4 ppt
however, all sources have contaminated the ocean to in the offshore California current, and less than 0.02 ppt
only extremely low levels, and only in coastal areas. in the North Central Pacific. In subsurface waters, by
DD7, the most ubiquitous pesticide, is undetectable in contrast, DDT levels were less than 0.01 ppt in the
Atlantic deep-sea water or sediments, but does appear in North Central Pacific and only 0.1 ppt in the offshore
water, sediments, shellfish, and finned fish along the current. The measurements also showed that concentra-
coast. However, concentrations in shellfish have declined tions of polychlorinated biphenyls were ubiquitous and
to insignificant levels since the curtailment of DDT use were as much as two orders of magnitude higher than
,'88) and, although not reported, concentrations in the those of DDT.

"V,*.PA"".'OF PEST?CDES ON THE AQUATIC ENVIRONMENT

System planners can best evaluate the need for Unless pesticide concentrations are very high, re-
instituting controls for pesticides in agricultural runoff if sponses of organisms in a particular aquatic system are
they understand the effects that the chemicals may extremely difficult to predict because of the great
produce in the downstream aquatic environment. The variability and natural complexity of ecosystems and the
information presented here will emphasize some major assortment of environmental insults that man imposes
effects but does not cover all that is known on the on the systems. Ponds, lakes, and streams vary in their
subject. content of water, dissolved salts, temperatures, acidity,
A variety of pesticide-induced effects on aquatic and nature and populations of plants and animals on the
birds, fish, aquatic plants, invertebrates and microorgan- bottom. Pesticide contamination in small bodies of
isms has been documented. Acute responses have been water, for example, has been judged to be more
measured quantitatively and subtle effects produced by transitory and less serious than in large bodies because of
long-term exposure to low, sublethal pesticide concen- greater bottom surface area per unit volume of water,
trations have been recognized, even though not higher flushing rates, and greater biological activity (95).
measured directly. Perhaps the most prominent effects Furthermore, different forms of the active pesticidal
have been the catastrophic fish kills during the 1960's in ingredient may differ in toxicity, and additives in the
which pesticides were implicated, though never posi- formulation, such as wetting agents or binders, may be
tively established as the cause. One such took place in more toxic to aquatic organisms than the active ingredi-
the Mississippi River, presumably caused by endrin; a ent itself (119).
second occurred in the Rhine River and was attributed In general, herbicides are less toxic to aquatic
to endosulfan. These and similar kills probably resulted organisms than insecticides (Table 8), though there are a
from high pesticide concentrations emanating from a number of exceptions (Vol. 1, Tables 8a and 9a).
point source rather than from nonpoint agricultural Herbicides, especially those applied directly, also have
runoff. Runoff was, however, probably partly responsi- desirable as well as undesirable effects on water bodies.
ble for contamination of Lake Michigan salmon by DDT They may be responsible for opening and maintenance
in 1969 that, though not fatal to the fish, resulted in of navigable waterways, saving of irrigation water,
widespread confiscation of the commercial catch, with increase in aesthetic and monetary value of waterfront
an economic loss estimated at $3 to $4 million (95). property, control of mosquitoes and snails by removal of

103

Table 8. Relative toxicity of selected pesticides to It is important to recognize that the high toxicity to
aquatic organismsI fish of some herbicides (trifluralin, for example) is
Pesticides Organism tempered in nature by processes that inactivate the
compound, such as strong adsorption and relative
Plankton Shrimp Crab Oyster Fish immobility on soil surfaces, so that contamination of
Herbicides . . . . . I I 1 1 1 natural water bodies is minimal if the chemical is used
according to label directions.
Phosphorus . . . . . 0.5 1000 800 1 2 Another aspect of toxicity to fish is the development
Insecticides of resistance to pesticides, which has been documented
DDT . . . . . . . . . . 2 400 200 300 700 for several species of fish. For example, fish in a
contaminated lake in Mississippi had higher tolerance for
From Butler (31). Based on the arbitrary assignment of endrin, DDT, and toxaphene than those in a relatively
the value of I to hJb-icides. clean lake (22). Toxicity will also result in the flourish-
ing of one group of organisms in an aquatic environment
aquatic weeds, restoration of recreational waters, im- while others are suppressed. Thus, elimination of algae-
provement in fish management, and elimination of eating species will produce increases in algae and
flavors and odors from algal blooms. On the debit side, anaerobic bacteria populations (130).
many herbicides are acutely toxic to fish (Vol. 1, Table
8a). Serious losses of fish and other aquatic fauna may Chronic Toxicity
also occur when herbicides kill aquatic weeds, which
gravitate to the bottom and decompose, removing Fish mortalities have been observed to occur in
necessary oxygen from the water. Moreover, phenols nature by long-term, low-level exposure to pesticides.
resulting from the hydrolysis of phenoxy herbicides such Numerous pathological effects on the tissues and organs
as 2,4-D may impart objectionable flavors and odors to of fish have also been noted, including lesions of liver
water. In comparison with insecticides, however, the and gills and changes in the intestines, kidneys, brain,
hazards of herbicides in the aquatic environment are and blood. However, some chemicals-notably meth-
small. Most herbicides have little or no toxicity to oxychlor and carbamate insecticides such as carbofuran
humans, wildlife, or livestock; they may reduce phy- and carbaryl-are rapidly hydrolyzed on ingestion and
toplankton populations initially, but recovery generally therefore do not have chronic effects.
occurs within 2 or 3 weeks; they do not undergo
biological magnification in food chains, and shellfish are Fish Reproduction and Growth
tolerant of them, accumulating residues only tempo-
rarily after exposure (72). Persistent pesticides such as DDT and dieldrin can
have strong adverse effects on reproduction in fish. In
Acute Toxicity one typical case, the hatching success of landlocked
Atlantic salmon from a lake contaminated with DDT
The toxicity of a pesticide to fish is affected by was 36% lower than in control fish (109). Mortality
numerous parameters, including the size, age, and species usually occurs in salmon sac-fry during the period of
of the fish; water temperature and acidity; and physical
differences at the aquatic site. Survival time after
exposure generally correlates directly with body weight, Table 9. Effect of water temperature and exposure time on
probably because the smaller fish consume a propor- the toxicity of trifluratin to bluegillsi
tionately greater diet and have less fat for storage
detoxification. Higher water temperature increases toxi- 48-Hour 24-Hour
city of some pesticides and decreases it for others. DDT Water temperature LC50 LC50
and methoxychlor are examples of insecticides that are
less toxic at higher temperature; toxaphene, endrin, 0
malathion, and parathion are more toxic (32). The effect F w1liter AgIliter
85 8.4 10
can be very pronounced, as shown in Table 9. There are 75 66 120
differences in response within species as well as between 65 200 360
species. Diquat, for example, was toxic to female 55 380 530
mosquitofish under conditions in which the males were 45 590 1300
not affected (170). From Cope (48).

104

yolk-sac absorption. Some herbicides also may produce One apparent and obviously serious effect is the disrup-
reproduction problems in fish, causing atrophy of tion of photosynthesis in phytoplankton: in a compre-
spermatic tubules and production of abnormal sper- hensive series of tests, carbon fixation by estuarine
matozoa (48). 'Ln addition to reproductive failures, loss phytoplankton was reduced by 45 of 54 chemicals
of appetite and restricted growth have been reported to tested, with reductions of over 90% for several of the
result from exposure of fish to pesticides. compounds (158). Some aquatic plants act as concen-
trating agents for the organochlorine insecticides, so that
Fish Behavior when the plants die, concentrations of the pesticides, as
well as of plant nutrients, are released into the water.
Cases have been reported of changes in the condi-
tioned responses and locomotor patterns of fish as a Odor and Taste
result of exposure to pesticides. One well-documented
effect is an increase in sensitivity to low water tempera- Several of the organochlorine insecticides, including
tures, including active avoidance, in fish exposed to DDT toxaphene, endrin, and heptachlor, impart objectionable
(32). odors to water at concentrations of only a few parts per
billion; a number of herbicides generate a strong odor;
Effects on Aquatic Plants and the solvents used in many formulations are highly
odorous in concentrations as low as 16 ppb (131). 7 e
lh
Herbicides, by their very nature, are more toxic to herbicide 2,4-D hydrolyzes in water to 4-chlorophenol
aquatic plants than insecticides, but adverse effects do and 2,4-dichlorophenol, both of which impart dis-
not always occur where they might be expected. pleasing flavors and odors at low ppb levels. However,
Phytoplankton are sometimes unaffected by pesticides, the phenols are only rarely detected in natural waters
sometimes multiply when predators are removed by the (72). Decomposing aquatic plants that have been killed
chemicals, and sometimes are seriously inhibited in by herbicides are a major source of foul odors in aquatic
growth, depending on the particular conditions at hand. environments.

REMOVAL OF PESTICIDES FROM THE AQUATIC ENVIRONMENT

Obviously, no removal of pesticide residues from conventional treatment eliminated less than 10% of the
bodies of water would be needed if chemicals that are lindane and only 20% of the parathion in the water, but
rapidly degradable in the aquatic environment were the removed 55% of the dieldrin, 63% of the 2,4,5-T ester,
only ones being used, but such is not the case. Pesticides and 98% of the DDT (135).
that are relatively persistent pose a th@eat to water Much research effort has been expended on adsorb-
quality that has prompted investigations of methods for ents to purify the water beyond the levels attainable by
their removal, chiefly in connection with the protection conventional treatment. Activated carbon is clearly the
of drinking water supplies. Residues can be removed most effective adsorbent for pesticides, having a removal
directly from water bodies by such measures as dredging efficiency about 4 orders of magnitude greater than that
sediments and removing weeds, debris, and coarse fish. of soil, 3 orders greater than that of algae, and 2 orders
However, these methods are generally not economically greater than that of coal (100). The effectiveness of
feasible and the method that is generally followed for removal depends on the contact time, the concentration
nondrinking waters is to simply allow a period of time of activated carbon, the concentration of the pesticides,
for natural renovation to occur. and the presence of organic material in the water that
With public water supplies, available data indicate may compete with the pesticides for adsorption sites on
that present-day conventional water-treatment processes, the carbon. If the water is clarified by other processes
such as lime-alum coagulation, sedimentation, sand before the activated carbon is introduced, the competi-
filtration, chlorination, and pH adjustment, will reduce tive organic matter can be at least partially controlled
high pesticide levels substantially, but are inadequate for (121). Removal efficiency decreases at pesticide con-
removal of chronic contamination at low levels (39). The centrations below I ppb. Although it is possible to
degree of removal depends on the water solubility and remove lower concentrations of organochlorine insecti-
adsorptivity of the individual pesticides, with more cides, inordinately large amounts of carbon are required
efficient removal for compounds of low solubility or (39). At the I-ppb level, organochlorine insecticides in
high adsorptivity. In one series of tests, for example, drinking water account for only about 5% of the dietary

105

intake of these pesticides and would not pose a threat to exchange resins will remove high concentrations of such
human health, at least with respect to acute effects (94). pesticides as 2,4-D salts (3). Use of reverse osmosis
Other techniques for pesticide removal from water membranes has shown promise for removal of a wide
have been explored, with limited success. Chemical or variety of pesticides (40). Other effective processes may
biological oxidation will degrade some pesticides, but yet be developed that will take advantage of specific
toxic products are formed in many cases (39); ozone will characteristics of individual pesticides, one possible
attack even the stable organochlorine insecticides, but example being the introduction of microorganisms that
only at large and impractical concentrations and with are specific for rapid inactivation of certain classes of
unknown products (135); and strongly basic anion- chemicals.

PRACTICES FOR REDUCING ENTRY OF PESTICIDES
INTO THE AQUATIC ENVIRONMENT

A total of 15 pesticide management practices, desig- Table 10 contains citations of articles supporting
nated as P I through P IS, are presented in Volume I direct statements made in Volume I and of articles
(Table 18 and Section 4.4). These practices reduce containing closely related information that may be of
pesticide losses in runoff from treated fields by manipu- benefit in evaluating the individual practices. Informa-
lation of the chemical itself and are meant to supple- tion for both Volume I and this volume was obtained
ment the basic control of runoff and erosion carrying not only from the published papers cited, but also from
the pesticide, which is dealt with in other sections of discussions and meetings with agricultural and pesticide
Volume 1. The various aspects of the practices are specialists and from internal progress reports of the
discussed in Volume I without supportive documen- CRIS (Current-Research-in-Science) information re-
tation. Appropriate documentation for each of the trieval system of the U.S. Department of Agriculture and
practices is, however, presented in Table 10. the State agricultural experiment stations.

RESEARCH NEEDS

The length of this review constitutes first-hand evi- new and important area of research. The ideal model is
dence that much is already known about pesticides in one that is able to predict the consequences of any given
the aquatic environment, yet numerous important ave- practice or set of conditions; applying it, one can
nues for future research remain. Further efforts should, identify optimum modes of pesticide use with respect to
of course, be directed to minimization of those agricul- some particular attribute. However, a large amount of
tural practices that contribute to erosion and runoff work is required to construct useful models of the
from cropland and thereby produce excessive losses of typically complex agricultural systems. Moreover, data
applied chemicals, but our concern here is with aspects collection could be a limiting step; a complete model
of the system that deal with the pesticides directly. Such may demand such an elaborate input of hydrologic,
needs appear to fall into five general areas: (1) predic- chemical, biologic, and management data that collection
tion of pesticide behavior in the aquatic ecosystem; (2) of real-world numbers, including analyses, might take so
definition of significance of residues occurring in water long that events would outrun predictions.
bodies; (3) investigation of means for lowering rates and Despite these difficulties, development and refine-
frequency of application of pesticides, so that the ment of exploratory models is being actively pursued.
potential for contamination of waters would be lessened; With respect to pesticide movement in runoff, a model
(4) development of new pesticides having environ- has been developed with the objective of minimizing
mentally favorable properties; and (5) research on water pollution (1Z 53). It takes into account condi-
corrective measures to reduce or remove contamination tions both during and between runoff events, and has
by applied pesticides. No order of priority among these given satisfactory predictions for pesticides moved en-
is intended in the brief discussions that follow. tirely on sediment, but not yet for those moved in both
water and sediment. Models in related areas have also
Prediction of Pesticide Behavior been proposed. The movement of agricultural chemicals
through the soil profile has been described mathemati-
The development of mathematical models to predict cally, but existing models do not take into account the
the behavior of pesticides after application is a relatively ongoing natural soil-forming processes, so that their

106

7able 10. Bibliography on pesticide management practices (Volume 1, Section 4.4)

Pesticide management practice
Page No. Citations Significant subjects
No. in Description
Vol. 1.

Pi 85 Using Alternative Pesticides Craig et al (L2) Typical examples of alternative pesticides
effective against same posts in same crops

Bailey (LO) Discussion of pesticide properties pertinent
to movement in runoff

Spencer (144) Discussion of pesticide properties pertinent
to movement in runoff

Erbach and Lovely (64) Desirability of rotating equally effective
pesticides in succeeding years on same crop

P2 85 Optimizing Pesticide Caro et al (35) Comparative pesticide loss in runoff: in-furrow
Placement With Respect vs. broadcast applications
to Loss

Ritter et al (134) Comparative pesticide loss in runoff: ridge
planting vs. surface-contour planting

Apple Q) Comparative toxicity to crop seed of insecti-
cides when placed in seed furrow

Constien et al (@4) Necessity for placing insecticides in seed furrow
in no-till management

Moomaw and Robison Qj6) Satisfactory performance of herbicides placed
in narrow bands

Reid and Peacock (132) Subsurface sweep applicators

Erbach, Lovely, and High efficiency of precise spacing of herbicides
Bockhop(65)

Bode and Gebhardt (25) Advantage of disk over other implements in
incorporating pesticides to minimize loss
in runoff

Wax (159) Current trends toward broadcast application

P3 85 Using Crop Rotation Epstein and Grant (L3) Lower runoff loss of pesticides from rotation

Wax (159) Weed reduction by crop rotation

Stockdale, DeWitt, and Improved insect control by crop rotation
Ryan (t47)

Daniels (L5) Improved insect control by crop rotation

Fleming (69), p. 327 Typical examples of improved insect control
by crop rotation

Blakely, Coyle, and Steele Reduction in erosional losses by rotation
(L3), p. 305

Wade (155) Intercropping of corn and peanuts to reduce
attack by corn borers

107

Table 10. (continued)

Pesticide Management Practice
Page No. Citations Significant subjects
No. in Description
Vol. 1.

Kuhlman, Cooley, and Comparative acreage receiving insecticides:
Walt (103) continuous crop vs. rotations

Allaway (1), p. 391-2 Comparative weed control: continuous crop
vs. rotations

P4 86 Using Resistant Crop Sprague and Dahms (146) Review of crop resistance to insects and
Varieties reductions in use of insecticides

Chant (38), p. 204 Wheat varieties resistant to Hessian fly

Hoffman (93) Examples of resistant crop varieties and insects
resisted

P5 86 Optimizing Crop Planting Fleming (69), p. 328 Time of crop planting: summary of effects
Time on insect infestations

Craig et al (5 2), p. 48 Advantages of early plantings for combatting
European corn borer

Wellhausen (L64) Break in sorghum plantings to combat sorghum
midge

Wax et al Q 60) Advantages of late plantings of soybeans to
combat weeds

Burkhead et al (L8) Summary of planting dates of field crops
P6 86 Optimizing Pesticide Wax (159) Addition of surfactants to increase penetration
Formulation of herbicides; comparability of liquids and
granules

Foy and Bingham (LO) Surfactants or oils to enhance herbicide
penetration in plants

Mullison Q 19) Toxicity of components of formulations other
than active ingredient

Barnett et al (L6) Comparative runoff potential: 2, 4-D esters
vs. amine salt

Miles and Woehst Q 15) Controlled release formulations

Clack (42) Use of foam formulations for weed control

Depew (57) Superiority of granular formulations over
liquids in seed-furrow applications

P7 87 Using Mechanical Control Burnside and Colville (29) Superiority of tillage-herbicide combination
Methods for weed control
Wax (L59) Discussion of tillage and flame cultivation for
weed control

Whitaker, Heinemann, and Ability of cultivation to reduce erosive soil
Wischmeier (165) loss

Crafts and Robbins (5 1), Discussion of tillage methods in weed control
p. 140-154
Behrens (20) Disadvantages of cultivation and tillage

108

Table 10. (continued)

Pesticide management practice
Page No. Citations Significant subjects
No. in Description
Vol. 1.

