AN ECO-BALANCE APPROACH TO EVALUATE THE IMPACT OF AGRICULTURAL LAND-USE ON REGIONAL SUSTAINABILITY

摘要

To evaluate the relation among production and environmental pollutions, historical changes of nitrogen flows of a city were analyzed. The system comprised of farmland-, human- and livestock-subsystems. The indicators were production, global warming potential (GWP), surplus nitrogen in farmland, and the proportion of nitrogen cycled in the system, export from the system, and losses from the system (sum of field surplus nitrogen, disposal nitrogen, and N_2O and NH_3 emissions) to the total system throughflow, referred as CI, ET and LI, respectively. Farmland productivity increased from 30kgN·ha~(-1) at the end of the 1950's to 80kgN·ha~(-1) in 2002, due to improvement in crop varieties and management methods. GWP increased 2 times from 1912 to 1960. It decreased gradually until 1985 and became almost constant afterwards. Surplus nitrogen increased due to manure input from 1912 to 1960. In the 1960's improved production and reduced manure application decreased surplus nitrogen. As chemical fertilizer increased in the 1970's, surplus nitrogen increased again. LI doubled from 1912 to 1970 and remained high until 2002. If the relation among production and the other indicators were negative, the historical changes of land-uses were able to maintain production while reducing pollution. For per unit area of farmland, negative correlation was found from 1958 to 1984. In this period, however, the relation of production of the total farmland and LI was positive. Thus, it is important to include the scale to analyze the trade-off relations in an Eco-Balance approach.