EPA-430/9-73-015
METHODS and PRACTICES for
CONTROLLING WATER POLLUTION
from
AGRICULTURAL NONPOINT
SOURCES
S. ENVIRONMENTAL PROTECTION AGENCY
Washington, D.C. 20460
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FOREWORD
This report is issued in response to Section 304(e)(2)(A)
of Public Law 92-500. This Section provides:
The Administrator, after consultation with appropriate
Federal and State agencies and other interested persons,
shall issue to appropriate Federal agencies, the States,
water pollution control agencies, and agencies designated
under section 208 of this Act, within one year after the
effective date of this subsection (and from time to time
thereafter) information including ... (2) processes,
procedures, and methods to control pollution resulting
from -- "(A) agricultural . . . activities, including
runoff from fields and crop . . . lands ..."
This report, prepared under contract by the Economic
Research Service, United States Department of Agriculture, for
the Environmental Protection Agency, provides general information
on alternative control measures and cultural practices. It is
intended to provide information that, when considered in the
light of local conditions, will give an indication of the kinds
of measures that may be useful in a program to control pollutants
from agricultural activities. Expertise, well-founded in the
utilization of such measures, must be brought to bear in the
final design of the control plan.
Riisst
Administrator
Environmental Protection Agency
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.10
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EPA-430/9-73-015
METHODS and PRACTICES for
CONTROLLING WATER POLLUTION
from
AGRICULTURAL NONPOINT
SOURCES
U. S. ENVIRONMENTAL PROTECTION AGENCY
Office of Water Program Operations
Water Quality and Nonpoint Source Control Division
Washington, D. C. 20460
OCTOBER 1973
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PREFACE
This report provides information on methods and practices that will control
or reduce water pollution from nonpoint agricultural sources.
Nonpoint agricultural pollutants are organic and inorganic materials entering
surface and ground water from nonspecific or unidentified sources in sufficient
quantity to constitute a pollution problem. They include sediment, plant
nutrients, animal wastes, and pesticides from cropland, rangeland, pastures,
and farm woo diets.
Both economic and environmental considerations are important in controlling
nonpoint sources of water pollution. This report does not provide sufficient
detail for selecting practices for specific regions, watersheds, or individual
farms. Methods selected by farm operators will depend on local climate, soil,
topography, and livestock and cropping patterns. The report does not evaluate
the economics of alternative methods, nor does it discuss methods for control-
ling pollution associated with irrigation, soil salinity, feedlots, and
commercial forests.
General information, research results, and technical assistance for water
pollution control are available from the local, state and regional offices
of the Soil Conservation Service, Extension Service, and Forest Service of
the U.S. Department of Agriculture; Soil and Water Conservation Districts;
state agencies; and the Regional and Headquarters Offices of the U.S.
Environmental "Protection Agency. Technical research results are available
from agricultural experiment stations at land grant colleges and universities;
froE USDA's Agricultural Research Service; from the Environmental Protection
Agency; and from state agencies. Additionally, various programs of the
Agricultural Stabilization and Conservation Service, Soil Conservation
Service, and Farmers Home Administration provide economic incentives for
carrying out certain conservation and water pollution control practices.
Appreciation is expressed to the many individuals, both inside and outside the
Government, for their critical review and relevant suggestions for this report.
Special appreciation is given to the land grant colleges and universities,
Regional Offices of EPA, and to USDA agencies, namely: Agricultural Research
Service, Agricultural Stabilization and Conservation Service, Animal and Plant
Health Inspection Service, Cooperative State Research Service, Extension Service,
Forest Service, and Soil Conservation Service.
The photographs in this report were used through the courtesy of the Soil
Conservation Service.
ii
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CONTENTS
Page
FIGURES v
HIGHLIGHTS vi
CHAPTER I - INTRODUCTION 1
CONTROL METHODS 1
SCOPE OF THE REPORT 2
CHAPTER II - WATER EROSION 3
INTRODUCTION 3
FACTORS AFFECTING WATER EROSION 7
CONTROL METHODS 8
Tillage Alternatives 8
Terraces 10
Diversions 15
Stripcropping 15
Contouring 15
Grassed Waterways 18
Pipe Outlets 18
Crop Rotations 18
Cover Crops 20
Other Practices 20
Range and Pasture Management 20
Farm Woodlot Management 22
REFERENCES 24
CHAPTER III - WIND EROSION 25
INTRODUCTION 25
FACTORS AFFECTING WIND EROSION 26
PRINCIPLES AND METHODS OF CONTROL 27
Establish and Maintain Vegetative or Nonvegetative Cover 27
Roughen the Land Surface 30
Produce Soil Clods or Aggregates 30
Reduce Field Widths Along the Prevailing Wind Direction 32
Level or Benched Land 35
REFERENCES 36
CHAPTER IV - PLANT NUTRIENTS 38
INTRODUCTION 38
FACTORS AFFECTING PLANT NUTRIENT LOSSES 39
Precipitation and Soil Moisture 39
Type of Crop 39
Temperature 40
Soil 40
Mineralization and Nitrification. 40
Denitrif ication 41
iii
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CONTROL METHODS 41
Fertilization 41
Timing 41
P lacement 42
Slow-release fertilizers. 42
Soil Testing and Plant Analysis 42
Tillage 43
Crops and Crop Rotation 43
Contouring and Terracing 43
REFERENCES 44
CHAPTER V - PESTICIDES 45
INTRODUCTION 45
PATHWAYS AND CONTROL METHODS 46
Erosion 46
Runoff 47
Application Methods 47
Volatilization 48
Container Disposal 48
Livestock Pest Control 49
Farm Woodlots 49
ALTERNATIVES TO CHEMICAL PESTICIDE USE 49
Cultural Practices 49
Biological Control 50
Insect Sterilization 50
Insect Toxins and Pathogens 51
Insect Attractants 51
Resistant Crop Varieties 51
Crop Rotation 51
REFERENCES 52
CHAPTER VI - ANIMAL WASTES 53
INTRODUCTION 53
WASTES REMOVED FROM ANIMAL CONFINEMENT FACILITIES 53
Methods of Waste Application 54
Runoff Control from Waste-Treated Land 55
LAND DISPOSAL OF RUNOFF FROM CONFINEMENT AREAS 55
Methods to Dispose of Runoff 56
Practices to Minimize Surface Runoff 56
PASTURE PRODUCTION OF LIVESTOCK 57
Pasture Operations 57
Practices to Minimize Water Pollution 57
REFERENCES 59
SUPPLEMENTAL REFERENCES 62
GLOSSARY 70
iv
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FIGURES
Page
1.—Sheet erosion on a cultivated bean field with about a 2 per-
cent slope 4
2.—Rill erosion 5
3.--Gully erosion, 15.2 to 18.2 meters (50 to 60 feet) deep in
places 6
4.—Gully erosion showing bank slough 6
5.—Zero tillage equipment. Seed will be planted in the wheat
stubble 9
6.—Till-planter, planting in old corn residue. No plowing is done
prior to planting 11
7.—Chisel planter and 4-v?heel-drive tractor. Surface is left
rough to hold and absorb surface moisture 12
8.—Planting corn in a blue lupine field, using lister-planter 13
9.—Plow-planting 14
10.—Diversion terrace draining after heavy rain 16
11 .—Contour stripcropping 17
12.--Clear water flowing through grassed waterway 19
13.—Range pasture management. Lightly grazed pasture in upper
right; overgrazed rangeland in lower left 21
14.—Woodland management. Pastured woods at upper right; protected
woodland at lower left 23
15.—Stubble mulching to maintain vegetative cover as protection
from wind erosion 28
16.—Soil cloddiness reduces wind erosion 31
17.—Stripcrops planted at right angles to direction of prevailing
winds 33
18.—Spaced shelterbelts of willow trees protect the fields from
wind erosion 34
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HIGHLIGHTS
Potential nonpoint agricultural sources of surface and ground water pollution
include sediment, pesticides, fertilizer, and plant and animal wastes and
residue from cropland, grazing areas, and farm woodlots. Sound management
practices are the key to achieving acceptable water quality.
Water and wind erosion, use of plant nutrients and pesticides, livestock
management, cultivation practices, and leaching are important factors to
consider in controlling water pollution. Because of the wide variations
in topography, climate, types of soil, and patterns of crop and livestock
production, no one method or practice is universally applicable. A combina-
tion of practices must be designed and selected to meet the situation for
any particular farm or region.
Water Erosion
Erosion occurs as a natural geological process, but may be accelerated by man's
actions—including agricultural activities. Water erosion is the basic factor
in nonpoint pollution of the Nation's water. Sediment is the major nonpoint
pollutant.
Soils are protected naturally by vegetation and vegetative residue. If
moisture or fertility is too low, the land is subject to periodic erosion.
Tilling the soil, overgrazing, crop harvesting, and burning of vegetation
remove or bury portions of the protective organic material and may bring
about more erodible conditions. This is particularly serious in areas of
high rainfall.
Proper land use and agricultural management practices will keep soil, plant
nutrients, and organic matter on the land, rather than allow them to become
part of the water-borne pollutant load. Erosion may be reduced by means of
conservation tillage, terraces, diversions, stripcropping, contouring, grassed
waterways, and crop rotations, and by more efficient range, pasture, and wood-
lot management.
Wind Erosion
Wind erosion is a relatively minor problem from the standpoint of water
pollution, accounting for only a small fraction of the sediment loads in
waterways. Major factors affecting wind erosion are soil cloddiness, surface
roughness, soil moisture, vegetative cover, wind velocity, and field length
along the prevailing wind direction.
vi
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Successful wind erosion control involves a combination of the following
practices: (1) stubble mulch or conservation tillage practices to prepare land
for crop production; (2) cover crops; (3) appropriate crop rotations;
(4) controlled grazing; (5) wind barriers and shelterbelts; (6) artificial
barriers; (7) hauled-in mulches; (8) emergency tillage; (9) deep plowing
and (10) land forming and benching. These practices also conserve moisture
and control water erosion.
Plant Nutrients
Plant nutrients are an environmental concern from the standpoint of increasing
eutrophication of surface waters and the high concentrations of nitrates in
both surface and ground waters. Agricultural operations have been identified
as a potential contributor of nutrients to water resources. It is extremely
difficult to identify the extent to which natural and applied plant nutrients
may contribute to water pollution.
Factors influencing nutrient losses are precipitation and other sources of
water, temperature, kind of soil, kind of crop, nutrient mineralization, and
denitrification. Reducing nutrient losses from agricultural operations can
be accomplished by three general approaches: (1) determining the proper
amount, time, and method of plant nutrient applications to ensure efficient
use by plants, (2) adopting approved cultural practices, including tillage
and crop rotations, that minimize nutrient losses, and (3) reducing soil and
water runoff by conservation measures such as contours and terraces.
Pesticides
The potential movement of chemical pesticides into water is of environmental
concern. Most pesticides fall into three major categories: insecticides, herb-
icides, and fungicides. There are several approaches to reduce the quantity
of pesticides entering surface and ground water. These include: controlling
erosion and minimizing wind drift; reducing the quantity of pesticides used by
applying minimum amounts needed, and/or substituting nonchemical methods of
pest control; and using biodegradable rather than persistent pesticides, to
the extent possible.
Animal Wastes
Disposal of animal wastes on land is a potential nonpoint source of water
pollution. Animal wastes applied to land come from (1) wastes removed from
feeding facilities, (2) contained runoff from feeding areas, and (3) excretion
from animals on pasture and rangeland. Proper application of animal wastes
provides nutrients for crop production and also reduces surface runoff.
Appropriate animal and land management practices should be followed. These
include: (1) spreading acceptable rates of manure uniformly on land; (2) apply-
ing feedlot runoff effluent on land as recommended for specific site conditions;
(3) maintaining an adequate land-to-livestock ratio on pastures; and (4) locating
feeders and waterers a reasonable distance from streams and water courses.
vii
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CHAPTER I - INTRODUCTION
Agricultural activities are widely dispersed over the 0.93 billion hectares
(2.3 billion acres) of the Nation's land. Approximately 25 percent of the
land is used for grazing and nearly 20 percent for crop production. A major
concern is the movement of plant and soil materials from agricultural and
other land areas into streams, lakes, and the ground water.
Nonpoint agricultural pollutants are organic and inorganic materials entering
surface and ground water from nonspecific or unidentified sources in sufficient
quantity to constitute a pollution problem. They include sediment, plant
nutrients, pesticides, and animal wastes from cropland, rangeland, pastures,
and farm woodlots. Sediment is the major pollutant in terms of volume, and
may be a carrier of some pesticides and plant nutrients.
CONTROL METHODS
Pollution from nonpoint sources can be controlled by the use of appropriate
production methods and practices. For the most part, methods and practices
currently used are technically and economically feasible from a production
rather than an environmental standpoint. Considerable progress is being
made in adapting water and wind erosion control measures so they are compatible
with modern agricultural practices. Equipment, plant varieties, fertilizers,
pesticides, and production practices are being developed that will be consistent
with environmental needs and will maintain high soil productivity. Practices
that have been developed vary from area to area because of differences in soil
and climate throughout the country.
Land use patterns and practices largely determine the degree of pollution of
surface and ground water. Crop rotations are used to control erosion, improve
tilth, and provide plant nutrients to row crops in the rotation. Conservation
tillage aids in controlling erosion and runoff, but may require additional
use of chemicals for pest control, depending on the crop and geographic
location. Crop residues and cover crops increase the permeability of soils,
reduce the velocity of runoff, and provide vegetative cover. Contouring,
stripcropping, and terracing, practiced alone or in combination, are effective
in reducing erosion.
Chemical residue and plant nutrient losses can be reduced by keeping these
materials in place—on plants and in the'soil—where they are beneficial.
Control of runoff and leaching is a basic requirement in reducing losses of
pesticides, plant nutrients, and animal wastes. Proper timing, rates, and
methods of application will increase the efficiency of these materials.
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A farm management program for minimizing nonpoint pollution may require the
use of many measures and practices. For example, the sequence of crops
within a system can be varied; tillage methods and conservation practices can
be selected to control erosion and runoff; crop residue can be removed, left
on the surface, incorporated near the surface, or plowed under; and seedbeds
can be left rough to provide greater capacity for surface storage of runoff.
Combinations of these alternatives will have varying effects on runoff, soil
loss, productivity, and net farm returns. Control measures and practices must
be blended into an economic program that is suited to local conditions.
SCOPE OF THE REPORT
This report provides general information on the problems, factors affecting,
and methods for controlling water pollution from nonpoint agricultural sources.
Because of the wide variation in climate, topography, soils, crops, and economic
factors throughout the country, this report does not provide specific information
on which to select methods and practices suitable to local conditions.
