Chemical Properties of Soil
Anion Exchange Capacity
Colloids contain some positive charges against which anions such as sulfate (SO42¯), nitrate (NO3¯), chloride (Cl¯), bicarbonate (HCO3¯), and dihydrogen phosphate (H2PO4¯), can be adsorbed. Any one of these anions or all can be replaced by a suitable anion. In other words, like cation exchange capacity, soils have anion exchange capacity (AEC) as well. In contrast to cation exchange capacities, AEC of soils generally decrease with increasing pH. The surfaces of kaolinite, allophane, and iron and aluminum oxides often carry positive charges.
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