Enhancing the Quality of Tomato Straw Waste Composting: The Role of Earthworm Stocking Density in Composting–Vermicomposting Integrated Systems

Recently, combining composting with vermicomposting has garnered growing interest as an efficient approach for the sustainable processing of agricultural waste. This study utilized composting as a pretreatment method to mitigate the salinity of tomato straw, employing four distinct earthworm stocking densities (0, 40, 80, and 120 worms/kg) to assess the feasibility of a combined composting–vermicomposting approach for stabilizing tomato straw waste. The results indicated that the total nitrogen, total phosphorus, total potassium, humification index, and germination index of the vermicompost products increased by 3.2–10.57%, 3.3–12.69%, 2.65–7.42%, 21.56–30.54%, and 36.57–91.68%, respectively. Relative to the control, the greatest improvement was observed at a density of 80 worms per kilogram of tomato straw compost. Moreover, the earthworm treatment group showed enhanced enzyme activity, bacterial abundance, and diversity relative to the control group. It can, therefore, be concluded that the integrated composting–vermicomposting system contributes to enhancing the quality of tomato straw waste compost. However, to further explore the treatment potential of high-salinity agricultural waste, future research could optimize the integrated composting and vermicomposting system and investigate the synergistic effects between earthworm stocking density and environmental factors.