Phosphorus Solubilization from Low-Grade Rock Phosphates in the Presence of Decomposing Soybean Leaf Litter

Abstract

The natural phenomenon of defoliation of mature soybean leaves onto the soil surface provides a large quantity of easily decomposable organic matter in the form of leaf litter. The potential of decomposing soybean leaf litter (SLL) to solubilize phosphorus (P) from two low‐grade rock phosphates, Jhabua rock phosphate (JRP) and Hirapur rock phosphate (HRP), alone or amended with pyrite, was assessed in an incubation study. Decomposing SLL solubilized P both from JRP and HRP and concurrently increased water‐soluble as well as organic P contents. Amending rock phosphates with pyrite (in a 1∶2 P to S ratio) promoted P solubilization. Approximately 71 to 92% of the total solubilized P was converted to organic P. The rate of P solubilization increased with SLL decomposition time, reaching its peak at 60 days with rock phosphates alone and at 90 days with pyrite‐blended rock phosphates. The maximum P solubilization (as a percentage of total P added) with different rock phosphates and their mixtures with pyrite followed this order: HRP (11.4%)<HRP+pyrite (16.5%)<JRP (20.2%)<JRP+pyrite (26.5%). These findings clearly suggest that the decomposing SLL has the potential to solubilize P from the otherwise insoluble low‐grade rock phosphates and can offer a natural opportunity for direct use of rock phosphates in the cropping systems that have soybean as a component crop.