Cations are held on the CEC by _______ charges on clay and organic matter.

Cations are positively charged ions that are held on the cation exchange capacity (CEC) sites of soil primarily due to the negative charges on clay particles and organic matter. Soil colloids, such as clay and organic matter, possess negative charges because of the isomorphic substitution in their crystal structures and the presence of functional groups that can ionize. This negative charge attracts and holds onto the cations, allowing them to be available for uptake by plants.

Understanding the mechanism of cation retention is crucial for soil fertility management, as it affects nutrient availability and overall soil health. The presence of negative charges enables the soil to retain cations like calcium, magnesium, potassium, and others, which are essential for plant growth. This positive relationship between negative charges in soil and the positive charges of cations is fundamental in soil chemistry and fertility practices.