PRESENCE OF WATER IN SOIL
Water present in the soil may be classified under three heads:
- Hygroscopic water,
- Capillary water,
- Gravitational 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
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.