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CHAPTER II - WATER EROSION
INTRODUCTION
Erosion and sedimentation are naturally and continually occurring geological
processes. Over long periods of time they have reshaped the earth. Soils
are protected naturally by vegetation and vegetative residue. In areas
where moisture is too limited or fertility too low to sustain close-growing
vegetation, the land is subject to periodic erosion from intense rains. In
areas of higher precipitation, some agricultural activities, particularly
row crop production, tend to increase the rate of erosion. Tilling the soil,
overgrazing, crop harvesting, and burning of vegetation remove or bury por-
tions of the protective organic material. Additionally, construction and
mining activities often remove all of the vegetation in localized areas.
Removal of this protective cover allows the forces of wind and water to
act more directly and forcefully on the exposed soil particles.
Sheet, rill, or gully erosion (Figures 1-4) occurs when increasing amounts
of water collect and move across the surface of the soil. Massive soil
movements, in the form of slides and slippages, can occur when steep soils
are tilled. These erosive actions carry away plant residues, soil and
associated plant nutrients, and pesticides.
Erosive actions may decrease the productive capacity of the land through:
the loss of valuable topsoil; changes in the soil structure, which reduce
aeration, infiltration, and drainage; exposure of unproductive soil materials;
or the intrusion of undesirable species of plants. Farm operations are
slowed and mechanical problems develop due to excessive roughness of the
fields* resulting from rill and gully erosion.
Downstream effects of erosion may include excessive quantities of sediment
that obstruct drainage, fill reservoirs, make streams turbid, and transport
plant and soil associated pollutants. Wise land use and management which
control erosion and runoff are the keys to reducing pollution from nonpoint
sources.
In 1967, approximately 97 percent of privately owned, non-Federal rural land
had soil limitations or conservation problems. Erosion was a limitation on 51
percent or 286 million hectares (706 million acres). On cropland only, erosion
was a dominant limitation on 55 percent or 89.5 million hectares (221 million
acres). (_3)I/
I/ Figures in parentheses refer to reference list at end of the various
chapters.
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Figure 3.—Gully erosion, 15.2 to 18.2 meters (50 to 60 feet) deep in places
Figure 4.—Gully erosion showing bank slough
6
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The following sections discuss factors affecting water erosion and measures
for controlling erosion on agricultural land.
FACTORS AFFECTING WATER EROSION
Water erosion, the major source of sediment, is a complex process. Climate,
topography, and kind of soil are important factors and generally are
uncontrollable. Land use, conservation tillage, and other conservation
measures are subject to management decisions and control.
The form, volume, intensity, and distribution of precipitation are important
determinants of erosion. Erosion of sloping land Increases as volume and
intensity of rainfall or runoff from snowmelt increase. Volume and intensity
of rainfall vary widely among areas of the Nation. Perhaps even more important
is the distribution of precipitation throughout the year. Rainfall of a given
volume and intensity, occurring during periods when ground cover is inadequate,
is more damaging than a similar rainfall when the ground is protected.
Length and gradient of slopes affect erosion. The erosion hazard increases
as slopes become longer and steeper. Slope shape determines whether soil
will move off the field or be deposited on the field at a point farther down
the slope. Complex topography makes installation of erosion control practices
difficult.
Soils vary in their susceptibility to erosion. Many factors are involved in
determining the erodibility of a particular soil. The most important of
these are particle-size distribution (texture), organic matter content,
soil structure, and soil permeability. If these four factors are known, the
erodibility of any given soil or subsoil can be predicted. (£)
The canopy protection of crops depends not only on the types of vegetation and
the quality of growth, but it also varies over the months and seasons. There-
fore, the overall erosion-reducing effectiveness of a crop depends directly
on how much protection the crop or management practices provide during those
portions of the year when most of the erosive rainstorms usually occur.
The interaction of the factors discussed above has been studied in many
locations for several decades, and scientists have devised ways of measuring
this interaction in order to predict erosion losses. The effects on soil
losses of various combinations of erosion control practices can also be
predicted. (8) Soil loss estimates can be used along with estimates of
sediment delivery ratios to determine the amount of sediment delivered to
streams. Research is continuing to refine and improve these techniques.
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CONTROL METHODS
There are many known control measures for reducing erosion resulting from
raindrop impact and surface runoff. These range from management of surface
cover and tillage to mechanical conservation measures or a combination of
measures. (4^ 6^ 7) This section discusses measures for controlling erosion.
Tillage Alternatives
Tillage systems are often used in combination with other erosion control
measures and in many cases may be the only control measures needed. Tillage,
in which the soil is inverted, generates the highest possible potential for
erosion by water and wind. This is the practice used in many areas.
A number of alternative systems have been developed over the years to reduce
the erosion potential of tillage. These systems have been identified under
several different names—minimum tillage, mulch tillage, stubble mulching,
and conservation tillage. Conservation tillage is the term used in this
report to describe tillage practices that reduce erosion potential below
that of conventional tillage. With some systems, a surface configuration
is achieved that will retain water and increase infiltration. With others,
residue from the previous crop is left on the soil surface to break raindrop
impact and reduce the flow velocity of the runoff. (2)
The conservation tillage system that best fits a farm operation depends on
the crops grown, soil characteristics, and climate of the area. Significant
progress has been made in developing successful conservation tillage systems
for a number of climatic areas and crop sequences. Research results and
farmer experience are available for the selection of the system that best
fits each situation. (90
The systems listed below have all been used and have been shown to be effective
in reducing water erosion. (1)
1. No-tillage or zero tillage (Figure 5)—This system uses a fluted
colter or double-disk openers to cut through residues of the
previous crop, ahead of the planter shoe. No seedbed preparations
precede this operation. This system leaves a maximum of residue
cover.
2. Ridge plant—This system gives a row configuration similar to
listing (see item 7), but planting is done on the ridges year
after year, with no seedbed preparation preceding planting. This
system has the most promise for controlling erosion in straight-
row farming. Rain falling on the ridge must run down the ridge
into the residue which has collected in the furrow. Most of the
sediment is deposited in the residue and is kept near the point
of detachment.
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3. Till-plant (Figure 6)—With this system, wide sweep and trash bars
clear a strip over the old row, and a narrow planter shoe opens
a seed furrow into which seed is dropped. A narrow wheel presses
the seed into firm soil; covering disks place loose soil over the
seed. This system controls erosion most satisfactorily when done
on the contour or across the slope.
4. Strip tillage—A narrow strip is tilled with rototiller gang or
other implement. Seed is planted in the same operation. This
system is applicable on soils where some tillage is desirable
in the row zone.
5. Sweep tillage*--This practice is used on small-grain stubble to
kill the early fall weeds. It shatters and lifts the soil, thus
enhancing infiltration while leaving the residue in place for
water and wind erosion control.
6. Chisel planter (Figure 7)—This system breaks or loosens the soil
without inversion. Most of the crop residue remains on the surface
for control of water and wind erosion.
7. Listing (Figure 8)—Plowing and planting are done in the same
operation. Flowed soil is pushed into ridges between rows, and
seeds are planted in the furrows between the ridges. When
operated on the contour, this system conserves soil and water.
8. Plow-plant (Figure 9)—Planting is done directly into plowed
ground with no secondary tillage. This system increases
infiltration, water storage in the plow layer, and surface
storage. Surface sealing is delayed because of the large
clods in the interrow zone.
9. Wheel-track plant—This system is similar to plow-plant, but is
not restricted to freshly plowed ground. Planting is done in
wheel tracks of the tractor or planter. Advantages are the same
as for plow-plant.
Terraces
Terracing is generally applied to fields where contouring, stripcropping, and
tillage operations do not offer adequate soil protection. Terraces break the
length of the slope into shorter segments. The volume and velocity of water
are effectively reduced when one or more terraces intercept the flow of
runoff.
Terraces usually consist of a ridge, or a combination of ridges and channels,
constructed across the slope. These ridges are placed high enough on the
slope to collect the expected volumes of surface runoff from above. Some
terraces on more permeable soils are designed to stop runoff and hold the
10
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water until it is absorbed. Others on less permeable soils are designed to
intercept and divert runoff in a controlled manner. Terrace design requires
detailed knowledge of probable rainfall totals and intensity, soil character-
istics, and cropping systems.
Terraces often require the adoption of new management practices to maintain
their desired effects. They should be planned to permit farming with large,
modern equipment. If terraces are improperly designed, or used with poor
cultural and management practices, they may increase rather than reduce soil
losses.
Diversions
Diversions (Figure 10) are large, individually designed terraces, constructed
across the slope to intercept and divert excess runoff to a stable outlet.
They are generally constructed above cropland fields, gully headcuts, or
other critical erosion areas. By reducing the volume of runoff water entering
the problem area, soil erosion is reduced.
Widely spaced diversions may be used to reduce the length of slopes in
conjunction with the planting of erosion-resistant crops or contour strip-
cropping. Diversions may also be useful in breaking up concentrations of
water on long, gentle slopes and on undulating or warped land surfaces
generally considered too flat or irregular for terracing.
Stripcropping
Stripcropping (Figure 11) is practiced as a means of reducing erosion on
tilled soils. The intent is to break the length of the slope into segments
by laying out strips across the natural slope of the land. Strips of close-
growing crops or meadow grasses are planted between tilled row crop strips
to serve as sediment filters or buffer strips in controlling erosion. The
practice effectively reduces the velocity of the water as it leaves the
tilled area. Additionally, water runoff is absorbed and soil particles are
retained in the buffer strip.
The system of cropping where the strips are laid out nearly perpendicular
to the direction of the slope is referred to as contour Stripcropping. The
buffer strips can vary in width across the field to make them compatible
with modern farm equipment use.
Contouring
Performing tillage operations on the contour, in a direction perpendicular
to the slope of the land, provides more protection from water erosion than
tilling parallel to the slope. The contour rows collect and hold water
during rainstorms and reduce runoff velocity, thereby increasing the time for
infiltration and reducing erosion. Contouring, practiced alone on gentle
slopes, or in combination with Stripcropping or terracing on moderate slopes,
can effectively reduce erosion.
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Grassed Waterways
Grassed waterways (Figure 12) are natural or constructed outlets, shaped to
required dimensions and established with erosion-resistant vegetation. They
are used for safe disposal of runoff from fields, diversions, terraces, and
other conservation measures. Grassed waterways are a basic conservation
practice commonly used by farmers. Stable outlets to transport concentrated
runoff are vital to the functioning of most conservation systems.
The most satisfactory location for a waterway is a well-vegetated natural
draw. Some shaping or enlarging may be required to handle the increased
flow. In this case, the design and construction should provide a stable
channel.
A pasture or meadow strip may be used in lieu of a constructed or natural
waterway. A design check should be made to ensure that the strip is wide
enough to carry the volume of flow, and that the type and density of
vegetation is adequate to withstand expected flow velocities.
Pipe Outlets
Many modern diversion and terrace systems utilize buried pipe rather than
grassed waterways for outlets. Terrace channels are graded to the outlet.
However, the terrace ridge is built level to provide sufficient detention
capacity to store the expected storm runoff.
Water enters the pipe through an outlet placed in the terrace channel. The
outlet is designed to remove the runoff gradually, but soon enough to prevent
crop damage from standing water. The combination of detention storage and
slow release provides greater opportunity for water to infiltrate into the
soil and for soil deposition.
Crop Rotations
In a crop rotation system,different crops are grown in a sequential pattern
on the same field. Combinations of soil conserving and depleting crops
provide opportunities for maintaining soil productivity and reducing soil
erosion.
Continuous row cropping can deplete the organic matter (the decaying plant
and animal residue) in some soils and thereby increase soil erodibility.
Sod-forming grasses and legume crops, used in rotation with row crops, are
highly effective in maintaining the soil structure and tilth and in reducing
soil and nutrient losses by erosion. In addition, the rotation of crops
often provides for the planting of both shallow- and deep-rooted plants;
this pattern improves the physical condition and the internal drainage of
both the surface soil and the subsoil.
18
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Cover Crops
Grasses and other close-growing crops provide more soil protection than row
crops such as corn and grain sorghum. Crops that leave large quantities of
residue after harvest offer more soil protection than crops with small
quantities of residue.
Cover crops are grown when there would otherwise be no growing plants and/or
residues to protect the soil from leaching and erosion. An example is winter
rye seeded immediately after a corn crop is harvested for silage. The
growing rye protects the soil during the fall, winter, and early spring when
the field would otherwise be bare and subject to erosion. Many cover crops
are left on the soil to serve as a protective mulch, or are plowed under for
soil improvement.
Cover crops may be special crops planted specifically to provide soil cover
and protection, or they may be crops typically found in the rotation but
planted at a different time, in some cases. An example is spring oats,
which are seeded in the fall, following a row crop. The growing oats freeze
in the winter and the tops protect the soil. In all cases, use of cover
crops provides better protection from the erosive effects of precipitation
than continuous intertilling of crops.
Other Practices
Trees, shrubs, grasses, and man-made structures may be needed to handle
severe erosion problems. Each alternative is adaptable to specific situations.
These alternatives are usually permanent and may require a conversion of crop-
land to grass or tr^es.
Structural measures include drop spillways, box inlet spillways, chute spillways,
pipe drop inlets, sod flumes, debris basins, and other grade-control structures.
These structures supplement sound conservation measures, reduce the grade in
water courses, reduce the velocity of flowing water, trap sediment, and reduce
peak water flows.
Range and Pasture Management
Lands used for grazing are characterized by a diversity of climate, topography,
soils, vegetative type, and vegetative condition. This diversity, coupled
with varying intensities of livestock use, creates the potential for varying
degrees of water erosion.
Prevention and control of erosion from grazing land is accomplished through
management practices that control the intensity of livestock use, and/or
increase the density and productivity of the vegetation (Figure 13). Over-
grazing results in soil structural changes because of soil compaction and
reduction of soil permeability. It also changes the density, vigor, and
species composition of vegetation and reduces the protective soil cover
afforded by vegetation. (4_)
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Grazing management practices that restrict livestock use to the carrying
capacity of range or pasture reduce water erosion and sedimentation. Some
of these practices are:
1. Rotation grazing permits intensive use of fields or portions of
fields on an alternating basis. The nonuse period encourages
vegetation recovery and renewed vigor prior to the return to
livestock use.
2. Water supply dispersal provides better distribution of livestock
use, reduces overuse or overgrazing in the vicinity of water
supplies, and reduces erosion hazard.
3. Seasonal grazing that is compatible with the most productive
period for the particular vegetation permits recovery and
resueding.
4. Range revegetation and pasture improvement increase the density,
vigor, and desirable composition of the vegetative cover, thereby
reducing runoff and erosion.
5. The dispersal and occasional relocation of salt, mineral, and
feed supplement sites avoids concentrated overuse of these
areas.
6. Ponds in pastures conserve water while providing water for
livestock.
Farm Woodlot Management
Compared with most other agricultural land uses, erosion and the associated
sediment from farm woodlots is relatively insignificant. Farm woodlots,
in general, produce less sediment per area unit than other agricultural land.
