Phosphorus Solubilization by Thermotolerant Bacillus subtilis Isolated from Cow Dung Microflora

Soil inoculation with phosphate-solubilizing bacteria is known to improve solubilization of fixed soil phosphorus (P). Cow dung (CD) is normally used as an organic manure for enhancing soil fertility in tropical agriculture. Thermotolerant (\50 C) Bacillus subtilis strains isolated from CD solubilized tricalcium phosphate (CP) to available (soluble) phosphate in culture and in autoclaved soil amended with 1 % CP. The solubilization of CP was associated with the phosphatase activity of the bacterium, particularly acid phosphatase (AcP). Autoclaved soil amended with CD (10 %) showed 25.3 and 12.6 % higher solubilization of P and AcP activity, respectively, than autoclaved soil inoculated with B. subtilis. Also, B. subtilis inoculation and CD amendment resulted in higher P solubilization and phosphatase activity in both rhizosphere and nonrhizosphere of soil planted with cowpea (Vigna unguiculata L.) than without these two treatments. Similarly, root length, plant height, and plant biomass of cowpea seedlings were higher in bacterium- or CD-treated soil than in untreated soil. These results suggest that these thermotolerant B. subtilis strains as bio-inoculant or CD amendment can be successfully employed in tropical agriculture for solubilization of P and maintaining soil health, being useful in the context of global warming.