What term refers to water that drains through soil and cannot be used by plants?

• A. Gravitational water
• B. Capillary water
• C. Field capacity water
• D. Groundwater

Answer: (A)

Gravitational water is the portion of soil water that drains downward through the pore spaces under the pull of gravity, leaving the root zone so plants cannot use it. After this rapid drainage, the water that remains is held by capillary forces and is available to plants, which is why capillary water is the plant-accessible portion. Groundwater refers to water in the saturated zone below the root zone, not the water that drains through soil in the unsaturated profile. Field capacity describes the soil’s water content after gravity drainage has occurred, representing how much water is left for potential plant use, rather than the water that drains away. So the water that drains through and cannot be used by plants is gravitational water.