Solubilization and Availability of Phosphorus during Decomposition of Rock Phosphate Enriched Straw and Urine

The solubilization and availability of phosphorus were measured during decomposition of wheat straw and cattle urine with two types of low grade rock phosphate, Mussoorie rock phosphate (M. phos) and Hyperphos. The rate of solubilization of insoluble phosphorus from both M. phos and Hyperphos increased significantly up to 60 days and thereafter decreased with increasing decomposition time. Molasses incorporation enhanced solubilization throughout the decomposing period of 120 days; it reached a maximum of 24.5 and 14.7% of the added insoluble phosphate for both M. phos and Hyperphos, respectively. About 95 to 99% of the solubilized P was converted into organic forms. In view of very high turnover of organic P, the availability of solubilized P was measured by fractionating organic P (Po) substrates. In the presence of both rock phosphates, with or without addition of molasses, organic Po was redistributed between 4–6, 68–72, 12–16 and 10–12% in labile, moderately labile, moderately resistant and highly resistant fractions respectively at 120 days of composting. M. phos solubilized more readily and retained a greater amount of labile and moderately labile Po than Hyperphos.