Grazing of farm woodlots increases susceptibility of the land to erosion
(Figure 14). However, this hazard will be minimized if livestock use is
managed to preserve ground cover. Animal access to tree seedlings should
be restricted. Browsing or trampling may destroy the seedlings and increase
erosion hazards.
Timber harvesting should be scheduled to coincide with low rainfall periods
to reduce erosion and the delivery of sediment and other inorganic materials
to streams. Selective tree cutting, the usual practice on farm woodlots,
generates low levels of sediment yield during harvest operations and for a
short period thereafter. Logging access roads and trails should be planned,
constructed, and stabilized so as to minimize the erosion runoff. (5)
22
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REFERENCES
1. Amemiya, M.
1970. Tillage Alternative for Iowa. Iowa State Univ. of Science
and Technology, Coop. Ext. Serv., Pm-488, Ames.
2. Soil Conservation Society of America
1973. Conservation Tillage. Ankeny, Iowa.
3. U.S. Department of Agriculture
1971. Basic Statistics—National Inventory of Soil and Water
Conservation Needs, 1967. Stat. Bui. No. 461, 211 pp.
4.
1972. The Nations Range Resources—A Forest-Range Environmental
Study. Forest Science Report No. 19.
5.
6.
7.
1973. Silvicultural Systems for the Major Forest Types of the
United States. Agr. Handbook No. 445.
n.d. Soil Conservation Service Engineering Field Manual for
Conservation Practices.
n.d. Soil Conservation Service National Handbook of Conservation
Practices.
8. Wischmeier, W. H. and D. D. Smith
1965. Predicting Rainfall-Erosion Losses from Cropland East of the
Rocky Mountains. U.S. Dept. of Agr., Agr. Res. Serv., Agr. Handbook
No. 282.
9. Wischmeier, W. H., C. B. Johnson, and B. V. Cross
1971. A Soil Erodibility Nomograph for Farmland and Construction
Sites. Jour. Soil and Water Conservation, Vol. 26, No. 5, pp. 189-193.
24
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CHAPTER III - WIND EROSION
INTRODUCTION
Wind erosion results in water pollution when materials eroded by wind are blown
into drainage ditches, streams, lakes, and reservoirs, or are dropped back to
the earth's surface where they become more susceptible to water erosion. It
increases susceptibility of land to water erosion, but as a factor in water
pollution, wind erosion generally is a minor problem compared to water erosion.
It may be more significant in localized geographic areas.
Less than 1 percent of the sediment entering the world's oceans is delivered
directly by the wind. (_5) There are no estimates of the proportion of wind-
blown materials going into inland waters, but it is believed to be small when
averaged over the Nation. Wind deposition of soil on land areas has been
measured in quantities ranging from more than 15.7 metric tons per hectare
(7 tons per acre) per year near sites of severe erosion to less than 112 kilo-
grams (100 pounds) in areas hundreds of miles from these sites. (8) Similar
amounts would be deposited in bodies of water. In addition to soil particles,
associated materials may include plant nutrients, animal wastes, residues from
trash burning, and pesticides. (10)
Wind erosion is a problem in any area of low, variable precipitation, where
drought is frequent, and temperatures, evaporation, and windspeeds are
high. (14) It is the dominant problem on about 28 million hectares (70 million
acres) or approximately 3 percent of the land in the United States—an area
that includes 22.3 million hectares (55 million acres) of cropland, 3.6 million
hectares (9 million acres) of rangeland, and 2.4 million hectares (6 million
acres) of "other" land. (9)
Wind erosion is most serious in the Great Plains, but it also occurs around the
Great Lakes in Michigan, Wisconsin, and Ohio, along the eastern seaboard, in
the southeastern coastal areas, in California, and in the Northwest, especially
in newly irrigated areas. (_14)
Good farming practices, such as crop rotation and controlled grazing, adequately
protect about 34 percent of this land, but specific wind erosion control is
needed on about 18.6 million hectares (46 million acres). Each year about
1.9 million of these hectares (4.8 million acres) undergo moderate to severe
damage from wind erosion. (9}
Successful systems of wind erosion control involve a combination of practices.
Most of the recommended practices are consistent with practices to conserve
moisture and control water erosion. The following sections discuss factors
affecting wind erosion and measures for controlling it.
25
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FACTORS AFFECTING WIND EROSION
Major factors affecting the amount of wind erosion from a given field are soil
cloddiness, surface roughness, windspeed and direction, soil moisture, field
length, and vegetative cover. (_1, 14) The cloddiness of a given soil largely
indicates whether it is susceptible to wind erosion. Soil clods prevent
erosion because they are large enough to resist the forces of the wind and they
shelter other erodible materials. Clods are formed during tillage. Their
firmness and stability depend on soil moisture, compaction, microbial activity,
and content of organic matter, clay, and lime. Clods are broken down by
weathering, tillage, implement and animal traffic, and abrasion. Coarse-
textured sandy loams and loamy sands are the least likely to form stable clods
and therefore are the most susceptible to erosion.
Ridges and depressions formed by tillage alter windspeed by absorbing and
deflecting part of the wind's energy. Rough surfaces also trap moving soil
particles. This reduces abrasion and the normal buildup of eroding materials
downwind. While the general effect of surface roughness reduces wind erosion,
it also increases wind turbulence and exposes smaller areas to greater
wind force. Therefore soil should not be too rough.
Wind erosion decreases as soil moisture increases. Air-dry soil erodes about
one and a third times more rapidly than soil with moisture at the approximate
wilting point for plants.
Windspeed and direction both affect wind erosion. The amount of soil lost from
a given field is determined by the width or length of field, the distance across
the field along the direction of the prevailing wind, and the windspeed. The
rate of erosion from a 48.4 kilometer-per-hour (30-mile-per-hour) wind is more
than three times that for a 32.3 kilometer-per-hour (20-m.p.h.) wind.
Living or dead vegetative matter protects the soil surface from wind action by
reducing windspeed and by preventing much of the direct wind force from reaching
erodible soil particles. It also reduces rates of erosion by trapping soil
particles; this, in turn, slows the movement of soil material downwind.
Interaction of the factors discussed above has been under study for several
decades in many wind erosion areas. An equation has been developed to express
the relationship between these factors and annual wind erosion losses from a
given field. (6^, 12) The equation is a useful management tool in (1) determining
potential wind erosion on any field under existing conditions, (2) determining
conditions of soil cloddiness, surface roughness, vegetative cover, and the
sheltering or width and orientation of the field necessary to reduce wind
erosion to a tolerable amount, and (3) predicting the effects of single or
combinations of wind erosion control practices.
26
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PRINCIPLES AND METHODS OF CONTROL
Five basic principles of wind erosion control are: (14)
1. Establish and maintain vegetative or nonvegetative cover
to protect the soil.
2. Produce, or bring to the soil surface, aggregates or
clods large enough to resist the wind forces.
3. Roughen the land surface to reduce wind velocity and
trap drifting soils.
4. Reduce field width along the prevailing wind direction
by establishing wind barriers or trap strips at intervals
to reduce wind velocity and soil avalanching.
5. Level or bench the land, where economically feasible,
to reduce effective field widths and erosion rates on
slopes and hilltops where wind forces are maximum.
These principles apply everywhere, but the usefulness of each varies with local
climate, soil, and land-use conditions. For example, it is usually difficult
to form stable clods on coarse-textured soils. For this reason, control of
wind erosion by producing and maintaining clods or by roughing the surface
is, at best, temporary. Maintaining vegetative cover is a far better way to
control erosion on these soils. Erosive situations may also arise where there
is no way of providing vegetative cover. In these situations, emergency
tillage should be used to roughen the land surface and produce clods.
The principles of wind erosion control can be applied by following a number of
practices—some permanent, some temporary. Methods and practices for applying
each of the principles are discussed below. (14)
Establish and Maintain Vegetative or Nonvegetative Cover
Establishing and maintaining cover is the cardinal rule of wind erosion
control. Cover can be maintained by:
a. Using stubble mulch or conservation tillage practices to
prepare land for crop production (Figure 15). The amount
of vegetative residues needed for control is related to
the five factors affecting wind erosion and can be calcu-
lated for a particular situation using the wind erosion
equation. (4, 6) Minimum quantities of standing wheat
stubble needed under Central Great Plains conditions are
840, 1,400, and 1,960 kilograms per hectare (750, 1,250,
and 1,750 pounds per acre) for silty clay loam, sand loam,
and loamy sand-textured soils, respectively. However, the
general goal is £0 maintain as much residue on the land
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surface in a standing or near-erect condition as is
compatible with seed planting procedures. Subsurface
sweeps, chisels, rotary tillers, and other types of
implements that do not invert the tillage layer leave
residues on the surface and are preferable over mold-
board plows or tandem or one-way disks. (19) Conser-
vation tillage methods, combined with herbicides to
control weeds, are also effective in providing
vegetative cover for wind erosion control. (11)
b. Planting cover crops when land is bare between regular
crops. A cover crop is any crop planted solely to
control erosion. Winter and spring wheat, rye, oats,
sorghums, winter peas, and vetch are excellent cover
crops. If soil moisture must be conserved, the crops
may be prevented from maturing by selecting a crop
that winter kills, e.g., oats; or the crop may be
killed by herbicides after growth is sufficient to
control soil blowing.
c. Using crop rotations in which two or more crops or
one crop and fallow are alternated on a given area
in a regular sequence. This prevents leaving large
blocks of land bare during the wind erosion season.
Common rotations in some wind erosion areas include
wheat-fallow, wheat-sorghum-fallow, and cotton-
sorghum.
d. Controlling grazing of both rangeland and winter
wheat to prevent complete denuding of vegetation
and pulverizing of the soil. Control on grazing
lands can be attained by (1) limiting livestock
numbers on any given area, (2) providing reserves
of harvested forage for use during drought periods,
(3) dividing pastures and using rotational grazing,
(4) supplying several watering and salt box sites
and moving them from time to time, (5) fencing
animals away from highly erosive spots, and (6) pro-
viding wind barriers to protect permanent watering
sites and lanes.
e. Regrassing and reforesting areas such as sand dunes,
blowouts, and other unproductive land to prevent the
spread of the erosion problem to more productive
land. Seeds and/or culms or stems of adapted grasses
can be planted, preferably with mulch, adhesive soil
stabilizers, or other protective material. Adapted
trees and shrubs can also be planted in some dune
areas.
29
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f. Applying hauled-in mulches or nonvegetative and processed
covers to areas of severe erosion or to areas with high
economic return potential. It is most economical to grow
cover in place; if this cannot be done, artifical cover
can be applied. Vegetative mulches and application rates
include cotton gin trash at 11.2 metric tons per hectare
(5 tons per acre), straw or hay at 2.2 to 4.5 metric tons
(1 to 2 tons), corncobs at 9 to 11.2 metric tons (4 to 5
tons), and manure at 33.7 to 67.4 metric tons (15 to 30
tons). Straw or hay mulches should be anchored with a
disk packer. Several spray-on adhesives of petroleum,
chemical, and organic origin are available for use as
temporary covers for wind erosion control. Amounts
needed vary from 533.3 decaliters per hectare (570 gal-
lons per acre) for fermented corn extract to 1,123
decaliters per hectare (1,200 gallons per acre) for
an^onic asphalt emulsion, with respective costs of
$24.72 and $130.91 per hectare ($10 and $53 per acre).
Roughen the Land Surface
The most effective roughness height for soil is 5.1 to 12.8 centimeters
(2 to 5 inches). Minimum and stubble-mulch tillage leave the soil in a rougher
condition than conventional tillage. Special planters, such as deep-furrow or
hoe drills, produce a roughness in the 5.1 to 12.8 centimeters (2 to 5 inches)
range and are especially effective in providing wind-resistant surfaces.
Emergency tillage, in which land is roughened with chisels or listers, is used
as a last resort when vegetative cover is not adequate to provide control.
Produce Soil Clods or Aggregates
Soil clods or aggregates larger than 0.84 mm. in diameter are not moved by
winds under 48.4kilometers per hour (30 m.p.h.). The degree of cloddiness
needed to control wind erosion depends on the levels of the other factors that
affect wind erosion. The size of clods required under various circumstances
can be calculated with the wind erosion equation. 04, 6) For example, a field
at Dodge City, Kansas, might require 1.25 mm. clods while a similar field at
La Crosse, Wisconsin, would require 0.92 mm. clods.
The degree of cloddiness produced by tillage depends on such factors as soil
texture, soil moisture, speed of operation, and kind of tillage tool. Generally,
the most cloddiness is achieved by using 5.1 centimeter (2-inch) chisels and
82 centimeter (32-inch) sweeps, followed in order by disks, rodweeders with
shovels, and large V-sweeps. (13) Soil aggregation and cloddiness are also
affected on a long-term basis by crop residue management (Figure 16). An
additional 1,120 kilograms per hectare (1,000 Ibs/acre) of residue per cropping
period, within the range of 0 to 6,720 kilograms per hectare (6,000 Ibs/acre)
will reduce the wind erodible soil fraction about 4 percent.
30
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Reduce Field Widths Along the Prevailing Wind Direction
Wind erosion is an avalanching process. The rate of soil flow is zero at the
windward edge of an eroding field and increases to a maximum that a given wind
can carry. Therefore, any measure that reduces field length along the pre-
vailing wind direction will reduce erosion.
Stripcropping, where strips of erosion resistant crops are alternated with
strips of erosion susceptible crops, wind barriers, and shelterbelts can be
used to reduce field widths along the prevailing wind direction. Erosion
resistant crops are small grains and other closely seeded crops that rapidly
produce a cover. Erosion susceptible crops include corn, cotton, tobacco,
sugarbeets, peas, beans, peanuts, asparagus, and most truck crops. In the
Great Plains, alternate strips of wheat and grain sorghum, or fallow wheat
stubble and newly seeded wheat, can be used. Permanent strips of tall
perennial grasses can be planted on fallowed wheat land to reduce erosion.
In vegetable growing areas, alternate strips of rye and vegetables are commonly
planted.
Stripcrops should be run at right angles to the prevailing winds (Figure 17).
The actual width of strips varies with factors affecting field erodibility,
e.g., soil texture, cloddiness, roughness, and wind velocity and direction.
The strips may range in width from a single row of grain sorghum or corn to
several meters. Information on widths needed for different soils can be
calculated with the wind erosion equation, or can be obtained from research
publications or from specialists in the Soil Conservation Service and
Extension Service.
In addition to their use in reducing field lengths, wind barriers and shelter-
belts reduce wind erosion by lowering windspeed in their lee, thereby decreasing
soil movement. (2) They also help retain moisture on the cropland by holding
snow that might otherwise be blown into gullies and roadside ditches. Trees
and shrubs in 1 to 10 rows, narrow rows of field crops, snow fences, solid
wooden or rock walls, and earthen banks—all are useful as wind barriers.
