"The conversion of degradable carbon to carbon that is orders of magnitude more stable than its feedstock carbon is what makes biochar a particularly appealing climate change mitigation technology."
By Stefan Jirka
The man heaves another shovelful of dirt out of the 2-meter deep pit. The sun blazes overhead, an eerie stillness blanketing the midday jungle. The two dozen people gathered around peer eagerly over the edge. Along the vertical face of the soil pit, pottery shards intermingled with blackened bits of charred material are clearly visible. The crowd murmurs a small gasp as the man passes up a handful of soil. Someone swats at a mosquito buzzing incessantly as a machete is unsheathed and used to separate a bit of pottery from the blackish clumps in the dirt.
Black Earth of The Amazon
This may sound like a scene from the latest Indiana Jones movie, but in fact, it was a recent excursion of researchers, environmentalists, and journalists to investigate the phenomenon known as terra preta do indio—Portuguese for “black earth of the Indian”—in the Brazilian Amazon.
Terra preta soils, found across vast areas of the Amazon Basin, are charcoal-enhanced soils associated with pottery shards, bones, and other signs of human habitation, and are thousands of years old. Compared to the acidic, nutrient-poor, red clay soils from which they’re derived, terra preta are dark (from the carbonized remains of plant and animal material) and, crucially, highly fertile. They can contain as much as 70% more organic carbon than the surrounding soils.
Archaeologists have known about these anthropogenic soils for decades but only in recent years have soil scientists and others begun to dig deeper. In doing so they’ve opened exploration of a new field of research around the sustainability benefits of “biochar”—defined by the International Biochar Initiative (IBI) as a solid material obtained from the carbonization of biomass that may be added to soils with the intention to improve soil functions. IBI is the leading global non-profit organization supporting research and commercialization for sustainable biochar production and use.
The questions researchers are finding answers to include:
- Can the process of enhancing soil fertility via the addition of biochar be re-created?
- What are the specific properties and mechanisms that biochar confers to the native soil matrix?
- Can biochar be used to significantly draw down atmospheric greenhouse gas (GHG) concentrations?
Biochar for Climate Change Mitigation
Biochar is obtained when biomass feedstocks such as wood- or crop-residues are heated in low- or no-oxygen conditions. In a thermochemical conversion process called pyrolysis, the cellulose, lignin, and other organic carbon compounds present in raw feedstock are physically and chemically changed to highly stable forms of carbon resistant to degradation. In biochar, organic carbon—typically consumed voraciously by soil microbes—is thereby locked away from rapid degradation. This explains in large part the persistence of charred materials—and fertility—in ancient terra preta soils.
Debbie Reed, IBI’s Policy Director explains:
The conversion of degradable carbon to carbon that is orders of magnitude more stable than its feedstock carbon is what makes biochar a particularly appealing climate change mitigation technology. The ability to turn waste biomass that will otherwise degrade into a stable, beneficial soil amendment with incredible co-benefits is compelling in its own right, but also why so many researchers and governments the world over are further investigating its potential to create large carbon sinks while helping to impart multiple benefits to the global soil resource.
Biochar is produced from biomass residues that would otherwise have released their carbon into the atmosphere via the carbon cycle. For example, residues such as straw or corn stalks are often burnt or left in fields to rot. Instead these residues are pyrolyzed into biochar and then placed in the soil where the stable carbon can remain for thousands of years or more. In this way, biochar is a “carbon negative” GHG mitigation strategy; it pulls carbon out of the biogeochemical carbon cycle and places it into long-term soil carbon pools.
It is important to note here that whereas dedicated “biochar crops” could be used to make biochar, IBI and other serious proponents of biochar strictly advocate the use of biomass residues deemed to be waste, i.e., residues from existing land management activities that have little or no economic value and that present waste management challenges. Numerous analyses have demonstrated that many gigatonnes of such residues are produced worldwide annually.
The American Carbon Registry’s Methodology for Biochar Projects
Recognizing biochar’s potential as a climate change mitigation strategy, a team of organizations including The Climate Trust, The Prasino Group, IBI and Carbon Consulting came together to develop a methodology to quantify biochar’s GHG sequestration potential with the intent to both enhance the economics of biochar projects and further increase knowledge and understanding of the climate mitigation potential of biochar. The result is the recently drafted Methodology for Biochar Projects, currently posted for public comment at the American Carbon Registry—a leading voluntary carbon offset registry that is a division of Winrock International.
The methodology quantifies two components of biochar’s carbon offsetting potential: 1) enhanced soil carbon sequestration via the addition of biochar to soil, and 2) avoided GHG emissions from decomposition or combustion of feedstock biomass.
In order to measure soil carbon sequestration, it was necessary to estimate the longevity (stability) of the stable carbon component of biochar. To this end, an expert panel of leading biochar researchers developed a Biochar Carbon Stability Test Method designed to quantify “BC+100”—defined as the stable carbon in biochar expected to remain 100 years after its addition to soil—using data from published laboratory and field experiments and a review of sophisticated analytical techniques.
For the avoided emissions component of the methodology, the baseline scenario assumes biochar feedstocks will be burned or decompose, thereby releasing CO2 and/or CH4. The project scenario entails the pyrolytic conversion of that feedstock into biochar and subsequent addition to the soil, thereby avoiding combustion or decomposition.
One Wedge of the Climate Change Mitigation Pie
Revenues from participation in carbon markets can enhance biochar project development and hasten scale-up of technology and production. Biochar could then join other GHG reduction measures as an important wedge of the climate change mitigation pie.
Parties interested to review and submit feedback on the Methodology for Biochar Projects are invited to do so until November 8, 2013 here.
More information on biochar is available at the IBI website.
About the Author:
Stefan Jirka received his B.S. and M.S. degrees in biology and environmental science from Cornell University. While at Cornell he conducted field research on tropical forest dynamics in the Brazilian Amazon and was introduced to biochar in the form of terra preta do indio soils. Prior to joining IBI, he worked for six years at the grant making foundation Blue Moon Fund leading program development in the Tropical Americas and Chesapeake-Appalachia regions. His work there focused on sustainable agriculture, biodiversity conservation and livelihood creation. Stefan is fluent in Spanish and Portuguese and has traveled and worked extensively in Central and South America and Europe.