Interaction effects of different sources of phosphorus and potassium on phosphate and potassium solubilizing behavior of some bacterial isolates

Potassium and phosphorus are essential elements for plant growth, and application of biological methods is one approach to supply them. This study was done, in order to evaluate the effect of soluble source of phosphorus (phosphate sodium) and insoluble (tricalcium phosphate) on K release from mica minerals (biotite and muscovite) and also the effect of mica minerals in dissolution of phosphorus from tricalcium phosphate. This test was carried out in the presence of some bacterial isolates belonging to the genus Pseudomonas (S10-3, S14-3, S19-1 and S21-1). It was conducted as a factorial experiment based on completely randomized design with three replication containing two factors including two source of phosphorus and two potassium sources. From overnight cultures of the bacteria (0.5 ml) were added to 30 ml of Aleksandrov medium. After incubation for one week at 26 ° C and shaking at 120 rpm, released K in supernatant was measured by using flame photometer and the dissolution of phosphate by using spectrophotometer at 430 nm (yellow method). The results showed that K releasing from the biotite was more than muscovite and bacterial isolates released more potassium (in average 15-48%) in the presence of tricalcium phosphate than sodium phosphate. The isolate S19-1 revealed highest potassium releasing (5.45 mg/l). The results displayed that the released potassium from biotite by bacteria 4.5 times was more than muscovite. Biotite and muscovite minerals did not significantly affect on the phosphate solubilization and the highest phosphate solubilization (488 mg/l) was obtained by S19-1.