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 (pHpzc) calculated from the model matched the pHpzc 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 pHpzc obtained from the SCM was better correlated with the acid-base properties of the soils, indicating that the pHpzc could be used to evaluate the main buffering processes. The surface site concentration (Hs) calculated from the SCM was significantly correlated with the soil CEC and OM (P < 0.01). Moreover, the Hs 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 Hs 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.