P8 87 Eliminating Excessive Turnipseed et al (15-2) Effectiveness of lower than recommended rate
Treatment for insect control in soybeans

Chiang (4 1) Development of recommendations for deter-
mining threshold pest damage
Shore (143) Mathematical computation of optimum dosages
P9 87 Optimizing Time of Day for Wareetal(157) Higher efficiency of early morning spraying
Pesticide Application

Cooperative Exten. Serv., Timing of spray to avoid harm to honeybees
Illinois (47), p. 238
PIO 87 Optimizing Date of Pesticide Apple, Walgenbach, and Comparative effectiveness: planting-time vs.
Application Knee (8) cultivation-time treatments for corn
rootworm

Harrison and Press (86) Timing of sprays against corn borer

Anderson (1) Optimization of time of foliar application of
herbicides

Texas Agr. Exten. Serv. Recommendations for long-interval preplant
(149) applications of herbicides on cotton and
peanuts

Erbach and Lovely (64) Critical period for applying herbicides on corn
and soybeans

Summers, Byrne, and Advantages of early insecticide application
Pimentel (148) for alfalfa weevil control
I'll 88 Using Integrated Control Hanson (84) Aspects of integrated pest control programs
Programs
Council Environ. Qual. (49) Aspects of integrated pest control programs
Chant(38) Aspects of integrated pest control programs
Casey, Lacewell, and Example of reduction in insecticide use by
Sterling (L7) introduction of pest management strategy
Giese, Peart, and Huber (7 3) Reliability of computer-based pest manage-
ment systems
P12 88 Using Biological Control Knipling (101) Overview of biological control of insects
Methods

Quraishi (L29) Aspects of biological control of insects

Putnam and Duke (128) Example of biological control of weeds

Patti and Carrier (124) Example of usefulness of Bacillus thuringiensis
P13 88 Using Lower Pesticide Turnipseed et al Q 5 2) Examples of effectiveness of rates less than
Application Rates recommended levels

Casey, Lacewell, and Sterling Example of lower dosage in an integrated
(L7 control program

109

Table 10. (continued)

Pesticide Management Practice

Page No. Citations Significant subjects
No. in Description
Vol. 1.

Johnstone (96) Insecticide application in ultra-low-volume
sprays

P14 89 Managing Aerial Applications Wax (159) Advantages and disadvantages of aerial
application of herbicides

Marston et al Q 11) Pesticide in stream water from aerial spraying

Cole, Barry, and Frear (43) DDT in environment after aerial application

Glotfelty and Caro (74) Movement of airborne pesticides

P15 89 Planting Between Rows in Coop. Exten. Serv. Ohio (46) Practice recommended for reduction of corn
Minimum Tillage rootworm populations
iWay (161) Disadvantages of practice

ability to predict field behavior is limited (24). A the broadest opportunity for decreasing the potential for
relatively simple model has been developed (79) in environmental contamination by pesticides. One impor-
which the quantities of pesticide to be applied are tant facet that will require considerable future effort is
optimized with respect to profits to the grower. Refine- the development of large-scale integrated control pro-
ment of this model could well lead to reduced use of grams in which minimum amounts of chemical pesticides
pesticides and lessened environmental contamination. are used. Much more information is needed for inte-
grated control than is generally required to use pesticides
Significance of Residues alone. A successful program for insect control, for
example, requires knowledge of the dynamics of the pest
The true significance of pesticide residues in the population, life history of the pest, natural enemies,
environment is perhaps the least understood aspect of nutritional requirements, host plants, economic thres-
the system, particularly with regard to chronic contami- hold of the insect population, and behavior of chemicals
nation at very low concentrations. Changes in behavioral and organisms used in the program with respect to
patterns of aquatic organisms have been observed as a effects on nontarget environmental components (93,
result of chronic exposure, but little is truly known of 114). Each of these must be examined in detail and
possible long-term, subtle effects (118). To aid in interrelated and there are also researchable associated
assessment of the haiard, we need (1) in-depth studies of matters, such as the selection of the most suitable of
declining species; (2) studies of the gain, loss, or change alternative methods of control for incorporation into a
in residues in both living and nonliving components of program, the use of adverse natural phenomena to signal
the environment, to relate trends to observable effects; the appropriate time for attacking insects by integrated
and (3) toxicological measurements under conditions control, and the bringing of experimentally proven
that simulate the natural environment more closely than integrated control methods up to practical application
the conditions used in such tests in the past. (38,93).
Several approaches to more efficient application and
utilization of pesticides are being actively investigated,
Reducing Pesticide Use but require additional effort. One such is the develop-
ment and testing of foams, gels, and polymer-encapsu-
Research directed to reduction in use of pesticides by lated slow-release fon-nulations that can reduce drift,
more efficient application of the chemical or by substi- minimize movement of the pesticide in the environment,
tution of nonchemical methods of pest control offers and perhaps decrease the number of applications needed

110

because the chemical will be used more efficiently. A nification; would be biodegradable, but only after its
second is the use of electrostatically charged sprays to intended function is completed; and would be nontoxic,
decrease drift and optimize deposition of the chemicals but convertible to a toxicant in the presence of the pest
onto plant surfaces. Optimization of spray droplet (113).
particle sizes for efficient on-target deposition is also
being investigated. A third avenue under investigation is
the reduction of pesticide volatilization from plant and Corrective Measures
soil surfaces, and a fourth is the precision placement of
pesticides in the soil by devices such as subsurface sweep Research should be conducted on means for shorten-
applicators. Another aspect worthy of further study is ing the persistence of relatively stable compounds at the
the development of computer programs to predict site of application or in the aquatic environment by
occurrences of pest infestations. Such a program has deliberate manipulation of their modes of dissipation.
already been successful with potato late blight, saving Work of this type would be directed to such goals as
growers an average of 4 sprays annually in comparison enhancement of volatility and photodecomposition or
with the normal practice of spraying at 10-day intervals adjustment of adsorptivity and leachability, perhaps by
(102). use of adjuvants. Other possible corrective efforts could
involve the use of aquatic plants as traps to remove
Development of New Pesticides residues from water by absorption, addition of an
inoculurn of microorganisms to degrade the pesticides
Present pesticides, although effective, are far from after their biocidal activity is no longer needed, direct
perfect. Opportunity is still great to develop new chemical inactivation in soil by addition of a reactant,
chemicals that are highly specific for the pest, safe to use of additives to control the metabolic degradation of
man and wildlife, and have little effect on the quality of herbicides within plant tissues, and use of new adsorp-
the environment. The ideal compound would have low tive media or ion exchange resins to remove residues
solubility in fats to minimize the possibility of biomag- from water (70).

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119

CHAPTER 6

INTERDISCIPLINARY RESEARCH NEEDS

B. A. Stewart

Me preceding chapters have listed research needs proach, therefore, is to develop predictive models. A
relative to particular disciplines. This chapter briefly major effort should be directed toward obtaining neces-
discusses their interrelationships as they relate to non- sary data and developing such models. Results from such
point pollution from cropland. Nonpoint pollution can an effort cannot be expected to be precise but should
best be controlled by controlling erosion. However, represent a statistical approach that establishes relation-
knowledge is critically lacking concerning the degree of ships and relative levels.
erosion and sediment control necessary to control The Universal Soil Loss Equation predicts average
nutrient and pesticide losses. annual soil losses. Additional accuracy is needed to
The Universal Soil Loss Equation is being used predict single events. These can be important in their
extensively in predicting nonpoint pollution. At is an effect on water quality, especially if the time of loss is
excellent tool because it quantifies soil loss and the associated with applications of agricultural chemicals.
effect of various practices on reducing this loss. The Again, information is needed on large watershed areas. It
Universal Soil Loss Equation, however, estimates the is fairly easy to instrument a field-sized area and measure
average annual soil loss from a field area and does not losses of sediment and associated pollutants. The diffi-
indicate the amount of sediment that is delivered to a culty is in determining how much of these actually reach
stream. The sediment delivery ratio is an attempt to the stream. The effects and proper design of filter strips,
relate field losses to amounts reaching the stream. The settling basins, and sediment traps should also be
difficulty with this concept for predicting water P01111- determined. Some evidence indicates that these can very
tion is that it takes into account both the deposition of effectively reduce losses; however, there are also indica-
sediment as it moves toward the stream and the gains tions that this deposited material may be moved during
from channel erosion. Pollutants, particularly pesticides extreme runoff events.
and nutrients from added fertilizers, are usually not No-till and conservation tillage systems are highly
associated with sediment from channel erosion. effective for controlling soil loss. Additional research is
The enrichment ratio is a measure of the increase in needed, however, because it is not known how widely
the concentration of a pollutant associated with the these practices can be used. --,nsect and disease hazards
sediment that actually reaches a stream compared to the are greater, and if these practices are used on vast
concentration in the watershed soil. The concentration acreages, outbreaks could occur. Also, in some areas, it
usually increases because more nutrients and pesticides may be necessary to occasionally plow to loosen the soil.
are adsorbed on fine-textured particles than on coarse More data are also required concerning pesticide and
particles, and more coarse particles are deposited as the nutrient losses from no-till and conservation tillage
sediment moves from the field area to the stream. systems as compared to conventional systems. Sediment
Consequently, the most pressing research need is to gain losses are drastically reduced, but the meager data
a better understanding of how the Universal Soil Loss available do not show proportionate losses in pollutants.
Equation, the sediment delivery ratio, and the enrich- Another primary research need is to evaluate the
ment ratio can be meshed. These measurements and economic impact of control measures for controlling
evaluations will not be made easily, cheaply, or quickly. sediment and chemical losses. Available technology is
Data obtained from small plots or field area can provide adequate to control these pollutants in most instances.
only crude applications because the size effect is so Implementation of these measures could produce major
significant. Since cropland is so diffuse, monitoring of changes in cultivation practices, timing of chemical
agricultural areas is impractical. The most likely ap- applications, and location of production and general

121

farming practices. These changes would have direct disciplines and the first step in any of them is to
effects on the profitability of agricultural production, quantify the relationships.
supplies of food and fiber, and rural land use. An urgent Ust, and perhaps most important, criteria must be
need is to appraise alternative procedures for controlling established as to what levels of sediment and chemicals
pollutants so that economic hardships can be minimized. constitute pollution. The criteria might be absolute
Since our landscapes are not uniform and all areas are limits (not to exceed X ppm) or conditional limits (not
not equidistant from a water body, numerous combina- to exceed Y ppm in Z years). Although the establish-
tions of practices can achieve the same water-quality ment of these criteria will require research outside of
goal. The most desirable approach is to give each farmer traditional agricultural areas -limnology, aquatic botany
the opportunity to select the appropriate combination and zoology, and water treatment-it is of great impor-
of practices. To do this, he needs to know how much tance to the agricultural community. Without these
control each practice will provide. The costs and benefits criteria it is impossible to deterinine which practice will
of implementing the various practices should also be be adequate, much less decide what the economic
known. This should include regional and national im- impacts will be.
pacts. Thus, much research is needed in a variety of

122

APPENDIX A

SIMIULAT@ON OF DAILY POTEN71AL DIRECT RUNOFF

1,NTRODUCTION

The amount and seasonal distribution of direct runoff tion and computer time. The national scope of this
was estimated to assess potential transport of pesticides report and the severe time constraints involved dictated
and nutrients. The effects of some land management the use of a rather simple method of estimating runoff
practices on direct runoff were also estimated. Hydrol- from rainfall. Any input information required must also
ogists have developed several rainfall-runoff models of be readily available. After considering several possi-
various degrees of complexity for making these esti- bilities, we decided to use the Soil Conservation Service
mates. 7he more physically realistic models are quite procedure for estimating direct runoff from storm
complicated and require a great deal of input informa- rainfall (4).

THF, SOH- CONSF.RVA"T';ON SERVICE PROCEDURE FOR ESTIMATING DIRECT RUNOFF
FROM STORM RAINFALL

@.he Soil Conservation Service procedure for estimat- which is the rainfall-runoff relation used in the SCS
ing direct runoff from storm rainfall (sometimes called method.
the SCS curve number method) was designed to use the The parameter CN (runoff curve number of hydrol-
most generally available rainfall data: total daily rainfall. ogic soil-cover complex number) is defined in terms of
@-or this reason rainfall intensity is largely ignored. 7 e
@h the parameter S as:
basic relationship is the equation: CN = 1000 (4)
1 )2 S+10
Q -a > a (1)
,"?-I ) + S
k a Note that runoff equals rainfall when S = 0 and CN
100.
where The potential maximum retention, S , and therefore
Q runoff in inches the runoff curve number are related to soil surface and
P rainfall in inches profile properties, the vegetative cover, management
la= initial abstraction in inches practices, and the soil water content on the day of the
S = potential maximum retention plus initial storm. Solutions of equation (3) are shown as a family
abstraction. of curves in Fig. 1.
he initial abstraction before runoff begins is con- Soil water content on the day of the storm is
sidered to consist mainly of interception, infiltration and accounted for by an Antecedent Moisture Condition
surface storage. Utilizing limited data from small experi- (AMC) determined by the total rainfall in the 5-day
mental watersheds, the following empirical relationship period preceding the storm.
was developed: Three AMC groups have been established with the
= (0.2"S . (2) boundaries between groups dependent upon the time of
a f year as shown in Table 1.
Substituting this relationship into equation (1) gives The seasonal difference in the AMC groupings is an
attempt to account for the greater evapotranspiration
between storms during the growing season.
Q = (P-0.2S)2 > (0.2) S (3) The different infiltration characteristics of soils are
P+0.8S accounted for by classifying soils into four groups based

123

(P-0.2 S 2
Q = P= 0 to 12 inches
HYDROLOGY: SOLUTION OF RUNOFF EQUATION P+0.8 S Q=O to 8 inches
8 Ra' i _@__ : *.' I* _1 _. 1!
11 (p),
P> S?i +F;
RUNOFF (0): -With 10; a
7 +S@
a P-Ia-01
and F

0
Rote
t:

case 0.2s, so that
:Curves on this sheet are fo

(p-o.p S)2
F ""o ...
6 -0-
Time P+O.8 S
M
io
0 1 nfiltration- 7
LU
.1nit I
z 10
n
-'abstroctio zi
... curv

z 0
0' C@ . ... . .. ool. o17
7. : * I I I .. :. I :' . . I @ . :

0!::
7.

