Superphosphate, Biochar, and a Microbial Inoculum Regulate Phytotoxicity and Humification During Chicken Manure Composting

Abstract

The germination index (GI) is the best index for evaluating compost phytotoxicity and maturity. The Chinese organic fertilizer standard requires a GI of ≥70% from 2021. Chicken manure compost with a high degree of phytotoxicity and low GI was determined in this study. Superphosphate, biochar, and a microbial inoculum were added to improve compost maturity. Maturity indices (pH, electrical conductivity, and GI), water-soluble ion, organic matter, and humic acid and precursor contents, and the bacteria community were assessed during the experiment. NH4+, volatile fatty acids, and humic acid strongly affected the GI, which increased as the humic acid content increased and the volatile fatty acid and NH4+ contents decreased. Biochar, the microbial inoculum, and superphosphate affected compost maturity differently. Adding biochar decreased microbial diversity and complexity, but improved the GI mainly by affecting abiotic factors (increasing adsorption and the pH). Adding the microbial inoculum increased biotic activity and promoted humus and precursor formation. Superphosphate activated core functional bacteria and increased bacterial diversity and complexity, and 16 genera and two phyla (Gemmatimonadota and Chloroflexi) were found only in this composting pile. Superphosphate markedly accelerated humification and decreased the salt and heavy metal ion contents, which in turn decreased the compost phytotoxicity and improved the GI.

Keywords: Composting；germination index；phytotoxicity； humification；superphosphate