Comparative effectiveness of composting sun-dried versus insect-bioconverted chicken manure: Impacts on maturity, early plant development, gaseous emissions, and microbial communities

The direct application of untreated chicken manure poses risks of phytotoxicity, nutrient loss, and environmental pollution. This study evaluated secondary composting as a stabilization strategy for sun-dried chicken manure (CM) and black soldier fly larvae frass (LF). Both materials achieved high maturity and low phytotoxicity after composting. LF compost showed superior agronomic properties, including higher germination index, phosphorus, potassium, and organic matter content, along with elevated early-stage enzyme activities. It also fostered a more diverse and abundant bacterial community, with marked enrichment of keystone phyla such as Patescibacteria (associated with compost maturity) and Actinobacteriota (linked to humification and CH₄ suppression), while reducing the abundance of Firmicutes and Bacteroidota associated with nitrogenous emissions. This distinct microbiota correlated strongly with substantially lower gaseous emissions: LF reduced cumulative CH₄, CO₂, N₂O, and NH₃ emissions by 41.90%, 25.09%, 14.50%, and 85.86%, respectively, compared to CM, thereby contributing to an overall 64.89% reduction in greenhouse gas emissions. Redundancy analysis further linked these microbial shifts directly to the emissions reduction, providing mechanistic insight into the mitigation process. Both composts enhanced early plant growth, with LF being more effective. Therefore, secondary composting is essential for safe fertilizer use, and BSFL frass demonstrates superior potential for producing high-quality compost while concurrently achieving major environmental benefits through microbially driven processes.