Chemical, Physical, and Surface Characterization of Biochar
The term biochar is relatively new, although the practice of its addition to soil can be traced back thousands of years to terra preta (dark earths) in the Amazon, China, and Africa (Glaser et al. 2001; Sombroek 1966; Sombroek et al. 2003). Although the effects of these soils on plant growth and soil tilth are well documented, the characterization of the pyrolyzed biomass (biochar) believed to have been integral in the formation of these soils is somewhat limited and hampered by several issues. For example, there is no consensus on the definition of biochar based on production method (production temperature, highest treatment temperature (HTT), time, pressure, and presence or absence of oxygen). In addition, there is large variability in the physical and chemical structure of biochar due to it being part of the black carbon continuum and its production from a variety of organic biomass feedstocks (Lehmann and Joseph 2009; Schmidt et al. 2001); and also, due to the ambiguity in the classification of biochar, there are a variety of characterization protocols developed for other materials (e.g., coal, charcoal, compost, and soil) that have been modified for biochar analysis. These inconsistencies in analytical approaches have made comparisons between literature biochar data very challenging (Fidel 2012; Spokas et al. 2011).