Biochar Key Characteristics

We conduct numerous studies and laboratory tests on the Green Man Char biochar that we produce.

Wherever possible, our biochars are characterised using the full range of tests according to the International Biochar Initiative (IBI) guidelines via independent third-party laboratories. A summary of the key parameters are shown below.

Source: SGS, 2013, SGS 2014 

Biochar characterisation tests for typical Green Man Biochars show that all parameters are within the IBI guidelines. The biochars exhibit very low levels of toxins (PCDD/F, PAH, PCB) making them suitable for soils, agriculture, filtration and feed additives etc. The pH is slightly alkaline so biochar addition to soil will have a mild liming effect. The cation exchange capacity (CEC) of 21.6 for the biochar is typical of a loam. (CEC generally ranges from 1-8 for a sandy soil and approximately 29-40 for a clay (Frack 2007)). Fresh biochars generally have low CEC (Lehmann et al 2011) but are likely to increase over time as biochar ages in soil, due to oxidation of biochar surfaces (Cheng and Lehman 2009:Cheng, Lehman and Engelhard 2008:Liang et al 2006). The CEC of 21.6 indicates that the biochar may have a positive influence on sandy soils over time.
Perhaps the most important parameters to note from the test results are organic carbon and surface area. Organic carbon content in the biochar was greater than 60%, which classifies it as a class 1 biochar according to the IBI guidelines. Soil organic carbon benefits the soil biologically, chemically and physically and it is thought that incorporation of biochar with high organic carbon content into soils will have the same effect (NSW DPI 2012). The biochar also has a high surface area, putting it in the lower range for activated carbons (generally between 500m2/g and 2,000m2/g (Shackley et al 2010:Anderson et al 2013)). High surface areas are associated with an increase in micropore volumes which make biochar highly adsorbent and aid in water and nutrient retention. Micropores can also provide a home for beneficial soil microbes and protect them from predation (NSW DPI 2012:Lehmann and Joseph 2009).



Anderson, N., Jones, J.G., Page-Dumroese, D., McCollum, D., Baker, S., Loeffler, D., Chung, W., 2013, ‘A comparison of producer gas, biochar, and activated carbon from two distributed scale thermochemical conversion systems used to process  forest biomass’. Energies, 6(1), 164-183.

Cheng, C. and Lehmann, J., 2009, ‘Ageing of black carbon along a temperature gradient’, Chemosphere, 75(8): 1021-1027.

Cheng, C., Lehmann, J., Engelhard, M.H., 2008, ‘Natural oxidation of black carbon in soils: Changes in molecular form and surface charge along a climosequence. Geochimica et Cosmochimica Acta, 72(6).

DPI NSW, 2012, ‘Biochar in horticulture: Prospects for the use of biochar in Australian horticulture’, New South Wales Department of Primary Industries, Link:, Last accessed online: 9 April 2018

Frack, S., 2007, ‘How to Interpret a Soil-Test Report’, Turf diagnostics and design website, Link:, Last accessed online: 9 April 2018.

Lehmann, J. and Joseph, S., 2009, ‘Biochar for Environmental Management: Science and Technology’, Earthscan, London.

Lehmann, J., Rilig, M.C., Thies, J., Masiello, C.A., Hockaday, W.C., and Crowley, D., 2011, ‘Biochar effects on soil biota: A review’, Soil Biology & Biochemistry, vol.43, no.9, pp.1812-1836.

Liang, B., Lehmann, J., Solomon, D., Kinyangi, J., Grossman, J., O’Neill, B., Skjemstad, J.O., Thies, J., Luizao, F.J., Petersen, J., Neves, E.G., 2006, ‘Black carbon increases cation exchange capacity in soils’. Soil Science Society of America Journal, 70:1719-1730.

Shackley, S., Sohi, S., Brownsort, P., Carter, S., Cook, J., Cunningham, C., Masek, O., 2010, ‘An assessment of the benefits and issues associated with the application of biochar to soil’, Department for Environment, Food and Rural Affairs, UK Government, London.

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