Modified Method of Determining Lime Buffer Capacity and Lime Requirement of Soils.

The University of Georgia Soil, Plant, and Water Laboratory (SPW) uses a single-addition titration with Ca(OH)₂ for estimating soil lime requirement (LR).  The LR depends in part on a soil’s pH buffering capacity (described as lime buffer capacity (LBC) with units of mg CaCO₃ kg^-1 pH^-1) , which is estimated from the rise in soil pH after Ca(OH)₂ is added and allowed to react for 30 min. This estimate of LBC is referred to as LBC_30min. The 30-min reaction time has not been sufficient to reach an equilibrium pH between acid soils and Ca(OH)₂, resulting in an underestimate of a soil’s true LBC. As a result, a correction factor has been applied to improve the accuracy of the LR. In a previous study in our laboratory, Thompson et al. (2010) showed that  25 soils from the Southeast US had reached an equilibrium pH by 84 h following Ca(OH)₂ addition and that the LBC calculated using the equilibrium pH (LBC_equil) could be predicted from the LBC_30min. An accurate estimate of LBC_equil should allow better lime recommendations across a range of initial soil pHs. The objective of the present study was to test the accuracy of an equation to predict LBC_equil from LBC_30min by determining if the LR calculated from LBC_equil was more accurate than those calculated by the equations used presently. This was done by incubating 70 acid Georgia soils with amounts of Ca(OH)₂ recommended using LBC_equil to achieve a target pH of 6.0. Results of the incubations will be discussed with regard to improving the LR calculated with the new equations.