Optimal cooperative application solutions of irrigation and nitrogen fertilization for high crop yield and friendly environment in the semi-arid region of North China

Optimizing irrigation and nitrogen (N) fertilization cooperative application to coordinate the balance between agricultural production and ecological environment is a vital challenge for sustainable agricultural production. Here, a three-year field experiment was conducted from 2018 to 2020 in the semi-arid region of north China to investigate the effects of different irrigation amounts (W1, 50% ETc, ETc is the crop evapotranspiration; W2, 75% ETc; W3, 100% ETc; W4, 125% ETc) and nitrogen fertilization rates (F1, 75 kg·ha−1, F2, 150 kg·ha−1, F3, 225 kg·ha−1, F4, 300 kg·ha−1) on growth, yield, water and fertilizer use efficiency, and soil N residue of spring wheat by drip fertigation, and explore the optimal combination of irrigation amount and N fertilization rate based on a multi-objective optimization method. The results showed that leaf area index (LAI), dry matter accumulation, yield, water use efficiency (WUE) and economic return of spring wheat increased first and then decreased with increasing irrigation at the same level of N fertilization. These parameters peaked at W3, with W1 performed poorly and low irrigation amount was detrimental to the function of fertilizer. At the same level of irrigation, LAI, dry matter accumulation, yield and economic return all demonstrated significant diminishing return effects with increasing N fertilization, whereas nitrogen partial factor productivity (NPFP) reduced with increasing N fertilization. Furthermore, with the simultaneous increase of irrigation and N fertilization, the accumulation of soil nitrate nitrogen (NO3-N) decreased in the 0 − 40 cm soil layer and increased in the 60 − 100 cm soil layer. The partial least squares path model (PLS-PM) revealed that irrigation had a direct positive effect on spring wheat yield rather than N fertilization, and irrigation had a direct negative effect on soil N residue. Based on the multi-objective optimization model established by multiple regression analysis and the elitist non-dominated sorting genetic algorithm (NSGA-II), the irrigation amount of 337.3–354.9 mm combined with the N fertilization rate of 181.2–198.6 kg·ha−1 could obtain the optimal comprehensive benefits of wheat yield, economic return, water and fertilizer utilization efficiency and environmental impact. This study can provide an important scientific basis for the management and optimization of irrigation and fertilization for spring wheat in semi-arid region of China and other similar regions around the world.