Effects of mealworm frass and frass-derived biochar on soil enzyme activity in an arid soil Author links open overlay panel

This study evaluated the effects of mealworm (Tenebrio molitor) frass and frass-derived biochar on microbial and enzymatic activity in an arid soil from Fuerteventura Island (Canary Islands, Spain), a region highly affected by desertification. Treatments included frass, biochar produced at 300°C and 600°C, and 1:1 frass-biochar mixtures, applied at 2.5% and 5% (w/w, dry basis). Over a three-month incubation, including a simulated dry-rewet cycle, extracellular enzyme activities related to C, N, and P acquisition were measured together with indicators of microbial activity and selected soil physicochemical variables. Frass produced the strongest response, significantly increasing enzyme activities, particularly those associated with P and N cycling. Biochar alone had weaker effects, but it did not inhibit microbial or enzymatic activity and appeared to reduce activity losses after drying. Ecoenzymatic stoichiometry and vector analysis indicated a treatment-related shift toward a more P-oriented relative enzyme-activity pattern in frass-containing treatments. The results show that mealworm frass can strongly stimulate soil biological functioning under controlled conditions, while frass-derived biochar may play a complementary role in maintaining enzymatic activity after soil desiccation. These findings support further evaluation of frass-based amendments for arid and semi-arid soils under field conditions and at agronomically realistic application rates.