All soils contains varying amount of salts in solution form as carbonate bicarbonates, sulphate, chlorides etc. determination of these salts in soil solution is very important in connection with interpretation of their harmful effects, on plant growth , seed germination etc. The electrical conductivity of water extract of soil gives a measure of these salts in the soil. Pure water as it doesn’t contains salts is a poor conductor of electric current where as water containing ample amount of salts conducts electric current approximately in proportion of amounts of salts.
Electrical conductivity or electrical conductance is the reciprocal of resistance ( R) in ohms.
C= I /R
Where, I= Current in atmosphere, R= Resistance in Ohms.
Conductance is expresses as millions (1000 times mhos)
Specific conductance ( L) of a solution is the conductance that would be measured at 25 0C between electrode 1 cm2 cross section and placed one cm apart and may be visualized as the conductance across a cm3 or mhos/cm. specific conductance may e measured with a cell of various dimension by means of cell constant. Because of number obtained expressing specific conductance of the solution are generally small it has been convenient to express specific conductance as millimhos/cm (1000 times mhos/cm,) and this unit is adopted widely.
1. AC potential application
2. Potentiometer resistance
3. Resistance cell
4. Ear phone or electric eye.
Significance of Electrical Conductivity:
The EC of the soil has direct relationship with growth of different crops.
Rating chart of soil EC:
Where, less than 1 dSm-1 Normal.
1-2 dSm-1: Critical for germination
2-3 dSm-1: Critical for salt sensitive crops.
Above 3.0: Injurious to most of crops.
Factors Affecting the Electrical Conductivity:
The EC meter is standardize at 25 0C and rise or decrease in temperature of solution needs correction. The correction factor should be multiplied with observed values.
EC at 25 0C = EC t X ft.
ECt = EC at temperature t, ft= correction factor at temperature.