The double‐buffer (DB) feature of the recently‐published Yuan method was applied to the Shoemaker‐McLean‐Pratt (SMP) method at several buffer pH levels, shaking times, and soil/solution ratios. The results, based on regression analysis of buffer‐indicated vs. Ca(OH) 2 ‐titrated acidities, indicate that the widely used SMP single‐buffer (SB) method can be improved considerably by incorporation of DB, quick‐test, and mathematical‐adjustment features. However, the SMP‐SB method is still probably the most satisfactory compromise between simplicity of measurement and reasonable accuracy of results for soils of a wide range in lime requirement (LR). The SMP‐DB method with narrow soil/solution ratio and shorter shaking time gave excellent indication of soil LR when adjusted for incomplete reaction with the soil during the shorter “quick‐test” reaction time. This adaptation which looks very promising as an improved method (especially for use on soils of low LR where the SMP‐SB method is known to lack desired accuracy) is included as a recommended improvement of the SMP‐SB method.
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McLean et al. (1978) studied this question.