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Solutions in the soil

Via Gary at Muck and Mystery, various reports on the conference on biochar/agrichar/terra preta nova/what-you-will that just ended down in Australia. If you’re not up to speed on this, the general idea is that people could help solve a great many problems by enriching soils with reduced carbon in charcoal-like form. This gets rid of the carbon for a long time (charcoal is very refractory) and improves the soil in various not yet fully understood ways. My colleague Emma wrote a lovely feature on the subject last year. There’s what seems to be a thriving discussion board on the subject at Hypography. And we have an article on the subject in Nature this week (see below).

The conference was opened by Tim “Weather Maker” Flannery, which is a pretty big name for a new field to manage to attract, I’d have thought. Here’s an overview of the conference by Kelpie Wilson of the Energy Bulletin. One interesting aspect is the idea of tying this issue to the issue of crappy stoves that drive indoor air pollution and waste a lot of energy.

Transect points, a blog by soil scientist Philip Small who, like Gary, is tracking this issue, has more reports in a round-up. As one of the people quoted says, the great thing about this field is that it opens up in so many different directions. Its also low tech enough to be of real use globally. The flip side of that is that different techniques will be needed in different places — this is unlikely to be a one-size-fits-all technology.

As I mentioned we’ve a look at the subject in Nature this week, too — a commentary (pdf) from one of the field’s main men, Johannes Lehmann of Cornell, which takes things forward nicely, I think. One of the advantages he points out for biochar sequestration — as opposed, say, to sequestration of carbon in aquifers — is that once the carbon is in the soil “it is difficult to imagine any incident or change in practise that would cause a sudden loss of stored carbon”. And he also argues that this sort of practise could be carried out at a serious scale:

I have calculated emissions reductions for three separate biochar approaches that can each sequester about 10% of the annual US fossil-fuel emissions (1.6 billion tonnes of carbon in 2005). First, pyrolysis of forest residues (assuming 3.5 tonnes biomass per hectare per year) from 200 million hectares of US forests that are used for timber production; second, pyrolysis of fast-growing vegetation (20 tonnes biomass per hectare per year) grown on 30 million hectares of idle US cropland for this purpose; third, pyrolysis of crop residues (5.5 tonnes biomass per hectare per year) for 120 million hectares of harvested US cropland. In each case, the biochar generated by pyrolysis is returned to the soil and not burned to offset fossil-fuel use. Even greater emissions reductions are possible if pyrolysis gases are captured for bioenergy production.

Similar calculations for carbon sequestration by photosynthesis suggest that converting all US cropland to Conservation Reserve Programs — in which farmers are paid to plant their land with native grasses — or to no-tillage would sequester 3.6% of US emissions per year during the first few decades after conversion; that is, just a third of what one of the above biochar approaches can theoretically achieve.

Those, Lehmann stresses, are rough calculations to highlight the potential, not realistic scenarios. But might it not make sense to start developing them into realistic scenarios? If you have inexpensive feedstock, this is a pretty intriguing technology.


  1. Report this comment

    bubba said:

    Interesting concept. But converting almost 2 billion tons of biomass into biochar sounds like no trivial task.

    Where does the, I assume, huge amounts of energy to generate the heat necessary for the pyrolysis come from?

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    Eli Rabett said:

    The indoor air pollution from crappy (in the literal sense in India) stoves is a tough one. The Indian government made a large push to replace the burning of dung with other fuels on more efficient burners, but this failed because the cost of cow crap was too low. Any attempt to meet this (and also replacing cooking stoves in China and most of SE Asia) will have to subsidize the fuel and the stoves.

    This is both an air pollution (brown cloud), a global climate and a major health issue, esp for women and children.

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    Hank Roberts said:

    Excellent. Thanks for covering this.

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    Erich J. Knight said:

    Hi All,

    Last months announcement by ConocoPhillips of a $22.5 M contract with Dr. Brown at Iowa State is significicant not only because of the magnitude of the grant, but also because of the company’s statement that it is interested in pursuing pyrolysis as a biomass conversion technology

    Erich J. Knight

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    Oliver said:

    Bubba: as I understand it, the pyrolysis is exothermic, which sort of sits with my childhood sense of how charcoal making works. The smouldering generates heat and gases, and the gases can be turned into fuel. If it’s not self perpetuating, I guess you could reuse some of the fuel gases for heating. Thus it is a less-efficient but not loss-making way of turning bimass into fuel, and the loss in efficiency is offset by the easily sequestered form in which the carbon ends up. There’s a useful diagram in a recent paper of Lehmann’s which is accepted for publication in “Frontiers in Ecology and the Environment” (pdf)

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    Oliver said:

    There’s an interesting post on the Lehmann paper and biochar economics over at Muck and Mystery. Key quote:

    People don’t need encouragement to use agrichar as a soil amendment, they just need information and an opportunity to get some.

