Wind Erosion And Its Control

G1537
Wind Erosion And Its Control
Drew J. Lyon, Extension Dryland Crops Specialist, and John A. Smith, Extension Machinery Systems Engineer
as 6 mph one foot above the soil surface is capable of
This NebGuide discusses how wind erosion
starting soil movement under highly erodible field condi-
occurs and presents methods for reducing wind
tions. Erodible field conditions consist of an unprotected
erosion on land devoted to crop production.
soil surface that is smooth, bare, loose, dry, and finely
granulated (Figure 1). If a 20 mph wind increases to 30 mph,
Wind erosion is widespread on agricultural land in the
the rate of erosion will triple. Any erosion control system
Great Plains, particularly in the semi-arid regions. Wind
that increases the minimum wind speed at which soil ero-
erosion physically removes the most fertile part of the soil
sion begins or reduces wind speed at the soil surface will
(organic matter, clay, and silt) and lowers soil productivity.
effectively reduce soil erosion.
This loss in productivity increases the costs of producing
The smallest soil particles, less than 0.004 inch in
crops. Blowing soil can reduce seedling survival and growth,
diameter, are most easily lifted from the soil surface and
depress crop yields, and increase the susceptibility of
suspended in the air stream where they may be carried many
plants to certain types of stress, including diseases.
miles before they fall. Larger soil particles, up to 0.02 inch
Some soil from eroded land enters suspension and
in diameter, are dislodged and propelled in a bouncing or
becomes part of the atmospheric dust load. Dust obscures
jumping manner across the soil surface. As they bounce,
visibility and pollutes the air, fills road ditches and impacts
the force of their impact dislodges other particles from the
water quality, causes automobile accidents, fouls machin-
soil surface and damages or destroys living plants. The
ery, and imperils animal and human health. Wind erosion
bouncing soil particles are responsible for setting in motion
is a threat to the sustainability of the land as well as the
other soil particles in an avalanching effect as erosion
viability and quality of life for rural and urban communities.
moves downwind. Still larger particles, 0.02-0.04 inch in
A strong, turbulent wind, coupled with highly erodible
diameter, move by rolling on the soil surface.
field conditions, causes wind erosion. A wind speed as low
Reducing Wind Erosion
Many practices can be used to reduce wind erosion,
but all are basically directed at accomplishing one or more
of the following:
• Reduce wind velocity at the soil surface. This is done
with windbreaks, crop residues, cover crops, surface
roughness, and strip cropping.
• Trap soil particles. This is accomplished by main-
taining crop residues on the soil surface and/or by
ridging or roughening the soil surface – all to trap
moving soil particles.
• Increase size of soil aggregates. This is done 1) by
using crop rotations that include grasses and le-
Figure 1. Blowing soil fills seed furrows and partially buries
gumes, 2) by growing high-residue crops and return-
small wheat plants in the spring, resulting in increased
ing crop residues to the soil, 3) by applying manure,
plant stress that weakens the plants and makes them
more susceptible to further damage by disease and
and 4) by using emergency tillage, which can create
other environmental stresses.
C-7

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stable clods on the soil surface if soil moisture and
texture allow (see NebGuide G75-282, “Emergency
1.0
Wind Erosion Control”). Increasing the size of
0.9
aggregates means that it takes a stronger wind to
0.8
move the soil.
0.7
A protective cover of living vegetation or crop resi-
0.6
dues on the surface is the simplest and surest way to reduce
0.5
wind erosion, except during periods of prolonged drought,
0.4
when it may be difficult to produce and maintain crop
0.3
residues. Crop residues or growing vegetation reduce wind
Soil Loss Ratio 0.2
speed at the soil surface and prevent much of the wind force
from contacting soil particles. Vegetative matter on the
0.1
surface also traps moving soil particles and reduces the
0.0
avalanching effect. The amount of crop residue required to
0.02
0.04
0.06
0.08
lessen wind erosion varies with residue type, height, posi-
Plant silhouette area ÷ Soil surface area
tion in relation to wind direction, and soil type.
