Composite Soil Samples Reflect the Arithmetic Mean pH of the Individual Cores

Abstract

The pH of composite soil samples has been reported to be well approximated by the arithmetic mean pH of the individual soil cores, rather than the arithmetic mean of (H + ) back transformed to pH. The calculations provided here show that this is due to the mixing of negatively charged soil colloids rather than the mixing of unbuffered solutions extracted from the soil by electrolytes such as 0.01 M CaCl 2 . Therefore, the conversion of pH to (H + ), averaging, and then back transform to pH is an unnecessary process when estimating the pH of combined soil samples and the use of the arithmetic mean is recommended.