Titratable Acidity at pH = 7 Estimated from the pH of a Soil:Buffer Mixture

Abstract

The value of titratable acidity in soil pH = 7 (AT_pH7) is used for taxonomic purposes and to estimate lime requirement. AT_pH7 could be predicted by the pH value of the mixture soil:buffer solution (pH_equilibrium). Calcium acetate buffered at pH = 7 was added to each sample and pH_equlibrium and alkali required to reach pH = 7 were measured. With pH_equilibrium the AT_pH7 was estimated by regression (AT_eq) and by the amount of alkali neutralized to achieve pH_equilibrium (AT_OH). There was an acceptable fit between AT_pH7, AT_eq and AT_OH, but their differences were not normally distributed. Both, AT_OH and AT_eq, underestimated the AT_pH7 average. The pH_equilibrium value was more accurate than AT_pH7, while AT_eq and AT_OH measurements were less accurate. The use of AT_OH and AT_eq did not introduce significant errors in classifying the soils by their saturation in bases. Both measurements wereperformed in a shortertime than AT_pH7.