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Fig. 4. Solubilities of Al and phosphate in soil solutions as a function of pH. The activities of Al3+ and H2PO-4 in soil solutions extracted from soil samples of sandy loam and clay loam (incubated for up to 64 d after rewetting) were plotted against soil-solution pH. Lines show the upper solubility limits of crystalline gibbsite and variscite in equilibrium with gibbsite. Data points within dotted ellipses are from soil solutions extracted 1 d after the soil samples were rewetted. Because of the limited sensitivity of the colorimetric assay used to quantify Alinorg, only {Al3+} values greater than 1 µM are shown in the top plot.
