Thermally Promoted Phosphate Rocks-II. Phosphate Release Characteristics in a Typic Ustochrept

Thermally promoled phosphale rocks (TPPRs) were prepared by heating phosphale rock samples obtain ftom Jhabua, Mussoorie, Purulia and Udaipur deposits alone or wilh Na, CO, or KCI in lwo PR to additive ratios at 500, 700 and 900°C and applied to a soil @ 50 and 100 mg P kg⁻¹ soil. Treated soils were ihcubated for 120 days at a temperature of 35±1°C and soil water content of 50 per cent of field capacity. Throughout the incubation period, phosphate treated soil samples maintained a higher level of Olsen P status as compared to control. TPPRs from Mussoorie rock were superior during lhe first six fortnights of incubation over olhers and subsequently it became on par wilh Udaipur rock in the remaining period of incubation. TPPRs prepared with Na,CO, maintained higher extractable P status in soils over those obtained with KCI. Increase in temperature or P rate was accompanied by a concurrent improvement in extractable P status of the soil. In general, after 45 days of incubation, the extractable P concentration dropped rapidly irrespective of sources of PRs, additives, temperature, PR 10 additive ratios and levels of P application.