Cation-exchange Capacity - PH and CEC

PH and CEC

Many soils' CEC is dependent upon the pH of the soil. This is due mostly to the lyotrophic series, which describes the relative strength of various cations' absorption, and is generally as follows:

Al+3 > H+ > Ca+2 > Mg+2 > K+ = NH₄+ > Na+

As soil acidity increases (pH decreases), more H+ ions are attached to the colloids and push other cations from the colloids and into the soil solution (CEC decreases). Inversely, when soils become more basic (pH increases), the available cations in solution decreases because there are fewer H+ ions to push cations into the soil solution from the colloids (CEC increases).