The Biochar Debate
by Avril David
Land-use practices ” including forestry and agriculture ” are responsible for nearly 40% of all greenhouse gas emissions, which is why accounting for land use, land-use change, and forestry (LULUCF) is a key point of contention in climate-change talks leading up to December’s Conference of the Parties in Copenhagen, Denmark. Ecosystem Marketplace summarizes the latest findings.
17 July 2009 | Thousands of years ago, South Americans of the Amazon Basin began using charred animal waste and wood to make what the Portuguese called “terra preta” (black earth). The terra preta soil they created remains fertile for thousands of years without the use of any fertilizer, thereby increasing agricultural yields and further reducing harmful emissions caused by inefficient farming practices and/or the use of chemical fertilizers.
Today, we call this “biochar” ” a highly porous charcoal made from any form of organic waste ” ranging from forest to manure ” through a process known as pyrolysis, which is when biomass is burned at 400-550 degrees without oxygen.
Due to its high carbon content and porous nature, biochar can help soil retain water and nutrients (it releases them very slowly over time), protect soil microbes, and ultimately increase crop yields in addition to acting as natural carbon sink by sequestering CO2 and storing it in the soil. A World Watch report on Mitigating Climate Change through Food and Land Use estimates that if “biochar additions were applied on just 10 percent of the world’s cropland (160 million hectares), the method could store 29 billion tons of carbon dioxide equivalent, offsetting nearly all the emissions from fossil fuel burning”. According to the report, “initial analyses suggest that planting vegetation for biochar on idle and degraded lands could be quite economical and is thus a promising option for carbon offset payments”.
Biochar essentially stabilizes soil, thereby allowing it to absorb and store more carbon and enhance its role as a carbon sink.
Left undisturbed or protected, soil serves as a vital carbon sink for the Earth. This function often breaks down, however, when soil is disturbed. Then, it can quickly change from carbon sink to major source of CO2 emissions.
That’s why burying biochar in the soil can improve its carbon sequestration potential just as conservation tilling and grass-planting do.
In terms of added agricultural and environmental benefits, the International Biochar Initiative states that, “char-amended soils have shown 50 – 80 percent reductions in nitrous oxide emissions and reduced runoff of phosphorus into surface waters and leaching of nitrogen into groundwater. As a soil amendment, biochar significantly increases the efficiency of and reduces the need for traditional chemical fertilizers, while greatly enhancing crop yields.” In addition, the process used to make biochar (pyrolysis) has useful by-products such as gases that can be converted into electricty, gasoline or industrial chemicals.
Issues and Concerns
During recent climate negotiations in Bonn, Germany, participants of a side event on biochar noted uncertainty around biochar’s ability to sequester carbon, the possibility that biochar might stimulate soil microbes that turn soil carbon into carbon dioxide, and the potential albedo (or reflective) effect of laying charcoal near the soil surface.
Participants also noted that biochar could have multiple unintended social and eco-side effects, for instance, biochar production could lead to the development of biochar plantations that take the place of forests. Negative impacts of plantations can include the appropriation of land from local communities, the loss of rural job opportunities, the loss of biodiversity, and soil degradation.
Furthermore, as according to the Guardian’s George Monbiot, “In some cases charcoal in the soil improves plant growth, in others it suppresses it”¦in some cases charcoal stimulates bacterial growth, causing carbon emissions from soils to rise.” Not to mention the fact that the process of pyrolosis itself can also be a source of harmful emissions if the gases emitted are not properly managed.
While biochar certainly has potential as a climate change mitigation tool in theory, continued research is needed to ensure that it is in fact viable in various soil types and that the potential adverse effects do not outweigh its benefits.
To that end, biochar pilot projects are currently underway in multiple countries.
