Deng MeiHua;Shi XiaoJun;Tian YuHua;Yin Bin;Zhang ShaoLin;Zhu ZhaoLiang;Kimura, S. D.

United Graduate School of Agriculture Science, Tokyo University of Agriculture and Technology, Tokyo 1838509 (Japan);College of Resources and Environments, Southwest University, Chongqing 310047 (China);State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China)

economic efficiency;environmental efficiency;n application rate;n loss;rice grain yield

To determine the optimal amount of nitrogen (N) fertilizer for achieving a sustainable rice production at the Taihu Lake region of China, two-year on-farm field experiments were performed at four sites using various N application rates. The results showed that 22%-30% of the applied N was recovered in crop and 7%-31% in soils at the rates of 100-350 kg N ha^-1. Nitrogen losses increased with N application rates, from 44% of the applied fertilizer N at the rate of 100 kg N ha^-1 to 69% of the N applied at 350 kg N ha^-1. Ammonia volatilization and apparent denitrification were the main pathways of N losses. The N application rate of 300 kg N ha^-1, which is commonly used by local farmers in the study region, was found to lead to a significant reduction in economic and environmental efficiency. Considering the cost for mitigating environmental pollution and the maximum net economic income, an application rate of 100-150 kg N ha^-1 would be recommended. This recommended N application rate could greatly reduce N loss from 199 kg N ha^-1 occurring at the N application rate of 300 kg N ha^-1 to 80-110 kg N ha^-1, with the rice grain yield still reaching 7 300-8 300 kg DW ha^-1 in the meantime.