The effectiveness of any barrier depends on the wind velocity and direction,
and on the shape, width, height, and porosity of the barrier. (_7) The speed
of wind blowing at right angles to the average tree shelterbelt is reduced
70 to 80 percent near the belt, about 20 percent at a distance 20 times the
height of the belt, and only about 2 to 5 percent at a distance 30 times the
height of the belt. (JL4)
Barriers used for wind erosion control provide protection for distances ranging
from 1 to 18 times their height, depending on the type used. These relatively
short distances require close spacing of barriers, which reduces field size and
is objectionable where large equipment or mobile irrigation systems are used.
For this reason, tree shelterbelts are usually planted at 402 meter (80-rod)
intervals along field boundaries, at 105- to 135-meter (350- to 450-foot)
intervals on highly erosive soils, or at 150- to 195-meter (500- to 650-foot)
intervals on moderately erosive soils (Figure 18). Other wind erosion control
practices, such as stubble mulching, are then applied to the land as supple-
mental control.
32
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Tree shelterbelts planted in the 1930's were generally wide—consisting of
10 to 12 rows. Experience and research indicate, however, that narrower belts
of medium porosity are equally effective and take less land out of production.
The ideal is a 1-row belt; however, in the more arid areas, 3 rows should be
planted to insure protection in the event that some trees die.
Nearly any plant that reaches substantial height and retains its lower leaves
can be used as an annual crop or grass barrier. These include pampas, tall
wheat, plains bristlegrass, hybrid forage sorghum, kenaf, corn, and sunflower.
Spacing between annual crop or grass barrier ranges from 3 to 18 meters (10 to
60 feet), depending on soil texture, control required, and other factors.
Artificial barriers (snow fencing, boardwalls, and earthen banks) provide
temporary protection for highly credible areas such as livestock watering sites
and traffic lanes. They can also be used to protect high-value crops, and can
help stabilize sand dunes. They provide a relatively short zone of protection;
a 1.2 meter (4-foot) snow fence protects for a distance of about 12 meters
(40 feet), and a 0.6 meter (2-foot) earthen bank protects for about 9 meters
(30 feet). These artificial barriers are costly to construct.
Level or Benched Land
Land is sometimes leveled or benched for purposes of irrigation, water erosion
control, and moisture conservation. These land modifications affect the rate
and amount of wind erosion.
Research information on the relationship between land modification and wind
erosion is meager. Estimates for average Great Plains conditions indicate
that shortening field lengths from 300 meters to 30 meters (1,000 to 100 feet)
by benching, reduces potential soil loss by wind 50 percent. Another
calculation concerning a 360 meter (1,200-foot-long) , 4 percent slope, benched
with a series of 72-meter-wide (240-foot-wide) level benches, shows that soil
loss from wind erosion was reduced 60 percent.
It is unlikely that land will be extensively modified to control wind erosion,
but it will doubtless be increasingly modified for irrigation and to control
water erosion. These land modifications will also provide substantial wind
erosion control.
35
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REFERENCES
1. Beasley, R. P.
1972. Erosion and Sediment Pollution Control. Iowa State Univ.
Press, Ames, 320 pp.
2. Ferber, A. E.
1958. Windbreaks in Conservation Farming. U.S. Dept. Agr., Misc.
Pub. 759, 22 pp.
3. Hagen, L. J. and N. P. Woodruff
1973. Particulate Loads Caused by Wind Erosion in the Great Plains.
Proc., 66th Annual Meeting, Air Pollution Control Assoc., Paper No.
73-102, Chicago, 111., 24 pp.
4. Hayes, William A.
1972. Designing Wind Erosion Control Systems in the Midwest. U.S.
Dept. Agr., Soil Cons. Serv., TRSC-Tech. Note, Agromony LI-1, Lincoln,
Neb., 41 pp.
5. Judson, Sheldon
1968. Erosion of Land. American Scientist 56 (4), pp. 356-374.
6. Skidmore, E. L. and N. P. Woodruff
1968. Wind Erosion Forces in the United States and Their Use in
Predicting Soil Loss. U.S. Dept. Agr., Agr. Handbook No. 346, 42 pp.
7. Skidmore, E. L.
1969. Modifying the Microclimate with Wind Barriers. Proc., Seminar
on Modifying the Soil and Water Environment for Approaching the
Agricultural Potential of the Great Plains, GPAC Pub. 34, Vol. 1,
pp. 107-120.
8. Smith, R. M. and Page C. Thuss
1965. Extensive Gaging of Dust Departion Rates.
Kansas Academy of Science, Vol. 62, No. 2, pp. 311-321.
9. U.S. Department of Agriculture
1965. Soil and Water Conservation Needs—A National Inventory.
Prepared by the Conservation Needs Inventory Committee, Misc. Pub.
No. 971, 94 pp.
10. Wadleigh, Cecil H.
1968. Wastes in Relation to Agriculture and Forestry. U.S. Dept.
Agr., Misc. Pub. No. 1065, 112 pp.
36
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11. Woodruff, N.P. and F. H. Siddoway
1973. Wind Erosion Control. Proceedings, National Conservation
Tillage Conf., pp. 156-162, Des Moines, Iowa.
12.
1965. A Wind Erosion Equation. Soil Sci. Soc. Amer., Proc., 29(5),
pp. 602-608.
13. Woodruff, N. P., C. R. Fenster, W. W. Harris, and M. Lundquist
1966. Stubble-Mulch Tillage and Planting in Crop Residue in the
Great Plains. Amer. Soc. Agr. Engin. 9 (6), pp. 849-853.
14. Woodruff, N. P., L. Lyles, F. H. Siddoway, and D. W. Fryrear
1972. How to Control Wind Erosion. U.S. Dept. Agr., Agr. Info.
Bui. No. 354, 22 pp.
37
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CHAPTER IV - PLANT NUTRIENTS
INTRODUCTION
Agriculture is concerned with producing an adequate supply of food and fiber
for domestic and export needs, with a minimum of water pollution. Nitrogen
and phosphorus needed to meet production goals may, under certain conditions,
adversely affect water quality through high accumulations of nitrate in surface
and ground water and eutrophication, which can lead to excessive algae growth.
The extent of the water quality problem associated with losses of nitrogen
and phosphorus varies from region to region. The need for and/or success of
particular methods for controlling or reducing nutrient concentrations also
vary. For example, almost all runoff from precipitation contains sufficient
nitrogen (1-2 mg/1) to permit algal blooms unless the precipitation runs off
grass or forest land. Control of phosphorus in runoff sediment and seepage
is much more important on land near tributaries to lakes and ponds than on
lands draining into fast-flowing rivers that run directly to the sea. Similarly,
in areas with high rainfall and well-drained soils, the potential for nitrate
accumulation in groundwater increases.
Most soils used for crop production need fertilizers to maximize yields and
profits. Before World War II, fertilizers consisted mainly of animal byproducts,
plant wastes, and some superphosphates. In 1972, 37.2 million metric tons
(41 million tons) of commercial fertilizers were applied to crops in the
United States, compared with 12 million metric tons (13.2 million tons) in 1945.
Future trends in fertilizer use can be influenced by a number of factors, in-
cluding changes in domestic and foreign demand for agricultural products,
relative cost of fertilizer to other inputs, and environmental considerations.
The sources of nitrogen and phosphorus, both natural and from fertilizers, are
numerous and interdependent. It is difficult and often impossible to estimate
the contribution of each source to surface water. Major sources of nitrogen
and phosphorus are precipitation, sediment, municipal and industrial effluents,
urban storm water drainage, and natural organic and inorganic materials.
This chapter discusses factors affecting plant nutrient losses and alternative
methods and practices for keeping the nutrients on the land where they can be
effectively utilized.
38
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FACTORS AFFECTING PLANT NUTRIENT LOSSES
The composition of phosphorus and nitrogen substances in the soil/water system
and the way they are lost from soils differ greatly, as do control practices.
Most of the phosphorus in soil, whether it comes from organic or inorganic
sources, is contained within, or is tightly attached to, soil particles.
Soluble phosphate content of surface runoff is usually very low, but concen-
trations may be significant in runoff from dead vegetation. Most cf the
phosphorus lost from land is associated with sediment. Thus, control of
phosphate pollution depends largely on control of soil erosion.
Organic or humus nitrogen lost from soils into water is associated witU
sediment, and erosion control is, again, an important control mechanism.
However, most nitrogen lost from the soil is in the form of nitrate, which is
not absorbed into the soil particles. It is completely soluble in water and
moves where water moves. Control of nitrate movement to surface water or to
aquifers depends on the control of runoff and leaching.
Precipitation and Soil Moisture
The amount and rate of precipitation and/or irrigation water applied to the
soil are important factors in determining the amount of runoff and nutrient
losses. Infiltration rates are influenced by the properties of the soil.
These rates can be changed to some degree by management. If rainfall or water
application exceeds the rate of infiltration, runoff will result.
Nitrogen in the water percolating below the root zone may contribute to nitrogen
concentrations in aquifers, whether the water is from rainfall or irrigation.
The nutrient content of rainfall and irrigation water varies with local
atmospheric conditions and the source of the water.
Irrigation can be controlled to reduce the leaching of nutrients. Prevention
of leaching from excessive precipitation must be controlled by surface drainage
and other management practices.
Type of Crop
The type of crop or land use has a major effect on nutrient losses through
erosion and leaching. Erosion of soil and loss of phosphorus and organic
nitrogen associated with sediment are much lower for sod crops such as pasture
and range grasses, than for row crops such as corn and soybeans. Erosion
control through land use practices is a well-established soil conservation
principle.
The kind and amount of vegetative growth, as well as the length of the growing
season, influence the amount of water available for leaching of nitrate. When
more water enters the soil than is lost by evapotranspiration of the crop, the
excess water can leach nitrate. Hence, nitrate loss is greater in the fall or
spring, when water demands of crops are low.
39
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Temperature
Temperature affects the mineralization or ammonification of nitrogen, which
influences the nutrient content of runoff and leached waters. During cold
periods, plant activity is retarded, thereby reducing the rate of nutrient
utilization and water consumption. Variability in temperature is also impor-
tant. If frozen land is thawed at the surface by rainfall, leaving a frozen
sublayer that prevents percolation of water, surface runoff and erosion occur.
Free zing of plant material tends to rupture plant cells, and nutrients are then
subject to leaching during spring thaw.
Si/tl
The nutrient content, permeability, and structure of agricultural soils are
important factors that may have a bearing on the nitrate in ground and surface
water. The nutrient accumulation in the soil and substrata is a function of
basic soil properties, geologic deposits, decomposition of organic matter and
peat, presence of nitrogen-fixing plants, soil organisms, animal and human
wastes, and inorganic sources such as fertilizer and precipitation. (7)
The energy associated with the impact of falling raindrops affects the amount
of sediment in runoff and the rate of water infiltration. Adequate ground
cover will absorb the raindrop impact and protect the surface cover. Forests
and grasslands generally have higher rates of water infiltration than plantings
of agricultural row crops when soil and slope conditions are otherwise equal.
Permeability and water retention characteristics of soil affect the amount of
water passing through the root zone. If nitrate is present, it will move with
the water and may eventually enter the groundwater. The concentration of
nitrate in the groundwater depends on the amount of nitrate leached, the volume
of water passing through the soil profile, and the transit time of the leachate
from root zone to water table. Transit time is related to the hydraulic
conductivity of the soil profile, depth of the water table, and degree of soil
saturation. In some areas it may take 20-30 years for the leachate to pass
from the root zone to the water table. 05) A sandy soil will not retain as
much water in the root zone as a loam soil, and so has a higher leaching hazard.
Therefore, less nitrogen is utilized by plants and more nitrogen is leached
below the root zone in sandy than in less permeable soils.
Geologic materials underlying soils may restrict the downward movement of water.
Under such circumstances, nitrogen will not contaminate deep aquifers, but may
accumulate in perched water tables.
Mineralization and Nitrification
Mineralization (or ammonification) is the breakdown of organic nitrogen to
ammonium. Nitrification is the oxidation of this ammonium, or ammonium from
fertilizers, to nitrate. Factors affecting this process are soil charac-
teristics, water content, aeration, and temperature. The rate of nitrification
tends to decrease sharply when the oxygen content of soil falls below 2 percent
or when soil air space is nearly saturated with water. The maximum rate of
nitrification occurs in soil temperatures of about 30° C. and is very slow
40
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at 70 c. Nitrate can be used by plants, denitrified, leached to groundwater,
or remain in the soil and be available for subsequent crops.
Denitrification
Denitrification is the microbial reduction of nitrate to harmless nitrogen
gas. It is an important factor in determining the amount of nitrate available
for leaching to groundwater. Denitrification generally takes place in soils
when anaerobic conditions prevail and an energy source such as decaying organic
mattec is present. Organic nitrogen and ammonium forms must be oxidized to
nitrate before denitrification takes place.
Under favorable conditions, a substantial amount of denitrification occurs in
or near submerged tile drains. This decreases the amount of nitrates present
in the tile drain effluent. Denitrification also removes nitrate from the
root zones of crops, such as rice, that are submerged in water for extended
periods of time.
CONTROL METHODS
Reducing nutrient losses from agricultural nonpoint sources can be accomplished
by three general approaches: (1) determining and applying appropriate amounts
of plant nutrients at the proper time and in the proper place, (2) adopting
improved cultural practices, including conservation tillage and crop rotations,
that minimize nutrient losses, and (3) controlling soil and water losses by
conservation practices such as contouring and terracing. Control measures
should be selected in light of their economic and technical feasibility, as
well as their effect in reducing nutrient losses.
Fertilization
The timing and placement of fertilizer affect the efficiency of plant utilization
of nutrients. Slow-release fertilizers have been developed to improve the
efficiency by providing nutrients as plants require them.
Timing—The timing of application is much more important for nitrogen fertilizers
that are easily leached than for phosphorus, which is adsorbed by soil parti-
cles. The leaching of nitrates below the root zone may be more prevalent on
sandy soils during periods of precipitation. During cooler periods of low
evapotranspiration, unused nitrates move downward within the soil profile.
.These factors should be considered in timing fertilizer applications to
maximize the efficiency of utilization by crops, and to minimize nutrient
losses by erosion and leaching.
In general, phosphate and potash fertilizer must be applied at seeding time or
earlier for satisfactory results. Nitrogen may be applied in the fall, or in
the spring for fall-sown green crops. For row crops, a portion of the nitrogen
may be applied at planting time. Additional amounts may be side-dressed.
The best time should be determined on the basis of soil, climatic conditions,
41
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and the crop being grown. In areas of high winter precipitation, where leaching
or denitrification losses may occur, spring application usually is best.
