Mild deficit irrigation: A water-saving strategy for enhancing fruit quality and water production of wolfberry

Soil salinization, exacerbated by water scarcity in arid and semi-arid regions, represents a major constraint on the sustainable intensification of commercial wolfberry production. Appropriate irrigation management offers an approach to reducing water demand, mitigating salt stress, and improving wolfberry production performance. To investigate this, a field experiment (2021–2023) was conducted to evaluate the effects of four irrigation levels—full irrigation (W0: 75–85% θ f ), mild deficit (W1: 65–75% θ f ), moderate deficit (W2: 55–65% θ f ), and severe deficit (W3: 45–55% θ f )—on wolfberry growth, physiology, yield, quality, and water productivity. The results demonstrated that wolfberry plant height, stem diameter, leaf SPAD values, net photosynthetic rate (P n ), transpiration rate (T r ), and stomatal conductance (Cond) were significantly decreased as water deficit intensified. All growth indicators peaked during the autumn fruiting stage, while photosynthetic parameters reached their maximum during the fruiting stage. Water regulation significantly affected wolfberry quality ( P < 0.01), with reduced irrigation leading to quality decline. Wolfberry yield, dry weight of fruits per plant, 100-fruit dry weight, dry-to-fresh ratio, and crop water productivity (WP c ) all peaked under the W1 treatment; irrigation and wolfberry evapotranspiration (ET c act ) were highest under the W0 treatment, increasing by 7.70%–91.36% and 5.22%–64.95% compared to other treatments. The ET c act showed a quadratic relationship with irrigation, as well as with wolfberry yield and quality. Application of partial least squares structural equation modeling (PLS-SEM) elucidated a direct and significant pathway from water regulation to both wolfberry growth and water productivity. Comprehensive evaluation using Entropy Weight-TOPSIS, RAR, and PCA methods revealed that the W1 treatment (65%–75% θ f ) synergistically enhanced wolfberry yield and quality while ensuring efficient water utilization. Therefore, mild deficit irrigation (W1) is proposed as a water-saving, yield-stabilizing, and quality-enhancing strategy for wolfberry production in arid and semi-arid regions.