Soil Erosion: What You Can't See Can Hurt You

By Amy O. Maxwell, Acting Public Affairs Specialist, NRCS

A problem that cannot be ignored. The father of soil conservation, Hugh Hammond Bennett, warned farmers of the evils of soil erosion through his impassioned speeches in the early 1930's. Many of his lectures were delivered at South Carolina's Clemson College where he educated agriculture teachers about erosion. The messages of his lectures still hold true today—essentially that erosion is a major menace on American cropland and must be prevented or treated, before it is too late. The challenge, however, is not in controlling erosion, but in the prevention of erosion. Many conservation practices prevent erosion; however, farmers and landowners often believe that erosion is not a problem until the evidence, such as visibly washed-out areas and roads, surfaces. Often in many cases it is too late, or extremely costly to repair the damage. USDA-NRCS develops comprehensive conservation plans that include practices to prevent soil loss, which are critical in the fight against erosion. Conservation practices assist farmers and landowners in taking action to prevent the harmful effects of soil erosion, including non-point source water pollution which has become a major concern in South Carolina.

The widespread effects. Soil erosion is a naturally occurring process on most lands caused by water and wind. The loss of soil can happen very quickly or over a period of time, going unnoticed, yet causing a serious loss of topsoil. Bennett cautioned farmers about the danger of sheet erosion which he described as "land washing, which removes a thin covering of soil from large areas, often entire fields, more or less uniformly during every rain, producing runoff. The process goes on slowly, so slowly that its effects are frequently unobserved until spots of clay and even rock begin to make their appearance over sloping fields." Jim Wilson, NRCS district conservationist in Calhoun County, SC, confirmed that, "Erosion creates sediment which is the number one pollutant by volume in South Carolina." When sediment reaches watercourses, downstream water quality is reduced, especially by pesticides and fertilizers. These pollutants are often carried along with eroding soil which contaminate water sources and recreational areas. The widespread impact of soil erosion is a major cause for concern and a call to action for the nation's land users.

A long history of fighting soil erosion. Significant achievements in slowing soil erosion have been made since the 1930's. Even before then farmers realized the need to protect the soil. In 1813, Thomas Jefferson wrote about his Albermarle County, Virginia, farm: "Our country is hilly and we have been in the habit of plowing in straight rows, whether up or down hill, in oblique lines, or however they lead, and our soil was all rapidly running into the rivers. We now plow horizontally following the curvature of the hills and hollows on dead level, however crooked the line may be. Every furrow thus acts as a reservoir to receive and retain the water, all of which go to the benefit of the growing plant instead of running off into the streams" (as quoted by H.H. Bennett in his 1932 lecture at Clemson College). This was one of the first recorded accounts of contour farming, which is still used today.

Options for prevention. Managing soil for water and wind erosion can be successfully achieved by maintaining good soil structure, protecting soil surface with vegetative/residue cover, and the use of specialized conservation practices (Stone and Moore "Control of Soil Erosion," 1997). Grassed waterways, terracing, field windbreaks, filter strips, riparian buffer strips, and residue management (no-till) are other practices used to control erosion. USDA offers incentive programs to encourage landowners to develop these conservation practices on their land to prevent erosion and enhance wildlife habitat. The Conservation Reserve Program (CRP) was created under the 1995 Farm Bill and offers per acre payments. Soil conservationists work with landowners on a variety of practices that prevent or reduce erosion. Following is a list of some of these practices and their functions (information from Core 4, Conservation for Agriculture's Future).

Terraces are used to shorten the length of long slopes and serve as small dams to catch water and guide it to an inlet. Terraces also serve as a guide for a contour row pattern in the field and help to improve water and soil quality. Grassed terraces also provide good nesting habitat.

Grassed Waterways are natural drainage ways that are graded and shaped to form a smooth, bowl-shaped channel. Runoff water that flows down the drainage way flows across the grass rather than tearing away soil and forming a larger gully. An outlet is often installed at the base of the waterway for stabilization and prevention of a new gully.

Contour Farming uses a method of tilling or planting on the contour to create hundreds of small dams. These ridges or dams slow water flow and increase infiltration which reduces erosion. During drought periods, contour farming helps conserve moisture for plant development and improves equipment efficiency.

Determining soil erosion. Appropriately applied conservation practices can reduce soil erosion by as much as 50 percent. They contribute to sediment reduction and runoff, increase water infiltration, and promote better water quality.

But how do soil scientists determine the extent of an erosion problem? Believe it or not, an actual equation is used that helps them measure soil erosion. NRCS uses the Universal Soil Loss Equation (USLE) to calculate sheet and rill soil loss from water and the Wind Erosion Equation to estimate soil loss rates from wind. The USLE considers soil loss per unit area, rainfall factor, soil erodibility factor, slope length, slope degree, crop practice, and conservation practices. These elements determine the average annual soil loss from erosion. The maximum amount of acceptable soil loss per acre per year is five tons. 

But, even if the equation indicates that soil loss is minimal, landowners should still practice preventive soil erosion measures. A combination of conservation practices provides a sound resource management plan which protects the soil and water resources.

The effects of large-scale farming. In Calhoun County, steep slopes contribute to erosion that is caused mainly by water. Also, the high erodibility of the soils means that farmers need to implement preventative conservation measures. Wilson points out that today's farms are bigger and so is the equipment. He emphasized that the demand for increased production has prompted landowners to clear larger tracts and marginal soils. "What most people don't realize is that expanded land clearing also removes existing hedgerows that reduce erosion and provide valuable wildlife habitat," he added.

The urgent need for prevention. With the addition of a quarter of a million people each day, the world population's food demand is increasing. Conservationists and farmers throughout the country and in South Carolina have made significant achievements in preventing soil erosion. However, work still needs to be done, including an effort to increase awareness of the effects of soil erosion.

The bottom line—landusers must counteract increased land use with proper conservation measures that will protect the land from the harmful effects of wind and water erosion. If you would like more information on how you can help fight erosion on agricultural lands, contact your local NRCS office.

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