Adjusting Nitrogen Application in Accordance with Soil Water Availability Enhances Yield and Water Use by Regulating Physiological Traits of Maize under Drip Fertigation

Knowledge of the interactive effects of water and nitrogen (N) on physio-chemical traits of maize (Zea mays L) helps to optimize water and N management and improve productivity. A split-plot experiment was conducted with three soil water conditions (severe drought, moderate drought, and fully water supply referring to 45%-55%, 65%-75%, and 85%-95% field capacity, respectively) and four N application rates (N-0, N-150,N- N-240, and N-330 referring to 150, 240, 330 kg N ha(-1) respectively) under drip fertigation in 2014 and 2015 in the Huang-Huai-Hai Plain of China. The results indicated that drought stress inhibited physiological activity of plants (leaf relative water content, root bleeding sap, and net photosynthetic rate), resulting in low dry matter accumulation after silking, yield, and N uptake, whereas increased WUE and NUE. N application rates over than 150 kg ha(-1) aggravated the inhibition of physiological activity under severe drought condition, while it was offset under moderate drought condition. High N application rates (N330) still revealed negative effects under moderate drought condition, as it did not consistently enhance plant physiological activity and significantly reduced N uptake as compared to the N-240 treatment. With fully water supply, increasing N application rates synergistically enhanced physiological activity, promoted dry matter accumulation after silking, and increased yield, WUE, and N uptake. Although the N-240 treatment reduced yield by 5.4% in average, it saved 27.3% N under full water supply condition as compared with N-330 treatment. The results indicated that N regulated growth of maize in aspects of physiological traits, dry matter accumulation, and yield as well as water and N use was depended on soil water status. The appropriate N application rates for maize production was 150 kg ha(-1) under moderate drought or 240 kg ha(-1) under fully water supply under drip fertigation, and high N supply (>150 kg ha(-1)) should be avoided under severe drought condition.