Determining Cation Exchange Capacity: A New Procedure for Calcareous and Gypsiferous Soils1
- Mario Polemio and
- J. D. Rhoades2
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 − 0.1N NaCl (saturating solution). The saturated sample then is extracted with three 33-ml increments of 1.0N, pH 7 magnesium nitrate. Total sodium (Nat) and chloride (Clt) are subsequently determined in the extracted solution. Chloride (Clt) is determined so that the soluble sodium (Nasol), from the excess saturating solution carried over from the saturation step to the extraction step, may be deducted from the total sodium (Nat) to obtain exchangeable sodium (Naexch), which is equivalent to the CEC. Thus, CEC = Naexch = (Nat − Nasol) = Nat − [Clt(Na/Cl)saturating solution] where (Na/Cl)saturating solution is the ratio of Na to Cl in the saturating solution.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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