LL
LL
7,

0 4
001. ... . . .
z
D
@7
@4
rd-

LLj 3
01
00, : ' '
oof@

7--.7 77
10;0#@ @Oj . . .
2 .io

0
0 1 2 3 4 5 6 7 8 9 10 11 12
RAINFALL (P) IN INCHES
REFERENCE U. & DEPARTIUMTOF AGRICULTURE STANDARD DWG. NO,
Mockus, Victor; Estimating direct runoff amounts from storm rainfall: SOIL CONSMVATION SERVICE ES- 1001
SHEET I OF 2
Central Technical Unit, October 1955 9NGDMERING MVIMON HYDROWGY @NCH DATE 6-29-56
REVISED 10-1-64
tIh@e`. @0,

Figure I.-Solutions of Eq. 3. [From SCS National Engineering Handbook (4)]

Table % Seasonal rainfall @,Lmfts for antecedent
@ he interaction of hydrologic soil group (soil) and
moisture c3nditionsl land use and treatment (cover) is accounted for by
assigning a runoff curve number for average soil moisture
Total 5-day antecedent rainfall condition (AMC 11) to important soil cover complexes
AMC group Dormant season Growing season for the fallow period and the growing season. Rainfall-
runoff data for single soil cover complex watersheds and
in ch es inches plots were analyzed to provide a basis for making these
< 0.5 < 1.4 assignments. Average runoff curve numbers for several
soil-cover complexes are shown in Table 3. Average
11 0.5 -1.1 1.4-2.1 runoff curve numbers (AMC 11) are for the average soil
III > 1.1 > 2.1 moisture conditions. AMC : has the lowest runoff
potential. AMC III has the highest runoff potential.
From SCS National Engineering Handbook (4). Under this condition the watershed is practically satu-
rated from antecedent rains. Appropriate curve numbers
for AMC I and III based upon the curve number for
upon the minimum rate of infiltration obtained for a AMC 11 are shown in Table 4.
bare soil after prolonged wetting. T he influences of both Curve numbers for a "good hydrologic condition"
were used in the potential direct runoff simulations.
the surface and the profile of a soil are in@luded. The "Hydrologic condition" refers to the runoff potential of
hydrologic soil groups as defined by SCS soil scientists in a particular cropping practice. A row crop in good
the National Engineering Handbook are: hydrologic condition will have higher infiltration rates
A. (Low runoff potential". Soils having high infiltration and, consequently, less direct runoff than the same crop
rates even when thoroughly wetted and consisting in poor hydrologic condition. Good hydrologic condi-
chiefly of deep, well to excessively drained sands or tion seemed an appropriate description of corn under
gravels. These soils have a high rate of water transmis- modern management practices.
sion. Seasonal variation not accounted for by the seasonal
B. Soils having moderate infiltration rates when dependency of the AMC classes is included by varying
thoroughly wetted and consisting chiefly of moderately the average moisture condition curve number according
deep to deep, moderately well to well drained soils with to the stages of growth of a particular crop. For the
moderately fine to moderately coarse textures. These simulations reported here, with straight row corn as the
soils have a moderate rate of water transmission. index crop, the average (AMC 11) curve number was set
C. Soils having slow infiltration rates when thoroughly equal to that for fallow for the period from March 1
wetted and consisting chiefly of soils with a layer that until the average emergence date for corn. Emergence
impedes downward movement of water, or soils with dates were assumed to be 2 weeks after the average
moderately fine to fine texture. These soils have a slow planting date reported by the USDA (5). During the
rate of water transmission. growing season, AMC -11 curve numbers for each day
D. (High runoff potential". Soils having very slow were calculated by the following equation:
infiltration rates when thoroughly wetted and consisting
chiefly of clay soils with a high swelling potential, soils CNi = F - Ci (F - CNave) (5)
with a permanent high water table, soils with a claypan Cave
or clay layer at or near the surface, and shallow soils where
over nearly impervious material. These soils have a very CNi = the curve number for the ith day for AMC
slow rate of water transmission.
The SCS has classified over 9,000 soils in the United = fallow curve number.
States and Puerto Rico according to the above scheme. Ci = crop coefficient for the ith day. Cr@ 1.
A sample from the extensive table in the SCS National Cave = average crop coefficient for the growing
Engineering Handbook is shown in Table 2. Rainfall- season.
runoff data from small watersheds or infilt 'rometer plots CNavd= average growing season curve number for
were used to make the classifications where such data AMC 11.
were available, but most are based on the judgement of The crop coefficients Ci are defined as the ratio of
soil scientists and correlators who used physical prop- the crop evapotranspiration to potential evapotranspira-
erties of the soils in making the assignments. tion for a given day when soil water is not limiting. Crop

125

Table 2.-Soil names and hydrologic classifications I (Sample)

AABERG C AHL C ALMY BANLAUF C AROOSTOOK
AASTAD B AHLSTROM C ALOHA C ANNABELLA B AROSA C
ABAC O AHMEEK B ALONSO B ANNANDALE C ARP C
ABAJD C AHOLT D ALOVAR C ANNISTON B ARRINGTON a
ABBOTT 0 ANTANUM C ALPENA B ANOKA A ARRITOLA D
ABBOTT STOWN C AHWAHNEE C ALPHA C ANONES C A RROLIME C
ABCAL D AIBUNITO C ALPUN B ANSARI D ARRON D
ABEGG B AIKEN B/C ALPOWA B ANSEL B ARROW B
ASELA B AIKMAN D ALPS C ANSELMO A ARROWSMITH B
ADELL B AILEY a ALSEA B ANSON B ARROYO SECO B
ABRERDEEN D AINAKEA B ALSPAUGH C ANTELOPE SPRINGS C AR T A C
ABESS D AIRMONT C ALSTAD B ANTERO C ARTOIS C
ABILENE C AIROTSA B ALSTOWN B ANT FLAT C ARVADA D
ABINGTON 0 AIRPORT D ALIAMONT D ANTHO B ARVANA C
ABIQUA C AITS B ALTAVISTA C ANTHONY B ARVESON D
ABO B/C AJO C ALTOORF D ANTIGO B ARVILLA B
ABOR D AKAKA A ALTMAR B ANTILON B ARZELL C
ABRA C AKASKA 8 ALTO C ANTIOCH D ASA a
ABRAHAM B AKELA C ALTUGA C ANTLER C ASBURY B
ABSAOKEE C ALADDIN B ALTON B ANTOINE C ASALON B
ABSCOTA D ALAE A ALTUS B ANTROBUS B ASCHOFF B
ABSHER D ALALLUA B ALTVAN B ANTY B ASHBY C
ABSTED C ALAGA A ALUM B ANVIK A ASHCROFT B
ACACID C ALAKA1 D ALUSA 0 ANWAY A ASHDALE B
ACADEMY C ALAMA B ALVIN B ANZA A ASHE B
ACADIA D ALAMANCE B ALVIRA C ANZIANO C ASHKUM C
ACANA D ALAMO 0 ALVISO D APACHE D ASHLAR B
ACASCO D ALAMCSA C ALVOR C APAKUIE A ASHLEY A
ACEITUNAS B ALAPAHA D AMADUR 0 APISHAPA C ASH SPRINGS C
ACEL C ALAPAI A AMAGON D APISON A ASHTON A
ACKER D ALBAN B AMALU D APOPKA A ASHUE B
ACKMEN D ALBANG D AMANA B APPIAN C ASHUELOT C
ACME C ALBANY C AMARGOSA D APPLEGATE C ASHWOOD C
ACO B ALBATON D AMARILLO B APPLETON C ASKEW C
ACOLITA B ALBEE C AMASA B APPLING A ASD C
ACUMA L ALBEMARLE B AMBERSON APRON B ASOTIN C
ACOVE C ALBERTVILLE C AMBOY C APT C ASPEN B
ACREE C ALBIA C AMBRAW C APTAKISIC B ASPERMONT B
ACRELANE C ALBION B AMEDEE A ARABY ASSINNBOLNE B
ACTON B ALBRIGHTS C AMELIA B ARADA C ASSUMPTION A
ALUFF 6 ALLALUE C AMENIA B ARANSAS D ASTATULA A
ACWORTH B ALCESTER B AMERICUS A ARAPIEN C ASTOR A/D
ACY C ALCOA B AMES C ARAVE D ASTORIA B
ADA B ALCONA B AMESHA B ARAVETON B ATASC0ERO C
ADAIR D ALCOVA B AMHERST C ARBELA C ATASCSA D
ADAMS A ALDA C AMITY C ARBONE A ATCO B
ADAMSON A ALDAX 0 AMMON B ARBOR B ATENCIO B ADAMSTOWN ALDEN D AMOLE C ARBUCKLE B ATEPIC D
ADAMSVILLE C ALDER B AMOR B ARCATA A ATHELWOLD A ADATON 0 ALDERDALE C AMOS C ARCH B ATHENA
ADAVEN D ALDLRWOOD C AMSDEN B ARCHBAL A ATHENS B
ADIELOU C ALDINO C AMSTERDAM B ARCHER C ATHERLY B
ADDISON U ALUWELL C AMTOFT D ARCHIN C ATHERTON B/D
ADDY C ALEKNAGIK B AMY D ARCO B ATHMAR C
AUE A ALMEDA C ANACAPA B ARCOLA C ATHOL A
ADEL A ALEX 8 ANAHUAC D ARD C ATKINSON A
AGELAIDE D ALEXANDRIA C ANAMITE D ARDEN A ATLAS D
ADELANTU B ALEXIS C ANAPRA B ARDENVOIR B ATLEE C
ADELANTO B ALFORD B ANASAZI B ARLDILLA C ATMORE B/D
ADELPHIA C ALGANSEL B ANATONE D AREDALE A ATJKA C
AUENA C ALGERITA B ANAVERDE B ARENA C ATON B
ADGER D ALGIERS C/D ANAWALT D ARENALES A ATRYPA C
ADILIS A ALGOMA B/D ANCH B ARENDOTSVILLE B ATSION C
ADIRUNDACK ALHAMBRA A ANCHORAGE A AREN0SA A ATTERBERRY B
AUIV B ALICE A ANCHOR SAY D ARENZVILLE A ATTEWAN A
ADJUNTAS C ALICEL B ANCHOR POINT D ARGONAUT D ATTICA B
ADKINS a ALICIA B ANCLOTE D ARGUELLO B ATTLEBORO
ADLER C ALIOA B ANCU C ARGYLE A ATWATER A
ADOLPH D ALIKCHI A ANDERLY C ARIEL C ATWELL C/D
ADRIAN A/D ALINE A ANDERS C ARIZO A ATWOOD B
AENEAS B ALKO D ANDERSON A ARKABUTLA C AUBBEENAUBBEE B
AETNA B ALLAGASH B ANDES C ARKPORT A AUBERRY B
AFTON D ALLARD B ANDORINIA C ARLAND B AUBURN C/o
AGAR B ALLEGHENY B ANDOVER D ARLE B AUBURNDALE D
AGASSIZ D ALLEMANDS D ANDREEN D ARLING D AUDIAN A
AGATE D ALLEN B ANDREESON C ARLINGTON C AU GRES C
AGAWAM B ALLENDALE C ANDRES B ARLOVAL C AUGSBURG B
AGENCY C ALLENS PARK B ANDREWS C ARMAGH D AUGUSTA C
AGER D ALLENSVILLE C ANED 0 ARMIJO D AULD D
AGNER B ALLENTINE D ANETH A ARMINGTON D AURA A
AGNEW B/C ALLENWOOD A ANGELICA D ARNO B AURORA C
AGNUS B ALLESSIO A ANGELINA B/D ARMOUR B AUSTIN C
AGUA a ALLEY C ANGELO C ARMSTER C AUSTNELL D
AGUAUILLA A ALLIANCE B ANGIE C ARMSTRONG 0 AUXVASSE D AGUA DILOE C ALLIGATOR D ANGLE: A ARMUCHEE D AUZQUI B
AGUA FRIA B ALLIS D ANGLEN D ARNEGARD B AVA C
AGUALT B ALLISON C ANGOLA C ARNHART C AVALANCHE B
AGUEDA B ALLOUEZ C ANGOSTURA B ARNHEIM C AVALON D AGUILITA A ALLOWAY ANHALT D ARNO D AVERY B
AGUIRRE D ALMAL B ANIAK D ARNOLD A AVON C
AGUSTIN B ALMENA C ANITA D ARNDT C/D AVONBURG D
AHATONE D ALMONT D ANKENY A ARNY AVONDALE E
NOTES A BLANK HYDROLOGIC SOIL GROUP INDICATES THE SOIL GROUP HAS NOT BEEN DETERMINED
TWO SOIL GROUPS SUCH AS B/C INDICATES THE DRAINED/UNDRAINED SITUATION

From SCS National Engineering Handbook (4).

126

Table 3.-Runoff curve numbers for hydrologic soil-cover complexesi

(Antecedent moisture condition 11, and Ia 0.2 S)

Cover
Hydrologic soil group
Land use Treatment or practice Hydrologic condition A B C D

Fallow Straight row ---- 77 86 91 94

Row crops Poor 72 81 88 91
Good 67 78 85 89
Contoured Poor 70 79 84 88
Good 65 7S 82 86
and terraced Poor 66 74 80 82
11 11 Good 62 71 78 81

Small grain Straight row Poor 65 76 84 88
/I Good 63 75 83 87
Contoured Poor 63 74 82 85
Good 61 73 81 84
and terraced Poor 61 72 79 82
It It Good 59 70 78 81
Close-seeded legurnes2 Straight row Poo'r 66 77 85 89
or rotation meadow 11 11 Good 58 72 81 85
Contoured Poor 64 75 83 85
Good 55 69 78 83
and terraced Poor 63 73 80 83
Good 51 67 76 80

Pasture or range Poor 68 79 86 89
Fair 49 69 79 84
Good 39 61 74 80
Contoured Poor 47 67 81 88
Fair 25 59 75 83
Good 6 35 70 79

Meadow Good 30 58 71 78

Woods Poor 45 66 77 83
Fair 36 60 73 79
Good 25 55 70 77

Farmsteads ---- 59 74 82 86
Roads (dirt) 3 3 ---- 72 82 87 89
(hard surface) ---- 74 84 90 92
IFrom SCS National Engineering Handbook (4).
2Close-drilled or broadcast.
3Including right-of-way.

127

Table 4.-Curve numbers (CN) and constants for the case la = 0.2S]

1 2 3 4 5 2 3 4 5
CN for Curve2 CN for Curve 2
condi- CN for S starts condi- CN for S starts
tion conditions values 2 where tion conditions values 2 where
P = 11 1 111 P =

(inches) (inch es) (inches) (inches)
100 100 100 0 0 60 40 78 6.67 1.33
99 97 100 .101 .02 59 39 77 6.95 1.39
98 94 99 .204 .04 58 38 76 7.24 1.45
97 91 99 .309 .06 57 37 75 7.54 1.51
96 89 99 .417 .08 56 36 75 7.86 1.57
95 87 98 .526 .11 55 35 74 8.18 1.64
94 85 98 .638 .13 54 34 73 8.52 1.70
93 83 98 .753 .15 53 33 72 8.87 1.77
92 81 97 .870 .17 52 32 71 9.23 1.85
91 80 97 .989 .20 51 31 70 9.61 1.92
90 78 96 1.11 .22 50 31 70 10.0 2.00
89 76 96 1.24 .25 49 30 69 10.4 2.08
88 75 95 1.36 .27 48 29 68 10.8 2.16
87 73 95 1.49 .30 47 28 67 11.3 2.26
86 72 94 1.63 .33 46 27 66 11.7 2.34
85 70 94 1.76 .35 45 26 65 12.2 2.44
84 68 93 1.90 .38 44 25 64 12.7 2.54
83 67 93 2.05 .41 43 25 63 13.2 2.64
82 66 92 2.20 .44 42 24 62 13.8 2.76
81 64 92 2.34 .47 41 23 61 14.4 2.88
80 63 91 2.50 .50 40 22 60 15.0 3.00
79 62 91 2.66 .53 39 21 59 15.6 3.12
78 60 90 2.82 .56 38 21 58 16.3 3.26
77 59 89 2.99 .60 37 20 57 17.0 3.40
76 58 89 3.16 .63 36 19 56 17.8 3.56
75 57 88 3.33 .67 35 18 55 18.6 3.72
74 55 88 3.51 .70 34 18 54 19.4 3.88
73 54 87 3.70 .74 33 17 53 20.3 4.06
72 53 86 3.89 .78 32 16 52 21.2 4.24
71 52 86 4.08 .82 31 16 51 22.2 4.44
70 51 85 4.28 .86 30 15 50 23.3 4.66
69 50 84 4.49 .90
68 48 84 4.70 .94 25 12 43 30.0 6.00
67 47 83 4.92 .98 20 9 37 40.0 8.00
66 46 82 5.15 1.03 15 6 30 56.7 11.34
65 45 82 5,38 1.08 10 4 22 90.0 18.00
64 44 81 5.62 1.12 5 2 13 190.0 38.00
63 43 80 5.87 1.17 0 0 0 infinity infinity
62 42 79 6.13 1.23
61 41 78 6.39 1.28

1 From SCS National Engineering Handbook (iD.
2For CN in Column 1.

128

coefficient curves for corn were obtained by fitting a K = degree-day snowmelt factor (inches/day/OC)
Fourier Series to a curve presented by Kincaid and T = mean daffy temperature, OC
Heermann (2).
Curve numbers for antecedent moisture conditions I A degree-day snowmelt factor K = 0.18 in/day/'C
and III were obtained from Table 4. (0.10 in/day/OF) was used in all calculations. This is
At harvesting date or when CNi = CNave, whichever approximately the mid-range of the values quoted by
came first, the curve number was set equal to CNave and Linsley, Kohler and Paulhus, (0.06 - 0.15in/day/OF)(3).
remained a constant until the next March 1. The SCS The snowmelt calculated in this manner was used to
recommends that the after-harvest curve number be set estimate the antecedent moisture condition and the SCS
equal to the average growing season curve number if 1/3 curve number procedure was used to estimate snowmelt
of the soil surface is exposed. This simulation represents' runoff. The SCS National Engineering Handbook does
a situation where residues are left on the field after not recommend the use of curve numbers in estimating
harvest. runoff from snowmelt, because there is no way to
Any precipitation that occurred when the mean air account for frozen ground. SCS considers the entire
temperature was less than OOC was assumed to be snow snowmelt as computed by equation (6) to be runoff,
and was accumulated as snow storage until the temper- which is good practice when one is concerned with
ature went above OOC. Snowmelt was calculated by floods. Because this study was not concerned with
using a degree-day factor: floods, it was deemed more appropriate to use the curve
S = KT (6) number procedure to estimate snowmelt runoff despite
where its limitations. Obviously, the snowmelt runoff as
S = snowmelt in inches calculated may have significant errors.

