Control of
WATER POLLUTION
from cropland
Volume I
A manual for
guideline development
Agricultural Research Service *"* , Office of Research and Development
Department of Agriculture , ^4^ Environmental Protection Agency
-------
REVIEW NOTICE
This report has been reviewed by the Office of Research and Development and the
Agricultural Research Service and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
DOCUMENT AVAILABILITY
While supply lasts, single copies may be requested from:
(1) U.S. Environmental Protection Agency
Agriculture and Non-Point Source
Management Division (RD-682)
Washington, D.C. 20460
To order please cite
REPORT NO. EPA-600/2-75-026a
(2) U.S. Department of Agriculture
ARS Information — Room 343A
Federal Center Building - No. 1
Hyattsville, Maryland 20782
To order please cite
REPORT NO. ARS-H-5-1
The public may also purchase this document from the National Technical Information
Service, 5285 Port Royal Road, Springfield, Virginia 221-51 and from the Superintendent
of Documents, U.S. Government Printing Office, Washington, 1>.C. 20402
-------
Control of
WATER POLLUTION
from cropland
Volume I
A manual for
guideline development
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
Economic aspects were authored by J. R. Schaub, L. M. Boone, K. F. Alt, G. L. Horner,
and H. R. Cosper, 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.
NOVEMBER 1975
^tD ST*ff
Agricultural Research Service I rW? - Office of Research and Development
U.S. Department of Agriculture 1533Z/ Environmental Protection Agency
-------
FOREWORD
In the years ahead, U.S. fanners will have to increase food and fiber production to meet
domestic and world needs. Increased production will require greater use of chemicals and
more intensive management of available but limited cropland. Existing and new
production technology must be integrated into cropping systems that will assure
sustained crop production and simultaneously protect or enhance the quality of our
environment. These cropping systems must include management elements that control
soil erosion and prevent the discharge of pollutants from cropland into the Nation's
waters. To assist U.S. farmers in increasing food and fiber production while protecting the
environment, the Agricultural Research Service (USDA) and the Office of Research and
Development (EPA) are issuing this informational report. This report is Volume I.
Volume II is a literature review and provides supplementary information in greater detail
to support Volume I.
This technical report was designed for use in the development of management guidelines
and should be used in conjunction with local expertise. The scope of the report is limited
to problems of non-irrigated agricultural lands and is based on current understanding. The
scope will be expanded and the contents updated as additional information becomes
available from ongoing research.
This joint USDA/EPA report is published as partial fulfillment of provisions of the
Federal Water Pollution Control Act Amendments of 1972, Public Law 92-500, which
reaffirms the objective of restoring and maintaining the quality of the Nation's waters.
T. W. Edminster Wilson K. Talley
Administrator Assistant Administrator
Agricultural Research Service for Research and Development
U.S. Department of Agriculture Environmental Protection Agency
111
-------
CONTENTS
Section Page
1. INTRODUCTION 1
2. USE OF THE MANUAL 3
3. IDENTIFICATION OF POTENTIAL NONPOINT POLLUTION PROBLEMS 5
3.1 LAND RESOURCE AREAS 5
3.2 ESTIMATING POTENTIAL DIRECT RUNOFF 5
3.3 ESTIMATING POTENTIAL EROSION 7
3.3a Estimating Potential Cropland Sediment 11
3.3b The Universal Soil Loss Equation (USLE) 16
3.3c Sediment Delivery Ratios 21
3.4 ESTIMATING POTENTIAL PERCOLATION 25
3.5 LOCATION OF CROPLAND AND MAJOR CROP AREAS 27
3.6 USE OF PLANT NUTRIENTS ON CROPLAND 27
3.6a Fertilizers 27
3.6b Animal Wastes 37
3.7 USE OF PESTICIDES ON CROPLAND 45
4. POLLUTION CONTROL PRACTICES 61
4.1 PRACTICES TO CONTROL EROSION 61
4. la Quantifying Potential Soil Loss Reductions 69
4.1b Selecting Erosion Control Practices for Specific Land Areas 69
4.1c Tolerance Limits 70
4.2 PRACTICES TO CONTROL DIRECT RUNOFF 70
4.3 NUTRIENT MANAGEMENT PRACTICES 76
4.4 PESTICIDE MANAGEMENT PRACTICES 84
5. ECONOMIC CONSIDERATIONS 91
5.1 EFFECTS ON INDIVIDUAL PRODUCERS 91
5.2 AGGREGATE ECONOMIC AND SOCIAL EFFECTS 93
6. DECISION FLOW CHARTS AND EXAMPLES 97
6.1 FLOW CHARTS 97
6.2 EXAMPLE FOR A FIELD-SIZED AREA 97
6.3 EXAMPLE FOR A LARGE AREA 107
-------
LIST OF FIGURES
Page
Figure 1. Master flow chart 4
Figure 2. Land resource regions and major land resource areas of the United States 6
Figure 3. Average annual potential direct runoff g
Figure 4. Average growing season potential direct runoff 9
Figure 5. Percentage distribution of annual potential direct runoff in 28-day intervals. Summer row crop
(corn-straight rows) JQ
Figure 6. Croplands as percentages of total land resource areas 12
Figure 7. Croplands on which erosion is the dominant limitation for their agricultural use, as percentages of
total land resource areas 13
FigureS. Rangelands as percentages of total land resource areas 14
Figure 9. Relative potential contribution of cropland to watershed sediment yields 15
Figure lOa. Average annual values of the rainfail-erosivity factor, R 17
Figure 1 Ob. Estimated average annual values of the rainfail-erosivity factor, R, in Hawaii 18
Figure 11. Nomograph for determining soil-erodibility factor, K, for U.S. Mainland soils 19
Figure 12. Average annual potential percolation 26
Figure 13. Corn harvested for all purposes 28
Figure 14. Sorghums harvested for all purposes except sirup 29
Figure 15. Wheat harvested 30
Figure 16. Cotton harvested 31
Figure 17. Soybeans harvested for beans 32
Figure 18. Land in orchards 33
Figure 19. Vegetables harvested for sale 34
Figure 20. Cattle fattened on grain and sold for slaughter 38
Figure 21. Milk cows 39
Figure 22. Hogs and pigs 40
Figure 23. Chickens 3 months old or older 41
Figure 24. Broilers and other meat-type chickens 42
Figure 25. Mean annual total snowfall 43
Figure 26. Depth of frost penetration 44
Figure 27. Acreage of crops treated with herbicides 46
Figure 28. Acreage of non-hay crops treated with insecticides 47
Figure 29. Maximum persistence of classes of pesticides in soils under moderate climatic conditions 60
Figure 30. Monthly distribution of erosive rainfall as percentage of annual 62
Figure 31. Average monthly distributions of soil loss from a 4-year rotation of meadow-corn-corn-wheat in
western Iowa 66
Figure 32. Definition of ranges of reduction in mean growing season direct runoff 74
Figure 33. Corn growth and nutrient uptake 80
Figure 34. Potential nitrate loss by leaching from fall-applied ammonium to corn 81
Figure 35. Potential nitrate loss by leaching from spring-applied ammonium to corn 82
Figure 36. Flow chart for assessing erosion problems and selecting physically feasible control practices for
large areas 98
Figure 37. Flow chart for assessing erosion problems and selecting physically feasible control practices for
field-sized areas 99
Figure 38. Flow chart for assessing potential nutrient problems and selecting physically feasible control
practices 100
Figure 39. Flow chart for assessing potential pesticide problems and selecting physically feasible control
practices 101
Figure 40. The Suwannee Basin 108
vi
-------
LIST OF TABLES
Page
Table 1. Conditions indicative of high sediment-yield potential that can usually be identified by
observation 11
Table 2a. Indications of the general magnitude of the soil-erodibility factor, K 20
Table 2b. Soil credibility (K) values for ten benchmark soils of Hawaii 21
Table 3. Values of the erosion equation's topographic factor, LS, for specified combinations of slope length
and steepness 22
Table 4. Generalized values of the cover and management factor, C, in the 37 states east of the Rocky
Mountains 23
TableS. Values of support-practice factor, P 27
Table 6. Acres receiving fertilizer and average fertilizer rates of four crops in the United States in 1974 . . 35
Table 7. Plant-available nutrients in common fertilizers 35
Table 8a. Agricultural herbicides: types, transport modes, toxicities, and persistence in soil 48
Table 8b. Often-used trade-name synonyms of agricultural herbicides 50
Table 9a. Agricultural insecticides and miticides: types, transport modes, and toxicities 51
Table 9b. Often-used trade-name synonyms of agricultural insecticides and miticides 53
Table lOa. Agricultural fungicides: transport modes and toxicities 54
Table 1 Ob. Often-used trade-name synonyms of agricultural fungicides 55
Table 11. Major crops and principal pesticides registered for use on them throughout the United States ... 56
Table 12. Principal types of cropland erosion control practices and their highlights 63
Table 13. Approximate length limits for contouring 67
Table 14. Practices for controlling direct runoff and their highlights 72
Table 15. Potential direct runoff and percentage runoff reduction for selected locations 75
Table 16. Practices for the control of nutrient loss from agricultural applications and their highlights 77
Table 17. Approximate yields and nutrient contents of selected crops 78
Table 18. Practices for the control of pesticide loss from agricultural applications and their highlights .... 84
Table 19. Factors that should be considered in budgeting alternative nonpoint pollution control practices . . 92
Table 20. Cropping options selected in example for erosion control and their estimated annual soil loss .... 102
Table 21. Costs and returns for selected options 106
Vll
-------
Control of
WATER POLLUTION
from cropland
Volume I--A manual for guideline development
SECTION 1
INTRODUCTION
In today's agriculture, the use of chemicals is clearly
necessary to maintain high yields and high quality of our
agricultural products and to provide economic benefits
to the farmer and the consumer. In today's concern for
clean water, there are demands for preventing pollutants
from entering ground and surface waters. Consequently,
agricultural practices are being examined as to their
contribution to water pollution.
Sources of pollutants are usually classed as "point"
and "nonpoint". "Point" sources have received most of
the attention and are covered by a permit system. The
permit defines the requirements and the compliance
schedule that must be followed. "Nonpoint" sources are
diffuse in nature and discharge pollutants into waters by
dispersed pathways. Examples are construction activ-
ities, mining areas, stormwater runoff from urban areas,
and agricultural runoff. The nonpoint agricultural pollut-
ants of primary concern are sediment, nitrogen and
phosphorus compounds, and pesticides. Oxygen-
consuming organic compounds, dissolved salts, and other
pollutants are of less general concern and are beyond the
scope of this manual.
The purpose of the manual is to provide information
to individuals or agencies charged with developing plans
for the control or reduction of pollution from nonpoint
agricultural sources. Information on the sources, causes,
and potentials of sediment, nutrient, and pesticide losses
from cropland is dealt with in depth, as is information
on selecting cropping systems, tillage practices, and
other measures that may be necessary to control
pollutants. It is important to recognize that the manual
does not specify that nonpoint pollution from agricul-
tural sources is necessarily a problem. Also, the manual
does not establish pollution control goals or specific
criteria that should be met by a control plan, since this is
the responsibility of the States or other governing
bodies. Pollution from irrigation return flow, forestry
activities, and transport of pollutants by wind are
excluded. Rangelands are not discussed specifically, but
the principles presented for cropland will apply.
The information presented should be useful in select-
ing the control measures that are appropriate for the
special conditions imposed by the climate, soils, topog-
raphy, and farming practices of a particular land area.
The manual also presents procedures for estimating the
cost of various control practices at the farm level. The
regional and national economic impacts of certain
nonpoint pollution control methods are also discussed.
Although it is difficult to conceive of a system that
would completely eliminate all possible risks to the
environment from the use of agricultural chemicals,
practices and systems can be developed that will greatly
reduce such risks. Agricultural chemicals may be trans-
ported to streams and lakes in solution in runoff water,
suspended in runoff water, or adsorbed on the entrained
soil particles. Phosphates, organic nitrogen compounds,
and the persistent organochlorine insecticides are exam-
ples of materials that may be carried primarily on the
sediment; nitrate exemplifies a potential pollutant that is
dissolved in water. The reduction of runoff and erosion
will clearly reduce chemical transport; consequently,
measures directed specifically to runoff and erosion
reduction are included in the manual. However, com-
plete elimination of surface runoff is not generally
1
-------
realizable or desirable and some portion of the chemicals
may leave treated areas in the runoff that does occur.
Methods of managing the chemicals themselves to
minimize pollution are, therefore, also included.
General information is included for identifying the
regions of the country where the transport of chemicals
into streams in runoff water or by eroded soil could be
most severe and the principal classes of chemicals that
may be carried within a given region. Methods of
controlling or reducing losses of chemicals from individ-
ual fields are presented along with guidelines and
methodology for choosing the most appropriate
methods. Guidelines for selecting appropriate control
methods for regions are developed by selecting practices
suitable for the predominant agricultural conditions
within a region.
Quantitative information was used in the develop-
ment of these guidelines wherever it was available in
sufficiently general form that it could be utilized in a
nationwide manual. Because of the variation of climate,
soils, and agricultural practices throughout the United
States, no single group of control measures can be used
for every region nor will the regional information
presented herein be accurate for all areas within the
region. More detailed procedures that are consistent with
the basic principles and concepts described in this
manual should be used where the necessary information
is available.
This manual, which is designated as Volume I of a
two-volume set, provides a systematic procedure to aid
the user in identifying specific potential problems and
appropriate corrective measures. Volume II reviews the
appropriate basic principles on which the instructions
are founded and provides documentation of the informa-
tion presented.
Material in this manual is based on the contributions
of many persons in the Agricultural Research Service,
Economic Research Service, Extension Service, Forest
Service, State Agricultural Experiment Stations, Soil
Conservation Service, and others, and all contributions
are gratefully acknowledged.
-------
SECTION 2
USE OF THE MANUAL
Agencies charged with the development of a program
to control pollution in waters discharging from a given
land area will, with use of the systematic procedures
shown in this manual, be able to identify potential
nonpoint pollution problems within the area and to
recommend one or more practical measures for control-
ling any likely or existing problems. The most effective
use of this manual will be achieved when it is used as a
guide by a group of specialists for developing specific
guidelines for a localized area. For example, a State
Government, a Soil Conservation District, or other
agency could bring together fanners, scientists, engi-
neers, and other specialists who are familiar with the
area. These representatives, working as a group and using
the manual as a guide, could develop a list of specific
practices for the area that would control or reduce
pollution from nonpoint agricultural sources. This type
of local input is essential to arrive at the best possible
choice of practices.
The general procedure to be followed is shown in
Figure 1. The scheme depends primarily on the answers
resulting from a sequential series of questions embodied
in four flow charts (Figures 36, 37, 38, and 39 for
control of erosion in large areas, erosion in field-sized
areas, plant nutrients, and pesticides, respectively)
shown in Section 6. If all pollutants from nonpoint
sources are to be considered, the appropriate flow chart
for erosion control should be consulted first, as shown in
Figure 1, followed by the flow charts for nutrient and
pesticide control. Erosion should be addressed first
because eroded sediment is not only the most serious
water pollutant in itself, but also poses a double threat
in that it often carries along adsorbed nutrients or
pesticides. If, on the other hand, a specific pollutant is
of concern, any one of the four flow charts may be
entered and followed individually to obtain the appro-
priate control practices. Sections 3, 4, and 5 give some
information required to respond to the questions posed
in the flow charts with respect to problem identification
(Section 3), specific control measures (Section 4), and
economic considerations (Section 5). More detailed
information about the specific area should be developed
by the user group. To aid the user of the manual,
examples showing how the scheme is applied to specific
land areas are included in Section 6 following the flow
charts. The final operation in the master flow chart,
Figure 1, constitutes an overall evaluation process. This
evaluation should be done by persons having knowledge
of the specific land areas and conditions.
-------
Consider a Specific Land Area
Develop List of Accepted
Practices for Erosion Control
With Use of Appropriate
Erosion Control Flow Chart.
Figure 36, p. 98 , or 37, p. 99
Develop List of Accepted
Practices for Nutrient
Control With Use of
Nutrient Control Flow
Chart. Figure 38, p. 100
Develop List of Accepted
Practices for Pesticide
Control With Use of
Pesticide Control Flow
Chart. Figure 39, p. 101
Formulate a Control Program
From the Most Favorable Practices.
Estimate Impacts of Applying
Practices. Section 5, p. 91
Figure 1 .-Master flow chart.
-------
SECTION 3
IDENTIFICATION OF POTENTIAL NONPOINT POLLUTION PROBLEMS
There must be transport of agricultural pollutants
from fields to water bodies before they can cause a
pollution problem. It is important to recognize, how-
ever, that even when there is transport, concentrations
may not be at damaging levels. The transport.processes-
direct runoff, sediment movement, and percolation—are
largely controlled by natural conditions such as the
characteristics of the land and the climate of the area.
An understanding of the relationships involved as well as
of the behavior of the chemicals after application is
necessary before measures to control pollution can be
intelligently applied. This section provides information
to help the user obtain such an understanding by (1)
showing geographical distributions of factors relating to
potential pollutant losses from cropland, and (2)
presenting the principal considerations necessary for
interpretation of the data. This information is basic to
the use of the decision-making flow charts, shown later,
that will serve as a guide to the appropriate corrective
measures.
3.1 LAND RESOURCE AREAS
Geographic potentials for direct runoff, erosion, and
percolation are presented below for Land Resource
Areas. These Areas were delineated in a classification
system devised by the Soil Conservation Service of the
U. S. Department of Agriculture and described in detail
in Agriculture Handbook No. 296, "Land Resource
Regions and Major Land Resource Areas of the United
States", which is available from the U. S. Government
Printing Office.1 In brief, a Land Resource Area is
defined as a geographic area characterized by a particular
pattern of soil type, topography, climate, water re-
sources, land use, and type of farming. The 156 Land
Resource Areas of the contiguous 48 states are shown in
Figure 2, along with their combinations into major Land
Resource Regions.
'Agriculture Handbook No. 296 is currently being revised.
The anticipated revisions include the subdivision of some of the
larger Land Resource Areas (such as 133 in the Southeast) and
should have only a minor effect on the material presented in this
manual.
Although it is recognized that considerable differ-
ences occur within a Land Resource Area, this unit is
used as an aggregate for presenting information relative
to water erosion and pollution. These units provide a
means of considering rather large areas, and the same
principles can be applied to smaller units where more
detailed information is available.
3.2 ESTIMATING POTENTIAL DIRECT
RUNOFF
Runoff (or streamflow) is that portion of the
precipitation that appears in surface streams. Precipita-
tion that falls on an arbitrary land area and eventually
becomes runoff may be classified as either surface
runoff, subsurface runoff, or groundwater runoff,
depending on the path of flow to the stream. Surface
runoff (or overland flow) is water that travels over the
ground surface to reach a stream. Subsurface runoff
(also called subsurface flow, interflow, subsurface storm-
flow, or storm seepage) is water that has infiltrated the
surface soil and moved laterally through the upper soil
horizons toward the stream as shallow saturated flow
above the main groundwater level. Groundwater runoff
(or groundwater flow) is water that has infiltrated the
surface soil, percolated to the general groundwater table,
and then moved laterally to reappear in the stream.
Surface runoff moves rather rapidly and is present
during and shortly after a storm. Subsurface runoff
moves somewhat more slowly than surface runoff, but
appears in the stream during or shortly after a storm.
Groundwater runoff may be in transit for days or years
before it reaches a stream. These three types of runoff
are not mutually exclusive in that an individual parcel of
water may use any one or combinations of more than
one of these modes of travel to a stream.
The amount of water that moves by each of these
three routes must be known before the transport of
agricultural chemicals from a field can be described in
detail. Surface runoff may carry chemicals in solution, in
suspension, or adsorbed to suspended soil particles.
Subsurface runoff and groundwater runoff can only
carry soluble chemicals that are not strongly adsorbed to
-------
AM) l< KOI- KI-XMONS \M» \i.\jdu I v\l> U1.S,,| |« ;| \KK\S
01 rill- IMTI-DSI Mis „„,«,» ...Atak..^ ii!
Figure 2.- Land resource regions and major land rcsouicc areas of the United States.
-------
soil particles. Because of the large travel time involved, a
nonpersistent chemical transported by groundwater run-
off may not be a hazard when it reaches a surface
stream. For example, nitrates that have leached below
the root zone could be denitrified if the groundwater
runoff is discharged to a surface stream through wet soils
where anaerobic conditions exist and an energy source is
present.
Maps of average annual "surface-water" runoff such
as those published by the U. S. Geological Survey are
based on measurements of streamflow and include
various amounts of surface runoff, subsurface runoff,
and groundwater runoff from watersheds with substan-
tial variations in land use. Because the pathway that
water takes from a field to a stream largely determines
what types and how much of a chemical may be
transported to a stream, the three types of runoff need
to be estimated separately to assess potential problems.
Rainfall and runoff data from plots and small
watersheds with various land uses and treatments have
been obtained at many locations in the United States
during the past 40 years. Unfortunately, with the type
of instrumentation used, it is not possible to separate
surface runoff from subsurface runoff, so these two
components are lumped together with precipitation
falling on the channels and called direct runoff. These
direct runoff data provide good estimates of surface
runoff because it is the primary component of direct
runoff from plots and small watersheds and, for most
agricultural plots, it is the only component.
Utilizing extensive plot and small watershed data, the
Soil Conservation Service, USDA, developed an empiri-
cal equation for predicting direct runoff from any given
rainfall. Although the Soil Conservation Service proce-
dure is highly simplified, it produces reasonable esti-
mates of direct runoff and is the only method that has
parameters defined nationally and that can be used with
readily available data. The different infiltration charac-
teristics of soils are accounted for by classifying soils
into four hydrologic soil groups based on the minimum
rate of infiltration obtained for bare soil after prolonged
wetting. "Curve numbers" have been developed for
several crops and management practices which, when
used in the equation, can show the effect of changes of
crops or land management practices on direct runoff.
For more detailed information on the Soil Conservation
Service procedure for estimating direct runoff, see
Appendix A, Volume II.
Potential direct runoff is defined here as the direct
runoff predicted by the Soil Conservation Service runoff
estimation procedure for an index row crop. Corn,
planted in straight rows, was chosen as the index crop
because it is grown widely in the United States and has
direct runoff characteristics similar to those of several
other row crops (cotton or soybeans, for example).
Straight rows were chosen because they have the highest
direct runoff potential of any cropland management
practice.
Potential direct runoff for each of the four hydro-
logic soil groups was simulated for a 20- to 25-year
period by using the Soil Conservation Service procedure
and daily precipitation data for 52 meteorological
stations in the 48 contiguous states. Most of the Western
United States was omitted because: (1) Rainfall gradi-
ents are usually steep and interpolation between widely
separated weather stations would be subject to large
errors; and (2) much of the cropland is irrigated, so the
SCS method of estimating direct runoff could not be
used without extensive modification. Mountainous,
forested, and swamp areas were also omitted because
they contained insignificant cropland. A degree-day
method was used to estimate snowmelt. A detailed
description of the simulation procedure used, maps of
potential mean-annual direct runoff and mean-growing-
season direct runoff for each hydrologic soil group, and
a brief analysis of relative errors are included in
Appendix A, Volume II.
Average annual and average growing season (planting-
to-harvest) potential direct runoff estimates for the
predominant agricultural soils in each Land Resource
Area are shown in Figures 3 and 4. The annual potential
direct runoff is the runoff estimated for a specified
condition and is not the actual direct runoff for a field.
It is only an index of the relative hazard of transport of
persistent chemicals in solution or suspension in surface
runoff. The growing-season potential direct runoff is
probably a better index of loss of nonpersistent pesti-
cides than is the annual potential direct runoff.
The time distribution of direct runoff within a year
may be an important consideration in the selection of a
chemical or its time of application. The percentage of
annual potential direct runoff occurring in each 28-day
period beginning January 1 is shown in Figure 5.
More detailed maps of potential direct runoff could
be prepared on a state or watershed basis by using
published or unpublished soil survey maps available from
the Soil Conservation Service.
3.3 ESTIMATING POTENTIAL EROSION
Sediment, which is an end product of soil erosion, is
by volume the greatest single pollutant of surface waters,
and it is also the principal carrier of some of the
chemical pollutants. In some watersheds, sediment from
7
-------
'
Mountain , Forest, Swamps , Desert
or Steep Rainfall Gradients
Figure 3.- Average annual potential direct runoff.
-------
> 7
n Mountain , Forest, Swamps , Deserts
or Steep Rainfall Gradient
Ngure 4.- Average growing season potential direct runoff.
-------
Figure 5.-Percentage distribution of annual potential direct runoff in 28-day intervals. Summer row crop (corn-straight rows).
-------
nonagricultural sources exceeds that from cropland, and
in regions of relatively low rainfall or sandy soils, wind
erosion may exceed water erosion. However, for the
purposes of this manual, the interest is in sediment from
cropland erosion by rainfall and runoff.
Although classified as nonpoint. most of a water-
shed's sediment may come from a few relatively small
areas that need special attention. Table 1 lists likely
sources that can usually be identified by observation.
Both agricultural and nonagricultural sources should be
identified, so that the sediment from the latter will not
be inadvertently ascribed to the cropland. A recent
estimate attributes about half of our country's total
sediment to cropland sources, but this ratio cannot be
applied to all watersheds.
For several decades, selections of cropland erosion-
control practices have been guided by estimates of the
average annual rates of soil movement from the field
Table 1. Conditions indicative of high sediment-yield
potential that can usually be identified by observation.
Cropland
1. Long slopes farmed without terraces or runoff diversions
2. Rows up and down moderate or steep slopes
3. No crop residues on surface after new crop seeding
4. No cover between harvest and establishment of new crop
canopy
5. Intensively farmed land adjacent to stream without inter-
vening strip of vegetation
6. Runoff from upslopc pasture or rangeland flowing across
cropland
7. Poor stands or poor quality of vegetation
Other Sources
1. Gullies
2. Residential or commercial construction
3. Highway construction
4. Poorly managed range, idle, or wooded areas
5. Unstablized streambanks
6. Surface mining areas
7. Unstablized roadbanks
8. Bare areas of noncropland
slopes. On this basis, potential water erosion losses range
from negligible to more than 100 tons per acre. A 1967
conservation needs inventory showed that about 20
percent of our country's 438 million acres of cropland
were averaging more than 8 tons of soil loss per acre per
year, 30 percent were averaging less than 3 tons, and the
other 50 percent between 3 and 8 tons. A ton of dry soil
is approximately 1 cubic yard in volume. Spread
uniformly over an acre of surface, it would have a depth
of less than one-hundredth of an inch.
Field soil loss data provide excellent guides for plans
to preserve the long-range productivity of our land
resource, but they are not quantitative estimates of
cropland contributions to watershed sediment. Most
eroded soil particles come to rest many times, and must
be moved again many times, before they reach a
continuous stream system. Fractions of the soil eroded
from upslope areas that actually reach a continuous
stream are discussed under Sediment Delivery Ratios,
Section 3.3c.
Erosion hazards are so extremely local in nature that
soil loss estimates and control guides can be accurate
only on a field basis. Procedures for use of this approach
will be presented, but first we will consider guides for
general appraisals of potential cropland-sediment hazards
on a broader scale.
3.3a Estimating Potential Cropland Sediment
The potential cropland contribution to sediment in
streamflow depends on the erosion rate, the sediment
delivery ratio, and the cropland density. Figures 6, 7,
and 8 were developed from the 1967 USDA Research
Needs Inventory data. Figure 6 shows cropland acreages
as percentages of total land area for the 156 major Land
Resource Areas that were defined in Figure 1. Figure 7
shows the distribution of cropland on which soil erosion
is the dominant limitation for agricultural use. Figure 8
shows percentages of rangeland and will help to account
for the sometimes quite substantial sediment content of
streamflows in resource areas having relatively little
cropland. The sparse natural cover on much of the
rangeland cannot protect the soil surface against the
occasional erosive rainstorms.
Neither actual nor potential erosion rates have been
quantitatively mapped nationally because they are
extremely localized. Soil properties, slope steepness, and
slope lengths usually vary widely even within a single
resource area. The important soil, topographic, and
cultural practice details are generally available only on a
locality basis. However, the geographic trends in the
levels of these parameters and in rainfall pattern were
estimated in relative terms and used to develop Figure 9.
11
-------
10 to 24.9%
] 25 to 49.9%
| 50 to 74.9 %
I 75 to 100 %
Figure 6.-Croplands as percentages of total land resource areas.
-------
Figure 7.-Croplands on which erosion is the dominant . Dilation lor their agricultural use as percentages of total land resource areas.
-------
5 to 25 %
25 to 50%
50 to 75 %
> 75 %
f-'igure X.- Range-buds ;is peixcntapcs ol total land resource
-------
Low
Moderate
High
Very High
Figure 9.- Relative potential contribution of cropland to watershed sediment yields.
-------
Figure 9 shows generalized regional differences in
potential sediment from cropland erosion by water. An
estimated erosion-potential index for each Land
Resource Area (LRA) was multiplied by the percentage
of the LRA in cropland. The erosion-potential index for
an LRA was derived as the acreage-weighted average of
indexes for all the respective land-use capability sub-
classes represented on the cropland. The index for each
subclass was an estimate of the erosion that would occur
on its predominant soil and slope if it were continuously
in a row crop or grain-fallow system with no conserva-
tion practices. The map reflects differences in sediment-
delivery ratios only to the extent that they may be
reflected in the cropland densities. The objective was to
show relative potential; actual erosion rates for relatively
uniform areas can be computed by the Universal Soil
Loss Equation, discussed later.
A first approximation of the cropland-sediment
potential in a particular region or watershed can be
obtained from Figure 9, and the problem can be further
defined by reference to Figures 7 and 8. For example, if
Figure 9 rates the area low but water quality samplings
show excessive sediment in a stream, Figure 8 may
suggest rangeland as the most likely source. If the area is
also rated low in Figure 8, existence of one or more of
the other special-problem areas listed in Table ] would
be suspected. A rating of moderate in Figure 9 with a
relatively low percentage rating in Figure 7 would
suggest that only a relatively small portion of the area
needs attention but that treatment on that portion may
need to be substantial. A moderate rating in Figure 9
with a high rating in Figure 7 would suggest widespread
need of relatively simple control measures. A rating of
high or very high in Figure 9 would indicate a more
critical problem, but the comparisons with Figure 7
ratings would still help to define the problem more
accurately with respect to its areal extent and com-
plexity of likely treatment needs. However, high ratings
in Figures 7 and 9 do not necessarily mean that
agriculture is the source of the stream sediment. One or
more of the nonagricultural situations listed in Table I
may be the primary sediment source. Figure 9 shows
potential hazard, not current practices. Adequate con-
trol practices may already exist on the problem crop-
land. The Soil and Water Conservation Districts or the
Soil Conservation Service can supply data on how much
of the potential problem acreage is already controlled
under existing conservation plans.
An alternative procedure for appraising the cropland
sediment hazard and treatment needs in a relatively
homogeneous region is to apply the individual-field
approach to a hypothetical field that is representative of
the soil and topographic features of the cropland in the
16
region. This approach utilizes the soil-loss prediction
technique described below.
3.3b The Universal Soil Loss Equation (USLE)
The msp in Figure 9 has serious limitations in that it
does not reflect the large local differences in erosion
hazard. Gross-erosion prediction and control planning
can be much more accurate on a field basis. More than
40 years of erosion research by the U. S. Department of
Agriculture in cooperation with state agricultural experi-
ment stations has identified the major erosion factors
and determined numerical relationships of these factors
to soil loss rates. The USLE combines these factors and
relationships to predict average annual soil losses from
sheet and rill erosion by rainfall and its associated runoff
on specific field slopes.
