In soils, cation exchange capacity tends to be higher in which texture?

• A. Sandy soils
• B. Loamy soils
• C. Clayey soils
• D. Gravelly soils

Answer: (C)

Cation exchange capacity (CEC) measures how many positively charged ions a soil can hold and exchange, and it depends mainly on the amount of charged surface area in the soil. Clay minerals provide a huge surface area and carry permanent negative charges, giving many sites for cations to adhere and be exchanged. That’s why soils with more clay can hold and exchange more nutrients than soils with little clay.

Sandy soils have less surface area and fewer charging sites, so their CEC is low. Gravelly soils have even less of the fine, charged material and often less organic matter, further reducing CEC. Loamy soils fall in between, with a mix of particle sizes and an intermediate CEC. So, among textures, clayey soils tend to have the highest CEC.