Processing poultry manure with black soldier fly technology lowers N₂O and CO₂ gas emissions from soil

Soil amended with poultry manure has many benefits including increased nutrient and organic carbon supply, enhanced soil structure and improved crop yield. However, the direct application of poultry manure to land can be associated with significant greenhouse gas (GHG) emissions. Black soldier fly (BSF) farming (Hermetia illucens) is an emerging technology that can convert manure into protein for animal feed, with larvae casting or frass produced as a waste by-product. BSF frass produced from poultry manure has potential to be used as a soil amendment with potentially lower GHG emissions than manure, but this has not been tested. To test this, a two-week microcosm experiment was used to investigate the impact of different soil amendments (poultry manure, BSF frass from poultry manure, urea and an unamended control) on nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) emissions. This study also aimed to examine bacterial populations associated with frass and poultry manure, as well as factors regulating their composition and the production of GHGs. Frass produced by BSF larvae fed poultry manure had up to 1.4 times lower N₂O and 1.5 times lower CO₂ cumulative emissions than poultry manure. Methane emissions were either minimal and/or balanced by oxidation across all treatments. Processing poultry manure with BSFL also altered the bacterial community composition and resulted in a proliferation of bacteria that were specific to BSFL frass, some of which have putative plant growth promoting properties. These results indicate that BSF technology holds promise for both reducing greenhouse gas emissions from poultry manure, as well as providing a sustainable soil amendment for productive agriculture.