Surface N Balances in Agricultural Crop Production Systems in China for the Period 1980-2015

Surface nitrogen(N) balances for China's crop production systems were estimated using statistical data collected from 1980 to 2004 at the national and provincial scale and from 1994 to 1999 at the county level.There was a surplus N balance throughout these periods,but the surplus was nearly stable in recent years.Projections using nonseasonal Box-Jenkins model or exponential models show that the N surplus for the total cultivated land in China was likely to increase from 142.8 kg ha?1 in 2004 to 168.6 kg ha-1 in 2015.The N balance surplus in the more developed southeastern provinces was the largest,and was slightly less in the central region,which caused the nitrate pollution in the ground water.The N surplus was much less in the western and northern provinces because of lower synthetic fertilizer inputs.The region with high N risk includes Beijing Municipality and Jiangsu,Zhejiang,Fujian,Guangdong,Hubei,and Shandong provinces for 2002-2004.The projections suggested that 15 provinces(or municipalities) in the middle and southeastern part of China except Jiangxi and Shanxi provinces would become the high-risk region by 2015.The level of economic development,transportation,and labor force condition had an important e?ect on the N balance surplus at the county level,but the last two factors showed remarkable impact at the provincial level.To decrease the nonpoint pollution(Npp) risk from crop production,the authors suggested to reduce the target level for national grain self-suflciency to 90%-95% and change the regional structure of grain production by moving some of the future grain production from the high Npp risk areas of eastern China to parts of the central and western provinces where the Npp risk was much less.

Surface nitrogen （N） balances for China＇s crop production systems was estimated using statistical data collected from 1980 to 2004 at the national and provincial scale and from 1994 to 1999 at the county level. There was a surplus N balance throughout these periods, but the surplus was nearly stable in recent years. Projections using nonseasonal Box-Jenkins model or exponential models show that the N surplus for the total cultivated land in China was likely to increase from 142.8 kg ha^-1 in 2004 to 168.6 kg ha 1 in 2015. The N balance surplus in the more developed southeastern provinces was the largest, and was slightly less in the central region, which caused the nitrate pollution in the ground water. The N surplus was much less in the western and northern provinces because of lower synthetic fertilizer inputs. The region with high N risk includes Beijing Municipality and Jiangsu, Zhejiang, Fujian, Guangdong, Hubei, and Shandong provinces for 2002-2004. The projections suggested that 15 provinces （or municipalities） in the middle and southeastern part of China except Jiangxi and Shanxi provinces would become the high-risk region by 2015. The level of economic development, transportation, and labor force condition had an important effect on the N balance surplus at the county level, but the last two factors showed remarkable impact at the provincial level. To decrease the nonpoint pollution （Npp） risk from crop production, the authors suggested to reduce the target level for national grain self-sufficiency to 90%-95% and change the regional structure of grain production by moving some of the future grain production from the high Npp risk areas of eastern China to parts of the central and western provinces where the Npp risk was much less.