0
20
40
60
80
100
120
140
Conservation tillage reduces wind erosion by leaving
crop residues on the soil surface and reducing soil pulveri-
Plant silhouette area (in2) from 1600 (in2)
zation, which may occur if soils are tilled when dry. Each
Figure 2. Relationship between silhouette area and soil loss
tillage operation reduces surface residue quantity and dries
ratio. The silhouette area is calculated by multiplying
stalk height in inches by stalk diameter in inches by the
the soil, making the soil more susceptible to wind erosion.
number of stalks per 1600 square inches (approximately
If soil moisture is adequate, tillage may bring erosion-
equivalent to 1 square meter or 11.1 square feet) of soil
resisting clods to the soil surface, but generally, this is only
surface area. The smaller the soil loss ratio, the smaller
the calculated soil loss will be.
a short-term solution.
is used in Figure 2 to determine their effect on soil erosion.
Comparing Crop Residue Effectiveness
The greater the plant silhouette area, the greater the reduc-
tion in wind speed at the soil surface, and consequently the
The effect of different vegetative covers on wind
greater the reduction in soil loss. The height is usually
erosion can be compared by converting to the percent of
determined by the harvesting process, the diameter by the
the soil surface that is covered. Covering 30 percent of the
crop type, and the number of stalks by the plant population.
soil surface will reduce soil losses by 70 percent compared
Table II lists examples of plant silhouette areas for
to the soil loss for a bare soil (Table I). The percentage of
several crops grown under rainfed conditions in western
the soil surface covered with crop residues can be visually
Nebraska. The soil loss ratio given in Table II is a multiplier
estimated or measured (see NebGuide G95-1132, “Estimat-
used in the Revised Wind Erosion Equation to compute soil
ing Percent Residue Cover”). The effect of surface cover on
loss. The smaller the soil loss ratio, the smaller the calcu-
soil erosion is the same regardless of residue type.
Table II. Examples of silhouette areas for several dryland crops
Table I.
Effect of nonerodible soil cover on relative soil loss
grown in western Nebraska.
reduction compared to bare soil.
Stalk
Stalk
Stalk
Silhouette Soil loss
Soil cover (%)
Relative soil loss reduction (%)
Crop
height diameter
no.a
area
ratio
0
0
---- inches ----
no./
in.2/
10
3 5
1600 in.2
1600 in.2
20
6 0
30
7 0
Winter wheat
1 0
0.12
3 0 0
3 6 0
0.01
40
8 0
Winter wheat
1 0
0.12
2 0 0
2 4 0
0.02
50
8 5
Proso millet
6
0.16
1 0 0
96
0.11
60
9 0
Corn
2 4
0.75
3.5
63
0.19
70
9 3
Sunflower (short)
1 2
0.85
3.7
38
0.30
80
9 6
Sunflower (tall)
2 4
0.85
3.7
75
0.15
90
9 8
aNumber of stalks in 1600 square inches, which is approximately equivalent
100
9 9
to 1 square meter or 11.1 square feet.
Standing residues are more effective at slowing wind
lated soil loss will be. For example, if stalk diameter and stalk
speed at the soil surface than the same quantity of residue
number per square yard are kept the same, the silhouette
flat on the soil surface. The higher the standing residues
area for sunflower can be doubled by cutting sunflower
are, the more they reduce soil movement by wind. To
stalks at a height of 24 inches rather than 12 inches (see
determine the effect of standing stubble on soil erosion, the
Table II). The result of the higher cutting height is a soil loss
height, diameter, and number of stalks in a given area (for
ratio that is half the value of the shorter cutting height, and
example, per square yard) must be estimated. The product
therefore, one could expect half the soil loss from wind
of these three values gives the plant silhouette area, which
erosion. The examples given in Table II should be used to

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get a feel for how plant silhouette area is influenced by
the clod is formed, soil density, soil texture, particle size
changes in crop type, cutting height, and stalk density, and
distribution, and microbial activity. Coarse-textured soils
not as absolute values representative of a specific crop.
