EVALUATION OF THREE BUFFER METHODS FOR MEASURING THE LIME REQUIREMENT OF ACID COARSE-TEXTURED SOILS.

Information on the ability of lime requirement (LR) methods to predict the amount of lime required to achieve a selected pH that if optimum for crop production is important in the management of acid agricultural and horticultural soils. The primarily aim of this study was to evaluate three quick buffer methods for measuring LR to target pH values using 28 acidic coarse-textured soils from Quebec (Canada). The buffer methods included the original Shoemaker, McLean and Pratt (SMP) single-buffer method (initial buffer pH 7.5) and modified SMP method (initial buffer pH of 6.0 and 5.5, and soil: CaCl2 0.01 M:buffer solution ratios of 1:1:2 and 1:2:2), the Adams and Evans (AE) method (initial buffer pH 8.0) and the Mehlich single-buffer method (initial buffer pH 6.6). The SMP procedures were compared on the basis of their ability to predict the lime requirement to pHwater values of 5.5, 6.0 or 6.5, and to pHCaCl2 values of 5.0 and 5.5 obtained from soil-CaCO2-moist incubation (ILR). LR values estimated from all procedures were significantly correlated with each other. Decreasing SMP buffer pH from 7.5 to 5.5 gave an accurate and precise estimation of the soil LR. In general, the best linear relationships between the ILR and soil:water:buffer equilibrium pH or soil:CaCl2:buffer equilibrium pH were obtained when the initial SMP buffer solution was adjusted to pH 5.5. The relationship between ILR and SMP-LR at 1:1:2 soil:CaCl2:buffer solution is better than that obtained at 1:2:2 ratio. Positive correlations were obtained between SMP-LR values and total and exchangeable acidity, extractable soil Al (Al2CaCl, AlKCl, Aloxalate, Aldithionite and Alpyrophosphate), and organic matter and clay particle content. The results indicate that the LR determination of acid coarse-textured soils is affected by soil buffer equilibrations and chemical properties that are associated with acidity factors and buffer capacity. [ABSTRACT FROM AUTHOR]