Interaction effects of irrigation and nitrogen on the coordination between crop water productivity and nitrogen use efficiency in wheat production on the North China Plain

Improving nitrogen use efficiency-yield (NUEYield) and crop water productivity (CWP) simultaneously has been a focus for sustainable wheat production, especially for the North China Plain, which faces challenges with limited water resources and low fertilizer use efficiency. With three-year wheat field experiments with two irrigation levels (rainfed, and irrigated at jointing and anthesis) and three N rates (0, 180, and 270 kg ha−1), we systematically investigated the effect of irrigation and nitrogen management on wheat water consumption at different growth stages, and further determined on the relationship between CWP and NUEYield simultaneously under different irrigation and nitrogen interactions. The results showed that N application and irrigation increased the total crop water consumption (1.2%−3.6% and 42.4%−44.4%, respectively). Increasing the N rate improved the soil water use (7.5%−10.3%) and reduced crop dependence on irrigation and precipitation, whereas irrigation reduced soil water utilization (54.4%−57.8%). Both irrigation and N application significantly increased the amount, percentage, and intensity of water consumption, especially during the grain filling period. There was a significant positive synergistic relationship between CWP and NUEYield under different irrigation and nitrogen treatments. For every 1 kg m−3 increase in CWP, NUEYield increased by 2.71–11.37 kg kg−1, depending on the N rate and water conditions. Increasing the N rate reduced the positive response of NUEYield to increasing CWP, while irrigation increased the positive response of NUEYield to increasing CWP. After decomposing NUEYield into nitrogen uptake efficiency (NuptE) and nitrogen utilization efficiency for yield (NutEYield), we found that the positive synergistic relationship between CWP and NUEYield was mainly due to the positive response of NuptE but not NutEYield to CWP. Irrigation increased the grain nitrogen accumulation efficiency by simultaneously increasing both pre-anthesis N translocation (GNAT) and post-anthesis N assimilation (GNAA) but increased GNAT more significantly than GNAA. Our results provide a theoretical basis for the efficient management of water and fertilizer in wheat production on the North China Plain and offer critical insights for improving the modeling of water-nitrogen relationships in wheat.