LIME REQUIREMENT OF ACIDIC QUEENSLAND SOILS .2. COMPARISON OF LABORATORY METHODS FOR PREDICTING LIME REQUIREMENT

A number of laboratory procedures for predicting lime requirement were evaluated by using 40 acidic surface soils from eastern Queensland. The methods were compared on the basisof their ability to predict the lime requirement to pHwvalues of 55 and65 obtained fromsoil-CaCC>3-moist incubations. The laboratory methods evaluated included 1mKC1 extractableAl, equilibration of soil: water suspensions with varying amounts of added Ca(OH>2, theShoemaker, McLean and Pratt (SMP) single-buffer method, the SMP double-buffer method, theYuan double-buffer method and the Mehlich single-buffer method. Aluminium extracted, with 1 m KC1 was a poor predictor of lime requirement to pHw5-5. In most of the soils tested, the actual amounts of lime required to reduce Al to apredetermined level far exceeded those calculated on the basis of 1mKC1 extractable Alvalues of untreated soils. Batch equilibration of soil: water suspensions containing Ca(OH)2proved a reliable but relatively time-consuming method of determining lime requirement. All of the buffer methods were reasonably well correlated with lime requirement (0-61 <r2<0-82). Buffer methods which had a high initial buffer pH and a relatively highbuffer strength were less well correlated with lime requirement than weaker buffers of lowerinitial pH. The Mehlich single-buffer method (initial pH6-6) fitted both these latter criteriaand gave good correlations with lime requirements to pHw5-5 (r2= 0-78) and pHw6-5(r2= 0-80). Compared with the single-buffer methods, neither of the double-buffer methods(which require two pH measurements) was better correlated with lime requirements. © 1990 CSIRO. All rights reserved.