129

SIMULATION PROCEDURE

Data Table 5- Meteorological records used in simulations

The daily precipitation data and temperature data
required for the simulations were obtained on magnetic Period of Missing Total
tape from the National Climatic Center, Environmental Location record years years
Data Service, NOAA, U. S. Dept. of Commerce, at
Asheville, N. C. The data set obtained is termed Day Wichita, KA 48-67 none 20
Deck 345. The normal period of record was from Columbia, MO 48-67 20
January 1948, through December 1973. A year begin- Dodge City, KA 48-67 20
ning on March I was used in all simulations. The stations Kansas City, MO 43-67 25
Springfield, MO 43-67 25
used are listed in Table 5. Chicago, IL 43-67 25
Simulations were performed only for stations cast of Cleveland, OH 48-67 20
the Rocky Mountains for the following reasons: Columbus, OH 48-67 20
Lansing, MI 49-5 3, 60-69 15
1. This report is intended to cover only nonirrigated Sault Ste. Marie, MI 47-66 20
cropland and much of the cropland in the West is Green Bay, WI 50-69 20
irrigated. Fargo, ND 48-67 20
2. Rainfall gradients tend to be very steep in the LaCrosse, WI 48-67 20
Des Moines, IA 46-70 25
West because of orographic effects. Therefore, interpola- Grand Island, NB 50-70 21
tion between widely separated meteorologic stations Huron, SD 43-67 25
Omaha, NB 48-67 20
would be misleading. Sioux Falls, SD 43-67 25
Bismark, ND 48-68 62 20
Computer Program Williston, ND 35-62 48,49,50 25
Scottsbluff, NB 48-67 none 20
The program SCSRO (Soil Conservation Service Rapid City, SD 49-68 11 20
Cairo, IL 30-67 48-53, 56-62 25
Runoff) was written in FORTRAN IV. A generalized Indianapolis, IN 48-67 none 20
flow chart is shown in Fig. 2. Lexington, KY 48-67 20
Springfield, IL 43-67 25
Savannah, GA 51-71 52 20
Assigning Hydrologic Soil Groups to Miami, FL 48-68 49 20
Land Resource Areas (LRAs) Houston, TX 48-68 49 20
Brownsville, TX 48-68 49 20
Raleigh/Durham, NC 48-68 49 20
Land Resource Areas (LRAs) are shown in the map in New Castle/Wilmington, 48-68 49 20
Fig. 2, Vol. I and are discussed in Section 3.1, Vol. 1. DE
Although Land Resource Areas are defined as geographic Charleston, SC 48-68 49 20
areas characterized by a particular pattern of soil type, Columbia, SC 48-68 49 20
Jacksonville, FL 48-68 49 20
topography, climate, water resources, land use and type Memphis, TN 48-68 49 20
of farming (1) they are large enough that each of these Mobile, AL 48-69 49,62 20
factors varies significantly within the area. Therefore, it Lake Charles, LA 48-58 49 10
Dallas, TX 48-68 49 20
is impossible to characterize an entire LRA by a single Little Rock, AR 48-68 49 20
soil series. In many cases, however, the major soil series Oklahoma City, OK 48-67 none 20
listed for a LRA have similar hydrologic characteristics Buffalo, NY 48-69 49,65 20
Newark, NJ 48-68 49 20
in that they fall into one hydrologic soil group. Where Boston, MA 48-68 49 20
there is a wide range of hydrologic characteristics within Portland, ME 48-68 49 20
a LRA the hydrologic soil group of the predominant Syracuse, NY 48-68 49 20
Wilkes-Barre/Scranton, 49-5 3, 5 6-71 50 20
agricultural soil was used. PA
The simulation results shown in Vol. I and in this El Paso, TX 48-68 49 20
Appendix should not be considered representative of the Amarillo, TX 48-68 49 20
Cape Hatteras, NC 57-69 58 12
entire LRA. However, they are representative of the Tallahassee, FL 48-68 49 20
predominant agricultural soils of the LRA, subject, of Pittsburgh, PA 48-68 49 20

130

Read
Field
Characteristics

@_GALL SUBROUTINE Subroutine CN computes
CN an average curve number for
each day of the year.

Subroutine TPRE&D reads in
CALL SUBROUTINE 1 year of daily precipita-
FLLTPREAD tion and temperature data.
LU

U_
C)
cc Subroutine SNOW determines
Uj
which daily values of precipi-
M CALL SNOW tation are snow, accumulates
a I it and converts it to snowmelt
C3
Uj on the appropriate days.
M
Cn
Uj
C3
Subroutine AMCF computes the
U_ r*----*1antecedent precipitation
index for each day.
W
0-
LU

Subroutine SRO computes daily
CALL SRO @-4F-w surface runoff using the SCS
curve number procedure.

Calculate rainfall
and runoff statistics@
for 14-day periods
seasons, and year.

Figure 2.--,Irogram SCSRO flowchart

131

course, to the limitations of the SCS runoff estimation (4). A list of the LRA's and the assigned hydrologic soil
procedure. Predominant agricultural soil series in each groups is presented in Table 6. These assignments were
LRA were obtained from Austin (1) and hydrologic reviewed and modified by personnel of the Technical
classifications for the soil series were obtained from Service Centers of SCS and their assistance is gratefully
Table 7.1 of the SCS National Engineering Handbook acknowledged.

Table 6.-Hydrologic soil group and available water holding Table 6-Hydrologic soil group and available water holding
capacities for predominant agricultural soils in land capacities for predominant agricultural soils in land
resource areas resource areas-Continued

Land Available water Land Dominant hydrologic Available water
resource Dominant hydrologic capacity in resource capacity in
area soil group 4-ft. root zone area Soil group 4-ft. root zone

(inches) (inches)
I Mountains 58 B *6
2 B 8 59 C 8
3 Mountains 60 D 4
4 Soil Information Lacking 61 B 8
5 Forest 62 Mountains
6 Mountains 63 D 4
7 B 8 64 B 8
8 B 8 - 65 A 2
9 C 8 66 B 8
10 C 8 67 B 8
11 B 8 68 B 8
12 Mountains 69 B 8
13 B 8 70 C 6
14 B 8 71 B 8
15 D 6 72 B 8
16 D 6 73 B 8
17 D 6 74 B 8
18 D 6 75 B 8
19 D 6 76 D *4
20 Mountains 77 C 8
21 D 6 78 C 8
22 Mountains 79 A 4
23 Soil Information Lacking 80 C 8
24 81 D 6
25 D 6 82 C 8
26 D 6 83 D 6
27 D 6 84 B 8
28 Desert 85 D 6
29 86 D 6
30 87 D 6
31 Irrigated Desert 88 Forest
32 B 8 89 Forest
33 Mountain 90 13 8
34 B 8 91 A 2
35 B 8 92 Forest
36 C 6 93 Forest
37 B 8 94 Forest
38 Mountain 95 B 8
39 96 A 2
40 Soil Information Lacking 97 B 4
41 98 B 8
42 B 8 99 D 6
43-51 Mountains too B 8
52 B 8 101 B 8
53 B 8 102 B 8
54 B *6 103 B 8
55 B 8 104 C 8
56 D 4 105 B 8
57 B 8 106 B 8

132

Table 6-Hydrologic soil group and available water holding
capacities for predominant agricultural soils in land
resource areas-Continued

Land Available water
resource Dominant hydrologic capacity in
area soil group 4-ft. root zone

(inches)
107 B 8
108 B 8
109 C *6
110 C *6
III C 8
112 D *4
113 D *4
114 D 4
115 B 8
116 C *4
117 Mountains
118 D 6
119 Mountains
120 C *4
121 C 8
122 B 8
123 C 8
124 C 8
125 Mountains
126 C 8
127 Mountah,s
128 B 8
129 B 8
130 Mountains
131 D 6
132 D 6
133 B 8
134 C 8
135 D 6
136 B 8
137 A 4
138 B 4-
139 C *4
140 C 8
141 C 8
142 D 6
143 Mountains
144 A 4
145 B 8
146 C 8
147 B 8
148 C 8
149 C 8
150 D 6
isi Swamp
152 D 6
153 C 6
154 A 4
155 B 8
156 Swamp

*Available water-holding capacity reduced because root
zone is shallower than 4 feet.

133

SIMULATION RESULTS

Program SCSRO output for each 14-day period for 4. The mean growing season simulated runoff.
the n years of record may include: Maps of the mean annual and seasonal simulated
1. A listing of rainfall amounts ordered by magni- runoff (potential direct runoff) are shown for each
tude. hydrologic soil group in Figs. 3 through 10. Because of
2. A listing of simulated runoff ordered by magni- the relatively small area of soils classified in hydrologic
tude. group A, simulations with this group were not per-
3. The mean and standard deviation of rainfall and formed for all rainfall stations. The growing season was
runoff events. taken as the time interval between emergence and
The statistical summary for the n-year simulation harvest and varied with location. These maps can be used
included: to supplement the information presented in Figs. 3 and
1. A table showing the number of runoff events for 4 in Vol. 1.
each 14-day period for each year. Too few rainfall stations were used in this analysis to
2. The probability that there would be no runoff depict climatic and orographic influences in the Appa-
events in any year for each 14-day period. lachian Mountains; therefore, care must be used in
3. The mean annual simulated runoff. interpreting the maps in these regions.

134

@30 6 1

.48
09
.64

@N (va
-38 1.00 k-
.14

3 9-@, 2*42\\ 2. 8
ILI
2
13.0
4.0

5.0
6. ?

Figure 3.-Mean annual potential direct runoff in inches. Straight-row corn in good hydrologic condition -Hydrologic Soil Group A.

0
0
Cli

- - - - -- 3.0
3.0

-4

7.0

0 C! 9.0
11.0 //.0
C@

Figure 4.-Mean annual potential direct runoff in incbes. Straigbt-row corn in good bydrologic condition -Hydrologic Soil Group B.

0
L6

5.0
5.0

v r,

9.0

q TA 13.0
C@

C! 0.
to \0

Figure 5.-M-ean annual potential direct runoff in inches. Straight-row corn in good hydrologic condition -Hydrologic Soil Group C.

9.0

(3.0
rI

/,3.0

Figure 6.-Mean annual potential direct runoff in inches. Straight-row com in good hydrologic condition -Hydrologic Soil Group D.

15 2

v -r->

.3
/__@ I .88
Z 2.0
.58
1.52.
21 10 2.0
1 2.0
2.46 _- -'2-.-54 -2. 6

2.94

Figure 7. -Mean growing season potential direct runoff in inches. Straight-row com in good hydrologic condition-Hydrologic Soil Group A.

1.0

ell
_A.
r

5.0
5.0

0
C@

Figure 8.-Mean growing season potential direct runoff in inches. Straight-row corn in good hydrologic condition -Hydrologic Soil Group B.

2.0
2.0
-6.0

5.0
_IY

-T.0

Figure 9.-Mean growing season potential direct runoff in inches. Straight-row com in good hydrologic condition-Hydrologic Soil Group C.

3.0

17--

(3.0
9.0

0
rti

Figure 10.-Mean growing season potential direct runoff in inches. Straight-row com in good hydrologic condition-Hydrologic Soil Group D.

CONSISTENCY CHECK AND DISCUSSION OF ERRORS

1he accuracy of the simulated runoff amounts was where
checked by comparing average annual potential direct Qs = simulated average annual direct runoff.
runoff with measured average annual runoff from several
small, single-crop watersheds in straight-row crops (pri- Q0 = observed average annual runoff.
marily corn and cotton) (7, 8). The watersheds used in The coefficient of variation (r 2) was 0.616. A scatter
this comparison and a brief data summary are presented diagram of computed versus observed average annual
in Table 7. The following linear regression equation was runoff is shown in Fig. 11. The vertical lines emanating
obtained: from the plotted points indicate the range in simulated
runoff that would occur if the soils were assumed to
Qs = 1.365 + 0.578 Qo (7) belong to adjacent hydrologic soil groups. This indicates

7able 7-Surface runoff consistency check

Watershed Area Crop Hydrologic Mean annual runoff (in.)
soil group Observed Simulated

acres@
College Park, MD W-3 6.06 Soybeans B 2.47 2.60
Sweet corn
Americus, GA W-1 17.9 Corn B 1.27 7.17
Cotton
Lafayette, IN W-4 2.01 Corn B 2.26 2.60
Soybeans
W-5 2.87 Corn 84% B 4.14 3.05
Soybeans 16% C
W-8 1.96 Corn B 4.89 2.60
Soybeans
W-10 2.06 Corn 66% B 5.88 3.57
Soybeans 34% C
W-12 3.37 Corn 89% B 3.98 2.91
Soybeans 11% C
W-13 3.02 Corn 80% B 3.93 3.17
Soybeans 20% C
W-15 3.59 Corn B 4.33 2.60
Soybeans
Clarinda, IA W-V 3.25 Corn 90% B 1.41 2.32
10% D
W-W 1.97 Corn 90% B 3.37 2.32
10% D
W-Y 3.25 Corn 727o B 1.06 2.89
28% D
Coshocton, OH W-115 1.61 Coin C 2.85 3.05
W-110 1.27 Corn C 2.41 3.05
W-118 1.96 Corn C 1.97 3.05
W-192 7.59 Coin C 3.13 3.05
W-106 1.56 Coin C 3.23 3.05
Guthrie, OK W-2 3.21 Cotton B 7.67 2.30
Garland TX W-Ill 10.4 Cotton D 11.67 8.30
Corn
Spur, TX W-2 9.39 Cotton 50% B 2.70 2.05
50% C
Riesel, TX Y-7 40.0 Row crops D 7.00 8.75
Hastings, NB 3-H 3.95 Corn B 4.85 1.65
Oxford. MS WC-1 3.88 Corn C 14.99 11.00
WC-3 1.61 Corn C 13.77 11.00
Chickasha, OK C-1 17.8 Corn 817o C 1.24 3.32
19% B

143

Qs Simulated Mean Annual Direct Surface F
0 N Uj -IS CD 0) --j Gow 0
0

0--
0

o
a- AQ for Change in
Cn s
CD Hydrologic Soil
CD (D Group
CL

F- (D
0
D 0
G

>
0)
0 CD

C
00
D

CD
Cn

CD
CD (n

0
(D 0

0
=r
CD

the inherent limitation in the SCS method caused by correlated with the average annual strearnflow from-the
lumping all soils into four distinct groups. Horizontal USGS maps.
bars emanating from plotted points indicate estimated The following regression equation was obtained be-
standard errors of the mean of observed data. This tween simulated direct runoff plus percolation and
illustrates the problem of short, fragmented records. The runoff 'Streamflow) from the USGS map for 45 of the
SCS method tended to underestimate runoff of more 52 meteorological stations used:
than 3 inches.
Meaningful comparisons are difficult because the (Qs + Qp) = 0.409 + 0.979 QG ; r' = 0.884 (9@
observations were made over such a long time. Agricul- where Q is the simulated average annual deep percola-
tural practices have changed drastically so the data are p
not stationary. For example, hybrid corn and higher tion. Seven stations in the karst area of Florida and in
fertility levels have led to rapid canopy establishment the coastal area of the Southeastern United States were
and more residues after harvest. The simulated condition omitted because anomalies on the USGS map indicate
after harvest-approximately 67% cover by residues- that much of the groundwater runoff flows directly into
probably is not consistent with the practices on water- the ocean. These crude checks indicate that the simula-
sheds where the data were obtained. One would antici- tions provide reasonable estimates of annual direct
pate that the simulated runoff would be less than the runoff and percolation,
observed in this case. Data from some of the watersheds Records of runoff from continuous straight-row corn
listed in 7 ble 7 were undoubtedly used in developing were not readily available for periods shorter than one
.a month so it was not possible to check the accuracy of
the SCS curve number procedure so this is not an the time distribution of simulated potential direct runoff
independent test of its predictive capabilities. within the year. However, 20 years of runoff data were
Although the relationship between simulated and available for a small watershed in meadow at Coshocton,
observed direct runoff shown in Fig. I I is not as good as Ohio. Direct runoff for 14-day periods simulated by the
one would wish, it must be compared with the available
alternatives before one can judge its usefulness. One SCS procedure was compared with observed data.
alternate that has been suggested is to use the map of Simulated and observed mean runoff per event, mean
surface-water runoff prepared by the U.S. Geological number of runoff events per period, and mean runoff
Survey (6) as an indicator of potential loss by direct amount per period are shown in Fig. 12. The standard
runoff. To test this method, consider the following deviation of the observed runoff per period is indicated
regression relationship between the average annual run- by a vertical line for each period.
off from the USGS map for the locations in Table 7 and The simulated runoff per period is within one
the observed average annual direct runoff: standard deviation of the observed runoff for 14 of the
26 periods. Assuming that the mean value is normally
QG = 6.74 + 0.503 Qo ; r2 = 0.138 t8) distributed for each period and that the 26 periods are
independent trials, the null hypothesis cannot be re-
jected at the 10 percent level.
where QG is average annual surface-water runoff from Sample distribution functions of runoff amount per
the USGS map. event for two periods are shown in Fig. 13. A Kolmo-
The simulated results obviously are superior to those gorov-Smirnov test comparing the distribution functions
obtained from the runoff map as indicators of potential indicates that the null hypothesis cannot be rejected at
direct runoff. the 10 percent level for both periods.
One would anticipate that the sum of the simulated Although it is impossible to make strong inferences
average annual direct runoff and the average annual deep on the basis of the limited tests performed, the SCS
percolation estimated by the procedures described in method appears adequate for arriving at a first estima-
Appendix 3 of this volume should be rather well tion of direct surface runoff.

145

Mean Number Events
1.2-

0'8-
E fik
z 0.4-

I I I I I- A I I I I I I'V I I
0 T
Mean Runoff per Event
0.35

0.30 Observed
0.25 - ---Simulated

0.20 -

0.15 -
cn 0.10-
0.05 -

0 0-35-
Mean Runoff per Period
0.30 -
1

0.25 -

0
0.20 -

0.15
0.10 - 4L
0.05

0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
MAR MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC JAN JAN
1 26 25 23 20 [a 15 12 10 7 5 2 30
Period

Figure 12-Comparison of simulated and observed runoff records by 14-day periods. Coshocton, Ohio meadow.
Ak

, j"'If

146

-X 1. 0

U-
0.9

0
0.8 -

C:
73 0.7 -
LL
.c 0.6 - x
Coshocton Ohio, Meadow
4 0.5
0.4 0 Observed
Ln
0 x Simulated
0.3 Period 1, Mar 1-14
0.2 Period It , July 18 - Aug 2
0

:3
E 0 .I

0
0 0.2 0.4 0.6 0.8 1.0 1. 2 1.4 1.6 1.8 2.0
x Runoff, inches

Fig-are 13-Sample distribution functions for simulated and obserived records. Coshocton, Ohio meadow.

