Recent trend of nitrogen flow associated with agricultural production in Japan

Abstract The excessive use of chemical fertilizers and manure in intensive agriculture sometimes causes environmental problems, including water pollution. Although it is speculated that surplus nitrogen (N) from Japanese agriculture may have had a strong impact on the environment, few quantitative assessments are available. In this study N flow in agricultural production was estimated from1980 to 1997. During this period, application of chemical fertilizers per unit area of farmland peaked in 1985 and then decreased. This was largely due to a decrease in the input of chemical fertilizer on paddy rice, although the input for vegetables per unit area increased. Even though the input of chemicalfertilizers for industrial crops decreased, it was still higher than for any other crop category. The amount of livestock wastes per unit area of farmland increased during the period and that of non-utilized livestock wastes also increased. Residual N on farmland and non-utilized livestock wastes could cause environmental pollution. The amount of residual N on farmland, which is expressed as the difference between N inputs and N outputs, was lowest in 1997because of the low input of chemical fertilizers and manure, though the amount of non-utilized livestock wastes was highest. Therefore the sum of the amount of residual N on farmland and non-utilized livestock wastes was not the lowest during the period and the sum of both was 141, 163, 158, and 148 kg N ha-1 in 1980, 1985, 1990, and 1997, respectively. To decrease these levels as well as the environmental risk associated with agricultural production, reduced input of chemical fertilizers for vegetables and industrial crops and, effective and active use of livestock wastes are important. Key Words: chemical fertilizerenvironmental risklivestock wastesnitrogen flow