From Fruit-Peel Waste to Soil Health: Anaerobic Biofertilizer Enhances Soil Microbial Function and Hot Pepper Productivity in Calabar, Nigeria

This study evaluated whether anaerobically digested fruit-peel wastes and cow dung could be converted into agronomically effective biofertilizers for restoring soil fertility, stimulating soil microbial communities and improving hot pepper (*Capsicum frutescens* L.) performance in the humid tropics. Banana, paw-paw and watermelon peels and cow dung were digested singly and in selected combinations for 45 days. Eleven bioslurry treatments, mineral NPK and an unfertilized control were evaluated in a randomized complete block design with three replications during wet and dry seasons. Substrate chemistry, digester temperature, pH, cumulative gas production, microbial counts, post-harvest soil properties, pepper growth and yield were assessed. Anaerobic digestion increased substrate nitrogen and shifted most acidic feedstocks towards near-neutral reaction. The four-substrate co-digestion treatment (W+C+P+B) recorded the highest cumulative gas production (49.4 units), retained the largest post-digestion bacterial and fungal populations, and produced bioslurry with 8.4% N. In the field, W+C+P+B increased soil pH from an initial 4.9 to 6.8, organic carbon to 3.4%, total N to 0.3%, available P to 40.1 mg kg−1 and base saturation to 91.3%. It also produced the greatest shoot and root biomass and the highest fresh fruit weights in both seasons. Balanced co-digestion can simultaneously divert biodegradable wastes, recover nutrients, improve acid-soil quality and reduce dependence on mineral fertilizer. Contribution: The study links feedstock transformation, microbial dynamics, soil restoration and crop response within one circular bioeconomy framework for smallholder production in humid tropical environments.