玉米、高梁、谷于、小麦和水稻等非豆科作物,都不能直接利用空气中的氮,只能吸收土壤中硝酸盐和氨盐等的水解氮。而有些土壤微生物却能吸收空气中的氮,并把它固定下来,贮存在土壤里,这叫“固氮作用”。据统计,地球上各种微生物,一年能固氮一亿七千五百万吨,等于全世界工业生产氮肥 Corn, sorghum, rice, wheat and rice and other non-leguminous crops, can not directly use the nitrogen in the air, can only absorb soil nitrate and ammonia nitrogen hydrolysis. Some soil microorganisms can absorb the nitrogen in the air and fix it and store it in the soil, which is called “nitrogen fixation.” According to statistics, all kinds of microorganisms on the earth can fix nitrogen of 175 million tons a year, which is equal to that of industrial production of nitrogenous fertilizers