How much negative impact does surplus nitrogen in the agricultural land give to environment?

以水田、旱田、果园、牧场等农业用地为研究对象，分析了不同种植季和非种植季土壤孔隙水中无机氮的变化规律。计算了这些农田1年90 cm深度的硝态氮排放量。根据这一分析结果，可以计算出不超过10 mg L^<-1>的土壤孔隙水硝酸盐氮浓度。

In the agricultural land such as paddy field, upland field, orchard land and pasture land, the authors analyzed the behavior of inorganic nitrogen in soil pore water during a year of cropped and non-cropped season. In these agricultural lands, the nitrate nitrogen which discharged from 90 cm depth during a year was calculated. From the results of this analysis, it became possible to calculate the nitrate nitrogen concentration of soil pore water which does not exceed 10 mg L^<-1>.