Water present in the soil may be classified under three heads:

  1. Hygroscopic water,
  2. Capillary water,
  3. Gravitational water.

1.Hygroscopic Water.

  • When a soil sample after having been completely dried in an oven is put in an open atmosphere,
  • It absorbs some amount of water from it.
  • The amount of water so absorbed by the oven-dried soil sample is termed as hygroscopic water.
  • This water is not capable of any movement by the action of gravity force or capillary force.
  • The amount of this water in the soil can vary only if there is a change in the moisture content in the atmosphere.
  • This water is not available for plant growth.

2. Capillary Water.

  • This water is that water content in soil excess of hygroscopic water,
  • which exists in the pore space of the soil, due to molecular attraction.
  • This water is held in the form of a thin continuous film around
  • The soil particles due to forces of surface tension.
  • It is this water that remains available for the plant growth between successive waterings to the crops. See Fig

Various forms of water

3. Gravitation Water.

  • It is that part in excess of hygroscopic and capillary water,
  • which will drain out of the soil under the action of gravity.
  • This water passes down and joins the groundwater table.
  • This water is also known as superfluous water.
  • It is also not available for the growth of plants as it readily gets drained whenever it finds conditions favorable for it.
  • Water present in the soil may be classified as unavailable, available
  • This classification is based on the availability of soil water for plant growth. See Fig.