Cation-exchange Capacity - Laboratory Determination

Laboratory Determination

There are two standardised International Soil Reference and Information Centre methods for determining CEC:

• extraction with ammonium acetate; and
• the silver-thiourea method (one-step centrifugal extraction).

There exist slightly conflicting ideas on which mechanisms to include in the term, "cation exchange", in soil chemistry. From a theoretical point of view, one should distinguish cation exchange from ligand exchange, and exchange of diffuse layer adsorbed cations. On the other hand, from a practical point of view, e.g. in forest and agricultural management, what is important is the soils' ability to replace one cation with another rather than the exact mechanism by which this replacement occurs. What is included in the term, "cation exchange", in soil science thus varies with the scientific context.