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

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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>.