The Phosphorns Sorption Potential of Selected Hawaiian Soils in Relation to Their Mineralogy and Chemistry

Jackman, James M.
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Eleven soils from Hawaii representing a wide range in properties that affect P sorption were used to quantify the effects of those factors on P sorption. The results were evaluated for a property's possible utility in predicting P sorption, which is important for improving P fertility management. Phosphorus buffering coefficients calculated from an incubation study and P sorbed at 0.2 mg P L’^ in solution from sorption isotherm data were correlated with soil properties. A prediction of the number of sorption sites per gram of soil was the property that best predicted P sorption. The number of sorption sites per gram were predicted from analysis of X-ray diffraction patterns that indicated the quantity and average size of crystallites for each mineral in a soil. The results indicate a strong dependency of P sorption on soil mineral type and content with less influence of other soil properties. Data from a 180 day incubation study were fit with a negative exponential equation, the parameters of which indicate the proportions of P sorbed instantaneously and sorbed with time. The parameter estimate associated in instantaneous P sorption was most closely related with the number of sorption sites. The parameter estimates did not correlate with other properties, indicating that other unmeasured -factors have an influence on the P sorption process.
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