Combined use of phosphorus containing calcium silicate and phosphate-solubilizing bacterium as a solid biofertilizer for sustainable soybean cultivation

Recycled phosphorus (P) from wastewater has attracted attention as an alternative P source for sustainable agriculture. We previously developed amorphous calcium silicate hydrate (aCSH) as a simple and efficient material for the recovery of inorganic P from wastewater. Although P recovered using aCSH (P_aCSH) is expected to be useful as a biofertilizer material, research on its effectiveness as a microbial carrier and fertilizer remains unexplored. In this study, we aimed to investigate the potential of the combined use of P_aCSH and a newly isolated phosphate-solubilizing bacterium, Burkholderia contaminans NKPB12, as a biofertilizer for soybean cultivation. Compared with conventional carriers, P_aCSH showed a higher cell immobilization capacity for NKPB12. Soybean cultivation test results confirmed the promotion of soybean growth when P_aCSH/crystalline CSH (cCSH) with NKPB12 was used as the sole P source. These results indicate that the combination of P_aCSH/cCSH and NKPB12 can be applied as a biofertilizer with recycled P for soybean cultivation. To our knowledge, this is the first report demonstrating the dual functionality of recovered P material as both a P source and bacterial carrier in biofertilizer applications.