Isolation, and selection of indigenous potassium solubilizing bacteria from Vietnam Mekong Delta rhizospheric soils and their effects on diverse cropping systems

Potassium (K) is an essential nutrient for plant growth, biosynthesis, and metabolism. It enhances plant tolerance to salinity and acidity by triggering various defense mechanisms. These characteristics are particularly important to agricultural production in the Vietnam Mekong River Delta, experiencing increased saltwater intrusion, precipitation extremes and unpredictable drought. This study isolated and selected indigenous potassium-solubilizing bacteria (PSB) from Vietnam Mekong Delta rhizospheric soils collected from three different ecological systems producing rice, maize, kumquat, and green onion. Experiments were conducted to evaluate the effect of indigenous PSB on rice seedlings and future potential as biostimulants for commercial field application. To isolate PSB, solid Aleksandrov medium supplemented with 0.2% muscovite was used. The soluble K was quantified using the atomic absorption method at a wavelength of 766.5 nm. Among 24 isolates, Burkholderia vietnamiensis L1.1 and Staphylococcus hominis T7.3 exhibited the highest K solubilization, releasing 567 mu g L-1 and 488 mu g L-1 liquid medium, respectively. The study explored the optimal conditions for K release, revealing that a temperature of 35 degrees C, a pH 5, and NaCl concentration up to 1 % in a medium favored K solubilization. B. vietnamiensis L1.1 significantly enhanced rice seed germination (95.3 %) compared to the control treatment without PSB (82 %). Furthermore, the combined application of B. vietnamiensis L1.1 and S. hominis T7.3 notably improved rice growth under K deficient conditions. This research suggests that these indigenous PSB can effectively increase plant available K and improve the productivity of rice and other crops grown under saline and acidic stresses.