Effects of combined N and Zn application on nitrogen translocation, yield and nitrogen and zinc efficiency of winter wheat

BACKGROUND In winter wheat, low nitrogen (N) and zinc efficiency limits production. Although combined application boosts yield and grain zinc, the underlying mechanisms and optimal rates remain unclear. This study aims to uncover these mechanisms and identify the best management strategy. RESULTS Applying N at 240 kg ha −1 significantly enhanced post‐anthesis glutamine synthetase (GS) and glutamate synthase (GOGAT) activities in flag leaves compared to 180 kg ha −1 , promoting pre‐anthesis N translocation and post‐anthesis N accumulation. This extended the grain‐filling period by 0.8–1.44 days, increased the maximum grain‐filling rate by 3.11–12.30% and boosted yield by 6–8% through improvements in spike number, grains per spike and thousand‐kernel weight. Grain Zn concentration and Zn use efficiency increased by 12–21% and 35%, respectively, but N uptake and utilization efficiency declined. Foliar Zn application at anthesis (2.4 kg ha −1 ) further enhanced GS and GOGAT activities during grain filling, increased post‐anthesis N accumulation and improved the grain‐filling rate by 0.63–9.96%. This raised thousand‐kernel weight by 0.70–10.97% and yield by 0.71–5.78%. Grain Zn concentration reached 40.59–41.12 mg kg −1 , whereas N uptake efficiency and partial factor productivity of N increased by 1.94–11.61% and 0.71–5.78%. Correlation analysis indicated strong associations of yield with grain N accumulation, post‐anthesis GS/GOGAT activities and N partial factor productivity, whereas grain Zn concentration correlated with Zn use efficiency and post‐anthesis N metabolism. CONCLUSION The combination of N at 240 kg ha −1 and foliar Zn at 2.4 kg ha −1 during anthesis optimized post‐anthesis N metabolism, prolonged grain filling and synergistically improved yield, grain Zn content and NZn efficiency.