[Nitrogen cycling and balance for wheat in China]

In this study, the input and output parameters of N for wheat production were collected from published literatures and International Plant Nutrition Institute in the period of 2000 to 2011 to evaluate N cycling and balances in North China, the middle and lower reaches of Yangtze River and Northwest China. The results showed that the N fertilizer application rates for each region were 170, 183 and 150 kg N . hm-2, the amounts of N from the previous crop were 74.6, 15.2 and 8.1 kg N . hm-2, and from seeds were 4.9, 4.2 and 3.5 kg N . hm-2, respectively. The N inputs from symbiotic fixation, atmospheric deposition and irrigation water in North China were 15, 12.9 and 9.9 kg N . hm-2, and in the middle and lower reaches of Yangtze River were 15, 14.5 and 5.8 kg N . hm-2, and in Northwest China were 15, 9.4 and 7.7 kg N . hm-2, respectively. The amounts of N uptake by aboveground plant at harvest time in North China, the middle and lower reaches of Yangtze River and Northwest China were 174.3, 144.4 and 122.3 kg N . hm-2, respectively, and the rates of ammonia volatilization, N20 emission and N leaching in North China were 19.9, 2.6 and 11.8 kg N . hm-2, in the middle and lower reaches of Yangtze River were 9.4, 2.4 and 15.5 kg N . hm-2, and in Northwest China were 3.4, 0.7 and 0 kg N . hm-2, respectively. As a result, the N balances in these three regions were all showing surpluses by 78.7, 66.0 and 67.3 kg N . hm-2. It is therefore necessary to adjust the N fertilizer application rates in these three regions to avoid the negative impacts on the environment.