Which pore space drains rapidly and holds little water for plant use?

• A. Micropores
• B. Ultramicropores
• C. Mesopores
• D. Macropores

Answer: (D)

Water moves fastest out of the soil through the largest openings. Macropores are big enough that gravity pulls water through them quickly, so they drain rapidly after rainfall or irrigation. Because their size means capillary forces are weak, they don’t hold much water against gravity, making the water they do contain largely unavailable to plant roots. In contrast, the smaller pore spaces—micropores and the finer end of mesopores—retain water more strongly and provide a reservoir of water that plants can access. So macropores drain rapidly and hold little water for plant use.