Enhancing phosphorus availability and growth of green gram (Vigna radiata) in acidic red and laterite soil through liquid formulations of native phosphate solubilizing bacteria

Phosphorus (P) availability in acid soils is often limited due to its fixation with various soil components. This leads to low use efficiency of P fertilizers and raises environmental concerns when they are used in excess. Phosphate-solubilizing bacteria (PSB) have the potential to enhance P availability by solubilizing insoluble P forms. In this study, twenty-five PSB strains were initially isolated from acidic red and laterite soils in eastern India. Among them, ten bacteria formed a clear halo zone in Pikovskaya agar plates. The P releasing ability of these bacteria from different insoluble P sources was evaluated. The PSB strain AJ14, identified as Enterobacter sp., exhibited high P releasing capacity from tri-calcium phosphate, rock phosphate, ferric phosphate, and aluminum phosphate. Additionally, the strain demonstrated the ability to release zinc and potassium from insoluble sources. To improve the shelf life and efficacy of the PSB strain, liquid biofertilizer formulations were developed using polymeric additives such as polyvinylpyrrolidone, polyethylene glycol, glycerol, carboxymethyl cellulose, and tween 20. The liquid formulations showed enhanced survival and viability of the PSB strain compared to solid carrier-based biofertilizers. In a pot culture experiment with green gram plants, the liquid formulations significantly increased soil available P, dry matter yield, and P uptake by plants compared to the control and solid carrier-based biofertilizer treatment. Mitscherlich equation parameters indicated the greater effectiveness of the liquid formulations. The results suggest that liquid formulations of the PSB strain AJ14 can improve P utilization efficiency and plant growth in acidic red and laterite soils.