PSB

Due to immobilization of phosphate by mineral ions such as Fe, Al and Ca and organic acids, the rate of available phosphate in soil is well below plant needs. Chemical fertilizers are also immobilized in the soil, immediately so that only 20% of added fertilizer is absorbed by plants. PSB converting insoluble phosphatic compounds such as rock phosphate, bone meal and basic slag particularly the chemically fixed soil phosphorus into available form. Such organism not only assimilates phosphorus but also cause a large amount of soluble phosphate to be released in excess of their own requirements and saves P2O5 up to 30 – 50 Kg/ ha. Phosphorus solubilizing activity is determined by the ability of microbes to release metabolites such as organic acid (lactic acid, malic acid, gluconic acid, fumaric acid, succinic and acetic acid). Inorganic phosphorus is solublizedby action of organic (gluconic, ketogluconic) and inorganic acids (Hcl) secreted by PSB and maintain the soil pH. The pH of rhizospheree is lowered the bio-carbonates release (anions/cation balance) and oxygen/carbon oxide gaseous exchange. Phosphorus solubilizing ability of PSB has direct correlation with pH of the medium.