A Conventional Method for Valid "Actual Soil pH" Measurement

After recognition of the Suspension Effect problem in potentiometric measurements in aqueous suspensions, no scientific consensus about its cause and nature was obtained. Numerous conventional methods of soil pH measurement were therefore introduced for practical soil pH determination. Most of the results of these methods are not valid with regard to the international pH scale. The method proposed in the present work rejects improper procedures and introduces correct soil sampling and a suitable pH measuring technique, as follows: the indicator glass electrode, substituting for roots in the soil, is inserted in a partly diluted sample suspension of the original soil and the modified reference electrode contacts the sample in a manner that eliminates the abnormal liquid junction potential. "Actual soil pH values" measured in this way are valid but the method used is a conventional one. Namely, the irreversible potential of the glass electrode includes the suspension effect of the first kind (SE1) and is a mixed steady-state potential. It is considered by convention as a substitute for and equivalent to the equilibrium potential which as a rule does not exist in a suspension. The soil pH values measured by the proposed conventional method are reproducible and valid with regard to the international hpH scale. They could be considered as the pH values, with uncertainty of +/- 0.1 pH unit, to which the roots are exposed.