Basically, the USLE has no geographic bounds, but its
application requires knowledge of the local values of its
individual factors. Its applicability in some regions is
presently limited by lack of research data from which to
obtain factor evaluations that are truly representative of
the climatic, physical and cultural conditions. In the
factor definitions below, the most serious knowledge
gaps are noted in parentheses. However, the available
information is adequate for the equation to provide
useful guides on most of our country's cropland.
The equation is:
A = R K LS C P
where A is the estimated average annual soil loss in tons
per acre and the other terms are defined as follows:
R is the rainfall and runoff erosivity index. Its local
value can generally be obtained by interpolating
between the iso-value lines of Figures lOa and lOb.
(Exceptions are the Coastal Plains of the Southeast
and the area that is shaded in Figure lOa. R values
presently used in the Coastal Plains do not exceed
350. In the shaded region of the Northwest, the
map values must be increased to account for effect
of runoff from thaw and snowmelt. Estimated
adjustments for specific locations in the shaded
region can be obtained from the Soil Conservation
Service Regional Technical Center, Portland,
Oregon. Research is needed to determine the
effective R values in these two regions more
accurately. For Hawaii, use Figure lOb.)
K is the soil-erodibility factor. It is the average soil
loss per unit of R under arbitrarily selected
"basic" conditions, and depends on soil properties.
The value of K for most of the U.S. mainland soils
can be obtained from Figure 11 if adequate soil
survey information is available. Values for specific
-------
35
'
pa
3
C
EL
o
tn
O
re
—
5'
r»
0
-------
oo
190
o
cr
o
d.
3
-
320
MAUI
150
190
KAUAI
!90
OAHU
MOLOKAI
-------
- vtry tin* granular
2-tin* granular
3-m«d or coorti granular
4-blocky, ploty, or mattiv*
* SOIL STRUCTURE
PERMEABILITY
PERCENT SAND
(0.10-2.Omm)
6- very slow
5- »low
4- slow to mod.
3- modtrott
2- mod to rapid
I - rapid
PROCEDURE: With appropriate data, enter scale at left and proceed to points representing
the soil's % s«nd (0.10-?.0 im), % organic nutter, structure, and permeability, In that sequence
Interpolate between plotted curves. The dotted line Illustrates procedure for a soil having
sl+vfs 651, sand 51, OH 1.91, structure 2, permeability 4. Solution: K - 0.31.
Figure 11.-Nomograph for determining soil-crodibility factor, K, for U.S. Mainland soils.
-------
soils are also available from state and local offices
of the Soil Conservation Service. Gross approxima-
tions based primarily on soil texture can be
obtained from Table 2a. Values for ten benchmark
soils in Hawaii are given in Table 2b. (Figure 11 is
less accurate for high-clay subsoils and sandy
loams than for the broad intermediate range of
medium-textured soils.)
LS is a dimensionless topographic factor that repre-
sents the combined effects of slope length and
steepness. Values of LS for uniform slopes are
given in Table 3. (The relationships on which the
table is based were derived from data taken on
slopes no steeper than 18 percent and no longer
than 300 feet. How much these dimensions can be
exceeded before these relationships change has not
been determined.)
C is the cover and management factor. C values range
from 0.001 for well-managed woodland to 1.0 for
tilled, continuous fallow. C for a given cropping
and management system varies with rainfall dis-
tribution and planting dates. Generalized values
for illustrative purposes are given in Table 4. Local
values can be computed by a procedure published
in Agriculture Handbook No. 282, or computed
values may be obtained from the Soil Conservation
Service.
P is the factor for supporting practices. Its value can
be obtained from Table 5. With no support
practices, P= 1.0.
Factors R, K, and LS are relatively fixed for a given
location. Their product is the basic erosion-potential
index, I, for the particular combination of rainfall
pattern, soil properties and topographic features. This is
the average annual soil loss that would occur without
any vegetation or erosion-reducing practices. Multiplying
this potential by appropriate values of factors C and P
reduces it for effects of the cropping system, cultural
management, and supporting control practices, so that
the complete equation predicts average annual soil loss
for specific cropland situations.
With the soil loss equation, estimating average annual
erosion rates at a particular site is a routine procedure.
Appropriate values of R, K, LS, C, and P are selected
from the sources indicated above. The product of all five
factors is the soil loss estimate for the cropping and
management system represented by the selected C and P
values.
The USLE can be very useful as a planning guide and
is the most feasible method available for calculating
sheet and rill erosion from specific land areas in most of
the United States. However, soil losses computed by the
equation must be accepted as estimates rather than as
20
absolutes. Derivations of site values of the equation's
five factors are based on relationships derived from the
erosion research of the past 40 years. These relationships
can, in specific situations, be significantly influenced by
interactions with other variables. Local weaknesses in
some of the primary factor values were pointed out
above. Sediment from gullies and channel erosion is not
included in USLE estimates.
The soil loss equation and supporting data tables were
designed to predict longtime average losses for specific
conditions. Specific-year losses may be substantially
greater or smaller than the annual averages because of
differences in the number, size and timing of erosive
rainstorms and in other weather parameters. The fre-
Table 2a. Indications of the general magnitude of the
soil-erodibility factor, K1
Texture class
Sand
Fine sand
Very fine sand
Loamy sand
Loamy fine sand
Loamy very fine sand
Sandy loam
Fine sandy loam
Very fine sandy loam
Loam
Silt loam
Silt
Sandy clay loam
day loam
Silty clay loam
Sandy clay
Silty clay
Clay
Organic matter content
-------
quency distribution of the rainfall factor, R, differs by
location, but the following generalities provide some
indication of the magnitude of yearly variations in R
value: less than average about 60 percent of the time;
greater than average about 40 percent of the time; 10
percent probability of being 50 percent greater than
average; 5 percent probability of being 75 percent
greater than average. A single extreme runoff event
shortly after crop seeding on clean-tilled seedbed could
erode as much soil as the annual average for the rotation,
but the probability of this is small.
3.3c Sediment Delivery Ratios
The soil loss equation computes gross sheet and rill
erosion but does not directly predict downstream
sediment yield. Sediment yield equals the gross erosion
minus what is deposited enroute to the place of
measurement. Materials derived from sheet and rill
erosion often move only short distances and may lodge
in areas remote from the stream system. They may
remain in the same fields in which they originated or be
deposited on more level slopes.
The sediment delivery ratio is defined as the ratio of
sediment delivered at a location in the stream system to
the gross erosion from the drainage area above that
point. Where this ratio is known or can be closely
approximated from known parameters, the sediment
yield is estimated by computing the gross erosion and
multiplying it by the sediment delivery ratio. This
method of computing sediment yields at points down-
stream has been used extensively and for many years by
the Soil Conservation Service, particularly in the humid
sections of the country.
Many factors influence the sediment delivery ratio.
No general equation for watershed delivery ratios has
been derived, but several observed relationships provide
guidelines for approximating them.
Size of drainage area is an important factor, because
the distance of sediment transport to downstream points
is greater in the larger watersheds, and the opportunities
Table 2b. Soil erodibility (K) values for ten benchmark soils of Hawaii.
Order
Ultisols
Oxisols
Oxisols
Vertisols
Aridisols
Inceptisols
Inceptisols
Inceptisols
Inceptisols
Inceptisols
Suborder
Humults
Torrox
Ustox
Usterts
Orthids
Andepts
Andepts
Andepts
Andepts
Tropepts
Great group
Tropohumults
Torrox
Eutrustox
Chromusterts
Camborthids
Dystrandepts
Eutrandepts
Eutrandcpts
Hydrandepts
Ustropepts
Subgroup
Humoxic
Tropohumults
Typic Torrox
Tropeptic
Eutrustox
Typic
Chromusterts
Ustollic
Camborthids
Hydric
Dystrandepts
Typic
Eutrandepts
Entic
Eutrandepts
Typic
Hydrandepts
Vertic
Ustropepts
Family
Clayey, kaolinitic,
isohyperthermic
Clayey, kaolinitic,
isohyperthermic
Clayey, kaolinitic,
isohyperthermic
Very fine,
montmorillonitic,
isohyperthermic
Medial, isohyperthermic
Thixotropic, isothermic
Medial, isohyperthermic
Medial, Isohyperthermic
Thixotropic,
isohyperthermic
Very fine, kaolinitic,
isohyperthermic
Series
Waikane
Molokai
Wahiawa
Lualualei
Kawaihae
(Extremely
stony phase)
Kukaiau
Naolehu
(Variant)
Pakini
Hilo
Waipahu
K
0.10
.24
.17
.28
.32
.17
.20
.49
.10
.20
21
-------
Table 3. Values of the erosion equation's topographic factor, LS, for specified combinations of slope
length and steepness.1
% Slope
0.5
1
2
3
4
5
6
8
10
12
14
16
18
20
25
30
40
50
60
Slope length (feet)
25
0.07
0.09
0.13
0.19
0.23
0.27
0.34
0.50
0.69
0.90
1.2
1.4
1.7
2.0
3.0
4.0
6.3
8.9
12.0
50
0.08
0.10
0.16
0.23
0.30
0.38
0.48
0.70
0.97
1.3
1.6
2.0
2.4
2.9
4.2
5.6
9.0
13.0
16.0
75
0.09
0.12
0.19
0.26
0.36
0.46
0.58
0.86
1.2
1.6
2.0
2.5
3.0
3.5
5.1
6.9
11.0
15.0
20.0
100
0.10
0.13
0.20
0.29
0.40
0.54
0.67
0.99
1.4
1.8
2.3
2.8
3.4
4.1
5.9
^ 8.0
13.0
18.0
23.0
150
0.11
0.15
0.23
0.33
0.47
0.66
0.82
1.2
1.7
2.2
2.8
3.5
4.2
5.0
7.2
9.7
16.0
22.0
28.0
200
0.12
0.16
0.25
0.35
0.53
0.76
0.95
1.4
1.9
2.6
3.3
4.0
4.9
5.8
8.3
11.0
18.0
25.0
--
300
0.14
0.18
0.28
0.40
0.62
0.93
1.2
1.7
2.4
3.1
4.0
4.9
6.0
7.1
10.0
14.0
22.0
31.0
--
400
0.15
0.20
0.31
0.44
0.70
1.1
1.4
2.0
2.7
3.6
4.6
5.7
6.9
8.2
12.0
16.0
25.0
--
500
0.16
0.21
0.33
0.47
0.76
1.2
1.5
2.2
3.1
4.0
5.1
6.4
7.7
9.1
13.0
18.0
28.0
--
600
0.17
0.22
0.34
0.49
0-82
1.3
1.7
2.4
3.4
4.4
5.6
7.0
8.4
10.0
14.0
20.0
31.0
--
800
0.19
0.24
0.38
0.54
0.92
1.5
1.9
2.8
3.9
5.1
6.5
8.0
9.7
12.0
17.0
23.0
--
--
1000
0.20
0.26
0.40
0.57
1.0
1.7
2.1
3.1
4.3
5.7
7.3
9.0
11.0
13.0
19.0
25.0
--
"
1 Values given for slopes longer than 300 feet or steeper than 18% are extrapolations beyond the range of the research data and,
therefore, less certain than the others. Adjustments for irregularity of slope are discussed in Volume II.
for deposition enroute are more numerous. The sedi-
ment discharged to large rivers is usually less than
one-fourth of that eroded from the land surface.
Sediment delivery ratios vary widely for any given size
of drainage area, but limited data have shown that,
roughly, they vary inversely as the 0.2 power of drainage
area. Rough estimates of delivery ratios can be made
from the following tabulation:
Drainage Area
(Square Miles)
0.5 . .
1 . .
5 . .
10 . .
50 . .
100 . .
200 . .
Sediment Delivery
Ratio
. . 0.33
.30
.22
.18
.12
.10
.08
However, the above estimates should be tempered
with judgment and consideration of other factors, such
as texture, relief, type of erosion, the sediment transport
systems, and areas of deposition within the watershed.
For example, when the eroding soil is very high in silt or
clay, the delivery ratio will be higher than indicated in
the tabulation; when the texture is coarse, it will be
lower. A transport system with a high channel density
generally has a high delivery ratio. The condition of the
channels (whether clogged or open, meandering or
straight) influences velocity and consequently the
delivery ratio. High stream gradients are generally
associated with steep slopes and high relief and provide
efficient transport of eroded material. The opposite is
true for low stream gradients.
The shape of the land surface is an inherent feature of
the physiographic region in which the watershed is
located. High relief is often indicative of high sediment
delivery ratios. The relief/length ratio apparently has a
substantial effect on the delivery ratio. The relief is the
difference between the average elevation of the water-
shed divide at the headwaters of the main stem drainage
and the elevation of the streambed at the point of
sediment yield measurement. Length is the maximum
valley length, measured essentially parallel to the main
22
-------
Table 4. Generalized values of the cover and management factor, C, in the 37 states east of the Rocky Mountains.1
Line ,
no Crop, rotation, and management
Base value: continuous fallow, tilled up and down slope
CORN
1 C, RdR, fallTP, conv(l)
2 C, RdR, spring TP, conv (1 )
3 C, RdL, fall TP, conv (1)
4 C, RdR, we seeding, spring TP, conv (1)
5 C, RdL, standing, spring TP, conv (1)
6 C, fall shied stalks, spring TP, conv (1)
7 C(silage)-W(RdL, fall TP) (2)
8 C, RdL, fall chisel, spring disk, 40-30% re (1)
9 C(silage), W we seeding, no-till pi in c-k \V (1 )
10 C(RdL)-W(RdL, spring TP) (2)
1 1 C, fall shred stalks, chisel pi , 40-30% re (1 )
1 2 C-C-C-W-M, RdL, TP for C, disk for W (5)
13 C, RdL, strip till row zones, 55-40% re (1)
14 C-C-C-W-M-M, RdL, TP for C, disk for W (6)
15 C-CVW-M, RdL, TP for C, disk for W (4)
16 C, fall shred, no-till pi, 70-50% re (1 )
1 7 C-C-W-M-M, RdL, TP for C, disk for W (5 )
18 C-C-C-W-M, RdL, no-till pi 2d & 3rd C (5)
19 C-C-W-M, RdL, no-till pi 2d C (4)
20 C, no-till pi in c-k wheat, 90-70% re (1 )
21 C-C-C-W-M-M, no-till pi 2d & 3rd C (6)
22 C-W-M, Rd L, TP for C, disk for W (3 )
23 C-C-W-M-M, RdL, no-till pi 2d C (5)
24 C-W-M-M, RdL, TP for C, disk for W (4)
25 C-W-M-M-M, RdL, TP for C, disk for W (5)
26 C, no-till pi in c-k sod, 95-80% re (1)
COTTON4
27 Cot, conv (Western Plains) (1 )
28 Cot, conv (South) (1)
MEADOW
29 Grass & Legume mix
30 Alfalfa, lespedeza or Sericia
3 1 Sweet clover
SORGHUM, GRAIN (Western Plains)4
32 RdL, spring TP, conv (1)
33 No-till pi in shredded 70-50% re
Productivity level2
High
Mod.
C value
1.00
0.54
.50
.42
.40
.38
.35
.31
.24
.20
.20
.19
.17
.16
.14
.12
.11
.087
.076
.068
.062
.061
.055
.051
.039
.032
.017
0.42
.34
0.004
.020
.025
0.43
.11
1.00
0.62
.59
.52
.49
.48
.44
.35
.30
.24
.28
.26
.23
.24
.20
.17
.18
.14
.13
.11
.14
.11
.095
.094
.074
.061
.053
0.49
.40
0.01
0.53
.18
23
-------
Table 4. Generalized values of the cover and management factor, C, in the 37 states east of the
Rocky Mountains.' —Continued
T .
LjnC
no.
Crop, rotation, and management3
SOYBEANS4
34
35
36
37
WHEAT
38
39
40
41
42
43
44
45
46
47
48
49
B, RdL, spring TP, conv (1)
C-B, TP annually, conv (2)
B, no-till pi
C-B, no-till pi, fall shred C stalks (2)
W-F, fall TP after W (2)
W-F, stubble mulch, 500 Ibs re (2)
W-F, stubble mulch, 1000 Ibs re (2)
Spring W, RdL, Sept TP, conv (N & S Dak) (1)
Winter W, RdL, Aug TP, conv (Kans) (1)
Spring W, stubble mulch, 750 Ibs re (1 )
Spring W. stubble mulch, 1250 Ibs re (1)
Winter W, stubble mulch, 750 Ibs re (1 )
Winter W, stubble mulch, 1250 Ibs re (1 )
W-M. conv (2)
W-M-M, conv (3)
W-M-M-M, conv (4)
Productivity level2
High
Mod.
C value
0.48
.43
.22
.18
0.38
.32
.21
.23
.19
.15
.12
.11
.10
.054
.026
.021
0.54
.51
.28
.22
This table is for illustrative purposes only and is not a complete list of cropping systems or potential practices. Values of C differ
with rainfall pattern and planting dates. These generalized values show approximately the relative erosion-reducing effectiveness of
various crop systems, but locationally derived C values should be used for conservation planning at the field level. Tables of local
values are available from the Soil Conservation Service.
2 High level is exemplified by long-term yield averages greater than 75 bu. corn or 3 tons giass-and-legume hay; or cotton manage-
ment that regularly provides good stands and growth.
3 Numbers in parentheses indicate number of years in the rotation cycle. No. (1) designates a continuous one-crop system.
4 Grain sorghum, soybeans, or cotton may be substituted for com in lines 12,14,15, 17-19, 21-25 to estimate C values for sod-
based rotations.
Abbreviations defined:
B - soybeans
C - corn
c-k - chemically killed
conv - conventional
cot - cotton
F -fallow
M - grass & legume hay
pi - plant
W -wheat
we - winter cover
Ibs re - pounds of crop residue per acre remaining on surface after new crop seeding
% re - percentage of soil surface covered by residue mulch after new crop seeding
70-50% re - 70% cover for C values in first column; 50% for second column
RdR - residues (corn stover, straw, etc.) removed or burned
RdL - all residues left on field (on surface or incorporated)
TP - turn plowed (upper 5 or more inches of soil inverted, covering residues)
24
-------
stem drainage from the watershed divide to the point of
yield measurement.
The sediment delivery ratio is usually based on total
erosion in the drainage area. This includes channel-type
erosion (gullies, valley trenches, streambank erosion,
etc.) along with sheet and rill erosion. Gross erosion
computations by the soil loss equation do not include
channel-type erosion, and this must be computed sepa-
rately if total sediment yield is desired. The delivery
ratios may differ significantly for the sediments from the
two types of sources. Channel erosion produces sedi-
ment that is immediately available to the transport
system, and much of it tends to remain in motion as
bedload and suspended sediment. A substantial reduc-
tion in the amount of sediment delivered to a stream
may sometimes result in a compensatory increase in
channel erosion. However, the composition of sediment
derived from channel erosion will usually differ substan-
tially from that derived from sheet and rill erosion on
cropland.
Settling basins, sediment traps, and vegetative filter
strips across the lower end of a slope trap sediments near
their origin, but their effect will not be reflected in the
sediment delivery ratios tabulated above. Therefore, the
portion of the sediment that is trapped by these devices
should be deducted from the computed field erosion
before applying the delivery ratio. Strip crop data
indicate that a 100- to 125-ft. wide filter strip of good
sod across the slope should filter about 75 percent of the
sediment from normal field runoff on moderate slopes.
With a properly designed terrace system, less than 20
percent of the soil eroded from the between-terrace
areas is transported completely off the field. The trap
efficiencies of settling basins and sediment traps vary
with design and location.
3.4 ESTIMATING POTENTIAL
PERCOLATION
Water that infiltrates the soil and percolates below
the root zone will eventually reach the water table and
may carry soluble agricultural chemicals to a well or to a
surface stream as groundwater runoff. The amount and
frequency of deep percolation depend on the precipita-
tion characteristics, the evapotranspiration potential, the
vegetative cover, the soil water storage characteristics in
the root zone, the soil and geologic conditions below the
root zone, and the amount and timing of direct runoff.
Potential percolation is defined here as the annual
amount of water that would percolate below the root
zone in a field of corn planted in straight rows.
Potential percolation was simulated for each of the
four hydrologic soil groups for a 20- to 25-year period
using precipitation data for 52 meteorological stations in
the contiguous United States. Available water-holding
capacity (the difference between field capacity and the
wilting point) in the root zone was estimated for the
predominant agricultural soils in each Land Resource
Area. The root-zone depth was taken as 4 feet for most
of the Land Resource Areas. Lesser depths were used in
some instances, based on the characteristics of the
predominant agricultural soils. Direct runoff was esti-
mated as described in Section 3.2. Potential evapotran-
spiration estimates were based on smoothed average
daily pan evaporation data multiplied by a pan coeffi-
cient. The mean annual potential percolation is shown in
five classes by Land Resource Areas in Figure 12. Most
of the Western United States was omitted for the reasons
mentioned in Section 3.2. Mountains, forested, and
swamp areas were also omitted because they include
insignificant cropland. A detailed description of the
procedures used in the simulation, maps of potential
percolation for combinations of hydrologic soil groups
and available water-holding capacities, and a discussion
of the errors involved are given in Appendix B, Volume
II.
The potential percolation estimates shown in Figure
12 are based on the assumptions that the soils are
uniform with depth and are well-drained. Planting and
harvesting dates used were the most likely for the
location. Subsurface drainage would not change the
model assumptions appreciably unless the effective root
zone was significantly different from that used in the
simulation. Because of departures from these assump-
tions and local differences in soil characteristics, actual
percolation losses will vary substantially within Land
Resource Areas. However, Figure 12 should provide a
reasonable ordering of regions with respect to their
potential for leaching of soluble agricultural chemicals.
Percolation will be higher than the potential percola-
tion as defined above if the crop being grown has a
shallower root system than corn or if the actively
transpiring canopy is present for a shorter time. The
potential percolation shown in Figure 12 will be an
overestimate for poorly drained soils.
More detailed maps of potential percolation could be
prepared on a state or watershed basis by using soil
survey maps and detailed data on water-holding
characteristics of soils included in the descriptions of soil
series. These data are available for many states from the
Soil Conservation Service or the state agricultural experi-
ment stations.
25
-------
Percolation
(inches )
0 to I
I . I to 3
3.lto7
Mountain, Forest , Swamps, Deserts
or Steep Rainfall Gradient
Figure 12.-Average annual potential percolation.
-------
Table 5. Values of support-practice factor, P.
Practice
Contouring (Pc)
Contour strip cropping (Psc)
R-R-M-M1
R-W-M-M
R-R-W-M
R-W
R-O
Contour listing or ridge planting
(Pel)
Contour terracing (Pj)
No support practice
Land slope (percent)
1.1-2
2.1-7
7.1-12
12.1-18
18.1-24
(Factor P)
0.60
0.30
0.30
0.45
0.52
0.60
0.30
3 0.6/V^
1.0
0.50
0.25
0.25
0.38
0.44
0.50
0.25
0.5/\/n
1.0
0.60
0.30
0.30
0.45
0.52
0.60
0.30
0.6/VrT
1.0
0.80
0.40
0.40
0.60
0.70
0.80
0.40
o.8/\/r
1.0
0.90
0.45
0.45
0.68
0.90
0.90
0.45
0.9/v^T
1.0
R = rowcrop, W - fall-seeded grain, O = spring-seeded grain, M = meadow. The crops are grown in rotation and so arranged on
the field that rowcrop strips are always separated by a meadow or winter-grain strip.
These Pt values estimate the amount of soil eroded to the terrace channels and are used for conservation planning, l-'or prediction
of off-field sediment, the Pt values are multiplied by 0.2.
3 „_
n = number of approximately equal-length intervals into which the field slope is divided by the terraces. Tillage operations must
be parallel to the terraces.
3.5 LOCATION OF CROPLAND AND MAJOR
CROP AREAS
Knowledge of the extent of cropland and the types of
crops grown in an area is essential to the identification
of potential sources of pollutants from agriculture,
because the soil management systems employed and the
agricultural chemicals used are dictated by the cropping
pattern. The information presented in this section will
help to define those areas requiring particular attention.
The contiguous 48 states contain 1.9 billion acres of
land, of which approximately 24% is cropland. Figure 6
shows the geographical distribution of cropland as a
percentage of the Land Resource Areas. Figures 13
through 19 show the distribution of acreages for corn,
sorghum, wheat, cotton, soybeans, orchards, and vege-
tables. These particular crops are shown because of their
importance from the standpoint of acreage, chemical
use, or both. Although the acreage has increased for
many crops since these figures were compiled, it is
believed that the geographical distribution has changed
only slightly. More detailed information for smaller areas
can be obtained from state offices of the Agricultural
Stabilization and Conservation Service, Soil Conserva-
tion Service, or other agencies. Comparison of the
information shown in these figures with that shown in
the Land Resource Area maps (Figures 3 and 4 for direct
runoff, Figure 9 for erosion, and Figure 12 for percola-
tion) will provide a clear indication of both the potential
problem areas and those areas where agricultural runoff
and percolation should be of little concern.
3.6 USE OF PLANT NUTRIENTS ON
CROPLAND
3.6a Fertilizers
The use of chemical fertilizers to supplement the
nutrients supplied by the soil has long been recognized
as necessary in most soils for optimizing crop yields and
plant quality, and reducing erosion by increasing vegeta-
tive cover. Limiting fertilizer to less than optimum rates
would require additional cropland to maintain produc-
tion and this land would be poorer and may be more
erodible. Fertilizers containing the plant nutrients
nitrogen (N), phosphorus (P) and potassium (K) are
now used abundantly on the commercial crops of the
United States. The nutrients N and P are of most
concern with respect to water pollution. Numerous
other chemicals are applied in fertilizer either as impuri-
ties or for specific nutritional problems. At present there
27
-------
I >
'
UNITED STATES
TOTAL
60,402,153
1969 CENSUS Of AGRICULTURE
DEPARTMENT OF COMMERCE
SOCIAL ANU ECONOMIC STATISTICS ADMINISTRATION
BUREAU OF THE CENSUS
Figure 13.—Corn harvested for all purposes.
-------
UNITED STATES
TOTAL
15,487,665
T969 CENSUS OF AGRICULTURE
DEPARTMENT OF COMMERCE
SOCIAL AND ECONOMIC STATISTICS ADMINISTRATION
li'SIH A1f OF THE CENSUS
Figure 14.—Sorghums harvested for all purposes except sirup.
! 3
I
-------
•
UNITED STATES
TOTAL
45,372,868
!3i(m CENSUS OF A'.l
DEPARTMENT OF COMMM1CI
SflCIAl. AND tCCINt.iMK. SiftHSTICS ADMINISTRATION
BUREAU OF THE CENSUS
F;igurc 15.-Wheat harvested.
-------
UNITED STATES
TOTAL
11,496,320
19G9 CENSUS OF AGRICULTURE
DEPARTMENT OE COMMERCE
SOCIAL AND ECONOMIC STATISTICS ADMINISTRATION
BUREAU OF THE CENSUS
Figure 16.—Cotton harvested.
-------
•
I -)
UNITED STATES
TOTAL
36,549,663
i-Hi'i i 1 H:;II'. in ci' i Mini
DEPAHTMtNI (IF (.'.(JMMEHCE
SOCIAL AND ECONtMKIC STATISTICS WJMIHIBTRATION
BUREAU Of THE CENSUS
Figure 1 7.-Soybeans harvested for beans.
-------
UNITED STATES
TOTAL
4,233.897
190!) CENSUS OF AtiHIUJI nil-r
DEPARTMENT OF COMMERCE
SOCIAL AND ECGNfJMK STATISTICS ADMINISTRATION
BUREAU OF rnr KINKUS
Figure 18.-Land in orchards.
-------
UNITED STATES
TOTAL
3,362.383
1969 CENSUS OF AGRICULTURE
DEPAH"•'-i > • i if "vn HC[
AMD ECONOMIC STATISTICS AUMIWIS.TRAT ION
BUREAU OF THE CENSUS
Figure 19.-Vegetables harvested for sale.
-------
is no indication that these other chemicals will ever pose
a significant problem. Although high concentrations of
nitrate-nitrogen in drinking water may be toxic to
animals and humans, the usual problem is one of
increasing the N and P contents of impounded water.
This can result in accelerated eutrophication. Eutrophi-
cation refers to natural or artificial addition of nutrients
to bodies of water and to the effects of added nutrients.
The potential for pollution from fertilizers will
generally be highest where large acreages are treated with
high rates of fertilizers. Large acreages treated with low
rates of fertilizers or small acreages treated with high
rates will usually not have a significant effect on
navigable waters, although they might be of concern
under localized conditions. Table 6 gives the percentage
of the acreage in different crops that is fertilized and the
average rate of fertilization. These values, however, are
national averages and more detailed data should be
obtained for assessing specific areas. Nevertheless,
combining this kind of information with maps showing
the distribution of the different crops, such as Figures
13 to 19, will help define potential problem areas. For
example, the states of Nevada, Utah, and Wyoming have
relatively little land in crops or orchards and, thus,
pollution from fertilizer would only be a problem in
localized areas, if at all. Another example is the wheat
areas such as in Montana and North Dakota. A smaller
percentage of wheat land is fertilized, particularly in
drier areas, and the rates applied to wheat are usually
only about half or less of those commonly applied to
corn or cotton. Consequently, extensive potential fertil-
izer pollution problems are less likely in these areas than
in areas where corn and cotton are the major crops.
Nutrients can be applied singly or in combinations.
Some examples of common fertilizers that contain a
single nutrient or two nutrients are given in Table 7 with
the percent of nutrient in each. In addition to these
materials, superphosphate can be ammoniated to pro-
duce fertilizers with a range of nitrogen and phosphorus
Table 7. Plant-available nutrients in common fertilizers.
Nitrogen
Anhydrous Ammonia
Urea
Ammonium Nitrate
Liquid Nitrogen Solution
Ammonium Sulfate
Calcium Cyanamide
Calcium Nitrate
Sodium Nitrate
Urea-Formaldehyde
Phosphorus
Rock Phosphate
Normal Superphosphate
Concentrated Superphosphate
Phosphoric Acid
Potassium
Muriate of Potash (KC1)
Potassium Sulfate (K2SO4)
Sulfate of Potash-Magnesia
Multinutrient
Monoammonium Phosphates
Diammonium Phosphates
Ammonium Polyphosphates
Potassium Nitrate
Nutrient Content
82% N
45% N
33.5% N
28-38% N
21% N
21 %N
16% N
16% N
38% N
2% P
9% P
21% P
23% P
51% K.
43% K.
19% K
11-16% N, 8-20% P
16-18%N, 20% P
10-15% N, 14-30%P
13% N, 37% K.
contents. Several materials can be mixed or blended
together to produce a great variety of nutrient contents.
Granulated mixes have uniform granules with good
physical properties and nearly the same amount of each
nutrient in each pellet. Bulk blends are simple physical
mixes that are not as homogenous as granulated mixes
but may be cheaper. Fertilizers containing various
nutrient contents can also be prepared as liquids,
suspensions, or slurries. If the fluid fertilizer contains
any free ammonia, it must be handled under pressure
and injected into the soil in a manner similar to
anhydrous ammonia.
Table 6. Acres receiving fertilizer and average fertilizer rates of four crops in the United States in 1974.
