Abstract
Laboratory studies have been undertaken to evaluate sequential extraction procedures to measure phosphate rock (PR) residues in a range of temperate (New Zealand) and tropical (Indonesian) soils. The amounts of soil and PR-P were measured by using a sequential procedure which involved pre-extraction with either 1M NaCl or 0.5M NaCl/TEA (pH 7), followed by 1M NaOH and mineral acids. The acids included varying concentrations of HCl or H2SO4 (0.5–4M) and a tri-acid mixture of HCl, HNO3 and HClO4 (5:5:7). Amounts of PR residues in the soil were estimated from increases in amounts of the acid-extractable P (Δacid-P) or Ca (Δacid-Ca) in the PR-treated over untreated soil.
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