Bacillus-based PGPR consortium enhanced soil microbial activity and function in soil amended with FGD-gypsum poultry litters

Poultry litter (PL) and plant growth-promoting rhizobacteria (PGPR) are being evaluated as cost-effective alternatives to conventional agrochemicals. Flue gas desulfurization (FGD) gypsum (FGD-gypsum) has also shown promise in recent years as a potential bedding replacement for poultry production. However, limited research has explored the effects of FGD-gypsum litter amendments alone or with PGPR on soil microbial functionality. This study aimed to (i) evaluate the impact of PGPR on soil microbial community function, dehydrogenase activity, and pH in soil amended with various FGD-gypsum PLs, and (ii) explore the relationships among microbial functional indices, dehydrogenase activity, and pH. Four PL types, SD (shaving, decaked), SWR (shaving, windrowed and rotovated), GD (FGD-gypsum, decaked), and GWR (FGD-gypsum, windrowed and rotovated), plus an unamended control (CTL) were evaluated, with and without a Bacillus -based PGPR consortium. The results showed that PGPR enhanced average well color development (AWCD) and substrate richness by 18.7% and 16.1% (SD), 38.7% and 29.6% (SWR), 84.6% and 60.9% (GD), 177.4% and 135% (GWR), and 4.4% and 15.9% (CTL), respectively. PGPR inoculation also increased dehydrogenase enzyme activity by 111.7%, 118.8%, and 274.6% in soils amended with SWR, GD, and GWR, respectively. While PL increased soil pH compared to CTL, PGPR had no significant effect on soil pH. Dehydrogenase activity was highly correlated with AWCD ( r ² = 0.82) and microbial diversity indices in PGPR-inoculated soils. In contrast, soil pH showed a weak relationship with microbial diversity indices. These findings suggest that combining a Bacillus-based PGPR consortium with FGD-gypsum PLs can sustainably enhance soil microbial function and overall soil health.