Crop
Corn
Cotton
Soybeans
Wheat
Acres harvested (million)
63.7
13.1
52.5
64.1
Percent
N
94
79
22
66
fertilized
P
87
58
28
46
Pounds/acre rate
N
103
78
15
46
P
27
23
18
17
35
-------
Slates have laws requiring that all fertilizer sold must
meet certain requirements, be registered with a state
agency, and be properly labeled. The label is usually
required to carry a statement of the net weight, brand,
grade, guaranteed analysis, and name and address of the
registrant. The grade is a series of three numbers giving
the percent of elemental nitrogen (N), available phos-
phorus (P2O5)and soluble potash (K20)in that order.
Some states are changing from the oxide basis
(P2OS and K20) to an elemental basis (P and K). The
available phosphorus is usually measured by citrate
solubility. The percentages given in Table 7 are for
available P, but with the exception of rock phosphate,
the total is only 1 or 2 percent higher than the
citrate-soluble amount. Rock phosphate has about 14
percent total P. The percent of the citrate-soluble P that
is water-soluble ranges from 85 to 100. All the potas-
sium carriers listed are completely water-soluble.
The importance of water solubility of phosphate
fertilizers has been controversial. Highly water-soluble
materials are important for starter fertilizers, for short-
season, fast-growing crops, and when the fertilizer is
applied in bands or rows. When the fertilizer is broad-
cast, or applied to long-season crops, acid soils, or
high-phosphorus soils, the source material is less
important. Rock phosphate is very insoluble and too
slowly available for most crops.
The nitrate in the fertilizers moves with water and is
easily leached, whereas the ammonium is adsorbed to
the soil and not easily leached. Urea is converted to
ammonium in a few days while the conversion of
cyanamid takes longer. Urea-formaldehyde provides a
slow release of nitrogen over the growing season.
Farmers may purchase a mixed fertilizer that contains
more of one nutrient than recommended because it is
cheaper or the desired ratio of nutrients is not available.
This can lead to some degree of overfertilization. The
excess nutrients will usually be P and K since the
amounts of N required usually predominate. Some
crops, particularly vegetables, may require special fertili-
zation practices. Rice is the only major crop that has a
special requirement, and that is the use of an ammonium
or ammonium-producing compound under the flooded
conditions.
Many forms of nitrogen are added to the soil. Once
applied, this nitrogen, as well as other forms of nitrogen
in the soil, is subject to many microbial transformation
processes and the basic transport processes-direct run-
off, erosion, and percolation. Leaching, the transport of
soluble salts by percolating water, can carry nitrate-
nitrogen vertically through the soil profile to ground
water and laterally downhill where it may emerge to join
the soluble nitrogen in the direct runoff. How long it
takes to travel the subsurface route depends on the
length of the path and on the amount of water available
for movement. Nitrogen in an organic form is associated
with the soil particles and is moved by erosion. Nitrate
can be produced in water bodies by microbes decom-
posing organic matter, nitrifying ammonium, and
indirectly from nitrogen fixed by algae. Nitrate, ammo-
nium, and phosphate occur in precipitation. The phos-
phate concentrations are usually quite low while the
nitrogen concentrations are often higher than those in
runoff water from unfertilized land. Sources of these
nutrients in the precipitation are principally industrial
centers, power plants, animal feed lots, etc.
A fundamental consideration before controls can be
applied is the identification of the primary transport
processes operating in the system. Conditions conducive
to each of the transport processes can be defined. For
example, the potential for nitrogen leaching is high
whenever percolating water and nitrate-nitrogen exist
simultaneously. Percolation increases with increasing
permeability and decreases with increasing water-holding
capacity of the soil. Generally, sandy soils are the most
permeable and have the lowest water-holding capacity,
loams are intermediate, and clays have the lowest
permeability and highest water-holding capacity. As
mentioned, nitrate must be present for nitrogen leaching
to occur. Nitrate is not adsorbed by the soil and can,
consequently, be moved. Ammonium adsorbs on clay
particles and is not subject to leaching. However,
microorganisms can convert ammonium ions to nitrate.
The potential for transport of N and P in overland
flow obviously is high when fertilizers are applied to
sloping lands and left on the surface. This is not a
normal practice on cultivated land; farmers conven-
tionally plow down surface-applied fertilizers or inject
anhydrous ammonia beneath the surface. With no-till
practices, fall-sowed small grains, or on rough hay or
pasture lands, however, applied fertilizers are often left
on the surface. Thus, nutrients may move in direct
runoff if they are not leached into the soil. Another
source of nutrients in overland flow is the leaching by
water of both dead and live plant tissues on the surface.
This is most noticeable with no-plow practices where
plant residues are left on the surface to reduce sediment
movement. Concentrations of soluble nutrients in the
runoff water are increased, but the total transport of N
and P is probably lower than from bare soil because
sediment loss and, usually, the amount of runoff are less.
Nitrogen transport by erosion is expected when the
surface soil has a high organic matter content, because
organic nitrogen is the principal form of nitrogen in
36
-------
sediment. The nitrogen in organic matter in surface soils
generally ranges from 0.07 to 0.3 percent. The organic
matter content of soils varies with climate and manage-
ment. Cultivation and warm temperature accelerate the
decomposition of organic matter and dry climates limit
the production of vegetative material, which replenishes
the organic matter.
The eroded material usually has a higher organic
matter content than the original soil because organic
matter particles are lighter than most mineral particles
and tend to remain in suspension. Also, the silt and clay
particles are more erodible and are higher in organic
matter content than sand particles. The nutrient content
of sediment is generally about 50 percent higher than
that of the soil, but values as high as fivefold are not
unknown. As a result of this enriching process, a
reduction in erosion may not give a proportional
reduction in nitrogen transport, because the coarser
particles are more easily controlled than the finer
particles. However, over a large watershed there are
other erosion processes in addition to surface erosion.
Sediments from gully and bank erosion, which are low in
organic matter content, tend to lower the average
organic matter composition of the eroded material. The
ultimate composition of the sediment is, therefore,
modified by two opposing processes.
Phosphorus moves primarily by erosion because
phosphate adsorbs strongly on soil particles, although
some soluble phosphorus compounds do move in runoff
water. The total P content of soils ranges from 0.01 to
0.13 percent. The P content of surface soils reflects farm
management, while that of subsoils is a result of geologic
conditions. Fertilizer phosphorus applied in soluble
orthophosphate form soon converts to insoluble forms
in the soil. This conversion prevents leaching and permits
a buildup of phosphorus in the plow layer. As with
nitrogen, the P concentration is higher in sediment than
in the original soil, because phosphorus is associated
with the finer particles. Thus, reducing the sediment
transport may not reduce the phosphorus transport
proportionately. Sediments from gully and bank erosion
may reduce the phosphate concentration in solution as a
result of their high phosphate adsorption capacities.
Only a small part of the N and P moved with the
sediment is immediately available to aquatic organisms.
Another part can slowly become available through
biophysiochemical reactions.
3.6b Animal Wastes
Animal wastes are applied to agricultural lands both
to improve soil fertility and structure and to dispose of
the wastes. Before supplies of synthetic nitrogen fertil-
izers became readily available, manure was a major
source of nitrogen for crop production. Today, commer-
cial fertilizer is the major source of nitrogen, supplying
over 9 million tons. Manure furnishes about 1.2 million
tons and legumes about 2 million tons. Manure increases
the organic matter content of the soils, which increases
the infiltration capacity and, thus, reduces runoff and
erosion.
The pollution potential from using manure with poor
management can be substantially higher than that from
using commercial fertilizers, because nearly all manure is
spread on the soil surface and can contain large amounts
of soluble carbon, nitrogen, and phosphorus compounds.
These constituents can be easily lost if runoff occurs
before the manure is incorporated in the soil. Also, it is
difficult to adequately determine the amount of nitro-
gen added in the waste and the rate at which the
nitrogen will become available for plant uptake. Conse-
quently, too much manure may sometimes be applied,
resulting in nitrate leaching.
Animal wastes are usually applied within a few miles
of their production site. The principal sources of manure
are confined beef and dairy cattle, swine, and poultry.
Figures 20, 21, 22, 23, and 24 show the geographical
distribution of these sources and the estimated amounts
of manure available for application to land in various
locations. These estimates, however, should be consid-
ered only as a first approximation and should be refined
for smaller areas with more recent and detailed informa-
tion. These maps can be used in conjunction with the
maps presented previously to estimate pollution poten-
tial from direct runoff and leaching. For example,
application of dairy wastes (Figure 21) to Land
Resource Area (LRA) 104 (Figure 2) with an annual
mean direct runoff of 3 to 5 inches (Figure 3) will have a
higher pollution potential than applying beef cattle
waste (Figure 20) to LRA 77 (Figure 2) with a mean
annual direct runoff of less than 1 inch (Figure 3). The
pollution potential from animal wastes is greatest when
manure is spread on snow or frozen ground. Because the
simulation procedure used to estimate potential direct
runoff did not account for frozen ground, Figures 25
and 26 are helpful in determining whether or not the
application of manure on frozen ground is a potential
problem. Figure 25 shows the average annual snowfall
and some indication of the snowmelt potential. Figure
26 shows the mean depth of frost penetration and in
conjunction with Figure 25 indicates the potential for
snowmelt runoff on frozen ground. These maps indicate
that the pollution potential from applying manure on
land during the winter would not be high in LRA 77 but
could be in LRA 104.
37
-------
,,
1809 CENSUS OF AGRICULTURE
DEPARTMENT OF COMMERCE
SOCIAL AND ECONOMIC STATISTICS ADMINtSTHAT ION
BUREAU OF THE CENSUS
Figure 20.-Cattle Fattened on Grain and Sold for Slaughter. (The U.S. total is about 23 million, representing about 13 million tons per year of manure
(dry weight) containing 330 thousand tons of N and 100 thousand tons of P. Each dot represents 5 thousand head and about 2800 tons per year of
manure.)
-------
1969 CENSUS OF AGfllCULTURE
DEPAflTMCN"! OF COMMERCE
SOCIAL AND ECONOMIC STATISTICS ADMINISTRATION
BUREAU OF THE CENSUS
Figure 21.-Milk Cows. (The U.S. total is about 11 million, representing about 17 million tons per year of manure (dry weight) containing 330 thousand
tons of N and 100 thousand tons of P. Each dot represents 1 thousand milk cows and about 16 hundred tons per year of manure.)
U)
!
-------
1
1B00 CFNSU5 OF AUIK Ml mill
NtPAHriWNI (II COMMI Hi I
,IA| ANN | I.MNI.WH. ;,| AM!, IICS ADMINIB1HATION
BUREAU OF THE CENSUS
Figure 22.-Hogs and Pigs. (The U.S. total is about 55 million, representing about 11 million tons per year of manure (dry weight) containing 300 thousand
tons of N and 110 thousand tons of P. Each dot represents 10 thousand hogs and about 2 thousand tons per year of manure.)
-------
I9B!) CENSUS OF AGRICULTURE
DEPARTMENT OF COMMERCE
SOCIAL AN!) ECONOMIC STATISTICS ADMINISTRATION
BUREAU OF THE CENSUS
Figure 23.-Chickens 3 Months Old or Older. (The U.S. total is about 370 million, representing about 2.8 million tons per year of manure (dry weight)
containing 125 thousand tons of N and 50 thousand tons of P. Each dot represents 50 thousand chickens and about 400 tons of manure.)
-------
I-
I ••
1969 CENSU$ OF AGHtCULTURE
DEPARTMENT OF COMMERCE
SOCIAL AND ICONOMIC STATISTICS ADMINISTRATION
IlllKI Ail 'K nil i III1 if,
Figure 24.-Broilers and Other Meat-Type Chickens. (The total sold annually in the U.S. exceeds 2.5 billion, representing about 3.2 million tons per year of
manure (dry weight) containing 120 thousand tons of N and 40 thousand tons of P. Each dot represents 500 thousand chickens and about 650 tons of
manure.)
-------
CAUTION SHOULD BE USED IN
INTERPOLATING ON THESE GEN-
ERALIZED HAP3, PARTICULARLY ]
IN MOUNTAINOUS AREAS.
DATA BASED ON PERIOD OF
RECORD THROUGH I960.
SNOW IN HIGH
MOUNTAINS, RARELY
AS LOW AS 6000 FT
ELEVATION
Figure 25.-Mean annual total snowfall, inches.
-------
!
Figure 26.-Depth of frost pentration, inches.
-------
3.7 USE OF PESTICIDES ON CROPLAND
The use of chemicals to control crop pests has
increased sharply in the last three decades and is still
rising, particularly that of herbicides. From 1964 to
1969, the acreage of U. S. cropland treated for weed
control increased by more than 42 percent, and the
acreage treated for insect control increased more than 22
percent. In 1971, over 158 million acres of land were
treated with herbicides, 65 million with insecticides, and
almost 7.5 million with fungicides (some receiving more
than one type of chemical). These represent 41, 17, and
2 percent of the nonpasture cropland, respectively. The
distribution of treated cropland acreage as of 1969 is
shown in Figure 27 for herbicides and in Figure 28 for
insecticides. These distributions probably have changed
little in the intervening years. Juxtaposition of the
chemical treatment maps with the Land Resource Area
maps for direct runoff (Figures 3 and 4) or erosion
(Figure 9) will help pinpoint potential areas of concern
with respect to environmental pollution by pesticides
transported off the treated fields in runoff water and
sediment.
Many investigations of losses of various agricultural
pesticides in runoff from treated land have been
reported. Nearly all lead to the same general conclusion:
except when heavy rainfall occurs shortly after treat-
ment, concentrations are very low and the total amount
of pesticide that runs off the land during the crop year is
less, often much less, than 5 percent of the application.
Nevertheless, some chemicals are highly toxic to fish or
other aquatic fauna and can persist in the aquatic
environment for a long time, so that even very low levels
of these pesticides in runoff may be of environmental
concern. On the other hand, many agricultural chemicals
are not acutely toxic to animal life, do not persist from
one crop season to the next, and do not accumulate in
food chain organisms; they may, consequently, be used
at normal application rates without fear of causing
unacceptable environmental damage.
Herbicides, insecticides, and fungicides commonly
used on cropland are listed in Tables 8a, 9a, and lOa,
respectively, along with certain properties of each
chemical that relate to pollution in runoff. The more
widely used trade names of the pesticides are given,
along with corresponding common names of the primary
listing, in Tables 8b, 9b, and lOb. Table 11 lists the
pesticides that may be used on the major crops of the
United States without geographic restriction. Other
pesticides are also registered, but may be used only in
specific areas of the country. The Cooperative Extension
Service of each state can supply the complete list of
pesticides registered for each locality. In addition to the
name of the pesticide, each registration specifies the
dosage, residue tolerances, formulations, and use limita-
tions and may include the name of the pest or pests to
be controlled. All registrations are listed in the "EPA
Compendium of Registered Pesticides," which may be
purchased from the Superintendent of Documents, U.S.
Government Printing Office.
The predominant transport mode, which indicates the
partitioning of the compound between water and soil, is
important in the movement of the chemicals in runoff
and is shown for each pesticide in Tables 8a, 9a, and
lOa. The transport modes were taken wherever possible
from field experiments reported in the literature or were
estimated from water solubilities of the chemicals where
no experimental data exist. The best criterion of how a
chemical partitions is its adsorption isotherm (curve
showing amount adsorbed at different solution concen-
trations), as measured by mixing solutions of the
chemical with known quantities of soil. However,
published information on adsorption of individual com-
pounds is fragmentary and water solubilities were used
instead because, in general, the more water-soluble a
compound is, the more it will appear in the aqueous
phase of runoff rather than in the sediment. The
solubility of some compounds depends heavily on the
formulation used; amines, for example, are far more
water-soluble than esters having the same active ingre-
dient. Often, more pesticide can be lost in the runoff
water than in the sediment even when pesticide concen-
tration is higher in the latter, because the amount of
water moved is so much greater than the amount of
sediment transported.
Acute oral toxicity to rats and 48- or 96-hour
toxicities to susceptible species of fish, usually rainbow
trout or bluegills, in static water tests are standard
indexes of mammalian and fish toxicity and are included
in the tables to permit a general evaluation of the hazard
that might exist if residues of specific chemicals occur in
runoff. Higher LDSO (lethal dose for 50 percent of the
rats being tested) and LCSO (lethal concentration for 50
percent of the fish being tested) values denote lower
toxicity. Where more than one toxicity value is reported
in the literature, the values denoting higher toxicity are
shown. Fish toxicity values represent concentrations in
water; pesticides adsorbed on sediment in the water are
less toxic to fish than when dissolved in water.
The persistence in soil of most of the individual
herbicides has been reported in the literature and is
shown in the last column of Table 8a. The values
correspond to the time required for 90 or more percent
of the applied pesticide to disappear from the site of
45
-------
I
I
'M ••***
vs%;:;;-v-^-#*5L'^
£*\x\&*£ffi£&j&
1 DOT-20,000 ACRES
UNITED STATES
TOTAL
84,913.547
i ,, , . . i • .
DEPARTMENT Ol UiMMERCE
MJC1AL AN!) KHH'.'r"" ' .'.ilNISt RATION
Hum nu M| I'n
Figure 27,—Acreage of crops treated with herbicides.
-------
UNITED STATES
TOTAL
39,881,566
,UIIU All 01 '"I • [ II . ,
Figure 28.-Acreage of non-hay crops treated with insecticides.
-------
Table 8a. Agricultural herbicides: types, transport modes, toxicities, and persistence in soil
Common Names of
Herbicides
Alachlor
Ametryne
Amitrole
Asulam
Atrazine
Barban
Benefin
Bensulidc
Bentazon
Bifenox
Bromacil
Bromoxynil
Butylate
Cacodylic Acid
CDAA
CDEC
Chloramben
Chlorbromuron
Chloroxuron
Chlorpropham
Cyanazine
Cycloate5
2,4-D Acid
2,44) Amine
2,4-D Ester
Dalapon
2,4-DB
DCPA
Diallate
Dicamba
Dichlobenil
Dinitramine
Dinoseb
Diphenamid
Diquat
Diuron
DSMA
Endothall
EPTC
Fenac
Fenuron
Fluometuron
Fluorodil'en
Glyphosate
Isopropalin
Linuron
MBR 825 1
MCPA
Metribuzin
Molinate
Monuron
MSMA
Naptalam
Chemical Class1
AM
TZ
TZ
CB
TZ
CB
NA
AM
DZ
AR
DZ
NT
CB
AS
AM
CB
AR
UR
UR
CB
TZ
CB
PO
PO
PO
AL
PO
AR
CB
AR
NT
NA
PH
AM
CT
UR
AS
PH
CB
AR
UR
UR
AR
AL
NA
UR
AM
PO
TZ
CB
UR
AS
AR
Predominant
Transport
Mode2
SW
s\v
W
W
sw
s
s
s
W
s
W
sw
s
s
W
sw
W
sw
s
sw
sw
sw
W
W
s
W
s
s
s
W
s
s
sw
W
s
s
s
W
sw
sw
W
sw
s
s
s
s
sw
sw
W
W
sw
s
W
Toxicity3
Rat, Acute
Oral LD5 „ ,
mg/kg
1200
1110
2500
>8000
3080
1350
800
770
1100
4600
5200
250
4500
700
850
3500
2150
3700
1500
334
2000
370
370
500-875
6590
300
3000
395
1028
3160
3000
5
970
400
3400
600
38
1360
1780
6400
7900
15000
4320
5000
1500
633
650
1930
501
3500
700
1770
Fish4 LC 5 ;, ,
mg/liter
2.3
Low toxicity
>50
6 5000
12.6
1 1.3
6 0.03
0.72
190
1.8
70
0.05
4.2
Q
8>40
2.0
4.9
6 7.0
0.56
8>15
6 10
4.9
4.5
9 >50
8>IS
8 4.5
>100
4.0
>500
5.9
35
10-20
6.7
7-100.4
25.0
12.3
>60
>15
1.15
19.0
15
53
10 >60
0.18
Low toxicity
Toxic
16.0
312
10.0
>100
0.29
1.8
> 15
>180
Approximate
Persistence
in Soil,
days
40-70
30-90
15-30
2540
300-500
20
120-150
500-700
40-60
700
40-80
2040
2040
40-60
300400
1 20-260
120-220
10-30
10-30
10-30
15-30
400
120
60-180
90-120
15-30
90-180
>500
200-500
30
350-700
30-270
150
150
120
30-180
150-200
80
150-350
20-60
48
-------
Table 8a. Agricultural herbicides: types, transport modes,
toxicities, and persistence in soil-(continued)
Common Names of
Herbicides
Nitralin
Nitrofen
Oryzalin
Paraquat
Pebulate5
Phenmedipham
Picloram
Profluralin
Prometone
Prometryne
Pronamide
Propachlor
Propanil
Propazine
Propham
Pyrazon
Siivex
Simazine
2,4,5-T
TCA
Terbacil
Terbutryne
"riallate5
Tritluralin
Vernolate5
Chemical Class1
NA
PO
AM
CT
CB
CB
AR
NA
TZ
TZ
AM
AM
AM
TZ
CB
DZ
PO
TZ
PO
AL
DZ
TZ
CB
NA
CB
Predominant
Transport
Mode2
S
S
S
S
S
S
w
S
S
S
S
w
S
S
w
w
sw
S
w
w
w
sw
S
S
sw
Toxicity
Rat, Acute
OralLD50,
mg/kg
2000
2630
> 10000
150
921
2000
8200
2200
1750
3750
5620
710
1384
5000
5000
2500
375
5000
300
3370
5000
2400
1675
3700
1625
Fish4 LQ „ ,
ing/liter
Low toxicity
Toxic
Low toxicily
6 400
11 6.3
10 20
2.5
Toxic
9>1.0
9 >1.0
1.3
>10.0
>100
6 32
12 40
9 0.36
5.0
0.5-16.7
1 3 > 2000
14 86
Low toxicity
4.9
6 0.1
9.6
Approximate
Persistence
in Soil,
days
>500
50-60
100
550
320-640
>400
30-90
60-270
30-50
1-3
200400
20-60
30-60
200400
20-70
700
20-70
3040
120-180
50
1 Chemical type designations: AL, aliphatic acids; AM, amides and anilides; AR, aromatic acids and esters; AS^ arsenicals; CB,
carbamates and thiocarbamates; CT, cationics; DZ_,diazines; NA, nitroanilines; >JT, nitriles;XH, phenols and dicarboxylic acids;
PO, phenoxy compounds; TZ, triazines and triazoles; UR, ureas.
2 Where movement of herbicides in runoff from treated fields occurs,^denotes those chemicals that will most likely move
primarily with the sediment, \V denotes those that will most likely move primarily with the water, and jiW denotes those that will
most likely move in appreciable proportion with both sediment and water.
3 Expressed as the lethal dose, or lethal concentration, to 50% of the test animals (LD5 0 or LC5 0, respectively).
4 48- or 96-hour LC. „ for bluegills or rainbow trout, unless otherwise specified.
10
Trade name; no corresponding common name exists.
24-hour LC5 0 .
For goldfish.
Forkillifish.
For spot.
7 ,,
8
12
For mullet.
For harlequin fish.
13 For catfish.
14 .-
For sunfish.
49
-------
Table 8b. Often-used trade-name synonyms of agricultural herbicides
Trade Name
AAtrex
Alanap
Amiben
Amino Triazole
Avadex
Avadex BW
Balan
Banvel
Basanite
Betanal
Betasan
Baladex
Bromex
Butoxone
Butyrac
Caparol
Carbyne
Casoron
Chloro-IPC
CIPC
Cobex
Dacthal
Destun
DNBP
Dowpon
Dymid
Enide
Eptam
Eiadicane
Far-Go
Furloe
Igran
JPC
Karmex
Name in
Table 8a
Atrazine
Naptalam
Chloramben
Amitrole
Diallale
Triallate
Benefin
Dicamba
Dinoseb
Phenmedipham
Bensulide
Cyanazine
Chlorbromuron
2,4-DB
2,4-DB
Prometryne
Barban
Dichlobenil
Chlorpropham
Chlorpropham
Dinitramine
DCPA
MBR8251
Dinoseb
Dalapon
Djphenamid
Diphenamid
EPTC
EPTC
Triallate
Chlorpropham
Terbutryn
Propham
Diuron
Trade Name
Lasso
Lorox
Maloran
Milogard
Mod own
Norex
NPA
Ordram
Paarlan
Planavin
Prefar
Preforan
Premerge Dinitro
Princep
Pyramin
Ramrod
Randox
Ro-Neet
Ryzelan
Roundup
Sencor
Sinbar
Sinox
Soyex
Stam F-34
Surflan
Sutan
Telvar
Tenoran
Tordon
Treflan
Vegadex
Vernam
Name in
Table 8a
Alachlor
Linuron
Chlorbromuron
Propazine
Bifenox
Chloroxuron
Naplalam
Molinate
Isopropalin
Nitralin
Bensulide
Fluorodifen
Dinoseb
Simazine
Pyrazon
Propachlor
CDAA
Cycloate
Oryzalin
Glyphosate
Metribuzin
Terbacil
Dinoseb
Fluorodifen
Propanil
Oryzalin
Butylate
Monuron
Chloroxuron
Picloram
Trifluralin
CD EC
Vernolate
50
-------
Table 9a. Agricultural insecticides and miticides: types, transport modes, and loxicities
Common Names of
Insecticides-Miticides
Aldicarb5
Aldrin
Allethrin
Azinphos ethyl
Azinphos methyl
Benzene hexachloride
Binapacryl
Bux6
Carbaryl
Carbofuran
Carbophenothion
Chlorbenside
Chlordane
Chlordimeform
Chlorobenzilate6
Qilorpyrifos
DDT
Demeton
Diazinon5'6
Dicofol6
Dicrotophos
Dieldrin
Dimethoate
Dioxathion
Disulfoton
Endosulfan
Endrin
EPN
Ethion
Ethoprop
Fensulfothion
Fonofos6
Heptachlor
Landrin
Lindane
Malathion
Metaldehyde
Methidathion
Methomyl
Methoxychlor
Methyl demeton
Methyl parathion
Mevinphos
Mcxacarbate
Monocrotophos
Naled
Ovex
Oxythioquinox
Parathion
Perthane6
Phorate5
Phosalone
Phosmet
Chemical Qass
CB
OCL
PY
OP
OP
OCL
N
CB
CB
CB
OP
S
OCL
N
OCL
OP
OCL
OP
OP
OCL
OP
OCL
OP
OP
OP
OCL
OCL
OP
OP
OP
OP
OP
OCL
CB
OCL
OP
O
OP
CB
OCL
OP
OP
OP
CB
OP
OP
S
S
OP
OCL
OP
OP
OP
Predominant
Transport
Mode2
W
S
S
S
S
S
U
S
sw
W
S
S
S
W
S
U
S
W
sw
S
W
S
W
S
S
S
S
S
S
U
sw
S
S
sw
S
W
W
U
U
S
W
sw
W
sw
W
S
S
S
S
S
sw
S
S
Toxicity
Rat, Acute
Oral LD,n,
mg/kg
0.93
35
680
7
11
1000
120
87
500
8
10
3000
335
162
700
97
113
2
76
684
22
46
185
23
2
18
7.3
8
27
61.5
2
8
90
178
88
480
1000
25
17
5000
65
9
4
22.5
21
250
2000
1100
4
>4000
1
96
147
Fish4 LC5 „ ,
mg/litcr
0.003
0.019
0.019
0.010
0.79
0.04
0.29
1.0
0.21
0.23
0.010
1.0
0.71
0.020
0.002
0.081
0.030
0.10
8.0
0.003
9.6
0.014
0.040
0.001
0.0002
0.10
0.23
1.0
7 0.15
0.03
0.009
0.95
0.018
0.019
> 100.0
-0.9
0.007
4.0
1.9
0.017
1.73
7.0
0.078
0.70
0.096
0.047
0.007
0.0055
3.4
8 0.03
51
-------
Table 9a. Agricultural insecticides and miticides: types, transport modes, and toxicities-(continued)
Common Names of
Insecticides-Miticides
Phosphamidon
Propargite6
Propoxur
TDE
TEPP
Tetrachlorvinphos
Tetradifon
Thionazin
Toxaphene
Trichlorfon
Chemical Class
OP
s
CB
OCL
OP
OP
OCL
OP
OCL
OP
Predominant
Transport
Mode2
W
u
W
s
W
s
sw
W
s
W
Toxicity3
Rat, Acute
OraILD§0,
mg/kg
11
2200
95
3360
1
4000
14000
12
69
275
Fish4 LC5 „ ,
mg/liter
8.0
0.03
9 0.025
0.009
9 0.39
0.53
1.10
7 0.10
0.003
0.16
Chemical type designations: CB. carbamates; N, miscellaneous nitrogenous compounds; O, cyclic oxygen compounds; OCL.
organochlorines; OP, organophosphorus compounds;_PY, synthetic pyrethrin; j>, aromatic and cyclic sulfur compounds.
2 Where movement of insecticides in runoff from treated fields occurs, ^denotes those chemicals that will most likely move
primarily with the sediment,_W denotes those that will most likely move primarily with the water, SW denotes those that will most
likely move in appreciable proportion with both sediment and water, and _U denotes those whose predominant mode of transport
cannot be predicted because properties are unknown.
3 Expressed as the lethal dose, or lethal concentration, to 50% of the test animals (LDSO or LCSO, respectively).
48- or 96-hour LC5 0 for bluegills or rainbow trout, unless otherwise specified.
Registered as both insecticide and nematicide. Nematodes are controlled only on limited acreage and predominantly in the
Southern states, but application rates when used as nematicides are 2- or 3-fold higher than when used as insecticides.
Trade name; no corresponding common name exists.
7 24-hour LCS „
8 For killifish
For minnows
52
-------
Table 9b. Often-used trade-name synonyms of agricultural insecticides and miticides
Trade Name
Acaraben
Azodrin
Basudin
Baygon
BHC
Bidrin
Cygon
Dasanit
ODD
Dclnav
Dibrom
Dlmecrom
Dipterex
Di-Syston
Dursban
Dyfonate
Dylox
Ethyl Guthion
Fundal
Furadan
Galecron
Gamma-BHC
Gaidona
Guthion
Name in Table 9a
Chlorobenzilate
Monocrotophos
Diazinon
Propoxur
Benzene Hexachloride
Dicrotophos
Dimethoate
Fensulfothion
TDE
Dioxathion
Naled
Phosphamidon
Trichlorfon
Disulfoton
Chlorpyrifos
Fonofos
Trichlorfon
Azinphos ethyl
Chlordimeform
Carbofuran
Chlordimeform
Lindane
Tctrachlorvinphos
Azinphos methyl
Trade Name
Imidan
Kelthane
Lannate
Mar late
Meta-Systox
Mocap
Morestan
Morocide
Neguvon
Omite
Phosdrin
Prolate
Rabon
Sevin
Spectracide
Supracide
Systox
Ted ion
Temik
Thimet
Thiodan
Trithion
Zectran
Zinophos
Zolone
Name in Table 9a
Phosmet
Dicofol
Methomyl
Methoxychlor
Methyl demeton
Ethoprop
Oxythioquinox
Binapacryl
Trichlorfon
Propargite
Mevinphos
Phosmet
Tetrachlorvinphos
Carbaryl
Diazinon
Methidathion
Demeton
Tetradifon
Aldicarb
Phorate
Endosulfan
Carbophenothion
Mexacarbate
Thionazin
Phosalone
53
-------
Table lOa. Agricultural fungicides: transport modes and toxicities
Common Names of Fungicides
Anilazmc
Benomyl
Captafol
Captan
Carboxin
Chloranil
Chloroneb
Cycloheximide
DCNA
Dichlone
Dichlozoline
Dinocap
Dodme
ETMT
Fenaminosulf
Ferbam
Folpet
Maneb
Metiram
Nabam
Ocycarboxin
Parinoi
PCNB
SMDC
Thiram
TPTH
Zincb
Ziram
Predominant Transport Mode
S
S
S
S
SW
w
u
w
S
S
u
S
w
u
w
SW
S
S
u
w
w
u
S
w
S
u
S
w
Toxicity 2
Rat, Acute Ora! LDsfj, ing/kg
2710
>9590
5000
9000
3200
4000
11000
2.5
4040
1300
3000
980
1000
2000
60
>17000
>10000
6750
6400
395
2000
>5000
1650
820
375
108
>5200
1400
Fish3 LCsQ. mg/liter
0.015
0.5
4 0.031
0.13
2.2
5.0
>4 200.0
1.3
0.047
5 0.14
0.9
23.0
4 12.6
6 t.56
7 1.0
>4.2
4 21.1
8~5.0
0.7
7 1.0
4 0.79
0.5
4 1.0
Where movement of fungicides in runoff from treated fields occurs, 55 denotes those chemicals that will most likely move pri-
marily with the sediment, W denotes those that will most likely move primarily with the water, SW denotes those that will most likely
move in appreciable proportion with both sediment and water, and U denotes those whose predominant mode of transport cannot be
predicted because properties are unknown.
