Irrigation Regime and Straw-Returning Mode Regulate Soil Conditions, Leaf Physiology, and Yield of Winter Wheat (Triticum aestivum L.) in Saline–Alkali Soil

Winter wheat (Triticum aestivum L.) production in the Yellow River Delta is limited by saline–alkali soils and freshwater scarcity, while the responses of different straw-returning modes under contrasting irrigation regimes remain unclear. A field experiment was conducted with two irrigation regimes, normal irrigation (W1) and deficit irrigation (W2), and four straw-returning modes, direct straw return (RS), straw-derived cattle manure return (RM), straw biochar return (RB), and straw pellet return (RG). The experiment followed a split-plot randomized block design with three replicates. Soil properties, leaf physiology, photosynthetic performance, grain yield, and irrigation water use efficiency (IWUE) were evaluated. Compared with W2, W1 increased mean grain yield by 9.4%, whereas W2 increased mean IWUE by 36.7%. Among the straw-returning modes, RS showed the most consistent performance. Under W1, W1RS produced the highest grain yield (3509.72 kg ha−1). The stable performance of RS was characterized by relatively favorable soil moisture status, lower MDA content, higher antioxidant enzyme activity, and better maintenance of Pn. Pearson correlation analysis showed that grain yield was positively correlated with Pn and CAT activity, whereas MDA was negatively correlated with Pn. These results suggest that RS may be a feasible straw-returning mode for winter wheat production in saline–alkali soil.