ISOLATION OF PHOSPHATE SOLUBILIZING BACTERIA FROM ANAEROBIC DIGESTION SLUDGE OF PALM OIL MILL EFFLUENT ON ULTISOLS

Biogas sludge of palm oil mill effluent results from anaerobic digestion from the biogas formation process and contains phosphate solubilizing microorganisms, which can increase phosphorus in the soil. This research aimed to obtain the characteristics and potential of Phosphate Solubilizing Bacteria (PSB) in the biogas sludge from anaerobic digestion of palm oil mill effluent in increasing phosphorus availability in ultisols. These research stages including isolating PSB and obtaining morphological characteristics, ability assessment for solubilizing phosphate, ability to available-P using the completely randomized design within three replications, and determining of organic acids. This research was conducted from January to August 2020. ANOVA and DMRT analyzed data on availability-P at the rate of 5% using SPSS v.21 software. The results showed that the PSB isolates from the biogas sludge dominant had flat elevation, smooth edges, white color, gram-negative, and cell shape of bacillus. The highest index and efficiency of phosphate solubilization were found in the P1 isolate and had the highest available-P from the aluminum phosphate source of 1.42-folds compared to the control. However, the P7 isolate had the highest available-P from the calcium triphosphate and rock phosphate sources (4.62- and 2.66-folds, respectively). It had the highest increase in the available-P in ultisols of 36.21% compared to the control. It also had the highest organic acids in sequence: lactic, oxalic, acetic, and citric acids. These results prove that PSB isolates from biogas sludge can be recommended to increase the availability-P in ultisols.