Which classification of soil water is described as providing the most water to plants and being the most important?

• A. Hygroscopic water
• B. Available capillary water
• C. Gravitational water
• D. Saturated water

Answer: (B)

Available capillary water is the portion of soil water that roots can readily extract, making it the most important for plant use. This water is held in the capillary pore spaces at tensions that plants can overcome, typically described as the water between field capacity and the wilting point. Because roots can draw on it as needed, it provides a sustained supply for growth and metabolism.

Hygroscopic water, by contrast, is tightly bound to soil particles in thin films and is not accessible to most plants, so it doesn’t contribute to available water. Gravitational water drains rapidly through the soil due to gravity after rainfall or irrigation and is quickly lost from the root zone, offering little lasting supply. Saturated water fills all pore spaces, but once drainage occurs, much of it leaves the root zone or drops below the point plants can efficiently exploit; it isn’t the readily available portion that supports regular plant water uptake.