Determination of effective cation exchange capacity and exchange acidity by a one-step BaCl2 method

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Routine laboratory procedures measure effective cation exchange capacity (ECEC) and exchangeable acidity (EA) using separate extractants. This study assessed the suitability of a one-step BaCl2 extraction for the analysis of both ECEC and EA on organic and mineral soils by comparing results to those of a multi-step BaCl2 extraction already in use by Europe's International Cooperative Programme (ICP)–Forest program. The proposed one-step BaCl2 extraction procedure saves time and resources by analyzing both with a single extractant. In both methods, ECEC was calculated by summing base and acid cations, including H+ determined by titration, and EA was determined by a second titration of the same BaCl2 extracts. The effect of the different solution/soil ratios of the one-step BaCl2 method was also evaluated. For organic soils, despite the greater solution/soil ratio of the one-step procedure, the multi-step procedure extracted more Al and Fe. For mineral soils, increasing the solution/soil ratio of the one-step method from 10:1 to 20:1 extracted more K, Al, H+, and EA. Adding the rinsing steps of the multi-step procedure (resulting in a solution/soil ratio of 40:1) not only extracted more of these cations, but also extracted more Ca, Fe, and Mn. The acid cations Al, Fe, and H+ were the most significantly affected cations resulting in 30 to 68% more EA and 11 to 41% greater ECEC obtained by the multi-step procedure. The one-step BaCl2 method offers a simpler, more efficient way to analyze these routinely tested parameters.

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