Development of organo-bioformulations for improved phosphorus availability and wheat productivity: insights from adsorption isotherms and field validation

Introduction: Low phosphorus (P) availability is a major constraint to crop productivity in calcareous soils due to higher P sorption and fixation processes. In these soils, applied phosphorus (P) is rapidly immobilized through precipitation with calcium and adsorption onto CaCO₃ surfaces, resulting in low P availability. Therefore, to mitigate this issue, the current research is focused on the development of organo-bioformulation and quantifying P sorption from diammonium phosphate (DAP) and organo-bioformulations to estimate the fertilizer requirement to maintain an optimal soil solution P concentration. Methods: Phosphate-solubilizing bacteria (PSB) were isolated from wheat rhizosphere soil collected from drought-prone regions of South Punjab. The isolates were characterized for plant growth-promoting traits and demonstrated high efficiency in solubilizing tricalcium phosphate (TCP) (up to 448 μg/mL), along with production of plant growth regulators such as indole-3-acetic acid (IAA) (up to 402 μg/mL), organic acids, siderophores, ACC deaminase activity and also exhibited zinc-solubilizing potential. Well-characterized PSB strains were formulated into consortia and used to develop two organo-bioformulations using Filter Mud (FM) and Cow Dung (CD) with 5% sodium alginate as a natural adhesive. Microcosm studies using Freundlich isotherms showed reduced P adsorption and enhanced P availability compared to diammonium phosphate (DAP). Results: evaluation on wheat crop showed that both organo-bioformulations significantly improved plant height up to 26%, biomass (24%), grain yield (16%), and grain P (53%) compared to the 80% uninoculated P fertilizer control. Microplot and field trials confirmed these findings, promoting vegetative growth, plant nutrient uptake, and elevated soil phosphatase activity. In field conditions, plant grain yield improved up to 17% and grain P up to 21% over 80% P control. Principal component analysis further confirmed positive effects on nutrient uptake, vegetative growth, and yield. Conclusion: Thus, these bioformulations provide a sustainable solution for nutrient management in calcareous soils, reducing chemical fertilizer use and supporting long-term soil health and crop productivity.