The Viability of Selected Potassium Solubilizing Rhizobacteria in a Mixture of K-Feldspar and Organic Matter as Carrier Material

The potassium solubilizing biofertilizer based on selected potassium solubilizing bacteria (KSB) can facilitate availability of potassium in primary silicate minerals containing potassium to be absorbed by the plants. The key to successful application of biofertilizer in showing positive effects on inoculated plants is the selection of a carrier material that can guarantee viability of inoculants during shelf life before being applied in the field. The purpose of this study was to determine viability of three selected KSB isolates which were formulated in a mixture of K-feldspar (KF), rice straw compost (RSC), rice husk biochar (RHB), and Aleksandrov liquid medium (ALM) as a carrier material for 24 weeks of shelf life. The experiment used a completely randomized design with nine treatments of carrier material composition and three replications. The results showed formula of potassium solubilizing biofertilizer with a composition of 1% mixed culture KSB + 15% KF + 30% RSC + 45% RHB + 9% ALM was the best formula with high inoculant viability during 4 weeks of shelf life. It was evidenced by the increase in respiration and total KSB population by 17.2% and 213.2%, respectively, compared to formula that produced the lowest respiration and total KSB population