Application of biochar-immobilized Bacillus megaterium for enhancing phosphorus uptake and growth in rice

Phosphorus (P) is essential nutrient for rice growth, and the presence of phosphate-solubilizing bacteria (PSB) is an effective mean to increase soil P content. However, the direct application of PSB may have minimal significance due to their low survival in soil. Biochar serves as a carrier that enhances microbial survival, and its porous structure and surface characteristics ensured the adsorption of Bacillus megaterium. Inoculating rice husk biochar-immobilized with B. megaterium (BMB) resulted in dissolved inorganic and organic P levels of 39.55 and 31.97 ml/L. Rice pot experiments were then conducted to investigate the response of soil microbial P mobilization and P uptake in rice to fertilizer input. The combination of organic fertilizer (OF) and BMB significantly increased soil available phosphorus (AP), as well as increased the levels of phoD bacterial communities compared with the control. Furthermore, the bioavailable P reservoir (H2O-Pi and NaHCO3-Pi) in soil was greatly increased through the fertilizer input and microbial turnover. Additionally, carbon utilization analysis were applied using the commercial Biolog system. The combination of BMB and OF significantly increased microbial catabolic activity, particularly for utilization of Carbohydrate, Carboxylic acid, Polymers and Amino acid carbon. Moreover, rice P content was significantly correlated with AP content, NaHCO3-Pi, NaOH-Pi and carbon source utilization. Our study demonstrated that the combination of OF and BMB displayed higher P levels in both soil and rice plants. This provides a theoretical basis for further understanding the role of biochar-based bacterial agents in rice P management.