三、氮肥的淋失 天然降水对土壤的淋溶,特别引起土壤有效氮和施入土壤的氮肥的损失。影响土壤氮素淋失的因素是多种多样的,各种农业技术措施、土壤改良措施、土壤含水量变化、土壤水分的运动以及土壤透水性等。尤其是滤过耕层的渗漏水,能带走大量的可溶性氮。据测定,一般农田每公顷耕层土壤含氮900—9000公斤,其中无机态氮占1～2％。这里,有机态氮和铵态氮淋失较少,而硝态氮的淋失相当严重。砂土内硝态氮的淋失达70％,黄土达65％,淤泥达45％。土壤氮素的淋失情况与土壤物理化学性质、土壤质地以及渗水性能有关。据计算,平均每年每公顷耕层土壤的氮素淋失量,砂土达75公斤,壤土达100公斤。 有人试验得出,施用氮肥后,土壤中肥料氮有30～10％因生物学反硝化作用而淋失了。 Third, the leaching of nitrogen Fertilizer leaching of natural precipitation on the soil, in particular caused by soil available nitrogen and nitrogen applied to the soil loss. The factors affecting soil nitrogen leaching are varied, and various agricultural technical measures, soil improvement measures, changes in soil moisture content, soil moisture movement and soil water permeability. In particular, seepage through the topsoil, can take away a large amount of soluble nitrogen. According to the determination, the general farmland per hectare topsoil nitrogen 900-9000 kg, of which inorganic nitrogen accounted for 1 to 2%. Here, organic nitrogen and ammonium nitrogen leaching less nitrate leaching is quite serious. Sand nitrate nitrate leaching up to 70%, 65% of the loess, silt up to 45%. Soil leaching of nitrogen is related to soil physical and chemical properties, soil texture and water seepage performance. According to calculations, the average amount of nitrogen leaching per hectare of topsoil per year is 75 kg of sand and 100 kg of loam. Some experiments have shown that after the application of nitrogen fertilizer, nitrogen fertilizer in the soil 30% to 10% due to biological denitrification lost.