Tapestry Press
Biochar
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Tapestry Press
Biochar
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Is Biochar
Valuable for Carbon Sequestration? Like all mineral elements, carbon is neither created nor destroyed, it cycles. An atom of carbon in atmospheric carbon dioxide, for example, by the processes of photosynthesis and polymerization can become carbon in cellulose in an oak leaf. That same atom from the oak leaf as it decomposes might be incorporated in humus in soil. All carbon slowly circulates between five global pools. In this example, the carbon moves from the atmospheric pool to the biota pool to the soil pool. The table below describes the five carbon pools. Pg abbreviates Petagrams which equal 1015g or one billion metric tons.
Each of these pools is dynamic; it is changing. Constantly, by certain processes carbon is added to each one and by other processes, it is removed. When additions exceed removals, that pool expands. Photosynthesis and other chemical reactions build carbon dioxide into structural plant molecules. As long as a tree lives, it’s biomass [living matter] traps carbon (in the biota pool). Huge old trees store much more than young saplings. When a tree burns or when it dies and decays, that releases the CO2 back to the atmospheric pool. When a tree is cut, sawdust decays rather quickly. Lumber made from the tree continues to store carbon until it decays.
Global Warming Combustion of fossil fuels moves carbon from the geologic pool to the atmospheric pool producing our most abundant greenhouse gas, carbon dioxide (CO2). Greenhouse gases accumulating in the atmosphere retain more heat near the Earth. As CO2 continues to accumulate, the atmospheric carbon pool expands producing more warming. Global warming threatens the survival of our civilization. To limit global warming we must reduce CO2 output and divert carbon into another pool. Trapping or storing carbon is termed carbon sequestration. The soil pool offers the most potential for possible carbon sequestration. (To learn more about processes in air, in soil and global warming consult the second edition of Environmental Science Workbook, published in 2008 and now available from Carolina Biological Supply online. Exercise 7 describes air; exercise 9 focuses on soil; exercise 29 introduces global warming. In exercise 29 students with access to a computer can estimate their personal carbon footprint, the amount of carbon dioxide their activity adds to the atmospheric pool each year.)
Biochar Ancient Brazilian natives converted crop wastes to biochar, literally biological charcoal. As North American pioneers made charcoal from tree trunks, stumps and roots, Amazonian natives smoldered saplings, crop stalks and vines from clearing gardens to make biochar. Smoldering is burning with little oxygen, typically in a trench or pit covered with soil or clay except for a smoke hole. Amazonian natives dug biochar into the soil of their vegetable plots. This produced terra preta or black earth. Soil there without biochar contains .5% carbon. Soil with it contains 9% carbon. Interestingly, it does not oxidize. It persists. Remarkably, biochar in Amazonian forest soil has been documented to remain for up to several thousand years! Long term sequestration benefits humanity. Terra preta holds mineral ions, especially cations (Ca++, Mg++ , K+ ) making them available for plant use. It also holds phosphate, an anion. These enrich the soil. Recent experiments prove that the presence of biochar increases bean production by 46%. Because biochar acts as a fertilizer, it provides a second major benefit to humanity. . Pyrolysis To produce biochar the modern technique is termed slow pyrolysis (literally "fire splitting"). Pyrolysis of plant or animal matter generates three products: biochar, biofuel and syngas. The biofuel provides a substitute for diesel fuel. The synthetic gas or syngas can be used to generate electricity. Only modern units recover the biofuel and syngas. When burned at about 500oC, the optimal temperature, about 50% of the biomass becomes biochar. Produced at this temperature, it has enormous surface area, a high capacity to hold cations and a high pH, all desirable characteristics of fertilizers. By its presence biochar reduces anaerobic soil conditions. This can decrease the emissions of two potent greenhouse gases, methane (CH4) and nitrous oxide (NOx). These retain many times (23x and 296x) the heat that carbon dioxide retains in the atmosphere. Biomass such as bagasse (sugar cane stalks after the juice has been squeezed out) or switchgrass now converted to ethanol could more efficiently be made into biochar. The conversion of sewage waste to biochar has been proposed.. Given that about 8% of atmospheric carbon dioxide is absorbed by plants every year, converting a fraction of this to biochar will have a dramatic impact. This has the potential to sequester Gigatonnes [109 metric tons (2200 lbs)] of carbon every year. (Note that one Gigatonne equals one Petagram.)
Is Biochar Valuable for Carbon Sequestration? Australian Professor Tim Flannery, author of an early, notable book on global warming, The Weather Makers, says, "Biochar may represent the single most important initiative for humanity’s environmental future. The biochar approach provides a uniquely powerful solution, for it allows us to address food security, the fuel crisis, and the climate problem, all in an immensely practical manner...." "Biochar represents a cornerstone of our future global sustainability. With the appropriate political and technical recognition, promotion and adoption, it will change our world forever, and very much for the better."
Sources Flannery, Tim. August 2008. An open letter on Biochar from Professor Tim Flannery. http://www/biochar-international.org/timflannery.html.Lehmann, Johannes. 2007. Bio-energy in the black. Front. Ecol. Environ. 5(7): 381-387. or www.frontiersinecology.org.Lehmann, Johannes, John Gaunt & Marco Rondon. 2006. Bio-char Sequestration in Terrestrial Ecosystems-a Review. Mitigation and Adaptation Strategies for Global Change, 11:403-427.
(c) 2009 Carolina Biological Supply Company. Used with permission Back to Tapestry Press
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