Although both positive and negative charges are present on colloid surfaces, soils of this region are dominated by negative charges and have an overall (net) negative charge.
Therefore, more cations (positive ions) are attracted to exchange sites than anions (negative ions), and soils tend to have greater cation exchange capacities (CEC) than anion exchange capacities (AEC).
Fine-textured soils usually have a greater exchange capacity than coarse soils because of a higher proportion of colloids (NM 2, Table 4).