such as sandy loams, loamy sands, and sands do not
The effect of different vegetative covers on wind
readily form stable clods due to their low clay and organic
erosion also may be compared by converting the vegetative
matter content. These soils need to be moist before tillage
covers to a small grain equivalent (SGe), which is a refer-
to successfully produce even fragile clods. Soils that pro-
ence condition defined as 10-inch long stalks of small grain
duce the most stable clods are silt loams, clay loams and
parallel to the wind and lying flat in rows spaced 10 inches
silty clay loams. Clods are broken down by raindrop impact,
apart perpendicular to the wind. Several crop residues have
weathering, tillage (especially when soils are dry), equip-
been tested in a wind tunnel to determine their SGes, while
ment traffic, and abrasion by moving soil particles.
other values have been determined by regression analyses
A rough surface formed by tillage may be very effective
and estimations. According to charts from the Natural
in temporarily reducing wind erosion. Ridges and depres-
Resources Conservation Service (NRCS), 1,000 lb/ac of flat
sions absorb and deflect part of the wind energy and trap
corn stalks are required to provide as much protection from
drifting soil particles. Too much surface roughness, how-
wind erosion as 200 lb/ac of flat small grain residues.
ever, causes turbulence that may accelerate soil particle
Therefore, 1,000 lb/ac of flat corn stalks has an SGe of 200
movement. Table IV indicates effective ridge heights for
lb/ac (Table III). Alternately, 1,000 lb/ac of standing winter
various ridge spacings, assuming wind direction is per-
wheat stubble, 10 inches high, in 10-inch rows perpendicu-
pendicular to the ridges. Generally, ridges 4 to 8 inches in
lar to the wind, has an SGe of 3,500 lb/ac. The NRCS may
height are effective in reducing wind erosion across the
discontinue use of SGe, but currently it is how they link an
most commonly used ridge spacings. Remember, however,
amount of residue with a corresponding reduction in wind
that the smaller ridges are more quickly destroyed by
erosion. If SGe use is discontinued, the concepts of ground
rainfall.
cover and plant silhouette area will likely replace it.
Table IV.
Effective (?) ridge heights for various ridge spacings,
Table III.
Small grain equivalents (SGe) for 1,000 lb/ac of vari-
assuming wind direction is perpendicular to the ridges.
ous vegetative covers.a Amended from 1988 Natural
Resources Conservation Service National Agronomy
Ridge spacing, feet
Manual.
Ridge height, inches
1
2
3
4
5
6
Vegetative cover
Small grain equivalents
1,000 lb/ac
lb/ac
2
?
Standing winter wheat stubble
4
?
?
?
?
?
(10 inches high, in 10-inch rows
6
?
?
?
?
?
perpendicular to wind)
3,500
8
?
?
?
?
Flat winter wheat stubble
1 0
?
?
(10 inches long, randomly distributed)
1,600
Growing small grain, flat surface
2,000
Flat corn stalks
200
Practical Suggestions for Reducing Wind Erosion
Standing millet stubble
1,700
Standing grain sorghum residue
1,300
Flat grain sorghum stalks
350
Keeping a protective cover of vegetative residues or
Standing alfalfa residue, stalks only
2,900
growing crops on the soil surface is the simplest and surest
Dry bean and soybean (random flat residue)
600
way to reduce both wind and water erosion. To maintain
Standing sunflower residue
(17 inches high, 30-inch rows
residue cover, many growers have used herbicides to
perpendicular to wind)
225
replace one or more tillage operations. The need for tillage
Properly grazed western wheatgrass,
is also reduced when straw and chaff are uniformly spread
4 inches high
4,800
behind the combine. Piles of straw, however, are difficult to
aNatural Resources Conservation Service may discontinue use of SGe, but
plant through and may require extra tillage operations to
SGe is currently the method used to link the amount of residue with a
destroy or spread the crop residues.
corresponding reduction in wind erosion.
