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为了使农作物增产,除了种植豆类作物以外,大多数田地每年需要施用氮肥。根据农作物和土壤状况的差别,施肥量为每英亩20-200磅氮。所用的氮肥可以是各种形式的化合物,如氨、尿素和硝酸盐等。空气中的氮必须通过某种方式使它变成化合物时,才能被农作物吸收。但豆类如黄豆可以通过与某些种类的土壤细菌的共生作用,从空气中直接吸收氮。其它农作物,都不能直接从空气中吸收氮。许多粮食作物,必须从某些类型的固定氮源如从每年施用的氮肥中获取氮。在一些富裕国家,目前最经济、使用最广泛
In order to increase crop yields, nitrogen fertilization is required annually in most fields except for the cultivation of legumes. Depending on the crop and soil conditions, the amount of fertilizer applied is 20-200 pounds of nitrogen per acre. The nitrogen fertilizer used can be various forms of compounds such as ammonia, urea and nitrate and the like. Nitrogen in the air must be absorbed by crops in some way to turn it into a compound. But beans such as soybeans can directly absorb nitrogen from the air through symbiosis with certain types of soil bacteria. Other crops can not absorb nitrogen directly from the air. Many food crops must obtain nitrogen from certain types of stationary nitrogen sources, such as nitrogen fertilizers applied annually. In some rich countries, the economy is the most widely used