Glossary Terms

Saturated zone

Subsurface area below unsaturated/ vadose zone that is permanently water-saturated.

Preferential flow

Water flow through macro-pores (e.g., cracks, root channels) in the unsaturated/ vadose zone.


The quality of the soil that enables water to move downward through the profile. Permeability is measured as the distance per unit time that water moves downward through the saturated soil. Terms describing permeability are: Very slow: 0.15 cm/hr Slow: 0.15-0.5 cm/hr Moderately slow 0.5-1.5 cm/hr Moderate 1.5-5 cm/hr Moderately rapid 5.00-15.00 cm/hr Rapid 15-50 cm/hr [...]


Application of water to soils to assist in production of crops.


The movement of water passing the soil surface into the soil (as contrasted with percolation, which is movement of water through soil layers moving down to the aquifers, or out to rivers).

Infiltration rate

The speed at which water can pass into the soil, being typically lower in wet clay than in dry sand (unless sand has become hydrophobic).

Infiltration capacity

The maximum rate at which water can infiltrate into a soil under a given set of conditions.


Freshwater found beneath the earth's surface that fills the cavities of the earth's crust (pores, crevices, etc. in soil, sand and rock) contiguously, – and that supplies wells and springs, excluding the water in the vadose (unsaturated) zone. The definition applies to all permanent and temporary water deposits, formed both artificially and naturally, of sufficient [...]

Field capacity

The moisture condition where a soil contains the maximum amount of water that it can hold against gravity, and where further wetting will result in drainage. Following saturation, soils typically return to field capacity, when the rate of downward movement of water has substantially decreased, usually 1-3 days after rain or irrigation after the gravitational, [...]

Drip irrigation

Application of water under low pressure through a piped network in a pre-determined pattern, applied as a small discharge close to each plant and adjustable by irrigation nozzles or droppers. Usually called “high frequency irrigation” since irrigation rates are usually very small and intended to compensate crop evapotranspiration during one or a few days.