Cation exchange capacity, exchangeable bases and base saturation

Method 5.2. Cation exchange capacity, exchangeabie bases and base saturation 

Cation exchange capacity (CEC) the sum total of exchangeable cations that a soil can adsorb 

CEC or CEC-7 the CEC determined with 1 M ammonium ethanoate (ammonium acetate) buffered at pH 7.0 

Effective cation exchange capacity (ECEC) the sum of the exchangeable cations (AF, H, Ca and Mg2+) extracted by 1 M potassium chloride 

Discussion. The colloidal clay and humus soil fractions are negatively charged and therefore attract and adsorb positive ions (cations) on to exchange sites. These may be the so-called basic cations defined above, or the acidic cations H+ and Al +. These cations are not soluble in water when in the adsorbed state, but can exchange with H+ which is present in the acidic vicinity of the plant root system. They are now in solution and able to be absorbed into the plant. The extent to which the exchange sites are saturated with cations, together with the ratios of the cations to each other, indicates the nutrient supplying power of the soil. 

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