Plant available water in soils equals FC minus PWP.

• A. Plant available water equals field capacity minus permanent wilting point.
• B. PAW equals FC plus PWP.
• C. PAW equals PWP only.
• D. PAW is independent of FC.

Answer: (A)

Plant available water is the amount of water in the root zone that plants can actually use, which corresponds to the moisture range between field capacity and the permanent wilting point. Field capacity is the water content left after gravity drainage has reduced the soil to a point where it can hold water against gravity. The permanent wilting point is the moisture level at which a plant cannot recover (turgor loss) and the water is effectively unavailable to most plants. The difference between these two moisture contents, FC minus PWP, represents the water that plants can access, hence PAW = FC − PWP. The other ideas mix or add these values incorrectly, or imply PAW doesn’t depend on FC, which isn’t true because the accessible water is defined by that FC-to-PWP range.