Soil erosion on agricultural land is a significant problem in Indiana. Not only is the productive potential on farmland decreased, but nutrient- and pesticide-containing sediment--the end product of erosion--is a major source of water pollution. Among the difficulties caused by sedimentation are: the silting-in of reservoirs, higher costs for domestic or industrial water treatment, restricted stream flow that increases flood hazards, and changes in or elimination of fish populations.
The key to minimizing soil erosion is the farmer himself. Ultimately, he is the one who must reduce the level at which erosion sediments are dislodged from his cropland. This publication discusses the erosion process, its effects on crop yields, and the practices that you, the farmer, can implement to limit or contain soil movement from your land.
To effectively control soil erosion, it's important first to understand the erosion process and what characterizes the various phases in that process.
A soil particle is an individual mineral grain. Soil particles are classified according to size--sand (the largest), silt and clay (the smallest). A soil aggregate is a grouping of individual soil particles and is considered the basic structural unit of soil. When aggregates begin to break down, the soil is in danger of eroding, which proceeds in the following sequence unless interrupted by erosion control measures.
The first step in the erosion process is splash erosion. Raindrops strike the earth with considerable energy. Some of the water infiltrates into the soil, while some stays on the surface, saturating the soil and weakening natural soil aggregates so that the impact of subsequent raindrops breaks them down. Erosion then occurs as dislodged soil particles travel with runoff water. To see the explosive dislodging effect of rain on soil, just look how far up on a garden stake or building foundation soil material is deposited after a rain.
Splashing can start the movement of many tons of fertile topsoil off a slope and into streams and lakes. Therefore, limiting the breakdown of soil aggregates or containing their movement at this stage is important. Soil breakdown can be considerably reduced: (1) if the soil is covered by growing plants or plant residue, (2) if the aggregation of soil particles i5 strong because of naturally high organic matter content, or (3) by residual effects of sod-based rotations and good crop residue management.
Sheet erosion occurs when rainfall runoff removes the soil surface uniformly over an area. This is difficult to see, because the water, in this case, doesn't cut deep channels when carrying away soil particles.
Sheet erosion is more common on short slopes, where the speed and carrying capacity of the runoff water are not as great as on longer and/or steeper slopes. The major `symptom' of sheet erosion is a deposit of sediment at the base of a slope.
Continued failure to protect the soil at this stage eventually results in exposure of the subsoil during plowing. This usually means reduced productivity, particularly when the subsoil is not a good medium for plant growth. And if the exposed subsoil happens to be a tight clay, productivity will likely be severely reduced.
Rill erosion develops when runoff water begins to cut definite channels. These become wider and deeper as the velocity of runoff increases. Rill erosion is responsible for large amounts of soil 055 and, thus, for serious reduction in productivity. While the rills are still only a few inches. deep, they can usually be obliterated by normal tillage.
Unchecked rill erosion can soon lead to gully erosion. A gully differs from a rill in that it is large enough to interfere with farm implement maneuvering and cannot be masked by normal tillage operations. Tremendous losses of topsoil and subsoil can occur as gullies develop, resulting in severe productivity losses.
Stream bank erosion normally begins along a permanent stream when flowing water undercuts the banks, causing soil material to fall into the channel. Where the stream curves, its outer banks are the most susceptible. Channel erosion occurs when the channel grade becomes steeper. thus causing the more rapidly flowing water to erode the channel bed.
If uncorrected, the erosion of farmland leads to productivity losses that eventually have economic consequences for everyone, not just the farmer. Table 1 shows the relationship between erosion and yield potential to be a significant one. And these yield loss figures may be low, because they don't take into account probable increased herbicide injury. While the direct causes of yield reduction relative to erosion are many, the two major ones are topsoil loss and fertility loss.
Yield loss from soil's predicted yield potential when erosion is- Moderate Severe (mixture of (topsoil Dominant soil texture top-/subsoil) eroded away) -------------------------------------------------------------- Sand, loamy sand, sandy loam 0 bu./a. -5 bu./a. Silt loam silty clay loam, -5 bu/a. -10 bu./a. loam, clay loam Clay 40-45% -5 bu./a. -15 bu./a. Clay> 45% or fragipan -10 bu./a. -20 bu./a. -------------------------------------------------------------
Topsoil is a fragile `rind' on the earth's surface that contains most of the nutrients needed for crop growth. Topsoil erosion takes away not only soil particles and organic matter, but also soil nutrients, resulting in reduced yield potential.
Researchers in Canada have illustrated the extent to which 1,055 of topsoil affects yield. When they removed several inches of soil with a scraper. yields for the subsequent barley crop dropped by 86 percent and for alfalfa by 31 percent!
Where topsoil erosion has occurred, crops must be grown in the subsoil material, which has less total available moisture (perhaps the most critical requirement for crop growth). This decreased moisture availability for the whole soil is due to the subsoil's higher clay content, which holds water more tightly so less is obtainable by plants. Exposure of subsoil also makes the plow layer more susceptible to subsurface compaction, resulting in reduced plant rooting and poor stands.
Topsoil erosion also means loss of organic matter. This leads to poorer soil structure, causing soil to crust easily, making it more difficult to till, and further reducing the rate at which soil receives moisture and the amount of moisture it can store.
Productivity losses are significantly related to fertility loss - i.e., loss in the soil's ability to provide sufficient nutrients for sustained plant growth.
Nutrients added to cropland over many years remain largely in the topsoil, whereas subsoil is much lower in nutrient content. For example, data from Purdue University's Soil Characterization Laboratory shows that, in some soils, there may be as much as 97 pounds of phosphorous per acre in the topsoil and as little as 4 pounds in the subsoil.
