Are calcium, magnesium, and potassium held onto the CEC considered immobile or mobile?

Calcium, magnesium, and potassium are positively charged cations that are held onto the cation exchange capacity (CEC) of soil. CEC is a measure of how well soil can retain and supply these essential nutrients to plants. These cations are considered immobile in the soil because they tend to remain in the soil matrix and do not easily move through the soil profile with water.

When plant roots uptake nutrients, they generally do so from the soil solution or from the layer of soil directly surrounding the roots. Since calcium, magnesium, and potassium remain strongly attached to soil particles, large amounts of water moving through the soil will not wash them away. Although some nutrient release can occur through processes like leaching or cation exchange, the majority of these cations remain relatively fixed compared to anions, which are more mobile. This characteristic is essential for crop nutrition, as it influences how and when plants can access these nutrients.

In summary, the immobility of calcium, magnesium, and potassium in relation to CEC is crucial for their availability to plants over time, ensuring that these vital nutrients remain within the root zone and are available as needed for plant growth.