For instance, at the University of Tarapacá in Chile, researchers are conducting a comprehensive pilot program that utilizes a lab-based pyrolysis unit that produces biochar. The researchers plan to study both availability and applicability of local feedstocks for biochar and will evaluate which feedstocks are the most efficient in producing biochar. After the initial phase, the project will be scaled up to increasingly larger farms with larger units and feedstocks. While the University of Tarapaca’ s project will likely yield some important findings for the further development and use of biochar as a carbon sequestration and soil enhancement tool, other biochar projects are focusing on the substance’s ability to supplement existing conservation efforts.
In Cameroon, a project sponsored by Belgium’s Biochar Fund plans to use biochar as a “buffer” to protect pristine rainforests threatened by slash-and-burn farming and increasing populations. The biochar could enable farmers to produce greater yields on existing agricultural lands rather than using the rainforest as a source for new land.
Avril David conducts research on the terrestrial carbon sector for Ecosystem Marketplace’s Forest Carbon Portal. She may be reached at firstname.lastname@example.org.
A new growth industry?
Aug 27th 2009
Biochar could enrich soils and cut greenhouse gases as well
CHARCOAL has rather gone out of fashion. Before the industrial revolution, whole forests disappeared into the charcoal-burners”™ maw to provide the carbon that ironmakers need to reduce their ore to metal. Then, an English ironmaker called Abraham Darby discovered how to do the job with coke. From that point onward, the charcoal-burners”™ days were numbered. The rise of coal, from which coke is produced, began, and so did the modern rise of carbon dioxide in the atmosphere.
It is a sweet irony, therefore, that the latest fashion for dealing with global warming is to bring back charcoal. It has to be rebranded for modern consumers, of course, so it is now referred to as “œbiochar”. But there are those who think biochar may give humanity a new tool to attack the problem of global warming, by providing a convenient way of extracting CO2 from the atmosphere, burying it and improving the quality of the soil on the way.
Many of those people got together recently at the University of Colorado, to discuss the matter at the North American Biochar Conference. They looked at various ways of making biochar, the virtues of different raw materials and how big the benefits really would be.
The first inkling that putting charcoal in the ground might improve soil quality came over a century ago, when an explorer named Herbert Smith noticed that there were patches of unusually rich soils in the Amazon rainforest in Brazil. Most of the forest”™s soil is heavily weathered and of poor quality. But the so-called “œterra preta”, or “œblack earth”, is much more fertile.
This soil is found at the sites of ancient settlements, but it does not appear to be an accidental consequence of settlement. Rather, it looks as though the remains of burned plants have been mixed into it deliberately. And recently, some modern farmers””inspired by Wim Sombroek, a Dutch soil researcher who died in 2003″”have begun to do likewise.
The results are impressive. According to Julie Major, of the International Biochar Initiative, a lobby group based in Maine, infusing savannah in Colombia with biochar made from corn stover (the waste left over when maize is harvested) caused crops there to tower over their char-less peers. Christoph Steiner, of the University of Georgia, reported that biochar produced from chicken litter could do the same in the sandy soil of Tifton in that state. And David Laird, of America”™s Department of Agriculture, showed that biochar even helped the rich soil of America”™s Midwest by reducing the leaching from it of a number of nutrients, including nitrate, phosphate and potassium.
All of which is interesting. But it is the idea of using biochar to remove carbon dioxide from the atmosphere on a semi-permanent basis that has caused people outside the field of agriculture to take notice of the stuff. Sombroek wrote about the possibility in 1992, but only now is it being taken seriously.
In the natural carbon cycle, plants absorb CO2 as they grow. When they die and decompose, this returns to the atmosphere. If, however, they are subjected instead to pyrolysis””a process of controlled burning in a low-oxygen atmosphere””the result is charcoal, a substance that is mostly elemental carbon. Although life is, in essence, a complicated form of carbon chemistry, living creatures cannot process carbon in its elemental form. Charcoal, therefore, does not decay very fast. Bury it in the soil, and it will stay there. Some of the terra preta is thousands of years old.
