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

Potassium (K) is the third major essential macronutrient for plant growth. The concentrations of soluble potassium in the soil are usually very low 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 from insoluble K-bearing minerals. In this study, bacterial isolates were obtained from wheat rhizosphere on modified Aleksandrov medium containing mica powder as potassium source. Twenty bacterial strains, among 137 cultures tested, showed significant potassium solubilization on mica powder supplemented plates and the amount of K released by different strains varied from 15 to 48 mg L-1. In glucose amended medium 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 maximum solubilization at 30°C. K solubilization was found more when bacterial strains were grown in medium broth with pH 7.0. Maximum 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 exploited for plant growth improvement under field conditions.