Effect of Partial Acidulation of Rock Phosphate with Sulphuric Acid and Pyrite on Release of Phosphorus

Mixing of acid equivalent quantities of pyrite with rock phosphate resulted in initial sharp reaction for 7 days followed by a slow phase between 7 and 30 days and once again enhanced reaction from 45 days. When sulphuric acid was used, most of the reaction occurred within the first 7 days. Pyrite was not effective in releasing P from rock phosphate. The ineffectiveness of added pyrite in mobilizing P from rock phosphate may be attributed to the release of appreciable quantity of active iron from pyrite upon oxidation and possible precipitation of released P by it. Among the extractants evaluated, 2 per cent citric acid solution was found to extract larger amounts of P from these fertilizer materials than Olsen's extractant and 2 per cent formic acid throughout the incubation period.