Nitrogen flow associated with agricultural practices and environmental risk in Japan

The excessive use of chemical fertilizers or manure in agriculture sometimes causes environmental problems, such as inland water pollution. In this study, we used a database for the estimation of the nitrogen how associated with agricultural practices in each prefecture in Japan. We also estimated the amount of residual N in farmland and non-utilized livestock waste N, as indices of environmental risk (i.e., possibility of inland water pollution). The amount of residual N in Japan was estimated of 445,985 t N (92 kg N ha(-1)), represented the difference between the total input (1,282,824 t N; 266 kg N ha(-1)) and total output (836,838 t N; 174 kg N ha(-1)) in farmland. It was estimated that 71% of the residual N was associated with chemical fertilizer application. The effective use of chemical fertilizers is important for reducing residual N in Japan. Non-utilized livestock wastes were estimated to amount to 82,832 t N (17 kg N ha(-1)). These values were higher in prefectures in which larger amounts of livestock feces were produced. Therefore, a mitigation plan for reducing environmental risk should be designed depending on the characteristics of the prefectures.