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Unformatted text preview: Soil Erosion and Control Erosion is by water and wind. Crudely, about 2/3 is by water and 1/3 by wind. The loss of topsoil means loss of soil fertility. Plant growth is reduced and the soil is even more subject to erosion. Erosion is a serious matter because arable land is finite and the population continues to increase. Not only is soil quality hurt where topsoil is lost but the eroded material is also transported to and deposited in low-lying positions causing problems with water quality and sedimentation in reservoirs, harbors and so forth. Water Erosion Though total runoff is greater in humid regions, intense rainfall may cause high runoff and soil erosion in arid regions. Erosion is a natural process but in the absence of site disturbance by construction or farming, the rate of soil loss is very small. Soil loss by geologic erosion is estimated to be < 0.5 Mg / ha-yr. If BD = 1.3 g / cm 3 , then this represents an annual loss of about 0.04 mm. Geologic erosion. However, accelerated erosion occurs where the soil has been disturbed. Accelerated erosion degrades soil quality and agricultural sustainability. Soil conservation- ists have established an upper limit to accelerated erosion below which agricultural sustainability may not be seriously affected. This rate of topsoil loss by erosion is 11 Mg / ha-yr. Using a BD = 1.3 g / cm 3 , this represents an annual loss of about 0.8 mm. Unfortunately, losses from 80 % of crop land in US exceed this amount. Average topsoil losses in countries that can even less afford a loss in agricultural sustainability, like China and India, are up to 3.3 mm annually. Accelerated erosion. It has been estimated that up to 38 million Mg (metric tons) N, P and K is lost annually in the US due to erosion. This is about equal to of the fertilizer additions of these nutrients....
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- Fall '08