Which soil texture would have the slowest infiltration and highest nutrient retention?

• A. Sandy soil
• B. Gravelly soil
• C. Silty sand
• D. Clay-rich soil with organic matter

Answer: (D)

Infiltration rate and nutrient retention are shaped by texture and organic matter. Fine-textured soils with abundant surface area and charge sites slow water movement and hold onto nutrients more effectively. Clay minerals provide a high cation exchange capacity, meaning positively charged nutrients like potassium, calcium, and magnesium stick to the soil particles rather than washing away. Adding organic matter boosts these effects by supplying additional sites for nutrient adsorption and by improving soil structure, which creates stable aggregates and micropores that slow infiltration and reduce rapid drainage.

Sandy soils, with large interconnected pore spaces, allow water to infiltrate quickly and have low nutrient retention due to minimal surface area and low cation exchange capacity. Gravelly soils are even more permeable and drain rapidly, offering little nutrient retention. Silty sands sit between these extremes—more infiltration resistance than pure sand and somewhat better nutrient retention, but not to the extent of clay-rich soils with organic matter.

Therefore, the clay-rich soil with organic matter best exhibits both the slowest infiltration and the highest nutrient retention.