ORGANIC-ANIONS EFFECT ON PHOSPHORUS RELEASE FROM SPODIC HORIZONS

The purpose of this research was to investigate the release of P from the spodic horizons of common forested soils in the Lower Coastal Plai n of Florida and Georgia. This was considered important because (i) th ese soils have a history of variable responses to P fertilization, (ii ) roots are known to grow in this material, and (iii) previous researc h has suggested that the P in this material might be available to plan ts. Desorption experiments using 0.001 M concentrations of a variety o f organic ligands (pH 4.3 for initial solutions) with a range of Al co mplexation constants were conducted by reacting the ligand solutions w ith spodic horizon soil. Inorganic P, organic P, and AL were measured in the resulting extracts. Results showed that the amount of extractab le inorganic P in these soils was variable. Some soils had detectable levels of extractable inorganic P, while others are essentially devoid of it. In those soils that had extractable P, the inorganic P release was correlated to the release of Al as the release of both moieties w as initiated by organic anions with logK(Al) values, the Al stability constant with that anion, of about 3.2 to 4.2 or greater. This suggest s that root exudates with logK(Al)s less than these values would not b e effective in making inorganic P in spodic horizons more available to plants. Organic P is a major component of the soil solution and is re leased by a mechanism unrelated to the logK(Al) Of the organic ligand.