Agronomic Effectiveness of Partially Acidulated Lalitpur Rock Phosphate in an Acid Inceptisol

Acidulated products of Lalitpur rock phosphate with mineral acids, viz., HNO₃, HCI, H₂SO₄ and H₃PO₄ at 25, 50, 75, and 100 per cent degree of acidulation were tested under field conditions on an acid Inceptisol (pH 4.8) with French bean as the test crop. Acidulation increased the solubility of rock phosphate, matching the degree of acidulation, irrespective of the acid used. Among different acidulants, H₂SO₄ was the best followed by H₃PO₄, HCI and HNO₃, Acidulation at 25 per cent with sulphuric acid recorded highest grain yield of French bean, maintained highest available P status of soil throughout crop growth period and recorded highest uptake of Nand P by crop. It also had pronounced effect on availability coefficient ratio (ACR), fertilizer use efficiency (FUE), P use efficiency (PUE) and relative agronomic effectiveness (RAE). RAE of PARP products followed the order: H₂SO₄-PARP>H₃PO₄-PARP>HCl-PARP>HNO₃-PARP>RP>SSP.