Adhesion, Cohesion and Soil Moisture tension | Agristudent.com

Adhesion and cohesion

Adhesion Cohesion and Soil Moisture tension

What are the forces responsible for water retention in Soil?

Adhesion and cohesion

Hydrogen bonding accounts for two basic forces responsible for water retention and movement in soils

These are Adhesion and Cohesion

The forces of adhesion and cohesion make it possible for the soil solids to retain water and control its movement and use

What is Adhesion?

Adhesion besically is the force of attraction between the two dissimilar molecules

Eg – attraction between soil and water molecule

In case of Soil, it is force of attraction between water molecules and solid surfaces

By adhesion some water molecules are held rigidly at the surfaces of soil solids

The adhesive force diminishes rapidly with distance from the solid surface

What is Cohesion?

Cohesion is basically the force of attraction between similar molecules

Eg – force of attraction between water and water molecule

In case of soil, it is the force of attraction between the water molecules for each other

These tightly bound water molecules hold by cohesion other water molecules farther away from the solid surfaces

The cohesion of one water molecule to another results in water molecules forming temporary clusters that are constantly changing in size and shape as individual water molecules break free to join up with others

This cohesive force between water molecules also allows the solid to indirectly restrict the freedom of water for some distance beyond the solid-liquid interface

What is Soil moisture tension?

Soil moisture tension is a measure of the tenacity with which water is retained in the soil and reflects the force per unit area that must be exerted by plants to remove water from the soil

Any thing in nature is attracted by gravitational force

Accordingly, even the water i.e. moisture in the soil is also attracted by gravitational force acting downwards

The plants have to exert some force to pull this water against the gravity into their own systems

What is the unit of measuring Soil moisture tension?

A common means of expressing tension is in terms of a bar, which equals the pressure exerted by a vertical water column

A pressure of one bar is approximately equal to the hydrostatic pressure exerted by a vertical column of water having a height of 1023 cm or a hydraulic head of 1023 cm

Similarly 1.0 bar is equivalent to 0.9869 atmospheres

This value approximates the standard atmosphere, which is the average air pressure at sea level i.e., equal to 14.7 lbs/in2 or a mercury head of 76 cm or 760mm.

The suction of water having a height of 10cm is equal to 0.01 bars or 10 millibars, that of a column of 100 cm high about 0.1 bar or 100millibars

Similarly 1.0 bar is equal to 100 centibars

The higher the height of water column or bars or atmospheres the greater the tension or suction measure

Further readings and references on Adhesion Cohesion and Soil Moisture tension

http://wikipedia.com

Handbook of Agriculture

 

 

 

Author: agristudent

Team Agristudent is a young and dynamic team of Agriculture specialists who have acquired specialised knowledge in their respective subjects. Their mission is to create a unique online encyclopedia of agriculture, which can be useful to millions around the world as an online reference library

Leave a Reply

Your email address will not be published.