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Determining Cation Exchange Capacity: A New Procedure for Calcareous and Gypsiferous Soils
Author(s) -
Polemio Mario,
Rhoades J. D.
Publication year - 1977
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1977.03615995004100030018x
Subject(s) - chemistry , sodium , cation exchange capacity , saturation (graph theory) , potassium , chloride , inorganic chemistry , magnesium , extraction (chemistry) , alkali metal , soil water , calcareous , analytical chemistry (journal) , mineralogy , chromatography , soil science , geology , paleontology , mathematics , organic chemistry , combinatorics
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.