CEC versus soil texture - click on figure to enlarge.
Source Ilaco, 1985
Cation Exchange Capacity
Cation Exchange Capacity (CEC) is the ability of the soil to retain cations (positively charged nutrients: Ca, Mg, Mn, Fe, Cu, Zn, NH4+).
CEC is strongly related to soil texture and soil organic matter content (Click on figure at left). The typical CEC of soil textural components in decreasing order is: Soil organic matter > Clay - Montmorillonite > Clay - Kaolinite > Silt > Sand (Click on Figure at left).
In some soils, CEC will increase as pH rises.