| Aiming at the problem of low utilization rate of water and fertilizer and unreasonable planting density in the semi-arid area of Northeast China, which leads to the decrease of maize yield, the effects of different planting density and nitrogen application rate on photosynthetic characteristics, relative chlorophyll content and yield of maize leaves ( different layers ) under drip irrigation with water and fertilizer integration were explored.From 2024 to 2025, it was set up in the science and technology park of Heilongjiang Bayi Agricultural University in Anda City, Heilongjiang Province according to the split-plot test. The main area was the planting density, which was set at 4500 (M1), 5500 (M2) and 6500 (M3) plants / mu, respectively. The sub-area was topdressing different nitrogen application rates, which were set as conventional nitrogen application rate (N1), 80% nitrogen application rate (N2) and 60% nitrogen application rate (N3). Set a one-time fertilization treatment (Y) as a control treatment. Leaf area index, dry matter accumulation, grain filling rate, yield, chlorophyll content and photosynthetic parameters of maize leaves under different layers were measured.The results showed that under M1 and M2 densities, the leaf area index increased first and then decreased with the decrease of nitrogen application rate, and the leaf area index of N2 treatment was the highest, which was 4.33 % ~ 17.6 % higher than that of Y treatment. The leaf area index under M3 density decreased continuously with the decrease of nitrogen application, and the N1 treatment was the highest, which was 23.91%~32.04% higher than that of Y. In terms of photosynthetic characteristics, the relative chlorophyll content, net photosynthetic rate and transpiration rate of the middle and lower leaves of M2N2 were the highest in the whole growth period, and M3N3 was the lowest. The light transmittance of canopy decreased with the increase of density. Under different nitrogen application levels, N1 had the lowest light transmittance, N3 had the highest light transmittance, and N2 was between the two and formed a better canopy structure and light conditions. In terms of dry matter accumulation, M2 had the highest accumulation after flowering and M3 had the lowest accumulation after flowering under the same nitrogen application rate, and N2 had the highest accumulation after flowering and N3 had the lowest accumulation after flowering under the same density. Among the grain filling characteristics, the grain weight and active filling period of N2 reached the maximum value (11.1 g and 40.4 d in 2 years), which was beneficial to the continuous accumulation of dry matter, while the average filling rate (0.63 g·d?1 in 2 years) and the maximum filling rate (0.95 g·d?1 in 2 years) of N1 were the highest, and the active filling period was the shortest (33.9 d in 2 years), showing the characteristics of high filling intensity and concentrated process. The final yield was the highest in M2N2 treatment, which was 22% (2024) and 19% (2025) higher than that of Y, respectively.In summary, compared with the traditional nitrogen application reduction of 20% combined with 5500 plants / mu planting density, combined with shallow buried drip irrigation water and fertilizer integration technology, sub-precision fertilization can be conducive to the interception of group light energy, promote grain filling, and then increase yield, achieve high yield and efficiency of maize nitrogen reduction. |