Biochar is black carbon produced from biomass sources [i.e., wood chips, plant residues, manure or other agricultural waste products] for the purpose of transferring the biomass carbon into a more stable form (carbon sequestration).
Black carbon is the name of the range of solid residual products resulting from the chemical and/or thermal conversion of any carbon containing material (e.g., fossil fuels and biomass) (Jones et al., 1997).
Biochar does not refer to a singular product with a given set of chemical and physical characteristics. Rather, biochar spans the spectrum of black carbon forms (Spokas, 2010) and it is chemically and physically unique as a function of the feedstock, creation process (pyrolysis unit), cooling, and storage conditions.
PURPOSE: The main purpose for the creation of biochar is for carbon sequestration. Biochar is speculated to have been used as a soil supplement thousands of years ago in the Amazon basin, where regions of fertile soil called "Terra Preta'" (dark earth) were created by indigenous people. Anthropologists hypothesize that inhabitants of the region produced biochar by practicing 'slash and char' management on vegetation to improve soil fertility and crop yields (Mann, 2005).
Biochar application to soil has been the assumed end use for the created biochar. Even though biochar can be used in other purposes as long as the biochar is not used for fuel or energy. The burning of biochar would not achieve the goal of carbon sequestration since this would allow the carbon to return to the atmospheric pool where it originated before being fixed in plants by photosynthesis.
HOW DOES THIS PRACTICE
Nevertheless, biochars are being manufactured to replicate the Terra Preta condition in worn-out or over-managed soils for restoring their crop productivity potentials. Unfortunately, there is not 'a-one-size-fits-all' biochar for soils (Novak and Busscher, 2011). The addition of biochar to soil has the potential of increasing soil carbon, soil nutrient content, and plant productivity. On the other hand, biochar additions have been observed to alter microbial populations and negatively impact plant growth. Thus, for a biochar to deliver a benefit, it is important to understand how biochar quality (physical and chemical properties) is influenced by the choice of feedstock and the pyrolysis conditions used in its manufacturer (Antal and Gr?nli, 2003; Lehmann and Joseph, 2009; Novak et al., 2009).
WHERE THIS PRACTICE APPLIES
EFFECTIVENESS: When examining the literature, there is large variability in the response of agronomic crop yield to biochar additions [negative to >2 fold improvements] (Spokas et al., 2012). From examining past studies, there is the suggestion that wood based biochar and biochar with higher nutrient contents (e.g., poultry and dairy manure biochar) have a higher likelihood of producing a positive yield improvement than other biochar source materials (Spokas et al., 2012). However, care must be taken when extrapolating results from past historical literature due to the skewed positive bias, since the publication of positive results is typically favored (M?ller and Jennions, 2001).
Antal M.J., Gr?nli M. (2003) The Art, Science, and Technology of Charcoal Production?. Industrial & Engineering Chemistry Research 42:1619-1640. DOI: 10.1021/ie0207919.
Denevan W.M. (1996) A Bluff Model of Riverine Settlement in Prehistoric Amazonia. Annals of the Association of American Geographers 86:654-681.
Glaser B., Lehmann J., Zech W. (2002) Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal - a review. Biol Fertility Soils 35:219-230. DOI: 10.1007/s00374-002-0466-4.
Jones T.P., Chaloner W.G., Kuhlbusch T.A.G. (1997) Proposed Biogeological and Chemical Based Terminology for Fire-Altered Plant Matter Springer-Verlag, Berlin.
Lehmann J., Joseph S. (2009) Biochar for environmental management science and technology, Earthscan, London ; Sterling, VA. pp. 1 online resource.
Liang C.S., Dang Z., Mao B.H., Huang W.L., Liu C.Q. (2006) Equilibrium sorption of phenanthrene by soil humic acids. Chemosphere 63:1961-1968. DOI: 10.1016/j.chemosphere.2005.09.05.
Mann C.C. (2005) 1491: New Revelations of the Americas Before Columbus Vintage and Anchor Books, New York, NY.
M?ller A.P., Jennions M.D. (2001) Testing and adjusting for publication bias. Trends Ecol Evol 16:580-586. DOI: 10.1016/s0169-5347(01)02235-2.
Novak J.M., Busscher W.J. (2011) Selection and use of designer biochars to improve characteristics of Southeastern USA Coastal Plain degraded soils Springer Science, New York, NY.
Novak J.M., Lima I., Xing B., Gaskin J.W., Steiner C., Das K.C., Ahmedna M., Rehrah D., Watts D.W., Busscher W.J., Schomberg H. (2009) Characterization of Designer Biochar Produced at Different Temperatures and Their Effects on a Loamy Sand. Annals of Environmental Science 3:195-206.
Spokas K.A. (2010) Review of the stability of biochar in soils: predictability of O:C molar ratios. Carbon Management 1:289-303. DOI: 10.4155/cmt.10.32.
Spokas K.A., Cantrell K.B., Novak J.M., Archer D.W., Ippolito J.A., Collins H.P., Boateng A.A., Lima I.M., Lamb M.C., McAloon A.J., Lentz R.D., Nichols K.A. (2011) Biochar: A synthesis of its agronomic impact beyond carbon sequestration. Journal of Envioronmental Quality:In press.