Buffer pH acidity in relation to nature of soil acidity and expression of lime requirement

The purpose of this investigation was to evaluate the relationship between forms of soil acidity and certain buffer pH (BpH) methods for predicting the amount of lime required to obtain a given pH. Exchangeable acidity (ACe) in 114 acid soils from North Carolina was determined by 0.6N BaCl2 and residual acidity (ACr) by BaCl2‐TEA procedures. The buffer pH acidity (BpHAC) was calculated from the methods of Shoemaker, McLean and Pratt (SMP) and Adams‐Evans (AE). BpHAC was not significantly correlated with ACe, but was highly correlated with ACe plus ACr. Highest correlations resulted between BpHAC and the simultaneous consideration of ACe and ACr by regression analysis, where R2=0.900 and 0.795, for the SMP and AE methods, respectively. This indicated that both forms of acidity must be considered if a wide range of soils are involved. By using BpHAC and soil pH in a hyperbolic surface type equation, it was possible to calculate lime requirement (LR) for a desired soil pH by the AE method. Calculated and LR values stored in massive Cable forms were observed to be highly correlated (mean r2 = 0.994). The equation LR was also highly correlated (r2 = 0.947) with the results of the Yuan double buffer method. The hyperbolic surface equation was not applicable to the SMP method. However, useful regression equations between BpHAC and LR to obtain a desired soil pH were obtained (r2 = 0.994).