Abstract
Based on the changes in food demand and production in East Asian counties, the temporal trends from 1980 to 2007 and spatial variation of nitrogen outflow via three channels (nitrogen balance (NB) in agricultural areas, human waste and atmospheric deposition) were estimated with a simple nitrogen flow model. In many countries, food consumption has rapidly increased due to population growth and increase in per capita food demand, especially demand for animal protein. In contrast, per capita food demand in India was almost stable despite economic growth. Reflecting these food demands, consumption of inorganic nitrogen fertilizer and resulting nitrogen balance (NB) per unit agricultural land have increased drastically in many countries. In some countries such as Cambodia, Laos and Myanmar, NB was very low or negative even in 2007 suggesting that soil fertility may become exhausted. NB varies significantly within countries and it was extremely high in cities and provinces in China facing the East China Sea and the western Plain of Hindustan in India.
Total nitrogen outflow from river basins, which is the sum of the outflows from the three channels in each 0.5 °×0.5° grid cell in the basins, also showed large variability. The Yangtze River basin accounted for the largest share of the total nitrogen outflow, about 20% of the total load of the study area. Comparing the average nitrogen outflow per unit land area in 2007, the Huai River basin had the largest value by a wide margin and may be severely polluted with nitrogen.
