Rapid Measurement of Soil pH Buffering Capacity

Soil pH buffering capacity, described here as lime buffer capacity (LBC), is a fundamental soil property needed to estimate the change in soil pH after a known quantity of acidity or alkalinity is added to soil. Its rapid determination can be useful for many purposes, for example, estimating the lime needed to raise pH or acid needed to lower pH to a desired level. The objective of the present study was to evaluate the statistical relationship developed in previous studies between LBC from 30-min equilibration with Ca(OH)2 (LBC30) and LBC from 5-d equilibration with Ca(OH)2 (LBCeq) on a larger set of soils from Georgia. Five days was considered adequate time for true pH equilibrium and obtaining a true LBC. Eighty-seven soils from Georgia were treated with Ca(OH)2 using standard procedures for both equilibrium times, and the statistical relationship between the two LBCs were developed. The relationship developed in the first study was further tested in a second incubation of 67 soils to determine its accuracy in achieving a target pHCaCl2 of 6.0. The data from the second incubation indicated that the target pH was exceeded by an average of 0.11 pH units and that the average pH spread around the acquired pH was ±0.1 pH unit. The results suggest that the prediction of soil pH buffering capacity based on the proposed protocols will be sufficiently accurate for making agricultural lime application recommendations.