CEC stands for Cation Exchange Capacity, or cation exchange capacity. This refers to a soil’s capacity to bind and exchange positively charged ions with the soil solution.

The CEC is formed by clay minerals and organic matter, together with the clay-humus complex, which has a negatively charged surface. This negative surface attracts positively charged ions, such as the nutrients calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+). However, aluminum (Al3+) and hydrogen (H+) can also be bound to the CEC. These positive ions then displace the beneficial nutrients. The binding of the CEC with beneficial nutrients is a measure of soil fertility.

The study Fertilization Manager gives insight into the CEC of a field.