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


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           To order please cite

           REPORT NO. EPA-600/2-75-026a

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 The public may also purchase this document from the National Technical Information
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                        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

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                                 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

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                                     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

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                                             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

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                                             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

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                                        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

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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.

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                                                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.

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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.

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                                               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

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    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.

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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

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'
                        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).

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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

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  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.

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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.

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   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

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                   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

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       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

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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

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           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

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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.

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                                  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

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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

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   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

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,,
                                                                                                                                     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.)

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                                                                                                                                   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)
 !

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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.)

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                                                                                                                          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.)

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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.)

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                                                                                          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.

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!
                                                        Figure 26.-Depth of frost pentration, inches.

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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.

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                                                                              UNITED STATES
                                                                                  TOTAL
                                                                                 39,881,566
                                                                                  ,UIIU All 01 '"I • [ II . ,
Figure 28.-Acreage of non-hay crops treated with insecticides.

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            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

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     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

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                     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

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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

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          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

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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

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                         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

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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

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      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

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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

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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

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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

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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.

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                                               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

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                                                                 0 JFMAMJJASOND
                                                                     Month
Figure 30.~Monthly distribution of erosive rainfall as percentage of annual.

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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

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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

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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

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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

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 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

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   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

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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

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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

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                        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

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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

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      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

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                                  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.

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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

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       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

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        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

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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

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    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

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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

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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

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 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

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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

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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
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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-
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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.
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                                               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
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     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.
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   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.
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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

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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

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                                               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

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\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.

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                       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.

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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.

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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.

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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

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                                           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

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                                          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

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     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
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                               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.
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   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

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                                                                               WILDLIFE?!



                                                                                 REFUGED
                                                                                     Gainesville
                                       Figure 40.-The Suwannee Basin.
108

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    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

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      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

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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

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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)

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