Determination of optimal biochar application and irrigation rate for tomatoes based on the EWM-TOPSIS evaluation method

Deficit irrigation (DI) enhances crop water use efficiency by moderately reducing the water supply; however, excessive DI poses risks of yield reduction and quality deterioration. Biochar (BA) improves soil structure and enhances water/nutrient retention capacity, but its efficacy in mitigating crop water stress varies with application rates. A two-season greenhouse experiment was conducted with distinct BA application rates (B0, B1, B2: 0, 25, 50 t ha⁻¹) and DI treatments (W1, W2, W3: 50%, 75%, 100% of crop evapotranspiration, ETc ). This study examined the combined effects of BA and DI on tomato growth parameters, physiological indicators, fruit quality, and economic value. Key findings include: BA significantly alleviated DI stress: Under moderate DI (W2), B2 increased leaf area index (LAI) and SPAD values by 28.7% and 7.3%, respectively, compared to severe stress (B0W1), while actual photochemical quantum yield (YII) rose by 11.5–15.5%. Synergistic optimization of quality and water use: B2W2 elevated total soluble solids (TSS), single-fruit weight, and solid-acid ratio by 23.2–33.3% versus non-BA groups (B0W2), with Irrigation Water Use Efficiency (IWUE) increasing by 17.8–23.9%.BA enhanced tomato yield: B2W3 boosted yield by 25.3–37.0% relative to B0W1, exhibiting a nonlinear yield response where benefits plateaued at higher BA rates. The entropy weight method EWM-TOPSIS comprehensive evaluation ranked B2W2, B1W3, and B2W3 as the top three treatments across both seasons, considering growth-physiology indicators, economic value, and production costs. This study confirms that integrating biochar with deficit irrigation is a viable strategy to optimize crop production and water utilization, particularly in water-scarce regions. Future research should elucidate region-specific synergies between BA and DI under diverse soil conditions to develop precision management protocols that are tailored to specific areas.