How is actual cation exchange capacity (CEC) measured directly?

Actual cation exchange capacity (CEC) is a critical property of soil that indicates its ability to hold and exchange positively charged ions (cations) such as calcium, magnesium, potassium, and sodium. The most direct measurement of actual CEC involves flooding or saturating the soil with a marker cation. This process allows for the assessment of how many cations the soil can hold and exchange when it is fully saturated, providing an accurate evaluation of its cation exchange capacity.

During this measurement, a specific cation, often one that is easily identifiable and can be quantified, is introduced to the soil. After saturation, the amount of this cation absorbed by the soil is analyzed. The results can indicate the CEC by measuring how many of these cations were retained versus how many were leached away. This method directly assesses the soil's ability to hold cations, giving a precise value for its CEC.

In contrast, drying the soil, analyzing organic matter content, or conducting a pH test do not provide a direct assessment of CEC. While these methods can give useful information about the soil, they do not accurately reflect the actual cation exchange capacity as the flooding method does. Therefore, saturating the soil with a marker c