Comparison of extraction techniques for measuring exchangeable cations in calcareous soils

Abstract

In this paper, 9 separate extraction techniques were undertaken to compare exchangeable cations for 25 calcareous soil samples taken from the central west of New South Wales. The variables evaluated included the means to extract (leach v. tumbler), the extraction solvents used to prewash soluble cations, the use of polyvinyl alcohol to reduce dispersion, and comparison with an unbuffered salt extraction. The time involved to conduct the extraction, along with correlations between methods, formed part of the assessment. The results provided verification that the concentration of the exchangeable cations extracted was based on the extraction technique, with each technique providing a slightly different result. Correlation showed that many of the extraction procedures yielded exchangeable cation results that showed a high level of agreement and demonstrated that the results from one extraction technique may be easily converted to another with a high degree of confidence. The end-over-end mixing method proposed by B. M. Tucker using ethylene glycol for a single soluble salt prewash and sequential ethanolic (60%) 1 M ammonium chloride extract was selected as the preferred method for this determination. Measuring ECEC using an unbuffered, low molarity salt solution was also found to be satisfactory. This assessment was based on the extraction efficiency for exchangeable sodium and potassium, agreement with other methods, time required to conduct the extraction and international acceptance.