A STUDY OF THE LIME POTENTIAL

Abstract

In recent years the lime potential, pH-p(Ca + Mg), has received considerable attention (3, 6, 8, 9, 10). It was proposed by Schofield (5) as a measure more fundamental of the base status of a soil than pH alone. It is true that the lime potential is a measure of the sum of the activities of calcium and magnesium hydroxides in solution and is, therefore, a measure of the base status of the soil solution, but a natural question is whether it is also a reliable measure of the per cent base saturation of a soil. Webster and Harward (10) investigated this by measuring the lime potential of a number of soils from experimental plots which had received various amounts of lime. They found a somewhat better correlation for pH-p(Ca + Mg) than for pH with per cent Ca + Mg saturation. There was, however, considerable scattering of their experimental values about the regression line of lime potential vs. per cent base saturation. It thus seemed impossible to predict the per cent base saturation from the measured lime potential for a given soil. The main object of the work reported here was to determine the real significance of the lime potential, in relation to per cent base saturation, with clays commonly found in soils. Before proceeding with the main objective, however, there were a number of questions concerning the lime potential that needed experimental investigation. These were: Is the lime potential independent of sait concentration regardless of the ratio of Ca to Mg ions in the System? Is there a ratio of exchangeable to solution Ca + Mg below which the lime potential is sensitive to sait concentration? Is the presence of exchangeable Al3+ a necessary and sufncient condition for the lime potential to be independent of sait concentration? Is the lime potential independent of sait concentration with organic exchange material? The present paper deals with experiments made to gather information about these questions. The significance of the lime potential relative to per cent base saturation is dealt with in a second paper soon to appear in this journal.