[Accumulation of soil inorganic nitrogen in mono-harvesting farmlands in northeast China in late autumn].

The study showed that in northeast China, the farmlands with a mono-harvesting agricultural system had a low accumulation of soil inorganic nitrogen after harvest. In late autumn, there was an interval of about 20-30 days when the temperature and humidity were appropriate to soil N mineralization, but the mineralized nitrogen could not be used by crops in this non-growing season. The accumulation of inorganic nitrogen in upland soil reached a high level before freezing. Its inorganic nitrogen content in 1 m depth soil was 99.9 kg x hm(-2) in the treatment of commercial fertilizers (N 150 kg x hm(-2); P 16.4 kg x hm(-2); K 62.3 kg x hm(-2))and 145.4 kg x hm(-2) in the treatment of commercial fertilizers plus manure (pig manure by a reutilization of 80% product). While in rice field, its inorganic nitrogen content was relatively low before freezing. The reason might be that the soil permeability was not as good as that in upland for its long-term water-logging, and its insufficient aeration would be favorable to denitrification which induces the inorganic nitrogen loss via N2O emission.