Which soil texture has the highest water-holding capacity but low permeability?

• A. Loam
• B. Sand
• C. Silt
• D. Clay

Answer: (D)

Water storage versus water movement in soil scales with particle size. The finer the texture, the more surface area and micro-pores it has to hold water, yet those tiny pores make movement through the soil very slow. Clay, with its extremely small particles, traps a lot of water on its surfaces and in its tiny pores, giving it a high water-holding capacity. But because the pores are so small and the particle arrangement is dense, water moves through clay very slowly, resulting in low permeability.

That’s why clay is the best fit for “highest water-holding capacity but low permeability.” Sand drains quickly and holds little water due to larger pores, loam strikes a balance between storage and drainage, and silt sits between sand and clay in both water-holding and permeability.