Cation-exchange capacity (CEC) is the soil's ability to hold positively charged ions and nutrients. Soils with higher clay or organic matter content have a greater CEC, allowing them to retain more nutrients and protect groundwater. The soil's pH also affects its CEC and nutrient availability. Higher pH increases CEC while acidic soils contain ions like hydrogen and aluminum that reduce CEC and nutrient uptake by plants.

1. Water & Soil Assessment Statements E.12.2 State what is meant by the term cation-exchange capacity (CEC) and outline its importance E.12.3 Discuss the effects of soil pH on cation-exchange capacity and availability of nutrients

2. E.12.2 Cation-exchange capacity (CEC) is the capacity of a soil for ion exchange of cations between the soil and the soil solution. Cation is a positively charged ion CEC is used as a measure of fertility, nutrient retention capacity, and the capacity to protect groundwater from cation contamination The two main particles in the soil are clay and humus

3. … The CEC of the soil is determined by the amount of clay and/or humus that is present. Cation ‘warehouse’ Nutrient and water holding capacity Sandy soils with very little organic matter have a low CEC Heavy clay soils with high levels of organic matter have a much greater capacity to hold cations.

4. E.12.3 Rise in pH = rise in CEC Acidic soil will have high concentrations of H+ and Al3+ In neutral to moderately alkaline soils, Ca2+ and Mg2+ will be prevalent Exchangeable cations are available to plants pH can have the following effects: K uptake by plants is limited by high levels of Ca in some soils. High levels of K can in turn, limit Mg uptake even if Mg levels in soil are high.