Stabilization of black soldier fly larval frass through vermicomposting with cattle manure: Agricultural and chemical assessment

Frass, a byproduct of Hermetia illucens (black soldier fly) rearing, contains high levels of nutrients, but its direct application to soil may be limited due to biological instability and phytochemical compounds. This study aimed to assess the vermicomposting of frass mixed with cattle manure at different proportions, targeting its stabilization for agricultural use. Five mixtures with increasing frass content (0–100 %) were prepared, and physicochemical parameters, germination index (GI), and structural characteristics were monitored using Fourier transform infrared spectroscopy (FTIR). Our findings revealed that high frass content compromises worm development and compost maturity. The mixture of 50 % frass and 50 % cattle manure showed the best results regarding stability, nutrient content, and cation exchange capacity (CEC) value, and was not phytotoxic (GI > 80 %). FTIR analysis confirmed the degradation of organic compounds and the formation of stable functional groups. In conclusion, vermicomposting with cattle manure is an effective strategy for frass stabilization, addressing an important gap in the literature and enhancing its potential as an organic fertilizer in sustainable farming systems. • Vermicomposting was used to stabilize frass from black soldier fly larvae. • Cattle manure enhanced frass degradation and earthworm development. • A 50:50 frass-to-manure ratio yielded mature, nutrient-rich vermicompost. • Phytotoxicity was reduced and seed germination index exceeded 100 %. • FTIR and PCA confirmed improved humification in blended treatments.