Classification of soil water

Classification of soil water

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