DOES DIRT BURN? APPLICATION OF SCANNING CALORIMETRY TO ESTIMATE SOIL ORGANIC MATTER LOSS AFTER FIRES

The heating of soil during fires cause dehydration and organic matter loss. While water content in the soil can often be restored from precipitation, accumulation of organic matter is a process which takes hundreds of years. In this work differential thermal analysis and thermogravimetry techniques (DTA/TGA) were used to evaluate their potential for estimation of the extent of loss of organic matter from soil after burning. A Netzsch 409 instrument was used to perform controlled heating of soil samples in static air, simulating wildlfire conditions. It was found that decrease in total enthalpy of combustion per gram of sample can serve as integral characteristic of soil organic matter (SOM) loss. We found that the ratio of combustion enthalpy of soil organic matter to the α-β quartz transition enthalpy (ΔHcomb SOM)/(ΔHtrQz)) can be used to compare heated and unheated soil due to the ubiquitous presence of quartz in soil. This eliminates the need to weigh samples and accounts for differences in water content between heated and unheated soils, making possible in-situ applications of the proposed method. Proposed (ΔHcomb SOM)/(ΔHtrQz) ratio was used for evaluation of soil organic matter loss on two pile burn sites at UC Berkeley’s Blodgett Forest Research Station.