Potassium Solubilization by Rhizosphere Bacteria: Influence of Nutritional and Environmental Conditions

Potassium (K) is the third major essential macronutrient for plant gro wth. The concentrations of soluble potassium in the soil are usually very lo w and more than 90% of potassium in the soil exists in the form of insoluble rocks and silicate minerals. Rhizosphere bacteria have been found to dissolve potassium fro m insoluble K-bearing minerals. In this study, bacterial isolates were obtained fro m wheat rh izosphere on modified A leksandrov med iu m containing mica powder as potassium source. Twenty bacterial strains, among 137 cu ltures tested, showed significant potassium solubilization on mica powder supplemented plates and the amount of K released by different strains varied fro m 15 to 48 mg L -1 . In glucose amended med iu m broth, bacterial strains WPS73 and NNY43 caused 41.0 and 48.0 mg L -1 of K solubilization. Bacterial strain WPS73 caused maximm solubilization (49.0 mg L -1 ) at 25°C whereas bacterial strain NNY43 caused maximu m solubilization at 30°C. K solubilization was found more when bacterial strains were grown in med iu m broth with p H 7.0. Maximu m K solubilization occurred when KCl was used as a potassium source followed by K2SO4. These results suggested that the environmental conditions could be optimized for growth of potassium solubilizing bacteria and these bacterial cultures could be exp loited for p lant growth imp rovement under field conditions.