The vadose zone is the ground between the land surface and the water table, where pores hold both air and water. It is also called the unsaturated zone.
The vadose zone, also called the unsaturated zone or zone of aeration, runs from the land surface down to the water table. Its pores contain both air and water, and the water is held by capillary forces at less than atmospheric pressure. Just above the water table is the capillary fringe, where water is drawn upward and the pores may be almost full. The zone can be absent in a marsh or hundreds of metres thick in a desert. Its thickness and texture control how long rain takes to become recharge. In thin sandy soils this may be hours or days. In thick dry layers it may be many years. The vadose zone matters for pollution, because it filters, delays or breaks down many contaminants before they reach groundwater. It also supplies water to plant roots. Its moisture is measured with soil moisture sensors, tensiometers and neutron probes. Because hydraulic conductivity falls sharply as soil dries, water movement here is much harder to predict than in the saturated zone, and it is usually modelled with the Richards equation.