Estimation Of The Environmental Effects Of Excess Nitrogen Caused ByIntensive Agriculture In East Asia Based On Global Nitrogen Balance

Abstract

We estimated the nitrogen budget of East Asia, mainly of China, at the 0.5 by 0.5 degree scale to identify the areas and seasons which suffer from the deteriorated effects of nitrogen due to food production and supply. Data on fertilizer consumption and food balance derived from FAO databases were used for calculating nitrogen balance in 1999 for each country. For China, province data on fertilizer consumption, rice and pulse production etc. were also used. China was divided into four zones (single-crop, double-crop (rice predominant), double-crop (wheat predominant) and double-crop-rice), and typical seasonal variations of fertilizer application and nutrient uptake were assumed for each zone. Nitrogen loads of each country were distributed among grid cells on the basis of farmland area and population in each cell and nitrogen concentrations in river water were estimated by assuming a first order reaction model. Nitrogen loads per unit area were high in the river basins close to the east coast of central China and southern part of the Asian Continent around Bangladesh to India where intensive agriculture is carried out, as well as the catchment of rivers in Japan and South Korea where NOx deposition due to energy production significantly contributes. Nitrogen concentrations in surface and ground water was expected to be high around the lower reaches of the Huang He and the Chang Jiang because of the high nitrogen load and limited amount of precipitation. The most severe water pollution by excess nitrogen was expected to occur in early spring and winter in those areas where cropping of winter-wheat was dominant. Transactions on Ecology and the Environment vol 63, © 2003 WIT Press, www.witpress.com, ISSN 1743-3541