Soil pH is the most important parameter to evaluate nutrient availability in the soil. The pH value of a given sample, however, may vary according to the sample manipulation after sampling and to the laboratory analytical procedures. This experiment was carried out to determine the effect of the solvem type, of the soil/solvent ratio, and of the sample incubation on the pH values of 49 Brazilian soils. The soil pH was determined using water (pH-H2O) or calcium chloride (pH-CaCl2) as solvent, in two soil/solvent ratios (1:1 and 1:2.5). in all natural samples (without limestone), with and without wet incubation. The pH was also determinated in the samples of the neutralization curves of some soils, after incubation, before and after leaching out the excess of salts by rinsing the samples with destilled water. The soil/solvent ratio had no effect on soil pH, on both solvents. There was a good positive association (r² = 0.96) between pH values in both solvents, and lhe pH-CaCl2 was, on average, 0.6 units lower than pH-H2O. The incubation of the samples with moisture decreased soil pH due to salt accumulation, especially when determined using water as solvent. Rinsing lhe samples offset the effect caused by salts on pH-H2O but had a small effect on pH-CaCl2. The lime requirement of the soils was overestimated when obtained from the pH-H2O neutralization curves.
pH; salts; liming
