Optimum combination of irrigation and nitrogen for high yield and nitrogen use efficiency in winter wheat and summer maize rotation system

【Objectives】 Inappropriate management of irrigation and fertilization is common in the winter wheat-summer maize rotation system in the piedmont plain of Taihang Mountain. Overuse of fertilizers and irrigation result in severe waste of water resources and agricultural non-point source pollution. Study on the appropriate water and nitrogen combination for high yields and N-fertilizer utilization will be necessary for profitable and sustainable agricultural production in winter wheat and summer maize rotation system in the region. 【Methods】 A two-factor complete split plot field experiment was conducted for 8 successive years. The main plots were irrigation volumes: one irrigation in jointing stage (W1) and twice in jointing and flowering stages (W2) for wheat, limited water (WL) and suitable water (WS) for maize. Subplots were consist of six N rates: 0(N0), 60(N60), 120(N120), 180(N180), 240(N240) and 300(N300) kg/hm2. The yields and plant N uptakes of wheat and maize were measured. 【Results】 The annual yields and N uptakes of wheat and maize varied significantly in all treatments. The annual differences of the yields and N uptakes were smaller in W2 and WS treatments than in W1 and WL ones for all the six N rates. Whatever the irrigation treatments, the yields and N uptakes in N0 and N60 treatments generally were significantly lower than in the other ones. In the yield levels of 7.0-9.5 t/hm2 for winter wheat and 8.5-11.0 t/hm2 for summer maize, the grain yields were significantly and positively correlated with the N uptakes. 8-years’ average of yields and N uptakes in both wheat and maize were increased significantly with increased N rates, but no significant increase in yields when N rate exceeded 120 kg/hm2 for yields nor in N uptake when N rate exceeded 180 kg/hm2. For the same N rate, the crop yields and N uptakes in W2 or WS were higher than in W1 and WL. Under the two irrigation conditions, the partial factor productivities from N-fertilizer (PFPN), N-fertilizer agronomic efficiency (NAE) and nitrogen utilization efficiency (NUtE) were reduced obviously with the increase of N fertilizer rate. In the same N rate, all the three indices in W2 and WS were higher than in W1 and WL. The accumulative apparent N-fertilizer recovery efficiencies (AANRE) in the wheat-maize rotation system were also decreased obviously with the increase of N rates. Under the condition of W1+WL, the AANREs were decreased from 51.8% in N60+60 to 22.3% in N300+300, and from 57.4% to 24.6% for W2+WS. For the same N rate, the AANRE under W2+WS was higher than that under W1+WL. 【Conclusions】 The peak yields and N uptakes are obtained with twice irrigation plus N rate of 120 kg/hm2 for wheat and suitable irrigation plus N 120 kg/hm2 for maize, and the partial production efficiency, agronomy efficiency and the cumulative agronomy efficiency of N fertilizer are all maintained at higher level. Therefore, under the annual grain yield target of 16-19 t/hm2, the optimal combination of water and nitrogen for winter wheat and summer maize is twice irrigation plus N 120 kg/hm2 in the piedmont plain of Taihang Mountain over a certain period of time.