Erosion of Soils
Soil erosion is the removal of the most fertile topsoil by the action of running water or wind. Another factor which enhances erosion of soil is the overgrazing of livestock which reduces grasses. Grass holds soil in place. This loss of soil is difficult to replace. According to Science Daily Magazine, the soil is being swept and washed away 10 to 40 times faster than it is being replenished around the globe. The loss of topsoil reduces soil fertility and crop production. Thus, soil erosion is detrimental for the environment and economy.
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Soil Erosion by Water
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Rainwater causes the erosion of soil. Other forms of soil erosion caused by rainfall are rill erosion and gully erosion. Running water on sloping fields causes rill erosion. Gully erosion occurs when water flows in narrow channels after heavy rains.
Soil Erosion by Wind
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Wind erosion is caused by high velocity wind. When soil devoid of vegetation is exposed to wind, wind's velocity overcomes the binding forces of soil and it moves the upper layer to other places.
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The Problem
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Soil formation is a very time-consuming process. Therefore, the renewal process of most soils is not complete while further erosion continues to degrade the soil. According to Spaulding Namowitz in "Heath Earth Science," topsoil is renewed at a rate of a few inches every thousand years, whereas the erosion rate in many areas is a few inches every decade. Soil erosion needs to be controlled to retain the productivity of the soil.
Effects
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The erosion of topsoil hampers crop yields. According to the U.S. Department of Agriculture, soil erosion caused productivity losses in cropland and pastureland in the United States of approximately $27 billion. As of August 1998, worldwide, erosion-caused damages are valued at $400 billion per year.
Ways to Prevent Soil Erosion
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A number of methods of soil conservation exist. The first method is the planting of windbreaks (belts of trees along the edges of fields). These trees slow the wind and reduce soil erosion from wind. Windbreaks are beneficial on level plains where strong winds blow at about all times.
The second method of soil conservation is contour farming. Crops are planted in rows parallel to land contours, instead of plowing up and down a hillslope. This prevents water from rapidly flowing downhill and carrying soil with it.
Strip cropping is the method of reducing soil erosion where a crop that leaves bare ground between rows is alternated with a crop that completely covers the ground. An example is planting corn and alfalfa (which covers the ground) in alternating strips of a field.
Another technique is no-till, where plowing, planting, fertilizing and weed control are done together. Since the ground soil is not disturbed until harvest, it reduces the chances of soil being carried away by wind.
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