Much of the soil eroded from farmland becomes sediment pollution that means problems elsewhere. Although erosion from urban areas also contributes to sediment load in streams, an Illinois study has shown that, because of the amount of land used for agriculture, farmland is by far the greatest contributor to sediment pollution.
The study, which sought to determine sediment sources, found that 87 percent was of agricultural origin, compared to 13 percent from urban sources. While the per-acre contribution by urban areas may be much higher, agriculture is clearly responsible for the greatest total amount of sediment, since significantly more land area is agricultural.
The study also revealed that, on 40 percent of all rural land in Illinois, soil loss exceeded 3-5 tons per acre. This 3-5 ton figure is what the U.S. Soil Conservation Service feels is the `permissible' amount of Soil that can be lost without reducing productivity. Considering that much of Illinois land is nearly level, the disturbing fact is that erosion can be a significant problem on even slightly sloping land; thus. erosion control practices deserve attention on almost every farm. The situation in Indiana is similar to that in Illinois.
There are a number of proven methods for controlling erosion to a level where the basic soil resource is not depleted. Soil conservation practices can be divided into two general types--those related to soil management and those related to specially built structures.
Soil management for conservation includes several commonly-accepted practices that can improve yield or profit while reducing soil erosion.
Conservation tillage. Although conservation tillage can take many forms, all of them either leave plant residue on the ground's surface or leave most of the surface rough (cloddy) to reduce erosion.
Residue left on the surface is effective because it protects the soil from rainfall impact, reduces soil detachment and prevents surface sealing so more rainfall can penetrate the soil. Residue also serves as a barrier to runoff, reducing its velocity and thus its soil transport capacity.
A rough, cloddy surface is also an effective runoff barrier. Again, a greater amount of rainfall enters the soil, because there is less surface sealing and more surface storage.
Chisel plowing, till planting and discing increase surface roughness while leaving crop residues on or near the surface. With narrow strip tillage, such as no-till, planting is done in virtually undisturbed residue from the previous crop or in a meadow or cover crop that has been killed with a contact herbicide.
Indiana soils vary in their suitability to these types of tillage systems. Generally, some form of conservation tillage is well adapted to all sloping, erosive soils in the state.
Other soil management practices. Several other practices help slow runoff and allow time for settling of suspended sediment from runoff water.
On slopes in the 2-6 percent range, contouring has been shown to cut soil erosion in half. Contour strip cropping (where strips of small grain or row crops are alternated with strips of sod on the contour) may be even twice as effective in reducing soil losses as simply contouring; this system fits well on uniform sloping areas where sod crops are to be planted. Grassed waterways provide another method of preventing major soil losses.
Spring tillage, rather than fall tillage, on sloping land allows crop residues to remain on the soil surface during the winter, protecting it from serious water erosion. If fall tillage is practiced, fall moldboard plowing should not be done on sloping land without water control by terracing or other structural measures.
In rolling terrain, rotation of row crops with small grains and hay is a highly valuable soil conservation practice. Rotation is still one of the best means of managing land safely, particularly if a forage (sod) crop is included, since hardly any erosion occurs during the year the field is in sod.
A rotation of corn and soybeans, on the other hand, can lead to more serious erosion than growing continuous corn. The reasons are that (1) soybeans produce little protective residue and what is produced decomposes very rapidly, and (2) soybean land is loose and easily transported by runoff water. A good means of controlling erosion after soybeans is a winter cover crop seeded into the soybean residue.
Another soil management practice is to use sod field borders, which stabilize areas next to drainageways. These are especially helpful where there are numerous natural or artificial drainageways in a field.
An alternate approach to conserving soil is that of structure construction and improvement. This includes improving terraces where suitable.
One recent innovation is parallel tile outlet (PTO) terraces. These structures are built in parallel to avoid point rows and to eliminate the need for sod waterways by removing the water collected in channels through underground tile systems. Terrace-tile systems are well adapted to deep soils on somewhat uniform slopes.
Other structural measures include: diversions designed to divert upland water away from bottomland, grade and channel stabilization structures, and sediment basins and ponds. Structural measures are usually more effective when used in combination with soil management practices.
The economic returns of erosion control practices will vary. For instance, a particular conservation tillage system may be as good a method from a yield and profit standpoint as plow-disc culture -- or even better. But remember, conservation tillage requires more careful management than conventional tillage.
With other erosion control practices, however, there are no significant short-term economic returns to the individual farmer. At this point, one must consider the larger view of the nation's future welfare.
Certain expensive structures must be amortized over many years; and some may never entirely pay for themselves, if the farmer must bear the entire cost. They nonetheless are apt to be critical to continued cropland productivity and/or sediment pollution control, and therefore must be considered in light of the community's, state's or nation's welfare, not just the farmer's.
If land needing erosion control is to be used more intensively, conservation measures become more important. Cost sharing, such as through the USDAs Agricultural Conservation Program, provides a major incentive for farmers to install these needed measures.
Control of soil erosion is needed to protect Indiana's productive crop land from further damage and to prevent pollution of our streams and lakes. Some agricultural conservation practices, such as certain tillage methods, are relatively low cost to the farmer and can be adopted without great difficulty. Others, such as terracing, are costly and may take some years to install and pay for completely.
Erosion control is a continuing effort. And those steps that conserve cropland soil must be taken to maintain its productive potential now and in future generations.
For additional information, contact your county Extension office, or write the Agricultural Communication Service, Media Distribution Center, 301 South Second Street, Lafayette, IN 47905-1092, for the following related publications:
AY-215 Types and Uses of Soils Information in Indiana
AY-221 Soil Compaction in Indiana
AY-230 Value of Crop Rotation Under Various Tillage Systems
Cooperative Extension work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture cooperating: H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an equal opportunity/equal access institution.