The four most important factors affecting erosion are soil texture and structure, roughness of the soil surface, slope steepness and length, and soil cover. There are several passive and active methods of erosion control that involve these four factors. Wind erosion, for example, is controlled by creating windbreaks, rows of trees or shrubs that shorten a field and can reduce the wind velocity by about 50 percent. Tillage perpendicular to the wind direction is also a beneficial practice, as is keeping the soil covered by plant residue as much as possible.
Highly erosive, steeply sloped land in the United States can be protected by placing it in the government-sponsored Conservation Reserve Program. The program provides incentives and assistance to farmers and ranchers for establishing conservation practices that have a beneficial effect on resources both on and off the farm. It encourages farmers to plant grass and trees to cover land that is subject to wind and water erosion.
Additional ways to prevent water erosion include planting permanent grass waterways in areas of cropland that are prone to water flow. Likewise, grass filter strips can be planted between cropland
Image Not Available and adjacent waterways to impede the velocity of surface runoff and cause suspended soil particles to sediment and infiltrate before they can become contaminants. In this way, vegetation can improve water quality or provide food and habitat for wildlife. Tillage practices are also beneficial in combating water erosion. Tillage can be done along the contour of slopes. Long slopes can be shortened by terracing, which reduces the slope steepness.
Conservation tillage practices, such as minimal tillage and no-tillage, are being widely adapted by farmers as a simple means of erosion control. As the names imply, these are tillage practices in which as little disruption of the soil as possible occurs and in which any crop residue remaining after harvest is left on the soil surface to protect the soil from the impact of rain and wind. The surface residue also effectively impedes water flow, which causes less suspension of soil particles. Because the soil is not disturbed, practices such as no-tillage promote rapid water infiltration, which also reduces surface runoff. No-tillage is rapidly becoming the predominant tillage practice in southeastern states such as Kentucky and Tennessee, where high rainfall and erodible soils are found.
Mark S. Coyne
See also: Agriculture: modern problems; Desertification; Nutrients; Soil degradation; Soil saliniza-tion.
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