『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 (Indonesia) soils. The amounts of soil and PR-P were measured by using a sequential procedure which involved pre-extraction with either 1 M NaCl or 0.5 M NaCl/TEA (pH 7), followed by 1 M NaOH and mineral acids. The acids included varying concentrations of HCl or H2SO4 (0.5-4 M) 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.
　Amounts of PR-P residues (measured by ΔHCl-P) in New Zealand soils varying in pH and Ca levels were completely recovered (±5％) when the soils were pre-extracted with 0.5 M NaCl/TEA, rather than 1 M NaCl (or no pre-extraction). Pre-extraction of acid soil/PR mixtures with 1 M NaCl caused dissolution of PR during the extraction. Although the ΔHCl-Ca also estimated the amount of PR residues well, particularly after a 0.5 M NaCl/TEA pre-extraction, this method was less sensitive than the ΔHCl-P method, particularly in the soils with high native Ca saturation.
　In contrast to the high recovery obtained from the New Zealand soils, the recovery of the PR-P residues in the Indonesian soils in the HCl extracts following the 0.5 M NaCl/TEA and 1 M NaOH extractions were low ranging from 62 to 86％. Although increasing the concentration of HCl (upto 4 M) did not cause any improvement in the recovery of PR-P, extraction with H2SO4 achieved complete recovery of PR-P. For all soils, a sequential extraction involving 0.5 M NaCl/TEA-1 M NaOH-0.5 M H2SO4 is recommended for measuring PR residues in pairs of PR-treated and untreated field or laboratory incubated soils.

Keywords: Indonesia; MCP; New Zealand; phosphate rock dissolution; phosphate rock residues; soil pH』

Introduction
Materials and methods
　　Soils
　　Phosphate sources
　Part 1. Development of pre-extraction methods
　　Extraction of soil and soil/PR mixture
　Part II. Use of sequential extraction procedures on a range of soils
　　Mixing NCPR and soil
　　Sequential extractions
Results and discussion
　Part 1. Development of the NaCl/TEA-HCl method
　　Recovery of PR-P and PR-Ca in different extractants
　　Comparison of ΔHCl-P vs ΔHCl-Ca
　Part 2. Evaluation of NaCl/TEA-Δ1 M HCl-P procedure
Conclusions
References