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Nitrogen Surplus Benchmarks for Controlling N Pollution in the Main Cropping Systems of China

Zhang, Chong, Ju, Xiaotang, Powlson, David, Oenema, Oene, Smith, Pete
Environmental science & technology 2019 v.53 no.12 pp. 6678-6687
double cropping, fertilizer application, field experimentation, nitrogen, nitrogen fertilizers, pollution, pollution control, soil, China
Nitrogen (N) surplus is a useful indicator for improving agricultural N management and controlling N pollution. Few studies have developed benchmark values for cropping systems in China, a country with the largest N fertilizer use in the world. We established N surplus benchmarks for 13 main cropping systems, at optimal N management, using results from >4500 on-farm field experiments and a soil surface balance approach. These cropping systems accounted for about 50% of total N fertilizer consumption in Chinese agriculture in 2009. The results showed that N surplus benchmarks for single cropping systems ranged from 40 to 100 kg N ha–¹ yr–¹ (average 73 kg N ha–¹ yr–¹), and for double cropping systems from 110 to 190 kg N ha–¹ yr–¹ (average 160 kg N ha–¹ yr–¹), roughly twice that of single cropping systems. These N surplus benchmarks may be further refined, following further decreases in N deposition rates and reactive N losses as a result of strict implementation of “4R-nutrient stewardship” and improvements in fertilization techniques and agronomic managements. Our N surplus benchmarks could serve as realistic targets to improve the N management of current conventional practices, and thereby could lay the foundations for a more sustainable N management in China.