Soil pH was determined in water, 0.01M CaCl2 and 0.1 MKCl at 1:2, 1:2.5 and 1:5 soil: solution ratio and were found to be correlated over a wide range. The regression equations obtained in a fairly large number of soils of West Bengal under certain rigid laboratory conditions were similar to those obtained in comparative studies from Britain (Davies 1971). The regression equation obtained for 0.01 M CaCl2versus water medium was found to be pHca = 1.05 pH 0.77 and is valid strictly for non-saline, net negatively charged soils. In general, the release of H+ [cmol (p+) kg+1] ions was linearly related to increased dilution ratio. Moreover soil/solution shaking time in excess of few hours is undesirable as there was fluctuation in pH with time as stability was not attained. Reversal in trend of pH-dilution curve was noted at lower soil solution-dilution ratio if sufficient reaction time was allowed.
Measurement of pH, regression-equation, pH-dilution curve, soil-solution shaking time
