Factors Affecting PH Measurement
1. Soil Solution Ratio:
Condition being the same, the more water added to the soil sample the higher the soil PH.
2. Salt and Electrolyte Content:
A salt also increases the hydrolysis of Al and Fe ions, increasing the H+ in solution. The salts lower the PH. The use of 0.01 M cacl2 has been recommend as a solution which masks small differences in salt contents without displacing a large fractions of the hydrogen ions.
3. Degree of Dissociations of Hydrogen Ions:
Soil colloids differ in the amounts of discrete hydroxyl groups capable of ionizing the hydrogen ions.
4. Type of the Acidity:
Hydrogen ions adsorbed to electrostatic bands that have great tendency to dissociate than those from the OH groups.
5. CO2 Content:
The CO2 dissolved in water forming H2CO3 lowers the PH markedly.
6. Liquid Junction Potential:
Appreciable liquid junction potential ( Ej) may occur at the liquid junction particularly into very concentrated colloidal electro suspension. Liquid junction potential kept low by the use of a saturated KCL solution.
7. Equipment and Procedure:
Major difference in the PH appears due to inadequate standardization of the equipment rather than a limitation of the equipment.