Biochar - Menace or Redeemer?
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Sometimes you have to hand it to capitalism. It’s sheer magic, the way the system takes promising concepts, steeps them in the transformative power of the market – and turns them into howling social and environmental disasters.
Take biofuels, for example. With fossil fuels warming the planet, why not, indeed, take advantage of the fact that plants use carbon dioxide from the atmosphere to produce sugars and oils that can be turned into substitutes for petrol and diesel?
We all know where that finished up. A big chunk of the US corn crop was distilled into grain ethanol. Corn prices soared on the extra demand, raising costs for a broad range of food production. Anyone unable to pay went hungry. When US drivers filled up with bio-ethanol, they were in effect burning the tortillas of the Mexican poor.
But was it the technology that was the problem? Or the system?
Whatever the case, when activists of the international group Biofuel Watch noted the attention being paid to another attractive concept – sequestering carbon by turning plant matter into biochar (finely divided charcoal), and incorporating it in agricultural soils – their suspicions were raised immediately. A research paper was prepared, critically examining biochar and the promises made for it. An international appeal was circulated, entitled “‘Biochar’, a new big threat to people, land and ecosystems,” and opposing calls to include biochar in the international carbon trading scheme, the Clean Development Mechanism (CDM).
So far, the appeal has been signed by about 120 environmental organisations around the world. Among their number is Friends of the Earth Australia.
To be sure, the biochar skeptics have a certain cause for suspicion. Enthusiasts for biochar now include Malcom Turnbull and the Australian federal opposition. Considering Turnbull’s other enthusiasms – “clean coal”, for one – his support should set alarm bells ringing immediately.
Added to which, some of the proposals made for biochar sequestration are downright barmy. British writer George Monbiot records New Zealand environmentalist Peter Read as calling for new world-wide biomass plantations of trees and sugarcane covering 1.4 billion hectares, with the plant matter to be turned into biochar and ploughed into soils. Trouble is, the world’s total cropland only comes to 1.36 billion hectares.
Furthermore, and as Biofuel Watch’s appeal rightly points out, the effects in the developing world of including biochar in the CDM trading scheme would be disastrous.
An assured world market for biochar would turn the substance into an internationally- traded commodity. Biochar is non-perishable and easily transported; give it a further boost by allotting it carbon credits, and producing it for export would in all likelihood yield better profits in developing-world settings than growing food crops.
In ideal circumstances, tree crops for biochar would be grown on degraded or marginal land used previously for sparse grazing. But inevitably under market conditions, the tree plantations would spread to prime agricultural land, enjoying first call on resources of water and fertiliser.
Generally speaking, land is better off under trees than under goats, but commercial tree plantations are not altogether benign. Monbiot sums up some of the dangers:
“Aside from trashing biodiversity, tree plantations have dried up river catchments, caused soil erosion when the land is ploughed for planting…, exhausted nutrients and required so many pesticides that in some places the run-off has poisoned marine fisheries.”
Dodgy Science
So should Australian environmental organisations sign up to Biofuel Watch’s appeal? As things stand, no. The document’s science is dodgy, and many of its arguments irrelevant or overblown. That may seem like a harsh judgment, but it is borne out if we look in more detail at some of the appeal’s assertions:
“It is not yet known whether charcoal in soil represents a carbon sink at all….”
In what is a relatively new field of research, many unanswered questions remain. This, however, is not one of them. In a set of notes posted in March one of Australia’s prime authorities on biochar, CSIRO Land and Water scientist Evelyn Krull, points out that biochar “has a chemical structure that makes it very difficult to break down by physical, biological and chemical processes.”
“We know,” Krull continues, “that biochar is stable over the timescales of any [carbon] abatement scheme (100 years).”
Not all biochars are the same – their individual properties depend on the feedstock and on the temperature and duration of the pyrolysis process through which they are made. But charcoal can remain intact in nature for more than 10,000 years – it provides, after all, the basis for carbon dating. Highly fertile, carbon-rich terra preta (dark earth) soils in the Amazon region of South America indicate very strongly that when incorporated into agricultural land, biochar can persist for thousands of years. The terra preta soils are believed to have been created deliberately by ancient peoples who produced charcoal and dug it into the ground along with food scraps and other organic matter.
“There is no consistent evidence that charcoal can be relied upon to make soil more fertile….”
If this were the case, the Amazonian peoples would hardly have bothered. True, the evidence is not 100 per cent consistent. But will, say, 90 per cent do?
Trials of biochar in relatively carbon-rich soils in Sweden found that soil fertility actually declined, apparently because the boost to soil microbial activity provided by the biochar speeded the decomposition of existing soil organic matter. But in leached tropical soils, and also in the ancient, low-fertility soils characteristic of Australia, the experience has been diametrically different. Evelyn Krull again:
“We know that biochar application can have positive results, particularly in sandy and infertile soils.
