Which term describes the soil's capacity to hold exchangeable cations?

• A. Cation exchange capacity
• B. Soil moisture
• C. Porosity
• D. Bulk density

Answer: (A)

The main idea is the soil’s ability to hold positively charged nutrients on its surfaces. Soils have negative charges mainly from clay minerals and organic matter, which attract and hold exchangeable cations such as calcium, magnesium, potassium, and ammonium. The term for how many of these exchangeable cation charges the soil can hold is cation exchange capacity. It’s usually expressed per weight or per soil mass, reflecting the total number of charge sites available. A higher CEC means more sites to retain nutrients and buffer against pH changes, helping plants access essential elements and reducing leaching. In contrast, a soil’s moisture, porosity, or bulk density describe water content, pore space, and compactness, respectively, and do not measure the soil’s nutrient-holding capacity.