Evaluation of Japanese Agricultural N and P Management by Integrated Environmental Impact Indicator in 1990 and 2005.

Agricultural nitrogen (N) and phosphorus (P) use cause various kinds of environmental impacts such as greenhouse gas emission, water pollution and eutrophicaction. These impacts had been estimated and evaluated individually. In this study, we examined single integrated environmental indicator (IEI) to evaluate total environmental impacts on agricultural N and P use. We employed distance to target method to integrate different environmental impacts. Accounted environmental impacts and its target are as follows, nitrous oxide emission (25% reduction against 1990), degradation of ground water by nitrate (make percentage of observation well that excess 10mg NO3-N/L zero), river water eutrophication by N and P (less than 2mgN/L, 0.1mgP/L in river water). We calculated environmental indicator in 47 prefectures in Japan in 1990 and 2005 to evaluate regional difference and temporal change. IEI was ranged from 7.3 to 41.7 (mean 24.4) in 1990 and from 4.9 to 40.5 (mean 20.7) in 2005, namely environmental impact had been reduced by 17% on average. The largest IEI was observed in Kagawa Pref. where was the most intensive egg production area and the least was Niigata Pref. where was paddy rice farming area with extensive livestock farming. Reduction of IEI was mainly caused by reduction of chemical N and P fertilizer use. However, 6 prefectures increase IEI in 2005 against 1990. The reasons were wide area of vegetable production and intensification of livestock production, because chemical N and P use on vegetable production had been increased (Mishima et al. 2009) for its cash commodity, intensification of livestock production caused increase of livestock waste N and P and these conditions increase N and P surplus. To improve IEI in regional bases, limiting livestock production or translation to the other prefecture and reduced input to vegetables are solutions.