Contributions of Soil Factors to Lime Requirement and Lime Requirement Tests

One hundred and twenty‐seven soils were examined for relationships existing between lime requirement and the pH‐dependent sites on organic matter and clay as well as “acidic Al.” The ranking of soil properties as predictors of the CaCO 3 ‐equilibrated lime requirement followed the order: pH‐dependent sites on organic matter > nonexchangeable acidic Al > exchangeable Al ≥ pH‐dependent sites on clay. This relationship is defined by the following equation which accounts for 89.5% of the observed variability of lime requirement as determined by neutralization with CaCO 3 to pH 6.0 in N KCl: LR (meq/100g) = 0.47 + 0.97 ΔpH(KCl) × % OM + 0.03 ΔpH(KCl) × % clay + 1.73 exchangeable Al + 0.53 non‐exchangeable acidic Al. A number of the more commonly used lime requirement tests were evaluated as predictors of the CaCO 3 ‐equilibrated lime requirement. Of these tests, the buffer methods were found to be superior to the ΔpH × % organic matter function and base unsaturation, which in turn were decidedly superior to percent base saturation for predicting soil lime requirement. The Shoemaker, McLean, and Pratt buffer was found to be somewhat better than the Woodruff buffer for measuring lime requirement, apparently because of its greater sensitivity to “acidic Al.”