Effects of water saving and nitrogen reduction on soil nitrate nitrogen distribution, water and nitrogen use efficiencies of winter wheat

In order to solve the problems of excessive nitrogen input and irrigation water resources scarcity in current winter wheat production in Guanzhong Plain, winter wheat grain yield, water and nitrogen use efficiency, and nitrate nitrogen leaching were investigated to hopefully provide a theoretical basis for determining water-saving and nitrogen-reducing cultivation model. The two-factor split-plot field experiment (2017‒2019) was conducted in Yangling, Shaanxi province, China, where the nitrogen application rates of N300 (300 kg hm–2), N225 (225 kg hm–2), N150 (150 kg hm–2), N75 (75 kg hm–2), N0 (0 kg hm–2, no nitrogen application) were assigned to the main plots, and the irrigation amount of W2 (1200 m3 hm–2), W1 (600 m3 hm–2), W0 (0, no irrigation) were assigned to the subplots. The amount of irrigation and nitrogen application had significant effects on wheat yield, water and nitrogen use efficiency, soil nitrate nitrogen content as well as its leaching loss. In the 2017–2018 and 2018–2019 wheat seasons, the irrigation treatments (W1 and W2) significantly increased the wheat yield by 14.88%–15.01% and 4.11–4.16 times, respectively, but the difference between them was not significant, while the risk of soil nitrate nitrogen leaching under irrigation of 600 m3 hm–2 in overwintering period was significantly reduced. Under the irrigation of 600 m3 hm–2 in overwintering period, the yield was the highest in N150 treatment in 2017–2018, and in N225 treatment in 2018–2019, the N150 treatment had higher nitrogen use efficiency, and soil nitrate nitrogen leaching was also reduced by 15.87% and 10.20% compared with that of N225 treatment in 2017–2019. Therefore, N150 treatment (with nitrogen application rate of 150 kg hm–2) combined with W1 treatment (irrigated 600 m3 hm–2 in overwintering period) can improve the water and nitrogen utilization efficiencies and reduce the risk of nitrate nitrogen leaching, realizing the water-saving and nitrogen reduction production of winter wheat in Guanzhong Plain.