The document classifies and describes the three main classes of soil water: 1) Capillary water, which exists in pore spaces by molecular attraction and surface tension, held at tensions from 1/3 to 15 atmospheres. 2) Gravitational water, which will drain out of soil pores due to gravity if drainage is provided, and is not available for plant growth. 3) Hygroscopic water, which is absorbed by oven-dried soil exposed to moist air and is held very tightly by adsorption forces at tensions from 10,000 to 31 atmospheres, making it unavailable to plants.

1. Classification of Water
Prof. S.R. Suryavanshi,
Asst. Professor of Agronomy,
Dr. D.Y. Patil College of Agriculture,
Talsande

2. When is water 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.

3. Adhesion:
It is the attraction of solid surfaces for
water molecules.
Adhesion is operative only at the solid-
liquid interface and hence the film of water
established by it is very thin.
Cohesion:
It is the attraction of water molecules for
each other.
This force makes possible a marked
thickness of the films of water established by
hydration until they attain microscopic size.

4. Classification of Water
The following re the three main classes of soil water:
A) Capillary water:
 Capillary water is that part, in excess of
hygroscopic water, which exists in the pore space
of the soil by molecular attraction.
 Water held by forces of surface tension and
continuous films around soil particles and in the
capillary spaces.
 Water left out in capillary pores after excess water
has drained– Held by surface tension – cohesive
force 1/3-15 atmp.– Available to plants

5. B) Gravitational water:
 Gravitational water is that part in excess
of hygroscopic and capillary water
which will move out of the soil if
favorable drainage is provided.
 Excess water in soil pores– drains out
due to gravitational force– Not available
for plant growth.
 Water that moves freely in response to
gravity and drains out of the soil.

6. C) Hygroscopic water:
 When an oven dried sample is kept open in the
atmosphere, it absorbs some amount of water
from the atmosphere.
 This is not capable of movement by the action of
gravity or capillary forces.
 Water held tightly to the surface of soil particles
by adsorption forces.
 Water absorbed by a oven dry soil when exposed
to a moist air.
 Held at high tension - tightly held by adhesion
force – water of adhesion 10000-31 atm p., water
not available – permanent wilting point

7. Thank you