Optimizing nitrogen fertilizer application under reduced irrigation strategies for winter wheat of the north China plain

Following reduced irrigation strategies in the north China plain (NCP), nitrogen (N) fertilizer application must be optimized in terms of the food production and resource use efficiency. In this study, experiments were conducted for three consecutive winter wheat seasons in 2013-2016. Treatments included pre-sowing irrigation of 750 m(3) ha(-1) season(-1) with no subsequent irrigation during the whole season (W0) and irrigation of 750 m(3) ha(-1) season(-1) at pre-sowing, jointing and anthesis (W2). N fertilizer was applied at sowing with three levels, i.e., 180 (N1), 225 (N2) and 270 (N3) kg ha(-1) for each irrigation regime. Results exhibited that the average wheat yield of W0 was 17.3% lower than that of W2, however, the increased thousand kernel weight under W0 upheld relatively high yield averaging 7328 kg ha(-1). In addition, increased water stress under W0 aided to improve pre-anthesis dry matter and N remobilization to grain which in turn, made larger N use efficiency and N harvest index. Furthermore, grain protein content ranged from 13.4 to 13.7% under W0, 13.0 to 13.3% higher than that of W2. At both irrigation levels, grain yield and grain protein content increased with an increase in N application rate, while no significant difference was observed between N2 and N3 under W0. Additionally, the N2 achieved the highest water use efficiency of 1.92 kg m(-3) under W0. Overall, N2 appeared to be the optimized N level under W0 in terms of yield and nitrogen use, though it was 13.6% less than the largest net income under W2N3 due to 18.9% of yield loss. Moreover, W0N2 could reduce 1500 m(3) ha(-1) season(-1) irrigation water, 45 kg ha(-1) N fertilizer and 289.77 $ ha(-1) total input and attain highest cost efficiency. The study demonstrated that disposable water and nitrogen applied at sowing of wheat is feasible, and N application rate of 225 kg ha(-1) was recommended for the W0 regime to maximize wheat yield, grain quality, ecological and economic benefits.