Test for Soil PH
The PH is the negative logarithm of the hydrogen ion activity or the logarithm of the reciprocal of the H ion concentration.
PH = long 10 (H+) = log 10 ( H)-1-
The PH of pure water at 25 0C is 7 while that of acid is below 7 and that of base is above 7.
Significance of Soil PH Measurement:
Plant can grow on different types of soils with wide varieties of properties and wide ranges of PH. However plants do have a preference for a specific range of soil reactions or soil PH. In above figure we have seen different ranges of soil PH like from slightly acidic to very strong acid from slightly alkaline to very strongly alkaline and intermediate of both, neutral.
This soil reaction does have its effects on availability of nutrients and thus on growth of plants. Soil PH has influence on various soil properties like chemical, physical and biological.
Rating Chart for Soil PH:
Less than 6.0: Acidic
7.0 – 8.5: Normal
8.6 – 9.0: Tendency to become alkaline.
Able 9.0: Alkali
Methods PH Measurement:
I. Glass Electrode PH Meter:
The glass electrode generally used for the PH measurement employes a glass membrane of special, chemically pure, soft glass paired with a calomel reference electrode are used for measuring the soil PH.
II. Hydrogen Electrode:
In order to measure hydrogen ion concentrations of pH of a solution use of hydrogen gas as a metal electrode and dip in a solution under test and measure the electrode potential.
III. Quinhydrone Electrode:
It consists of equimolecular mixture of quinone and hydroquinone added directly to the solution under test. This electrode does not give correct reading in alkaline solution for PH grater than 9.0.