Nitrogen fertilizer should never be broadcast on frozen land.
Placement — The method of application and placement of fertilizers in relation
to root distribution and moisture is important in increasing the effectiveness
of fertilizers. General methods for applying fertilizer include: broadcasting
and disking, plowing before planting, and top dressing after the crop has been
established. The placement of phosphate fertilizer with respect to the plant
root system is critical because of its limited movement. If the phosphorus is
not utilized by the plant, it is subject to erosion with soil particles.
On soils of low or moderate fixing capacities, broadcasting the fertilizer
on the surface and plowing it under is one of the most economical methods of
application, but nutrients may be lost if the fertilizer is not plowed under.
Fertilizers should be incorporated in the soil by such methods as disking
and drilling.
Placement of fertilizer in bands under the surface is art efficient use of
nutrients and minimizes losses by surface erosion. Top dressing of phosphate
fertilizer is often the only method of fertilizing established pasture and
some forage crops.
Slow-release fertilizers — Slow-release fertilizers may be used to minimize
possible nitrogen losses on soils subject to leaching. Chemical inhibitors
that can be incorporated with nitrogen fertilizer have been developed to delay
nitrification. The technical feasibility of this approach has been demonstrated.
(2) Presently, the general use of these inhibitors in agriculture is restricted
by the high cost.
As mentioned in a previous section, nitrification is very slow at lower soil
temperatures. Hence, anhydrous ammonia can have slow-release properties if
the soil temperature is low.
A "slow-release" nitrogen fertilizer is also a "long- release" fertilizer;
therefore, this may not be the total answer to controlling nutrient pollution.
If nutrients are not adequately used by a crop during the growing season, high
levels of nitrate may remain in the soil during noncrop months and nutrient
pollution may result. These materials are most effective on pastures, or with
plants having a long growing season.
Soil Testing and Plant Analysis
Soil testing is a laboratory method of estimating the amounts of various plant
nutrients that may become available to a crop. When properly correlated with
field fertilizer trials, the tests help determine how much fertilizer is needed
to produce a specified yield. To determine application rates, it is important
to know whether nitrogen, phosphorus, and potassium are in correct proportions
in the soil. Application rates should not be based on crop requirements alone.
For example, in many soils the level of available phosphorus, as measured by
soil tests, has gradually risen. In such a situation, fertilizer application
based on crop requirement without any knowledge of soil fertility could lead
to over fertilization and possibly excessive nutrient loss.
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Plant analysis measures the total nutrient uptake and determines nutrient
status. It has been used extensively for many tree crops. The presence of
sufficient nutrients in the soil at the start of the growing season does not
mean the plant will be able to use them, or that adequate nutrients will be
available throughout the season. (1_) Consequently, plant analysis provides
information that can be used to adjust fertilizer application rates and
timing, or to adjust other cultural practices.
Plant nutrient composition is closely related to soil fertility, climatic
factors, and methods of management. Hence, soil and plant analyses are
useful in developing fertilizer recommendations. (6) If fertilizer is
applied at rates determined by these methods, crops will have adequate
nutrients at the least cost, and nutrient losses via leaching and runoff
will be minimized.
Tillage
Some type of tillage is necessary in the production of most crops. It is
important to select a tillage method that will provide for high productivity,
and will also reduce soil and nutrient losses. Inadequate tillage results in
large soil aggregates and pore spaces that prevent adequate seed-to-soil
contact. Excessive tillage compacts the soil. The soil tends to seal or
crust, promoting water runoff and erosion. See Chapter II for a discussion
of conservation tillage.
Crops and Crop Rotation
The selection of appropriate crops and crop rotation systems that help control
erosion and prevent leaching is important in reducing nutrient loss. Rotation
is more important in soil systems maintained at high fertility levels. Rotation
of corn and soybeans with cover crops has been long recognized as a good
erosion control method. Similarly, winter cover crops are useful in reducing
soil and water loss.
Grasslands generally have the lowest nitrate loss because of the plant's
extensive root systems, which can absorb nitrate over a long growing season.
Legumes may fix nitrogen in their root nodules which adds nitrogen to the
soil in organic form that is not readily susceptible to leaching. Alfalfa
can effectively remove nitrate that has accumulated below the root zone of
more shallow-rooted crops such as wheat or corn.
Contouring and Terracing
Contour planting and tillage can control runoff by retaining water until it
can be absorbed by the soil. The crop rows are oriented on the contour to
pond the runoff and allow more time for penetration of water into the soil,
and to reduce the velocity of water flow and thereby reduce soil erosion.
Ridges and terraces, established across the slope of the land, reduce the
slope length and retain the water for removal from the land via surface or
subsurface outlets. Terracing used with contour cultivation provides maximum
protection against soil erosion. See Chapter II for a discussion of
conservation practices.
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REFERENCES
1. Fitts, J. W. and J. J. Hanway
1971. Prescribing Soil and Crop Nutrient Needs. In: Fertilizer
Technology and Use, pp. 57-59, Soil Science Society of America Inc.,
Madison, Wis.
2. Hauck, R. D. and M. Kashino
1971. Slow-Release and Amended Fertilizers. In: Fertilizer Technology
and Use, pp. 455-494, Soil Science Society of America, Inc., Madison,
Wis.
3. Patrick, W. H., Jr. and D. S. Mikkelsen
1971. Plant Nutrient Behavior in Flooded Soil. In: Fertilizer
Technology and Use, pp. 187-215, Soil Science Society of America, Inc.,
Madison, Wis.
4. Pesek, John, 6. Stanford, and N. L. Case
1971. Nitrogen Production and Use. In: Fertilizer Technology and
Use, pp. 217-269, Soil Science Society of America, Inc., Madison, Wis.
5. Pratt, P. F.
1972. Nitrate in the Unsaturated Zone under Agricultural Land.
Environmental Protection Agency Project No. 16060 DOE, U. S. Gov. Printing
Off., Washington, B.C.
6. Sarkadi, J.
1962. The Effects of Edaphic Factors on Nutrient Uptake. Agrochemical,
Vol. 6, pp. 275-285.
7. Viets, F. G. and R. H. Hagerman
1971. Factors Affecting the Accumulation of Nitrate in Soil, Water
and Plants. U.S. Dept. Agr., Agr. Res. Serv., Agr. Handbook No. 413.
44
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CHAPTER V - PESTICIDES
INTRODUCTION
In 1971, production and sales of synthetic organic pesticides amounted to
0.5 billion kilograms (1.1 billion pounds). The use of pesticides has
increased production and improved the quality of foods and fibers. However,
there are environmental problems associated with chemical control of crop
and livestock pests.
Most pesticides fall into three major categories: insecticides, herbicides,
and fungicides. Discussion here refers primarily to the use of pesticides
on crops. Some pesticides are also used on livestock and farm woodlots.
The following table indicates the extent and use of pesticides on selected
crops in 1966:
Pesticide Use for Selected Crops in the United States, 1966
Crops
Cotton
Tobacco
Corn
Peanuts
Rice
Wheat
Soybeans
Pasture, hay,
and range
Potatoes
Apples
Citrus
Proportion
Insecticides : I
54
81
33
70
10
2
4
0.5
89
92
97
of Crop Acres
terbicides :
Percent
52
2
57
63
52
28
37
1
59
16
29
Treated
Fungicides
2
7
2
35
0
0.5
0.5
0
24
72
73
Source: Pimentel, D. Compilation of U.S. Department of
Agriculture data.
Quoted in: (2)
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This chapter discusses methods that can be used to reduce the quantity of
pesticides moving into the aquatic environment. There are several approaches:
(1) reduce the movement of pesticides into water by controlling erosion and
minimizing wind drift, (2) reduce the quantity of pesticides used by applying
minimum amounts needed to control the pests or by substituting non-chemical
methods of pest control, and (3) substitute biodegradable for persistent
pesticides to the extent possible.
PATHWAYS AND CONTROL METHODS
Agricultural pesticides enter the Nation's waterways by several means:
(1) erosion, (2) runoff water, (3) escape of pesticides during application,
(4) volatilization and redeposition of pesticides, and (5) accidents and
incorrect container disposal. An obvious but fundamental means of reducing
potential water pollution from pesticides is correct usage. It is essential
that users follow recommended application techniques and not exceed
prescribed dosages for specific pest problems. Methods of controlling
pollution from various sources are discussed below.
Erosion
The major route of pesticides to the waterways is via erosion.
Because of the tight binding characteristics
of pesticide residues to soil particles, it
is suggested that the general pollution of
waters by pesticides occurs through the
transport of soil particles to which the
residues are attached. (4, p. 118)
Suspended plant particles or leachates from crop residue also carry pesticides
to waterways. Since most pesticides adhere readily to soil, any cropping
pattern or practice that is likely to cause erosion is also likely to foster
entry of pesticide materials into lakes and streams. Limiting the use of
pesticides on erosion-prone soil will reduce the pollution potential. Water
and wind erosion control measures are discussed in Chapters II and III.
Nonpersistent pesticides pose only short-term problems from erosion or runoff.
Persistent pesticides are a more serious threat to waterways from water and
wind erosion. However, the threat of polluting waterways is reduced by
practices that minimize soil erosion.
Pesticide persistence depends primarily on the structure and properties of the
compound and, to a lesser degree, on location in or on the soil and soil
particles. There is wide variation in persistence among different pesticides.
For example, the highly toxic phosphate insecticides are relatively nonpersistent
in soils. In contrast, some of the chlorinated hydrocarbon insecticides may
46
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persist 4 to 5 years under normal rates of application. The longer a pesticide
remains in the soil, the more likely it is to move from target sites to non-
target areas by water or wind erosion.
Runoff
Pesticides also enter waterways through surface runoff and groundwater supplies.
As a group, pesticides have low solubility in water, but small amounts are
transported in solution. Herbicides are generally more water soluble than
insecticides, and a few are freely soluble. Frequently, a choice can be made
between two chemicals of varying degrees of solubility. It is easier to prevent
runoff of pesticides in arid regions, where crops are irrigated and application
of water can be controlled.
Application Methods
The amount of pesticides entering lakes and streams is influenced by the method
of application and the solubility and volatility of pesticides. Pesticides
incorporated into the soil, rather than left on the surface of soil or plants,
are less subject to movement by runoff waters and to evaporation.
Pesticides are applied in liquid form as a spray or in solid form as a dust or
granule. Present methods of application are imperfect in that some of the
pesticide reaches nontarget organisms. The major reasons are lateral displace-
ment (i.e., wind drift) and volatilization of the water carrier and the
pesticide. In each case, the pesticide material may enter open bodies of water
directly, or after fallout and washout from nontarget areas.
Dusted and sprayed pesticides are subject to considerable drift. Drift is
related to particle size, wind speed, climatological inversion, and height of
pesticide emission. In certain circumstances, such as application on dense
foliage, where the underside of the leaves must be treated, a certain amount
of drift is needed to provide complete coverage. However, such drift may result
in the movement of pesticides into neighboring fields and open bodies of water.
Drifting can be reduced by spraying and dusting when wind and other weather
conditions are suitable.
Research shows the potential of engineering techniques that will produce
particles of more uniform sizes and thus reduce the number of small particles
that are apt to drift. Various emulsifiers and oils can be added to the spray
to increase droplet size and thereby reduce drift. The table on the following
page shows the relationship between drift and particle size.
Of the various forms of pesticides used, granules drift the least. Their
value in certain above-ground uses is limited, however, because they do not
provide as complete physical coverage as a spray or dust.
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Drift Pattern in Relation to Particle Size
Particle Type
Aircraft spray:
Coarse
Medium
Fine
Air carrier sprays
Fine sprays and dusts
Usual dusts and aerosols
Aerosols
Drop Diameter
Microns
400
150
100
50
20
10
2
•
: Drift!/
•
•
Meters Feet
2.6 8.5
6.7 22
15 48
54 178
338 1,109
1,352 4,436
33,795 110,880
JL/ Distance a particle would be carried by a 4.8 km/h (3 mph) wind while
falling 3 meters (10 feet).
Source: (1)
Volatilization
For certain pesticides, volatilization can be a significant means of introducing
pollutants into the environment. This applies to volatilization after appli-
cation, as well as to evaporation between nozzle and ground during application.
Small spray droplets result in high rates of evaporation of the water carrier.
This leaves small particles of dry pesticides to drift into nontarget areas.
Amine stearates and other additives can be used to decrease the evaporation
and drift potential, thus reducing pollution from pesticides.
Container Disposal
Pesticides can enter the environment through careless or improper disposal of
containers and unused materials. If these items are deposited or buried near
waterways, the groundwater may become polluted. If they are burned, pollution
may result through washout or fallout. Section 19 of the Federal Insecticide,
Fungicide, and Rodenticide Act as amended in 1972 (Public Law 92-516)
directs the Administrator of the Environmental Protection Agency to issue
procedures and regulations governing the disposal of pesticide containers.
Implementing regulations were published on May 23, 1973 (40 CRF, Part 165).
Further dissemination of these regulations, and continuing education on the
problems of incorrect disposal and on the dangers of accidental poisoning,
can be expected to reduce pollution from these sources.
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Livestock Pest Control
Insecticides used to control livestock pests are applied by various means, such
as feed additives, backrubbers, sprays, pour-ons, liquid dips, or barn fumi-
gations. Pesticide exposure to the environment is minimal with correct use.
Barring dumping or accidental spillage, the potential for environmental pollution
from this source is minimal.
Farm Woodlots
Pesticides are not used extensively on farm woodlots. Because of the relatively
small size of tracts, aerial application is seldom used. Herbicides are perhaps
the most frequently used pesticide on farm woodlots. They are selectively applied,
frequently on stumps or at the base of trees. In the case of many pests, losses
can be reduced through good farm woodlot management.
Control techniques are specific to each disease. Some examples are the timely
removal of infected trees, pruning of infected parts, and elimination of alter-
nate plant hosts in the case of rusts. Careful logging practices minimize
mechanical injuries to trees. Injuries may serve as entry points for fungi.
ALTERNATIVES TO CHEMICAL PESTICIDE USE
Non-chemical methods of pest control can reduce the use of pesticides and thus
their entry into the environment. However, for the foreseeable future, there
will be a continuing need for pesticides in combination with these methods.
Non-chemical methods of pest control,
biological or cultural, will be used and
recommended whenever such methods are
economically feasible and effective for
the control or elimination of pests.
When non-chemical control methods are not
tenable, integrated control systems
utilizing both chemical and non-chemical
techniques will be used and recommended
in the interest of maximum effectiveness
and safety. (3, p. 1)
Cultural Practices
A number of cultural practices can partly substitute for pesticides to prevent
or reduce crop damage from insects, nematodes, weeds, and diseases. These
practices include changes in methods of cultivating and harvesting crops that
make the environment less hospitable to pests. Cultural practices are most
successful if applied at a vulnerable stage in the pest's life cycle. Examples
are the removal of crop debris to eliminate host sites, and adjustments in
planting schedules to minimize pest influence on the crop. Tobacco stalks re-
maining after harvest support large numbers of tobacco hornworms, budworms,
diseases, and several nematodes. Destruction or removal of the stalks
immediately after harvest aids in controlling these pests.
