Wilting point

From Glossary of Meteorology

wilting point

The water content of a soil when an indicator plant (or common agricultural crop) can no longer draw water from the soil, even if atmospheric water demand is zero (near saturated atmosphere and plant and atmosphere at uniform temperature); often estimated as a soil water potential at 15 bars (or atmospheres).

For many agricultural soils, this represents a loss of about half the total water-holding capacity of a soil.