Characteristics of Phosphorus Activation and Identification of Phosphorus-Solubilizing Bacteria During Composting of Livestock and Poultry Manure with Phosphogypsum

Phosphogypsum (PG) has the potential to elevate phosphorus levels in compost; however, it may also retard the composting maturation process, and its underlying mechanism for phosphorus activation remains unclear. In this study, sawdust was mixed with pig manure or chicken manure at a ratio of 1:4 (m:m, fresh weight) and added 10% PG as the treatment group, and added no PG as control treatment. The entire composting process lasts for 60 days. During the composting process, temperature was monitored daily, pH, electrical conductivity (EC), germination index (GI), phosphorus and its distribution were measured to monitor the composting process, and bacterial communities and predict phosphate-solubilizing genes and bacteria through the KEGG database. Pearson correlation analysis between phosphate-solubilizing bacteria and phosphorus components was conducted. The results demonstrated that (1) PG supplementation delayed the temperature rise and humification during composting, yet the final compost maturity was maintained (GI ≈ 90%). (2) PG addition increased the abundance of the ppx-gppa and phoR genes in pig manure compost, while enhancing the phnE and phoP genes in chicken manure compost. (3) In pig manure composting, Dietzia and Clostridium sensu stricto_1 were identified as key bacteria responsible for phosphorus activation, and promoting their growth favored phosphorus mobilization. (4) In chicken manure compost, Lactobacillus and Pseudomonas played crucial roles in phosphorus activation, though inhibiting their growth was found to enhance phosphorus availability. Overall, PG addition promoted phosphorus activation in compost, significantly increasing the NaHCO3-P content in both pig manure and chicken manure composts (by 9.36 and 17.86 percentage points, respectively).