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Bio-Char Sequestration in Terrestrial Ecosystems - A Review


The application of bio-char (charcoal or biomass-derived black carbon
©) 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 degrees C common for pyrolysis).
Existing slash-and-burn 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 Pg C yr-1 . Biofuel
production using modern biomass can produce a bio-char by-product
through pyrolysis which results in 30.6 kg C 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
Pg C yr-1 if this demand for energy was met through pyrolysis, which
would exceed current emissions from fossil fuels (5.4 Pg C yr-1 ).
Bio-char soil management systems can deliver tradable C emissions
reduction, and C sequestered is easily accountable, and verifiable.