The potential use of black soldier fly larvae residue as a fertilizer

Abstract: In sub-Saharan Africa (SSA), the primary constraint of agriculture productivity has consistently been ascribed to soil fertility. A common approach to improve soil fertility is the use of fertilizers, both organic and inorganic. Though recently interest is increasing in the use of newer alternatives like biostimulants. Biostimulants are found to contribute to plant growth as well as to plant health. There are different forms of biostimulants, such as phytohormones, humic substances amongst others, and it can be applied from different sources, for example vermicompost. For similar reasons to the earthworms in the vermicomposting process, the Black Soldier Fly (BSF) received growing attention. The larvae of the BSF can convert organic waste into valuable products. The larvae themselves can be used as feed for pigs, poultry and fish, or can be further processed to obtain biodiesel, chitin and/or essential fatty acids. The residue of the bioconversion process has the potential to be used as a fertilizer. However, previous literature showed mixed results regarding the effect on the plant and on the characteristics of the residue. This study confirmed the assumption that the quality of the residues depend on the substrate fed to the Black Soldier Fly larvae (BSFL). Furthermore, the study compared the physico-chemical characteristics of the BSFL residues with other fertilizers, a commercial inorganic fertilizer, a commercial organic fertilizer, chicken manure and vermicompost. Based on the NPK content, the BSFL residues could not replace the commercial inorganic fertilizer. However, based on other physico-chemical characteristics, like the pH, EC or OM content, the BSFL residues can have an advantage over the inorganic fertilizer. Compared to the other organic fertilizers, the BSFL residues of the study have remarkably higher OM content. Though regarding the other characteristics, the data found for the BSFL residues are not remarkably higher nor remarkably lower than of the other organic fertilizers. Besides the characteristics of a fertilizer, several other factors determine the use of it. Socio-economic characteristics, like the cost of a fertilizer, the availability, and the lack of knowledge regarding a fertilizer, but also specific household characteristics, such as household size and composition, education level, gender, and ownership of livestock and/or poultry, can either constrain or promote the use of a certain fertilizer. Moreover, all these factors are interlinked. As for each fertilizer, BSFL residue has its’ own advantages and disadvantages. A SWOTanalysis combining the bio-physical and socio-economic factors regarding BSFL residues as a fertilizer is included in the study. Even though there is a major potential to use BSFL residues as a fertilizer, further research should be done. Further research should be done to the characteristics, in particular to the presence of biostimulants in the residues. Furthermore, the effect of the residues on soil fertility should be determined in the mid and long-term.