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Soil conservation is the prevention of soil from erosion or reduced fertility caused by overuse, acidification, salinization or other chemical soil contamination. Slash-and-burn and other unsustainable methods of subsistence farming are practiced in some lesser developed areas. A sequel to the deforestation is typically large scale erosion, loss of soil nutrients and sometimes total desertification. Techniques for improved soil conservation include crop rotation, cover crops, conservation tillage and planted windbreaks and affect both erosion and fertility. When plants, especially trees, die, they decay and become part of the soil. Code 330 defines standard methods recommended by the US Natural Resources Conservation Service. Farmers have practiced soil conservation for millennia. Conservation practices fall in multiple categories: == Contour barriers == Contour farming orients crop furrows following the contour lines of the farmed area. Furrows move left and right to maintain a constant altitude, which reduces runoff. Contour farming was practiced by the ancient Phoenicians, and is effective for slopes between two and ten percent.〔''Predicting soil erosion by water, a guide to conservation planning in the Revised Universal Soil Loss Equation'', United States Department of Agriculture, Agricultural Research Service, Agricultural handbook no. 703 (1997)〕 Contour plowing can increase crop yields from 10 to 50 percent, partially as a result from greater soil retention. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「soil conservation」の詳細全文を読む スポンサード リンク
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