Phosphorus-Mobilizing Rhizobacterial Strain Bacillus cereusGS6 Improves Symbiotic Efficiency of Soybean on an Aridisol Amended with Phosphorus-Enriched Compost

Legume plants are an essential component of sustainable farming systems. Phosphorus (P) deficiency is a significant constraint for legume production, especially in nutrient-poor soils of arid and semi-arid regions. In the present study, we conducted a pot experiment to evaluate the effects of a phosphorus-mobilizing plant-growth promoting rhizobacterial strain Bacillus cereusGS6, either alone or combined with phosphate-enriched compost (PEC) on the symbiotic (nodulation-N2fixation) performance of soybean (Glycine max(L.) Merr.) on an Aridisol. The PEC was produced by composting food waste with addition of single super phosphate. The bacterial strain B. cereusGS6 showed considerable potential for P solubilization and mobilization by releasing carboxylates in insoluble P (rock phosphate)-enriched medium. Inoculation of B. cereusGS6 in combination with PEC application significantly improved nodulation and nodule N2fixation efficiency. Compared to the control (without B. cereusGS6 and PEC), the combined application of B. cereusGS6 with PEC resulted in significantly higher accumulation of nitrogen (N), P, and potassium (K) in grain, shoot, and nodule. The N:P and P:K ratios in nodules were significantly altered by the application of PEC and B. cereusGS6, which reflected the important roles of P and K in symbiotic performance of soybean. The combined application of PEC and B. cereusGS6 also significantly increased the soil dehydrogenase and phosphomonoesterase activities, as well as the soil available N, P, and K contents. Significant positive relationships were found between soil organic carbon (C) content, dehydrogenase and phosphomonoesterase activities, and available N, P, and K contents. This study suggests that inoculation of P-mobilizing rhizobacteria, such as B. cereusGS6, in combination with PEC application might enhance legume productivity by improving nodulation and nodule N2fixation efficiency.