The Measurement of Soil pH

Summary

This 1955 paper presents experimental evidence that soil pH values depend critically on the electrolyte concentration of the measurement solution, interpreted through electrical double-layer theory. The authors demonstrate that 0.01 M CaCl₂ provides the optimal balance for standardised, reproducible soil pH measurement in non-saline soils, yielding values largely independent of soil/solution ratio and enabling reliable lime potential determination. The work emphasises the necessity of using a defined electrolyte solution composition to ensure comparability of soil pH measurements across different samples and laboratories.

Regional applicability

This foundational methodological paper established principles of soil pH measurement that became internationally standardised practice. The findings are directly applicable to UK soil testing laboratories and remain relevant to current soil pH protocols, though regional soil types and salinity contexts may require validation of the 0.01 M CaCl₂ recommendation.

Key measures

Soil pH values measured at varying CaCl₂ concentrations; soil/solution ratios; electrolyte concentration effects on pH; lime potential calculations

Outcomes reported

The study demonstrated that soil pH values vary systematically with electrolyte concentration and identified 0.01 M CaCl₂ as the optimal solution for standardised, reproducible pH measurement in non-saline soils. The findings showed that pH measurements using this electrolyte concentration are largely independent of soil/solution ratio and permit accurate calculation of soil lime potential.

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