Exploring optimal irrigation and nitrogen fertilization in a winter wheat-summer maize rotation system for improving crop yield and reducing water and nitrogen leaching

Irrigation and nitrogen (N) fertilization play important roles in grain yield. However, amounts supplied in excess of crop demand are responsible for water and N leaching during intensive agricultural production. A three-year winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation experiment involving varied irrigation and N fertilization treatments was conducted in the Jinghui Canal irrigation area of Guanzhong Plain in China. To develop a more sustainable agroecosystem taking into account crop yields, deep percolation and N leaching, the RZWQM2 model was used to simulate crop production. Various irrigation and N fertilization strategies were simulated to obtain high crop yields and to reduce water and N leaching in different precipitation years, using long-term historical weather data spanning 57 years (1961–2017). The simulated soil water and NO₃-N content, grain yield, water and nitrogen use efficiencies (with nRMSE values ranging from 5.3–25.1 %), and the simulated crop biomass and N uptake (with RE values ranging from -16.4–18.3 %) were in good agreement with observed data. Simulated LAI values were acceptable (with RMSE ranging from 0.31 to 1.68 and index of agreement, d, ranging from 0.28 to 0.94), with the poorer simulations occurring with water and N stress. Maize seedling stage and wheat jointing stage were the phases most sensitive to water deficit, and optimal irrigation schedules could be adjusted according to variable precipitation and other climate changes. The best irrigation strategies for maize in the Guanzhong Plain were irrigation applied at the seedling stage in wet and normal years, and two irrigations applied at the seedling and jointing stages in dry years. The best irrigation strategies for wheat were two, three, and four irrigations applied in wet, normal, and dry years, respectively. Irrigation at different crop growth stages significantly influenced N leaching and nitrogen use efficiency. Increasing N input led to greater water use efficiency and less deep percolation water. Considering the interactive effects of water and N input on yield, deep percolation, and N leaching, the most appropriate N application rates in all precipitation years were 140 kg N ha⁻¹ for maize and 240 kg N ha⁻¹ for wheat, coupled with the recommended irrigation strategies. Improving water and N management can significantly reduce deep percolation of water and N leaching while maintaining agricultural productivity and environmental sustainability.