“Due to its chemical and physical nature (e.g. high degree of porosity and absorptive capacity), biochar has been shown to enhance soil fertility, resulting in increased productivity and in turn a build-up of organic matter in soil.”
“Combinations of charcoal with fossil fuel-based fertilisers made from scrubbing coal power plant flue gases… will help to perpetuate fossil fuel burning as well as emissions of nitrous oxide, a powerful greenhouse gas.”
One suspects energy companies have weightier reasons for continuing to burn coal than supplying biochar firms with extracts of flue gases. Meanwhile, there is good evidence that biochar, by improving soil structure and retention of plant nutrients, can allow crops to flourish with markedly lower applications of artificial fertilisers.
Nitrous oxide, which volume-for-volume has hundreds of times the warming effect of carbon dioxide, enters the atmosphere largely through the breakdown of nitrogen fertilisers. Not only does biochar allow the use of these fertilisers to be cut, but as NSW Department of Primary Industries scientist Annette Cowie observes, the reduction in nitrogen dioxide exceeds what would be expected from lower fertiliser use. “It seems that when you apply the biochar, that nitrogen transformation process is inhibited,” the G-Online site reported Cowie as saying in March. Studies have found that in some soils, nitrous oxide emissions decline by as much as 80 per cent.
“The process for making charcoal and energy (pyrolysis) can result in dangerous soil and air pollution.”
In principle, the slow pyrolysis process used to create biochar is exceptionally clean. Plant matter is heated in an enclosed, oxygen-poor environment at about 500º Celsius. Volatile carbon compounds are driven off, some of them to be condensed into a useful bio-oil. The remaining gases are burnt to provide heat to sustain the process, and (in many cases) to generate carbon-neutral electricity. The exhaust gases that result from this combustion consist almost entirely of water vapour and carbon dioxide; small quantities of oxides of nitrogen that are created can be scrubbed from the exhaust stream using the biochar itself. The solid residues from the pyrolysis process are inoffensive – apart from the biochar, silica ash, plus nutrient elements including potassium and phosphorus.
That’s provided the initial feedstock consists of plant matter, and not of wastes containing toxins able to survive pyrolysis. But the need to exclude these wastes is an argument for appropriate regulation and good management, not for rejecting the process out of hand.
No to “Cap and Trade”
Where people presented with Biofuel Watch’s appeal spot its rich content of scientific “howlers”, they will not be encouraged to support the document’s valid and necessary criticisms of the CDM and of other “cap and trade” emissions abatement schemes. And where people are not so scientifically astute, they will be needlessly prejudiced against one of the more useful technologies available for the fight against global warming.
This begs the question: if organisations like Friends of the Earth are indignant at the effects of market-based abatement schemes (and they should be), why don’t they circulate their own appeal explaining why?
Furthermore, why don’t they take a leading role in the campaign to stop the Rudd-Wong variant of “cap and trade”, the “Carbon Polluters Reward Scam”?
Copyright:Issued by: Critical Times
Author: Renfrey Clarke
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Issue date: April 7, 2009
Link to Article: Origin of text
Researchers from U. of Wisconsin–Green Bay have published what must be the most extensive evaluation of microbial response to charcoal application in soils from managed temperate systems.
Insights abound (Text as
Download, 800 kB)
Lacking are any insight into the proportion of the effect to allocate to the charcoal-C relative to the reactive effects of the ash component.
Our understanding of the mechanisms by which charcoal influences soil processes is limited primarily by a lack of information on how charcoal affects microbial biomass and activity. ... there is no currently accepted range of effective application levels, which is not surprising given that the effects of charcoal application will probably depend on how the microbial community interacts with both soil and charcoal properties.
One has to admire the clean lines, simple controls, and rugged build of the studied conditions. Charcoal was custom produced for uniformity, with 0, 1.0, 2.5, 5.0, and 10% by weight added to four classic soil types (Mollisol, Entisol, Spodosol, and Alfisol) in pint jars, moistened to 60% AWC, incubated at 250C for 3 months. Burped and re-moistened as needed. Three replicates, sacrificed to analysis at 0, 6 weeks, and 12 weeks. Findings:
[microbial respiration levels were] significantly affected by charcoal application, soil type, and incubation duration. ... despite significant interaction effects, the differences in [substrate induced respiration] SIR and [basal respiration] BR were primarily driven by differences in soil type and charcoal application levels, respectively. ... As hypothesized, both SIR and BR increased significantly with increasing charcoal application in all soil types; however, the strong influence of soil type ... is highlighted by the fact that, in general, the larger the level of SIR in the unamended soil, the larger the level of SIR at the highest charcoal application levels.
