Objective This study aimed to investigate the effects of different water gradient treatments on soil nutrient changes, plant physiological characteristics, leaf photosynthetic characteristics, yield, and fruit quality of walnut trees, and to select the optimal irrigation quota treatment based on the comprehensive benefit evaluation of each water gradient treatment, so as to provide a theoretical reference for the scientific management of walnut trees.

Methods Taking the walnut variety 'Wen 185' as the research object, four irrigation amount treatments were set up: W1 (6 750 m³/hm²), W2 (7 500 m³/hm²), W3 (8 250 m³/hm²), and CK (9 000 m³/hm²). Soil nutrient content, leaf photosynthetic parameters, fruit quality, and yield were measured. Correlation analysis was conducted, and principal component analysis was used for comprehensive evaluation.

Results Under different water treatments, there were significant differences in walnut branch growth, leaf water content, soil nutrients, soil moisture, and fruit quality. The branch diameter growth under different water treatments ranked as W2>W1>W3>CK. The contents of soil available phosphorus, available potassium, and alkali-hydrolyzable nitrogen showed a decreasing trend with increasing soil depth. Net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr) showed a decreasing–increasing–decreasing trend across different growth stages. Correlation analysis revealed strong correlations among fruit quality indices. Principal component analysis of fruit quality under different water gradients yielded a comprehensive score ranking of W2>W3>CK>W1.

Conclusion The irrigation quota of 7 500 m³/hm² is suitable for walnut trees, as this treatment can achieve better production benefits. This finding provides a theoretical basis for optimizing water-saving irrigation schedules for walnut trees in Southern Xinjiang.