Leaving taller residues at harvest is also effective at
Soil Differences and Field Conditions
reducing wind speeds near the soil surface and reducing
soil erosion. In small grains, a stripper header can be used
A coarse-textured soil requires more crop residues to
to leave a taller stubble that does an excellent job of
protect it from wind erosion than a fine-textured soil.
trapping snow for additional soil water recharge as well as
Coarse-textured soils may be high in calcium carbonate and
reducing soil loss from wind erosion; however, when using
low in silt, clay, and organic matter, which results in a high
a stripper header, be sure to select small grain varieties with
wind erodible fraction, fragile clods, and a low resistance to
strong straw or much of the residue may fall over with the
wind erosion. Stable soil clods help reduce wind erosion.
first wet snowfall (Figure 3).
Soil clods formed by tillage should be large enough to resist
Another means of increasing silhouette area is to
the erosive force of the wind and protect smaller material.
increase the number of stalks in a given area. Be careful not
Clod stability depends on soil moisture content at the time
to increase plant density too much or crop performance may

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Figure 3. This wheat field south of Sidney, Nebraska was har-
Figure 4. Carl Mortensen, Jr., has found that stripcropping
vested with a Shelborne Reynolds Combine Stripper
reduces wind erosion and winterkill problems on his
Header. The use of a stripper header for wheat harvest
Kimball County farm. Soil type is one factor that
can leave a tall wheat stubble that provides excellent
determines the width of strips. Strips should be
protection against wind erosion. Additionally, a taller
arranged perpendicular to the prevailing wind direc-
stubble has been found to decrease soil water loss
tion.
through evaporation, reduce weed infestations, and
catch and retain more wind-driven snow in fields where
the extra moisture can significantly increase the yield
of the following crop.
suffer. For example, planting rainfed sunflower at too high
establishment of a cover crop, producers should consider
a population for a given site may result in weakened stalks
increasing surface roughness with tillage or by applying
that break more easily, resulting in a shorter stalk height and
manure or crop residues.
reduced silhouette area. Despite their smaller stalk diam-
Stripcropping can help control soil erosion by reduc-
eter, small grains usually do a better job of reducing wind
ing soil avalanching (Figure 4). The rate of soil avalanch-
erosion than crops like corn or sunflower because they
ing varies directly with the erodibility of the soil and the
have many more stalks per given area (Table II).
width of the eroding field. Soil type is one factor that
Irrigated crops like sugarbeet and dry bean leave little
determines the width of strips. Strips should be arranged
residue cover. A cover crop such as winter wheat or winter
perpendicular to the prevailing wind direction. Visit your
rye may be planted after dry bean to provide soil cover, but
local USDA-NRCS office for specific information on using
the crop must be planted early enough (by mid-September)
stripcropping on your farm.
to allow sufficient establishment of the cover crop to
prevent soil blowing during the winter and early spring. To
Acknowledgments
increase the odds of success with a fall cover crop, growers
may want to consider planting a short season dry bean
The authors acknowledge the contributions made to
variety in late May to help assure an early harvest. Irriga-
this publication by Dr. Donald W. Fryrear, former USDA-
tion before planting the cover crop should be considered
ARS scientist, Big Spring, Texas. Dr. Fryrear spent many
if soil conditions are extremely dry in order to ensure
years studying wind erosion in the Great Plains and sup-
consistent and uniform seeding depth and rapid crop emer-
plied much of the information on silhouette area used in this
gence. The cover crop rows should be planted perpendicu-
publication.
lar to the prevailing wind direction, which is usually from
An earlier version of this material was published in
the northwest. If using a disk drill, row spacings should be
Conservation Tillage Systems and Management, Second
narrow (6 to 8 inches). Wider row spacings are acceptable
Edition, MidWest Plan Service, Ames, Iowa; 2000. This is
if a hoe drill is used and ridges are formed. If crops are
used with permission.
harvested too late in the season to allow for adequate
File under:
SOIL RESOURCE MANAGEMENT
C-7, Conservation
Issued May 2004, 2,000
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© 2005, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension. All rights reserved.

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