Unreasonable nitrogen (N) fertilizer rates and application timings pose significant challenges to maize production in the central region of Gansu province. This study aimed to clarify the effects of N application rate and timing on maize photosynthetic physiology, yield, and grain quality. Furthermore, it explored the physiological mechanisms underlying nitrogen transport to improve kernel development and quality. The research was based on a long-term field experiment initiated in 2012, with data collected from 2022 to 2023. A split-plot design was employed, with four N application levels in the main plot (N0: 0 kg hm-2, N1: 100 kg hm-2, N2: 200 kg hm-2, N3: 300 kg hm-2) and two fertilization timings in the sub-plots: T1 (1/3 basal + 2/3 at jointing stage) and T2 (1/3 basal + 1/3 at jointing stage + 1/3 at trumpet stage). The results showed that: (1) N application significantly increased the leaf area index (LAI), leaf area duration (LAD), and relative chlorophyll content. However, no significant differences in average LAI and total LAD were observed among the N2T1, N2T2, N3T1, and N3T2 treatments. (2) The N3T1 and N3T2 treatments exhibited higher photosynthetic rates, stomatal conductance, and transpiration rates from the jointing to the large trumpet stage. However, from the milking to wax maturity stages, these parameters declined and were lower than those observed in N2T1 and N2T2. Notably, at the milking stage, photosynthetic rates under N2T1 and N2T2 increased by 12.78% and 18.81%, respectively, compared to N3T2 (P < 0.05). (3) N application significantly increased the leaf nitrogen content per unit area. Although no significant differences in leaf N content were observed between N2T1/N2T2 and N3T1/N3T2, the photosynthetic nitrogen use efficiency (PNUE) under N2T1 and N2T2 improved by 16.85% and 26.44%, respectively, relative to N3T1 and N3T2 (P < 0.05). (4) Linear regression analysis between yield and N application rate indicated that the optimal N rate for both T1 and T2 closely approximated the N2 level (200 kg hm-2). Compared with other treatments, N2T1 and N2T2 increased grain yield by 5.75%-142.53% and 13.32%-159.91%, respectively. Additionally, N fertilization enhanced grain protein content while reducing starch content. (5) Correlation analysis revealed significant positive relationships between both grain yield and protein content with photosynthetic performance (P < 0.05). Principal component analysis showed no significant differences in certain variables between the N1T1 and N3T1 treatments. Overall, N2T1 and N2T2 demonstrated superior performance in photosynthetic characteristics, grain yield, and quality compared with other treatments. However, excessive N application reduced photosynthetic performance and PNUE in the later growth stages, ultimately leading to lower grain yield and quality. In conclusion, applying 200 kg hm-2 of N fertilizer using a 1/3 basal plus 2/3 jointing stage strategy significantly enhances photosynthetic capacity during maize growth in the central region of Gansu Province. This approach helps maintain a higher green leaf area, improves photosynthetic performance, and mitigates the decline in PNUE. Considering both yield and quality, applying 200 kg hm-2 of N with a (1/3):(2/3) basal-to-jointing allocation is recommended as an optimal N management strategy for achieving high-quality and high-yield dryland maize production.
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