Comparison of two calorimetric methods to determine the loss of organic matter in Galician soils (NW Spain) due to forest wildfires

Seven forest soils, Cambisols under pinus, located at Galicia (NW Spain) and affected by forest wildfires were collected to determine the loss of organic matter due to the effect of burning, using calorimetric methods. The enthalpy of combustion, ΔH, of the organic matter of the burnt and the corresponding unburnt soils was calculated from the thermograms obtained with a differential scanning calorimeter (DSC-7, Perkin-Elmer). From these data, the loss of organic matter during the fires was calculated. On the other hand, the organic matter content for each burnt and unburnt soil studied was determined by thermogravimetry (TG) and, in the same way, the loss of organic matter was obtained. High linear, significant correlations were found between the enthalpy of combustion of the soil organic matter (SOM) and the organic matter content measured by thermogravimetry. Consequently, comparison of the loss of organic matter obtained by both methods indicated that the quantitative results are similar. Both techniques allow to determine the degradation level of the soils affected by forest wildfires, taking the loss of organic matter during the fire as a degradation index.