Use of a flat‐surface combination pH electrode for measurement of soil pH

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Abstract
Studies to evaluate a flat‐surface combination pH electrode (Sensorex Model 450C) for measurement of soil pH showed that it permitted direct, nondestructive measurement of the pH of soils at natural water contents and had the additional advantages of being durable, inexpensive, and easily cleaned. The electrode gave stable and reproducible pH values when pressed into 15 diverse soils at water potentials ranging from ‐15 bars to ‐0.3 bar, and these values were similar to those obtained when glass and reference electrodes were inserted into suspensions of these soils in 0.01M CaCl2. The pH values obtained by the electrode studied were, on the average, 0.2 pH units higher for a soil saturated with water than for the same soil at 15‐bar water percentage. The pH values of soils at water contents between permanent wilting percentage and saturation average 0.2–0.6 pH units lower than those of 1:1, 1:2, or 1:5 soil:H2O suspensions and averaged 0.4–0.6 pH units higher than those of 1:1 soil:1M KCl suspensions, but they were highly correlated (r>0.98) with the pH values of these suspensions.

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