Comparison of methods for determining lime requirements of New Zealand soils

Methods for measuring the lime requirement (LR) of New Zealand mineral soils were evaluated. All the laboratory methods examined underestimated the LR to reach a target pH of 6.0 as determined from field trials (field LR). The Shoemaker, McLean, and Pratt (SMP) single and double buffer methods, the Adams-Evans buffer method, and a Ca(OH) 2 titration procedure gave similar correlations with field LR (rank correlation coefficients (r s ) = 0.68, 0.77, and 0.67 respectively). Yuan's buffer method and Metson's base saturation method were poorly correlated with field LR (r s = 0.52 and 0.34 respectively). Field LR was significantly correlated with soil pH (H 2 0) and exchangeable aluminium (r s = 0.66 and 0.66), and was not related to soil texture. Regression analysis showed that a simple model based on soil pH plus organic carbon (%C) or cation exchange capacity (CEC) could account for 43% of the variation in field LR. This model was successfully used to predict the field LRs of a further 24 soils.