Direct titration for measurement of soil lime requirement and indirect lime requirement estimation by soil properties
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Previous studies about the titration curves of acid soils reported a linear relationship in the approximate range 4.5 < pH(H2O) < 6.5. It appears possible to establish the slope of the titration curve with 3 aliquots of Ca(OH)2 and then predict the lime requirements (LRs) to pH 6.5. The objective of this study was to evaluate the possibility of developing a direct titration procedure to measure the LRs of acid soils for routine use in soil testing laboratories. Seventeen soil samples with a wide range of clay and soil organic carbon contents were collected from five of the major land resource areas of Georgia. A 30 minute interval time between additions was found to be relatively short but adequate for the base added to react with the soil acids. A 3-day Ca(OH)2 incubation study revealed that the 3-points prediction from the direct titration with 30 minute interval time between additions estimated approximately 80% of the soil acidity. To simplify the procedure, one dosing of Ca(OH)2 was also tried to establish the titration slope in both water and 0.01 M CaCl2. Although the 2-point titration in water was subject to errors, the two point prediction of the LRs in 0.01 M CaCl2 estimated approximately 83% of the soil acidity. The CaCO3 incubation was found to overestimate the LRs. The LRs were highly correlated with initial pH and total carbon content.