Why does clay usually hold more nutrients than sand?

• A. Clay soils have better drainage
• B. Higher CEC and more negative charges
• C. Sand holds more organic matter
• D. Clay has fewer minerals

Answer: (B)

The key idea is how soils hold onto nutrient cations. Clay minerals have a very large surface area and carry a net negative charge. Those negative sites act like tiny holding spots (cation exchange sites) that attract and hold positively charged nutrient ions such as potassium, calcium, magnesium, and ammonium. This keeps nutrients in the root zone and makes them available to plants, rather than letting them wash away with water. Sand, on the other hand, has much less surface area and far fewer exchange sites, so it cannot retain as many nutrient ions and nutrients are more easily leached.

The statement about drainage isn’t correct here, because clays tend to drain poorly despite their nutrient-holding ability. It’s not that sand holds more organic matter; clay and silt actually help stabilize organic matter due to their surfaces and charges. And clay isn’t lacking minerals; it’s the mineral structure and the resulting charge and surface area that give clays a higher capacity to hold nutrients.