Kinds of soil water

• When water is added to a dry soil, it is distributed around the soil particles where it is held by adhesive and cohesive forces; it displaces air n the pore spaces and eventually fills the pores.
• When all the pores are filled , the soil is said to be saturated and is at its maximum retention capacity.

Soil water classes

a. Hygroscopic water:

• Water held at 30-10,000 atm.
• Not available for plants.

b. Capillary water:

• Water held at 15 – 31 atm pressure.
• available to plants.

c. Gravitational water:

• Held at < 1/3 atm.
• Available to plants.

Notes:

• Adhesion is operative only at the solid – liquid interface.
• Cohesion is the attraction of water molecules for each other.
• When a dry soil sample is exposed to water vapour, it will take up moisture. The amount adsorbed depends on the nature and magnitude of the surface exposed.
• The finer the texture of mineral soil particles, the greater is likely is capillary capacity.
• Presence of organic matter increases the capillary capacity.