Isolation and Characterization of Potassium-Solubilizing Bacteria from Paddy Rhizosphere (Oryza sativa L.)

Potassium is one of macronutrients required by plants. The concentrations of soluble Potassium in the soil are usually very low, more than 90% of Potassium in the soil are (K)-bearing minerals form,-one of them is Feldspar which quite abundant found in Indonesia. Rhizobacteria have been found to solubilize (K)-bearing mineral into a form that plants can access. This study aims to isolate and characterize Rhizobacteria from paddy rhizosphere that potentially dissolve mineral feldspar as potassium source. This study was conducted on February-June 2018 in Microbiology Laboratory, Department of Biology, Universitas Negeri Surabaya. Seven bacteria isolates capable of solubilizing potassium were LJK 1, LJK 2, LJK 4, LBK 4, LBK 5, PSUK 4, and PSIK 6. Based on the potassium-solubilizing index, seventh isolates were capable of solubilizing feldspar in Alexandrov solid medium, the best isolate with the highest score was LJK 2 (5,25 cm in diameter), contrary with the lowest score was LBK 4 (2,37 cm). In amended Alexandrov broth, isolate suspension of LJK 2 caused maximum solubilization (6,846 mg/L), while the minimum solubilization was PSIK 6 (6,724 mg/L). All these isolates were characterized on the basis of morphological and physiological-biochemical test up to 39 characteristics.