Determining Cation Exchange Capacity: A New Procedure for Calcareous and Gypsiferous Soils

TLDR

A two‑step procedure is introduced to determine the cation exchange capacity of calcareous and gypsiferous soils. The method saturates soil with sodium via four successive equilibrations using a 0.4 N NaOAc–0.1 N NaCl solution, then extracts with three 1.0 N Mg(NO₃)₂ solutions, and calculates CEC from total and soluble sodium after chloride correction. This approach reduces the errors typical of conventional CEC determinations.

Abstract

Abstract A new, two‐step procedure is presented for determining the cation exchange capacity (CEC) of calcareous and gypsiferous soils. The method eliminates most of the errors inherent in conventional methods. The cation exchange sites are saturated with sodium by four successive “equilibrations” of the soil (4–5 g) with 33‐ml increments of a pH 8.2, 60% ethanol solution of 0.4N NaO Ac − 0.1 N NaCl (saturating solution). The saturated sample then is extracted with three 33‐ml increments of 1.0 N , pH 7 magnesium nitrate. Total sodium (Na t ) and chloride (Cl t ) are subsequently determined in the extracted solution. Chloride (Cl t ) is determined so that the soluble sodium (Na sol ), from the excess saturating solution carried over from the saturation step to the extraction step, may be deducted from the total sodium (Na t ) to obtain exchangeable sodium (Na exch ), which is equivalent to the CEC. Thus, CEC = Na exch = (Na t − Na sol ) = Na t − [Cl t (Na/Cl) saturating solution ] where (Na/Cl) saturating solution is the ratio of Na to Cl in the saturating solution.