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Mechanical weed control is a generally accepted farm management practice. Such
measures as row cultivation, proper seedbed preparation, and mowing of weeds on
uncropped land reduce the production of weed seeds. Herbicides can then be
applied at lower levels than under conservation tillage methods. Conservation
tillage may increase certain disease and insect problems which could require
increased use of pesticides. A higher level of pesticide use under these
conditions may not increase water pollution, however. A reduction in tillage
means a reduction in soil erosion, a major source of pesticide movement and
water pollution.
Biological Control
Natural enemies can be a major factor in controlling pests. A substantial
number of devastating and extensive pest problems have been resolved by
introducing or conserving natural pest enemies. Some examples are the control
of Klamath weed in the Pacific Northwest, alligator weed in Florida, Comstock
mealybug on apples in the Eastern United States, purple scale on citrus in
Texas and Florida, citrophilus mealybug on citrus in California, alfalfa weevil
in mid-Atlantic States, Rhodesgrass scale in Florida and Texas, European pine
sawfly and European wheat stem sawfly in the East, larch casebearer in the
Northeast, and satin moth in New England and the Pacific Northwest. But, in
general, the augmentation of natural populations of insect enemies with program-
med releases of mass-reared specimens is still largely in the research stage.
The conservation of natural enemies is receiving considerable attention in the
United States. This approach is currently fostered by a federally assisteu
program of 39 pest management projects in 29 states, and the program is
expanding each year. Commodities involved include tobacco, cotton, alfalfa,
field corn, grain sorghum, fresh market and processing corn, peppers, beans,
potatoes, apples, citrus, and pears.
Boll weevils are controlled on several million hectares of cotton by means of
cultural methods and fall insecticide applications, in order to delay spraying
in the spring. In this way, natural enemies of other insect pests will not be
destroyed by early spraying for boll weevils.
At the present time, biological methods of controlling diseases, nematodes,
and most weeds do not appear reliable.
Insect Sterilization
The use of sexual sterility is one of the most selective and environmentally
acceptable methods of suppressing insect populations. Although the development
of this approach has not received significant support from the private sector,
it is operational in four instances: (1) the management of screwworm popu-
lations in the Southwestern United States and Northern Mexico, (2) protection
of California citrus by release of sterile Mexican fruit fly pupae in North-
western Mexico, (3) the protection of 364,372 hectares (900,000 acres) of
cotton in the San Joaquin Valley (California) from incipient populations of the
pink bollworm, and (4) the suppression of pink bollworm on wild cotton in the
Florida keys. The method was recently employed against the boll weevil in an
areawide test in Mississippi, and holds potential, when integrated with other
techniques^ for eliminating this pest from the United States.
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Insect Toxins and Pathogens
Over 363,636 kilograms of the toxin of Bacillus thuringiansis were marketed
in 1972 in the United States for the control of caterpillars on lettuce, cole
crops, tobacco, and ornamentals. With improved efficiency of the toxin and a
reliable and adequate supply, the toxin could be marketed for wide use in
controlling pests on cotton, forests, and other large-volume crops. A number
of insect viruses are also being developed. For example, the Heliothis virus
was recently registered for control of bollworms on cotton. However, the
virus is not yet sufficiently persistent.
Insect Attractants
Various insect attractants have been developed to aid in insect control.
International airports, harbors, and other ports of entry into the United States
are ringed with light and other traps to attract various foreign species
of insect pests. These devices are valuable in attracting alien insects, and
have reduced the need for scheduled insecticide spraying for these pests. In
orchards, sex attractants are being used in traps to determine pest levels and
the need for pesticide application. In pilot tests, a sex attractant is being
applied to the forest canopy in gelatin microcapsules in an attempt to prevent
male gypsy moths from locating females. This same approach is being developed
for the codling moth and other major moth species. Commercial use of these
methods awaits further development.
Resistant Crop Varieties
Use of plant varieties that are resistant to diseases, insects, and nematodes is
one means of solving pest problems in an economical and relatively desirable
manner. Many crops could not be profitably grown in numerous locations except
for the use of insect resistant varieties. These crops include alfalfa, corn,
cotton, tobacco, small grains, clovers, and grasses. Soybeans, wheat, and
sugar crops would not be commercially profitable in the United States except
for the use of disease and nematode resistant varieties. The use of resistant
varieties has been the only practical method found to suppress a large number
of disease and insect pests of wheat, corn, barley, oats, grain sorghum, and
rice. Many tolerant varieties of crops are available. Absolute resistance
to pests is rare. However, even modest resistance can greatly reduce the need
for pesticides. Resistant varieties are not available and cannot be foreseen
for all pests that attack major crops in the United States.
Crop Rotation
For centuries, farmers have used crop rotation to control pests. Rotations can
be designed to partially reduce populations of a wide variety of diseases,
insects, and nematodes. They are most effective in controlling pests on
cultivated annual crops in areas of mixed agriculture.
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REFERENCES
1. Brooks, F. A.
1947. The Drifting of Poisonous Dusts Applied by Airplanes and Land
Rigs. Jour. Agr. Engin., Vol. 28, No. 6, pp. 233-239.
2. Council on Environmental Quality
1972. Integrated Pest Management. U.S. Gov. Printing Off., Washington,
D.C.
3. U.S. Department of Agriculture
1973. Secretary's Memorandum No. 1799.
4. U.S. Department of Health, Education and Welfare
1969. Report of the Secretary's Commission on Pesticides and their
Relationship to Environmental Health (the "Mrak Report"). The
quotation given cites Lichtenstein, E., et. al., 1966. Toxicity in Fate
of Insecticide Residue in Water. Arch. Environ. Health, Vol. 12,
pp. 199-212.
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CHAPTER VI - ANIMAL WASTES
INTRODUCTION
The management of animal wastes has received considerable attention in recent
years because of their water and air pollution potential. Much of the concern
has resulted because of a major trend toward large confined livestock and
poultry operations. Even so, as much as 40 percent of all livestock is
produced on pasture.
Confined feeding operations result in vast accumulations of wastes in localized
areas. There is potential for the movement of animal waste in runoff from
these operations, and systems for control have become a necessary and required
part of the facilities. Runoff from these areas is usually applied to the land,
since there is no practical treatment to render it acceptable to stream discharge.
Solid wastes must be removed from these installations and the most widely used
disposal practice is to spread them on agricultural land. (3, llt 17, 33)
Land is a nonpoint source of pollutants to water systems, mainly by means
of erosion. The application of animal wastes to land can increase pollution
if proper practices are not followed. When animal wastes are properly applied
to land, the practice is a highly effective and acceptable means for disposal.
The wastes can be beneficial to the land in providing nutrients for growing
crops and organic matter for improving the physical properties of the soil,
thereby reducing soil erodibility. (6^, 16^ 18. 25, 34) Animal wastes applied
to agricultural land come from three basic sources: (1) waste removed from
feeding facilities, (2) storm runoff and snowmelt captured as it leaves feeding
areas, and (3) excretion from animals grazing on pasture and rangeland. Feedlot
facilities, per se, will not be discussed in this report because they are
considered point sources of water and air pollution.
The following sections discuss alternative management practices for applying
various animal wastes to land.
WASTES REMOVED FROM ANIMAL CONFINEMENT FACILITIES
The wastes removed from confinement facilities vary greatly. Many dairy
operations and some beef cattle and swine operations utilize slurry or other
systems that involve regular removal of wastes. On the other hand, wastes
are generally removed from cattle feedlots and loose housing barns only once
or twice a year. Water accounts for 50 percent or more of the total weight
of most animal wastes.
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The nutrient content of animal wastes is highly variable. The major factors
influencing nutrient content include animal species, feed ration, storage
conditions, and rainfall. Poultry waste generally contains the highest
concentration of nutrients. (17, 19)
The most common and ecologically accepted method for disposing of wastes
from feeding facilities is application to the land. This is also the lowest
cost method of disposal for most systems.
In general, where land is readily available and transportation is not a major
problem, manure is applied to land. This practice emphasizes utilization of
the wastes as primary plant nutrients in a recycling process. The waste
produced per animal unit can be applied on less land than is required to
produce feed for an animal unit. The application rate is determined largely
on the basis of the nitrogen content of the waste and the plant species grown.
Weed seeds, salt content, and toxic substances may become limiting factors
under some conditions. (9_, 13, 14, 22, 28, 29)
When sufficient cropland is not available, large amounts of manure are
sometimes applied to land with emphasis on disposal rather than plant
utilization. Although this practice can alleviate disposal problems, it
can create other problems. Nitrate, salts, and other compounds may accumulate
to undesirable levels in the soil profile, or leach into underground water
supplies. Yields and quality of crops may also be adversely affected. The
loading rate should be based on the characteristics of the waste, kind of
soil, climatic conditions, plant species, and depth to water table. (14, 20, 30)
Methods of Waste Application
The alternative methods of applying solid waste on cropland consist of surface
application followed by (1) no incorporation into the soil, (2) immediate
incorporation, or (3) incorporation at a later date prior to planting a crop.
The frequency of spreading solid manure on land varies from daily, in the case
of many dairy operations, to periodically, such as after marketing of beef
cattle. The preferred method for reducing the pollution potential is to
incorporate the manure with the soil as quickly as feasible after spreading.
This practice greatly reduces the possibility of pollution from runoff, and
also prevents loss of nitrogen compounds through volatilization. Losses
through volatilization can be great and should be minimized, especially
when the waste is applied as a source of plant nutrients. Adverse weather
and soil conditions, crop stage, and the inability to direct necessary labor
and machinery to this effort are potential constraints. (4^ 5_, 23)
Slurry wastes (a mixture of solid and liquid materials) are also commonly
applied to the land surface, although some soil injection systems are used.
The surface application methods include surface and sprinkler irrigation
techniques, and tank spreaders. Wastes applied by irrigation cannot be
immediately incorporated with the soil because of the wet condition. If
precipitation occurs shortly after irrigation, runoff will increase. The
tank spreader methods require more labor than irrigation methods, but
54
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generally the wastes can be incorporated into the soil sooner. The injection
system has a distinct advantage from a pollution abatement standpoint in that
the waste is immediately incorporated into the soil,thereby reducing odor and
largely eliminating the possibility of polluted runoff. (1, 2_, 8_, 27)
Runoff Control from Waste-Treated Land
Rates and methods for applying animal waste on agricultural land are so
diverse that specific recommendations cannot be given that will apply in
all cases. However, some good management practices are:
1. Estimate the plant nutrient value of the waste, and apply it on land
uniformly in accordance with crop requirements. (The nitrogen
requirement of the crop is often a convenient basis for determining
the amount of waste to be applied.)
2. Schedule the time and frequency of manure applications for maximum
nutrient utilization by plants.
3. Incorporate manure into the soil as quickly as feasible following
application, or inject the liquid wastes into the soil.
4. Ensure enough land is available at the appropriate time for disposal
of manure. For example, to maximize the utilization of waste,
approximately 1 hectare (2.4 acres) of land will be required for
every 3 to 6 dairy cows, 5 to 10 beef animals, 20 to 40 hogs, and
400 to 800 layers.
5. When large amounts of wastes are applied to the land, a highly
productive crop should be planted to utilize the nutrients, reduce
runoff, and reduce the amounts of nitrate and other pollutants
that may reach the gound water.
6. Wet land, steep land, frozen or snow-covered land, and grassed
waterways generally should not be treated with wastes since the
material will not be readily absorbed and may result in polluted
runoff.
7. Use good water erosion control practices, as outlined in Chapter II,
to control runoff.
LAND DISPOSAL OF RUNOFF FROM CONFINEMENT AREAS
Most confined animal facilities must include a system for capturing and
disposing of storm runoff. This problem is greatest in areas of high
rainfall. Generally, about one-fourth to one-half of the annual precipitation
ends up as runoff. However, the percentage may be smaller in arid and semi-
arid areas because the drier conditions of the soil in feeding pens permits
more absorption of the moisture. (4^ 21, 25)
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The runoff from a confinement area can contain high concentrations of organic
matter and salt. The degree of concentration is primarily determined by the
amount of precipitation, number of animals, size of the confined area, and
management practices. Other important factors include the intensity, duration,
and frequency of rainfall, size and topography of the drainage area, and type
of facilities. (10, 12_, 15., 2£, 31)
Retention ponds or basins are used to store runoff prior to land disposal.
Runoff effluent should be removed from the retention pond and applied on
land as soon as possible after a runoff event, or additional storage should
be provided for runoff from subsequent storms.
Methods to Dispose of Runoff
There are basically two conventional methods for land disposal of feedlot
runoff. First, runoff can be pumped, hauled, and spread. The second method
is by irrigation, using one of the conventional methods such as sprinklers,
ditches, or flooding. The method used depends on the kind of soil, slope,
crops being grown, climate, and costs. The pump, haul, and spread method
is restricted to the smaller operations; irrigation is suitable for larger
operations.
The composition of the runoff should be known before it is applied to land.
In many cases, the effluent may have minimal value as a source of plant
nutrients. Some effluent may have salt concentrations that are detrimental.
In this case, some dilution is necessary before the waste is applied to
land, especially when growing crops are present. (]_t 20, 24)
Evaporation ponds are an alternate method of disposing of runoff effluent.
However, this method is restricted to areas of the country where evaporation
exceeds precipitation.
Practices to Minimize Surface Runoff
Good land use management is essential to prevent water pollution from
feedlot runoff applied on land. General practices to minimize pollution
include:
1. Use recommended irrigation management practices.
2. Ensure that enough land is available for disposing of runoff
applications. The amount of land required depends on whether
the land is used as a disposal site (applying the maximum
permissible amount without causing surface runoff or ground
water pollution) or for growing crops (applying the amount of
effluent to provide enough water for optimum crop growth).
3. Attempt to maintain a cover crop that utilizes large quantities
of water. Since feedlot runoff generally contains a low concentra-
tion of nutrients, it is not normally a major source of nutrients
for growing crops.
56
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4. Apply effluent uniformly to minimize the possibility of surface
runoff or ponding, which may result in leaching.
5. Use recommended water erosion control practices outlined in
Chapter II to control runoff. Avoid spreading feedlot runoff
on land after heavy rains, on frozen or snow-covered land, and .
on grassed waterways.
PASTURE PRODUCTION OF LIVESTOCK
Pasture Operations
The use of pastures and ranges is a major component of livestock production.
Feeder calves are produced almost exclusively from cow-calf enterprises on
pasture and range systems. A substantial portion of hog production is a
pasture operation, handled with portable facilities and mobile equipment.
