What is the name of soil water held in extremely fine pores with such high matric tension that plant roots cannot absorb it?

Correct answer: Hygroscopic water

Correct answer: B, hygroscopic water. Soil particles, especially clay and organic matter, attract water molecules strongly. A very thin film becomes attached to particle surfaces by adhesive and molecular forces. Because the water is held at very high matric tension, plant roots cannot exert enough suction to remove it. This water is therefore considered unavailable to plants, even though it is present in the soil. A is wrong because free gravitational water occupies larger pores and moves downward under gravity; too much of it may drain away. C is wrong because available capillary water is held with a force that roots can overcome and is an important source of plant water. D refers to water stored below the soil in saturated underground formations, not a microscopic film around soil particles. The distinction is based on how tightly water is held, not simply on how much water is present. Memory cue: hygroscopic water is “hugged” tightly by soil particles.