Cation exchange capacity (CEC) refers to the ability of a soil or other porous material to retain and exchange positively charged ions, or cations. It is a fundamental property of soils and plays a crucial role in nutrient availability and plant growth.
CEC is determined by the presence and activity of negatively charged sites, or exchange sites, on the surface of the soil particles. These sites are typically comprised of clay minerals, organic matter, and certain types of oxides. Cations, such as potassium (K+), calcium (Ca2+), and magnesium (Mg2+), are attracted to these negatively charged sites, where they can be held tightly (adsorbed) or exchanged with other cations.
Soils with a high CEC are capable of retaining and delivering greater amounts of plant nutrients. This is because the exchange sites provide binding sites for cations, preventing them from being washed away by rainfall or leaching. The retained cations can then be gradually released back into the soil solution, becoming available for plant uptake.
Measurement of CEC is usually expressed in units of centimoles of charge per kilogram of soil (cmol/kg). It can vary widely depending on the soil type, with clayey soils generally having higher CEC values than sandy or loamy soils.
Understanding the cation exchange capacity of a soil is essential for soil fertility management, as it helps determine the soil's ability to retain plant nutrients and influences the need for fertilizer applications. Additionally, it impacts the soil's pH buffering capacity and water holding capacity.
