The recent trend of agricultural nitrogen flow in Japan and improvement plans

Abstract

Nitrogen (N) flows associated with agricultural practices and environmental N risk, which is an index of environmental impact, in Japan from 1980 to 1997 were estimated, and the effect of improvement plans for reducing environmental N risk was simulated for two important prefectures. Recent trends have shown that the input of chemical fertilizer and manure is lower compared to crop production, which is also lower. Environmental N risk peaked in 1985 then became lower, and its content changed. Residual N on farmland, defined as N inputs onto farmland (chemical fertilizer, etc.) minus N outputs from farmland (crop uptake, etc.), peaked in 1985, then decreased, although non-utilized livestock excreta increased during the period. To simulate reduction of the environmental N risk, two prefectures that had high applications of chemical fertilizer and high livestock excreta production were selected. Simulated improvement plans were based on the results of past studies, such as low inputs of chemical fertilizer in crop production, substitution of chemical fertilizer by livestock excreta and/or active use of livestock excreta in forage production. Incorporation of these methods was successful in reducing environmental risk in those prefectures, although prefectures that had a large amount of livestock excreta could not find any effective improvement plan, due to lack of appropriate local land use.