Comparison of two enthalpic models for the thermodynamic characterization of the soil organic matter in beech and oak forests

The thermodynamic characterization of the soil organic matter could be achieved by different enthalpic models little explored for soil. This paper compares two of them for calculating the enthalpy change, the Gibbs energy change and the entropy change of the soil organic matter combustion reaction, by simultaneous differential scanning calorimetry and thermogravimetry. Soil samples were collected in beech and oak forests from different geographical areas, and at different depths to represent the L/F horizon and the mineral soil, at each sampling site. The thermodynamic state variables were calculated using two different enthalpic models, to examine how they differed in relation to different types of SOM and different forest ecosystems. Both models yielded thermodynamic variables, which although closely and significantly correlated, were statistically significantly different. All the thermodynamic variables depended on the different forest types and the different nature of the soil organic matter under study. Results allowed to discern which of the models applied better to the SOM combustion reaction designed.