Most dairy farms, except for certain areas of the country, use pasture when
seasonal conditions permit, but probably all use confined areas for milking.
Winter housing is necessary in many major milk producing states. Sheep produc-
tion is also mainly a range and pasture operation. Confinement operations
dominate the production of fed beef cattle, broilers, turkeys, and eggs. (32)
In pasture production, manure is deposited directly on the land by grazing
animals. Even though a relatively large land area may be available to animals
on pasture, they tend to concentrate around feeding, watering, and resting sites.
Concentration of wastes at these sites can be quite high, creating potential
water pollution. (6) Good drainage around these sites is essential, but may
increase the possibility of contaminated runoff. Flowing streams also attract
animals, particularly in hot weather, which can lead to contamination of water.
Practices to Minimize Water Pollution
Good management is the best insurance against pollution of water from pasture
or range systems of livestock production. The relative importance of production
practices differ by types of livestock and regions of the country, but the
following generally apply:
1. Maintain an adequate land-to-livestock ratio. Avoid concentrations
of animals that will create holding areas rather than grazing areas.
2. Maintain a highly productive forage on the land to retard runoff,
entrap animal wastes, and utilize nutrients.
3. Plan a stocking density and rotation system of grazing to prevent
overgrazing and eroding of the soil.
57
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A. Locate feeders and waterers a reasonable distance from streams and
water courses. Move them to new locations often enough to avoid
creating erodible paths through repeated trampling by livestock.
5. Provide an adequate land absorption area downslope from feeding
and watering sites, preferably with a filter strip of lush forage
growth between such sites and the streams.
6. Provide limited access to streams and ponds. Use fencing to
keep livestock from entering critical stream reaches.
7. Provide fences to prevent animals from wading in streams at
points where they may concentrate for drinking. Fencing may
be impractical, however, for many pasture operations.
8. Pump water from a stream, farm pond, or well to watering troughs
or tanks where the number of animals or the characteristics
of land present critical pollution problems.
9. Provide summer shade, using trees or artificial shelters to lessen
the need for animals to enter the water for relief from the heat.
The same precautions used in locating feeders and waterers should
be followed in locating shelters.
10. Install and maintain a good overall program of water erosion control,
as described in Chapter 11.
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1966. Guide for Wind Erosion Control in the Northeastern States.
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Spencer, W.
1973. Pesticide Volatilization as Related to Water Loss from Soil.
Jour. Environ. Quality, Vol. 2, No. 2, pp. 284-289.
Sprague, G. and R. Dahms
1972. Development of Crop Resistance to Insects. Jour. Environ. Quality,
Vol. 1, No. 1, pp. 28-33.
Trichell, D., et al.
1968. Loss of Herbicides in Runoff Water. Weed Science, Vol. 16, No. 4,
pp. 447-449.
Upchurch, R.
n.d. Behavior of Herbicides in Soil. Residue Review, Vol. 16, pp. 47-85.
Wlese, A. and R. Davis
1964. Herbicide Movement in Soil with Various Amounts of Water. Weeds,
Vol. 12, No. 2, pp. 101-103.
Animal Wastes
Agnew, R. W. and R. C. Loehr
1966. Cattle Manure Treatment Techniques. Proc., National Symposium
on Animal Waste Management, ASAE Pub. No. SP-0366, pp. 81-85.
Boyd, J. S.
1970. Alternatives for Handling Manure. Agr. Eng. Dept. Inf. Series No. 257,
Coop. Ext. Serv., Mich. State Univ., East Lansing.
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Good, D., L. J. Connor, J. B. Johnson, and C. R. Hoglund
1973. Impact of Imposing Selected Pollution Controls. Mich. Farm Econ.
Report No. 360, Coop. Ext. Serv., Mich. State Univ., East Lansing.
Graves, R. E. (ed.)
1972. Proceedings, Farm Animal Waste Conference. Univ. of Wis. Coop.
Ext. Program, Madison.
Jacobs, J. J. and G. L. Casler
1972. Economic and Environmental Considerations in Dairy Manure Management
Systems. Dept. Agr. Econ., AE Res. 72-18, Cornell Univ., Ithaca, N.Y.
Johnson, J. B., C. R. Hoglund, and B. Buxton
1972. An Economic Appraisal of Alternative Dairy Waste Management Systems
Designed for Pollution Control. Presented, Amer. Assoc. Dairy Science,
Blacksburg, Va.
Jones, D. D., D. L. Day, and A. C. Dale
1970. Aerobic Treatment of Livestock Wastes. Univ. of 111., Exp. Sta.
Bui. 737, Urbana.
Loehr, R. C.
1969. The Challenge of Animal Waste Management. Proc., Cornell Agrl.
Waste Management Conf., pp. 17-22.
Madden, J. M. and J. N. Dornbush
1971. Pollution Potential from Livestock Feeding Operations. Amer. Soc.
Agr. Engin. Paper No. 71-212.
Minshall, N.
1970. Runoff Losses. In: A Study of Farm Waste (ed. by S. A. Witzel,
££ a^.). Office of Water Resources Research Project B-004-WIS, Univ. of
Wis., Madison.
Olson, E. A.
1971. Guidance for Livestock Producers on Waste Management Systems.
Neb. Agr. Exp. Sta. EC-71-794, Univ. of Neb., Lincoln.
Reddell, D. L., P. J. Lyerly, and J. J. Hefner
1970. Crop Yields from Land Receiving Large Manure Applications. Amer.
Soc. Agr. Engin. Paper No. 72-960.
Resnik, A. V. and J. M. Rademacher
1969. Animal Waste Runoff—A Major Water Quality Challenge. 2nd
Compendium of Animal Waste Management, Federal Water Pollution Control
Administration (now Environmental Protection Agency), Kansas City, Mo.
Viets, F. G., Jr.
1971. The Mounting Problem of Cattle Feedlot Pollution. Agr. Science
Review, Vol. 9, No. 1, pp. l-r8.
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Webber, L. R.
1971. Animal Wastes. Jour. Soil and Water Conservation, Vol. 26, No. 2,
pp. 47-50.
Wells, D. M., R. C. Albin, W. Grub, E. A. Coleman, and G. F. Meenaghan
1971. Characteristics of Wastes from Southwestern Cattle Feedlots.
Environmental Protection Agency Report No. 13040 DEM.
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GLOSSARY
The glossary consists of selected
terms and definitions from the
Resource Conservation Glossary
published by the Soil Conservation
Society of America, Ankeny, Iowa,
1970.
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absorption - The movement of a chemical into a plant.
adsorption - Adhesion of a chemical to a soil particle.
agricultural land - Land in farms regularly used for agricultural production.
The term includes all land devoted to crop or livestock enterprises; for
example, the farmstead lands, drainage and irrigation ditches, water supply,
cropland, and grazing land of every kind in farms.
agronomic practices - The soil and crop activities employed in the production
of farm crops, such as selecting seed, seedbed preparation, fertilizing,
liming, manuring, seeding, cultivation, harvesting, curing, crop sequence,
crop rotations, cover crops, stripcropping, pasture development, etc.
ammonification - The biochemical process whereby ammoniacal nitrogen is
released from nitrogen-containing organic compounds.
ammonium fixation - The adsorption or absorption of ammonium ions by the
mineral or organic fractions of the soil in a manner that they are
relatively insoluble in water and relatively unexchangeable by the usual
methods of cation exchange.
animal unit - A measure of livestock numbers based on the equivalent of a
mature cow (approximately 1,000 pounds live weight). An animal unit is
roughly one cow, one horse, one mule, five sheep, five swine, or six goats.
application rate - Rate that material is applied to a given area.
arid - A term applied to regions or climates that lack sufficient moisture
for crop production without irrigation. The limits of precipitation vary
considerably according to temperature conditions, with an upper annual
limit for cool regions of 10 inches or less and for tropical regions
as much as 15 to 20 inches.
available nutrient - That portion of any element or compound in the soil
that readily can be absorbed and assimilated by growing plants.
available water-holding capacity (soils) - The capacity to store water
available for use by plants, usually expressed in linear depths of water
per unit depth of soil. Commonly defined as the difference between the
percentage of soil water at field capacity and the percentage at wilting
point. This difference, multiplied by the bulk density and divided by 100,
gives a value in surface inches of water per inch depth of soil. See
field capacity.
blowout - An excavation in areas of loose soil, usually sand, produced by
wind.
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buffer strips - Strips of grass or other erosion-resisting vegetation
between or below cultivated strips or fields.
canopy - The cover of leaves and branches formed by the tops or crowns
of plants.
check dam - Small dam constructed in a gully or other small watercourse to
decrease the streamflow velocity, minimize channel scour, and promote
deposition of sediment.
chiseling - Breaking or loosening the soil, without inversion, with a
chisel cultivator or chisel plow.
clean tillage - Cultivation of a field so as to cover all plant residues
and to prevent the growth of all vegetation except the particular crop
desired.
climate - The sum total of all atmospheric or meteorological influences,
principally temperature, moisture, wind, pressure, and evaporation,
which combine to characterize a region and give it individuality by
influencing the nature of its land forms, soils, vegetation, and land
use.
compaction - To unite firmly; the act or process of becoming compact,
usually applied in geology to the changing of loose sediments into hard,
firm rock. With respect to construction work with soils, engineering
compaction is any process by which the soil grains are rearranged to
decrease void space and bring them into closer contact with one another,
thereby increasing the weight of solid material per cubic foot.
conservation - The protection, improvement, and use of natural resources
according to principles that will assure their highest economic or social
benefits.
conservation district - A public organization created under state enabling
law as a special-purpose district to develop and carry out a program of
soil, water, and related resource conservation, use, and development
within its boundaries; usually a subdivision of state government with a
local governing body and always with limited authorities. Often called
a soil conservation district or a soil and water conservation district.
conservation plan for farm, ranch, or nonagricultural land unit - The
properly recorded decisions of the cooperating landowner or operator
on how he plans, within practical limits, to use his land in an operating
unit within its capability and to treat it according to its needs for
maintenance or improvement of the soil, water, and plant resources.
contour - (1) An imaginary line on the surface of the earth connecting
points of the same elevation. (2) A line drawn on a map connecting
points of the same elevation.
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contour farming - Conducting field operations, such as plowing, planting,
cultivating and harvesting, on the contour.
contour furrows - Furrows plowed approximately on the contour on pasture
or rangeland to prevent soil loss and increase infiltration. Also,
furrows laid out approximately on the contour for irrigation purposes.
contour stripcropping - Layout of crops in comparatively narrow strips
in which the farming operations are performed approximately on the
contour. Usually strips of grass, close-growing crops, or fallow are
alternated with those in cultivated crops.
cover crop - A close-growing crop grown primarily for the purpose of
protecting and improving soil between periods of regular crop produc-
tion or between trees and vines in orchards and vineyards.
cover, ground - Any vegetation producing a protecting mat on or just
above the soil surface. In forestry, low-growing shrubs, vines, and
herbaceous plants under the trees.
cover, vegetative - All plants of all sizes and species found on an area,
irrespective of whether they have forage or other value. Syn. plant cover.
cropland - Land used primarily for the production of adapted cultivated,
close-growing, fruit, or nut crops for harvest, alone or in association
with sod crops.
crop residue - The portion of a plant or crop left in the field after
harvest.
crop residue management - Use of that portion of the plant or crop left
in the field after harvest for protection or improvement of the soil.
crop rotation - The growing of different crops in recurring succession
on the same land.
debris - A term applied to the loose material arising from the disintegration
of rocks and vegetative material; transportable by streams, ice, or floods.
debris dam - A barrier built across a stream channel to retain rock, sand,
gravel, silt, or other material.
degradation - To wear down by erosion, especially through stream action.
denitrification - The biochemical reduction of nitrate or nitrite to
gaseous nitrogen, either as molecular nitrogen or as an oxide of nitrogen.
deposit - Material left in a new position by a natural transporting agent,
such as water, wind, ice, or gravity, or by the activity of man.
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deposition - The accumulation of material dropped because of a slackening
movement of the transporting agent—water or wind.
desiltlng area - An area of grass, shrubs, or other vegetation used for
inducing deposition of silt and other debris from flowing water, located
above a stock tank, pond, field, or other area needing protection from
sediment accumulation. See filter strip.
detention dam - A dam constructed for the purpose of temporary storage of
streamflow or surface runoff and for releasing the stored water at
controlled rates.
dispersion, soil - The breaking down of soil aggregates into individual
particles, resulting in single-grain structure. Ease of dispersion is
an Important factor influencing the erodibility of soils. Generally
speaking, the more easily dispersed the soil, the more erodible it is.
disposal field - Area used for spreading liquid effluent for separation of
wastes from water, degradation of impurities, and improvement of drainage
waters. Syn. infiltration field.
diversion terrace - Diversions, which differ from terraces in that they
consist of individually designed channels across a hillside, may be used
to protect bottomland from hillside runoff or may be needed above a
terrace system for protection against runoff from an unterraced area.
They may also divert water out of active gullies, protect farm building
from runoff, reduce the number of waterways, and are sometimes used in
connection with stripcropping to shorten the length of slope so that
the strips can effectively control erosion. See terrace.
drainage - The removal of excess surface water or groundwater from land
by means of surface or subsurface drains.
drop-inlet spillway - Overall structure in which the water drops through
a vertical riser connected to a discharge conduit.
drop spillway - Overall structure in which the water drops over a vertical
wall onto an apron at a lower elevation.
duckfoot - An implement with horizontally spreading, V-shaped tillage
blades or sweeps which are normally adjusted to provide shallow culti-
vation without turning over the surface soil or burying surface crop
residues.
duff - The more or less firm organic layer on top of mineral soil, consisting
of fallen vegetative matter in the process of decomposition, including
everything from pure humus below to the litter on the surface. Duff is
a general, nonspecific term.
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environment - The sum total of all the external conditions that may act
upon an organism or community to influence its development or existence.
erosion - (1) The wearing away of the land surface by running water, wind,
ice, or other geological agents, including such processes as gravitational
creep. (2) Detachment and movement of soil or rock fragments by water,
wind, ice, or gravity. The following terms are used to describe different
types of water erosion.
accelerated erosion - Erosion much more rapid than normal, natural,
or geologic erosion, primarily as a result of the influence of
the activities of man or, in some cases, of other animals or
natural catastrophies that expose base surfaces; for example,
fires.
geological erosion - The normal or natural erosion caused by
geological processes acting over long geologic periods and
resulting in the wearing away of mountains, the building of
floodplains, coastal plains, etc. Syn. natural erosion.
gully erosion - The erosion process whereby water accumulates in
narrow channels and, over short periods, removes the soil from
this narrow area to considerable depth, ranging from 1 to 2 feet
to as much as 75 to 100 feet.
natural erosion - Wearing away of the earth's surface by water,
ice, or other natural agents under natural environmental con-
ditions of climate, vegetation, etc., undisturbed by man. Syn.
geological erosion.
normal erosion - The gradual erosion of land used by man that
does not greatly exceed natural erosion. See natural erosion.
rill erosion - An erosion process in which numerous small
channels only several inches deep are formed; occurs mainly
on recently cultivated soils. See rill.
sheet erosion - The removal of a fairly uniform layer of soil
from the land surface by runoff water.
splash erosion - The spattering of small soil particles caused
by the impact of raindrops on wet soils. The loosened and
spattered particles may or may not be subsequently removed
by surface runoff.
erosive - Refers to wind or water having sufficient velocity to cause
erosion. Not to be confused with erodible as a quality of soil.
eutrophication - A means of aging of lakes whereby aquatic plants are abundant
and waters are deficient in oxygen. The process is usually accelerated by
' enrichment of waters with surface runoff containing nitrogen and phosphorus.
