Cation Exchange Capacity and Exchange Coefficients

The origin of cation exchange capacity (CEC) lies in the negative charges carried by soil particles, usually clay, organic matter and sesquioxides. An excellent parallel discussion of how the views on soil acidity developed during this period is presented by G. W. Thomas. It is interesting to speculate what course CEC method development might have taken had the work been conducted in the humic tropical areas of Latin America, Mrica and Asia where the soils are generally highly acid. The criteria for methodology selection will be divided on a final use basis. Most measurements of exchange coefficients are made at 0.01 to 0.05 M ionic strength, largely in order to provide sufficient solution cations to effect the desired exchange with the solid phase. Arid region soils often contain carbonates and other soluble salts, resulting in complications with respect to the quantities of exchangeable cations extracted.