Responses of Tomato Growth and Soil Environment Properties to Integrated Deficit Water-Biogas Slurry Application Under Indirect Subsurface Drip Irrigation

To explore the feasibility of integrated deficit water-biogas slurry irrigation under indirect subsurface drip irrigation, three deficit irrigation levels (60%FC, 70%FC, and 80%FC; FC represents field capacity) were established during the three growth stages of tomatoes. The results indicated that biogas slurry irrigation treatments increased the soil organic matter content in the root zone and water use efficiency (WUE) and reduced soil pH. As the degree of deficit increased, the plant height and stem diameter of tomatoes decreased significantly (p < 0.05), particularly during the seedling and flowering-fruiting stages. A mild deficit during the seedling stage was beneficial for subsequent plant growth, yielding maximum leaf area (6871.42 cm2 plant−1). Moderate deficit treatment at the seedling stage maximized yield, which was 19.79% higher than the control treatment in 2020 and 19.22% higher in 2021. The WUE of severe deficit treatment at the maturity stage increased by 26.6% (2020) and 31.04% (2021) compared to the control treatment. Comprehensive evaluation using TOPSIS combined with the weighted method revealed that severe deficit treatment at the maturity stage provided the best comprehensive benefits for tomatoes. In summary, deficit irrigation at different growth stages positively influenced tomato growth, quality, and soil environment in response to water-biogas slurry irrigation.