When is added to a dry soil either by rain or irrigation, it is distributed around the soil particles where it is held by adhesive and cohesive forces; it displaces air in the pore spaces and eventually fills the pores. When all the pores, large and small, are filled, the soil is said to be saturated and is at its maximum retentive capacity.
The following re the three main classes of soil water:
(i) Hygroscopic water. Water held tightly to the surface of soil particles by
(ii) Capillary water. Water held by forces of surface tension and continuous films
around soil particles and in the capillary spaces.
(iii) Gravitational water. Water that moves freely in response to gravity and drains
out of the soil.