Soil Lime Requirement By Direct Titration with Calcium Hydroxide
2004
Liu, Min | Kissel, D. E. | Vendrell, P. F. | Cabrera, M. L.
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)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-min 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.
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