what is cec in soil

Cation exchange capacity (CEC) is a measure of the total negative charges within the soil that adsorb plant nutrient cations such as calcium, magnesium, and potassium. It is a property of soil that describes its capacity to supply nutrient cations to the soil solution for plant uptake. CEC is usually measured in millequivalents per 100 grams of soil (meq/100g) or centimoles of positive charge per kilogram of soil (cmol(+)/kg) . The CEC value included on typical soil testing laboratory reports is calculated by adding together the concentrations of potassium, magnesium, calcium, sodium, and hydrogen, which are extracted from soils using an appropriate extraction method. The CEC of soils varies according to the type of soil, clay percentage, soil pH, and amount of organic matter. Sandy soils low in organic matter have a very low CEC, while heavier clay soils or soils high in organic matter generally have a much higher CEC. CEC affects fertilization and liming practices, as soils with high CEC retain more nutrients than low-CEC soils.