Capillary action
The radial (outward and upward) movement of water through the soil that fills the spaces between particles with capillary moisture.

Capillary moisture
The water held in pore spaces by the surface tension between the water and the soil particles. This is the primary source of water for plants and is also referred to as "available moisture".

Gravitational water
Free water in the soil which moves downward due to gravity. After a soil has been saturated, the gravitational water percolates downwards, leaving the soil at field capacity.

Field capacity
As much water as the soil can hold against the influence of gravity. If a soil is saturated by rainfall or irrigation and then allowed to drain freely for 24 hours, the soil is usually at field capacity.

Infiltration range
The rate at which water enters the soil. This rate varies greatly, and may impose a limitation upon the design of an irrigation system since water application rates may result in runoff and erosion.