CONTROLLING SOIL EROSION
WITH AGRONOMIC PRACTICES
Department of Agronomy
Soil is the basic resource of all farming
operations. Field layout, cropping systems, and, ultimately, livestock
enterprises relate directly to the nature and characteristics of the soil.
Although lime and fertilizer treatments can adequately supply plant nutrients,
other soil characteristics such as organic matter content, soil texture
and soil structure are difficult or practically impossible to modify. Because
of this, and the fact that it takes hundreds of years for even an inch
of soil to form, soil is considered a fixed, non-replaceable resource.
Topsoil losses from erosion-prone fields can reduce soil productivity significantly.
To maximize economic returns, it is necessary to evaluate each land tract
to determine its erosion potential and then develop a cropping system which
will enable that tract to be used to its maximum intensity without undue
Much of Kentucky's erosion-prone land
can be protected adequately from erosion by using certain agronomic practices
suitable to the particular field. These practices are listed below.
•contour plowing and planting
•use of cover crops
•use of perennial sod crops
•adequate liming and fertilization
•use of rotations
•establishment and maintenance of sod
All these practices are useful in erosion
control. Each field should be evaluated to determine which of these practices,
or which combinations, are appropriate for use in that field. Although
it may be necessary to construct erosion control structures in some specific
situations, using these agronomic practices is preferable whenever possible
because they cost less and also tend to stop erosion at its source.
Land is often classified for agricultural
purposes by the intensity with which it can be used for crop production
and by the nature of the limiting problem. Class l land has no limitations
for agricultural use, while Class VII land is severely limited. If the
limitation for use is because of erosion hazard (slope), a subscript "e"
is included with the land class. Table 1 outlines this classification system
for land with an erosion hazard and relates it to steepness of slope.
The nature and degree of erosion risk
will largely determine how the various agronomic practices should be used.
The following discussion relates these practices to the production systems
appropriate for the various land classes.
Steep and Strongly Sloping Fields (20 to 50 percent slope)
The steeper land classes (VIe and VIIe)
with slopes from 20 to 50 percent should be kept in a sod-forming crop
or forest. Although slopes of 30 to 50 percent should be in forest, there
are sizeable acreages of this steep land that are cleared in eastern Kentucky
and the Eden Hills area and smaller acreages that are cleared in other
areas of the state. Such steep slopes don't lend themselves to mechanized
equipment and are difficult to lime, fertilize and seed to maintain good
soil cover. Carrying capacity for grazing cattle is usually low.
Slopes of 20 to 30 percent should be
maintained in forage crops with livestock grazing the forage produced.
Returns per acre may not be as high as with row crops, but using such land
for forages is the best alternative. Much of this steeper land can produce
good yields of livestock products with proper liming, fertilizing and grazing
Moderately Sloping Fields (12 to 20 percent slope)
Production of row crops on such fields
(Class IVe and VIe) requires a high degree of management to prevent excessive
erosion. A rotation should be established that will allow the row crop
to be no-till planted following two or more years of permanent cover. Growing
the row crop and the permanent cover crop in parallel strips and then rotating
between strips will provide extra erosion protection. If the row crop is
to be kept on the same field or strip for more than one year, a winter
cover crop should be seeded following the row crop. Examples of useful
rotations for such slopes in Kentucky would be either corn-red clover or
corn-alfalfa with the corn being no-till planted whenever possible.
Sloping Fields (6 to 12 percent slope)
On Class IIIe or IVe land with 6 to 12 percent slope where Johsongrass
is under control, intensive production of row crops is possible if they
are no-till planted and winter cover crops are used. Corn, soybeans or
grain sorghum may be no-till planted into killed cover crops or small grain
If such fields are very large and have
long slopes, further reduction of erosion can be obtained by strip cropping.
In this situation, strips of equal width are laid off across the slope.
It would be ideal for these to be on the contour, but because of problems
from point-rows, contour strips are not always feasible. Strip width depends
on how steep and long the slopes are. On fields of near 6 percent slope,
the strips could be wider than those on steeper fields. Strips should always
be in multiples of the width of the planter equipment.
Gently Sloping Fields (2 to 6 percent slope)
Land (Class IIe or IIIe) with a 2 to
6 percent slope will be less likely to erode but will still need crop residue
management and cover crops on long slopes to prevent excessive erosion
under intensive row crop production. Strip cropping works well on those
fields with long slopes of 3 percent or greater. This would make erosion
control easier without sacrificing yields while adding only minimal expense.
Nearly Level Fields (0 to 2 percent slope)
Soils with a 0 to 2 percent slope (Class
I land) have little erosion hazard and can be continuously row cropped.
lt would still be wise to use crop residue management on these areas.
There are many small Kentucky fields
on nearly level, narrow bottoms and basins at the foot of hills that are
subject to slopewash from adjacent hillsides. A diversion terrace built
at the foot of these slopes will move water away from the level land to
waterways or streams, preventing erosion, silting or gullies. On some such
fields, a grass strip at the base of these slopes may be all that is needed
to slow the water and allow it to spread over the level area with little
Table 1.-Land classifications related to steepness of slope.
1Severely eroded soils or those with potentially severe
problems are often classified into the next higher land class than the
slopes shown above. For example, a severely eroded soil on 2 to 6 percent
slopes may be classified as IIIe instead of IIe.
||Risk of Erosion Damage
||little, if any
Using sod waterways in natural drainage
ways on sloping fields will greatly aid in controlling gulley erosion.
Although it may sometimes be necessary to reshape a drainage way before
seeding it to grass, waterways often can be established with conventional
farm tillage tools. In cases where a field already in a sod crop is being
brought into row crop production, it is necessary only to flag off the
desired waterway and then leave it uncultivated and unsprayed. Be sure
to leave the waterways wide enough to run mower equipment over them. This
will also assure that they have the needed water-carrying capacity. Mowing
keeps the waterways attractive, and the grass produced on them can often
be harvested for hay. Waterways will periodically need fertilization in
order to maintain a vigorous grass cover that can carry large amounts of
water without washing out.
Farmers cropping large acreages for
grain often find it necessary to do some of their primary tillage in the
fall. This greatly increases the erosion risk on sloping fields. To reduce
such risks from fall tillage, some form of residue management should be
used, and tillage should be performed along the slope contours. If deep
tillage is necessary, a chisel plow is preferred since it loosens the soil
to a depth of several inches, yet doesn't leave a bare surface by burying
all the surface residues. This is particularly important when fall plowing
soybean fields which will be fallowed overwinter. If deep tillage isn't
necessary, a heavy disk is also preferable to a moldboard plow since it
too will leave some surface residues to provide some overwinter erosion
protection. If a moldboard plow is used in the fall for fields to be fallowed
overwinter, the surface should be left rough and undisturbed until spring