A large amount of nitrogen that is not absorbed by crops enters as nitrate nitrogen into soils of the aeration zone after nitrification by microbial processes.

• 大量的氮素没有被农作物吸收,经微生物硝化作用后,以硝态氮的形式进入包气带土体,使包气带土体普遍受到氮素不同程度的污染。