Is there a nitrogen fertilizer threshold emitting less N(2)O with the prerequisite of high wheat production?

Excessive use of synthetic nitrogen (N) fertilizer and lower nitrogen use efficiency (NUE) are threatening the wheat production in the middle and lower reaches of Yangtze River. Excess input of N fertilizers also results in severe environmental pollution, climate change and biodiversity loss. However, the study on reasonable nitrogen application and NUE improvement with the prerequisite of stable and high yield remains unexplored. In our study, the four different levels of nitrogen were applied to find out the nitrogen threshold which could be both friendly to environment and promise the stable and high yield. The experiment was carried out in Yangzhou University (Yangzhou, China). The wheat cultivar Yangmai 23 was selected as the research material. The four nitrogen levels were as follows: 0, 189, 229.5, and 270 kg ha(-1). The results showed that the grain yield under the application of 229.5 kg ha(-1) N was as high as that under 270 kg ha(-1) N level, with the observation of 20.3% increase in agronomic efficiency. The N(2)O emission of 229.5 kg ha(-1) N application was as low as that of 189 kg ha(-1) N, but the grain yield and agronomic efficiency were significantly higher (11.9%) under 229.5 kg ha(-1) treatment than the lower one. Taken together, this indicated the nitrogen level at 229.5 kg ha(-1) could be identified as the fertilizer threshold, which will be beneficial for the future fieldwork.