Effect of Regulated Deficit Irrigation on the Growth, Yield, and Irrigation Water Productivity of Processing Tomatoes under Drip Irrigation and Mulching

The application of regulated deficit irrigation (RDI) strategies with high water-saving effects for processing tomatoes is an important current research trend. In this study, we aimed to reveal the patterns of growth, yield, and irrigation water productivity (WP_I) in response to the water deficit in processing tomatoes under drip irrigation and plastic mulching in Xinjiang. To determine a more precise irrigation regime, various degrees of RDI treatments were applied to processing tomatoes in 2022 and 2023. A total of five water gradients were set up: RI (Regular Irrigation; 4500 m³/ha), W₁ (4185 m³/ha), W₂ (3870 m³/ha), W₃ (3555 m³/ha), and W₄ (3240 m³/ha). The results revealed that under RI, the yield and irrigation water productivity were 142 t/ha and 31.49 kg/m³, respectively. Compared with RI, W₁ exhibited an increase in yield and irrigation water productivity of 12.13% and 22.39%, respectively; however, other treatments exhibited a decrease. The main reasons for the increase in yield under the W₁ treatment were: the W₁ treatment, improved photosynthetic performance, increased dry matter accumulation, and improved soil moisture conditions, thus promoting plant growth and development. In addition, in terms of water regulation at various fertility stages, moderate water deficiency at the seedling stage (S), flowering stage (F), and maturity stage (M) and rewatering at the fruit expansion stage (E) were more conducive to optimizing the yield structure. In conclusion, considering plant growth status, dry matter accumulation, yield, and WP_I, we suggested that the W₁ treatment is the optimal RDI mode most suitable for drip irrigation under mulching for processing tomatoes in Xinjiang. This study provided a theoretical and technical basis for the promotion of “water-saving and efficiency-enhancing” production of processing tomatoes.