| To clarify the effects of nitrogen application rate and frequency on corn canopy nitrogen distribution and nitrogen efficiency, a field experiment was conducted from 2022 to 2023. The experiment included two nitrogen application rates (270 and 360 kg N·hm?2) and two fertilization frequencies (3 and 5 times) to investigate the effects of each treatment on the dynamic distribution of canopy nitrogen and nitrogen efficiency in spring maize. A systematic analysis was conducted on indicators such as leaf area index, specific leaf nitrogen, nitrogen attenuation coefficient, and nitrogen efficiency. The results showed that increasing nitrogen application rate and frequency significantly improved the leaf area index and specific leaf nitrogen at all canopy levels. The treatment of 270 kg N·hm?2 combined with five fertilizations (N270-F5) reduced the nitrogen attenuation coefficient by 1.6% to 6.2%, optimizing the uniformity of canopy nitrogen distribution. This further promoted the transfer of nitrogen from vegetative organs to grains, resulting in an increase of 7.2% to 21.04% in nitrogen agronomic efficiency and 7.1% to 19.2% in nitrogen physiological efficiency. Moreover, the structural equation model revealed that the leaf area index of the lower leaves directly regulated specific leaf nitrogen and the nitrogen attenuation coefficient, enhancing the nitrogen accumulation in the middle leaves and the contribution of nitrogen translocation to grains, ultimately driving the improvement of nitrogen efficiency. This study provides new insights into the physiological mechanisms for improving nitrogen efficiency through optimized nitrogen management. Considering comprehensive nitrogen efficiency indicators, the treatment of 270 kg N·hm?2 combined with five fertilizations (N270-F5) significantly improved the vertical distribution of canopy nitrogen, enhanced nitrogen accumulation and translocation capacity, and increased both yield and nitrogen efficiency. This model can provide technical support for green production of spring maize in irrigated areas. |