Improved SMP buffer method for determining lime requirements of acid soils

Single buffer‐two pH and two‐buffer adaptations were compared as double buffer features of the SMP method using a group of 54 soils of wide range in lime requirement (LR). Data from both methods were highly correlated both with each other and with Ca(OH)2‐titrated acidity. Formulas for LR based on the schematics of similar triangles relating differences in measured pH vs corresponding acidities for the double buffer system were developed. A regression equation relating buffer‐indicated LR and Ca(OH)2 titrated acidity was used to adjust the quick‐test double buffer‐indicated values to levels nearer the actual ones. A recommended SMP double buffer procedure, and a formula for computing LR from soil‐buffer pH's measured by the double buffer, quick‐test method are presented.