Ion Exchange Capacity
Ion Exchange It is interchange of ions between colloids and soil solution and/or between the solid phases if these are in a close contact. If the process is between cations; it is called cation exchange and for anions it is termed as anion exchange. These are reversible reactions. Cations are positively charged ions. Soil colloids have negative charges on their surfaces. Cations are adsorbed at these negatively charged sites. The adsorbed cations can be exchanged by other cations present in soil solution. This change of one positive ion by another is called cation exchange. For example, when an NH 4 + containing fertilizer is added to a soil, many of the numerous NH 4 + ions replace the other cations that are already adsorbed to the exchange sites. Cations exchange takes place on the surface of clay and humus colloids as well as on the surface of plant roots. The cations mostly present on the cation exchange sites of the soil colloids are Ca + , Mg + , H + , Na + , K + and Al