Moreover, soil containing biochar releases less methane and less nitrous oxide than its untreated counterparts, probably because the charcoal acts as a catalyst for the destruction of these gases. Since both of these chemicals are more potent greenhouse gases than carbon dioxide, this effect, too, should help combat global warming. And the process of making biochar also creates beneficial by-products. These include heat from the partial combustion, a gaseous mixture called syngas that can be burned as fuel, and a heavy oil.
Taking all these things together””the burial of the charcoal and the substitution for fossil fuels of the heat, gas and oil produced by its manufacture””Johannes Lehmann of Cornell University and Jim Amonette of the Pacific Northwest National Laboratory in Washington state suggest that a reduction of between one and two gigatonnes of carbon-emission a year might be achievable. That compares with current annual emissions of some 9.7 gigatonnes. But the truth is that the computer modelling involved in making these estimates is a work in progress, as researchers do not know a lot of pertinent things accurately enough: how much material is available for conversion, for example; how much land is available for biochar to be ploughed into; how much char that land could handle. Dr Amonette”™s estimate is that 50 tonnes per hectare””a figure larger than that used in most of the experiments conducted so far””could go into soils without harming productivity.
Some soils could take even more.
The claims for biochar are not supported by all, however. Biofuels Watch, a British lobby group, worries that a craze for the stuff could see virgin land tilled specifically to grow crops such as switchgrass, whose only purpose was to be pyrolised and buried. That tillage would release carbon dioxide and methane. But the alternative, growing those crops on existing farmland, would encourage the clearance of more land to grow the food crops that had been displaced. Indeed, Kelli Roberts, another researcher at Cornell, told the meeting that, taking all factors into account, growing switchgrass for biochar may do more harm than good. Corn stover, garden waste such as grass clippings, and offcuts from forestry and timber production are better bets, she reckons.
And if sequestration by biochar is deemed sensible, there remains the question of how, exactly, to go about it. Making the charcoal is not a problem. Pyrolising stoves are easy to construct and available models range from the portable to industrial-scale machines costing tens of thousands of dollars. Moreover, Jock Gill of Pellet Futures, a company based in Vermont that makes grass and wood pellets for use as fuel, told the meeting that a teenage protégé of his has invented a stove that can be fed continuously, rather than processing batches of raw material. If that proves successful, it would be a breakthrough of the sort that has enabled other industries (not least ironmaking) to take off in the past.
The benefits of improving their soil should be enough to persuade some farmers to make and bury biochar. Others, though, may need more incentives””probably in the form of carbon “œoffsets” that compensate for emissions elsewhere. In the rich world, Europe already caps carbon-dioxide emissions, and trades permission to emit the gas. America may soon do so too. CO2-emitting industries could pay farmers to buy stoves to char and sequester farm waste. That would mean working out how much of what kind of biochar counts as a tonne of CO2sequestered, and would also need a lot of policing.
A charcoal sketch
If the details can be nailed down, though, farmers in poor countries could get in on the act too, through the Clean Development Mechanism, a United Nations”™ programme that allows rich-world emitters to buy offsets in the poor world. And Lakshman Guruswamy, of the University of Colorado, told the meeting of another advantage if poor-world farmers can be brought in. Many of them burn wood, waste and dung indoors for heating and cooking. The soot released into the air as a consequence is also a climate-changer because, being dark, it absorbs heat. Much worse, though, about 1.6m people are killed each year by inhaling it. But pyrolytic stoves produce almost no soot””the carbon is all locked into the biochar. Worldstove, a firm based in Italy, seeks to provide small and simple pyrolising stoves to poor countries.
It is all, then, an intriguing idea. It certainly will not solve the carbon-dioxide problem, but it could be what Robert Socolow of Princeton University refers to as a wedge””one of a series of slices that, added together, do solve it. And there would be a nice historical justice in the substance that was displaced by coal playing an
important role in cleaning up the mess that coal has left behind.