Postponed and reduced basal nitrogen application improves nitrogen use efficiency and plant growth of winter wheat

Excessive nitrogen (N) fertilization with a high basal N ratio in wheat can result in lower N use efficiency (NUE) and has led to environmental problems in the Yangtze River Basin, China. However, wheat requires less N fertilizer at seedling growth stage, and its basal N fertilizer utilization efficiency is relatively low; therefore, reducing the N application rate at the seedling stage and postponing the N fertilization period may be effective for reducing N application and increasing wheat yield and NUE. A 4-year field experiment was conducted with two cultivars under four N rates (240 kg N ha^?1 (N240), 180 kg N ha^?1 (N180), 150 kg N ha^?1 (N150), and 0 kg N ha^?1 (N0)) and three basal N application stages (seeding (L0), four-leaf stage (L4), and six-leaf stage (L6)) to investigate the effects of reducing the basal N application rate and postponing the basal N fertilization period on grain yield, NUE, and N balance in a soil-wheat system. There was no significant difference in grain yield between the N180L4 and N240L0 (control) treatments, and the maximum N recovery efficiency and N agronomy efficiency were observed in the N180L4 treatment. Grain yield and NUE were the highest in the L4 treatment. The leaf area index, flag leaf photosynthesis rate, flag leaf nitrate reductase and glutamine synthase activities, dry matter accumulation, and N uptake post-jointing under N180L4 did not differ significantly from those under N240L0. Reduced N application decreased the inorganic N content in the 0–60-cm soil layer, and the inorganic N content of the L6 treatment was higher than those of the L0 and L4 treatments at the same N level. Surplus N was low under the reduced N rates and delayed basal N application treatments. Therefore, postponing and reducing basal N fertilization could maintain a high yield and improve NUE by improving the photosynthetic production capacity, promoting N uptake and assimilation, and reducing surplus N in soil-wheat systems.