Which soil texture would contain the most adsorptive sites and pore spaces per unit area?

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

Answer: (C)

Clay has the most adsorptive sites and pore spaces per unit area because its very small particles create a huge surface area and a layered, plate-like structure with many tiny pores. This gives clay a high specific surface area, so there are more sites for adsorption of water and nutrients (high cation exchange capacity) and more micro-pores to hold water—much more than coarser textures. Sand has larger particles, which means fewer surface sites and fewer micro-pores, even though its pores are bigger. Sandy loam and silt fall between them, with intermediate surface area and porosity. So the abundance of surface area and micro-pores in clay makes it the most adsorptive per unit area.