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Determination of Ionic Activities in Soil Solutions and Suspensions: Principal Limitations¹

ABSTRACT

A review of the theoretical and experimental limitations of the measurement and calculation of ionic activities in soil solutions and suspensions was conducted. Ion-selective electrode methods, ion speciation models, and metal ion-chelate equilibria methods were reviewed. The lack of sensitivity, the presence of numerous interferences, and the existence of liquid junction potentials can severely limit ion-selective electrode methods. The completeness of the ion speciation model and the reliability of the analytical data and the species formation constants greatly affect the quality of the results of this approach. The failure of the chelate and trace metal ions to reach equilibrium with a specific solid phase in the soil in a reasonable time period limits the metal ion-chelate equilibria methods. Further work is needed to identify and overcome limitations in the determination of ionic activities in soil solutions and suspensions.

¹ Approved for publication as Journal Series no. 6821 of the Pennsylvania Agric. Exp. Stn., University Park, PA 16802. Presented at the Div. S-2 Symposium "Chemistry in the Soil Environment: Activities," Soil Sci. Soc. Am., 29 Nov. 1982, Anaheim, CA.

² Formerly Assistant Professor of Soil and Environmental Chemistry, Dep. of Agronomy, The Pennsylvania State Univ., University Park, PA 16802, presently Assistant Professor, Dep. of Agronomy, Louisiana State Univ., Baton Rouge, LA 70803.

Received for publication July 13, 1983. Accepted for publication November 14, 1983.