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Bio-char sequestration in terrestrial ecosystems - a review

TitleBio-char sequestration in terrestrial ecosystems - a review
Publication TypeJournal Article
Year of Publication2006
AuthorsLehmann, J., Gaunt J., and Rondon M.
JournalMitigation and Adaptation Strategies for Global Change
Volume11
Start Page403
Abstract

The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is proposed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver immediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (<10–20% after 5–10 years), therefore yielding more stable soil C than burning or direct land application of biomass. This efficiency of C conversion of biomass to bio-char is highly dependent on the type of feedstock, but is not significantly affected by the pyrolysis temperature (within 350–500 ?C common for pyrolysis). Existing slash-andburn systems cause significant degradation of soil and release of greenhouse gases and opportunies may exist to enhance this system by conversion to slash-and-char systems. Our global analysis revealed that up to 12% of the total anthropogenic C emissions by land use change (0.21 Pg C) can be off-set annually in soil, if slash-and-burn is replaced by slash-and-char. Agricultural and forestry wastes such as forest residues, mill residues, field crop residues, or urban wastes add a conservatively estimated 0.16 PgCyr-1. Biofuel production using modern biomass can produce a bio-char by-product through pyrolysis which results in 30.6 kgC sequestration for each GJ of energy produced. Using published projections of the use of renewable fuels in the year 2100, bio-char sequestration could amount to 5.5–9.5 PgCyr-1 if this demand for energy was met through pyrolysis, which would exceed current emissions from fossil fuels (5.4 PgC yr-1). Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable.