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Self-Diffusion of Phosphorus in Clays and Soils: II. The Effect of pH¹

ABSTRACT

The effect of pH on the self-diffusion coefficient of ³²P was measured in kaolinite, montmorillonite, illite, Dundee silt loam, and Sharkey clay. Six fractions of soil phosphorus were evaluated and related to the effect of pH on the self-diffusion coefficients of ³²P by multiple linear regression analysis. The free iron oxide content was determined in each medium and related to the variation in self-diffusion coefficients between media.

The self-diffusion coefficients were significantly affected by pH in all media. A multiple regression analysis for individual clays and soils where self-diffusion was the dependent variable and water soluble-P, Al-P, Fe-P, occluded Fe- and Al-P, and Ca-P were the independent variables revealed that water soluble P in kaolinite was positively correlated (R² = 0.673) and occluded Al-P in montmorillonite was negatively correlated (R² = 0.402). There were no significant terms in the other media. The magnitude of the self-diffusion coefficients between media was kaolinite > montmorillonite > Dundee silt loam > illite > Sharkey clay. When the self-diffusion coefficients and phosphorus fractions were averaged over all pH values, self-diffusion increased as the water soluble- and Al-P concentrations increased and the Fe-P and free ion oxide contents decreased.

¹ Contribution from the Department of Agronomy, Arkansas Agr. Expt. Sta., Fayetteville. Presented before Div. S-2 Soil Sci. Soc. Am., Stillwater, Okla., Aug. 24, 1966.

² Assistant Professor of Agronomy, Associate Professor of Agronomy, and Professor of Agronomy, respectively.

Received for publication March 4, 1968. Accepted for publication May 15, 1968.