Assessment of Phosphate Solubilization and Indole Acetic Acid Production of Phosphate Solubilizing Bacteria Isolated from Acid Soils, Lampung, Indonesia

Phosphorus is the main macronutrient required by plants for growth and development. Phosphorus in the soil in bonds with metals such as Al and Ca, especially in acid soils such as ultisols. This form of phosphate must be mineralized or dissolved using phosphate solubilizing bacteria. The ability to dissolve phosphate also correlates with the production of Indole Acetic Acid (IAA), which can increase plant growth. This study aims to assess the ability of phosphate dissolution and IAA production of three phosphate solubilizing bacteria (EF.NAP 5, EF.NAP 7, and EF.NAP 10) which have been isolated from acid soils, Lampung. The method used was the clear zone test for bacterial isolates, phosphate solubility, and measurement of IAA production during the phosphate solubility process. EF.NAP 7, EF.NAP 5 and EF.NAP 10 isolates had phosphate dissolution indexes of 0.986 (6th day), 0.828 (7th day) and 0.789 (3rd day), respectively. EF.NAP 7 isolate (392.87 mg/L) was able to dissolve phosphate better than EF.NAP 10 (311 mg/L) and EF.NAP 5 (213.37 mg/L). The pH conditions on the highest phosphate solubility were EF.NAP 7 (4.94), EF.NAP 10 (4.19) and EF.NAP 5 (6.01), respectively. The three isolates of phosphate solubilizing bacteria were able to produce IAA during the phosphate dissolving process in the Liquid Pikovskaya medium without the addition of Tryptophan with IAA concentrations of EF.NAP 5 (12.5 mg/L), EF.NAP 7 (8.0 mg/L) and EF.NAP 10 (8.5 mg/L), respectively.