Thermochemical Characterization of Biochar in Relation to Its Biodegradation in Soil.

Biochar technology is emerging as a potential tool for carbon sequestration in soil. One of the critical issues facing biochar research is the lack of analytical techniques that not only characterize biochar but also link the analytical properties to its environmental functionality. In this study we characterized the thermochemical properties of switchgrass (Panicum virgatum) biochars using a multi-element scanning thermal analysis (MESTA) technique. MESTA shows that switchgrass biochar produced at 400°C is comprised mainly of high-temperature (>425°C) thermally stable carbon components. To connect the thermochemical properties of biochar to its biodegradation in soil we conducted a soil incubation study using a Northern Florida forest soil. We were able to monitor the relative amount of biochar and soil organic matter (SOM) biodegradation by tracing the C-13 signature of the switchgrass biochar that is distinctive from the native soil organic carbon (SOC). Our C-13 isotopic analysis shows that in the mixed biochar-soil system the rate of SOC decomposition is unchanged relative to the control soil indicating that the addition of switchgrass biochar does not increase the rate of native SOM decomposition. The rate of biochar decomposition decreased substantially within the first 4 weeks and stabilized at a rate significantly lower than that of the native SOC. The biodegradable portion of the biochar seems to coincide with the less thermally stable component as observed with MESTA, however further investigation is needed to confirm this observation over a longer time scale. Overall, our initial results suggest that biochar technology may be an effective means to sequester carbon in soils.