Evaluation of common lime requirement methods

Accurately estimating lime requirements (LR) of acidic soils has been a concern since liming praci tices began. The objectives of this study were to: (i) determine if the Shoemaker-McLean-Pratt (SMP) buffer is accurately predicting the LR of Kansas soils, (ii) calibrate the SMP and Mehlich buffers to accurately estimate the LR of Kansas soils to specific target pH values, and (iii) compare the effectiveness of 60-d incubations vs. field-observed lime response in determining LR. Kansas soils were use to evaluate the current LR according to the SMP buffer and calibrate SMP and Mehlich methods. Slope values (SMP LR vs. 60-d LR) < 1 and y intercepts > 0 indicated that the SMP either overestimated the LR at low values or underestimated the LR at relatively high LR values compared with 60-d incubations with CaCO3. Calibration of the Mehlich buffer to a target PH of 6.8 provided a better fit than the SMP buffer but the opposite was true at target pHs of 5.5 and 6.0. Titration with 0.022 MCa(OH)(2) resulted in a LR (target pH 6.8) 55% less than that measured by the 60-d incubation. Evaluation of the SMP buffer, Mehlich buffer, and Ca(OH)(2) titration method on 12 soils indicated that the LR estimated by the Mehlich buffer was not significantly different than the LR from the 60-d incubation. Comparison of the LR from 60-d incubations with field-observed lime response showed that the actual LR in the field was greater than that predicted by the 60-d incubation, which warrants further investigation.