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fallow - Allowing cropland to lie idle, either tilled or untilled, during
the whole or greater portion of the growing season.
farm management - The organization and administration of farm resources,
including land, labor, crops, livestock, and equipment.
farm operator - A person who operates a farm either by performing the
labor himself or directly supervising it.
fertility, soil - The quality of a soil that enables it to provide
nutrients in adequate amounts and in proper balance for the growth
of specified plants when other growth factors, such as light, moisture,
temperature, and the physical condition of the soil, are favorable.
fertilizer - Any organic or inorganic material of natural or synthetic
origin that is added to a soil to supply elements essential to plant
growth.
field capacity (field moisture capacity) - The amount of soil water
remaining in a soil after the free water has been allowed to drain
away for a day or two if the root zone has been previously saturated.
It is the greatest amount of water that the soil will hold under
conditions of free drainage, usually expressed as a percentage of
the oven-dry weight of soil or other convenient unit.
field stripcropping - A system of stripcropping in which crops are grown
in parallel strips laid out across the general slope but which do not
follow the contour. Strips of grass or close-growing crops are
alternated with strips of cultivated crops.
filter strip - Strip of permanent vegetation above farm ponds, diversion
terraces, and other structures to retard flow of runoff water, causing
deposition of transported material, thereby reducing sediment flow.
See desilting area.
flume - An open conduit on a prepared grade, trestle, or bridge for the
purpose of carrying water across creeks, gullies, ravines, or other
obstructions. It may also apply to an entire canal where it is
elevated above natural ground for its entire length. Sometimes used
in reference to calibrated devices used to measure the flow of water
in open conduits.
furrow dams - Small earth dams used to impound water in furrows.
grade - (1) The slope of a road, channel, or natural ground. (2) The
finished surface of a canal bed, roadbed, top of embankment, or bottom
of excavation; any surface prepared for the support of construction
like paving or laying a conduit. (3) To finish the surface of a canal
bed, roadbed, top of embankment, or bottom of excavation.
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grade stabilization structure - A structure for the purpose of stabilizing
the grade of a gully or other watercourse, thereby preventing further
headcutting or lowering of the channel grade.
gradient - Change of elevation, velocity, pressure, or other characteristics
per unit length; slope.
grassed waterway - A natural or constructed waterway, usually broad and
shallow, covered with erosion-resistant grasses, used to conduct surface
water from cropland.
groundwater - Phreatic water or subsurface water in the zone of saturation.
gully - A channel or miniature valley cut by concentrated runoff but
through which water commonly flows only during and immediately after
heavy rains or during the melting of snow. A gully may be dendritic or
branching or it may be linear, rather long, narrow, and of uniform width.
The distinction between gully and rill is one of depth. A gully is
sufficiently deep that it would not be obliterated by normal tillage
operations, whereas a rill is of lesser depth and would be smoothed by
ordinary farm tillage. Syn. arroyo. See erosion; rill.
gully control plantings - The planting of forage, legume, or woody plant
seeds, seedlings, cuttings, or transplants in gullies to establish or
reestablish a vegetative cover adequate to control runoff and erosion
and incidentally produce useful products.
herbicide - A chemical substance used for killing plants, especially
weeds.
humus - That more or less stable fraction of the soil organic matter
remaining after the major portion of added plant and animal residues
have decomposed; usually amorphous and dark colored.
impoundment - Generally an artificial collection or storage of water, as
a reservoir, pit, dugout, sump, etc. See reservoir.
infiltration - The flow of a liquid into a substance through pores or
other openings, connoting flow into a soil in contradistinction to
the word percolation which connotes flow through a porous substance.
infiltration rate - A soil characteristic determining or describing
the maximum rate at which water can enter the soil under specified
conditions, including the presence of an excess of water.
intensive cropping - Maximum use of the land by means of frequent
succession of harvested crops.
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land capability class - One of the eight classes of land in the land
capability classification of the Soil Conservation Service. These eight
, land capability classes, distinguished according to the risk of land
damage or the difficulty of land use, are:
Land suitable for cultivation and other uses.
I. Soils in class I have few limitations that restrict their use.
II. Soils in class 11 have some limitations that reduce the choice
of plants or require moderate conservation practices.
III. Soils in class III have severe limitations that reduce the choice
of plants or require special conservation practices, or both.
IV. Soils in class IV have very severe limitations that restrict
the choice of plants, require very careful management, or both.
Land generally not suitable for cultivation (without major treatment).
V. Soils in class V have little or no erosion hazard but have
other limitations, impractical to remove, that limit their
use largely to pasture, range, woodland, or wildlife food and
cover.
VI. Soils in class VI have severe limitations that make them
generally unsuited for cultivation and limit their use
largely to pasture or range, woodland, or wildlife food and
cover.
VII. Soils in class VII have very severe limitations that make
them unsuited to cultivation and that restrict their use
largely to grazing, woodland, or wildlife.
VIII. Soils and landforms in class VIII have limitations that
preclude their use for commercial plant production and restrict
their use to recreation, wildlife, water supply, or esthetic
purposes.
land leveling - Process of shaping the land surface for better movement
of water and machinery over the land. Also called land forming; land
shaping, or land grading.
leaching - The removal of materials in solution from the soil.
manure - The excreta of animals, with or without the admixture of
bedding or litter, in varying stages of decomposition.
mechanical practices - Soil and water conservation practices that primarily
change the surface of the land or that store, convey, regulate, or
dispose of runoff water without excessive erosion.
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minimum tillage - That amount of tillage required to create the proper
soil condition for seed germination, plant establishment, and pre-
vention of competitive growth.
mulch - A natural or artificial layer of plant residue or other materials,
such as sand or paper, on the soil surface.
nitrification - The biological oxidation of ammonium salts to nitrites
and the further oxidation of nitrites to nitrates.
no-tillage - A method of planting crops that involves no seedbed preparation
other than opening the soil for the purpose of placing the seed at the
intended depth. This usually involves opening a small slit or punching
a hole into the soil. There is usually no cultivation during crop
production. Chemical weed control is normally used. Also referred to
as slot planting or zero tillage.
overgrazing - Grazing so heavy that it impairs future forage production
and causes deterioration through damage to plants or soil or both.
pesticide - A chemical agent used to control pests.
plant nutrients - The elements or groups of elements taken in by a plant
which are essential to its growth and used .in elaboration of its food
and tissues. Includes nutrients obtained from fertilizer ingredients.
plant residue - See crop residue; humus.
plow layer - The soil ordinarily moved in tillage; equivalent to surface
soil.
plow-plant - Plowing and planting a crop in one operation, with no
additional seedbed preparation.
pollution, water - Any change in the character of water adversely affecting
its usefulness.
rainfall intensity - The rate at which rain is falling at any given
instant, usually expressed in inches per hour.
reservoir - Impounded body of water or controlled lake in which water
is collected or stored.
rill - A small, Intermittent water course with steep sides, usually only
a few inches deep and, hence, no obstacle to tillage operations.
rotation pasture - A cultivated area used as a pasture 1 or more years
as part of crop rotation.
row crop - A crop planted in rows, normally to allow cultivation between
rows during the growing season.
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runoff (hydraulics) - That portion of the precipitation on a drainage area
that is discharged from the area in stream channels. Types include
surface runoff, groundwater runoff, or seepage.
sediment - Solid material, both mineral and organic, that is in suspension,
is being transported, or has been moved from its site of origin by air,
water, gravity, or ice and has come to rest on the earth's surface
either above or below sea level.
sediment discharge - The quantity of sediment, measured in dry weight or
by volume, transported through a stream cross-section in a given time.
Sediment discharge consists of both suspended and load and bedload.
sheet flow - Water, usually storm runoff, flowing in a thin layer over
the ground surface. Syn. overland flow.
slope - Degree of deviation of a surface from the horizontal, usually
expressed in percent or degrees.
soil-conserving crops - Crops that prevent or retard erosion and maintain
or replenish rather than deplete soil organic matter.
soil erosion - The detachment and movement of soil from the land surface
by wind or water. See erosion.
soil management - The sum total of all tillage operations, cropping
practices, fertilizer, lime, and other treatments conducted on, or
applied to, a soil for the production of plants.
soil organic matter - The organic fraction of the soil that includes
plant and animal residues at various stages of decomposition, cells
and tissues of soil organisms, and substances synthesized by the soil
population. Commonly determined as the amount of organic material
contained in a soil sample passed through a 2-millimeter sieve.
soil structure - The combination or arrangement of primary soil particles
into secondary particles, units, or peds. The secondary units are
characterized and classified on the basis of size, shape, and degree
of distinctness into classes, types, and grades, respectively.
soil texture - The relative proportions of the various soil separates in
a soil. The textural classes may be modified by the addition of suitable
adjectives when coarse fragments are present in substantial amounts;
for example, gravelly silt loam. Sand, loamy sand, and sandy loam are
further subdivided on the basis of the proportions of the various sand
separates present. The limits of the various classes and subclasses
are as follows:
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sand - Soil material that contains 85 percent or more of sand. The
percentage of silt plus 1.5 times the percentage of clay shall
not exceed 15.
coarse sand - 25 percent or more very coarse and coarse sand and
less than 50 percent any other one grade of sand.
sand - 25 percent or more very coarse, coarse, and medium sand and
less than 50 percent fine or very fine sand.
fine sand - 50 percent or more fine sand, or less than 25 percent
very coarse, more fine sand, or less than 25 percent very coarse,
fine sand.
very fine sand - 50 percent or more very fine sand.
loamy sand - Soil material that contains, at the upper limit, 85 to
90 percent sand, and the percentage of silt plus 1.5 times the
percentage of clay is not less than 15. At the lower limit, it
contains not less than 70 to 85 percent sand, and the percentage
of silt plus twice the percentage of clay does not exceed 30.
loamy coarse sand - 25 percent or more very coarse and coarse
sand and less than 50 percent any other one grade of sand.
loamy sand - 25 percent or more very coarse, coarse, and medium
sand and less than 50 percent fine or very fine sand.
loamy very fine sand - 50 percent or more very fine sand.
stabilized grade - The slope of a channel at which neither erosion nor
deposition occurs.
stubble - The basal portion of plants remaining after the top portion
has been harvested; also, the portion of the plants, principally grasses,
remaining after grazing is completed.
stubble mulch - The stubble of crops or crop residues left essentially
in place on the land as a surface cover during fallow and the growing
of a succeeding crop.
subsoiling - The tillage of subsurface soil, without inversion, for the
purpose of breaking up dense layers that restrict water movement and
root penetration.
summer fallow - The tillage of uncropped land during the summer in order
to control weeds and store moisture in the soil for the growth of a
later crop.
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terrace - An embankment or combination of an embankment and channel
constructed across a slope to control erosion by diverting or storing
surface runoff instead of permitting it to flow uninterrupted down the
slope. Terraces or terrace systems may be classified by their align-
ment, gradient, outlet, and cross-section. Alignment is parallel or
non-parallel. Gradient may be level, uniformly graded, or variably
graded. Grade is often incorporated to permit paralleling the terraces.
Outlets may be soil infiltration only, vegetated waterways, tile out-
lets, or combinations of these. Cross-sections may be narrow base,
broad base, bench, steep backslope, flat channel, or channel.
terrace interval - Distance measured either vertically or horizontally
between corresponding points on two adjacent terraces.
tillage - The operation of implements through the soil to prepare seedbeds
and root beds.
transportation - The movement of detached soil material across the land
surface or through the air. May be accomplished by running water, wind,
or gravity. Soil erosion.
undergrazing - An intensity of grazing in which the forage available for
consumption under a system of conservation pasture management is not
used to best advantage. Contrast with overgrazing.
universal soil loss equation - An equation used for the design of water
erosion control systems: A » RKLSPC wherein A » average annual soil
loss in tons per acre per year; R » rainfall factor; K » soil erodibility
factor; L - length of slope; S « percent of slope; P - conservation
practice factor; and C * cropping and management factor. (T - soil loss
tolerance value that has been assigned each soil, expressed T/A/Year.)
water control (soil and water conservation) - The physical control of
water by such measures as conservation practices on the land, channel
improvements, and installation of structures for water retardation and
sediment detention (does not refer to legal control or water rights
as defined).
weed - A plant out of place.
wheel-track planting - Plowing and planting in separate operations with
the seed planted in the wheel tracks.
windbreak - (1) A living barrier of trees or combination of trees and
shrubs located adjacent to farm or ranch headquarters and designed to
protect the area from cold or hot winds and drifting snow. Also head-
quarters and livestock windbreaks. (2) A narrow barrier of living trees
or combination of trees and shrubs, usually from one to five rows,
established within or around a field for the protection of land and
crops. May also consist of narrow strips of annual crops, such as corn
or sorghum.
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wind erosion - The detachment and transportation of soil by wind.
wind erosion equation - An equation used for the design of wind erosion
control systems. E « f (IKCLV) wherein E * average annual soil loss,
expressed in tons per acre per year; f » a function of; I = soil
erodibility; K * soil ridge roughness; C - climatic factor; L m unsheltered
distance across the field along the wind erosion direction; and V * vege-
tative cover.
wind stripcropping - The production of crops in relatively narrow strips
placed perpendicular to the direction of prevailing winds.
woodland - Any land used primarily for growing trees and shrubs. Woodland
includes, in addition to what is ordinarily termed "forest" or "forest
plantations," shelterbelts, windbreaks, wide hedgerows, containing
woodland species for wildlife food or cover, stream and other banks with
woodland cover, etc. It also includes farmland and other lands on which
woody vegetation is to be established and maintained.
woodland management - The management of woodlands and plantations that
have passed the establishment stage, including all measures designed
to improve the quality and quantity of woodland growing stock and to
maintain litter and herbaceous ground cover for soil, water, and other
resource conservation. Some of these measures are planting, improvement
cutting, thinning, pruning, slash disposal, and protection from fire and
grazing.
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