Based on agricultural nitrogen (N) balance model and field experiments, the impacts of farming system changes of Taihu Region of China on surface water environment were studied. During past 60 years, farming systems changed greatly in Taihu Region. The traditional method of manure collection and application was replaced by chemical fertilizer utilization gradually. Chemical N fertilization intensity decreased greatly due to the abolition of "3 crops per year" and reduction of cropland area in

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... 90-2010. Crops depleting soil fertility increased, while those improving soil fertility decreased, leading to an excessive dependence on chemical fertilizer application, which increased the risks of soil N loss to surface water environment in Taihu region. However, field experiments showed that the agricultural N loss with runoff only accounted for 2% of fertilizer N application rate. The majority of N was exported by crop harvesting. Our findings showed that the agricultural N loss might not be the main source of N pollution in Lake Tai after 2000. To control N pollution of Lake Tai, more attention should be paid to industrial and domestic wastewater from urban and rural areas, wastes from livestock and poultry breeding, bait input for aquaculture, etc in the Taihu Region, China.