LITERATURE CITED

1. Austin, M. E. 1965. Land resource regions and major 6. U. S. Geological Survey. 1970. The National Atlas of
land resource areas of the United States. SCS USDA the United States of America. 417 p.
Agriculture Handbook No. 296, 82 p.
2. Kincaid, D. C. and Heermann, D. F. 1974. Scheduling 7. U. S. Dept. of Agriculture. Hydrologic Data for
irrigations using a programmable calculator. ARS Agricultural Watersheds in the United States. USDA
NC- 12. 55 p. Misc. Publications No. 945 (1956-59); 994(60-61);
3. Linsley, R. K., Jr., Kohler, M. A. and Paulhus, .J. L. 1070(1962); 1164(1963); 1194(1964); 1216(1965);
H. 1958. Hydrology for Engineers. McGraw-Hill, N. 1226(1966); 1262(1967).
Y.
8. U.S. Dept. of Agriculture. 1957. Monthly precipita-
4. Soil Conservation Service, USDA. 1971. SCS Na- tion and runoff for small agricultural watersheds in the
tional Engineering Handbook, Section 4, Hydrology. United States. USDA ARS, Soil and Water Conservation
U.S. Govt. Printing Off., Washington, D.C. Research Branch, Washington, D.C. (June).

5. USDA Statistical Reporting Service. 1972. Usual
planting and harvesting dates. Agr. Handbook No.
283.

148

APPENDIX B

SIMULATION OF POTENTIAL PERCOLATION AND NITRATE LEACHING

INTRODUCTION

Potential percolation was defined in Section 3.4, Soluble agricultural chemicals that are not strongly
Volume 1, as the annual amount of water that would adsorbed by the soil may be carried below the root zone
percolate below the root zone in a field of straight-row by percolating water. After the percolating water has
corn. reached the ground water table, it will move laterally
The relationship between potential percolation and and eventually reappear in a stream, lake or possibly the
other hydrologic variables can be expressed by the ocean. Some ground water may also flow into the root
vertical water balance equation for a column of soil as zone in seepage areas and be transpired by vegetation.
Because precipitation can be considered as a stochas-
P = Qs+E+Q +AS tic process, all of the other variables in Eq. (1) are
p stochastic in nature. A simulation approach is necessary
to estimate each of the other terms because of the rather
where P is the precipitation, Q. is the direct runoff, E is complex relationships between them. To carry out the
the evapotranspiration, Qp is the percolation from the simulation we need a soil water model, a direct runoff
bottom of the root zone and nS is the change in soil model and an evapotranspiration model. The SCS
water storage in the root zone during the time under procedure as described in Appendix A was used as the
consideration. in Eq. (1), it is assumed that imported direct runoff model. The soil-water model and the
water, lateral porous media flow, and change in surface evapotranspiration model are described in this Appen-
detention storage are negligible. dix.

THE SO! L-WATER MODEL

The soil-water model described in this section utilizes surface layer is d I and d2(t) is the time varying depth of
the approximation that soil-water moves readily under the root zone. The extraction of water from different
gravitational forces when its water content is above field depth zones varies with stage of crop development, so
capacity. It is further assumed that water does not move the capacities of compartments 2 and 3 vary with time
downward when the water content is below field as the crop canopy expands but their sum is a constant.
capacity and that when the water content reaches the The maximum capacities of the compartments can be
wilting point it is no longer available to plants. interpreted as the available water-holding capacity per
The structure of the three-compartment soil-water unit area for the depths dl, d2(t)-dl and d3-d2(t)-
model used is shown in Fig. 1. The water content of Input to the system is XI(t), which is the difference
compartment i is designated as Si(t) and the maximum between daily rainfall plus snowmelt and direct runoff.
capacity of the ith compartment is Ki, which corre- System Output is Y I (t), Y2(t) and Y3(t) where
sponds to field capacity. Compartments I and 2 repre-
sent the active root zone and compartment 3 represents Y, (t) = daily evaporation from the soil surface
the water storage below the current root zone and above Y2 (t) = daily transpiration
the maximum depth of rooting, d3. The depth of the Y3 (t) = daily seepage below the maximum root zone

149

The evaporation and transpiration model will be
described in the next section, The rules for movement of
water between compartments are as follows:
S1(t+') = S, (t) + X, (t+1) - Y1(t+1) -y4(t+)- Y12(t+1)
Y12(t+1) = 0 IfS1 (t) + XI(t+)-Yl(t+1) _Y4(t+1) < K, (2
YI 2 (t+') = Si (t) + X1(t)- Yi (t+1) -Y4(t+1) - K, ; otherwise
where Y12(t+1) is the flow from compartment I to com- transpiration and flow to compartment 2. Flow from
partment 2. compartment I to compartment 2 exists only if the
Equation (2) states that the water content of com- available waterholding capacity of compartment I is
partment I in period t+I is equal to the water content in exceeded. No provision is made for upward flow in this
period t plus the infiltration on day t+I less evaporation, model, although such flow is physically possible.

S 2(t+1) = S2(t) + Y1 2(t+l)-y5(t+) Y23 (1+l)

Y23(t+1)=S2(t)+YI2(t+1)-Y5(t+1)-5 K2 (3)

Y23(t+1)=S3(t)+yl2(t+1) - Y5 (t+ 1) - K2 ; otherwise.

S3(t+1)=S3(t)+y23(t+l)-y3(t)

Y3(t)=OifS3(t)+y23(t+l)K 3 (4)

Y 3 (t) = S3 (t) + Y2 23 (t+1) - K3; otherwise.

Flow relationships for compartments 2 and 3 are where 0 is the volumetric available water holding capac-
similar to those for compartment I except that there is ity defined as the difference between field capacity and
no evaporative loss from compartments 2 and 3 and no wilting point, and tj and t2 are the emergence date and
transpiration loss from compartment 3. full canopy date, respectively.
A schematic drawing of the seasonal variation in the - K2 (t+ 1) + K2 (t) (6)
root zone is shown in Fig. 2. The depth of the soil layer K3 (t+ 1) K 3 (t)
from which evaporation can occur, d 1, is assumed to be
constant throughout the year. The total depth of the S S, (t) +[K2 (t+ I)-K2 (01 S3 (t) (7)
zone from which evaporation and transpiration losses 2 (t+ 1) K3 (t)
occur remains at dl throughout the dormant period,
then is approximated by a linear expansion beginning at S 3 (t+ 1 S 3 (t) - S2 (t+ 1 ) + S2 (t) (8)
the plant emergence date tI, and reaches its full
extension' to d3 when the crop canopy factor has The capacity of compartment 2 increases in propor-
reached its maximum at time t2. The zone depth then tion to the increased rooting depth and the water
remains constant until harvest, t3, when it instantane- content is increased by the amount of water in the
ously goes back to d I. The assumption is made for this incremental depth. The capacity and water content of
simulation that there is no weed growth or winter cover the third compartment are decreased by equivalent
crop withdrawing moisture from harvest until spring amounts.
plowing date. While the root zone is expanding, the The soil-water model is similar in many respects to

capacities and contents of compartments 2 and 3, K2(0, some of the simple models that have been used in
K3(t), S2(t) and S72P) are changing each day according irrigation and hydrology for many years (11, 13, 2 7).
to the following equations: This model obviously preserves mass continuity as
d3-di expressed by Eq. (1). It does not incorporate relation-
t2_-t1 (5) ships between potential gradients, hydraulic conductiv-
K2 (t+1)K 2 (t)+ ity and water flux in porous media, using instead the

150

Transpiration Evaporation I nfiltration

Y2(t) YJ (t) XI(t)

I SIM K, d, F-1
Y4 (t)

d2(0

Y5 (t) 2 S20) K2(t) d

Y?_

S5(t K5(t)

Y3 (t)

Percolation

Figure l.-Soil-water model schematic.

crude concept of "field capacity." The approximations Substantial errors may occur where water tables are
and assumptions included in the model probably would shallow or in soils with shallow, relatively impermeable
not lead to serious errors in deep, well-drained soils. layers.

THE EVAPOTRANSPi RATION MODEL

e evapotranspiration IET) model is based on the The model can be described by the following equa-
h k
frequently used assumption that ET will take place at tions:
the "potential" rate if the soil has adequate water and a Evaporation:
complete crop canopy or if the surface is wet. Actual
evapotranspiration rates will be less than potential as the Yj (t) I-C(t)] KP P(t) S I (t) (9)
soil dries. K,

151

0
Q

CL 0

C:
0

E 0
LU U_

dp7d,

d3- 2

tj t2 t3

Time

Figure 2.-Seasonal variation of root zone.

where C(t) is a time varying crop coefficient related to S, (t)
the portion of the soil surface covered by vegetation, K p Y 4 (t) = Y2 (t) [K I + K2 (t+ 1)]
is a coefficient to convert pan evaporation to potential
ET, P(t) is the pan evaporation in inches per day and and the transpiration loss from compartment 2 is:
SI(t) and KI have been previously defined. Ys (t) = Y2 (t) - Y4 (t) (12)
Total transpiration is given by:
Y2 (t) = C (t) Kp P(t) f (10) An examination of Eqs. (9) through (12) reveals that
for bare fallow conditions, [C (t) = 01 only evaporation
where f is the ratio of actual to potential evapotranspira- occurs, i.e., Y2(t) = 0. For full canopy conditions C(t) =
tion and depends on the water content of compartments I,YI(t) = 0 and all loss is through transpiration. The
I and 2 as shown in Fig. 3. form of this evapotranspiration model is identical to that
The transpiration loss from compartment I is: used by Hanson (5).

NITRATE LEACHING MODEL
@
d27 d I

3
d2

The purpose of this model is to gain a quantitative extension in the following crop year. Any nitrogen
insight into what percentage of nitrogen applied as present in the profile at the time of fertilization is
ammonium in the fall or spring would move below the ignored as are denitrification losses. It is also assumed
root zone before the roots had reached their full that there is no nutrient uptake by weeds or winter

152

0
0 0.6 1.0
Is, (f) + S? (o] K, (0+ K,(O]
Figure 3. -Relationship between actual and potential evapotranspiration and root zone water content.

cover crops. Water flow through the soil during the Y12(0 is nonzero, a new increment is introduced,
dormant period is assumed to be piston flow. 7.7he upper pushing all those ahead of it down a distancenZ.
compartment with capacity K, was retained in the soil A number of studies (9, 12, 28) have shown that
model. At the time ammonium was applied in the fall, anions, like nitrate, move with the wetting front through
the water in compartments 2 and 3 was assumed to be dry soil. 7he depth to the peak concentration can often
uniformly distributed in the depth d3 - dj. Any time the be estimated by the ratio of infiltration to field capacity.
capacity of compartment I is exceeded, the volume of Laboratory leaching studies (21, 22) with water contents
water y, 2 (t) moves as a piston flow, displacing some of near saturation show that these anions are excluded
the soil water ahead of it as shown in Fig. A. from some of the soil water and thus move faster than
The depth increment of the ith output from compart- the total soil water does. 'pinions differ as to the
ment I to the lower zones is given by the expression '@j
importance of this factor for field conditions. Some
Z (13) consider it important (23"y, others do not (1). We have
i = YI 2 OMOF - E) chosen to incorporate an exclusion factor because a large
where E is an exclusion factor to account for the part of the nitrate movement being modeled will occur
fraction of the soil water not containing nitrate and OFis at moisture contents above field capacity and it will also
the volumetric field capacity (21, 22). E as used in these reflect some of the channelized flow in clay soils (8).
calculations is the ratio of the volume of soil water When ammonium fertilizer is applied, it is assumed to
excluding nitrate to the total soil volume. Each time be concentrated at depth, dj. Ammonium is converted

153

Y1 (t)

SI(t) di
Z (2) Z (1)
N y 12 Z
N 21F
AZ
12
.............. ...... ......................... .

d3
E (d3 - dd

Figure 4.-Piston flow soil water model.

to the nitrate according to the following temperature- by Van Wijk et al (26) this appears to be a reasonable
dependent relation after a lag of 5 days: approximation.
Nitrate -nitrogen accumulates in the upper compart-
N(t+l) = N(t) + k(T) A(t) (14) ment until the available water storage capacity is
exceeded by infiltration during a rainy day, then all of
where N(t) is the nitrogen in the nitrate form on day (t), the nitrate -nitrogen is apportioned to the appropriate
A(t) is the nitrogen in the ammonium form on day (t), element AZ. To each AZi there is an associated weight of
and k(T) is a temperature-dependent rate function given nitrate N, wi. As shown in the right hand side of Fig. 5,
by the following equations (4, 19): the depths, Zi, of each front and the weight of N, wi,
carried by each LZ increment are recorded and changed
K = 0.0032T -.012 ; IOOC <. T < 350C as each recharge event occurs. When the root zone
reaches its maximum depth in the following crop year,
K = 0.00105T + 0.000095T 2 ; 00 C < T < 10' C (15) all of the wi below the depth d3 are summed up to give
the nitrate leaching loss from fall fertilization. The
K=O ; T<00 nitrate loss from spring fertilization is obtained by
recording the amount of ammonium nitrogen remaining
where T is the soil temperature in "C. Soil temperature at the time of spring fertilization, and the number NR of
was approximated by a 5-day moving average of mean recharge events that have occurred since fall fertilization
daily air temperature. According to the data presented (in Fig. 5 the value would be 4). On the date of full root

154

0
C
0 0 0
0 C:
N .2
0
0 0
C
a
0 in
0) C) LL

OL D 0
U) LLJ LL LL

7-
W4 W2 W4
............. d?(f) Z2
....... WFA WP-
d5
W4
.................
W2 . ..................
---@W2
MW2 - W4 W4

2
77@1-1-

Time
March I

Figure S.-Nitrate leaching model operation in time.
...........
..........
W13L
W_ W4;7@

zone extension, all wi from NR-I that are below the root fertilization was not below the root zone. In the piston
zone are summed and divided by the ammonium flow model for water movement and nitrate leaching it is
nitrogen present at spring fertilizations to give the assumed that the nitrate is completely mixed within
percentage loss. Note that for the case portrayed in Fig. each element AZ, but that there is no diffusion or
5, no nitrate would be lost from spring fertilization dispersion allowing nitrate exchange between elements.
because the first increment of recharge after spring

SIMULATION PROCEDURE

Data capacities, and exclusion fractions most commonly used
in the simulations are shown in Table 1.
Daily precipitation and temperature data used in the
simulations were obtained - on magnetic tape from the Table I.-Most commonly use
National Climatic Center, Environmental Data Service, d soil-water model parameters
NOAA, U.S. Dept. of Commerce, Asheville, N. C. The Hydrologic soil grOLIP
data set obtained is termed Day Deck 345. The normal Parameter -A B C D
period of record was from January 1948 through
December 1973. A year beginning on March I was used d...... 4 in. 4 in. 4 in. 4 in.
in all simulations. The stations used are listed in Table 5,
Appendix A. Simulations were limited to stations east of d3 . . . . . . 4 ft. 4 ft. 4 ft. 4 ft.
the Rockies because of the steep rainfall gradients in the K, ...... .33 in. .67 in. .67 in. .50 in.
West and because most of the situations where leaching KI+K2+K
may be a problem are in irrigated areas and thus are 3 4.0 in. 8.0 in. 8.0 in. 6.0 in.
excluded from this -report. 0F. . . . . . .123 .237 .327 .345
Mean monthly pan evaporation data were obtained E. . . . . . .04 .07 .10 .15
for the stations used or for nearby stations from a U. S.
Weather Bureau publication (25). Fourier series were fit IRoot zone depths were reduced for shallow soils.
to these monthly values and were converted to mean
daily values. A single harmonic explained more than 97%
of the variance for most of the stations. The mean daily It was assumed that the available water-holding
evaporation and the amplitude and phase angle of the capacity of a soil was the difference between the water
first harmonic were plotted on maps and isolines were content at 0.3 bars and 15 bars tension. (Approximate
drawn. These parameters were then estimated by inter- field capacity and wilting point). Typical textures of
polation from the maps for stations where evaporation soils in each hydrologic soil group were then selected
pan data were not available. The pan coefficient, Kp, and the total available water content was rounded to the
was obtained from the map presented by Kohler, nearest inch. The storage capacities were assigned to land
Nordenson and Baker (10). resource areas on the basis of the characteristics of t he
predominant agricultural soils. The assignments were
reviewed and corrected where necessary by soil scientists
Estimation of Parameters of the SCS Technical Service Centers. The assignments
by land resource areas are shown in Table 6, Appendix
The index crop considered was straight-row corn. A. The values of the exclusion fraction, E , were
Planting and harvesting dates for each locality were estimated for the assumed water-holding capacities from
obtained from maps prepared by the USDA Statistical published data on 15 soils (21).
Reporting Service (24). Plowing and spring fertilization
were arbitrarily assumed to have been done 14 days Computer Program
before planting. The fall fertilization date was the day
the 5-day moving average temperature went below 50* F The subroutinc@ ETRANS (Evapotranspiration) was
(10' C) or December 15, whichever occurred first. Corn written in FORTRAN IV. It is called from program
was assumed to reach full canopy 80 days after planting. SCSRO described in Appendix A. A generalized flow
Root zone depths, available soil water capacities, field chart is shown in Fig. 6.

