Evaluation of HCI-Acidulated Products of Different Phosphate Rocks in Relation to Phosphorus Availability in Rice Soils

Hydrochloric acid acidulated phosphate rock (PR) of Jordan, Kasipatnam, Purulia and Mussoorie were evaluatedfor their effectiveness as P carriers. About 72 to 88 per cent of total P in the product remained as a mixture of water soluble and citrate soluble P fraction (AOAC) in case of PRs acidulated to the extent of full requirement of HCI. The amount of such available P is lower proportionately in case of products of lower degree of acidulation. However, in case of Mussoorie PR the reaction of acid and apatite is partially hampered under each degree of acidulation leading to lower AOAC available P in these products due to the presence of high amount of accessory carbonate minerals in the phosphate rock. At the extent of 50 per cent to full requirement of acidulation with HCI about 38 to 60 per cent of total P in the products remained in the available form. The effect of these HCI-aciduiated products on phosphorus availability in two rice soils were studied. It was found that initial P availability (Olsen P) in soil due to application of acidulated phosphate rocks is largely governed by the AOAC available P content of the product. The effect of such acidulated products derived from Mussoorie phosphate rock was very much inferior.