Effect of Acidification on Cation Exchange Capacity of Eight Finnish Mineral Soils

The effect of acidification on cation exchange capacity was studied with eight Finnish mineral soils by adding HCl 0-320 meq/kg soil. Without acid the effective CEC ranged from 29 to 343 meq/kg soil, pH from 5.0 to 6.2. The acid treatment lowered the pH to 1.3–2.5 and reduced CEC to 23–169 meq/kg soil. The decrease of CEC ranged from 6 to 174 meq/kg soil, corresponding to 21–59% of the initial value. Two pH-regions with enhanced decrease in CEC were observed at pH 6-5 and 4-2, possibly being connected with buffering of organic matter and amorphous oxides, respectively. The quantity of acid needed to reduce the soil pH to 3.8 (ANC3.8) ranged from 18 to 140 meq/kg soil and decreased CEC by 2–105 meq/kg soil. The acid-neutralizing ability of a coarse soil had a maximum between 10 and 80 meq/kg soil and was nearly broken up by acid treatment 160 meq/kg soil. In two soils the maximum was between 160 and 320 meq/kg soil.