Effects of Bacillus subtilis and Pseudomonas fluorescens as the soil amendment

The application of soil beneficial bacteria (SBB) in agriculture is steadily increasing as it provides a promising way to replace chemical fertilisers and other supplements. Although the role of SBB as a biofertiliser is well under-stood, little is known about the response of soil physiochemical properties via the change in soil enzymatic ac-tivities with SBB growth. In this study, sterilised bulk soil was inoculated with Bacillus subtilis (BS) and Pseudomonas fluorescens (PF), which exhibit excellent characteristics in vitro for potentially improving soil quality. It is found that the contents of bioavailable nitrogen and ammonium in soil inoculated with SBB increased significantly, up to 34% and 57% relative to a control. This resulted from the enhancement of soil urease activity with BS and PF treatments by approximately 90% and 70%, respectively. The increased soil urease activity can be explained by the increased microorganism activity evident from the larger population size of BS (0.78-0.97 CFU mL-1/CFU mL-1) than PF (0.55-0.79 CFU mL-1/CFU mL-1) (p < 0.05). Results of principal component analysis also reinforce the interaction apparent in the significant relationship between soil urease activity and microbial biomass carbon (p < 0.05). Therefore, it can be concluded that the enhancement of soil enzymatic activities induced bulk soil fertility upregulation because of bacterial growth. These results demonstrate the application of SBB to be a promising strategy for bulk soil amendment, particularly nutrient restoration.