This study explores the effects of vermicompost on the chemical and biological properties of soils, their nutrient content, and the impact on the growth and phenolic content of basil (Ocimum basilicum L.). Using a controlled experimental setup, we tested five dosages of vermicompost (0%, 4%, 12%, 20%, and 24%) to evaluate their influence on soil biological activity by measuring basal respiration (CO2-C), microbial biomass C (MBC-C), and dehydrogenase enzyme activity (DHA) as well as on basil's growth parameters and total phenolic content (TPC). The results show that vermicompost addition to soil enhanced soil microbial activity in direct proportion to the dose of vermicompost. The application of lower dosages of vermicompost (4% and 12%) significantly enhanced both fresh and dry weights, suggesting an improvement in nutrient uptake and soil structure, which likely facilitated better root growth and nutrient absorption. However, higher dosages (20% and 24%) were associated with reduced growth metrics, likely due to nutrient overload or salt stress. Notably, the highest vermicompost concentration (24%) led to a substantial increase in total phenolic content (TPC) in basil leaves, correlating with decreased growth metrics. This response indicates the plant's defensive mechanism against oxidative stress caused by excess nutrients or salinity from the vermicompost. A multiple regression analysis following a correlation analysis also revealed an inversely proportional relationship between phosphorus content in the soil and total phenolic content in basil leaves. Our findings illustrate that while moderate vermicompost dosages optimize plant growth and health, higher concentrations can strategically enhance phenolic content due to nutrient overload or salt-induced stress. These results offer critical insights for tailoring organic amendment applications to balance plant growth and biochemical properties in agricultural practices.