156

Read
Field
Characteristics@

Read evaporation
and crop coeffi.
series parameters

Call CN

< Call TPREAD
LU

LL.
For explanation of these sub-
Call SNOW i@ routines, see Fig. 2,
Appendix A.

LU
a, Call AMCF

Call SRO

LLJ
Q= W I Subroutine STEKP computes a
Call STEMP 5-day moving average temperature
for use in the nitrification
calculations.

Subroutine MANS computes evapo-
Call ETRANS
ration,transpiration, percolation
nitrification and nitrate move-
ment on a daily basis for 1 year.

Compute rainfall,
runoff, percolation
evapotranspiration
and N loss
statistics.
Write
Output
Summary

Figure 6.-Generalized flow chart. Program SCSRO with percolation and nitrate leaching option.

157

SIMULATION RESULTS

The program output for each 14-day period included: 5. Distribution functions of loss of fall-applied nitro-
1. An ordered listing of daily rainfall. gen, spring-applied nitrogen and leaching.
2. An ordered listing of simulated runoff. 6. Mean annual percolation.
3. An ordered listing of daily percolation. 7. Mean annual evapotranspiration.
4. The mean and standard deviation of each of the Maps of the mean annual percolation, fall-applied N
above. loss and spring-applied N loss for each of four available
The statistical summary for the n-year simulation soil water-holding capacities are shown in Figs. 7
included: through 18. Because of the limited area in which soils of
1. A table showing the number of runoff events for flydrologic Group A are predominant, simulations were
each 14-day period for each year. not performed for all stations. Therefore, isolines could
2. The probability that there would be no runoff in not be drawn in the east central portion of the United
any year for each 14-day period. States. The mean annual precipitation for the period of
3. The mean annual simulated runoff. record used in the simulation is shown in Fig. 19.
4. The mean growing season simulated runoff.

158

7
1 3 6
e.e

01
2.18

1 5 4. 5 5

18.5
"N 2
12 .1

22.8

Figure 7-Mean annual percolatlon below a 4-foot root zone in inches. Hydrologic Soil Group A. Four inches available water-holding capacity. Straight-row com.

0
00
C@ 4

0 ro.0
C@

12.0

12.0
14.0
7-

(P 'd
-0
*0
*0
'0
Figure 8.-Mean annual percolation below a 4-foot root zone in inches. Hydrologic Soil Group B. Eight inches available water-holding capacity. Straight-row corn.

12.0
10.0
@0-0
JI

0. .0

Figure 9.-Mean annual percolation below a 4-foot root zone in inches. Hydrologic Soil Group C Eight inches available water-holding capacity. Straight-row corn.

'ZO

7.0

Figure IO.-Mean annual percolation below a 4-foot root zone in inches. Hydrologic Soil Group D. Six inches available water-holding capacity. Straight-row corn.

ao 50
50
6.
23. 32.2
10.0

I
27.

7. 49.7
-8-472- q

\8Z6
52. 0
97.

0.0

Figure I I. -Mean percentage loss of fall-applied nitrogen. Straight-row com in good hydrologic condition. Fydrologic Soil Group A. Available water-holding capacity - 4 inches.

IIj

Figure 12-Mean percentage loss of fall-applied nitrogen. Straight-row corn in good hydrologic condition. Hydrologic Soil Group B. Available water-holding capacity - 8 inches.

10-0
O-P
000
8-5-10
0-0 3-2 @-'5-7
1000 .1 0*0 13-3
00 16 -1
21*1
1000 000 90 14o
0 Ir
000 00, 804 50 --1501
k------y 1-3 112-81
f I **, 5o2
0.00-0 1
I / .28-3
000 000
P- @5 - 5 @'' -15*-3-
29 1
'30
-N- - -,
10-0 000 11 35o845-9 26*9
I @206 \
141o7 34o
29 24\ 30

480 .3 iO 5*3

290

0
0)
0 34oR
\@Ir

Figure 13.-Mean percentage loss of fall-applicd nitrogen. Straight-row com in good hydrologic condition. Hydrologic Soil Group C Available water-holding capacity - 8 inches.

000
000
000 0 11 8-6@10
0-0 000 97 @-@5-0
1000 A \0 14 -7
0.0 2
-N. 4 -- 003
IV- 3o5
10.0 000 18-0
3 6 o 6 21o
000
129,4
000 1501
%I. \ Io5 I
04,3 102 \ I
) , /-4@ 4-
29o2
5e9
000 0-0 11 1*8 2 18-527*7

46-3
000 1 000 35*2
141o7 @5*0 \27*6
291 31.7 a
1 L @.5 4198 14*6
000
3003.,@@
0 30
0 3Z,-O
j

Figure 14.-Mean percentage loss of fall-applied nitrogen. Straight-row com in good hydrologic condition. Hydrologic Soil Group D. Available water-holding capacity - 6 inches.

10
4
10.1 65\5

2.
10.0

5.2
V
'ba
J 1 6.8
5

I %454
117.1 0

67.
'30
L__, 5.
50

110

Figure IS. -Mean percentage loss of spring-applied nitrogen. Straight-row corn in good hydrologic condition. Hydrologic Soil Group A- Available water-holding capacity - 4 inches.

0
0
@

0.
6-\O
0.0
0.0

0.0 ).0
0.01 vP@
0 0.0
0.0 0.0 6,0
0.6

0.0
16,

0.7

L
8.3 1 -50 -50
150 E)O

Figure 16-Mean percentage loss of spring-applied nitrogen. Straight-row corn in good hydrologic condition. Hydrologic Soil Group B. Available water-holding capacity - 8 inches.

1 000
06P
0*0 090

000 000
0-0
0*0 1 00
'0 '00
0*0
-4 0*0 0 - 0@-_O;@
10.0 0*0 N 000-
0 @1000 __0
0*0 0
1 000
V 'r
0
\0,0 10 1
I @-, 090
04,00.0
000 000
10-0 dOTO
06
1 0-0 11 0@ 0
10-0 0-0 000
1000 0* 0-0
000 000

0*0 101 26-0
10*0
0 0.1@@

2690
\.Oi

Figure 17. -Mean percentage loss of spring-applied nitrogen. Straight-row corn in good hydrologic condition. Hydrologic Soil Group C. Available water-holding capacity - 8 inches.

C\
@C

000 11
060
0-0 11 / 0-0

00
0-0 000 1 d-O
10-0 0-0
0-0 -----A
000 000
10-0 000 '1 0*0 0-0
000 10-0--0.0
0-0
1 000 '10-0,
I? \060 I I I
0.0000 P --,ro -0
000
000 0-0 0
1060 00
000 000

000
10-0 0-0 1 00
0-0 /
1 000. 0 000
-J, I I
0-0 1 0-0
I)0-0 0-0 2 0*0
0-0,,@

1902
%.Ij

Figure 18.-Mean percentage loss of spring-applied nitrogen. Straight-row corn in good hydrologic condition. Hydrologic Soil Group D. Available water-holding capacity - 6 inches.

NII

rN- N

(D
40
60
to

'Figm, I g.-Mean annual (wo6pitation for period of reoard used in simulations.

DISCUSSION
Simulated mean annual percolation and nitrate leach- Simulated mean annual percolation is compared with
ing cannot be compared with observations because such lysimeter data in Table 2. Only one set of data is for
data are not generally available. However, the excellent corn (Coshocton, Ohio), and the simulated percolation is
correlation between the sum of the simulated potential very close to the observed. The other data sets agree
direct runoff and percolation and the surface runoff favorably with the simulated percolation when the crop
from USGS maps as presented in Appendix A suggests canopy differences are considered. The shallow lysime-
that the simulated results are reasonable. ters at Windsor, Conn. probably account for much of the
Isolated bits of data are available for additional difference between observed and computed percolation.
checks. Minshall (14) in a study of 25 years of runoff We were unable to find any data showing the
data (1940-1964) on the Platte River in southwestern percentage of fall-applied nitrogen lost during the winter
Wisconsin found that the mean annual base flow was 5.7 and spring.
inches. The mean annual potential percolation for Although the comparisons between simulated per-
Hydrologic Group B is somewhat greater than 5 inches colation and data cannot be considered as conclusive,
(Fig. 8). they do suggest that the simulations provide a reasonable
Hanway and Laflen (6) reported 3-year averages of ordering of Land Resource Areas with respect to
1.11 and 4.64 inches of subsurface drainage for tile percolation losses. The absolute amounts also appear to
be realistic.
outlet terraces in Creston, Iowa and Charles City, Iowa, The only way a technique such as this can be judged
respectively. From Fig. 8, the mean annual potential is against readily available alternatives. The leaching
percolation for these -sites is about 2 inches and 3 inches, hazard map prepared by Nelson and Uhland (18) is
respectively. One would anticipate greater percolation shown in Fig. 20. The material presented in this
losses from tile outlet terraces than from straight row Appendix and in Vol. I clearly presents a more detailed
corn but the period of record is too short to make valid picture of percolation and of the relative hazards of
comparisons. Again it appears that the simulated per- nitrate leaching from fall fertilization.
colation is reasonable. Care should be used in interpreting the maps of
Saxton, Spomer and Kramer (20) reported on meas- potential percolation and nitrate leaching where it is
urements of base flow for small watersheds with contour known that the model assumptions are seriously in error.
corn near Treynor, Iowa. Six-year average base flow For example, in the Southern United States the assurnp-
from two watersheds was 2.52 and 2.47 inches. From tion of no nutrient uptake or transpiration during the
Fig. 8, simulated deep percolation in this area is about 2 winter would be inaccurate if winter cover crops are
inches. Rainfall during the 6-year period was above planted. In this case, both the percolation and the
average for 5 of the 6 years. nitrate loss would be overestimated.
Table 2.-Comparison of simulated mean annual percolation with lysimeter data

Average percolation
Location Citation Soil Hydrologic Crop Simulated
Soil Group Observed (corn)

inches inches

Ithaca, N.Y. Bizzell (2) Pet oskey gritty A Vegetables 17.76 13
sandy loam B 11 17.76 11
Geneva, N.Y. Collison et al. (3) Ontario, Dunkirk B Barley-clover 12.7 11
rotation

Knoxville, Tenn. Mooers et al. (15) Cumberland B Fallow 22.5 15
Windsor, Conn. Morgan & Merrimac, A Tobacco 13.63 20
Jacobson (16) 20" depth
Windsor, Conn. Morgan, et al. Merrimac, A Tobacco with 12.45 20
(17) 30" depth winter cover
Coshocton, Ohio Harrold & Muskingum C Corn years in 7.43 7
Dreibelbis (7) CWMM rotation

172

. . . . . . . . . . .

Figure 20.-Relation of degree of leaching to geographic area. Leaching ranges from nil in Area I to very high in Area IV.
From Nelson and Uhland (L8).

173

LITERATURE CITED

I. Appelt, H., Holtzclaw, K., and Pratt, P. F. 1975. 11. Kohler, M. A., Nordenson, T. J., and Baker, D. R.
Effect of anion exclusion on movement of chloride 1963. Rainfall-runoff models. General Assembly of
through soils. Soil Sci. Soc. Amer. Proc. 39:264-267. Int. Assoc. of Scientific Hydrology Surface Waters,
Berkeley, Calif.: 479-491.
2. Bizzell, J. A. 1943. Lysimeter experiments-VI: The
effects of cropping and fertilization on the losses of 12. Levin, 1. 1964. Movement of added nitrates through
nitrogen from the soil. Cornell Univ. Agr. Exp. Sta. soil columns and undisturbed soil profiles. Proc. 8th
Memo. No. 252: 1-24. Intern. Congress of Soil Science, Bucharest,
Romania.
3. Collison, R. C., Beattie, H. C., and Harlan, J. D.
1933. Lysimeter investigations: 111. Mineral and 13. Makkink, G. F. and van Heemst, H. D. J. 1966.
water relations and final nitrogen balance in legume Water balance and water bookkeeping regions.
and nonlegume crop rotations for a period of 16 Verslagen en mededlingen van de Commissie voor
years. New York (Geneva) Agr. Exp. Sta. Tech. Bull. Hydrologisch Orderzock T. N. 0. No. 12, 9-112.
212:1-81. Cited by F. E. Schulze, Chapter 1, Rainfall and
rainfall excess in recent trends in hydrograph
4. Frederick, L. R. 1956. Formation of nitrate from synthesis. Proc. of Tech. Meeting 21. Versl. Medel
ammonium nitrogen in soils: 2. Effect of population Comm. Hydrol. Onderz. T.N.O. 12. The Hague. 103
of nitrifiers. Soil Sci. 83:481-485. P.

5. Hanson, C. L. 1973. Model for predicting evapotrans- 14. Minshall, N. E. 1967. Precipitation and base flow
piration from native rangelands in the Northern Great variability. Proc. International Assoc. of Scientific
Plains. Ph.D. dissertation, Utah State University, Hydrology, Bern: 137-145.
Logan.
15. Mooers, C. A. MacIntire, W. H., and Young, J. B.
6. Hanway, J. J. and Laflen, J. M. 1974. Plant nutrient 1927. The recovery of soil nitrogen under various
losses from tile-outlet terraces. Jour. Environ. Quality conditions as measured by lysimeters of different
3(4):351-356. depths. Tennessee Agr. Exp. Sta. Bul. 138: 1-30.

7. Harrold, L. L. and Dreibelbis, F. R. 1958. Evaluation 16. Morgan, M. F. and Jacobson, H. G. M. 1942. Soil
of agricultural hydrology by monolith lysimeters and crop interrelations of various nitrogenous fertil-
1944-5 5. U. S. Dept. Agr. Tech. Bul. 1179, 166 p. izers: Windsor lysimeter Series B. Connecticut Agr.
Exp. Sta. Bul. 458: 269-328.
8. Kissel, D. E., Ritchie, J. T. and Burnett, E. 1973.
Chloride movement in undisturbed swelling clay soils. 17. Morgan, M. F., Jacobson, H. G. M., and Lecompte,
Soil Sci. Soc. Amer. Proc. 37:21-24. S. B. Jr. 1942. Drainage water losses from a sandy
soil as affected by cropping and cover crops:
9. Kolenbrander, G. J. 1970. Calculation of parameters 'Windsor lysimeter Series C. Connecticut Agr. Exp.
for the evaluation of the leaching of salts under field Sta. Bul. 466: 729-759.
conditions, illustrated by nitrate. Plant and Soil
32:439-453. 18. Nelson, L. B. and Uhland, R. E. 1955. Factors that
influence loss of fall applied fertilizers and their
10. Kohler, M. A., Nordenson, T. J., and Baker, D. R. probable importance in different sections of the
1959. Evaporation maps for the United States. U. S. United States. Soil Sci. Soc. Amer. Proc.
Weather Bureau Tech. Paper No. 37, 13 p. 19(4):492-496.

174

19. Sabey, 3. R., Bartholomew, W. V., Shaw, R., and 24. USDA Statistical Reporting Service. 1972. Usual
?esek, j. 1956. Influence of temperature on nitrifi- planting and harvesting dates. Agr. Handbook No.
cation in soils. Soil Sci. Soc. Amer. Proc. 283.
20:357-360.
25. U. S. Weather Bureau. Climatography of the United
20. Saxton, K. E., Spomer, R. G., and Kramer, L. A. States. Climatic summary of the United States-
197 1. Hydrology and erosion of loessial watersheds. Supplement for 1951 through 1960.
?roc. ASCE Sour. Hydr. Div. 97 (HYIl): 1835-1852. 26. Van Wijk, W. F., Larson, W. E. and Burrows, W. C.
21. Smith, S. J. 1972. Relative rate of chloride move- 1959. Soil temperature and the early growth of corn
ment in leaching of surface soils. Soil Sci. from mulched and unmulched soil. Soil Sci. Soc.
114(4):259-263. Amer. Proc. 23(6): 428-434.
27. Wiser, E. H. and van Schilfgaarde, J. 1964. Predic-
22. Smith, S. J., and Davis, R. J. 1974. Relative tion of irrigation water requirements using a water
movement of bromide and nitrate through soils. balance. Proc. VIth International Congress of Agr.
Jour. Environ. Qual. 3(2):152-155. Engr., Lausanne: 121-129.

23. Thomas, G. W. 1970. Soil and climatic factors 28. Yaalon, D. H. 1965. Downward movement and
which affect nutrient mobility. In Engelstad, 0. P. distribution of anions in soil profiles with limited
ed., Nutrient mobility in soils: accumulation and wetting. In Experimental Pedology. William Cloves
losses, Soil Sci. Soc. Amer., Inc., Madison, Wisc. and Sons, Ltd. London: 157-164.

