Optimizing irrigation salinity for cotton production through cotton yield and fiber quality and water use efficiency in arid regions

Irrigation with brackish irrigation sources puts forward a viable strategy to mitigate agricultural water scarcity in arid regions. Earlier investigations have established the inhibitory impacts of salt stress on cotton growth, yield, and quality, there remains a critical gap in identifying salinity thresholds that simultaneously optimize yield, quality of cotton, and WUE. To address this, a comprehensive two-year field investigation (2021–2022) was conducted in Shihezi, Xinjiang, utilizing a mulched drip irrigation system under four irrigation water salinity regimes: 0.85 g L −1 (control), 3 g L −1 , 5 g L −1 , and 8 g L −1 . The study systematically evaluated the impact of brackish irrigation on cotton development parameters, physiological traits, crop output, and fiber properties to identify the optimal salinity range for enhanced productivity and resource efficiency. Results showed that 3 g L −1 salinity irrigation significantly enhanced growth parameters, including plant height (Ph), stem diameter (Sd), leaf area index (LAI), aboveground dry matter accumulation (Ab), net photosynthetic rate ( P n ), transpiration rate ( T r ) and stomatal conductance ( G s ), ultimately enhancing both yield and fiber properties. In contrast, higher salinity levels (5 g L −1 and 8 g L −1 ) negatively impacted crop development and productivity. Compared to the control, 3 g L −1 salinity increased yields by 5.92 % (2021) and 4.76 % (2022). Path analysis using structural equation modeling (SEM) revealed that salinity primarily influenced yield through its effect on T r , which mediated changes in LAI and Ab, ultimately determining seed cotton yield (SCY). Salinity also directly affected fiber quality, particularly micronaire value (MIC) and uniformity index (UFI). Regression analysis identified an optimal salinity range of 1.76–3.00 g L −1 for achieving balanced improvements in yield, fiber quality, and WUE. These findings provide a scientific foundation for optimizing brackish water use in cotton production, delivering practical guidance for eco-efficient farming systems across water-scarce zones globally.