2 Expressed as the lethal dose, or lethal concentration, to 50% of the test animals (LDfrj or LC.50, respectively).
3 48- or 96-hour LC$Q for bluegillsor rainbow trout, unless otherwise specified.
For catfish
For harlequin fish
For mullet
* LC100
For fathead minnow
54
-------
Table lOb. Often-used trade-name synonyms of agricultural fungicides
Trade Name
Actidione
Ben late
Botran
Cyprex
DCNA
Demosan
Difolatan
Dexon
Dyrene
Karathane
Parnon
Name in Table lOa
Cycloheximide
Benomyl
DCNA
Dodine
Botran
Chloroneb
Captafol
Fenaminosulf
Anilazine
Dinocap
Parinol
Trade Name
Phaltan
Phygon
Plantvax
Polyram
Spergon
Terrachlor
TMTD
Vapam
Vitavax
Name in Table lOa
Folpet
Dichlone
Oxycarboxin
Metiram
Chlorani)
PCNB
Thiram
SMDC
Carboxin
55
-------
Table 11. Major crops and principal pesticides registered for use on them throughout the United States
Crop
Alfalfa
Corn
Cotton
Fruit crops
Herbicides
Benefin EPTC
Chlorpropham MCPA
2, 4-DB Nitralin
Diallate Propham
Dinoseb Simazine
Diuron Trifluralin
Atiazine Dalapon
Butylate DCPA
CDAA Dicamba
CDEC Dinoseb
Chloramben Diuron
C>'anazine EPTC
2,4-D Linuron
Paraquat
Prometryne
Propachlor
Simazine
Bensulide EPTC
Cacodylic acid Fluometuron
DCPA MSMA
Dm tram in e Nitralin
Diphenamid Paraquat
Diuron Prometryne
DSMA Propachlor
Endothall Trifluralin
Bromacil Diuron
Chlorpropham EPTC
2, 4-D Naptalam
Dalapon Paraquat
DCPA Simazine
Dichlobenil Terbacil
Dinoseb Trifluralin
Diphenamid
Insecticides and miticides
Azinphos methyl
Carbaryl
Carbofuran
Carbophenothion
Demeton
Diazinon
Dimethoate
Disulfoton
Endosulfan
Malathion
Bux
Carbaryl
Carbofuran
Carbophenothion
Chlordane3
Diazinon
Disulfoton
EPN
Ethoprop
Fcnsulfothion
Fonofos
Aldicarb
Azinphos methyl
Carbaryl
Carbophenothion
Chlordane3
Chlordimeform
Chlorobenzilate
Demeton
Diazinon
Dicofol
Dicrotophos
Dimethoate
Disulfoton
Endosulfan
Endiin
Azinphos methyl
BHC
Binapacryl3
Carbaryl
Carbophenothion
Chlordane3
Chlordimeform
Chlorobenzilate
Demeton
Diazinon
Dicofol
Dimethoate
Dioxathion
Endosulfan
EPN
Ethion
Methomyl
Methoxychlor
Methyl parathion
Mevinphos
Naled
Parathion
Phorate
Phosmct
Toxaphene
Trichlorfon
Heptachlora
Landrin
Malathion
Methomyl
Methoxychlor
Methyl parathion
Mevinphos
Parathion
Phorate
Tetrachlorvinphos
Toxaphene
Trichlorfon
EPN
Ethion
Malathion
Methidathion
Methyl parathion
Monocrotophos
Naled
Parathion
Phorate
Phosphamidon
Propargite
Toxaphene
Tfichiorfon
Lindane
Malathion
Metaldehyde
Methoxychlor
Methyl parathion
Mevinphos
Naled
Ovex
Oxythioquinox
Parathion
Perthane
Phosalone
Phosmet
Phosphamidon
Propargite
Tetrachlorvinphos
Tetradifon
Toxaphene
56
-------
Table 11. Major crops and principal pesticides registered for use on them throughout the United States-Continued
Crop
Peanuts
Rice
Small grains1'
Sorghum
Soybeans
Sugarbeets
Sugarcane
Herbicides
Alachlor
Benefin
2, 4-DB
Dinitramine
Dinoseb
Chlorpropham
2, 4-D
MCPA
Molinate
Bromoxynil
2, 4-D
Diallate
Atrazine
Bifenox
CDAA
2, 4-D
Dalapon
Alachlor
Bar ban
Bifenox
CDEC
Chloramben
Chloroxuron
Chlorpropham
Dalapon
2, 4-DB
DCPA
Dinitramine
Barban
Chlorpropham
Cycloate
Dalapon
Diallate
EPTC
Paraquat
Ametryn
Atrazine
2, 4-D
Dalapon
Fenac
Diphenamid
Naptalam
Nitralin
Vernolate
Propanil
Silvex
2, 4, 5-T
Dicamba
Djnoseb
MCPA
Dicamba
Linuron
Paraquat
Propachlor
Propazine
Dinoseb
Diphenamid
Fluorodifen
Linuron
Naptalam
Nitralin
Paraquat
Trifluralin
Vernolate
Pebulate
Phenmedipham
Propham
Pyrazon
Trifluralin
Fluometuron
Simazine
Trifluralin
Insecticides and miticides
Carbaryl
Diazinon
Fensulfothion
Fonofos
Malathion
Methom vl
Carbaryl
Chlordane3
Disulfoton
Chlordane3
Demeton
Diazinon
Disulfoton
Endosulfan
Endrin
Carbaryl
Carbophenothion
Demeton
Diazinon
Dimethoate
Disulfoton
Ethion
Azinphos methyl
Carbaryl
Carbophenothion
Chlcrdane3
Diazinon
Disulfoton
EPN
Aldicarb
Carbaryl
Carbophenothion
Demeton
Diazinon
Disulfoton
Endosulfan
EPN
Fensulfothion
Azinphos methyl
Carbofuran
Diazinon
Monocrotophos
Parathion
Phorate
Toxaphene
Trichlorfon
Malathion
Methyl parathion
Parathion
Toxaphene
Heptachlor3
Malathion
Methyl parathion
Parathion
Toxaphene
Trichlorfon
Malathion
Methyl parathion
Mevinphos
Parathion
Phorate
Toxaphene
Heptachlor3
Malathion
Methomyl
Methoxychlor
Methyl parathion
Parathion
Toxaphene
Trichlorfon
Fonofos
Malathion
Methyl parathion
Parathion
Phorate
Trichlorfon
Endosulfan
Endrin
Fonofos
Parathion
57
-------
Table 11. Major crops and principal pesticides registered for use on them throughout the United States-Continued
Crop
Tobacco
Vegetable crops
Herbicides
Benefin
Diphenamid
Isopropalin
Barban
Bensulkle
CD A A
CDEC
Chloramben
Chlorbromuron
Chloroxuron
Chiorpropham
Dalapon
DCPA
Diallatc
Pebulate
Dinoseb
Diphenamid
Endothall
EPTC
Flurodifen
Linuron
Nitralin
Paraquat
Propham
Trifluralin
Vernolate
Insecticides and miticides
Azinphos methyl
Carbaryl
Carbofuran
Chlordanea
Diazinon
Dimethoate
Disulfoton
Endosulfan
Ethoprop
Fensulfothion
Azinphos methyl
BHC
Carbaryl
Carbophenothion
Chlordanea
Demeton
Diazinon
Dicofol
Dimethoate
Disulfoton
Endosulfan
EPN
Ethion
Fensulfothion
Fonofos
Heptachlor3
Fonofos
Heptachlor*
Malathion
Methidathion
Methyl parathion
Monocrotophos
Parathion
Trichlorfon
Lindane
Malathion
Metaldehyde
Methomyl
Methoxychlor
Methyl parathion
Mevinphos
Naled
Parathion
Perthane
Phorate
Phosphamidon
Tctradifon
Toxaphene
Trichlorfon
a Registration status under review.
Wheat, oats, barley, millet, rye.
58
-------
application under most conditions. Many of the missing
values, as well as those of the insecticides in Table 9a,
may be estimated by referring to Figure 29, which
indicates the persistence, as defined above, of broad
classes of pesticides. Persistence is a quite variable
characteristic that may be influenced by such factors as
climate; soil texture, moisture content, acidity, and
temperature; and microbiological activity in the soil.
Furthermore, members of a given class often vary widely
in their persistence under the same soil conditions. The
values shown in the figure represent the behavior of the
longer-lived members of the classes under moderate
conditions.
In evaluating the potential environmental impact of
specific pesticide's in runoff, persistence and toxicity
should be considered together, because a toxic com-
pound that rapidly degrades will pose only a temporary
threat when residues are transported from treated areas.
Pesticide residues dissolved in runoff water are more
difficult to control and move greater distances in
drainage streams than those adsorbed on sediments;
hence, they are potentially more hazardous to the
environment. Some highly soluble pesticides, especially
salt formulations of the acid herbicides, are mobile in
soil and move downward with percolating rainwater.
Thus, they are less available for removal in direct runoff.
Fortunately, even the most mobile herbicides rarely
contaminate the ground water, because the adsorption
capacity in most soils above the water table is sufficient
to retain the chemicals until they decompose. However,
in an area with high percolation potential (Figure 12),
some groundwater contamination is a possibility.
The movement of pesticides on sediment is affected
by the enrichment process, discussed above under
Section 3.6a, in much the same way as is nutrient
movement. Pesticides are adsorbed primarily on organic
soil colloids, which remain in suspension longer than the
coarser soil particles. A reduction in erosion may,
therefore, not reduce pesticide loss proportionately.
59
-------
s
^
ARSENICAL AND CATIONIC HERBICIDES
PHENOXY HERBICIDES
ORGANOPHOSPHORUS INSECTICIDES
.•»-t---L-..L_-u--t.-..U__L--_i---i.
02 46 8 10 12 14 16 18
MONTHS
Figure 29.—Maximum persistence of classes of pesticides in soils under moderate climatic conditions.
-------
SECTION 4
POLLUTION CONTROL PRACTICES
The approach used in identifying potential pollution
problems in Section 3 was based on Land Resource
Areas, which are broad geographic entities. Control
measures, on the other hand, must be applied to
individual fields and are applicable wherever deemed
necessary, irrespective of geographic location. The fol-
lowing discussions deal with the various measures that
can be taken to prevent or control pollution problems.
Practices that are primarily directed to the control of
erosion, the reduction of runoff, the management of
fertilizers or animal wastes, and the management of
pesticides are each dealt with in separate sections. It
should be recognized, however, that important interrela-
tionships exist among the four groups of practices that
may affect the choice of a particular practice in a given
situation. For example, the introduction of a conserva-
tion tillage practice to control erosion may result in the
use of greater amounts of chemicals to control crop
pests, so that the net benefit to the quality of the
drainage streams may not be as great as might be
expected. Some of the more important interrelationships
are described in the discussions of individual control
practices, and the flow charts presented in Section 6 also
call attention to these interrelationships. Some practices
are listed and discussed that are marginal in most cases.
However, in some circumstances, one of these practices
could be the best recommendation.
4.1 PRACTICES TO CONTROL EROSION
The goal of control practices is to keep erosion rates
within tolerances compatible with good water quality,
wholesome environment, and preservation of the pro-
ductive capacity of the land. Where rainfall is adequate
for crop production, some of it generally falls at
intensities greater than the rate at which the soil can
absorb it even under the most favorable conditions, and
the excess runs off. However, erosion can usually be
controlled by practices that minimize raindrop im-
pact on the soil surface and weaken the erosive
forces of the runoff by reducing its velocity and
channelization.
Distribution of erosive rains within the year differs
significantly for different sections of the country, as
shown in Figure 30. When the major concentrations of
erosive rainfall coincide with periods of little or no soil
cover, most of the year's erosion is likely to occur within
a relatively short period. With the conventional practice
of seeding crops on plowed and smoothed seedbeds, the
soil has very little protection during the first 2 months
after crop seeding. On the Western Plains and in the
Great Lakes Region, from 40 to 50 percent of the year's
erosive rainfall normally occurs within 2 months after
the average planting dates for corn, soybeans, and grain
sorghum. In most of the Corn Belt and the eastern parts
of Kansas, Oklahoma, and Texas, the corresponding
percentage is about 35; and in the lower Mississippi
Valley and Southeast, about 20 to 25. In the dryland
grain-growing region of the Pacific Northwest, about 80
to 90 percent of the year's erosion occurs in the winter
months, when the soil frequently has little cover because
the grain is seeded so late in the fall. It is particularly
important that control practices be highly effective
during these critical periods.
In many situations, erosion can be controlled with
agronomic practices that improve crop residue manage-
ment, cropping sequences, seeding methods, soil treat-
ments, tillage methods, and timing of field operations.
Generally, farming parallel to the field contours will
further reduce erosion. However, contouring and some
of the agronomic control practices are not effective
where slope length or the area from which runoff
concentrates is excessive. They must then be supported
by practices such as terraces, diversions, contour fur-
rows, contour listing, contour strip cropping, waterways,
and control structures.
Table 12 lists the principal types of erosion-control
practices and some of their favorable and unfavorable
features. Under many conditions, it may be necessary to
apply various combinations of these practices. Modifica-
tions of specific practices within these general types
affect their adaptability and also their effectiveness. The
general types of practices are discussed below, with
particular reference to their relation to pollution control.
61
-------
0 JFMAMJJASOND
Month
Figure 30.~Monthly distribution of erosive rainfall as percentage of annual.
-------
Table 12. Principal types of cropland erosion control practices and their highlights.
No.
E 1
E2
E3
E4
E5
E6
E7
E8
E9
E10
Ell
E12
E13
E14
E15
E16
E17
Erosion Control Practice
No-till plant in prior-
crop residues
Conservation tillage
Sod-based rotations
Meadowless rotations
Winter cover crops
Improved soil fertility
Timing of field
operations
Plow-plant systems
Contouring
Graded rows
Contour strip cropping
Terraces
Grassed outlets
Ridge planting
Contour listing
Change in land use
Other practices
Practice Highlights
Most effective in dormant grass or small grain; highly effective in crop residues; minimizes
spring sediment surges and provides year-round control; reduces man, machine and fuel re-
quirements; delays soil warming and drying; requires more pesticides and nitrogen; limits
fertilizer- and pesticide placement options; some climatic and soil restrictions.
Includes a variety of no-plow systems that retain some of the residues on the surface; more
widely adaptable but somewhat less effective than E 1 ; advantages and disadvantages generally
same as E 1 but to lesser degree.
Good meadows lose virtually no soil and reduce erosion from succeeding crops; total soil loss
greatly reduced but losses unequally distributed over rotation cycle; aid in control of some
diseases and pests; more fertilizer-placement options; less realized income from hay years;
greater potential transport of water soluble P; some climatic restrictions.
Aid in disease and pest control; may provide more continuous soil protection than one-crop
systems; much less effective than E 3.
Reduce winter erosion where corn stover has been removed and after low-residue crops;
provide good base for slot-planting next crop; usually no advantage over heavy cover of
chopped stalks or straw; may reduce leaching of nitrate; water use by winter cover may reduce
yield of cash crop.
Can substantially reduce erosion hazards as well as increase crop yields.
Fall plowing facilitates more timely planting in wet springs, but it greatly increases winter and
early spring erosion hazards; optimum timing of spring operations can reduce erosion and
increase yields.
Rough, cloddy surface increases infiltration and reduces erosion; much less effective than E 1
and E 2 when long rain periods occur; seedling stands may be poor when moisture conditions
are less than optimum. Mulch effect is lost by plowing.
Can reduce average soil loss by 50% on moderate slopes, but less on steep slopes; loses
effectiveness if rows break over; must be supported by terraces on long slopes; soil, climatic,
and topographic limitations; not compatible with use of large farming equipment on many
topographies. Does not affect fertilizer and pesticide rates.
Similar to contouring but less susceptible to row breakovers.
Rowcrop and hay in alternate 50- to 100-foot strips reduce soil loss to about 50% of that
with the same rotation contoured only; fall seeded grain in lieu of meadow about half as
effective ; alternating corn and spring grain not effective ; area must be suitable for across-slope
farming and establishment of rotation meadows; favorable and unfavorable features similar to
E 3 and E 9.
Support contouring and agronomic practices by reducing effective slope length and runoff
concentration; reduce erosion and conserve soil moisture; facilitate more intensive cropping;
conventional gradient terraces often incompatible with use of large equipment, but new
designs have alleviated this problem; substantial initial cost and some maintenance costs.
Facilitate drainage of graded rows and terrace channels with minimal erosion; involve establish-
ment and maintenance costs and may interfere with use of large implements.
Earlier warming and drying of row zone; reduces erosion by concentrating runoff flow in
mulch-covered furrows; most effective when rows are across slope.
Minimizes row breakover; can reduce annual soil loss by 50%; loses effectiveness with post-
emergence corn cultivation; disadvantages same as E 9.
Sometimes the only solution. Well managed permanent grass or woodland effective where
other control practices are inadequate; lost acreage can be compensated for by more intensive
use of less erodible land.
Contour furrows, diversions, subsurface drainage, land forming, closer row spacing, etc.
63
-------
E 1. No-Till Plant in Prior-Crop Residues
The term "no-till" as used in this manual refers to
planting in narrow slots opened by a fluted coulter or
other device, without tillage. The crop residues remain
distributed over the soil surface throughout the year.
The planting can be in chemically killed meadow or
winter cover, small-grain stubble, chopped cornstalks, or
other crop residues. The residue mulch protects the soil
surface against erosion during the highly vulnerable
crop-establishment period and is also effective during the
growing season and after harvest.
Where residues are adequate to provide nearly com-
plete surface cover, no-till planting can be the most
effective year-round erosion-control practice compatible
with intensive grain production. No-till planting in
chemically-killed sod can reduce soil loss to less than 5%
of that from the conventional plow, smooth, plant and
cultivate system. Uniformly distributed cornstalks at a
rate of 3 tons or more per acre can reduce soil loss by
about 85% on moderate slope lengths. However, lesser
rates of residues are less effective (Table 4), and
supporting practices are still needed when slope lengths
are excessive. No-till planting without surface residues is
not recommended as an erosion-control practice. Use of
no-tillage for soybeans following corn reduces erosion
potential and may produce greater yields than plow-
based systems. No-till planting reduces man and machine
hours and soil compaction by implements. Where the
residue cover is adequate, it also reduces sealing and
crusting of the soil surface.
The advantages of no-till may be partially offset by
problems that are inherent in no-plow systems. More
herbicides and insecticides are usually required than with
plow systems, and nitrogen and phosphorus can be
leached from the plant residues left on the surface.
However, any increase in runoff pollution by soluble
chemical compounds is usually offset by a greater
reduction in sediment-transported compounds. Elimina-
tion of tillage reduces the options for fertilizer place-
ment and eliminates the soil loosening associated with
inversion plowing. More nitrogen is sometimes needed to
maintain yields. An initial outlay for equipment modifi-
cation or replacement may be required. Residue mulch
on the surface retards drying and warming of the soil
surface in the spring and may delay planting or seedling
emergence. No-till planting in complete residue cover is
usually not recommended on fine-textured soils in the
northern states, but other forms of conservation tillage
(E 2) may be adaptable.
Reports from the Northwest point out that iio-till
techniques for winter wheat as now used in that region
lead to serious weed problems, poor seedling develop-
ment in heavy residues, and reduced yields, and that
plant toxicity problems may exist where crops are
planted in heavy residues.
E 2. Conservation Tillage Practices
Some of the limitations of no-till planting can be
alleviated by use of conservation tillage systems that
have broader adaptability but are somewhat less effec-
tive. These systems usually replace moldboard plowing
with some form of non-inversion tillage that retains
some of the residue mulch on the surface. In some of the
systems, a chisel, field cultivator, or disk is used over the
entire area. In others, row zones are tilled while the
inter-row zones are left untilled with the residue cover
intact. Strip tillage overcomes some of the disadvantages
of no-till and is highly effective when the rows are across
slope. If they are up and down slope, the runoff may be
channeled to flow in the tilled zone, where it can still be
quite erosive.
Conservation tillage systems can be suited to a
broader range of soil and climatic conditions than no-till,
and options for fertilizer placement are usually more
than for no-till. Crop yields are as good as, and
sometimes higher than, those with the plow-based
systems. Some of the practices require equipment
modification, but man and machine hours and soil
compaction by implements are usually reduced.
The degree of effectiveness of a particular system or
machine depends on the surface conditions induced. The
effectiveness is directly related to the amount of residues
left on the surface, amount of residues mixed into the
upper few inches of topsoil, surface roughness, and
ridges or residue strips on the contour; it is inversely
related to the amount of soil pulverization.
E 3. Sod-Based Rotations
Sod-based rotations have been successfully used for
many years to reduce erosion from the conventional
plow-based systems in regions adapted to rotation
meadows. Soil loss from a good quality grass and legume
meadow is negligible, and when the sod is plowed out,
residual effects improve infiltration and leave the soil
less credible. These effects are very substantial in the
first year after sod is inverted and remain significant
during the second year. With good fertility management,
annual soil losses from 4-year rotations of wheat, hay,
and 2 years of conventionally planted corn usually
average about one-third of those from conventionally
planted continuous corn.
Sod-based rotations with conventional tillage allow
more fertilizer placement options, provide better control
64
-------
of some plant diseases and pests, and have less soil-
temperature problems than no-till or mulch tillage
systems. Legumes in the meadow mixture can help meet
nitrogen requirements.
But there are disadvantages. Substituting hay for
corn, soybeans, grain sorghum, or cotton on a sub-
stantial portion of a farmer's potential cash-crop acreage
is likely to reduce his income because of lower cash
value of the hay crop. Meadow crops have a high mineral
requirement. Where hay is removed, higher fertilizer
rates are needed to maintain stands. The potential foi
transport of soluble phosphorus is greater from meadows
than from row crops, but sediment-transported P is
much less. Wireworms, cutworms and army worms are
more prevalent in first-year corn after meadow.
For off-site sediment control, another consideration
is the unequal distribution of soil loss within a rotation
cycle (Figure 31). In this example, just 5 of the 48
months in the rotation cycle accounted for half of the
total soil loss. The first 2 months of the second-year
corn accounted for 28%. No-till planting the second-year
corn in chopped cornstalk residues would greatly reduce
the hazard of high 1 -year sediment yields and would cut
the average annual soil loss for the 4-year rotation in
half. The rotation soil loss could be further reduced by
no-till planting the first-year corn in chemically killed
sod instead of turning the meadow.
E 4. Meadowless Rotations
Rotating two kinds of row crop, or a row crop and
small grain, has far less erosion-control potential than
sod-based systems, but such rotations aid in control of
some diseases and pests and usually reduce the amount
of herbicides required. A row crop and fall-seeded grain
system reduces erosion by shortening the time the soil is
bare. Soybeans following corn or grain sorghum lose less
soil than second-year soybeans. Conversely, corn after
soybeans has a higher erosion potential than corn after
corn. Small grain seeded in disked corn residues will
likely lose from 50 to 70% less soil than grain planted on
a plowed and fitted seedbed. Soil loss from corn planted
on plowed wheat land is nearly equal to that from
plowed corn land where the residues are incorporated.
However, winter grain chemically killed at corn-planting
time provides an excellent condition for no-till planting
of corn.
Where the growing season is long enough to permit
following winter grain with soybeans in a 1-year system,
the double cropping shortens the time when the soil
surface is poorly protected and the grain residue reduces
erosion from the soybeans.
E 5. Winter Cover Crop
When corn or sorghum is harvested for grain only,
leaving the shredded stalks on the field will probably
provide more protection during the winter than a
late-seeded small grain winter cover on plowed ground.
However, a winter cover seeded early enough to attain
good fall growth is beneficial following crops that leave
little residue cover, and on fields where the corn stover is
harvested for silage or other use. If the cover crop is
chemically killed and left in place for no-till planting of
a row crop, it also provides excellent control during the
crucial May and June period.
Where soil wetness in spring is a problem, such as on
the claypan soils, the early spring growth of a wheat
cover crop can enable earlier corn planting by removing
excess water from the soil. Conversely, where soil
moisture supplies are critical, the water used for growth
of the winter cover may deprive the ensuing crop of
needed moisture and thereby reduce yields.
E 6. Improved Soil Fertility
Improving soil fertility and general crop management
to increase crop yields has the additional advantage of
substantially reducing soil erosion. This reduction is
attributable to improved crop canopy, increased water
use by the plants, and availability of more residues for
soil protection. The magnitude of potential soil loss
reduction through improved crop productivity is indi-
cated by the differences in the paired C values of Table 4.
E 7. Timing of Field Operations
Erosion data indicate that fall plowing for corn will
generally increase the annual soil loss at least 10%
relative to spring plowing, and by two to tenfold relative
to no-plow systems where residues are retained on the
surface. The soil is exposed to die erosive forces of thaw
runoff and early spring rains, and soil porosity at
planting time is less than with spring plowing. However,
fall plowing facilitates more timely planting where
wetness is a problem in early spring and may thereby
increase yield averages. It is usually recommended on
nearly level soils of moderately fine to fine texture.
The precise timing of field operations also influences
erosion losses. Early-seeded wheat protects against
erosion by spring thaw and snowmelt more than does
late-seeded wheat. Delaying spring plowing and corn
planting beyond the optimum dates usually increases the
erosion potential, because the most erodible period is
then during a time of greater rainfall erosivity.
65
-------
iua;sa/tt ut leaif/Yv-iuoa-inoMopBaui jo UOIJBJOJ
LUOIJ ssoj pos jo suoiinqujsip Xppuoui
-' l£
en
O
tx
Month: SONDJ FMAMJnJ ASONDJaFMAMJnJASONDJaFMAMJnJASONDJ F M A M Jn J A
M
•o
o
en
o
o
c
a
0.
£ CJ
o F
fo C Residue o
o
•o *_
a> $ c
^ 50
en Q.Q.
TD
O
"B
0)
W
I
CD
>
M
n
5
(/)
-------
E 8. Plow-Plant Systems
In plow-plant and wheeltrack-plant systems the field
is tumplowed but secondary tillage is minimized. The
plant residues are covered, but the surface remains rough
and cloddy after planting. The rough surface decreases
sealing, increases surface detention of excess water, and
reduces runoff velocity. Erosion from moderate rains is
greatly reduced, but if the plow layer becomes saturated
and runoff is substantial, the surface has no protection.
The principal disadvantage is difficulty in obtaining
stands. Weeds must be chemically controlled if the rough
surface is to be maintained. This is not a common
practice but may be advantageous in some situations.
E 9. Contouring
Contouring is a supporting practice that is widely
recommended where drainage is not a problem. The crop
rows follow the field contours across the slope. This
slows the movement of excess rainfall from the field and
thereby reduces soil detachment and increases infiltra-
tion. Contouring provides excellent erosion control for
moderate rainstorms, but is ineffective if the capacity of
the rows to hold or conduct runoff is exceeded. The
average soil loss reduction from contouring is about 50%
on moderate slopes, but less on steeper slopes.
Contouring is not effective on long slopes unless
supported by terraces or runoff diversions. Length limits
given in Agriculture Handbook No. 282 for the conven-
tional plow-based systems are listed in Table 13.
Adjusted limits for conservation tillage practices that
retain substantial amounts of residues on the surface
throughout the year are also given.
Following field contour lines with mechanized equip-
ment is time consuming, and point rows are often
involved. On much of the cropland topography, the
practice is incompatible with use of massive multiple-
row equipment. On poorly drained soils, contouring may
aggravate wetness problems.
E 10. Graded Rows
Graded rows are land-formed to a precise gradient.
This improves surface drainage and decreases the likeli-
hood of row breakovers.
Ell. Contour Strip Cropping
Strips of sod alternated with strips of row crop,
across the slope, are much more effective than contour-
ing alone. The sod strips serve as filters if rows break.
High-quality sod strips reportedly have filtered 75% or
Table 13. Approximate length limits for contouring1
Slope (%)
2
4 to 6
8
10
12
Length (feet)
Conventional
tillage2
400
300
200
100
80
Mulch
cover3
500
375
250
125
100
Slope-length limits depend also on runoff rate, soil credi-
bility, and type of vegetation, but the relationships have not
been established. When the lengths in the table are exceeded,
factor P should be assumed equal to 1.0 unless the field is
terraced. However, the approximate lengths shown in this table
are not sufficiently accurate to serve as terrace spacing guides.
' Limits given in Agriculture Handbook No. 282 for systems
in \viiich the crop residues are removed or covered by inversion
plowing.
Limits adjusted upward for effects of at least 50% residue
cov^ during crop establishment and after harvest.
more of the suspended soil from the runoff from the
cultivated strips. Stripcrop systems generally use a 4-year
rotation—2 years of meadow, 1 of row crop, and 1 of
small grain in which new meadow is established. This
system reduces the field soil loss to about half of the
average for the same rotation contour farmed without
the alternating strips, or about 25% of the rotation
average with rows up and down a moderate slope.
Stripcropping 3-year systems of meadow, row crop and
small grain is less effective. Alternate strips of corn and
spring-seeded small grain do not significantly reduce
water erosion.
The practice has the same limitations as those listed
for sod-based rotations and for contouring. However, it
also has all the advantages of both, plus a large
additional reduction in soil loss. Strip cropping has not
been generally adopted in the western part of the Corn
Belt because the strips of low-growing meadow give
increased access of hot winds to corn strips in late July
and early August and result in greater drought damage to
the corn.
E 12. Terraces
Terrace systems support contouring by acting as a
safety measure to prevent serious rills and field gullies
when contour rows break. They reduce slope length by
dividing the overall slope into segments equal to the
horizontal terrace spacing. Excess water is "walked" off
67
-------
the field through nearly level terrace channels to a
grassed outlet or is removed through a subsurface drain.
Shortening the effective slope lengths decreases soil loss
from the strips between the terraces, and up to 80% of
the soil that is moved from the between-terrace strips is
deposited in the terrace channels. For resource conserva-
tion, only the reduction in erosion between the terraces
is usually credited. However, for sediment and pollution
control purposes, the large amount of deposition in the
channels is also creditable.
Terrace systems have the highest initial cost of all the
conservation practices, and they require continuous
maintenance. However, they permit more intensive
cropping on sloping land, and on long slopes they are
needed to supplement agronomic and cultural practices
because the effectiveness of these practices breaks down
when slope lengths exceed certain limits (Table 13).
Optimum horizontal spacing of the terraces depends on
the slope steepness, soil, rainfall, and crop management.
Standard formulas are readily available.
