A MODIFIED METHOD FOR DETERMINING BASE-EXCHANGE CAPACITY OF SOILS

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Abstract
A modified method for determining base-exchange capacity of soils is described which eliminates the necessity of washing out the excess saturating soln. In the modified method as outlined the soil sample is leached first with 250 ml. of a N soln. of the saturating salt and then with 250 ml. of a 0.1 N soln. of the salt. The quantity of excess 0.1 N soln. is detd. by subtracting the dry wt. of the funnel, filter paper, and sample from the combination after the sample has been leached with 0.1 N soln. The excess 0.1 N soln. and the adsorbed cation are leached out with 0.2 N HCl and the total quantity of cation detd. The total cation minus that present as excess 0.1 N soln. is equal to the base-exchange capacity. This method may be used with any saturating soln. provided the saturating cation can be detd. accurately. The modified method gave the same results as the "standard method" (washing out the excess saturating soln. with 80% alcohol) when barium acetate was used but gave higher results in most cases with ammonium acetate. Base-exchange capacity increased appreciably with time of intermittent leaching when Ba acetate was used and the addition of 0.5% n-butyl alcohol lowered the leaching time necessary to reach equilibrium. In the case of ammonium acetate base-exchange capacity did not change appreciably with time of leaching or with the addition of n-butyl alcohol. Nine Florida soils showed about the same exchange capacity as measured by Ca or Ba but values as measured by ammonium were only 65% as high on the average as the Ca and Ba values.

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