Nitrogen flow associated with agricultural practices and environmental risk in Japan

The excessive use of chemical fertilizers or manure in agriculture sometime s causes environmental problems, such as inland water pollution. In this st udy, we used a database for the estimation of the nitrogen how associated w ith agricultural practices in each prefecture in Japan. We also estimated t he 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 h a(-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 farmlan d. It was estimated that 71% of the residual N was associated with chemical fertilizer application. The effective use of chemical fertilizers is impor tant for reducing residual N in Japan. Non-utilized livestock wastes were e stimated 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. T herefore, a mitigation plan for reducing environmental risk should be desig ned depending on the characteristics of the prefectures.