Fertilizing Effects of Black Soldier Fly Larval Frass Composts Sourced from Pig and Chicken Manure on Soil Microbial Community and Maize Seedling Growth

The biotransformation of livestock manure by black soldier fly larvae (BSFL) provides a new way for the resource utilization of manure, while the efficient utilization of BSFL frass fertilizers needs further research.

This study applied different types of organic fertilizers originated from pig and chicken manure into soil for maize cultivation, including natural composts (PNC, CNC), fresh frass after BSFL transformation (PBF, CBF), and BSFL frass composts (PBC, CBC).

The application of fresh frass and frass composts reduced soil pH, while increased the electrical conductivity, available nitrogen (AN), available phosphorus (AP), available potassium (AK) and NO₃^--N contents, as well as enzyme activities (urease, phosphatase and sucrase) in soil. For two manure groups, frass composts treated-soil exhibited higher NO₃^--N and AN levels than their respective fresh frass treated-soil, but had lower AP contents. Besides, the application of fresh frass and frass composts remarkably stimulated the plant height, total nitrogen (TN) and total potassium (TK) contents of maize seedling than CK. Moreover, fertilizer application had no significant influence on soil bacterial richness or diversity, but dramatically altered the microbial community structure. Compared to CK and natural composts treatments, fresh frass and frass composts fertilizers enhanced the abundances of certain beneficial microbes (e.g., Sphingomonas, Lysobacter, Gemmatimonas, Bryobacter and Pseudomonas) in soil, probably contributing to their better effects on improving soil available nutrients and crop growth.

Overall, pig manure sourced-BSFL frass composts had better effects on promoting maize seedling growth than fresh frass, while no significant differences were observed between chicken manure sourced-frass composts and fresh frass.