What does CEC measure?

• A. Soil's ability to hold positively charged nutrients
• B. Soil's water-holding capacity
• C. Soil pH buffering capacity
• D. Soil color or texture

Answer: (A)

CEC measures the soil's ability to hold and exchange positively charged nutrients on negatively charged surfaces of clay minerals and organic matter. These exchange sites attract cations such as potassium, calcium, magnesium, and ammonium, and the soil can swap these cations between the solid phase and soil solution to make nutrients available to plants. The higher the CEC, the more nutrients the soil can retain and supply, which is typical of soils with more clay and organic matter; sandy soils usually have lower CEC. This concept is different from how much water the soil can hold (water-holding capacity), how well the soil resists pH changes (pH buffering capacity), or simple physical descriptors like color or texture.