Recent trends in nitrogen and phosphate use and balance on Japanese farmland

We estimated recent trends in nitrogen (N) and phosphate (P2O5) application, crop production and surpluses on Japanese farmlands, and calculated the N and P2O5 and balances in kind in crop types for 2002. Overall, chemical N and P2O5 fertilizer application peaked in 1985 and then decreased. Crop N production was reduced after 1985 and crop P2O5 production was reduced after 1990. This lag in crop P2O5 decline may have resulted from the accumulation of P2O5 in farmland soils before 1990. Nitrogen and P2O5 balances in 2002 indicated large surpluses in vegetables and industrial crops, despite the reduction in chemical fertilizer application, although chemical fertilizer and manure application levels were still higher than in other crops. The reduction in chemical fertilizer and manure application eventually reduced the N and P2O5 surplus. Substitution of currently non-utilized livestock excreta in place of chemical fertilizers would be worthwhile.