Respiration is the cleanest proxy we have for measuring soil life. Increasing respiration accompanies increasing microbial biomass, and we soil scientists are not going to ignore a tool that enables us to increase and sustain higher levels of soil life. Several of us suspect the ability to goose soil microbial respiration to be a universal characteristic of biochar, but have so far only caught glimpses of this based on indirect observations. Two recent examples:
Wardle et al 2008 (Text as Download, 140 kB) showed that biochar increases the decomposition rate of soil humus in boreal forests on a long-term basis.
Yoshizawa et al 2008 (Text as Download, 340 kB) attributed a 33% reduction in time needed to produce finished compost to 1%v/v charcoal. Counter indications occur also, but my understanding is that the no-effect results have been on low organic matter, low nutrient, moisture deficient desert soils, thus entirely consistent with this new research.
I want to believe, I truly do. Unfortunately, this research does not establish as universal a relationship between charcoal and soil respiration that one might be tempted to read into it. Biochar includes material with low reactivity, and this material was apparently not a low reactivity charcoal. The biochar stock used was capable of moving the soil pH from 6.3 to 8.9 (Entisol w/ 10% char). Raising soil pH (and surely compost pH) boosts microbial respiration. This effect is masking microbial effects due solely to the addition of charcoal-C. Reactivity can happen when you use manure as a biochar feedstock. Reactivity increases with pyrolysis temperature. Reactivity increases with ash content. Because these researchers did not characterize reactivity we are left to wonder how much increased respiration was due to charcoal, and how much effect was due to the ash reactivity.
One could ask somewhat the same of the Wardle study, and of the Yoshizawa observations, although their biochar stocks looked to me to have low reactivity potential. Still, without the data, whose to say. I look forward to the day when biochar researchers make the simple experimental design adjustments that will control for reactive effects.
Laboratory protocols established (and regulated) for characterizing materials used in mining and agriculture should port easily for biochar characterization. Google "acid-base accounting" and "acid neutralizing potential ANP" for how this plays out in the mining industry. For the agriculture context, Google "Effective Neutralizing Power ENP", "Neutralizing Index NI" and "Effective Calcium Carbonate Equivalent ECCE".
Limitations Of Charcoal As An Effective Carbon Sink
ScienceDaily (May 4, 2008) — Fire-derived charcoal is thought to be an important carbon sink. However, a SLU paper in Science shows that charcoal promotes soil microbes and causes a large loss of soil carbon.
There has been greatly increasing attention given to the potential of ‘biochar’, or charcoal made from biological tissues (e.g., wood) to serve as a long term sink of carbon in the soil. This is because charcoal is carbon-rich and breaks down extremely slowly, persisting in soil for thousands of years. This has led to the suggestion being seriously considered by policy makers worldwide that biochar could be produced in large quantities and stored in soils. This would in turn increase ecosystem carbon sequestration, and thereby counteract human induced increases in carbon-based greenhouse gases and help combat global warming.
However, a new study by Professors David Wardle, Marie-Charlotte Nilsson and Olle Zackrisson at SLU, the Swedish University of Agricultural Sciences, in Umeå, scheduled to appear in this Friday’s issue of the prestigious journal Science, suggests that these supposed benefits of biochar may be somewhat overstated. In their study, charcoal was prepared and mixed with forest soil, and left in the soil in each of three contrasting forest stands in northern Sweden for ten years.
They found that when charcoal was mixed into humus, there was a substantial increase in soil microorganisms (bacteria and fungi). These microbes carry out decomposition of organic matter (carbon) in the soil, and consistent with this, they found that charcoal caused greatly increased losses of native soil organic matter, and soil carbon, for each of the three forest stands. Much of this lost soil carbon would be released as carbon dioxide, a greenhouse gas.
Therefore, while it is true that charcoal represents a long term sink of carbon because of its persistence, this effect is at least partially offset by the capacity of charcoal to greatly promote the loss of that carbon already present in the soil.
The study finds that the supposed benefits of biochar in increasing ecosystem carbon storage may be overstated, at least for boreal forest soils. The effect of biochar on the loss of carbon already in the soil needs to be better understood before it can be effectively applied as a tool to mitigate human-induced increases in carbon-based greenhouse gases.
Copyright:Issued by: Science Daily
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Issue date: May 4, 2008
Link to Article: Origin of text
Study on BIOCHAR by researchers from Swansea University in the U.K. and the Pacific Northwest National Laboratory in Richland, Washington (published 10 August 2010):
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