Acid-base buffering characteristics of non-calcareous soils: Correlation with physicochemical properties and surface complexation constants

The soil acid-base buffering capacity (BC) of twelve non-calcareous soil samples was determined by titration. The results of the correlation analysis show that the soil cation exchange capacity (CEC), organic matter (OM), and amorphous Al compounds (Ox-Al) were mainly responsible for the acid-base buffering reactions in the pH range from 3 to 8. A surface complexation model (SCM) was applied to further evaluate the acid-base buffering properties of the soils by assuming the buffering system to be a protonation-deprotonation process. The point of zero charge (pH(pzc)) calculated from the model matched the pH(pzc) values obtained from the continuous potentiometric titrations (CPTs), indicating that it is feasible to apply a SCM to non-calcareous soils. Compared with the pH, the pH(pzc). obtained from the SCM was better correlated with the acid-base properties of the soils, indicating that the pH(pzc), could be used to evaluate the main buffering processes. The surface site concentration (H-s) calculated from the SCM was significantly correlated with the soil CEC and OM (P < 0.01). Moreover, the H-s had a stronger correlation with the lime buffering capacity (LBC) than the multivariate relationships with the soil CEC and OM, suggesting that the SCM-calculated H-s can be used as an effective indicator of the lime requirement (LR). Our findings demonstrated that it is feasible to use the surface complexation constants to quantitatively evaluate the acid-base buffering process and predict the potential lime requirements for acidic soils.