DETERMINING CATION EXCHANGE CAPAClTY AND EXCHANGEABLE SODIUM IN ALKALI SOILS

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Abstract
Following two widely used procedures, we determined the cation exchange capaClty (CEC) and exchangeable sodium in highly alkali soils assoClated with two benchmark soil series. We observed that the conventional procedures of Bower et al. and of Polemio and Rhoades overestimate the CEC of alkali soils. This paper presents a new procedure for determining the CEC of calcareous alkali soils that contain Na-zeolites and feldspathoids. In this procedure soil samples presaturated with sodium, using aqueous 0.4 N NaCl and 0.1 N NaOAC (pH like that of the soils), are extracted in 100 ml of 1 N Mg (NO3)2, pH 8.6 solution. Anion exclusion corrections for entrained soluble Na, carried over from the saturation step to the extraction step, are applied to obtain the CEC. For determining exchangeable Na, separate soil samples are directly leached with 100 ml of extracting solution, and the leachates are analyzed for total sodium. Soluble Na in the saturation paste extracts, corrected for anion exclusion, is subtracted from the total sodium to obtain exchangeable sodium.

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