INFLUENCE OF OXALATE LOADING ON PHOSPHORUS AND ALUMINUM SOLUBILITY IN SPODOSOLS

Organic anions can increase the solubility of P and Al in soils and may influence nutrient availability and soil weathering. In Spodosols of the southeastern USA, oxalate has been identified as the dominant organic anion. Therefore, the objectives of this study were to examine the influence of oxalate on the release of inorganic P, organic P, and Al from A, and Bh horizons of two forested Spodosols from the Lower Coastal Plain. Oxalate loading rates ranging from 0 to 125 mmol kg-1 soil were examined in a series of batch experiments using single, one-time additions and repeated sequential additions of oxalate. Oxalate had a negligible effect on P and Al release from the A horizon soils. In contrast, oxalate had a large effect on both inorganic and organic P, as well as Al release from the Bh horizon soils. The effect of sequential additions of oxalate on P and Al release from these soils was found to be cumulative. The amount of Al or P released was primarily controlled by the cumulative oxalate loading rate. In addition, the manner of oxalate loading (single vs. sequential) had relatively little effect. At the same total, cumulative oxalate loading rate, the cumulative amount of Al or P released following sequential additions of oxalate at low concentrations were essentially the same as the amount released following a single addition of oxalate at a much higher concentration. This suggests that a continuous release of even small amounts of organic anions in forest soils could solublize large amounts of P and Al on an annual basis.