The conventional gradient terrace systems make the
use of large farm equipment difficult because of the
winding rows and because the distance between the
terraces is not uniform. This difficulty is largely allevi-
ated by use of parallel grass-backslope terraces with
subsurface drains. However, these terraces are not
adaptable to all conditions, and construction costs are
higher than for conventional systems. Level closed-end
terraces reduce erosion and have little runoff. They can
be a major pollution-abatement practice.
E 13. Grassed Outlets
Grassed outlets are stabilized channels that receive
the drainage from contoured or graded rows or from
terrace channels and remove it from the field. They are a
highly effective erosion-control practice. Disadvantages
include establishment and maintenance problems and
incompatibility with use of large farm equipment and
with use of herbicides to control grass in the row crops.
E 14. Ridge Planting
The rows are planted on existing or preformed ridges
from which the residues have been moved to the
between-row furrows. The ridges warm and dry more
quickly and facilitate earlier planting. When the ridges
are on the contour or very slight row gradient, they
function as small, closely spaced terraces and are very
effective. The practice is less effective when the rows are
not on the contour, but large amounts of residues in the
furrows can substantially reduce soil loss even with row
gradients up to 6 or 8%. Disadvantages include problems
with stand establishment, fertilizer placement, and weed
control. If the ridges break, deep rilling may occur.
E 15. Contour Listing
The rows are planted in contoured furrows, which
reduce the velocity of water movement down the slope.
Row breakover during crop establishment is much less
likely than with standard contouring. If the corn is
cultivated, the furrows are gradually closed and, there-
fore, are less effective after the corn has developed a
canopy cover. The practice is most effective during the
crop establishment period, which is the time when
erosion hazards are greatest. The problems and disadvan-
tages are similar to those listed for contouring (E 9). In
plot studies, the reduction in annual soil loss has
averaged about 50%.
E 16. Change in Land Use
Change in land use is sometimes the only solution.
Properly managed hay or pasture furnishes adequate
erosion control over a wide range of slopes throughout
most humid sections of the country. Managed perma-
nent woodland with duff and underbrush cover permits
almost no erosion. Sometimes, a change to annual
cropping of small grains and other closely seeded crops,
with appropriate tillage practices and residue manage-
ment, will suffice.
E 17. Other Practices
Contour furrows are sometimes used instead of
terraces.
Diversions are sometimes used to channel excess
water from a field where terraces are not needed.
Subsurface drainage systems provide another means
of removing excess water without erosion.
Land forming can sometimes alleviate the problems
of irregular topography for contouring or terracing and
also improves surface drainage.
Rows on 30-inch spacing hasten development of an
effective canopy and provide a more complete canopy
cover than the traditional 40- or 42-inch spacing. Tests
have shown some associated reduction in erosion,
particularly during the first 2 months of the crop year.
Vegetative sediment filters, settling basins, and sedi-
ment traps represent another approach to sediment
reduction. They are not erosion control practices, but
they can be very effectively used to trap sediments near
their source.
68
-------
The above list covers only the major types of control
practices, not all the specific forms. Also, practices that
are basically the same may be known by different names
in different sections of the country. Several alternative
field-tested erosion control practices are available for
any particular geographic region, but the options are not
the same for all regions or for all fields within a region.
Use of a specific practice may be limited by soil,
climatic, or topographic restraints. Some of these re-
straints can be overcome by changing specific details of
the practice to suit local conditions. Also, the relative
importance of raindrop impact, surface runoff, and
topographic features as erosion-producing factors is not
the same for different regions such as the humid Central
Valley, the wheat belt of the Pacific Northwest, and the
coastal plains of the Southeast. The dominance of one of
these factors over the others influences the type and
specific form of control practice needed.
Potential soil loss reductions by the various types of
agronomic practices were not quantified in the preceding
discussion because the effectiveness of a given type of
practice depends on its specific form and on the crop
system and general management level with which it is
used.
4.1 a Quantifying Potential Soil Loss Reductions
The cover and management factor, C, of the soil loss
equation that was introduced in Section 3.3b is evalu-
ated for specific agronomic practices in combination
with specified crop systems. Illustrative C values were
presented in Table 4. These values can be used to
estimate how much a change from one crop-and-
management system to another would reduce soil loss.
For example, conventionally planted continuous corn
with residues turned under in spring (line 5) has a
C-value of 0.38 for the high productivity level. For
continuous corn that is no-till planted in a 70% surface
cover of fall-shredded stalks (line 16), C = 0.11.
Therefore, the estimated reduction in soil loss by
changing from the first practice to the second is
(0.38-0.11)/0.38 = 0.71, or 71%. This procedure can also
be used to estimate the erosion reduction from improved
soil fertility and crop management (practice E 6). In line
16 of Table 4, for example, C = 0.18 for the moderate
productivity level and 0.11 for the high productivity
level. The estimated soil loss reduction attainable by
increasing the average annual corn yield from about 50
bushels to more than 75 bushels and retaining the same
percentage of the residues on the surface would be
(0.18-0.11)/0.18 = 0.39, or 39%.
Factor C is the ratio of the average soil loss with a
given combination of cropping and cultural practices to
the erosion-potential index defined in Section 3.3b,
Since the erosion-potential index is determined by the
location's soil, rainfall pattern and topographic features,
it has a fixed value for a given land area. Therefore, the
C values for alternative practices for that area are
fractions of the same number and the procedures used in
the preceding paragraph are mathematically valid.
Potential reductions by supporting practices, such as
contouring, terracing, etc., can be estimated from Table
5 by subtracting the appropriate P value from 1.0.
Potential reductions by combinations of supporting
practices (Table 5) and agronomic practices (Table 4) are
computed as progressive reductions. Changing from the
system in line 5 to the one in line 15 would decrease C
from 0.38 to 0.12, but changing from line 5 with tillage
up and down slope to line 15 supported by contour
strip-cropping on a 10% slope would reduce the com-
bined value of C and P from 0.38 to (0.12 x 0.6). The
estimated soil loss reduction by the two concurrent
changes would be (0.38-0.072)/0.38 = 81%.
These estimates of potential reduction are helpful
guides, based on averages. However, both C and P are
affected by interactions with physical and farm-operator
variables and are, therefore, not identical for all situa-
tions.
4.1b Selecting Erosion Control Practices for
Specific Land Areas
The combination of agronomic and supporting prac-
tices required to reduce soil loss to any specific limit is
dictated by the severity of the erosion hazard and the
effectiveness of each of the various practices that can be
adapted to the situation. Erosion hazards often differ
widely within a relatively small geographic area. There-
fore, control practices can be most accurately prescribed
on an individual-field basis. However, plans can be
developed for larger areas if they allow flexibility in
practice selection to correspond with differences in soil
type and slope characteristics.
With the help of the soil loss equation, erosion
control planning can be a process of systematic deci-
sion-making based on logical evaluation of the alterna-
tives for land use and treatment. For this purpose, the
equation is used with a numerical soil loss tolerance, T,
which is the maximum allowable erosion rate based on
the particular soil and environment. This rate can be
either a prescribed standard or a voluntary goal selected
by the farmer or the community. (T values will be
discussed later.)
The soil loss equation (A = R x K x LS x C x P)
estimates the average annual soil loss from sheet and rill
erosion (A), in tons per acre, for specific combinations
69
-------
of rainfall pattern (R), soil type (K), topographic
features (LS), crop system and cultural management (C)
and supporting erosion control practices (P). Procedures
and data for estimating local values of the equation's
individual terms were presented in Section 3.3b.
For practice selection, it is convenient to substitute
the maximum allowable soil loss, T, for A in the
equation and to rearrange the terms into the form:
maximum CP = T/RKLS.1 The product R x K x LS is the
computed estimate of the site's erosion-potential index
(Section 3.3b). To hold soil loss below the tolerance, T,
the crop system, cultural management and support
practices must be such that C x P does not exceed the
quotient T -r RKLS. Each of these terms has a numerical
value for the particular land area, so the maximum
permissible CP value is defined. For example, if in a
given situation the tolerance goal were 5 tons per acre,
the rainfall-erosivity index 190, the soil factor 0.32, and
the topographic factor 1.4, the product of factors C and
P would not be permitted to exceed 5/(190 x 0.32 x
1.4), which is 0.059.
With no supporting practice, P = 1.0, and the
maximum allowable C value would be 0.059. With a
supporting practice, the limiting C value would be 0.059
times 1/P, where the value of P is taken from Table 5
and is always less than 1.0.
The maximum C derived by this procedure is the
threshold value for entering a regional table of C values
such as illustrated by Table 4. Each line in the table
denotes a specific crop and management system. All
systems for which C is less than the computed threshold
value qualify as options for the particular area if the
designated crops and practices are suitable for the
climate and soil. Supporting practices increase the
threshold value and the number of acceptable alterna-
tives.
The practice selection procedure is outlined by
successive steps in the erosion flow charts, Figures 36
and 37, and is illustrated by detailed examples in Section
6.
4.1c Tolerance Limits
Nothing in this manual is intended as a recommenda-
tion of any specific soil loss tolerance standard, but
some of the consideratioriS involved in setting such
standards are appropriate.
For conservation planning purposes, the Soil Con-
servation Service has found tolerances ranging from 5 to
'In the flow chart, Figure 37, the product RKLS is
represented by I, and T/RKLS is represented by A. Hence, the
maximum permissible value of CP is Xand the maximum C is
2 tons (depending on characteristics of the soil profile)
feasible and adequate when defined in terms of average
annual soil loss. These limits were selected primarily to
conserve or improve the long-range productivity of the
cropland; they are not necessarily the most appropriate
ones for pollution control.
For controlling water pollution from nonpoint
sources, a limit on the potential amount of off-farm
sediment would seem more appropriate than a limit on
soil movement within field areas. Sediment filters and
traps would then also be possible options as control
measures. Soil texture and the location of the cropland
relative to streams, lakes, reservoirs, or critical areas are
also important in determining how much field soil loss
could be tolerated. Texture is important because col-
loidal materials remain in suspension longer than larger
particles and are probably the primary carriers of
chemical compounds. Soil loss tolerances related to
classifications of cropland with reference to location and
texture may be more appropriate than a statewide
uniform standard.
Short-time peak sediment loads may be more impor-
tant in pollution control than they are in preservation of
the land resource. Limits based on the most credible
crop in the rotation, or perhaps even on seasonal soil loss
probabilities, may be appropriate. However, such limits
could not be as low as limits on average annual losses
and would be more difficult to monitor. A tolerance as
low as 5 tons per acre on peak-year losses would
drastically limit grain production on much of our highly
productive cropland. Merits and limitations of tolerance
limits based on other than longtime-average soil losses
are further discussed in Volume II of this report.
4.2 PRACTICES TO CONTROL DIRECT
RUNOFF
Surface runoff from cropland can rarely be elimi-
nated. However, it can be substantially affected by
agronomic and engineering practices. If the direct runoff
from a summer row crop with straight rows is taken as
the basis for comparison, land use and treatment
practices can affect direct runoff in two ways: (1)
change the volume of runoff, and (2) change the peak
rate of runoff. A change in runoff volume will generally
change the peak runoff rate in the same direction;
however, peak runoff rates can be changed without
affecting the volume.
Direct surface runoff volumes can be reduced by
measures that: (1) increase infiltration rates, (2) increase
surface retention or detention storage, allowing more
time for water to infiltrate into the soil, and (3) increase
interception of rainfall by growing plants or residues.
70
-------
The first two measures are the most important. Infiltra-
tion rates are increased by agronomic practices that
result in dense vegetative cover, abundant mulch or
litter, high soil organic matter content, good soil
structure, and good subsurface drainage. A dense vegeta-
tive cover not only protects the soil surface from the
sealing effect of raindrops but also provides for maxi-
mum transpiration loss and lowered soil water content.
Subsurface drainage systems drain excess water between
storms, thus resulting in higher infiltration rates. Higher
fertility levels and management practices that increase
vegetative cover result in lower direct runoff. Manage-
ment practices such as contouring or engineering prac-
tices such as contour furrowing, graded terracing, and
level terracing can substantially increase surface storage.
Dense vegetative cover, mulch, and rough, cloddy
surfaces also increase retention and detention storage.
Peak runoff rates can be decreased by treatments that
increase the hydraulic resistance of the surface, decrease
the land slope, or increase the length of flow path. Such
practices or treatments will generally reduce erosion too,
but it is difficult to assess the effects on the transport of
weakly adsorbed chemicals. A reduction in erosion may
reduce the amount of mixing of the soil with water;
however, the longer contact time may increase the
opportunity for solution of chemicals. Apparently, one
way to reduce the loss of agricultural chemicals in direct
runoff is to reduce the volume of runoff.
How much direct runoff can be reduced depends on
the number and type of control measures used and on
the characteristics of the soils and climate of the
particular location. A reduction of surface runoff may
result in a somewhat smaller increase in subsurface
runoff and deep percolation. Therefore, where leaching
is a serious problem, it may not be desirable to reduce
surface runoff.
Practices that reduce erosion will usually reduce
runoff, although to a lesser extent. Therefore, the first
16 runoff control measures have been assigned the same
reference numbers as the identical erosion control
measures; only the alphabetical prefixes differ (i.e.,
Practice R 1 is the same as E 1).
Erosion control practices have been described in
detail in the erosion control section, so only those
aspects related to runoff control are discussed in the
following paragraphs. Runoff control measures and their
highlights are summarized in Table 14.
Continuous meadow has the lowest annual and
seasonal direct runoff of all the practices in Table 14
with the possible exception of level terraces. Therefore,
the percentage reduction in potential direct runoff
achieved by a change in land use from straight-row
summer crops to continuous meadow represents the
maximum that runoff can be reduced in most instances.
The percentage reduction that can be achieved by
runoff control practices varies significantly with the
amount of potential direct runoff, as shown by the
upper curve in Figure 32. This curve serves as the basis
to divide the percent reduction achieved by runoff
control practices into three somewhat arbitrary zones,
"slight," "moderate," and "substantial," as shown in
Figure 32. These three terms are used to describe the
amount of runoff reduction in the "practice highlights"
in Table 14.
The Soil Conservation Service method was used in a
simulation procedure to estimate the mean annual and
seasonal reduction in direct runoff that might be
achieved by some runoff control methods. The appro-
priate empirical parameters or "curve numbers" are not
available for all practices listed. Where it is stated that a
practice reduces direct runoff, such a reduction is
relative to direct runoff from a straight-row summer
crop (corn, cotton, soybeans).
R 1. No-Till Plant in Prior-Crop Residues
This practice increases infiltration rates by maintain-
ing either a plant canopy or a mulch of plant residues on
the surface the entire year. Residues on the surface tend
to form small dams, which increase surface storage. The
Soil Conservation Service has not developed curve
numbers for this practice, but limited data indicate a
range of response from an increase in growing-season
runoff to a substantial decrease. In general, the high
percentage reduction will occur in years of low runoff
and for the smaller storms. In some circumstances, soil
compaction and reduction of evaporation from the
surface due to the residues may lead to increases in
runoff.
R 2. Conservation Tillage
Among the many practices that can be included in
this classification are those known as till plant, strip
tillage, sweep tillage and chisel plant. Only fragmentary
data are available to quantify the runoff reduction that
might be achieved by each practice. Their relative
effectiveness can be judged by the amount of residue left
on the surface and the amount of surface storage created
by the tillage operation. When used without support
practices, runoff will be reduced slightly to moderately.
Runoff may be reduced substantially if conservation
tillage is used in conjunction with contouring.
71
-------
Table 14. Practices for controlling direct runoff and their highlights.1
No.
Rl
R2
R3
R4
R5
R6
R7
R8
R9
R 10
R 11
R 12
R 13
R 14
R 15
R 16
R 17
R18
Runoff Control Practice
No-till plant in prior crop residues
Conservation tillage
Sod-based rotations
Meadowless rotations
Winter cover crop
Improved soil fertility
Timing of field operations
Plow plant systems
Contouring
Graded rows
Contour strip cropping
Terraces
Grassed outlets
Ridge planting
Contour listing
Change in land use
Other practices
Contour furrows
Diversions
Drainage
Landforming
Construction of ponds
Practice Highlights2
Variable effect on direct runoff from substantial reductions to
increases on soils subject to compaction.
Slight to substantial runoff reduction.
Substantial runoff reduction in sod year; slight to moderate
reduction in rowcrop year.
None to slight runoff reduction.
Slight runoff increase to moderate reduction.
Slight to substantial runoff reduction depending on existing
fertility level.
Slight runoff reduction.
Moderate runoff reduction.
Slight to moderate runoff reduction.
Slight to moderate runoff reduction.
Moderate to substantial runoff reduction.
Slight increase to substantial runoff reduction.
Slight runoff reduction.
Slight to substantial runoff reduction.
Moderate to substantial runoff reduction.
Moderate to substantial runoff reduction.
Moderate to substantial reduction.
No runoff reduction.
Increase to substantial decrease in surface runoff.
Increase to slight runoff reduction.
None to substantial runoff reduction. Relatively expensive.
Good pond sites must be available. May be considered as a
treatment device.
Erosion control practices with same number are identical. Limitations and interactions shown in Table 12, Principal Types of
Cropland Erosion Control Practices and Their Highlights, also apply to runoff control practices.
2 The ranges in percent reduction of potential direct growing season runoff for the descriptive terms, "slight," "moderate," and
"substantial" are shown in Figure 32.
R 3. Sod-Based Rotations
R 4. Meadowless Rotations
Long-term average direct runoff can be reduced
substantially by sod-based rotations. The amount of
reduction depends primarily upon the percent of time
that the land is in sod, although the residual effects of
the meadow increase infiltration rates and may cause a
slight to moderate reduction in direct runoff from a row
crop in the following year.
Direct runoff may be slightly reduced or increased in
the years the field is in small grain, but it apparently has
no residual effect on infiltration capacity in the row-
crop year. Rotations involving only row crops (corn and
soybeans, for example) would have approximately the
same direct runoff potential as continuous com.
72
-------
R5. Winter Cover Crop
This practice may reduce direct runoff in the fall,
winter, and spring if the crop residues are not plowed
under. It would have little or no effect on growing
season runoff. Limited data indicate that dormant
season runoff may be slightly to moderately reduced. If
the residues are plowed under before planting the cover
crop, direct runoff may be increased.
R 6. Improved Soil Fertility
High soil fertility leads to a rapid extension of the
crop canopy, rapid water removal from the soil by
plants, and copious plant residues-all of which tend to
increase infiltration rates and reduce runoff. Runoff
reduction depends on the fertility level of the standard
for comparison. Slight to substantial effects have been
reported.
R 7. Timing of Field Operations
Direct runoff can be reduced by planning field
operations to minimize the time that the soil is bare.
Depending on climatic conditions, fall, winter, and
spring runoff may be reduced by leaving crop residues
on the surface after harvest and plowing in the spring.
Manning field operations solely on the basis of minimiz-
ing runoff or erosion losses could result in economic loss
to the farmer if bad weather prevented planting at the
best time for crop production.
R8. Plow-Plant Systems
The rough surface left by the plow-plant operation
increases infiltration rates and surface storage. Direct
runoff may be moderately reduced during the growing
season.
R9. Contouring
Contouring reduces direct runoff by increasing sur-
face storage. Direct runoff will be eliminated or reduced
substantially for small storms, but may not be reduced
for large storms if the contour ridges are breached by
runoff. This practice reduces growing season runoff
more than dormant season runoff, because the contour
ridges become weathered and less effective as the season
progresses. This practice is most effective on slopes of 2
to 8%. It is not usually feasible for slopes of less than 1%
or on very irregular topography. Direct runoff reduc-
tions achieved by contouring according to the Soil
Conservation Service procedure are shown for several
locations in Table 15. The reductions range from slight
to moderate. For slopes of less than 2%, straight rows
across the slope are considered to be as effective as
contouring.
R 10. Graded Rows
This practice reduces direct runoff by increasing
surface storage and allowing more time for infiltration.
Runoff reduction for small storms may not be as great
with this practice as with practice R 9. However, this
practice will be more effective than R 9 for larger
storms. Runoff reduction should be similar to that
shown for contouring in Table 15 and should range from
slight to moderate.
R 11. Contour Strip Cropping
Contour strip cropping reduces direct runoff by
increasing infiltration rates on strips in small grains and
meadow and by increasing surface storage on contour-
tilled strips. For storms in which the infiltration capaci-
ties of meadow or grain strips are not exceeded, some
direct runoff from intertilled crops may be infiltrated
into grassed waterways or lower strips of meadow or
small grains. Although the direct runoff from a given
land area is less than it would be if the entire area were
in a row crop, the runoff from a row crop strip is
probably only slightly less than that from an intertilled
contoured field.
R 12. Terraces
Gradient and level terraces reduce direct runoff by
increasing surface storage and increasing the time that
infiltration can occur. Terraces may also make contour-
ing more effective by shortening the effective length of
slope and thereby reducing the likelihood of the contour
ridges being breached. Estimates of the percent reduc-
tion in direct runoff that might occur for contoured and
terraced fields (a combination of practices R 9 and R
12) are shown in Table 15 and are in the moderate to
substantial range. Gradient terraces alone (without con-
touring) may increase direct runoff in some instances,
but usually would reduce it slightly.
Level terraces are constructed with the channel level
and the ends blocked so that runoff is stored until it can
infiltrate. The reduction of runoff depends on how
much storage the terraces provide. In areas with low
rainfall and permeable sofls, surface runoff can be nearly
eliminated. In areas where retaining all the rainfall and
runoff that accumulates in the channel would damage
73
-------
100
90
80
70
I 60
o
T3
0>
50
c
0>
e 40
0>
O_
30
20
0
0
Reduction Achieved by Changing from Row
Crop to Continuous Meadow
(SCS Method)
Substantial Reduction Zone
Moderate Reduction Zone
Slight Reduction Zone
0123456789 10
Mean Growing Season1 Potential Direct Runoff (inches)
Figure 32.—Definition of ranges of reduction in mean growing season direct runoff.
the crop, outlets must be provided to increase the rate of
water removal. Surface runoff will be substantially
reduced, but the amount will depend on the design of
the terrace system and on climatic and soil factors. By
substantially reducing or eliminating surface runoff,
subsurface runoff and deep percolation will be increased
and may cause a leaching problem.
R 13. Grassed Outlets
No good data are available for grassed outlets, but
they may slightly reduce direct runoff.
R 14. Ridge Planting
The amount of direct runoff reduction depends upon
the size of the ridges and how closely they follow the
contour. Reductions should usually be greater than
those shown for the contoured and terraced practice in
Table 15.
R 15. Contour Listing
Contour listing can reduce direct runoff by increasing
surface storage. In some systems residues are concen-
trated in the furrows and infiltration rates may also be
74
-------
Table 15. Potential direct runoff and percentage runoff reduction for selected locations.
Location
Wichita, KS
Columbia, MO
Columbus, OH
Des Moines, IA
Grand IsL, NB
Sioux Pall, SD
Cairo, 1L
Indianapolis, IN
Springfield, 1L
Houston, TX
Raleigh, NC
Charleston, WV
Birmingham, AL
Columbia, SC
Dallas, TX
Little Rock, AR
Buffalo, NY
Boston, MA
Scranton, PA
Pittsburgh, PA
Seattle, WA
Hydrologic1
soil group
B
D
C
B
B
B
B
C
B
D
B
C
B
B
D
D
B
A
C
C
B
Estimated
mean annual
direct runoff
(inches)
2.2
5.3
3.6
1.6
1.5
1.2
4.7
5.2
2.6
11.3
2.4
4.0
7.2
4.4
8.3
13.4
1.5
2.2
2.6
3.2
2.9
% reduction in annual runoff
Contouring,
R9
11
20
12
18
16
8
1
11
12
17
16
14
11
17
15
12
13
6
16
10
20
Contoured and
terraced, R 9, R 12
22
37
21
27
23
16
9
21
22
36
32
25
21
31
32
24
23
15
30
19
35
Meadow
R16
81
75
75
89
88
94
78
75
89
52
88
75
72
83
55
58
89
94
82
83
85
Estimated
mean growing
season direct
runoff (inches)
1.7
2.9
1.0
0.9
0.9
0.7
.3
.7
.4
.9
.1
.2
.8
2.3
5.1
5.5
0.7
0.6
0.8
0.9
0.1
% reduction in growing season runoff
Contouring,
R9
15
31
10
24
12
13
11
23
12
17
19
25
14
21
14
11
33
11
21
22
33
Contoured and
terraced, R 9, R 1 2
29
53
24
38
26
28
24
42
24
36
39
36
29
39
29
24
54
26
32
41
55
Meadow
R 16
80
68
73
85
90
95
80
74
83
49
88
62
74
82
53
57
100
85
78
85
89
More than 4,000 soils in the United States and Puerto Rico have been assigned by the Soil Conservation Service to Hydrologic soil groups A through D on the basis of their
runoff potential. Hydrologic group A has low runoff potential; group D has a high runoff potential; and Band Care intermediate. For a more detailed discussion, see Volume II,
Appendix A.
-------
increased. Runoff reduction may be somewhat greater
than that shown for contour fanning (Practice R 9) in
Table 15.
R 16. Change in Land Use
A change in land use from row crop to permanent
meadow may greatly reduce direct runoff. The amount
of reduction for several locations as indicated by the Soil
Conservation Service method is shown in Table 15 and
in Figure 32. Observations range from a moderate
reduction to greater than that shown by the upper curve
in Figure 32.
Obviously, substantial local changes in land use wfll
often have serious adverse economic effects on the
farmer and the region. A change in land use from
straight row summer crops to meadow will give the
maximum reduction in direct runoff that can be
achieved under usual farming systems. Direct runoff may
be reduced still further by conversion to forest.
R 17. Other Practices
Contour furrows are sometimes used to conserve
moisture on native range or pasture and will reduce
direct surface runoff. The amount of reduction will
depend on the size and spacing of the furrows and how
closely they follow the contour. The effectiveness of the
practice decreases with time as the furrows weather or
are overtopped and eroded by surface runoff. In low
rainfall areas, contour furrows can almost eliminate
surface runoff.
Diversions are sometimes used to channel excess
water from a field where a terrace system is not needed
for erosion control. Diversions may increase the time of
travel and may increase infiltration in the channels.
However, they probably wfll not significantly affect
direct runoff.
Drainage is ordinarily installed to improve crop
yields. It may either increase or decrease direct runoff
that reaches a stream or lake. If it is "pothole" drainage,
direct runoff from cropland may reach a stream rather
than a local depression. Subsurface drainage will gen-
erally reduce direct runoff but may increase total runoff
by reducing evaporation and transpiration. Subsurface
runoff will be increased and may cause leaching prob-
lems.
Land forming may decrease direct runoff by allowing
some of the preceding practices to be used. Runoff may
increase, however, if soil horizons with lower infiltration
rates are exposed or if the soils are compacted.
R 18. Construction of Ponds
Where suitable sites are available, direct runoff may
be reduced by constructing ponds to collect runoff from
agricultural areas. If the precipitation is low compared to
the evaporation, runoff can be reduced. The amount of
reduction would depend on the pond's storage capacity
relative to the annual runoff from the catchment area.
Where actual evapotranspiration equals potential evapo-
transpiration throughout the year, evaporation loss from
the pond wfll approximately equal evapotranspiration
losses from the same area without a pond so runoff will
not be reduced, although some of the water will seep
through the pond and appear as subsurface or ground-
water runoff. The amount of runoff reduction will be
highly site-dependent and may range from none to
substantial. If the mean detention time in the pond is
long enough, it may reduce the peak concentration of
dissolved agricultural chemicals discharged to receiving
waters. Chemical transformations and deposition of
sediment will also take place in a pond, so it can be
considered as a treatment device.
Under appropriate climatic conditions, runoff to
streams could be reduced by using the water stored in a
pond for irrigation.
4.3 NUTRIENT MANAGEMENT PRACTICES
Nutrients are moved from agricultural land by leach-
ing, direct runoff, and in association with sediment from
erosion. A number of practices will reduce direct runoff
and/or erosion and, thus, reduce nutrient transport.
These practices will usually be adequate for controlling
overland nutrient transport in addition to sediment and
pesticide transport. However, in some cases, such as
leaching, additional and/or alternative practices will have
to be used to achieve the desired degree of control.
These practices involve changing the use of nutrients. A
list of these practices and their highlights are given in
Table 16.
N 1. Eliminating Excessive Application of
Nutrients
To control pollution, one must first eliminate the
excessive applications of nutrients. Because we lack the
technology to accurately predict the amount of fertilizer
required, some growers have tended to overfertilize so
that lack of nutrients would not limit yields. However,
the energy shortage has caused a dramatic increase in the
cost of fertilizer, which should result in a more careful
appraisal by farmers of fertilizer use.
76
-------
Table 16. Practices for the control of nutrient loss from agricultural applications and their highlights.
No.
Nl
N2
N3
N4
N5
N6
N7
N8
N9
N10
N 11
Nutrient Control Practice
Eliminating excessive fertilization
Practice Highlights
May cut nitrate leaching appreciably, reduces fertilizer costs;
has no effect on yield.
Leaching Control
Timing nitrogen application
Using crop rotations
Using animal wastes for fertilizer
Plowing -under green legume crops
Using winter cover crops
Controlling fertilizer release or transformation
Reduces nitrate leaching; increases nitrogen use efficiency;
ideal timing may be less convenient.
Substantially reduces nutrient inputs; not compatible with
many farm enterprises; reduces erosion and pesticide use.
Economic gain for some farm enterprises; slow release of
nutrients; spreading problems.
Reduces use of nitrogen fertilizer; not always feasible.
Uses nitrate and reduces percolation; not applicable in some
regions; reduces winter erosion.
May decrease nitrate leaching; usually not economically
feasible; needs additional research and development.
Control of Nutrients in Runoff
Incorporating surface applications
Controlling surface applications
Using legumes in haylands and pastures
Decreases nutrients in runoff; no yield effects; not always
possible; adds costs in some cases.
Useful when incorporation is not feasible.
Replaces nitrogen fertilizer; limited applicability; difficult to
manage.
Control of Nutrient Loss by Erosion
Timing fertilizer plow-down
Reduces erosion and nutrient loss; may be less convenient.
Many environmental factors, such as weather, pests,
etc., influence the potential yield of a crop and the
amount of plant nutrients released by the soil for plant
uptake. Experience, either by farmers or extension
workers, provides the best estimates of the potential
yields for crops under local conditions. Given the
potential yield, the nitrogen and phosphorus uptake by
the crop can be estimated. The values shown in Table 17
are typical of some leading crops, but the values should
be adjusted for yields common to a local area. Some-
times, the soil will provide adequate nutrients, but
fertilizers are usually required to supplement the soil
supply. The plant use of applied fertilizer varies between
40 and 80% for nitrogen and 15 to 20% for phosphorus.
Fertilizers should not be added unless they are
actually needed. Recommendations based simply on
"maintenance" or "balance" approaches to replace the
nutrients removed by the crop should be discouraged.
These approaches have been used partly because of a
lack of confidence in soil tests. However, soil tests are
available that are very useful for predicting fertilizer
requirements, particularly phosphorus. In some parts of
the country, the "residual" nitrate present in the top 2
feet of soil has been found useful in predicting nitrogen
fertilizer needed. In other areas, this nitrate is leached
between the time the soil is sampled and the time the
plant needs it. The prediction of nitrogen release from
soils is more difficult because it is largely controlled by
microbiological processes, which are affected by many
factors. No rapid soil test is available that provides an
adequate estimate of the amount of nitrogen the soil can
supply during the growing season, but research for the
development of such a test is being conducted. Experi-
ence with local field experiments is the best tool
currently available to estimate the nitrogen-supplying
capacity of the soil and the efficiency of the applied
77
-------
Table 17. Approximate yields and nutrient contents of selected crops. Values can vary by a factor of
two across the country.
