Which statement best describes the property measured by CEC in soils?

• 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)

Cation Exchange Capacity describes how many exchangeable positively charged ions a soil can hold on the negatively charged surfaces of clay minerals and organic matter. These exchange sites attract nutrients such as calcium, magnesium, potassium, ammonium, and sodium, keeping them in the soil solution until plants need them. Because those ions can be swapped with ions in the soil water, soils with higher CEC can retain more nutrients and supply them more readily, especially under leaching conditions. This makes CEC a direct measure of the soil’s ability to hold positively charged nutrients. The other options describe different properties: water-holding capacity depends on soil texture and structure; pH buffering capacity relates to resistance to pH change (influenced by CEC and organic matter but not the same as nutrient-holding capacity); and color or texture are simply physical characteristics not describing CEC.