What is Cation Exchange Capacity (CEC) in soils?

• A. The soil's ability to hold and exchange positively charged nutrient ions with plant roots.
• B. The soil's pH level.
• C. The soil's texture classification.
• D. The soil's color.

Answer: (A)

Cation Exchange Capacity shows how many positively charged nutrient ions soil particles can hold and swap with the water around roots. The negative sites on clay minerals and on organic matter attract and hold cations such as calcium, magnesium, potassium, and ammonium. This capacity allows nutrients to be stored in the soil and released to plant roots as needed, helping supply nutrients over time and buffering against changes in availability. Soils rich in clay and organic matter tend to have higher CEC and can hold more nutrients, while sandy soils have lower CEC and nutrients are more easily lost. The other options describe pH, texture, or color, which don’t measure this nutrient-holding and exchange ability.