Which term describes water in soil that is available for plant uptake?

• A. Gravitational water
• B. Capillary water
• C. Groundwater
• D. Runoff water

Answer: (B)

Water that plants can take up is the water held in the soil by capillary forces within the pore spaces. This capillary water sits in the smaller pores and remains available to roots between the point where water becomes unavailable to plants (wilting point) and where soil is filled to its capacity (field capacity). After rainfall, some water drains away due to gravity (gravitational water) and isn’t reliably available for uptake. Groundwater lies in the deep, saturated zone below the root zone, not typically accessible to roots in the near term. Runoff water flows over the surface and isn’t stored in the soil for plant use. Capillary water is thus the water most readily available for plants.