Effects of Synergistic Regulation of Functional Fertilisers and Vermicompost on Soil Fertility and the Growth and Quality of Two Tomato Varieties

The quality of tomato fruit represents a key determinant of consumer preference, while functional fertilisers significantly contribute to quality enhancement. Limited research has investigated the synergistic mechanisms between functional fertilisers and vermicompost in tomato cultivation systems. The present study was designed to investigate the effects of synergistic regulation between functional fertilisers and vermicompost on soil fertility, as well as the growth and quality of two tomato cultivars, with the ultimate goal of identifying the functional fertiliser treatment exhibiting optimal comprehensive performance. A completely randomised block design was adopted, involving two tomato cultivars (DRK0568 and Sangfen 180), five functional fertiliser treatments (T1–T5), and a water-only control (CK). Measurements included tomato growth parameters, photosynthetic characteristics, fruit quality indices, yield components, biomass accumulation, soil nutrient levels, and enzyme activities. The results demonstrated significant varietal-specific responses to different functional fertiliser treatments. In terms of growth and yield, the T1 treatment exhibited a significant advantage, as it significantly increased the plant height, stem thickness, biomass, and yield of both varieties (DRK0568 and Sangfen 180) by 6.86% and 10.41%, respectively, while also significantly reducing the malformed fruit rate. For photosynthetic analyses, the T1 treatment significantly increased the chlorophyll a and total chlorophyll content in Sangfen 180, as well as the transpiration rate of both tomato varieties. The T4 treatment resulted in the highest chlorophyll b content and optimal water use efficiency in Sangfen 180. Regarding nutritional quality, the T1 treatment significantly increased the vitamin C and soluble sugar content in DRK0568; both varieties exhibited higher sugar–acid ratios under the T3 and T4 treatments. A comprehensive evaluation using the entropy-weighted TOPSIS method for multiple quality indicators (excluding yield parameters) showed that the T4 treatment achieved the highest score. Soil nutrient analyses revealed that the T1 treatment significantly increased the soil organic matter and available potassium content in DRK0568, while the T4 treatment significantly increased the urease activity in Sangfen 180. In conclusion, the T1 treatment (mineral-sourced potassium fulvate fertiliser) exhibited excellent performance in both increasing yield and improving quality, while the T4 treatment (Type II algal polysaccharide fertiliser additive) demonstrated unique advantages in enhancing fruit quality indicators.