Optimized water and nitrogen management improves photosynthesis, yield, and resource use efficiency of maize under mulched drip irrigation

Photosynthesis underpins crop yield formation, and understanding its response to integrated water-nitrogen management is essential for sustainable agricultural development. While drip fertigation has proven effective in conserving water, enhancing yield and reducing nutrient losses, its regulatory effects on photosynthetic performance of densely-planted maize under plastic-mulched drip irrigation in arid regions remain poorly understood. To address this knowledge gap, a two-year field experiment was conducted from 2024 and 2025 to investigate the combined effects of irrigation and nitrogen fertilization on maize photosynthesis and yield formation, with irrigation amounts ranging from 42.75 to 52.5 mm and nitrogen application rates from 0 to 360 kg ha−1. The results showed that moderate nitrogen application significantly increased relative chlorophyll content, net photosynthetic rate, maximum quantum efficiency, effective quantum yield of PSII, and photochemical quenching, while markedly reducing non-photochemical quenching. These combined effects promoted carbon assimilation and assimilate accumulation, benefiting grain yield formation. However, excessive nitrogen application diminished these beneficial effects. Among all treatments, irrigation with 47.25 mm of water combined with 240 kg ha−1 of nitrogen fertilization was identified as optimal for improving photosynthesis and grain yield, achieving a two-year average yield of 20,873.78 kg ha−1.Compared with conventional fertigation practices used by local farmers, this optimal treatment reduced irrigation water and nitrogen fertilizer inputs by 10.0 % and 33.3 %, respectively, while increasing grain yield, irrigation water use efficiency, and nitrogen partial factor productivity by 18.77 %, 30.56 %, and 78.17 %, respectively. Structural equation modelling revealed that the optimal fertigation enhanced grain yield primarily through increasing photosynthetic capacity and PSII function. A comprehensive evaluation using the TOPSIS method further indicated that the optimal fertigation provided the greatest synergistic benefits in photosynthetic performance, and resource-use efficiency. Overall, this study results demonstrate that optimizing fertigation can synergistically improve photosystem function, resource-use efficiency and crop productivity, they provide practical guidance for sustainable and efficient maize production under drip irrigation in arid regions.