Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi, 110012
1Present address: Soil Science and Agricultural Chemistry, Agricultural College and Research Institute, Madurai, 625104
Two finely ground (<100 mesh sieve) indigenous phosphate rock samples from Purulia (West Bengal) and Udaipur (Rajasthan) were partially acidulated with H2S04 at three levels (20, 40 and 60%) under five different methods. The products were then dried under ambient condition, and analysed for various fractions of phosphates. The possibility of partially acidulated phosphate rocks (PAPRs) as a source of P to green gram was also evaluated in a pot culture experiment and applied @ 25, 50 and 75 mg P kg−1 soil. The results revealed that irrespective of method of acidulation, the PAPRs for Purulia prepared at 60% level of acidulation took 7 days for complete drying due to iron and aluminium impurities. The total P content of PAPRs as compared to raw phosphate rock decreased with increasing level of acidulation. The method of acidulation did not show any significant effect on total P content. Both water and citrate soluble P fractions (available P) increased with successive level of acidulation. Among the methods of acidulation, the products prepared with pre-diluted acid at 60% level of acidulation yielded higher available P content. Different levels and methods of acidulation and doses of P significantly increased the dry matter yield of green gram, P uptake, P recovery and residual available P (Olsen's P) in both the sources compared to no-P control. However, the water soluble phosphate (DAP) treatments were superior to all PAPRs in all these respects.
Phosphate rocks, levels and methods of partial acidulation, water and citrate solubility, P recovery
