Salty bio-converted organic fertilizer modulates soil greenhouse gas emissions

The black soldier fly frass (BSFF) can be applied as a bio-converted organic fertilizer in agriculture and has been shown to affect soil properties and plant growth. However, the impacts of salty BSFF derived from kitchen waste (KW) on soil properties and greenhouse gas emissions are unclear. The impacts of salty black soldier fly (Hermetia illucens) frass derived from KW on soil properties and greenhouse gas emissions were investigated. The frass amendments increased soil dissolved organic carbon and nitrogen (0.5-1.6 and 0.1-15 fold) and soil ammonium (0.5-31 fold) content, with a similar trend as soil pH (0 similar to 0.4 fold) and electrical conductivity (2-131 fold). Soil gas emissions (CO2 and N2O) increased by frass amendments. The frass amendment affected the microbial communities followed by the addition rates, with the enriched beneficial bacteria (Nocardioides) and depleted denitrification fungi (Penicillium) as well as the C- and N-cycle related microbial functional genes. The nirS and amoB genes were the critical factors in the soil N2O emission with the frass amendment ratio in the soil. The lig and glx genes involved in lignin decomposition contributing to the increase of soil CO2 emission. These findings indicated that there is a need to inform research and policy decisions aimed at developing and promoting appropriate standards and guidelines for quality production, sustainable utilization, and successful integration of the frass into existing organic fertilizer framework and soil systems.