Phosphate availability indices related to phosphate fractions in selected malawi soils

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Abstract
The amounts of soil P extracted by the methods of Olsen P, Bray‐P1, Williams and Stewart, Morgan, Aslyng, anion exchange resin, Saunder, Dyer, and North Carolina were significantly interrelated. P fractionation studies indicated that a relatively high proportion of the inorganic P was accounted for by iron‐bound and reductant‐soluble P fractions. The most important variable contributing to the total variation in the regressions of equilibrium phosphate potential and Morgan‐P values was the saloid‐bound P fraction. Al‐P was the major source of variation in Dyer‐P, North Carolina P, Olsen‐P, Bray‐P1, resin extractable P, and acetic acid soluble P values. The extraction of Al‐P by the chemical soil tests was in the decreasing order of Dyer‐P > North Carolina P>0.1M‐NaOH‐extractable P>0.5m‐CH3 COOH > Olsen‐P >Bray‐P1 anion exchange resin. Fe‐P was the second most important variable contributing to the total variation in 0.1M‐NaOH extractable P, Olsen‐P, North Carolina P, resin extractable P and Dyer‐P values. Practical implications of the findings were discussed.