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ABSTRACT
A simple method for titrating acidic soils could be used by soil testing laboratories as an alternative method for routinely determining the lime requirement (LR) of soils. Because soil pH as a function of added base is linear in the pH range of 4.5 to 6.5, it may be possible to determine the slope of this relationship by regression analysis using a minimum number of base additions. The LR could then be determined by calculating the corresponding amount of lime required to reach the target pH using the regression equation. Our objectives were to determine reaction times needed for saturated Ca(OH)^sub 2^ solution to reach an equilibrium pH with 17 widely different soils, and then test a simple titration procedure for its ability to predict the LR, determined first by a full titration curve and then by a standard incubation method. All titrations were performed in a 1:1 soil/water ratio with calcium hydroxide as the base. Using the regression procedure to estimate LR, equilibration times of 30 min between base additions gave greater LRs than 15-inin equilibration, but the same as 45-min equilibration. When all 17 soils were considered, the LR from extrapolation of the linear regression yielded the same, as did the full titration curve (TC). The LR from titration with three base additions and 30-min equilibration time between additions estimated an average of 80% of the LR determined by the 3-d incubation. The Adams-Evans (AE) buffer procedure overestimated and underestimated the LR for soils with relatively low- and high-LRs, respectively. Based on these results, titration appears promising for routine use, but it needs more research to determine whether it can be simplified further.
Abbreviations: AE, Adams Evans; LR, lime requirement; MLRA, Major Land Resource Area; TC, titration curve.
BUFFER METHODS are typically used by soil testing laboratories in the USA for the prediction of the LR of acid soils. For example, the AE buffer procedure (Adams and Evans, 1962) is used widely in the southeastern and mid-Atlantic regions of the USA, and the SMP buffer (Shoemaker et al., 1961) is widely used in the Midwest regions (Sims, 1996). The accuracy of these buffers has been widely studied (Follett and Follett, 1980; Tran and van Lierop, 1981; Alabi et al., 1986)....