Crop
* Alfalfa
Apples
Barley
*Beans
Bermudagrass
Bluegrass
Cabbage
*Clover
*
Corn
Cotton
*Cowpea hay
Lettuce
*Lespedeza
Oats
Onions
Oranges
Peaches
*Peanuts
Potatoes
Rice
Rye
Sorghum
*Soybean
Sugarbeets
Sugar cane
Timothy
Tobacco
Tomatoes
Wheat
grain
straw
(dry)
red
white
grain
stover
silage
lint and seed
stalks
grain
straw
nuts
tubers
vines
grain
straw
grain
straw
grain
stover
grain
straw
roots
tops
stalks
tops
fruit
vines
grain
straw
Yield/acre
4 tons
500 bu
40 bu
1 ton
30 bu
8 tons
2 tons
20 tons
2 tons
2 tons
150 bu
4.5 tons
25 tons
1 ton
1 ton
2 tons
20 tons
2 tons
90 bu
2 tons
7.5 tons
28 tons
600 bu
1.5 tons
400 cwt
1 ton
90 bu
2.5 tons
30 bu
1 .5 tons
60 bu
3 tons
45 bu
1 ton
20 tons
12 tons
30 tons
13 tons
25 tons
1 .5 tons
25 tons
1 .5 tons
50 bu
1.5 tons
Lbs N/acre
200
30
35
15
75
200
60
150
80
130
135
100
200
60
45
120
90
85
55
25
45
85
35
110
95
90
55
30
35
15
50
65
160
25
85
110
100
50
60
115
145
70
65
20
Lbs P/acre1
18
4
6
2
10
30
8
16
10
10
24
16
30
12
6
10
12
8
10
8
8
12
8
6
12
8
12
4
4
4
10
8
16
4
14
10
20
10
10
10
20
10
14
2
*Legumes that do not require fertilizer nitrogen
1 Ibs P = 0.436 Ibs P205
nitrogen. The nutrient contents of some crop residues
are also given in Table 17. Residues may be left on the
field for erosion protection or removed for livestock
feed. The disposition of these residues also has to be
considered in fertilizer recommendations. These esti-
mates of potential yield, soil and residue nutrient
supplies, and fertilizer efficiency, along with soil tests,
can be used to estimate an adequate fertilization level.
N 2. Timing Nitrogen Application
Fertilizer nutrients, particularly nitrogen, are used
most efficiently when the time of application closely
coincides with the time of absorption by the plant.
Consequently, the ideal time to apply an available
nitrogen source is when the plant's need is greatest.
Sources that must be converted to an available form
78
-------
need to be applied earlier. For example, nitrate should
be applied to corn about 3 to 4 weeks after emergence
(Figure 33). This practice is generally known as summer
sidediessing and has many environmental advantages.
Nitrogen is generally injected as ammonia gas, which
converts to nitrate in a couple of weeks, or granular
materials are mixed into the soil. Consequently, the
nitrogen is unlikely to be lost in runoff and is taken up
rapidly by the plant, so the leaching potential is greatly
reduced. Since weather is the most unpredictable varia-
ble in crop production, delayed fertilization allows a
reduced rate of fertilizer to be applied to late-planted or
drought-retarded crops. There are disadvantages that
make many growers reluctant to use this practice.
Rainfall must be sufficient to move the nitrogen down
into the root zone, but wet periods can delay applica-
tions until yields are decreased. Also, root pruning
during delayed fertilization may reduce plant growth.
Present storage and transportation facilities may not be
adequate and should be considered. Large applications
of fertilizers close to young plants can be toxic. Split
application, applying part of the fertilizer preplant and
the rest as a summer sidedressing, is an effective way to
avoid the toxic effects.
For summer row crops, nitrogen is most often applied
2 to 3 weeks before planting, although some is applied in
the fall. Fall fertilization is convenient, because the
farmer is less busy and it benefits the fertilizer dealer by
spreading out the distribution period. Fall fertilization,
recommended in -some areas, is generally limited to
incorporating ammonium fertilizer into soils, except
sands, at soil temperatures of 50° F or less. Ammonium
ions do not leach, and their biochemical conversion to
mobile nitrate ions is greatly reduced below this tem-
perature. However, because the conversion is not com-
pletely stopped until the soil freezes, the variations in
temperature and rainfall patterns across regions can
result in different leaching potentials. The runoff-
producing characteristics and the water-holding capaci-
ties of the soil are major characteristics controlling
percolation and, thus, affect the leaching potential. In
general, sandy soils have low runoff characteristics and
low water-holding capacities so that the potential for
percolation is high. Figure 34 shows the estimated
average fraction of fall-applied ammonium that was
nitrified and leached below the root zone in selected
Land Resource Areas. The estimates were made from
calculations of the amount of ammonium converted and
the amount of water percolating through the root zone
of the predominant soil in each Land Resource Area.
Corn was used to represent summer row crops. Twenty
to twenty-five years of weather records were used to
provide the average estimates presented. Average losses
in excess of 10% are probably real and, thus, present a
potential nitrate leaching hazard. However, the esti-
mated losses in Figure 34 neglect the possibility that
part of the nitrate may be denitrified, thus reducing the
pollution hazard. Some denitrification is quite possible,
and the loss estimates shown cannot be used to predict
the amount of nitrate that might reach a water body. In
any event, the possibility of denitrification reducing
pollution should not be a controlling factor in recom-
mending this practice. A detailed description of the
calculations used for preparing Figure 34 is given in
Volume II.
Figure 35 shows leaching losses from spring-applied
ammonium fertilizers applied 2 weeks prior to planting.
These losses were estimated in a manner similar to those
shown in Figure 34. Losses are significant in a few areas.
In these areas, summer sidedressing must be seriously
considered as the method of applying at least part of the
nitrogen,
N 3. Using Crop Rotations
The rotation of crops requiring little (small grains,
grasses) or no fertilizer nitrogen (soybeans and other
legumes) with crops requiring large amounts can reduce
the long-term average amount of nitrogen available for
leaching. Including a deep-rooted crop, such as alfalfa, in
a rotation can also decrease nitrate leaching, because the
plants can utilize nitrates from depths below the normal
rooting zone. Even though alfalfa is a legume and
normally obtains most of its nitrogen from the air, it will
absorb nitrate if present. Rotations often offer advan-
tages for erosion and pesticide control, as well as for
nutrient control, and should be considered whenever
applicable. The use of sod crops usually requires an
animal enterprise for economic use and would probably
reduce the amount of cash crops grown or lead to the
cropping of less fertile and more erosive land.
N 4. Using Animal Wastes for Fertilizer
One advantage of using animal wastes as fertilizer is
that the nitrogen becomes available over a longer period
of time. Consequently, less nitrate is available at any one
time for leaching. A disadvantage is that nitrogen release
will continue after the crop is harvested, and this nitrate
will be subject to leaching during the fall and winter
months.
There are three major considerations in using animal
wastes to supply nitrogen for crop production: (1)
determining the amount of nitrogen actually being
applied to the land; (2) preventing loss of nitrogen
before incorporation with the soil; and (3) determining
79
-------
IOO
MATURITY
DAYS
0
25 50 75
DAYS AFTER EMERGENCE
Figure 33.-Corn growth and nutrient uptake.
the rate that the incorporated nitrogen wfll become
available for crop uptake. The use of commercial
fertilizers offers a relatively high degree of control for
each of these factors. This added control, coupled with
the fact that commercial fertilizers are generally more
easily and more quickly applied, accounts for the
preferred use of commercial fertilizers by many farmers.
Manure improves soil physical properties and provides
several plant nutrients, but not always in the correct
proportions. Manure applications can cause salinity
problems, but seldom if application rates are limited to
those necessary to supply adequate nitrogen for crop
production, commonly from 5 to 15 tons per acre.
The manure, whether applied as a liquid, slurry, or
solid, should be incorporated with the soil as quickly as
feasible and preferably on the day of application. This is
necessary to reduce volatilization losses of nitrogen and
prevent pollution of runoff water. Where incorporation
is not feasible, such as on frozen ground or pastures,
special care is required. Manure should not be applied to
frozen fields if runoff from snowmelt occurs, as dis-
cussed in Section 3.6b. This may require facilities for
storing the manure until a suitable time for land
application. Whenever animal wastes are used, the
practices N 8, Incorporating Surface Applications; N 9,
Controlling Surface Applications; and N 11, Timing
Fertilizer Plowdown, should be considered.
N 5. Plowing-Under Green Legume Crops
Legumes can supply substantial amounts of nitrogen
to the soil. The quantities of nitrogen fixed will depend
on the plant, which acts as the host for the nitrogen-
fixing bacteria, and the environmental conditions.
Amounts as high as 500 Ibs/A. have been reported, but
more commonly reported values range from about SO
Ibs/A. for red clover to 200 Ibs/A. for alfalfa. Like
-------
Nitrogen
Loss
0%
< 10%
10 to 30 %
> 30%
Simulations not Performed
ERRATUM: THIS MAP AND THAT ON
PAGE 82 ARE INTERCHANGED. THIS
IS THE MAP FOR SPRING-APPLIED
AMMONIUM.
Figure 34.-Potential nitrate loss by leaching from fall-applied ammonium to corn.
-------
•
' .
Simulations not Performed
ERRATUM: THIS MAP AND THAT ON
PAGE 81 ARE INTERCHANGED. THIS
IS THE MAP FOR FALL-APPLIED
AMMONIUM.
Figure 35.-Potential nitrate loss by leaching from spring-applied ammonium to corn.
-------
fertilizers, some of this nitrogen can be lost as the
legume decomposes. When legumes are used as the
principal source of nitrogen for nonlegume crops, careful
planning is required. A summer legume can be grown
and plowed under, but this practice does not allow any
benefit from the legume other than providing soil
fertility. If rotations are used, a system of leaving a
legume on the land for 2 to 5 years will help supply
nitrogen for subsequent crops and also allow economic
benefit from the legume crop. Major difficulties are the
loss of cash crop income, the lack of legumes adapted to
the particular soil and climate, and the need of a
livestock enterprise.
N 6. Using A Winter Cover Crop
The use of winter cover crops, such as small grains,
can reduce nitrate leaching in two ways. First, the cover
crop extracts soil water during fall and spring so that less
water is available for leaching. Second, the crop will
utilize nitrate remaining from the preceding crops. Some
of this nitrogen will become available to the succeeding
crop following the plowing under of the cover crop.
Winter erosion is also decreased. In low rainfall areas, the
moisture used by the cover crop will decrease the yield
of the cash crop.
N 7. Controlling Fertilizer Release or
Transformation
Slowly available nitrogen compounds have been
developed that release their nitrogen over a long period
of time. Also, nitrification inhibitors have been synthe-
sized to reduce the rate at which ammonium fertilizers
are nitrified. These allow the expanding root system to
absorb the nitrogen both as ammonium and nitrate
throughout the growth period. Further development of
these compounds could be very significant in increasing
the use efficiency of fertilizer nitrogen and reducing
leaching losses. However, their use is not yet economi-
cally feasible in most cases and, also, too much nitrate
could be released in the fall in some cases.
N 8. Incorporating Surface Applications
Applications should be timed so that the period
between spreading and incorporating is as short as
feasible, particularly in areas where, and at times when,
direct runoff is likely. Loss of fertilizer and manure in
runoff water from cultivated fields is generally not great,
since farmers normally inject anhydrous ammonia or
liquid fertilizers into the soil and plow under broadcast
applications. Hay and pasture land, and the use of
conservation tillage systems for erosion control, can
present special challenges for managing nutrients because
of limited opportunities for incorporation. Nutrient
management practices N 9, Controlling Surface Applica-
tions, and N 10, Using Legumes in Haylands and
Pastures, must be carefully considered as a part of these
systems to insure that nutrient pollution is not accentu-
ated.
N 9. Controlling Surface Applications
Often fertilizer applications cannot be incorporated
on hayland, pastures, or cropland in no-plow tillage
systems. If not, one must try to apply the fertilizer when
the runoff potential is low (Figure 5). An example is to
delay applying manure or fertilizer to frozen sloping
lands until snowmelt runoff has stopped. However, the
fertilizers applied prior to an extended dry period may
be very ineffectively used. Another possibility is to
apply the fertilizer in a fluid form. The fluid is a liquid
or suspension of microcrystals which permits quicker
movement into the soil than the slower dissolving
granules. Some fall-planted small grains are pastured
during the winter, top-dressed with nitrogen in the
spring, and harvested for grain in the late spring. This
topdressing would be a potential problem if runoff were
high following the application. In this case, the option of
topdressing and its potential loss must be compared with
the loss from applying all the nitrogen at planting.
N 10. Using Legumes in Haylands and Pastures
Legumes have root nodules containing bacteria that
form organic nitrogen compounds from the nitrogen gas
in the air. The decomposition of old legume roots and
residue can provide sufficient nitrogen for the grasses in
a grass-legume mixture. This eliminates the need for
nitrogen, but not phosphate, fertilizers- If the phosphate
level in the soil is high when the meadow is started,
phosphate fertilizer does not need to be applied often.
Maintaining a healthy, high-yielding mixture is difficult
because the grasses tend to crowd out the legumes.
N 11. Timing Fertilizer Plowdown
When surface-applied fertilizers are incorporated by
plowing or disking, the resultant land surface is quite
susceptible to erosion. Shortening the time that the
surface is vulnerable to erosion will reduce the amount
of erosion and loss of associated nutrients. Changing the
time of application and incorporation from fall to spring
could, however, overtax an already crowded schedule.
83
-------
4.4 PESTICIDE MANAGEMENT PRACTICES
Clearly, a reduction in runoff or erosion will also
reduce loss of applied pesticides, and practices that
control runoff and erosion should always be considered
in pesticide pollution control. In addition to these
practices, a number of options exist, and are often used,
that involve manipulation of the pesticide itself. These
can be used alone or in conjunction with the runoff and
erosion control measures. Table 18 lists 15 such prac-
tices, divided into two groups based on their applicabil-
ity.
Obviously, good basic management of the chemicals
should be practiced wherever pesticides are used,
whether or not runoff control measures are necessary.
Pesticides should always be used strictly in accordance
with instructions on their labels; to do otherwise is
illegal. The chemicals should be stored so as to minimize
the hazard of possible leakage, and containers should be
disposed of after use in accordance with procedures
Table 18. Practices for the control of pesticide loss from agricultural applications and their highlights.
No,
P 1
P2
P3
P4
P5
P6
P7
P8
P9
P10
Pll
P12
P13
P14
P15
Pesticide Control Practice
Practice Highlights
Broadly Applicable Practices
Using alternative pesticides
Optimizing pesticide placement with respect to
loss
Using crop rotation
Using resistant crop varieties
Optimizing crop planting time
Optimizing pesticide formulation
Using mechanical control methods
Reducing excessive treatment
Optimizing time of day for pesticide application
Applicable to all field crops; can lower aquatic residue levels;
can hinder development of target species resistance.
Applicable where effectiveness is maintained; may involve
moderate cost.
Universally applicable; can reduce pesticide loss significantly;
some indirect cost if less profitable crop is planted.
Applicable to a number of crops; can sometimes eliminate need
for insecticide and fungicide use; only slight usefulness for
weed control.
Applicable to many crops; can reduce need for pesticides;
moderate cost possibly involved .
Some commercially available alternatives; can reduce necessary
rates of pesticide application.
Applicable to weed control; will reduce need for chemicals
substantially; not economically favorable.
Applicable to insect control; refined predictive techniques
required.
Universally applicable; can reduce necessary rates of pesticide
application.
Practices Having Limited Applicability
Optimizing date of pesticide application
Using integrated control programs
Using biological control methods
Using lower pesticide application rates
Managing aerial applications
Planting between rows in minimum tillage
Applicable only when pest control is not adversely affected;
little or no cost involved.
Effective pest control with reduction in amount of pesticide
used; program development difficult.
Very successful in a few cases; can reduce insecticide and
herbicide use appreciably.
Can be used only where authorized; some monetary savings.
Can reduce contamination of non-target areas.
Applicable only to row crops in non-plow based tillage; may
reduce amounts of pesticides necessary.
84
-------
approved under the provisions of the Federal Environ-
mental Pesticide Control Act of 1972 (Public Law No.
92-516). The best disposal method at present involves
burying the containers in an approved landfill. Con-
tainers should be triple-rinsed and punctured before
burying, and the rinsings should be added to the spray
tank if possible. Otherwise, the rinsings should be
treated as excess pesticide and buried along with the
container. If adequate pesticide application equipment is
not available or if the farm operator is untrained and
uncertain of proper application procedures, considera-
tion should be given to the employment of certified
commercial applicators. When feasible, farm operators
should seek training and certification themselves.
In addition to the practices listed below, other
measures can be taken to reduce runoff contamination
by pesticide residues, but they are not listed directly
because they are either in the exploratory stage with
more research required, or they have deficiencies that
cancel their environmental advantages. Among these are
the use of controlled-release pesticides, the use of
synergistic pesticide combinations, the use of foams, the
destruction of plant residues after harvest, and the
practice of increasing the pest damage threshold before
pesticides are applied.
Broadly Applicable Practices
P1. Using Alternative Pesticides
When more than one chemical of comparable cost
and efficacy is available to control a specific pest, one
should use those compounds that are least likely to
cause water pollution. Pesticides that have low toxicity,
are not persistent, and do not build up through food
chains should be given preference. In an area of
appreciable surface runoff but with little erosion, pesti-
cides that move primarily with sediment should be
favored over those that are readily dissolved in and move
with the water. Table 11 lists the chemicals that are used
on the major field crops and Tables 8, 9, and 10 and
Figure 29 give specific information bearing on water
pollution. Not all of the chemicals listed in Table 11 for
a particular crop are interchangeable, only those groups
among them that are effective against the same pest.
Direct alternatives are noted in the pesticide recom-
mendations of the Cooperative Extension Service of the
individual states and the United States Department of
Agriculture.
The use of different chemicals in successive years that
are equally effective against the same insects or weeds is
also beneficial. This acts against the buildup of resistance
in the target species and will also result in lower residue
levels of those compounds that are relatively stable in
the aquatic environment.
P 2. Optimizing Pesticide Placement with
Respect to Loss
The manner of placement of a herbicide or insecticide
in or on the soil can significantly affect the potential for
contamination of runoff. To minimize the hazard, the
pesticide is best placed in a narrow band well below the
soil surface; broadcast applications on the surface are the
least desirable. Pestic.dal effectiveness must obviously be
maintained and, consequently, soil incorporation is
often not practicable. On the other hand, it is more
effective in certain situations, such as with volatile or
photosensitive herbicides, and is widely used. Other
favorable practices include the application of insecticides
directly into the seed furrow in row crops and the
placement of herbicides in narrow rather than wide
bands. The first of these is as effective as band
application over the row, provided that the chemical is
not toxic to the plants. Only a few chemicals, notably
carbofuran and diazinon, can be used in this way. When
herbicides are placed in narrow bands centered over the
planted row, a supplemental cultivation is necessary to
control the weeds between the treated bands. Bands
must be wide enough to ensure that weeds do not
compete with the crop and to permit cultivation to the
edge of the band without injury to the crop. Subsurface
swe^p applicators that allow precision band placement
of herbicides at a predetermined depth are being used
with persistent, nonleachable herbicides. Despite the
increased power requirements, this equipment is very
much needed because precision placement of granules
can cut herbicide requirements by as much as 50%.
Fuel shortages could restrict the use of the environ-
mentally desirable band applications. It has been sug-
gested that, to economize on both fuel and labor,
farmers might gradually have to replace band application
with broadcast methods, with a resultant large increase
in pesticide applied per acre. The trend among soybean
growers is already toward increased broadcast applica-
tion of herbicides. Broadcasting is also the only feasible
treatment in closely drilled crops.
P 3. Using Crop Rotation
Crop rotation, a practice that is used primarily when
crops complement each other economically, can lessen
85
-------
the pesticide contamination of runoff. Sometimes, crop
rotation will suppress insects, weeds, or plant diseases, so
that less chemical pesticide is required, and it can also
reduce soil erosion. Therefore, the advantage of the
technique should be explored and exploited wherever
possible. Crop rotation has lost favor recently because of
the development of new, efficient pesticides that permit
continuous cropping of economically advantageous
crops. However, the present energy shortage and in-
creased costs of chemicals may well reawaken interest in
rotation.
Evidence for the environmental benefits of crop
rotation is abundant. For example, a potato-oats-sod
rotation reduced runoff losses of organochlorine insecti-
cides as much as 40% in comparison with losses from
continuous potatoes. In insect control, rotations sup-
press the buildup of resistance to insecticides and break
the life cycle of certain insects that require specific host
plants to survive. The favorable action of rotations in
insect control is typified in Illinois, where almost 70% of
the fields in continuous corn were treated with soil
insecticides in 1972, whereas only 42% of the fields in
first-year corn were treated. Rotations also help to
control weeds because some weeds are harder to control
in some crops than in other crops. On the other hand,
control of a few weeds, such as Johnsongrass in cotton,
is simplified if a single crop is planted in successive years.
P 4. Using Resistant Crop Varieties
The use of crop varieties resistant to attack by
diseases or insects will obviously reduce the need for
chemical treatment. Some crop varieties are more
competitive with weeds than others, but generally such
differences are only moderate and other weed control
practices are required. Two examples of resistance
against insects are hybrid corn varieties resistant to
first-generation corn borers and potato varieties resistant
to the golden nematode. Crop resistance is generally
insufficient in itself to control insects and supplemental
chemicals may have to be used, but fewer treatments are
needed. There are exceptions, however: certain wheat
varieties are practically immune to Hessian-fly attack
and require no chemical treatment. A minimum-hazard
pest control program should include the use of resistant
varieties.
P 5. Optimizing Crop Planting Time
Agronomically, the recommended time of planting
many crops in any given area covers a range of several
weeks. For certain insects, the precise time of planting
within this period can strongly influence infestation of
the crop and can thus affect the eventual need for
insecticides. With corn, for example, early planting is
preferable with respect to infestations of the European
corn borer. First-generation borers, to which many
hybrid corn varieties are resistant, lay most of their eggs
in early-planted fields; eggs of second- and third-genera-
tion borers, which must be controlled by insecticides,
are usually concentrated in late-planted fields. Early-
planted corn is subject to less attack by the corn
earworm in northern states than later corn, but the
reverse is true in southern states because crops that are
more attractive to the insects than corn are not available
until later. Late planting also helps to combat damage by
white grubs and seed maggots in corn, because of the
early active life of the insects. However, an inherent
disadvantage of late planting is that rain delays could
greatly reduce yields. With wheat, an effective way to
avoid infestation by the Hessian fly is to seed late in the
fall after the fly has disappeared. Damage by white grubs
and wireworms is also prevented. Early planting of
sugarcane (August) produces less injury by sugarcane
beetles and by wireworms than late plantings (Septem-
ber-October). A break of several weeks between early
and late planting of sorghum in an area can help reduce
populations of the sorghum midge.
P 6. Optimizing Pesticide Formulation
The formulation in which a pesticide is applied can
affect the runoff contamination potential. For example,
the addition of surfactants or nonphytotoxic petroleum
or linseed oils to the spray mix of foliar-applied
herbicides can increase the penetration and translocation
of the chemicals within the target plants, so that the
efficiency of action is increased and less active ingredient
is needed.
Some formulations are a greater hazard than others
having the same active ingredient because other compo-
nents in a pesticide formulation—solvents, additives, or
diluents—may be more toxic to fish and other aquatic
organisms than the herbicide itself. Newer formulations,
such as controlled-release products and foams, may
increase effectiveness and reduce treatment rates, but are
still largely experimental. Granular formulations, partic-
ularly if incorporated in the soil to avoid losses by
erosion, are environmentally preferable to liquids be-
cause application losses are lower. It has been predicted
that the trend in the pesticide industry will be away
from solvents and emulsifiable formulations and toward
wettable powders and more concentrated formulations
because of impending shortages in petrochemical feed-
stocks.
86
-------
P 7. Using Mechanical Control Methods
Sound management of cropland requires a careful
balancing of the various interacting agronomic, eco-
nomic, and environmental factors; nowhere is this more
evident than in the choice of chemical or mechanical
control of weeds or a combination of the two, which is a
common practice. Mechanical weed control includes
hand pulling, mowing or cutting, flooding, covering with
mulch, oiling, and burning, but the most important
method by far is tillage. Preplant tillage is useful not
only for controlling weeds but also for proper seedbed
preparation. If rainfall is not very heavy or intense, it
may reduce soil loss in runoff by breaking up the surface
layer of soil so that infiltration is increased. It obviously
reduces the necessity for herbicide application and
disperses phytotoxic residues from any herbicide applied
in the previous year.
There are, however, drawbacks to tillage that counter-
balance its benefits. Erosion may be substantial if heavy
rain falls while the soil is bare. Repeated manipulation of
soil may deteriorate soil structure, especially with moist
soils. Moreover, frequent use of heavy machinery can
compact the soil so that air and water movement is
restricted and crop yield is reduced. The most severe
shortcoming of tillage, and the one factor that seems to
be causing a current trend away from mechanical
cultivation, is the economic consideration. Tillage re-
quires manpower, machinery, and fuel. It has been
estimated that, if herbicides were unavailable, an addi-
tional 100 million gallons of fuel would be needed
annually in this country to control weeds by mechanical
cultivation. In view of the presently sharply rising costs
not only of fuel but also of labor and equipment, it is no
surprise that herbicides are finding increasing favor
among our farmers.
P8. Eliminating Excessive Treatment
A common practice in insect control is to apply an
insurance treatment of a chemical to guard against a
possible outbreak of a particularly destructive pest. For
soil insects, this is often the only safe policy to follow,
because it cannot generally be predicted where popula-
tions will be of economic proportion and the insects
may otherwise destroy the crop. As a result, high
percentages of the soil insecticides are applied need-
lessly. Where predictive techniques have not been devel-
oped, cultural or biological controls should be instituted
whenever possible to reduce unnecessary applications.
Control of aboveground insects should always be
based on plant damage and actual pest counts and
should be used only where potential economic losses
justify the pesticide application. For larger fields, careful
treatment of infested areas only should be considered
rather than spraying entire fields. Often, the decision to
apply pesticides is now made in the field by insuffi-
ciently trained personnel; clearly, additional educational
efforts are needed. Use of the "scout" system, in which
professional entomologists are employed by responsible
agencies to survey crop areas and determine when
insecticide application is needed, will reduce unnecessary
treatments and is strongly recommended.
There is also a tendency to use unnecessarily wide-
spread treatments for weed control. It is important to
identify specific weed problems so that judicious con-
trols may be instituted. Fall weed surveys, as well as
follow-up surveys during the subsequent growing season,
which might be done in conjunction with insect or
disease scouting, could improve efficiency through appli-
cation of chemicals only where needed.
P 9. Optimizing Time of Day for Pesticide
Application
If pesticide spraying is confined to the early morning
or evening hours when the air is relatively still, better
on-target deposits will be obtained and the rate of
application could well be reduced. This is particularly
important with aerial sprays. Evening spraying of chemi-
cals that are toxic to beneficial honeybees, such as the
methylcarbamate insecticides, is preferable because the
bees generally stop seeking pollen in the late afternoon.
Irrespective of the time of day, spraying should be
postponed under windy conditions, when a temperature
inversion (warm air overlying cool air) exists, or in the
face of forecasts of impending heavy rain.
Practices Having Limited Applicability
P 10. Optimizing Date of Pesticide Application
Pesticides usually must be applied within a relatively
brief time period to be effective against the target
organisms, so few options are open with respect to
reducing runoff contamination by changing the applica-
tion date. Unfortunately, the best time for applying
many pesticides, early spring, coincides with the time
that high rainfall and accompanying high runoff and
sediment transport often occur. Because losses of pesti-
cide in runoff are relatively large only when rainfall
occurs shortly after application, any action taken to
move the pesticide treatment away from peak runoff
periods while maintaining pesticidal effectiveness is
87
-------
advantageous. Thus, where runoff is high in the spring
and where the options are practicable, postemergence
treatments are preferable to preemergence treatments,
treatments late in the season when the crop canopy has
closed are potentially less hazardous than earlier treat-
ments, and fall treatments are more desirable than spring
treatments. Due regard must, of course, be given to the
nonenvironmental disadvantages of the practices, and
judgments must be made after weighing the offsetting
factors. For example, postemergence herbicide applica-
tions are disadvantageous in that they allow early
competition of weeds with crops; require labor at a
critical time on many farms; often are not as effective as
preemergence treatments; and allow no later options, as
do preemergence applications, if weather interferes with
the treatment.
The timing of preplant soil-incorporated chemicals is
less critical than that of preemergence types, so very
early preplant applications can be considered for some
chemicals, particularly insecticides, having sufficient
persistence in the soil. Some insecticides are equally
effective whether applied in early spring at planting or in
late spring. The later treatment is preferable not only
because the runoff hazard is less but because shorter-
lived chemicals can be used effectively.
P 11. Using Integrated Control Programs
An effective integrated control program-defined as
any combination of chemical, biological, cultural, or
mechanical control techniques—to eradicate a pest or to
decrease its population to acceptable damage levels and
maintain it there is the ideal in pest management. Some
outstanding successes have been achieved with integrated
programs, one example being the control of the spotted
alfalfa aphid in western U.S. fields during the 1950's, in
which resistant alfalfa varieties, parasites, predators,
pathogens, and pesticides were effectively combined.
Other experimental programs hold promise for over-
coming very important pests, such as the boll weevil and
bollworm in cotton. Another attribute of integrated
control is that it can be far more economical than
pesticide use alone; the amount of pesticide needed can
often be reduced substantially.
The building of an integrated control program by
design, however, is a complex task that requires lengthy
research and many different talents. The dynamics of
pest populations must be studied and the most effective
combination of available control techniques identified.
On the other hand, present-day economic and environ-
mental pressures are not expected to ease, so that
integrated control will continue to be actively developed
in the coming years.
P 12. Using Biological Control Methods
Biological methods hold promise for control of
damaging insects and weeds, but the achievements to
date, although significant, are still relatively small
compared to the great number of pests. In insect
control, biological methods appear to be most effective
against pest populations that had been reduced by
preliminary treatment with insecticides. Other inherent
problems in using biological methods include the control
of selectivity, parasites of the biological agents, and the
fact that insects cannot be introduced to control plants,
such as cactus, that are serious weeds in agricultural
situations but desirable in others (cactus is used for feed
or food in some locations). Although results have been
dramatic and advantageous in a number of cases,
biological control of insects and weeds has not been used
widely on agronomic crops.
The methods include the use of sex attractants,
warning or aggregating chemicals that influence the
behavior of insect colonies, insect growth regulators,
sterilized male insects, insect pathogens (disease-causing
agents), antifeeding compounds, and parasitic or preda-
tory insects. Research on each of these is being pursued
and there have been a number of successful applications.
One insect pathogen, Bacillus thuringiensis, is now
commercially produced. It is, however, useful only
against insects whose gut is alkaline (moth larvae,
caterpillars, butterflies), it must be ingested, and it is
rapidly destroyed by sunlight. Biological methods are
most useful against insects and mites, but there have
been a few cases of successful control of weeds, notably
Klamath weed (St. Johnswort), alligator weed and cactus
(in foreign locations), by introduction of insect preda-
tors.
