Validation of soil phosphate removal by alkaline and acidic reagents in a vertosol soil using XANES spectroscopy

There is a paucity of information on the soil phosphorus (P) forms removed by alkaline and acidic reagents in Vertosols. The first aim of this study was to identify which soil phosphates are removed by a two-step sequential fractionation (0.1 M NaOH and 1 M HCl) and by a dilute acid extractant (0.005 M H₂SO₄; Bureau of Sugar Experiment Stations (BSES) soil P test) on an "untreated" Vertosol using P K-edge x-ray absorption near-edge structure (XANES) at the Australian Synchrotron. There was supporting evidence that the 0.1 M sodium hydroxide (NaOH), 1 M hydrochloric acid (HCl), and 0.005M sulfuric acid (H₂SO₄) extractants remove soil phosphates according to the chemical solubility of known P minerals. The XANES spectra revealed the 1 M HCl and 0.005 M H₂SO₄ extractants remove calcium (Ca) phosphates from Vertosols, suggesting the latter extractant could be used as an alternative for a rapid and cost-effective measure of Ca phosphates in Vertosols.