The effect of soil texture on the dissolution of North Carolina phosphate rock

SUMMARY Laboratory investigations of the dissolution of North Carolina phosphate rock (PR) in soil, as affected by soil texture, were conducted using soils created by mixing various proportions of the <45 μm and >45 μm fractions of a lateritic soil. The dissolution of PR in soil, and the resulting changes in plant available P, were estimated by measuring increases in exchangeable Ca (ΔCa) and NaHCO 3 ‐extractable P (ΔP b ), respectively. The total fertilizer phosphate dissolved (ΔP) was calculated from δCa values based on the assumption that dissolution of PR released amounts of Ca and P in a constant ratio determined by the stoichiometry of the PR. δP increased with increasing content of <45 μm particles. AP b also increased with the percentage of <45μ fraction, with about 20% of AP being recovered as AP b . A smaller proportion of dissolved P was soluble in NaHCO 3 for the soil comprising only the <45μ particles. The increase in δP with increased percentage of <45 μn soil was probably due inter alia to the greater P‐sorption, Ca‐sorption and the pH buffering capacity of the fine grained soil constituents.