Determination of pH in water, 0.01 M CaCl2, and 0.1 M KCl, at dilution ratios 5:1, 2.5:1, and 2:1 solution: soil, were found to be highly correlated over a wide pH range. The regression equations, obtained on a small group of New South Wales soils under strict laboratory conditions, were similar to those reported in comparative studies from Britain (Davies 1971) and Canada (van Lierop 1981). The relationship between pH in water (pHw) and 0.01 M CaCl2 (pHca) at 2.5:1 solution: soil was found to be
pHca = 1.05 pHw - 0.9
The regression equation is valid only for nonsaline, net negatively charged soils.
Our study demonstrates that wide dilution ratios result in the release of hydrolyzable acidity that nearly maintains the pH registered at narrower ratios. Between 2:1 and 10:1 dilution ratios, the release of H+cmol(+)/kg soil was linearly related to the dilution ratio. Periods of solution-soil shaking in excess of a few hours are undesirable because the pH meanders with time and a stable pH is not attained.
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