Tuesday, 7 October 2008: 3:15 PM
George R. Brown Convention Center, 360C
High concentrations of two greenhouse gases, nitrous oxide (N2O) and carbon dioxide (CO2), in the stratospheric ozone layer are believed to be responsible for global climate change. We hypothesize that conversion of biomass to liquid fuel stocks by pyrolysis and returning the biochar co-product to the soil is a mean of reducing net greenhouse gas emissions. We studied the effect of biochar additions to the soil on changes in total soil organic C and emissions of N2O and CO2 during a one-year soil column incubation study. Four rates of biochar 0, 5, 10, and 20g kg-1 soil were applied to Clarion fine-loamy soils. Recoveries of biochar C ranged from 98 to 109% indicating that little or no biochar C was mineralized during incubation. Biochar additions reduced N2O emissions (measured once near the end of the one-year incubation) but consistently increased CO2 emissions (measured 13 times during the one-year incubation) relative to controls receiving no biochar additions. The reduced N2O emissions were correlated with reductions in soil bulk density, suggesting that enhanced aeration of the soil may have contributed to the reductions in N2O emissions. Increased CO2 emissions with biochar additions apparently due to enhanced mineralization of biogenic soil organic matter may partially offset the C sequestered by addition of the biochar. However, increased respiration also implies enhanced microbial activity and nutrient cycling, which could increase plant biomass production and hence the biological fixation of CO2-C through photosynthesis. Biochar may also influence the rate at which organic C from plant and animal residues is transformed into stabilized humic substances. For the studied system, we conclude that biochar additions sequestered large amounts of highly stable C, reduce N2O emissions, and increased CO2 emissions. Understanding the net effect of biochar additions on levels biogenic soil organic C, however, will require additional study.