175

APPENDIX C

ECONOMIC ANALYSIS METHODOLOGY

The following discussion details the application of the Table @. Broadbase terrace construction and maintenance costs
method presented in Section 5, Volume !, to evaluate
the decision-maker's optimal choice in the example given Item Amount
in Section 6.2, Volume 1. This example is clearly
site-specific and cannot hope to show the full gamut of Terrace spacing, feet . . . . . . . . . . . 120
variables which may potentially be of significance in other Slope length, feet . . . . . . *' * * ' * * 350
situations, such as irrigation, hired labor, other crop Number of terraces per slope ....... 2
Feet terrace/acre .............. 249
rotations and the like. T he decision-maker will have to Construction cost/foot terracea, s ..... 0.60
adjust the budgeting system shown here to his particular Construction cost/acre, $ ......... 149.40
situation. Prorated construction costb, $ . . . . . . . 13.74
Maintenance cost, foot3, $ . . . . . . . . . 0.00023
Several important assumptions were made. For cer- Maintenance cost, acre, $ . . . . . . . . . 0.06
tain computations, the size of the farm became a Yearly terrace charge/acre, $ . . . . . . . 13.80
parameter, and the assumption was made that the Total yearly terrace charge (250 acres), 3,450.00
example farm had 250 tillable acres. Other assumptions I Source: Sidney James (ed), Midwest Farm Planning
are detailed in the following tables. In addition, it was Manual, 3rd Edition, ISU Press, Ames, Iowa, 197 3, p. 3 3.
assumed that none of the macro effects described in b Assume 20 year life of terrace. Interest at 8 percent.
Section 5.2 of Volume @' influence any of the decision
variables noted here. 11his assumption implied that any located on Monona silt loam with more than 3 percent
machinery which may become obsolete due to a change organic matter, a land slope of 6 percent, and an average
in cropping practices would be sold at a cost close to its slope length of 350 feet. According to the technical
depreciated value and that, consequently, there was standards' for terrace construction, the construction of
no cost of disposing of obsolete equipment to be added level broadbase terraces with a spacing of 120 feet would
to the actual machinery costs. be appropriate in this situation. Table I shows the
,Lhe determination of the relevant production alterna- assumptions used in the computation of the cost of
tives resulted in five potential choices, namely, (1) terracing the entire farm.
continuous corn no-till planted in 70 percent residue Each of these production systems requires a specific
cover, contoured, (2) a corn-corn-corn-wheat-meadow set of field operations and implements. Table 2 lists the
rotation with moldboard plowing on the first year corn implements considered in this study and the computa-
and no-till planting on the second and third year corn, tion of the fixed costs for each machine. The computa-
contoured, (3) continuous corn with rotary strip tillage, tion of the depreciation cost used the straight-line
terraced, (4) continuous corn with chisel planting, method over the economic life of the implement. Not all
terraced, and "5) a corn-soybean rotation with no-till
k of the implements were used in any particular crop
planting, terraced. The costs and returns for a sixth production activity; Table 3 shows which implements
production method (i.e. continuous corn, residue left, were used in each production alternative, the total hours
with moldboard plowing, straight row) are shown for of machinery use, and the total implement cost. These
comparison purposes only. 77his particular production costs did not include the cost of the tractor (listed
method does not meet the soil erosion limitation and
can therefore not be considered as an available alterna-
tive. I J.S. Department of Agriculture, Soil Conservation Service,
Three of the five viable alternatives required terrac- Iowa, Technical Standards and Specifications for Conservation
ing, which contributed an additional production cost, Practices, Section 4A-Cropland, Work Unit Technical Guide,
summarized in Table 1. The example assumed a farm Code No. 600 and 602, January 1973.

177

Table 2. Machinery fixed costs
00
Initiala Salvageb Economicc Yearly Taxes, insuranced Yearly
Machine Size cost value life depreciation and housing Intereste fixed cost

Dollars Percent Years Dollars Dollars Dollars Dollars
Stalk shredder . . . . . . . . . . . 12'flail 2,350 13.7 12 169.00 70.50 101.83 341.33
Moldboard plow . . . . . . . . . . . 5-16" 2,590 17.7 10 213.16 77.70 113.96 404.82
Chisel plow . . . . . . . . . . . . . 15' 1,700 13.7 12 122.26 51.00 73.67 246.93
Disk, tandem . . . . . . . . . . . . . 20' 4,385 17.7 10 360.89 131.55 192.94 685.38
Harrow . . . . . . . . . . . . . . . . 20' 340 17.7 12 23.32 10.20 14.73 48.25
Sprayer . . . . . . . . . . . . . . . tractor mounted 680 17.7 10 55.96 20.40 29.92 106.28
Planter - conventional . . . . . . . 4-38" 1,430 17.7 10 117.69 42.90 62.92 223.51
Rotary strip planter . . . . . . . . . 4-38" 3,675 17.7 10 203.45 110.25 161.70 574.40
No-till plant (fluted coulters) . . . 4-38" 4,375 17.7 10 360.06 131.25 192.50 683.81
Wheat drill (with grass seeding
attachments) . . . . . . . . . . . 12' 2,740 9.7 14 176.73 82.20 117.43 376.36
Cultivator . . . . . . . . . . . . . . . 4-38" 1,470 17.7 to 120.98 44.10 64.68 229.76
Duster . . . . . . . . . . . . . . . . . 4-row 400 13.7 12 28.77 12.00 17.33 58.10
Combine, self-prop . . . . . . . . . . small 70-80 hp 16,100 18.9 10 1,305.71 483.00 708.40 2,497.11
Com head . . . . . . . . . . . . . . . 2-38" 2,800 18.9 10 227.08 84.00 123.20 434.28
Platform ................. 13' 2,500 18.9 to 202.75 75-00 110.00 387.75
Hay mowers . . . . . . . . . . . . . 7' 960 12.5 i2 70.00 28.80 41.60 140.40
Hay conditioners
. . . . . . 7' 1,300 12.5 12 94.79 39.00 56.33 190.12
Hay take . . . . . . . . . . . . . . . side delivery 980 12.5 12 71.46 29.40 42.47 143.33
Hay baler . . . . . . . . . . . . . . . PTO 3,500 21.1 8 345.19 105.00 157.50 607.69

a Source: Background Information for Use with CROP-OPT System, FM 1628, ISU Cooperative Extension Service, Ames, Iowa, November 1974.
b Source: George E. Ayres, Estimating Used Machinery Costs, A.E. 1078, ISU Cooperative Extension Service, Ames, Iowa, January 1974.
c Source: Sidney James (ed), Midwest Farm Planning Manual, 3rd Edition, ISU Press, Ames, Iowa, 197 3, Table IV-7, p. 129.
d Taxes and insurance at 2 percent of initial cost; housing at I percent of initial cost. Source: George E. Ayres, Estimating New Machinery Costs, A.E. 107 7 , ISU Cooperative
Extension Service, Ames, January 1974.
e Assumed at 8 percent per annum.

Table 3. Machinery costs

Implement Hours per Acres of Times Total Repair cost er Total repair Yearly fixed Total
acrea useb overc hours 100 hoursy cost cost cost

Corn, residue left, spring tu n-plow, conventional Dollars Dollars Dollars Dollars
Stalk shredder . . . . . . .18 250 1 45.0 94.00 42.30 341.33 383.63
Moldboard plow . . . . . . .36 250 1 90.0 129.50 116.55 404.82 521.37
Sprayer . . . . . . . . . . .21 250 1 52.5 34.00 17.85 106.28 124.13
Disk . . . . . . . . . . . . .10 250 1 25.0 219.25 54.81 685.38 740.19
Harrow . . . . . . . . . . .10 250 1 25.0 10.20 2.55 48.25 50.80
Planter . . . . . . . . . . .22 250 1 55.0 114.40 62.92 223.51 286.43
Cultivator . . . . . . . . .21 250 2 105.0 73.50 77,18 229.76 306.94
Combine . . . . . . . . . . .63 250 1 157.5 322.00 507.15 2,497.11 3,004.26
Corn head . . . . . . . . . .63 250 1 157.5 56.00 88.20 434.28 522.48
Total . . . . . . . . . . . . 5,940.23

Corn, fall shred stalks, chisel plant, 3040% residue cover
Stalk shredder . . . . . . .18 250 1 45.0 94.00 42.30 341.33 383.63
Chisel plow . . . . . . . . .17 250 1 42.5 85.00 36.13 246.93 283.06
Sprayer . . . . . . . . . . .21 250 1 52.5 34.00 17.85 106.28 124.13
Harrow . . . . . . . . . . .10 250 1 25.0 10.20 2.55 48.25 50.80
Planter . . . . . . . . . . .22 250 1 55.0 114.40 62.92 223.51 286.43
Cultivator .21 250 2 105.0 73.50 77.18 229.76 306.94
Combine . . . . . . . . . . .63 250 1 157.5 322.00 507.15 2,497.11 3,004.26
Corn head . . . . . . . . .63 250 1 157.5 56.00 88.20 434.28 522.48
Total . . . . . . . . . . . . 4,961.73

Corn, residue left, strip-till row zones, 40-50% residue cover
Stalk shredder . . . . . . . .18 250 1 45.0 94.00 42.30 341.33 383.63
Sprayer . . . . . . . . . .21 250 1 52.5 34.00 17.85 106.28 124.13
Rotary strip-till planter . . .22 250 1 55.0 294.00 161.70 574.40 736.10
Cultivator . . . . . . . . . .21 250 2 105.0 73.50 77.18 229.76 306.94
Combine . . . . . . . . . . .63 250 1 157.5 322.00 507.15 2,497.11 3,004.26
Corn head . . . . . . . . . .63 250 1 157.5 56.00 88.20 434.28 522.48
Total . . . . . . . . . . . . 5,077.54

Corn, fall shred, no-till plant, 50-70% residue cover
Stalk shredder . . . . . . . .18 250 1 45.0 94.00 42.30 341.33 383.63
Sprayer . . . . . . . . . . .21 250 1 52.5 34.00 17.85 106.28 124.13
No-till planter . . . . . . . .22 250 1 55.0 350.00 192.50 683.81 876.31
Duster . . . . . . . . . . . . .21 250 1 52.5 8.00 4.20 58.10 62.30
Combine . . . . . . . . . . .63 250 1 157.5 322.00 507.15 2,497.11 3,004.26
Corn head . . . . . . . . . .63 250 1 157.5 56.00 88.20 434.28 522.48
Total . . . . . . . . . . . . 4,973,11

Corn-corn-corn-wheat-meadow, residue left, no-till plant 2nd and 3rd corn
Stalk shredder . . . . . . . .18 150 1 27.0 94.00 25.38 341.33 366,71
Moldboard plow . . . . . .36 50 1 18.0 129.50 23.31 404.82 428A3
Sprayer . . . . . . . . . . .21 150 1 31.5 34.00 10.71 106.28 116.99
Disk . . . . . . . . . . . . .10 100 1 10.0 219.25 21.93 685.38 707.31
Harrow . . . . . . . . . . .10 50 1 5.0 10.20 0.51 48.25 48.76
No-tifl planter . . . . . . . .22 150 1 33.0 350.00 115.50 683.81 799.31
Wheat drill . . . . . . . . . .25 50 1 12.5 219.20 27.40 376.36 403.76
Duster . . . . . . . . . . . .21 150 1 31.5 8.00 2.52 58.10 60.62
Combine corn . . . . . . . @63 150 1
Combine wheat . . . . . . .30 50 1 109.5 322.00 352.59 2,497.11 2,849.70
Corn head . . . . . . . . . .63 150 1 94.5 56.00 52.92 434.28 487.20
Platform . . . . . . . . . . .30 50 1 15.0 50.00 7.50 387.75 395.25
Hayinower . . . . . . . . .31 50 3 46.5 96.00 44.64 140.40 185.04
Hay conditioner . . . . . . .31 50 3 46.5 52.00 24.18 190.09 214.27
Hay rake . . . . . . . . . . .30 50 3 45.0 58.80 26.46 143.33 169.79
Hay baler . . . . . . . . . .63 so 3 94.5 210.00 198.45 607.69 806.14
To tal . . . . . . . . . . . . 8,038.98

179

Table 3. (continued)

Hours per Acres of Times Total Repair cost er Total repair Yearly fixed Total
Implement acrea. useb overc hours 100 hourss cost cost cost

Corn-soybeans, no-till plant, fall shred corn stalks Dollars Dollars Dollars Dollars
Stalk shredder . . . . . . . .18 125 1 22.5 94.00 21.15 341.33 362.48
Sprayer . . . . . . . . . . . .21 250 1 52.5 34.00 17.85 106.28 124.13
No-till planter . . . . . . . .22 250 1 55.0 350.00 192.50 683.81 876.31
Duster . . . . . . . . . . . . .21 125 1 26.25 8.00 2.10 58.10 60.20
Combine corn . . . . . . . .63 125 1
Combine soybeans . . . . .30 125 1 116.25 322.00 374.32 2,497.11 2,871.43
Corn head . . . . . . . . . .63 125 1 78.75 56.00 44.10 434.28 478.38
Platform . . . . . . . . . . .30 125 1 37.5 50.00 18.75 387.75 406.50
Total . . . . . . . . . . . . 5,179.43

aSource: Background information for use with CROP-OPT system, FM 1628, ISU Cooperative Extension Service, Ames, Iowa,
November 1974.
b Acres on which implement is used each year.
c Number of trips through field with implement.
d Computed as percentage of list price. Used 2% for combine, platform, corn head and duster; 4% for stalk shredder and hay condi-
tioner; 5% for moldboard plow, chisel plow, cultivator, sprayer, and disk; 6% for hay rake and hay baler; 8% for planters and wheat
drill; 10% for hay mower. Source: George Ayres, Estimating new machinery costs, AE 1077, ISU Cooperative Extension Service,
Ames, Iowa, January 1974.

180

separately in Table 4) or fuel and lubrication (Table 5). per acre was estimated as 130 percent of the tractor
The implement hours per acre (from Table 3) were hour requirement to account for overhead labor in
aggregated for each production alternative. The total was addition to the direct requirements. The labor cost per
augmented by a 10 percent figure for traveling to field, hour was assumed equal to the present average wage rate
idling, etc., to result in the total tractor hours figure for Iowa.
listed in Table 4. The depreciation cost assumed a Table 10 presents two additional cost components,
straight-line depreciation over the economic life of the namely the corn drying costs and interest charges. It was
tractor. assumed that the costs (variable and fixed) of drying
The fuel costs for the tractor and the combine were corn amounted to 12 cents/bushel, which is the current
4
computed as shown in Table 5. These fuel costs were charge for custom drying in Iowa. It was assumed that
presented separately from the other machinery and the out-of-pocket costs involved the use of borrowed
tractor variable costs for the purpose of emphasizing the capital. The interest costs on machinery and the tractor
differences in fuel consumption among production were included in their total costs and are not repeated
alternatives. here.
Table 6 shows the computations for the seed costs of The gross revenue for each of the production alterna-
the five production alternatives. The assumption was tives was computed as shown in Table 11. The no-till
made that the no-till alternatives would be subject to a alternatives were assumed to have a slightly lower yield
higher seed mortality rate than the other alternatives, than the more conventional tillage alternatives due to
due to the higher crop residue levels. increased production and harvesting complexities.
Agricultural chemicals were selected on the basis of The final table, Table 12, summarizes all of the
the recommended nutrient and pesticide practices. It preceding computations and shows the gross revenue
was assumed that the nitrogen was applied in NH3 form and net return figures for each of the six production
and the phosphate and potassium in granular bulk form methods, A land cost was included based on an assumed
(Table 7). The restrictions on optimal timing (N2) are land value of $974.00 per acre 5 and a cash rent of $7.40
6
assumed to be met by fertilizer application just prior to per $100 value. Since this land charge applied equally
planting, which in the case of two alternatives (corn to all six production methods, any error in this land
chisel-plant and corn ro tary-strip -till) also implies incor- charge will change only the absolute levels and not the
poration (N8 and 12). differences in net returns among the six alternatives.
The pesticide costs (Table 8) were estimated on the It appears that the (unavailable) alternative of con-
basis of pesticide recommendations by the ISU Exten- tinuous corn with conventional moldboard tillage has a
2, 3
sion Service for control of the major pests. The significantly higher net revenue than any of the other
pesticide costs for the several production alternatives (available) production alternatives. There is only a small
may vary since each rotation requires the use of a unique variation in net return of the top three (available)
mix of pesticides. For example, the herbicide cost for production alternatives with a major net return drop to
the no-till alternatives was higher than for conventional the corn-soybeans alternative. The corn-corn-corn-
tillage because greater amounts of and more expensive wheat-meadow rotation has by far the lowest net return
types of herbicides were assumed to be used with this among these six alternatives, indicating that the savings
alternative. The insecticide cost for the rotation includ- in fertilizer cost generated by the nitrogen nutrient
ing meadow was assumed greater than for continuous credit from the legume meadow are not sufficient to
corn alternatives due to the expected incidence of the offset the increases in other costs.
first-year corn insect complex. No insecticide cost was
assumed for soybeans, since the acreage of soybeans
ordinarily treated with insecticides was quite small.
Labor costs for the five production alternatives were 4
computed as shown in Table 9. The labor requirement Estimated 1975 Iowa Custom Rates, ISU Cooperative
Extension Service, I'M 1698, Ames, Iowa, January 1975.
5$974.00 is the November 1, 1974 average price for high
grade farmland in West Central Iowa, reported in William Murray
2 etal., Land ValuesDouble in 5years, FM 1681, ISU Cooperative
Harold J. Stockdale, Insect Pest Control Recommendations Extension Service, Ames, Iowa, January 1975.
for 1975, IC-328 (Rev.), ISU Cooperative Extension Service, 6A rent of $7.40 per $100 value is the average cash rental
Ames, Iowa, January 1975. rate for corn and soybean land reported in E. G. Stoneberg and
3Vivan M. Jennings, Weed Control Guide for 1975, Pm 601 Ronald Winterboer, Cash Rental Rates from Iowa Farm Land,
(Rev.), ISU Cooperative Extension Service, Ames, Iowa, January FM 1626 (Rev.), ISU Cooperative Extension Service, Ames,
1975. Iowa, August 1973.

181

Table 4. Tractor costs
Item Straight-row Contour Terraced
C conv. C no-t. CCCWM no-t. C chisel C strip CB no-t.

