Integrating insect frass biofertilisers into sustainable peri-urban agro-food systems

The larvae of black soldier fly (BSF) have shown great promise in transforming organic wastes into a more valuable larval biomass. Importantly, after insects have been harvested the remaining by-product, comprised of the spent substrate and frass (insect faeces), has the potential to be used as a biofertiliser. Three field-scale experiments to investigate whether frass biofertilisers (made from either poultry waste, brewery waste or green market waste) could be successfully incorporated into current small-holder farming practices were undertaken in Ghana, West Africa. In general, BSF frass biofertilisers performed as well as the local practice of amending Zai planting pits with chicken manure, or incorporating uniformly broadcast fertilisers. For short-cycle cash crops such as chilli pepper and shallots, brewery waste biofertilisers performed better than poultry waste biofertilisers, particularly when added in combination with inorganic NPK fertilisers. For maize, green market waste biofertiliser did not significantly improve yield at applications of either 5 or 10 t/ha, even when combined with inorganic fertilisers. However, frass biofertiliser amendment did significantly reduce the loss of cowpea plants due to Fusarium wilt disease. We hypothesise that the fragments of chitin (originating from 4-5 larval moults) in frass biofertilisers can induce disease resistance in crop plants grown in biofertiliser-amended soil. The benefit of frass as a by-product of insect larvae production can increase the profitability of this burgeoning industry in developing countries, and provide employment opportunities and self-sufficiency in the nutrient supply chain by integrating organic waste management and insect farming into peri-urban agro-food systems.