P 13. Using Lower Pesticide Application Rates
Federal pesticide registrations, including recom-
mended rates of application that appear on pesticide
labels, are issued on a nationwide basis. Because of the
very large number of formulations and the broad areas
involved, it is not possible to test rigorously each
pesticide in each local situation. Consequently, there
may be situations in which climatic and geographic
conditions are such that doses below the minimum
recommended rates will control a pest. Several such
cases have in fact been noted by the Environmental
Protection Agency. Furthermore, doses lower than
recommended rates may be adequate for use in inte-
grated pest management programs. Since rates below
label recommendations are now permitted for agricul-
88
-------
tural uses provided that they are authorized by appropri-
ate agencies such as the Cooperative State Extension
Service, State agricultural experiment stations, or
offices of County Agricultural Commissioners, it is
recommended that such authorized rates be used when-
ever possible, to save pesticide costs and to lower the
potential environmental hazard.
Reduced-spray techniques can also be used effectively
in some instances, with accompanying reduction in total
pesticide applied. On fruits, for instance, reduced or
half-sprays with extended intervals between spraying or
alternate middle-row treatments have provided adequate
control. Similarly, spraying with low-volume concen-
trated sprays rather than with dilute sprays at high
volume can reduce insecticide use as much as 20% while
maintaining the same level of pest control.
P 14. Managing Aerial Applications
Aerial applications of pesticides are not environ-
mentally favorable and special precautions should, there-
fore, be taken when such treatment is necessary. Aerial
treatment can only be applied broadcast, increases the
likelihood of uneven distribution of pesticide on the
crop, and increases spray volatilization and drift that
may injure susceptible crops in adjoining areas and
directly contaminate nearby surface waters. A smaller
amount of chemical reaches the target and, therefore,
somewhat higher treatment rates may be needed to
achieve the same degree of pest control. Because of the
drift hazard, aerial spraying should be limited to periods
of low wind and when the wind is blowing away from
susceptible crops. Spraying should not be conducted
when there is a temperature inversion, because such
conditions favor horizontal transport of airborne pesti-
cides. Where contamination of areas adjacent to the
treated area must particularly be avoided, special pesti-
cide formulations, special nozzles, and/or low pressures
should be used.
Despite these problems, aerial treatment is the only
practical means of spraying in some agricultural situa-
tions (close-growing crops, rangeland) and its use on
field crops is increasing. It can be used in areas of
excessive rainfall where ground equipment would fail,
eliminates wheel track compaction that can reduce crop
yields, and is the only effective means to combat
sudden, widespread pest infestations.
P 15. Planting between Rows in Minimum
Tillage
Planting between last year's rows rather than on them
in continuous minimum tillage systems helps somewhat
to reduce populations of soil insects and may lessen the
need for heavy insecticide applications. The practice
does, however, have disadvantages. Planting would be
more difficult in the areas that had been compacted by
wheeled equipment travel of the previous year, and row
fertilizer placed for the previous crop would not be used
by the new planting.
89
-------
SECTION 5
ECONOMIC CONSIDERATIONS
The definition of pollution implies that one group in
society creates and deposits in the environment certain
materials that degrade the aesthetic environment or raise
costs for others. The imposition of pollution controls is
designed to prevent environmental degradation through
the encouragement of production methods that will not
cause off-site pollution.
The purpose of this manual, as already stated, is to
provide information to individuals or agencies charged
with developing plans for the control or reduction of
pollution from nonpoint agricultural sources. The infor-
mation presented in preceding sections dealt with the
technical aspects of nonpoint pollution control. How-
ever, responsible officials also must consider the various
positive and negative economic impacts that pollution
and pollution control plans have upon agricultural
producers and the economy as a whole.
The assessment of these economic impacts involves
first the decision-making process of individual farmers
faced with new pollution tolerances or recommended
runoff control practices, since all efforts to manage
pollution alter the decision-making options of the
farmer. Pollution control agencies may forbid selected
methods of production or prescribe certain activities
that are deemed desirable for the environment. The
individual farmer is concerned with adjusting his farm
cropping plan and production activities to the new
standards in a manner to ensure that his operation is
profitable. This problem is addressed in Sec. 5.1.
The sum of independent decisions of individual
farmers caused by the imposition of pollution standards
has positive and negative effects on society. These social
impacts may include: increases in food prices; changes in
demand for and prices of inputs such as energy,
pesticides, and labor that are used in all sectors of the
economy; and changes in the availability and quality of
some agricultural products. Additionally, there may be
secondary effects such as the changed volume of
business for suppliers of affected inputs, adjustments in
land value, and changed employment requirements in
agriculture where cropping intensities are changed. The
social benefits may include cleaner water, longer lasting
reservoirs, reduced water purification costs, more fish,
and less eutrophication of lakes. These issues will be
discussed in Sec, 5.2.
This overview of economic considerations can esti-
mate neither the social costs and returns nor farmers'
reactions in specific cases. It tries only to set a
framework and to alert drafters of pollution regulations
to potential local and national economic impacts of their
actions. These impacts will have to be quantified on a
case-by-case basis for specific pollution regulations. This
is not easy and may require a substantial research effort.
This effort can be aided by conceptualizing the impacts
in large-scale models, such as interregional linear pro-
gramming or simulation models or by use of input-
output multipliers and similar tools. The policy maker
may wish to seek specialized assistance from economists
with state or national agencies, universities, and private
firms in the process of formulating the most socially
responsible pollution control program.
5.1 Effects on Individual Producers
If a pollution control board promulgates a new
environmental standard, some individual farmers must
adjust their production methods to satisfy the restric-
tions, while others may find that the new standards
place no restriction on their practices. The actions of
any one farmer will have no measurable influence on the
regional-national markets. The farmer's attention is thus
logically focused on the maximization of his average net
returns over time. To aid in his decision-making process,
he could use a partial budget framework. He would
select, from the physically feasible set of production
methods permitted under the standards, those alterna-
tives that yield the highest average annual net return for
his resources. Table 19 lists variables that should be
considered in the budgeting framework. Use of the
procedure is demonstrated in the farm example in Sec.
6.2.
Expected gross revenue is expected crop yield times
expected selling prices. Alternative production methods
may reduce or increase expected yields. Examples of
91
-------
Table 19. Factors that should be considered in budgeting alternative nonpoint pollution control practices
A. GROSS REVENUE:
1. Expected prices
2. Expected production
Gioss Revenue = (1X2)
B. PRODUCTION COSTS BY OPERATION:
1. Land Charge
2. Tillage
Labor
Equipment
Fuel
Interest
Scheduling
3. Fertilization
Labor
Equipment
Fuel
Fertilizer
Interest
Scheduling
4.
Pest Control
Labor
Equipment
Fuel
Pesticides
Interest
Scheduling
5. Planting
Labor
Equipment
Fuel
Seed
Interest
Scheduling
6. Harvesting
Labor
Equipment
Fuel
Interest
Scheduling
7. Storage and Transport
Labor
Equipment and Facilities
Fuel
Interest
Scheduling
8. Pollution Control Practice Design, Construction,
Installation, Operation and Maintenance
Labor
Equipment
Fuel
Interest
Scheduling
TOTAL PRODUCTION COSTS = 1 +2 +3-M +5 +6 +7 +8
NET REVENUE = (Gross Revenue - Total Production Costs)
C. OTHER FACTORS (Risk, Uncertainty, Attitudes, Preferences, etc.)
such yield differences are increased yields on terraced
acres (in some cases) because of improved moisture
retention or decreased yields for no-till fields as a result
of the requirements for more precise management and
timeliness compared with conventional tillage.
Tillage, fertilization, pest control, planting, harvest-
ing, storage and transportation may change independ-
ently with the imposition of pollution standards. All
changes should be carefully considered for both cost and
yield effects.
The cost of equipment and facilities used currently
should be amortized over their expected life, and their
annual operating and maintenance cost budgeted accord-
ing to their level of use. Adoption of new production
practices may make some equipment obsolete. Any such
capital loss should be charged to the new practice in the
budget, amounting to current depreciated value less
salvage value of the obsolete equipment. One method of
including such capital loss is to amortize it over the life
of the new equipment. Thus, the new practice is charged
with both the new capital costs plus the capital loss
which would result from its adoption.
Both inputs and products should be included in
budgeting storage and transportation costs. A given
alternative practice may change the requirements for
storing fertilizer, fuel, product, or equipment.
92
-------
The cost for the control (Item 8, Table 19) refers to
the cost of land structures such as terraces, ponds and
drainage ditches. This cost includes the prorated annual
opportunity costs J of the capital investment plus any
annual operation and maintenance costs.
All production costs should include a charge for
interest. This charge refers to either the opportunity cost
of capital involved in the operation, such as implements,
or to interest charges for loans to purchase fertilizer,
seed, etc. The opportunity cost for capital should be
prorated over the economic life of the capital item,
whereas short-term interest costs are charged only for
the period for which money is working.
No management decision is made exclusively on the
basis of monetary costs and returns. Other variables
(Item C, Table 19) such as risk, uncertainty, grower
attitudes, preferences, education, size of operation, work
scheduling problems, alternative investment opportuni-
ties, tax structures, and tenure status, will also influence
the individual's decision. The final choice must be left to
the producer, but the profit maximizing farm plan is a
good indicator of what farmers may do as a result of a
new regulation.
If the user wishes more detail on partial budgeting
techniques and related information than is presented in
this chapter, the example in Section 6.2 or in Volume II,
Appendix C, other works are available. Such references
as the following could be consulted: Emery N. Castle,
Manning Becker and Fredrick Smith Farm Business
Management, second edition, The Macmillan Company,
New York, 1972; J. H. Herbst, Farm Management:
Principles, Budgets, Plans, third revised edition, Stipes
Publishing Company, Champaign, Illinois, 1974; Sydney
C. James and Everett Stoneberg, Farm Accounting and
Business Analysis, Iowa State University Press, Ames,
Iowa, 1974.
5.2 Aggregate Economic and Social Effects
A pollution control board should recognize that any
action it takes may cause large numbers of farmers to
change their production practices. These changes would
be expected to improve the environment and thus
benefit society. However, the net effect of many changes
in production decisions may reflect costs to society. For
example, total production may be reduced, food prices
raised, and regional specialization and the general level
of business activity and employment may be changed.
Of course, a lack of adequate environmental stand-
ards also may have pervasive economic and social effects.
For example, high rates of soil erosion reduce the future
yield capability by removing the surface layers of large
tracts of soil.2 The eroded soil enters waterways, causing
complex problems involving water purification for
down-stream users, out-of-bank flows, and accelerated
siltation of reservoirs and shipping lanes. The pollution
boards, acting on behalf of society, will have to compare
the social costs and benefits of nonaction to those of
imposing alternative types and levels of environmental
standards.
To evaluate the social costs and benefits of imposing
an environmental standard, one must first assess and
aggregate the adjustments individual fanners will make
in their production plans. Previous sections of this
manual will help users identify the type and scope of
pollution problems to be expected in broad areas of the
country. By the method outlined in Section 5.1, users
may obtain a general idea of the type and size of the
adjustments that will be required from farmers in local
areas as a result of specific pollution tolerances and
practice restrictions.
The environmental standards will necessitate changes
in production methods of those farmers whose previous
production practices would cause pollution in excess of
the standards. Once the cumulative changes have been
estimated, a series of direct and indirect impacts must be
considered. These impacts include changes in production
costs, aggregate farm income, crop prices, acreage of
cropland, location of production, land values, foreign
exchange earnings, economic viability of rural busi-
nesses, the tax base of rural communities, and social and
cultural values of rural people3.
These impacts are highly interrelated. Assuming
impacted farmers had already utilized their resources to
maximize net income, their net income after making
necessary changes is likely to be reduced both because of
changes to lower valued crops and the likelihood of
increased production costs. For farmers not directly
impacted, the situation is more difficult to estimate. The
situation is affected by the cumulative decisions of
impacted producers including the effect these decisions
'Opportunity cost is defined as the return which the capital
would have been expected to earn if it had been invested
elsewhere.
2 Part of this yield decline may be offset by increases in
fertilizer use. In this case, there are also social cost? to consider.
First, the increased fertilizer demand may raise the price of
fertilizer, increasing production costs for all agricultural pro-
ducers. Second, the higher-price fertilizer may cause a subse-
quent increase in the production of fertilizer, drawing raw
materials away from other uses. Third, in the case of fertilizer
materials that are imported from foreign sources, there will be a
direct effect upon the foreign trade balance of the United States.
93
-------
have on aggregate output and demand for inputs. The
interaction between actions taken by affected and
nonaffected producers creates implications for land
values, total acreage used for cropland and relocation of
production. For example, if producers with highly
erodible land have to produce lower valued crops as a
result of a pollution control regulation, the agricultural
value of their land would be expected to decrease.
Similarly, less erodible lands could increase in value,
bringing windfall gains to owners. Additionally, it could
b; expected that shifts in location of production would
occur if a regulation changed the competitive production
aspects among regions. The final effect of an aggregate
change in output on crop prices and on gross revenues of
farmers will depend upon the nature of the demand and
the structure of the market for outputs, i.e., the ability
of farmers to pass cost increases to consumers.
Changes in variables mentioned above, in turn, have
implications for rural businesses such as fertilizer dealers,
grain elevators, and banks. Additionally, rural communi-
ties are potentially affected through changes in the tax
base, demand for services, employment opportunities,
etc. Also, social and cultural values, quality of life and
related issues enter into a complex set of impacts and
interactions. For example, in certain situations, produc-
tion cost increases resulting from the imposition of an
environmental standard can be passed on to consumers
in the form of higher food prices. In such cases,
3Some attempts have been made to evaluate a few of these
potential impacts. For example, a recent Iowa State University
Study; Nicol, K. J., Madsen, H.C. and Heady, E.G. "The Impact
of a National Soil Conservancy Law", Journal of Soil and Water
Conservation, Sept-Oct. 1974, Vol 20, No. 5; indicated shifts in
location of production would occur if a national soil loss
restriction of 5 tons per acre per year were imposed. The acreage
used for cropland would be reduced by more than 14 million
acres from the 1969-71 level. Changes varied by region of the
country with decreases in 4 major regions and increases in other
regions. Associated with these changes would be reductions in
row crop acreage and shifts to close-grown cover crops. This
study also predicted that prices at the farm level would generally
rise.
Another study; Rosenberry, P. and Alt, K. "Gross Soil
Erosion and Crop Production in Iowa-Cedar River Basin",
Economic Research Service, USDA Draft Report; indicates that
restricting soil loss to 3 tons per acre per year in the Iowa-Cedar
River Basin increased variable costs of production more than 5
percent. Preliminary results show a major portion of this cost
impact falls on producers in land areas with highly erodible soils.
The study also concludes there would be significant shifts in
location of production from more to less erodible soils, changes
in crop rotations, and a general shift from conventional to
minimum tillage.
relatively more of the impact of the standard will be
borne by those members of society who spend relatively
large portions of their income on food. Detailed analyses
are required to sort out these interactions. Various
analytical techniques, as mentioned previously, have to
be employed. This brief chapter cannot include a
discussion of these analytical methods.
For a more complete discussion of some of the
concepts introduced here, the user may wish to consult
works such as Joseph J. Seneca and Michael K. Taussig,
Environmental Economics, Prentice Hall Incorporated,
Englewood Cliffs, New Jersey, 1974. Application of
these concepts to environmental problems is described
in many works, including Allen V. Kneese and Blair T.
Bower, Managing Water Quality: Economics, Technol-
ogy, Institutions, Johns Hopkins University Press, Balti-
more, Maryland, 1968; and Earl O. Heady and Uma K.
Srivastava, Spatial Sector Programming Models in Agri-
culture, Iowa State University Press, Ames, Iowa, 1975.
If a basic treatment of analytical methods is desired,
such works as the following may be helpful: William H.
Miernyk The Elements of Input-Output Analysis,
Random House, New York, New York, 1965; J.B. Dent
and J. R. Anderson, editors, Systems Analysis and
Agricultural Management, John Wiley and Sons, Sydney,
Australia, 1971; and Fredrick Hillier and Gerald Lieber-
man, Introduction to Operations Research, Holden-Day
Incorporated, San Francisco, 1967.
Of equal importance in setting priorities on pollution
control is a recognition of the private and social benefits
to be derived from such control. To the extent feasible,
these benefits should be assessed. Typically, the costs of
pollution control have some effect on different groups in
society and different geographical areas than those
groups or areas receiving benefits. This makes an
assessment difficult. Also, many of the benefits are more
difficult to quantify relative to costs. Regardless of these
quantification difficulties, a decision on nonpoint pollu-
tion control regulation will be made and should be based
on a comparison of the total benefits received relative to
the total costs to society. Obviously, benefits should
exceed costs.
Benefits potentially can occur at various levels. There
may be on-farm, local-area, regional and national bene-
fits. On-farm benefits can be in the form of reduced
gully and sheet erosion, more efficient use of plant
nutrients and pesticides, increased organic matter in the
soil, and increased water retention in fields resulting in
decreased production costs, higher yields and more
cultivatible area within given fields. Local-area benefits
may include better drinking water; more recreation; less
stream, channel and bridge repair; less in-stream dredg-
94
-------
ing; and general aesthetic improvement. Regional and
national benefits are similar to potential benefits to local
areas, although they may be more extensive and less
easily attributed to specific pollution control regulations
or practices. Benefits could include less flooding poten-
tial, better use of natural resources, maintaining produc-
tivity of agriculture, better health conditions and lower
fuel consumption.
An approach to assess benefits is to cost out
alternatives. This approach has several advantages. In a
partial budget analysis some of the on-farm benefits,
particularly costs of production and yield effects, would
be included. Consequently, these benefits would be
known. The same is not true for area, regional and
national benefits. However, it must be recognized that
pollution control is being demanded by many groups in
society. These demands are based upon their perception
of pollution problems and environmental quality. If a
decisionmaker can present to society the private and
social costs associated with alternative standard1? and
regulations, then both' the decisionmaker and society, in
general, should be in a better position to judge the
desirability of and need for alternative levels of control.
In the final assessment, if the total benefits greatly
exceed the private and social costs and if severely
disadvantaged social groups could be compensated ap-
propriately, then a special pollution standard or practice
should be imposed. Unless there is compensation in
some form (such as cost sharing or tax write-offs), the
burden of the regulation may fall relatively heavily upon
the region that imposes the standard. There may,
therefore, be some income transfer from this area to
other areas as a result of the regulation.
The agency charged with setting pollution tolerances
and developing control programs may be urged to
consider more strongly the local costs and benefits than
the regional-national costs and benefits. However, to the
extent feasible, boards should also consider the national
and regional implications of their actions.
Hopefully, actions to control pollution from non-
point sources would address those problems offering the
greatest benefits to society, i.e., benefits per person
times number of people benefited. Regulations or
recommended practices selected should be those with
the least negative economic and social impacts on
individuals and society.
95
-------
SECTION 6
DECISION FLOW CHARTS AND EXAMPLES
6.1 FLOWCHARTS
Determining whether a nonpoint pollution problem
may exist and, if so, what measures may be taken to
alleviate it most effectively involves a logical sequence of
decisions. This sequence can be illustrated schematically
by flow charts. Flow charts for assessing erosion
problems and selecting physically feasible control prac-
tices are shown for large and field-sized areas in Figures
36 and 37, respectively. Similar flow charts are shown
for nutrients and pesticides in Figures 38 and 39,
respectively. Then, examples are given showing how the
flow charts can be applied to both large and small areas.
Quantitative information is available to permit devel-
opment of definitive answers for most of the questions
posed in the flow charts. The figures and tables
referenced within the charts give the needed data for
relatively large areas, and similar information can be
easily obtained for individual fields or other small areas.
Certain of the questions, however, require more detailed
analysis before an adequate answer can be obtained. One
such question, "IS TRANSPORT OF PLANT NUTRI-
ENTS ON SEDIMENT A HAZARD?," is posed in Figure
38. Here, it is desirable to refer first to Figure 9 for
relative erosion potential, but this in itself will not
provide the needed answer. Reference to a soil-loss
tolerance goal as in Figure 37 is not much help and can
even be misleading. This is because tolerances are
selected for reduction of soil loss to maintain the
productivity of the land; transport of sediment itself is
of concern, not transport of plant nutrients attached to
the sediment. Thus, the recommended use of a 3- or
4-year crop rotation to reduce soil loss to an acceptable
average annual loss over the period of the rotation would
not necessarily eliminate the nutrient hazard, because
nutrient movement could be quite high during the worst
year of the rotation. To answer the question properly,
one must consider not only the long-term erosion
potential but also the potential for gross sediment loss in
any given year in which fertilizers are applied. Similarly,
to answer the question in Figure 39, "IS TRANSPORT
OF THESE PESTICIDES ON SEDIMENT A HAZ-
ARD?," one must consider not only the relative erosion
potential (Figure 9) but also whether persistent and/or
toxic chemicals can be moved on eroded material to an
unacceptable extent even when gross sediment move-
ment is low. Thus, the user of the flow charts must
occasionally obtain additional information pertaining to
the land areas under consideration to supplement the
information in the figures and tables.
6.2 EXAMPLE FOR A FIELD-SIZED AREA
Consider a field in Western Iowa on a 6% slope of
Monona silt loam with organic-matter content above 3%.
The slope length is about 350 feet and the topography is
suitable for contour farming. The farmer wishes to
produce as much corn as is feasible. What are his
alternatives?
Proceed as outlined in the Master Flow Chart, Figure
1, to the Erosion Flow Chart for field-sized areas, Figure
37.
1. R = 160 (Figure 1 Oa); K = 0.37 (SCS, or Table 2a);
LS = 1.3 (Table 3); I = 160 x 0.37 x 1.3 = 77 T/A.
2. For this example, we will assume a tolerance goal,
T, of 5 T/A. It is not the intent here, however, to
recommend this as an overall goal.
3. X = T/I = 5/77 = 0.065.
4. X is less than 1.0; therefore, erosion is a potential
hazard.
5. Enter Table 4 with the threshold value X = 0.065.
Lines 20 through 26 have C values less than X and
would meet the soil-loss tolerance goal of 5 T/A.
However, only No. 20 allows corn on the field
more than half the years, and it requires no-till
planting in a wheat winter cover that is chemically
killed at corn planting time. The example location
is in an area of moderate annual rainfall that
receives only 8 inches from November 1 though
April 30, and water use by the winter cover may
significantly reduce corn yields. Use of supporting
practices will make options available that do not
involve this risk. Consequently, none of these
options are selected.
97
-------
\o
oo
4. Return to Master Flow Chart,
Figure 1, p. 4
Usually Requires Single
Practices on Relatively
Large Acreage, Table 12, p. 63
Consider a Specific Land Area
c
Moderate or High
2. Evaluate Percent
Erodible Cropland.
Figure 7, p. 13
Field-Sized Area
1. Determine Cropland
Sediment Potential.
Figure 9, p. 15
1
Usually Requires Highly Effective
Single Practices or Combinations
of Practices on Relatively Small
Acreage, Table 12, p. 63
3. Evaluate Percent
Erodible Cropland.
Figure 7, p. 13
Proceed to Figure 37, p. 99
1
Usually Requires Highly Effective
Single Practices or Combinations
of Practices on Relatively Large
Acreage, Table 12, p. 63
Usually Requires Combinations
of Practices on Relatively
Small Acreage, Table 12, p. 63
Figure 36.-Flow chart for assessing erosion problems and selecting physically feasible control practices for large areas.
-------
Consider a Specific Field Area
2. Select Soil Loss
Tolerance Goal
(T) in Tons/Acre
1. Compute the Erosion-Potential Index (I) in Four Steps:
a. Obtain Rainfall-Erosivity Index (R) From Figure 10, p. 17-18
b. Obtain Soil Factor (Kl for the Predominant Soil From Figure 11, p. 19
or From Area Soil Conservation Service, or Estimate From Table 2, p. 20-21
c. Estimate Representative Slope Length and Steepness and Obtain LS Value
From Table 3, p. 22
d. R x K x LS = I
5. STRAIGHT-ROW FARMING:
Select From Table 4, p. 23
All Systems That Have C Values
Less Than X and Are Suitable
for the Climate and Land Area.
YesW.
Proceed to Steps 7 and 8
Consider Four Alternatives for
Selection of Erosion-Control
System (Steps 5, 6, 7, and 8 Below)
6. CONTOURING:
Is the Field Topography
Compatible With Contouring?
Does the Slope Length Exceed
Safe Limits? Table 13, p. 67
Obtain Appropriate PC Value for
Contouring From Table 5, p. 27
i
Divide X by Pc
Select From Table 4, p. 23, All
Systems That Have C Values Less
Than X /Pc and Are Suitable for
the Land Area.
7. STRIPCROPPING:
Are Rotation Meadows
a Practical Option?
Obtain Appropriate PSC Value
From Table 5, p. 27
Divide X by PSC
From Table 4, p.23 , Select All
Systems That Include Meadow or
Winter Grain in 50% of the Years
and Have P Values Less Than X /P,
sc
8. TERRACING:
Obtain Appropriate P, Value
From Table 5, p. 27
DivideX by P
From Table 4, p.23. Select All
Systems That Have C Values Less
Than X /Pt and Are Suitable for
The Land Area.
List All Qualifying Acceptable
Options for the Four Alternatives
and Note New Nutrient or Pesticide
Problems That These Options May
Create.
10. Return to Master Flow
Chart, Figure 1, p. 4
Figure 37.-Flow chart for assessing erosion problems and selecting physically feasible control practices for field-sized areas.
-------
8
12. Return to Master Flow
Chart, Figure 1, p. 4
No Potential Problem
at This Time
11. List All Physically Feasible
Practices and Note New Erosion
and Pesticide Problems That
These Practices May Create.
NoW-
7. Are Nutrients
Surface Applied?
Consider a Specific Land Area
1
1. Are Fertilizers or Animal
Waste* Used?
Section 3.6, p. 27
Is There Substantial Direct Runoff?
Figures 3-5, pp. 8-10
5. Is Transport of Plant Nutrients on
Sediment a Hazard? Text, p. 97
8. Select Appropriate Nutrient
and Runoff Control Practices.
Table 16, p. 77 , N 1, N 8-N 10
Table 14, p. 72 , R 1-R 18
10. Select Appropriate Nitrate
Leaching Control Practices.
Table 16, p. 77, N1-N7
; YesV*-
2. Is Percolation Greater Than
1 Inch? Figure 12, p. 26
3. Select Appropriate Nitrate
Leaching Control Practices.
Table 16, p. 77, N1-N7
6. Select Appropriate Erosion Control
Practices With Use of Erosion Flow
Chart (Figure 37, p. 99 ) and
Appropriate Nutrient Control Practices
(Table 16, p. 77 ,N1,N11)
9. Will the Control Practices
Introduce a Leaching Problem?
(Sees. 4.1, p. 61; 4.2, p. 70)
Figure 38.—Flow chart for assessing potential nutrient problems and selecting physically feasible control practices.
-------
12. Return to Master Flow
Chart, Figure 1,p. 4
No Potential Problem
at This Time
Consider a Specific Land Area
*-
i
1. Are Pesticides Used?
Figures 27, p.46
and 28, p. 47
2. List Pesticides That Are Used
on the Major Crops of the Area.
Figures 13-19, pp. 28-34
Table 11, p. 56
Consider Two Questions
(Steps 3 and 8, Below)
3. Are Pesticides Used That Move
Primarily With the Sediment?
Tables 8a-10a, pp. 48-54
Are Pesticides Used That Move
Primarily With the Water?
Tables 8a-1 Da, pp. 48-54
4. Is Transport of These Pesticides
on Sediment a Hazard? Text, p. 97
9. Is There Direct Runoff During
the Application Period?
Figures 3-5, pp. 8-10
Select Appropriate Erosion Control Practices
With Use of Erosion Flow Chart (Figure 37, p. 99)
and Appropriate Pesticide Control Practices
(Table 18, p. 84, P1-PI 5)
11. List all Physically Feasible Practices and Note
and Evaluate Any New Erosion and Nutrient
Problems That These Practices May Create.
10. Select Appropriate Pesticide
and Runoff Control Practices.
Table 18, p. 84, P1-PI 5
Table 14, p. 72, R1-R18
Will Selected Practices Create
a Serious Percolation Problem?
(Sees. 4.1, p. 61; 4.2, p. 70)
Evaluate Potential Leaching
Problem With Use of Nutrient
Flowchart. Figure 38, p. 100
Figure 39.~Flow chart for assessing potential pesticide problems and selecting physically feasible control practices.
-------
6. The field topography is suitable for contouring.
The slope length of 350 feet does not exceed the
limit given in Table 13 for effective contouring on
6% slope if the system provides at least 50%
surface cover by residue mulch when canopy cover
is absent or poor. Therefore, contouring is an
important option.
For contouring on 6% slope, Pc = 0.5 (Table 5) and
X/PC = 0.065/0.5 = 0.13. With this larger threshold value,
lines 15 through 19 of Table 4 would also meet the
5-ton tolerance goal. With contouring, the farmer could
no-till plant corn annually in 70% residue cover (No. 16)
or could produce corn 3 years in 5 (No. 18) by
moldboard plowing for first-year corn and no-till plant-
ing the second and third years of corn. In some years the
harvest of corn may be too late for planting wheat and a
spring-seeded small grain would be used. For conveni-
ence, only the wheat system will be considered in this
example.
7. For contour stripcropping with alternate strips in
meadow, Psc = 0.25, and X/PSC = 0.065/0.25 =
0.26. This higher threshold value would qualify
additional lines of Table 4, but the requirement of
having only half the field in corn would not be
compatible with the farmer's cropping goals.
8. Two terraces could divide the 350-foot slope
length into three 117-foot slopes. If the 5-ton
tolerance is for the purpose of maintaining the
productivity level of the field, it is applied to the
amount of soil moved to the terrace channels. For
this purpose, Pt= 0.5//3 = 0.29 (Table 5), and
X/Pt= 0.22. The farmer then has the additional
options of continuous corn using conservation
tillage practices that are less restrictive than no-till
(Nos. 11 and 13), a no-till planted corn-soybean
rotation (No. 37), or corn 3 years in 5 using the
conventional plow system (No. 12).
If the tolerance limit were established solely for
pollution control, it is much less restrictive on the
terraced field than indicated in the preceding paragraph.
Because of deposition in the terrace channels and outlet,
not more than 20% of the soil eroded to the channels is
likely to leave the field. With the 117-foot terrace
spacing on 6% slope, the annual contribution to off-field
sediment would probably average only about 2 T/A if he
doubled the computed 0.22 threshold value. Therefore,
conventional plow systems for continuous corn or a
corn-soybean rotation would also be acceptable for
pollution control.
9. For this illustration, we will assume that the goal is
to hold average annual soil movement to the
channels within the 5-ton limit. The farmer then
has at least five options for comparative evaluation
on the basis of chemical pollution and economic
return. Although each of the five satisfies the
tolerance goal, some provide more control than
others, as shown by Table 20.
10. Master Flow Chart says to evaluate potential
nutrient problems, Figure 38.
Table 20. Cropping options selected in example for erosion control and their estimated annual soil loss.
Supporting practice
Contoured
Contoured
Terraced (2
terraces)
Terraced
Terraced
(None
Table 4 line no.
16
18
13
11
37
25
System
Corn annually, no-til] plant in 70% residue cover
C-C-C-W-M rotation with turnplowing for first year corn: no-
till second and third corn
Corn annually, tillage in row zones only
Corn annually, chisel plant
Corn-soybean rotation, no-till
For comparison, not an option
Estimated soil loss
T/A.
