A computer‐assisted method for CEC estimation and quality control in a routine soil‐test operation

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Abstract
Cation-exchange capacity (CEC) of 30 Alabama [USA] soils was estimated by 2 different methods based on routine soil-test results consisting of soil-water pH, Adams-Evans buffer pH, and Mehlich-1 extractable cations (K, Mg and Ca), which were obtained automatically by a computerized data acquisition system. In 1 method, CEC was calculated by solving a quadratic equation involving soil-water and buffer pH. In the other, CEC was estimated as the summation of extractable cations and exchangeable acidity. The 2 estimated CEC agreed well with each other and also had the same magnitude as CEC determined by the normal NaOAc, pH 8.2 method. By averaging the 2 calculated values, an even closer estimation of the measured CEC was found. These calculations and comparisons can be accomplished quickly and efficiently by a minicomputer via a simple FORTRAN program. A discrepancy between the 2 estimated CEC would indicate possible errors in analytical determinations and/or the inadequacy of the soil testing procedures. Comparing the 2 CEC values is an additional means for quality control in a routine soil-test operation.

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