Effects of black soldier fly frass on plant and soil characteristics : a literature overview

Black soldier fly (BSF) frass, resulting after bioconversion of organic materials by Hermetia illucens larvae can be used as fertilizer. This overview provides a literature summary of the main (macronutrient) components in frass and its reported effects on plant growth/health and soil. Frass composition is highly dependent on the substrate. Based on average composition, BSF frasses show resemblances to cow manure (C/N ratio, N content), pig slurry (P content), poultry manure (DM, Kcontent) and compost (DM). The frass has a higher organic matter content than compost and beforementioned manure types. Frass seems to be a fast acting fertilizer. Most of the nitrogen is organic,but ammonia content is highly variable. Reported effects on plant growth were often positive or neutra lbut also sometimes negative compared to organic and mineral control fertilizers and there seem to be maximum application rates above which positive effects diminish. Several authors mention that post-treatment of frass (for example by aerobic composting) is necessary to obtain a stable/mature product.Usually the frass is relatively high in P content, which may require extra N fertilizer addition. Severa lauthors state that chitin in the BSF frass likely benefits resistance to plant pathogens. Finally, adding frass can induce changes in the microbial community of the soil/plant rhizosphere. BSF frass can be used as a circular fertilizer in agriculture.