Influence of Phosphate Sorption Parameters of Soils on the Desorption of Phosphate by Various Extractants
- S. Kuo,
- E. J. Jellum and
- W. L. Pan
Seven different soils enriched with varying amounts of phosphate were extracted with NaHCO3, NaOAc, or NH4F-HCl solution for determining how phosphate sorption parameters affect such extractions. While the amount of phosphate extracted increased with increasing amount of phosphate sorbed, it varied considerably among the soils. The fraction of added phosphate recovered by the extractants was highly correlated with phosphate sorption capacity (Xm), but not with either the phosphate affinity constant (K) or the maximum buffering capacity (KXm) estimated by the Langmuir isotherm. Since the affinity constant is a component of the maximum buffering capacity, poor correlation between the affinity constant and the phosphate recovery may have contributed to the relatively low correlation of the maximum buffering capacity with the phosphate recovery. The quantity of phosphate desorbed was not affected by the phosphate affinity constant but by the fraction of phosphate coverage of the soils. Regression equations were developed for estimating the amount of phosphate sorbed based on the amount of phosphate desorbed by the extractants. The amount estimated based on NaHCO3-extractable phosphate was highly correlated with that based on NaOAc-extractable phosphate, which suggests the feasibility of using the regressions to convert NaOAc-extractable phosphate to NaHCO3-extractable phosphate, or vice versa.
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