Abstract
Nitrogen flows five-year intervals during for the period from 1982 to 1997 were estimated by "Domestic Nutrition Balance Estimation System" that represents the flow of production-processing-consumptiondisposal of foods and feeds in Japan. The trend over this period can be summarized as follows : 1) Total nitrogen discharge to the environment (total annual consumption) recorded the peak at 1,706 Gg in 1992, and it slightly decreased in 1997. On the supply side, domestic production of nitrogen has been decreasing since 1987, and the shortage is supplied from continuously increasing import. 2) As regards the increase of import in the "Livestock industry", the relative importance of feed imports decreased, while that of imports in the form of products such as dressed carcasses and unprocessed milk increased. In addition, trends of the increasing dependence on foods from overseas are recognized in every phenomenon, such as an increase in import ratio in the supply to the "Food processing" and a decrease in "Crop residues" in domestic production. We examined the accuracy of the estimation of discharge from "Human food consumption" and "Livestock industry", which accounted for approximately 86% of total discharge to the environment in 1997 by evaluating the goodness of fit to the relevant organic waste data. Out of the nitrogen discharge from "Human food consumption" (643 Gg), 601 Gg was considered to be discharged from domestic wastewater. The difference between this figure and a value of 543 Gg estimated using the nitrogen basic unit in sewage was about 10%. In addition, the nitrogen discharge from livestock excreta was estimated at approximately 731 Gg out of that from "Livestock industry" to the environment. This figure was equal to a value of 721 Gg estimated using the nitrogen basic unit in excreta of domestic raising livestock in 1999.
