Tropical forests account for between 20 and 25% of the world terrestrial carbon (C). Soils under tropical forest contain approximately the same amount of C as the lush vegetation above it. The current conversion of Amazonian forest to agricultural land makes disturbance of this C stock important to the global C balance and net greenhouse gas emissions. Changes in land use, particularly by clearing forests, reduce organic C by 20% to 50% in the upper soil layers. Furthermore, this reduction of soil organic matter (SOM) is causing soil degradation. Thus agriculture is not sustainable without nutrient inputs beyond 3 years of cultivation. The efficiency of conventional fertilizers (such as nitrogen (N)) is limited by a low nutrient retention capacity conjoined with strong tropical rains. On the other hand, large amounts of phosphate fertilizers are needed to overcome the soil’s high P-fixation capacity.
The existence of an anthropogenic and C-enriched dark soil in different parts of the world and especially in Amazonia (Amazonian Dark Earths (ADE) or Terra Preta de Índio) proves that the predominant Ferralsols and Acrisols can be transformed into fertile soils. The ADE’s fertility is most likely linked to an anthropogenic accumulation of phosphorus (P), calcium (Ca), and black C as charcoal. Charcoal persists in the environment over centuries and is responsible for the stability of the ADE’s SOM. Today and as assumed also in the past, those soils have been intensively cultivated by the native population. 
Charcoal production is a common activity of many settlers in the Amazon and is frequently used as an alternative land clearing method. The residues from charcoal production are abundant and used to some extent for soil amelioration purposes. However, many farmers fail to produce enough crops for a sufficient family income mainly due to the soils’ infertility and the family’s incapability to afford fertilizers.
Most C is lost if burned in a slash‑and‑burn scenario and lost to a high percentage (~50%) if used for charcoal production. Therefore, a C trade could provide an incentive to cease further deforestation; instead reforestation and recuperation of degraded land for fuel and food crops would gain Charcoal is influencing soil quality in manifold ways, most importantly by reducing available Al and reducing acidity. Furthermore, charcoal has the potential to reduce N leaching and adds potassium (K) to the soil. The effects of charcoal on soil biological, chemical and physical properties are complex, making it difficult to isolate single significant charcoal effects, but added up charcoal amendments caused a significant increase in crop production.
On a global scale, crop residue biomass represents a considerable problem as well as new challenges and opportunities. Before the green revolution and the introduction of mineral fertilizers, crop residues were a valued resource and mostly either returned to the soil as organic fertilizer or used for various other purposes (fuel, fodder, building material, others). Since then, the importance of these uses declined continuously, mainly because of the availability of cheap inorganic fertilizer and the increasing opportunity costs of organic fertilizer use. Simultaneously, increasing yields lead to ever greater quantities of residues available and intensification of land use resulted in less and less decomposition time between cropping seasons for managing them. Therefore, many farmers find it more expedient to burn crop residues than to incorporate them into the soil. The field burning is causing severe air pollution.
Currently most biomass conversion systems produce either charcoal (mainly in Japan as waste management) or energy through complete biomass gasification (Güssing GMBH, Austria, Choren, Germany. Incomplete gasification results in charcoal production. A system converting biomass into energy (hydrogen-rich gas) and producing charcoal as a by-product (Day et al. 2005) might offer an opportunity to address these problems. Charcoal (bio-char, agri-char) can be produced by incomplete combustion from any biomass and it is a byproduct of the pyrolysis-technology used for biofuel and ammonia production. This establishes the possible link of this technology to crop residues in general and the now widespread new interest in bioenergy. Energy from crop residues could lower fossil energy consumption and CO2-emissions, and become a completely new income source for farmers and rural regions. Linking energy production with charcoal production results in 30.6 kg C sequestration for each GJ of energy produced. The bio-char byproduct of this process could serve to recycle nutrients, improve soils and sequester carbon. A review by Lehmann et al. (2006) and the article “Black is the new green” (Marris 2006) emphasise the potential of bio-char on a global scale. A 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. 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 form 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. The described mixture of driving forces and technologies has the potential to use residual waste carbon-rich residues to reshape agriculture, balance carbon and address nutrient depletion.
Further Literature:
Day D, Evans R J, Lee J W and Reicosky D 2005 Economical CO2, SOx and NOx capture from fossil-fuel utilization with combined renewable hydrogen production and large-scale carbon sequestration. Energy 30, 2558-2579
Lehmann J, da Silva Jr J P, Rondon M, Cravo M d S, Greenwood J, Nehls T, Steiner C and Glaser B 2002 Slash and char - a feasible alternative for soil fertility management in the central Amazon? In 17th World Congress of Soil Science, Bangkok, Thailand, 14. - 21. 08. 2002, 2002. Ed T I U o S Sciences. pp 1-12.