4.2
2.9
3.6
4.2
4.0
29.0)
1 Estimated soil toss is equal to the product of the erosion potential index (1), the cropping and management factor. C, and the
support-practice factor, P.
2 Line 5 represents continuous corn with crop residues plowed under in spring, planting in smoothed seedbed, and post-
emergence cultivation.
102
-------
Nutrient Flow Chart
1. Yes, fertilizers are needed in this area for eco-
nomic yields of row crops in the five options for
erosion control under consideration (Table 20).
2. Yes, the Monona silt loam is classed in hydrologic
group B (Table 7.1, Hydrology, SCS National
Engineering Handbook), which is the same as the
predominant hydrologic group used for LRA 107
in Figure 12. The average annual percolation is
estimated to be 1 to 3 inches.
3. Nl. Prevent Excessive Application of Nutrients
Suppose soil samples had been sent to the Iowa State
University Soil Testing Laboratory and the phosphorus
level was found to be in the medium class. Their
fertilizer recommendations would probably be:
Corn - 170 Ibs. N and 13 Ibs. P per acre (30 Ibs.
P205)-
Small Grain - 60 Ibs. N and 11 Ibs. P per acre (25 Ibs.
P205).
Soybeans - 0 Ibs. N and 15 Ibs. P per acre (35 Ibs.
P205).
Grass-legume pasture — No N or P.
Following these recommendations will provide ade-
quate but not excessive amount of fertilizer except
under unusual conditions such as drought.
N 2. Timing Nitrogen Applications
Figures 34 and 35 indicate leaching potential is low
for nitrogen applied either in the fall or spring in this
area.
N3. Using Crop Rotations
The use of the corn-soybean rotation reduces the
long-term nitrogen fertilizer requirement by more than
half, since soybeans are legumes.
The use of wheat and a meadow in 2 of 5 years
reduces the total N applied in 5 years from 850 to 570
Ibs/A.
N 5. PI owing-Under Green Legume Crops
The meadow contains N which will reduce fertilizer
requirements. It is estimated that the total fertilizer
requirement during the 5-year rotation is 400 Ibs.
Practices N 4, N 6, and N 7 are judged to be not
applicable on this farm.
4. The average direct runoff is 1 to 3 inches annually.
Figure 5 shows that most of this occurs during
May and June.
5. Erosion is potentially very severe in this area, and
thus nutrient transport by sediment may be a
hazard.
6. Five cropping practices have been selected (listed
earlier under erosion part of the example) that will
provide adequate erosion control. Meeting sedi-
ment loss goals does not guarantee the nutrient
loss goals will be met, but since there is a lack of
quantitative information, it will be assumed that
adequate erosion control will provide adequate
nutrient loss control. Since only 10 to 20% of the
sediment that reaches terraces actually leaves the
field, terrace systems may meet more restrictive
nutrient loss goals without a reduced sediment
goal.
7. Most phosphate fertilizer is applied broadcast.
8. Incorporating surface applications, practice N 8,
will be achieved to a limited extent in the options
with chisel plant and strip till plant. Controlling
surface applications, practice N 9, can be used by
applying the broadcast phosphate fertilizer in the
fall or early spring. The most erosive period is
from May to June (Figure 30) so that plowing in
early spring should be acceptable. The fertilizer
should not be applied to frozen or snow-covered
ground.
The cropping practices selected to control erosion
will also reduce the frequency and total amount of
runoff. Runoff will be slightly reduced for no-till
systems, and moderately reduced for strip tillage and
chisel plant systems. Contouring and terracing in addi-
tion to the above practices will reduce runoff (Tables 14
and 15).
9. Decreased runoff means increased percolation, but
its occurrence in May and June is not expected to
cause a problem since plant growth is underway.
Any additional nongrowing-season nitrate leaching
should be controlled by the practices already
recommended, N 1, N 3, and N 5.
11. N 1. Eliminating Excessive Fertilization
N 3. Using Crop Rotations
N 5. Plowing-Under Green Legume Crops
N 8. Incorporating Surface Applications
N 9. Controlling Surface Applications
N 10. Using Legumes in Haylands and Pastures
Nil. Timing Fertilizer Plow-Down
12. The Master Flow Chart indicates we are now
ready to evaluate potential pesticide problems,
Figure 39.
103
-------
Pesticide Flow Chart
1. The five crop management options for erosion
control that are under consideration (listed earlier
in the erosion part of the example), as well as the
annual corn with no supporting practice included
for comparison, all require the use of both
herbicides and insecticides to maintain productiv-
ity.
2. In 1973, the Iowa State Cooperative Extension
Service recommended 7 herbicides and 18 insecti-
cides for use on corn, as follows:
Herbicides—alachlor, atrazine, cyanazine, 2,4-D, li-
nuron, propachlor, butylate
Insecticides-Bux, carbaryl, carbofuran, chlordane,
Diazinon, disulfoton, EPN, ethoprop,
fensulfothion, fonofos, heptachlor, Lan-
drin, malathion, methyl demeton, naled,
phorate, toxaphene, trichlorfon.
All of the insecticides are compatible with non-till
management, as are all of the herbicides except
butylate, which must be incorporated perplant
and, therefore, cannot be used with no-till.
For soybeans, the Extension Service recommended
10 herbicides and 4 insecticides:
Herbicides—alachlor, chloramben, chloroxuron,
chlorpropham, dinoseb, fluorodifen, linuron,
dinitramine, nitralin, trifluralin
Insecticides-azinphos methyl, carbaryl, malathion,
toxaphene
All of these insecticides and the first seven
herbicides listed are compatible with no-till pro-
duction. For wheat and meadow, pesticides com-
patible with no-till can be taken from Extension
Service recommendations and listed in the same
way.
3. Yes, by reference to the above lists and to Tables
8a and 9a. (The selection of a small number of
specific pesticides for use by the farmer may, of
course, create a "No" answer.)
4. Biologically significant concentrations of pesti-
cides could be delivered to drainage streams by
adsorption on sediment particles.
5. Five feasible erosion control practices have already
been selected by following the erosion control
flow chart. Accompanying pesticide control prac-
tices that should be considered for this farm can
be obtained from Table 18. These would appear to
be practices P 1, P 2, P 4, P 5, P 6, P 8, P 9, and P
11. Each will be discussed individually in develop-
ment of recommendations below.
6. The estimated annual percolation of 1 to 3 inches
(Figure 12) is insufficient to threaten the quality
of ground water during the residence time in the
soil of the pesticides being used.
8. Yes by reference to the lists of pesticides and to
Tables 8a and 9a. (As in question 3, choice by the
farmer of a small number of specific pesticides
may result in a "No" answer.)
9. In Iowa corn is usually planted during May, and
the period of highest direct runoff is during May
and June (Figure 5). Except for later postemer-
gence treatments, herbicides and insecticides are
also applied during this period.
10. Pesticide practices will duplicate those selected in
Number 5 for sediment-borne pesticides; some
runoff control will be achieved by options selected
for erosion control. Additional runoff control
practices that are physically feasible for this area
are level terraces, discussed in R 12, and farm
ponds, R 18. However, these practices are more
expensive to install and will not be considered in
this example.
11. The eight pesticide control practices noted above
that can be recommended to minimize pesticide
movement off the farm have attributes that
sometimes vary with the crop management option
chosen for erosion control, as follows:
P 1. Using Alternative Pesticides
Use of less-toxic (Tables 8a and 9a) and less-persistent
(Figure 29) pesticides is recommended on this farm
when alternatives are available, as is use of different
pesticides in succeeding years. For example, seven
different insecticides-carbaryl, carbofuran, Diazinon,
EPN, phorate, toxaphene, trichlorfon-are suggested by
the Iowa Cooperative Extension Service for control of
the corn borer. Reference to the cited tables and figures
will provide a rational basis for selection. With the no-till
practice options, pesticides that move primarily with the
sediment (Tables 8a and 9a) are preferred over those
that move primarily with the water, because no-till
reduces erosion more than runoff.
P 2. Optimizing Pesticide Placement
Whenever possible, pesticides should be incorporated
into the soil. In no-till practice, the insecticide should be
placed in the seed furrow at corn planting time and
covered with untreated soil. Only one of the insecticides
recommended by the Extension Service for use against
soil insects in corn, carbofuran, is not toxic to the seed
and can be used in this way.
104
-------
P 4. Using Resistant Crop Varieties
Use of resistant corn hybrids is already accepted
practice in Iowa.
P 5. Optimizing Crop Planting Time
Corn can be planted in Iowa as early as April 20,
although most planting is done in May. The earliest
possible planting is recommended to minimize corn
borer attack and to avoid the peak direct runoff period.
P 6. Optimizing Pesticide Formulation
Granular pesticides should be used in preference to
liquid or dust formulations.
P 8. Eliminating Excessive Treatment
Elimination of insurance treatments with soil insecti-
cides is not recommended for continuous corn. For
aboveground insects, treatment should not be begun
until the economic threshold is reached, preferably as
determined by a professional entomologist.
P 9. Optimizing Time of Day for Pesticide Appli-
cation
If liquid formulations of pesticides must be used,
early morning or evening spraying is recommended to
increase on-target deposits and to minimize potential
damage to honeybees.
P 11. Optimizing Date of Pesticide Application
The preplant herbicides—on corn: alachlor and atra-
zine in no-till plus butylate in tillage practices; on
soybeans: alachlor in no-till plus dinitramine, nitralin,
and trifluralin in tillage practices-should be applied as
early in the spring as possible, to avoid peak runoff
periods (Figure 5). Post-emergence insecticides should be
applied as late as possible while maintaining good pest
control.
12. The Master Flow Chart, Figure 1, shows that we
are now ready to estimate costs of applying
practices.
Economic Evaluation
The following discussion uses the methodology pre-
sented in Section 5.1 to evaluate the options. This
example is clearly site-specific and cannot hope to show
the full gamut of variables which may potentially be of
significance in other situations. The size of the farm is
250 acres and the costs and returns are for the whole
farm for a single (average) year.
Only a summary of the calculations is presented here
(Table 21). Detailed tables and sources of information
are given in Appendix C, Volume II. It was assumed that
none of the macroeffects described in Section 5.2
influence any of the decision variables of this example.
It is implicitly assumed that any machinery that might
become obsolete because of a change in cropping
practices could be sold at a cost close to its depreciated
value.
The terracing options require 62,250 feet of terraces
costing $0.60 per foot to construct and $0.06 per foot
per year to maintain. The construction cost is prorated
over a 20-year economic life, discounted at 8% p.a.
interest.
Each of the options requires a specific set of field
operations and implements. Tractor costs and fuel and
lubrication costs are listed separately. Depreciation was
calculated by the straight-line method. Interest charges
(at 8%) were included in the tractor and implement cost.
The no-till options were assumed to have a higher
seed mortality rate due to higher crop residue levels.
Nitrogen was applied as anhydrous ammonia and the
phosphate and potassium were applied in granular bulk
form.
The herbicide costs for the no-till options were higher
because both greater amounts and more expensive
herbicides were assumed to be used. The insecticide cost
for the corn years of the rotation including meadow was
greatet, due to the expected incidence of the first-year
corn insect complex. The average per-year cost for all
years in the rotation, however, was reduced by the
inclusion of wheat and meadow since these crops are
assumed to require no insecticides. No insecticide cost
was included for soybeans, since soybeans are seldom
treated in this area. Therefore, the insecticide costs for
the corn-soybean rotation were 50% of the insecticide
costs for continuous corn.
The labor requirement per acre was estimated as
130% of the tractor-hour requirement to account for
overhead. The cost per hour was $2.50.
Cost of corn drying was $0.12 per bushel and 8%
interest costs for operating expenses (excludes land,
tractors, and implements). These costs are shown as
"other" expenses.
The costs and returns for continuous corn (residue
left, with turn plow, straight row) are shown for
comparison purposes only. This system does not meet
the erosion limitation and is not an available option.
Yields were 110 bushels per acre for corn except for
the no-till options, which were estimated at 105 bushels
per acre. The yields for wheat, soybeans, and meadow
105
-------
Table 21. Costs and returns for selected options.
Item
Gross revenue
Costs
Tractor (excl. fuel)
Implements (excl. fuel)
Fuel
Seed
Fertilizer
Pesticides
Labor
Terracing
Other
Land charge {see text)
Total costs
Net return
Straight-row
C conv.
$75,625.00
3,430.25
5,940.23
1,432.85
1,712.50
7,912.50
4,500.00
1,803.75
0
4,195.00
18,020.00
48,947.08
26,677.92
Contour
C no-till
$72,187.50
3,066.46
4,973.11
1,113,92
1,937.50
7,912.50
5,750.00
1,178.12
0
4,088.09
18,020.00
48,039.70
24,147.80
C-C-C-W-M
no -till
$61,312.50
3,426.24
8,038.98
1,427.16
2,947.50
4,452.50
3,750.00
1,659.12
0
2,691.01
18,020.00
46,412.51
14,899.99
Terraced
C chisel
$75,625.00
3,238.69
4,961.73
1,267.69
1,787.50
7,912.50
4,500.00
1,568.12
3,450.00
4,190.96
18,020.00
50,897.19
24,727.81
C strip
$75,625.00
3,066.70
5,077.54
1,113.92
1,787.50
7,912.50
4,500.00
1,348.75
3,450.00
4,183.51
18,020.00
50,460.42
25,164.58
CB no-till
$66,093.75
2,887.79
5,179.43
937.36
2,155.00
4,782.50
4,500.00
885.62
3,450.00
2,246.64
18,020.00
45,044.34
21,049.41
were 45 bushels per acre, 40 bushels per acre, and 4 tons
per acre, respectively.
Table 21 summarizes all of the preceding computa-
tions and shows the gross revenue and net return for
each of the six systems. A land cost was included based
on an assumed land value of $974.00 per acre and a cash
rent of $7.40 per $100 value. Since this land charge
applied equally to all six production methods, any error
in this land charge will change only the absolute levels
and not the differences in net returns among the six
alternatives.
The (unavailable) alternative of continuous corn with
conventional turn plow tillage has a significantly higher
net revenue than any of the available options. There is
only a small variation in net return of the top three
available options with a major net return drop to the
corn-soybeans alternative. The corn-corn-corn-wheat-
meadow rotation has by far the lowest net return,
indicating that the savings in fertilizer cost generated by
the nitrogen nutrient credit from the legume meadow
are not sufficient to offset the loss of gross revenue.
An important consideration is that the yield varia-
tions under no-till are higher than for options utilizing
tillage. This higher variation for no-till may be partly due
to the growers' lack of familiarity with this method. In
this example, the no-till options were assumed to have a
lower yield than the others to account for this potential
yield impact. A farmer who is a risk-averter or who is
unfamiliar with no-till planting may be willing to accept
a lower net return with a higher degree of certainty if
that option excludes no-till planting.
One additional consideration is related to the cost of
terracing. The present example assumes that the farmer
bears the full cost of terracing. Historically, society has
reimbursed terracing costs through various government
programs so that the farmer usually paid half the cost or
even less. Under any such cost-sharing program the
relative differences in net revenue will change. In the
present example, a cost-sharing program with a 50-50
split would give two of the terraced alternatives a net
revenue practically identical to the conventional tillage,
continuous corn activity.
106
-------
In conclusion, the final decision has to remain with
the farm operator. His decision will depend on the value
he places on minimizing risk, his expectation of risk for
each alternative, his familiarity with the alternative
production method, his reluctance to try a method with
which he is unfamiliar, and, as shown above, which
cost-sharing program he can enter to help pay for his
terrace construction costs. He may place no value on
these intangibles, in which case he would probably
choose the alternative with the highest net return.
Summary
Five options were selected that limit annual soil loss
to less than 5 T/A. These options and their estimated
soil losses are contoured no-till corn, 4.2 T/A.; con-
toured C-C-C-W-M rotation, 2.9 T/A.; terraced corn
tilled in row zones only, 3.6 T/A.; terraced corn, chisel
plant, 4.2 T/A.; and terraced corn-soybean rotation,
no-till, 4.0 T/A. Estimated soil loss for continuous corn
without erosion control is 29 T/A. Nutrient use was
similar for all options except for the rotation options,
which use substantially less fertilizer nitrogen. Nitrate
leaching is not a major problem in this location. Loss of
nitrogen and phosphorus with sediment is not antici-
pated to be a problem when soil loss is controlled by the
selected options. Surface-applied phosphate should be
incorporated soon after application to prevent losses in
runoff.
The control of sediment will probably reduce pesti-
cide losses substantially. However, eight other practices
were selected and listed in the pesticide portion of the
example that could provide additional reduction. Pesti-
cide use is lower for some options and may result in
reduced pesticide loss. For example, insecticide usage
was 50% lower for the corn-soybean rotation and 25%
lower for the corn-wheat-meadow rotation, as compared
to the other options. Herbicide usage was highest for the
no-till options, but herbicides generally have less impact
on the environment than insecticides.
The economic analysis indicates that the rotation
options, particularly the one containing meadow,
produce significantly lower net returns. The other
options also reduce net return by about 6 to 9% as
compared to continuous corn without erosion control.
However, the example assumed the farmer bore the full
cost of erosion control. Incentives, such as a 50-50 cost
sharing for terracing, would make the net revenue from
the terraced options similar to that from the conven-
tional corn system.
6.3 EXAMPLE FOR A LARGE AREA
Suppose that a commission responsible for planning
the resource development of the Suwannee River Basin
is charged with identifying potential nonpoint pollution
problems and selecting appropriate control measures. A
map of the Suwannee River Basin is shown in Figure 40.
From Figure 2 the Land Resource Areas to be con-
sidered are: 133, Southern Coastal Plain; 38, North
Central Florida Ridge; 152, Gulf Coast Flatwoods; and
153, the Atlantic Coast Flatwoods. To illustrate the
procedures developed in this manual we will consider
that part of Land Resource Area 133 in the Suwannee
Basin. Now that a specific land area has been selected,
the first step is to obtain localized information. Rather
detailed reports have been prepared for major river
basins of the United States and are a good source of
additional information. The Suwannee Basin is included
in the Report of the United States Study Commission-
Southeast River Basins.1
A brief description of important characteristics of
Land Resource Area 133, quoted from USDA Agricul-
ture Handbook No. 296, follows:
133-SOUTHERN COASTAL PLAIN
Georgia, Alabama, Mississippi, Louisiana, Texas, Arkansas,
Tennessee, North Carolina, South Carolina, Virginia,
and Florida
145,300 square miles
LAND USE: Nearly all the area is in farms. A small
acreage is owned by the Federal Government, and
additional small areas are urban or in other uses.
Between one-half and three-fourths is woodland,
nearly all in small holdings but some in large
tracts. The proportion of woodland is greatest in
the west. Lumber, pulpwood, and naval stores are
the major forest products. Between one-tenth and
one-third is cropland; the largest acreage is in the
east. Less than one-tenth is in pasture. This is a
cash-crop area, and cotton is a major crop.
Peanuts, tobacco, melons, various vegetable crops,
and corn are important also. The trend recently is
to more pasture and woodland and less cropland.
ELEVATION AND TOPOGRAPHY: 100 to 600
feet, increasing gradually from the lower Coastal
HI. S. Study Commission. 1963. Plan for development of the
land and water resources of the southeast river basins. Appendix
5, Suwannee Basin.
107
-------
WILDLIFE?!
REFUGED
Gainesville
Figure 40.-The Suwannee Basin.
108
-------
Plain to the Piedmont. The gently to strongly
sloping dissected coastal plain is underlain by
unconsolidated sands, silts, and clays. In their
upper reaches stream valleys are narrow, but the
lower parts of the valleys are broad and have
widely meandering stream channels. Local relief is
mainly in a few tens of feet, but some of the more
deeply dissected parts have relief of 100 to 200
feet.
CLIMATE: Average annual precipitation-^ to 60
inches; lowest in autumn throughout the area and
highest in midsummer in the east and in winter
and spring in the west. Average annual tempera-
tures—6Q° to 68° F., increasing from north to
south. Average freeze-free period-200 to 280
days, increasing from north to south.
WATER: Rainfall, many perennial streams, and
ground water provide an abundance of water. Even
though summer rainfall is fairly high, droughts are
common and then good returns are obtained from
irrigation on all but the wettest soils. Drainage is
necessary before the wet lowlands can be used for
crops. Domestic water supplies are obtained
mainly from shallow wells and water for livestock
from perennial streams and small farm ponds. The
many perennial streams are potential water sources
that have been little used in most of the area.
SOIL: Red-Yellow Podzolic soils are dominant
throughout (Ruston, Norfolk, Orangeburg. Saffell,
and Lexington from sandy or gravelly materials;
Marlboro, Bowie, Savannah, Shubuta, Kirvin, and
Silerton from medium to moderately fine textured
materials; and Boswell, Susquehanna, Sawyer, and
Cuthbert in fine-textured materials). Associated
with them on wet lowlands are Low-Humic Gley
soils (Plumme/, Bladen, Bibb, Falaya, and Cox-
vUle) and Humic Gley soils (Portsmouth, Bayboro,
Weeksville, and Johnston). Reddish-Brown Lateri-
tic soils (Greenville, Red Bay, and Nacogdoches)
are important locally, mainly in the south, but are
of small total extent. Regosols (Eustis, Lakeland,
and Kershaw) are on gently rolling to steeply
sloping areas underlain by sands. Alluvial soils
(Mantachie and luka) on narrow bottom lands are
important to agriculture locally. In Texas and
Louisiana, where the alluvium contains a large
amount of material from red rocks, Miller and
Yahola are important soils. (In current terminol-
ogy, these soils are called Ultisols and Entisols).
From the U. S. Study Commission Report we find
that the Suwannee Basin comprises 7 million acres.
Approximately 4 million acres could be cropped but
only 1.6 million acres were cropped in 1961. Most of the
cropland in the basin is in LRA's 133 and 138.
Additional information could be obtained from reports
from USDA, the Georgia Coastal Plain Experiment
Station, Tifton, and the Florida Experiment Station,
Gainesville.
Identifying potential nonpoint pollution problems
and appropriate control measures for LRA 133—Follow-
ing the Master Flow Chart, Figure 1, the first step is to
evaluate the erosion potential using the flow chart in
Figure 36.
1. The cropland sediment potential is moderate.
2. Erosion is the dominant limitation on less than
10% of the cropland. Since this can be classed as
low, fairly severe erosion from limited acreage is
indicated. To correct this erosion problem, highly
effective single practices or combinations of prac-
tices (Table 12, E 1-E 17) will be required on the
credible areas. Specific control practices can be
selected only for individual fields.
4. In returning to the Master Flow Chart, Figure 1,
the next step is to evaluate runoff pollution
problems by the Nutrient Flow Chart, Figure 38.
Nutrient Flow Chart
1. The figures in Section 3.5 show the distribution of
major crops. Corn is the predominant crop and
requires substantial nitrogen and phosphorus for
good production. Acreages of cotton and vegetable 2.
crops also are substantial. Additional information
from Agriculture Handbook No. 296 and the U. S. 3.
Study Commission Report shows a substantial
acreage of peanuts. Consequently, commercial
fertilizers are applied. In addition, poultry and
swine wastes are available for spreading on crop-
land.
The percolation is estimated to be greater than 7
inches in this Land Resource Area.
This area is very susceptible to leaching and
excessive fertilization should be avoided (N 1).
Therefore, correct timing of fertilization is neces-
109
-------
sary to supply adequate nutrients to crops (N 2).
Practices N 3 to N 6 should also be used in this
area when applicable to the cropping system.
4. Runoff (greater than 7 inches) is distributed
relatively uniformly throughout the year. Growing
season runoff is 3 to 7 Inches.
5. Transport of nitrogen and phosphorus on sedi-
ments may be a hazard because erosion is severe in
some portions of the area.
6. Erosion control practices have already been se-
lected. Nutrient control practice N 11, Timing
Fertilizer Plow-Down, would further reduce the
loss of nitrogen and phosphorus.
7. Manures and some commercial fertilizers are sur-
face-applied.
8. Nutrient control practices N 8, N 9, and N 10
(Table 16) and runoff control measures R 2, R 3,
R5, R7, R8, R9,R 10, R 12, R 13, R 15, and R
16 (Table 14) that offer moderate to substantial
runoff reductions should be considered.
9. Any practice which reduces the direct runoff will
increase the amount of percolation. However, a
severe leaching problem already exists and the
increase in percolation will not create any addi-
tional problems.
11. Nutrient and runoff control practices that should
be used in the area when applicable to the
cropping systems are as follows:
N 1. Eliminating Excessive Fertilization
N 2. Timing Nitrogen Application
N 3. Using Crop Rotations
N 4. Using Animal Wastes for Fertilizer
N 5. Plowing-Under Green Legume Crops
N 6. Using Winter Cover Crops
N 8. Incorporating Surface Applications
N 9. Controlling Surface Applications
N 10. Using Legumes in Haylands and Pastures
Nil. Timing Fertilizer Plow-Down
R 2. Conservation Tillage
R3. Sod-Based Rotations
R5. Winter Cover Crop
R 7. Timing of Field Operations
R8. Plow Plant Systems
R 9. Contouring
R 10. Graded Rows
R 12. Terraces
R 13. Grassed Outlets
R 15. Contour Listing
R 16.Change in Land Use
Pesticide usage may vary depending on the individual
practices selected. For example, Conservation Tillage
usually requires additional pesticides, particularly herbi-
cides.
12. The Master Flow Chart shows that we are now
ready to evaluate pesticide problems by the flow
chart shown in Figure 39.
Pesticide Flow Chart
1. Figures 27 and 28 indicate that considerable
amounts of pesticides are used in the area.
2. Table 11 lists the specific pesticides used on major
crops—corn, cotton, vegetables, and peanuts.
3. Yes, by reference to the specific pesticides listed in
Tables 8a and 9a.
4. Biologically significant concentrations of pesti-
cides could be delivered to drainage streams by
adsorption on sediment particles.
5. Specific erosion control practices will have to be
selected for individual fields. Pesticide control
practices that are applicable to this area should be
selected from Table 18. These would appear to be
practices P 1,P 2, P 3, P 4, P 5,P 6, P 8, P 9, P 10,
and P 14. However, the other practices might be
applicable in specific situations.
6. A serious percolation problem exists. Pesticides
usually do not leach because of their adsorption
characteristics. The best control is selecting pesti-
cides that are less persistent (Figure 29). Within a
given persistence class, those pesticides that move
primarily with the sediment should be favored
(Tables 8a and 9a).
8. Yes, by reference to the specific pesticides listed in
Tables 8a and 9a.
9. Yes, runoff is substantial during the entire year
(Figures 3 to 5).
10. Pesticide practices will duplicate those selected in
No. 5 for sediment-borne pesticides. Runoff con-
trol practices will duplicate those selected earlier
for nutrient control.
11. The pesticide practices selected for additional
control when applicable to the cropping systems
are as follows:
P 1. Using Alternative Pesticides
P 2. Optimizing Pesticide Placement with Respect to Loss
P 3. Using Crop Rotation
P 4. Using Resistant Crop Varieties
P5. Optimizing Crop Planting Time
P 6. Optimizing Pesticide Formulation
110
-------
P 8. Reducing Excessive Treatment
P 9. Optimizing Time of Day for Pesticide Application
P 10. Optimizing Date of Pesticide Application
P 14, Managing Aerial Applications
These practices should not create any new or addi-
tional pollution problems.
12. The Master Flow Chart directs us now to Eco-
nomic Considerations.
Economic Considerations
The decision makers will have to determine the level
of control desirable. In arriving at a decision, both
physical and economic factors should be considered. The
physically feasible alternatives have been discussed.
Attention can now be turned to the economic feasibility
of the alternatives.
In this example, erosion is the dominant limitation on
less than 10% of the cropland. Highly effective single
practices or combinations of practices will be required.
Furthermore, specific control practices can be selected
only for individual fields. Given this information, the
analytical procedure used in the small area example
would be applicable for identifying on-farm costs and
benefits in credible areas.
Since the highly erodible acreage of the land area is
relatively small, it does not appear that practices or
procedures needed for erosion control would have
significant regional or national impacts. However, certain
control levels could require large investments for erosion
control or shift cropping combinations and the level of
production of specific crops for this area. Any signifi-
cant changes in levels of production could have notice-
able impacts upon the agricultural input and processing
industries. For example, reductions in the cotton acreage
would reduce ginning demands and the effective utiliza-
tion of ginning capacities. These impacts would, in turn,
affect other sectors of the local economy.
The highly erodible land might be better used for
other than row crop production. A trend in this area
away from cultivated agriculture toward forest produc-
tion suggests this as a possible alternative land use. The
effect of changes on off-farm employment as well as
adverse economic impacts on individuals and measures
to alleviate these impacts must be considered.
Similarly, benefits should be assessed. Potential bene-
fits could include less sediment in streams, thus benefit-
ing aquatic populations and possibly enhancing recrea-
tion potential. The trend toward forest production also
could enhance recreational potentials. Other benefits
could include: increased soil conservation and agricul-
tural productivity, less flooding, less dredging and
channel repairs, and aesthetic improvements.
No attempt is made to estimate costs and benefits in
this example because of the complexity of the task and
the time required. However, in an actual situation those
responsible for making a decision probably would want
to draw upon specialized expertise to make an assess-
ment. This expertise would likely use analytical tech-
niques mentioned in Sec. 5., and be concerned with
factors such as historical changes in the area and the
reason for these changes, sources of revenue, direct and
indirect effects of changes in income and employment,
overall economic importance of agriculture in the area,
degree of off-site damage from erosion, and nonagricul-
tural employment opportunities.
Ill
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-75-026a
4. TITLE AND SUBTITLE
Control of Water Pollution
A Manual for Guideline Dev
2. 3. RECIP
ARS-H-5-1
5. REPO
Jul
from Cropland Volume I — e. PERFC
elopment
7.AUTHORIS) 8. PERF1
B. A. Stewart, D. A. Woolhiser, W.H. Wischmeier,
J. H. Caro, and M. H. Frere
9.PERFORMING ORGANIZATION NAME AND ADDRESS 10. PRO
Agricultural Research Service IBB
U. S. Department of Agriculture 11. CON
Washington, D. C. IAG
12. SPONSORING AGENCY NAME AND ADC
U. S. Environmental Protec
Environmental Research Lab
Athens, Georgia 30601
3RESS 13. TYP
tion Agency 14.spor
oratory-Athens
EPA
15. SUPPLEMENTARY NOTES _. ., ... ,,.
Prepared as a joint publication of Office
Development, EPA, and Agricultural Research Service, USDA.
lENT'S ACCESSION-NO.
RT DATE
y 1975
DRMING ORGANIZATION CODE
DRMING ORGANIZATION REPORT NO.
GRAM ELEMENT NO.
039
TRACT/GRANT NO.
Dli-oU85
E OF REPORT AND PERIOD COVERED
al Jan '7' Julv '75
MSORING AGEhjCY"ck5"bfe ' ^
-ORD
of Research and
16. ABSTRACT
Engineering and agronomic techniques to control sediment, nutrient, and
pesticide losses from cropland were identified, described, and evaluated. Methodologj
vas 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 information is presented in the form of regional maps,
decision flow charts, tables, and brief technical highlights.
17.
a. DESCRIPTORS
runoff
pesticides
nutrients
non-point source pollution
hydrology
sediment control
erosion
13. DISTRIBUTION STATEMENT
Unlimited
KEY WORDS AND DOCUMENT ANALYSIS
b.lDENTIFIERS/OPEN ENDE
19. SECURITY CLASS (This
20. SECURITY CLASS (This
ED TERMS C. COSATI Held/Group
Report) 21. NO. OF PAGES
page) 22. PRICE
EPA Form 2220-1 (9-73)
------- |