    Right now those few who can get it in bulk quantities are paying serious money for it as a soil amendment. The lowest price I’ve heard of is $125 per ton in truckload quantities, about 20 tons or so at a time. Lehmann argues that:

    “biochar sequestration in conjunction with bioenergy from pyrolysis becomes economically attractive under one specific scenario, when the value of avoided carbon dioxide emissions reaches $37 per tonne.”

    The unsubsidized value of agrichar is higher than that, it just isn’t available. If it was available at $37 per ton it would sell like crazy. People pay more than that for agricultural lime, which is just crushed limestone rocks, mostly calcium carbonate, which is abundant and easily mined. Besides, among the chief beneficiaries of this technology are small growers in developing regions who make and use agrichar locally, perhaps as part of an integrated energy/fertilizer/soil amendment system.

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    Erich J. Knight said:

    For anyone wanting to research deeper;

    This Earth Science Forum thread on these soils contains further links, and has been viewed by 40,000 self-selected folks. ( I post everything I find on Amazon Dark Soils, ADS here):

    Here’s a Terra Preta web site at REPPCREST I’ve been drafted to administer .

    It has been immensely gratifying to see all the major players, both academic and private companies, join the mail list & discussion, Cornell folks, T. Beer of Kings Ford Charcoal (Clorox), Novozyne the M-Roots guys(fungus), chemical engineers, Dr. Danny Day of G. I. T. , Dr. Antal of U. of H., many Virginia Tech folks and many others who’s back round I don’t know have joined.

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    Michael W. I. Schmidt said:

    Biochar: not so easy to monitor

    The recently published commentary in Nature by J. Lehmann (Nature 447, 143-144) highlighted the potential of biochar to sequester organic carbon in soil. I fully agree with the main point of Lehmann’s comment. Adding biochar to soil can be a pragmatic and straightforward approach, probably much less prone to unpredictable side effects potentially associated with high-tech geoengineering approaches, as highlighted in the same issue (Nature 447, 132-136).

    The accounting of biochar in soil, however, is not as easy as it may seem. First, not all char is created equal. Depending on the conditions of formation (type of biomass, heating atmosphere, heat development and most importantly maximum temperature), chars with very different properties will form. Thus, biochars can span a whole spectrum of possible chemical and physical properties. As an example, char produced in a kiln have very different properties than industrially produced activated coal. Depending on the type of biochar, beneficial effects on soil properties and longevity of biochar in the soil (i.e. long-term carbon storage) will vary. Understanding underlying formation processes and qualities of biochar needs further research.

    Second, quantification of biochar in soil can be very tricky, as a recent ring trial of biochar materials showed ( A large number of laboratories worldwide quantified the biochar component in a set of reference materials including soil and sediment using several methods using several standard methods. One sobering result was that different measurements yielded different quantities of biochar, with no clear systematic offsets between methods. An important take home message for carbon accounting is that biochar quantifications obtained by different methods cannot be compared. Determining which method is most suitable to quantify soil biochar and standadize it would be a first crucial step. Thus, soil biochar is not so easy to monitor.

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    Ole Hendrickson said:

    Johannes Lehmann’s commentary, A handful of carbon examines the potential for biochar and associated bioenergy production via pyrolysis to withdraw significant amounts of carbon dioxide from the atmosphere. While applauding this aim, we urge biochar proponents to keep habitat conservation, traditional use, and sustainable use objectives in mind, and to strive for biodiversity-climate change synergies in applying this technology.

    Previous work by Lehmann and others traces the origins of the biochar concept to the rediscovery of the ancient practice of adding charcoal to soil to create “terra preta”, or Amazonian Dark Earths. While this practice has been abandoned, these soils retain their enhanced fertility and sequestered carbon.

    Pyrolysis of biomass, like all bioenergy technologies, creates both opportunities and challenges for sustainability. A recent UN report, Sustainable Bioenergy: A Framework for Decision Makers notes that bioenergy crops could have negative impacts if wild forests, grasslands, or traditional uses by marginalized indigenous groups are replaced. It also emphasizes that sufficient carbon residues and nutrients must remain in feedstock ecosystems to maintain soil and ecosystem health. Soil sequestration of biochar derived from pyrolysis would create an incentive to “close the loop” with regard to maintenance of soil carbon. However, proponents of this technology should recognize the offsetting incentive to reduce transport costs by applying biochar in large amounts over limited areas of the landscape. Guidance on rates of biochar application should take into account the desirability of optimizing fertility enhancement and the need to avoid impoverishment of the wider landscape.

    Ole Hendrickson, Dianne Watkins

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