What soil component greatly increases CEC?

• A. Sand content
• B. Organic matter
• C. Clay mineral content
• D. Silt content

Answer: (B)

Organic matter increases CEC the most because humus and other organic fractions have many functional groups (such as carboxyl and phenolic groups) that can deprotonate and carry negative charges. Those negative sites become exchangeable locations for cations like calcium, magnesium, potassium, and others, giving the soil a strong capacity to hold and exchange nutrients. Clay minerals also contribute to CEC, but when organic matter is present in significant amounts, it adds a large number of exchange sites per unit mass and often dominates the CEC, especially in soils with limited clay. In contrast, sand provides very few exchange sites due to its low surface area, and silt has more than sand but still far less impact on CEC than organic matter or clay.