Dear Ajay,
sum of exchangeable cations can not be higher than the CEC of a soil. If soluble salts are not completely removed from the soil before determination of exchangeable cations, water-soluble cations are erroneously included in the analysis and measurement of exchangeable cations. In such cases, sum of the measured cations (exchangeable plus water-soluble) will be higher than the CEC of the soil.
Yes, as it was stated by Dilip, the sum of cations should be lower, than CEC (CEC=exch.acidity+exch.cations). Other result is not correct. However, the methods of CEC determinations and extraction of exchangeable cations are imperfect.
For example, there is an issue with most used and treated as "standard" ammonium acetate method. Some people, including me, think that ammonium acetate, even at pH 7.0 may dissolve some carbonates and thus increase exchcngeable calcium. Mainly in calcareous soils, but I think also in soils containing smaller amount of carbonates (0,1-0,5%), undetectable by HCl. You can see, that USDA procedures for texture determination recommend ammonium acetate at pH 5.0 do remove carbonates from the soil, before determination of particle size distribution.
Please, see the paper attached, which describes the issue of interaction between carbonates and ammonium acetate during determination of CEC.
Dear Dr. Kundu and Stepien,
Thank you for such information and i will try to wash the soluble salts properly. I once again appreciate your quick response.
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