Lehmann J, Gaunt J and Rondon M 2006 Bio-char sequestration in terrestrial ecosystems - a review. Mitigation and Adaptation Strategies for Global Change 11, 403-427
Mann C C 2002 The Real Dirt on Rainforest Fertility. Science 297, 920-923
Marris E 2006 Black is the new green. Nature 442, 624-626
Steiner C, Teixeira W G, Lehmann J and Zech W 2004a Microbial Response to Charcoal Amendments of Highly Weathered Soils and Amazonian Dark Earths in Central Amazonia - Preliminary Results. In Amazonian Dark Earths: Explorations in Space and Time. Eds B Glaser and W I Woods. pp 195-212. Springer Verlag, Heidelberg.
Steiner C, Teixeira W G and Zech W 2004b Slash and Char: An Alternative to Slash and Burn Practiced in the Amazon Basin. In Amazonian Dark Earths: Explorations in Space and Time. Eds B Glaser and W I Woods. pp 183-193. Springer Verlag, Heidelberg.
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is Australia's national science agency and one of the largest and most diverse research agencies in the world. As part of CSIRO’s National Flagship Program, under the Sustainable Agriculture Flagship (SAF), two national biochar research projects are being carried out by the biochar research team, led by Dr Evelyn Krull, and funded by the Australian Government through the Department of Agriculture, Fisheries and Forestry's Climate Change Research Program and the Grains Research & Development Corporation.
Jason Aramburu started working on biochar as a research scientist in 2005, through Princeton's Climate Mitigation Initiative and the Smithsonian Tropical Research Institute and in 2008 formed re:char. His initial intention was to develop fast and slow pyrolysis systems for farms in the US, however after he connected with an organization in Western Kenya, Aramburu saw a real need for biochar and a great potential for rapid scale-up. re:char now focuses its work to empower subsistence farmers in the developing world to enhance their crop yields and supplement their income through biochar production and use (which can also improve soils and sequester carbon). The organization has raised over $370,000 to date to support this work. Specific funders include the Hitachi Foundation, Echoing Green, the Dutch Postcode Lottery, and DOEN Foundation.
By Thayer Tomlinson
As the first IBI regional group in China, China-CAU introduced biochar experimental sites to other IBI members, such as the Biochar Yunnan Project of FAO. We had a useful discussion on biochar experiments in Africa with Ms. Christelle Braun from Ingenieur des Mines de Nancy, Paris, France. We are also in contact with Chinagreenzone, Sigma Innova LLC, and the Blue Moon Fund. We have also paid some attention to biochar demonstrations, for example, making simple biochar experiments together with the teachers of the Canadian International School of Beijing to show the children the effect of biochar on vegetables. Last week, we had a successful discussion with Mr. Chai Y. from Hebei School of Tourism, Chengde, and agreed to work together on producing biochar from civil wastes and to use biochar for tree planting.
An international symposium focusing on the environmental behavior and effects of biochar was held in Hangzhou, China, from October 9–11, 2010. Approximately 80 people attended this conference, coming from China, Japan, North America, New Zealand, Australia and Europe. IBI Board Vice Chairman Stephen Joseph and IBI Executive Director Debbie Reed both attended, and made presentations at the symposium.
All of the papers and posters were of a very high standard (see presentations list below for author submitted presentations). A very interesting talk was given by Professor Weixiang Wu of Zhejiang University on the discovery of a Chinese Terra Preta site. Professor Akira Shibata of Ritsumeikan University in Japan presented the results of a marketing campaign in Kyoto of “Cool” vegetables produced using bamboo biochar. Other talks focused on the changes in microbial population observed when biochar was applied to soil (Professor Janice Thies of Cornell University, and Mr Yu Luo of Rothamsted Research Center, UK). Dr Jim Amonette of the Pacific Northwest National Laboratory, USA, Dr Christoph Steiner of Austria, and Dr Saran Sohi of the University of Edinburgh, UK presented work on the potential of biochar to sequester carbon and improve soils. Professor Yunhan Xiao of the Power and Energy Research Center, Chinese Academy of Science, presented a novel design of a circulating fluid bed gasifier that could produce biochar as well as oils and syngas. Dr Stephen Joseph discussed how surfaces of biochars could be altered to make them more effective in promoting plant growth at lower application rates. Other presentations focused on the agronomic benefits and adsorption of toxic substances.