Tractor hours per acrea . . . . . . . . 2.21 1.65 2.20 1.92 1.65 1.34
Total tractor hoursb . . . . . . . . . . 607.75 453.75 605.00 528.00 453.75 368.50
Tractor initial cost,' dollars . . . . . 18,230.00 18,230.00 18,230.00 18,230.00 18,230.00 18,230.00
Economic life, yearsd . . . . . . . . 11 13 11 12 13 14
Salvage value, percente . . . . . . . 27.5 23.5 27.5 25.5 23.5 21.5
Yearly depreciation, dollars . . . . . 1,201.52 1,072.52 1,201.52 1,131.78 1,072.76 1,022.18
Taxes, insurance and housing,f 546.90 546.90 546.90 546.90
dollars . . . . . . . . . . . . . . 546.90 546.90
Average annual interest,g dollars . . 795.49 785.29 795.49 789.97 785.29 781.29
Total fixed costs, dollars . . . . . . 2,543.91 2,404.95 2,543.91 2,468.65 2,404.95 2,350.36
Repair costs,h dollars . . . . . . . . 886.34 661.75 882.33 770.04 661.75 537.42
Total tractor costs, dollars (excl.. . . 3,426.24 3,238.69 3,066.70 2,887.79
fuel) . . . . . . . . . . . . . 3,430.25 3,066.46
a Assume tractor is required for harvest hauling, in amount equivalent to time requirements for combine. Add 0.2 hours per acre
for application of fertilizer with rented implements.
b Increased by 10 percent for idling, travel to field, etc.
c 100 PTO hp diesel.
d From Sidney James (ed.) Midwest Farm Planning Manual, 3rd Edition, ISU Press, Ames, Iowa, 1973, Table IV-7, p. 129.
e From George E. Ayres, Estimating Used Machinery Costs, A.E. 1078, ISU Cooperative Extension Service, Ames, Iowa, January
1974.
f Taxes and insurance at 2 percent and housing at 1 percent of initial cost. Source: George E. Ayres, Estimating New Machinery
Costs, AE 1077, ISU Cooperative Extension Service, Ames, Iowa, January 1974.
9 Assume 8 percent interest.
h 0.8 percent of list price per 100 hours of use. Source: Ibid.

Table 5. Fuel costs
Straight-row Contour Terraced
Item
C conv. C no-t. CCCWM no-t. C chisel C strip CB no-t.

Total tractor hours . . . . . . . . . . 607.75 453.75 605.00 528.00 453.75 368.50
Fuel cost per tractor hour,a dollars . 2.071 2.071 2.071 2.071 2.071 2.071
Tractor fuel cost, dollars . . . . . . 1,258.65 939.72 1,252.96 1,093.49 939.72 763.16
Total combine hours . . . . . . . . . 157.50 157.50 109.5 157.50 157-50 116.25
Fuel cost per combine hour,b dollars 1.106 1.106 1.106 1.106 1.106 1.106
Combine fuel cost, dollars . . . . . . 174.20 174.20 121.11 174.20 174.20 128.57
Total fuel cost, dollars . . . . . . . . 1,432.85 Ij t3.92 1,374.07 1,267.69 1,113.92 891.73
a Fuel consumption gallons per hour = 0.044xPTO hp. Lubrication costs at 15 percent of fuel cost. Source: Sidney James (ed.)
Midwest Farm Planning Manual, 3rd Edition, ISU Ness, Ames, Iowa 197 3, p. 125. Assume diesel fuel at $0.40/gal.
b Gasoline consumption= 2.3 5 gal. /acre. Source: George E. Ayres, Fuel Required for Field Operations, AE 1079, ISU Cooperative
Extension Service, Ames, Iowa, March 1974. Lubrication costs at 15 percent of fuel costs. Assume gasoline at $0.40/gal.

182

7abIe 6. Seed costs

Item Straight-row Contour Terraced
C conv. C no-t. CCCWM no-t. C chisel C strip CB no-t.

Corn
Seeding rate (seeds/acre) . . . . 23,000 26,000 26,000 24,000 24,000 26,000
Assumed mortality,'X . . . . . . 10 20 20 13 13 20
Final stand ............... 20,700 20,800 20,800 20,880 20,880 20,800
Seed amount', bu . . . . . . . . . 0.274 0.310 0.310 0.286 0.286 0.310
Seed costb, dollars . . . . . . . . 6.85 7.75 7.75 7.15 7.15 7.75

Wheat
Seed amount, bu . . . . . . . . . 1.5
Seed costc, dollars . . . . . . . . 11.25

Hay
Seed amountd, lbs . . . . . . . . 15
Seed -oste, dollars . . . . . . . . 24.45

Soybean
Seed ainountf, bu . . . . . . . . . I
Seed costg, dollars . . . . . . . . 9.50
Seed cost per acreh, dollars . . . . . 6.85 7.75 11.79 7.15 7.15 8.62
Total seed cost, dollars . . . . . . . . 1,712.50 1,937.50 2,947.50 1,787.50 1,787.50 2,155.00
a Based on 84,000 seeds per bushel.
b Assuming price of $25.00 per bushel (Iowa price, U.S. Department of Agriculture, Agricultural Prices. Apr. 15, 1974.
c Price of $7.50 per bushel (U.S. Department of Agriculture, Agricultural Prices, Sept. 15, 1974).
d Source: Sidney James (ed.), Midwest Farm Planning Manual, 3rd Edition, ISU Press, Ames, Iowa, 1975, p. 18.
c Price of $163.00 per 100 lbs. (U.S. Department of Agriculture, Agricultural Prices, Sept. 15, 1974).
f Source: Sidney James, op. cit., p. 20.
9 Price of $9.50 per bushel (U.S. Department of Agriculture, Agricultural Prices, Sept. IS, 1974).
h Average seed cost.

183

Table 7. Fertilizer costs
Item Straight-row Contour Terraced
C conv. C no-t. CCCWM no-t. C chisel C strip CB no-t.

Corn ----------------------------- Pounds per acre ------------------------- 150b---
Na . . . . . . . . . . . . . . . . . . 170 170 113b 170 170
P205 .... 30 30 30 30 30 30
K20 . . . . . . . . . . . . . . . . 20 20 20 20 20 20

Wheat
N 60
P205 . . . . . . . . . . . . . . . . 25
K20 . . . . . . . . . . . . . . . . 30

Soybeans 30
P20S . . . . . . . . . . . . . . . . 30
K20 . . . . . . . . . . . . . . . .

Average amounte 75
N . . . . . 170 170 80 170 170
P20S . . . . . . . . . . . . . . . . 30 30 23 30 30 30
K20 . . . . . . . . . . . . . . . . 20 20 18 20 20 25
Cost of fertilizer per acred, dollars. - 30.90 30.90 17.06 30-90 30-90 18.38
Total cost of fertilizer, dollars . . . . 7,725.00 7,725.00 4,265.00 7,725.00 7,725.00 4,595.00
Rental of application equipmente,
dollars . . . . . . . . . . . . . . . . 187.50 187.50 125.00 187.50 187.50 125.00
Total fertilizer cost, dollars . . . . . . 7,912.50 7,912.50 4,390.00 7,912.50 7,912.50 4,720.00
a Fertilizer recommendations based on: Regis D. Voss, General Guide to Fertilizer Recommendations in Iowa, AG-65 (rev.), ISU
Cooperative Extension Service, Ames, Iowa, August 1973.
b Includes fertilizer credit from meadow or soybeans.
c Amount per year of rotation if other than continuous corn.
d Assume N as NH3 and P205 as 46 percent P205 - Prices per pound are $0.136 for N, $0.206 for P205, and $0.080 for K20-
Source: Iowa price in U.S. Department of Agriculture, Agricultural Prices, September 15, 1974.
e Assume 50@/acrc for NI-13 knife and 250/acre for 4-ton bulk spreader.

Table 8. Pesticide costs

Straight-row Contour Terraced
Item
C conv. C no-t. CCCWM no-t. C chisel C strip CB no-t.

Corn
Herbicide, dollars . . . . . . . . 11.00 16.00 16.00 11.00 11.00 18.00
Insecticide, dollars . . . . . . . . 7.00 7.00 9.00 7.00 7.00 7.00
Acres 250 250 150 250 250 125
Total cost, dollars . . . . . . . . 4,500.00 5,750.00 3,750.00 4,500.00 4,500.00 3,125.00

Soybeans
Herbicide, dollars . . . . . . . . . 11.00
Acres . . . . . . . . . . . . . . . . 125
Total cost, dollars . . . . . . . . 1,375.00
Total pesticide cost, dollars . . . . 4,500.00 5,750.00 3,750.00 4,500.00 4,500.00 4,500.00

184

Table 9. Labor costs

Straight-row Contour Terraced
Item
C conv. C no-t. CCCWM no-t. C chisel C strip CB no-t,

Total direct labor, hours . . . . . . 765.25 611.25 714.50 685.50 611.25 484.75
Overhead (30%), hours . . . . . . . . 229.58 183.38 214.35 205.65 183.38 145.43
Total labor, hours . . . . . . . . . . 994.83 794.63 928.85 891.15 794.63 630.18
Cost per hour, dollars . . . . . . . . 2.50 2.50 2.50 2.50 2.50 2.50
Total labor cost, dollars . . . . . . . . 2,487.08 1,986.58 2,322.13 2,227.88 1,986.58 1,575.45

Table 10. Other costs
Item Straight-row Contour Terraced
C conv. C no-t. CCCWM no-t. C chisel C strip CB no-t.

Corn drying ------------------------------------ bu ------------------------------------
Grain harvested . . . . . . . . . . . 27,500 26,250 16,500 27,500 27,500 13,125
----------------------------------- dollars -----------------------------
Cost per bushel . . . . . . . . . . . 0.12 0.12 0.12 0.12 0.12 0.12
Total cost . . . . . . . . . . . . . . . 3,300-00 3,150.00 1,980.00 3,300.00 3,300.00 1,575.00

,Interest (8%) on ogerr@@
Fertilizer (8 mo.) . . . . . . . . . . 558.98 558.98 342.19 558.98 558.98 340.32
Seed (8 mo.) . . . . . . . . . . . . . 91.28 103.27 157.10 95.27 95.27 114.86
Pesticide (6 mo.) . . . . . . . . . . . 180.00 230.00 150.00 180.00 180.00 180.00
Fuel (3 mo.) . . . . . . . . . . . . . 28.66 22.28 28.54 25.35 22.28 18.75
Labor (3 mo.) . . . . . . . . . . . . 36.08 23.56 33.18 31.36 26.98 17.71
Total interest . . . . . . . . . . . . . 895-00 938.09 711.01 890.96 883.51 671.64
Total other costs . . . . . . . . . . . . . 4,195.00 4,088.09 2,691.01 4,190.96 4,183.51 2,246.64

185

Table 11. Revenue

Straight-row Contour Terraced
Item C conv. C no-t. CCCWM no-t. C chisel C strip CB no-t.

Corn 110.0 105.0
Expected yield, bu./ac ........ 110.0 105.0 105 110.0 125
Area cropped, acres . . . . . . . . 250 250 150 250 250 13,125
Total output, bu . . . . . . . . . 27,500 26,250 15,750 27,500 27,500
Expected price, dollars/bu. . . . . 2.75 2.75 2.75 2.75 2.75 2.75
Gross revenue, dollars . . . . . . 75,625.00 72,187.50 43,312.50 75,625.00 75,625.00 36,093.75

Wheat
Expected yield, bu./ac . . . . . . . 45.0
Area cropped, acres . . . . . . . . 50
Total output, bu . . . . . . . . . 2,250.0
Expected price, dollars/bu .. . . . 4.00
Gross revenue, dollars . . . . . . 9,000.0

Meadow
Expected yield, tons/ac . . . . . 4.0
Area cropped, acres . . . . . . . . 50
Total output, tons . . . . . . . . 200.0
Expected price, dollars/ton . . . . 45.00
Gross revenue, dollars . . . . . . 9,000.00

Soybean 40.0
Expected yield, bujac . . . . . . 125
Area cropped, acres . . . . . . . 5,000-00
Total output, bu . . . . . . . . . . 6.00
Expected price, dollars[bu. . . . - 30,000.00
Gross revenue, dollars . . . . . .
Total gross revenue, dollars . . . . . . 75,625.00 72,187.50 61,312.50 75,625.00 75,625.00 66,093.75

Table 12. Summary

Straight-row Contour Terraced
Item C conv. C no-t. CCCWM no-t. C chisel C strip 03 no-t.

---- ----------------------------- dollars -----------------------------------
Gross revenue . . . . . . . . . . . . . . 75,625.00 72,187.50 61,312.50 75,625.00 75,625.00 66,093.75
Costs
Tractor (excl. fuel) . . . . . . . . 3,430.25 3,066.46 3,426.24 3,238.69 3,066.70 2,887.79
implements (excl. fuel) . . . . . . -5,940.23 4,973.11 8,038.98 4,961.73 5,077.54 5,179.43
Fuel . . . . . . . . . . . . . . . . 1,432.85 1,113.92 1,374.07 1,267.69 1,113.92 891.73
Seed . . . . . . . . . . . . . . . . 1,712.50 1,937.50 2,947.50 1,787.50 1,787.50 2,155.00
Fertilizer . . . . . . . . . . . . . . 7,912.50 7,912.50 4,390.00 7,912.50 7,912.50 4,720.00
Pesticides . . . . . . . . . . . . . . 4,500.00 5,750.00 3,750.00 4,500.00 4,500.00 4,500.00
Labor . . . . . . . . . . . . . . . .. 2,487.08 1,986.58 2,322.13 2,227.88 1,986.58 1,575.45
Terracing . . . . . . . . . . . . . . 0 0 0 3,450.00 3,450.00 3,450.00
Other . . . . . . . . . . . . . . . . 4,195.00 4,088.09 2,691.01 4,190.96 4,183.51 2,246.64
Land charge (see text) . . . . . . 18,020.00 18,020.00 18,020.00 18,020.00 18,020.00 18,020.00
Total cost . . . . . . . . . . . . . . 49,630.41 48,848.16 46,959.93 51,556.97 51,098.25 45,626.04
Net return . . . . . . . . . . . . . . . 25,994.59 23,339.34 14,352.57 24,068.05 24,526.75 20,467.71

186

As the discussion in Section 5, Volume 1, points out, utterly unfamiliar with no-till planting may be willing to
there are a number of intangible variables not accounted accept a lower net return with a higher degree of
for in the net return figures. One of these intangibles, certainty if that alternative excludes no-till planting.
that of scheduling, may be of only minor significance in On-e additional consideration related to the cost of
this example. The scheduling of alternatives with the terracing. The present example assumes tacitly that the
highest net returns does not differ sufficiently to full cost of terracing is borne by the farmer. Historically,
influence the decision. society has reimbursed terracing costs through various
A more important consideration is the variability of government programs so that the farmer usually paid
yields. The variance of yield under no-till is higher than half the cost or even less. Under any such cost-sharing
for production alternatives utilizing more tillage. This program, the relative differences in net revenue will
higher variance for no-till may be partly due to a lack of change. In the present example, a cost-sharing program
familiarity with this method on the part of growers. In with a 50-50 split would give two of the terraced
the present example, the no-till production alternatives alternatives a net revenue practically identical to the
were assumed to have a lower yield than the other (unavailable) conventional tillage continuous com. activ-
production alternatives to account for this potential ity,
yield impact. A farmer who is a risk-averter or who is

*U.S. GOVERNMENT PRINTING OFFICE: 1977 722-669

187

TECHNICAL REPORT DATA
(Please read Inwwctions on the reverse before completingj
1. REPORT NO. 3. RECIPIENT'S ACCESSIOr+NO.
EPA-600/2-75-026b
4. TITLE AND SUBTITLE 5. REPORT DATE
June 1976
Control of Water Pollution from Cropland: Volume 1I__ 6. PERFORMING ORGANIZATION CODE
An Overview

7. AUTHOR(S) S. PERFORMING ORGANIZATION REPORT NO.
6. A. Stewart, D. A. Woolhiser, W. H. Wischmeir,
J. H. Caro, and M. H. Frere ARS-H-5-12
9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO.
Agricultural Research Service INB617
U.S. Department of Agriculture 11. CONTRACT/G RANT NO.
Washington, D.C. 20250 IAG D4-0485
12. SPONSORING AGENCY NAME AND ADDRESS 13. -F@PE OF REPORT AND PERIOD COVERED
inal Jan. '74 - June '76
Environmental Research Laboratory - Athens 14. SPONSORING AGENCY CODE
U.S. Environmental Protection Agency
Athens, Georgia 30601 EPA-ORD
15. SUPPLEMENTARY NOTES
Prepared as a joint publication of Office of Research and Development, EPA, and
Agricultural Research Service, USDA.
16-.A-B-ST RACT
Engineering and agronomic techniques to control sediment, nutrient, and
pesticide losses from cropland are identified, described, and evaluated. Method-
ology is developed to enable a user to identify the potential sources of pollutants,
select a list of appropriate demonstrated controls, and perform economic analyses
for final selection of controls. The basic principles on which control of specific
pollutants is founded are reviewed, supplementary information is provided, and
some of the documentation used in Volume I is presented. Volume I (Report No.
EPA-600/2-75-026a) -'s available from NTIS as report no. PB 249-517.

117. KEY WORDS AND DOCUMENT ANALYSIS
a DESCRIPTORS b. IDENTIFIERS/OPEN ENDED TERMS C. COSATi Field/Group
runoff agriculture 13 B
pesticides cropland
nutrients
non-point source pollution
hydrology
sedirrient control
erosion -1
18.-DISTRIBUTION STATEMENF__ 119. SECURITY CLASS (This Report) 21. NO. OF PAGES
Unl imited 20. SECURITY CLASS (Thispage) 22. PRICE

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