Science in Society Archive

Beware the Biochar Initiative

Turning bioenergy crops into buried charcoal to sequester carbon does not work, and could plunge the earth into an oxygen crisis towards mass extinction Dr. Mae-Wan Ho

The story goes that charcoal buried in the soil is stable for thousands if not hundreds of thousands of years and increases crop yields. The proposal to grow crops on hundreds of millions of hectares to be turned into buried ‘biochar’ is therefore widely seen as a “carbon negative” initiative that could save the climate and boost food production.

That story is fast unravelling. Biochar is not what it is hyped up to be, and implementing the biochar initiative could be dangerous, basically because saving the climate turns out to be not just about curbing the rise of CO2 in the atmosphere that can be achieved by burying carbon in the soil, it is also about keeping oxygen (O2) levels up. Keeping O2 levels up is what only green plants on land and phytoplankton at sea can do, by splitting water to regenerate O2 while fixing CO2 to feed the rest of the biosphere [1] (Living with Oxygen, SiS 43).

Climate scientists have only discovered within the past decade that O2 is depleting faster than the rise in CO2, both on land and in the sea [2, 3] (O2 Dropping Faster than CO2 Rising, and Warming Oceans Starved of Oxygen, SiS 44). Furthermore, the acceleration of deforestation spurred by the biofuels boom since 2003 appears to coincide with a substantial steepening of the O2 decline. Turning trees into charcoal in a hurry could be the surest way to precipitate an oxygen crisis from which we may never recover.

Burying charcoal to save the climate

The International Biochar Initiative (IBI), according to its website [4], was formed in July 2006 at a side meeting of the World Soil Science Congress at Philadelphia, Pennsylvania, in the United States, by people from academic institutions, commercial ventures, investment banks, non-government organizations and federal agencies around the world, dedicated to research, development, demonstration, deployment, and commercialisation of biochar on a global scale.

IBI has introduced biochar into the 2008 US Farm Bill, so it now counts among a handful of “new, high-priority research and extension areas”. IBI is also working with the United Nations Convention to Combat Desertification to promote biochar in the post-Kyoto climate agreement. And the United Nations Framework Convention on Climate Change has already included biochar in a section entitled: “Enhanced Action on Mitigation” to serve as basis for negotiations during pre-Copenhagen meetings [5].

Biochar is just charcoal, produced by burning organic matter such as wood, grasses, crop residues and manure, under conditions of low oxygen (pyrolysis). A number of different pyrolysis techniques exist depending on temperature, speed of heating, and oxygen delivery [6, 7], resulting in different yields of biochar and co-products, “bio-oil” (with energy content value approx 55 percent that of diesel fuel by volume) and “syn-gas” (a mixture of hydrogen, carbon dioxide, carbon monoxide, and hydrocarbons), which can be used to generate electricity, or as low-grade fuel for ships, boilers, aluminium smelter and cooking stoves.

IBI has encountered strong criticism as a “new threat to people, land and ecosystem” in a declaration signed by more than 155 non-profit organisations worldwide [8]. But patent applications have been made, and companies formed for commercial exploitation of biochar production. Intense lobbying is taking place for biochar to be included in the Kyoto Protocol’s Clean Development Mechanism for mitigating climate change [9, 10], so people implementing that technology would be able to sell certified emission reduction (CER) credits.

Things have moved forward so fast with so little public awareness and debate that critics are alarmed, especially over the proposal from some prominent advocates that 500 million hectares or more of ‘spare land’ could be used to grow crops for producing biochar [11, 12], mostly to be found in developing countries; the same as was proposed in the biofuels initiative several years earlier.

Biofuels proving disastrous

The biofuels ‘boom’ has already exacerbated climate change by speeding up deforestation and peatland destruction, loss of habitats and biodiversity, depletion of water and soil, and increased the use of agro-chemicals. Above all, it has generated poverty, land grab, land conflicts, human rights abuses, labour abuses, starvation and food insecurity as documented by BiofuelsWatch and 10 other groups [13, 14] (see also [15] (Biofuels: Biodevastation, Hunger & False Carbon Credits, SiS 33). Calls for moratorium on biofuels came from Africa, the US, and the United Nations [16] (UN 'Right to Food' Rapporteur Urges 5 Year Moratorium on Biofuels, SiS 36).

Biofuel production - mainly bioethanol and biodiesel - more than doubled between 2003 and 2008, driven by rising oil prices; while food prices rose 70 percent between 2005 and 2008 [17], according to data compiled by the international Monetary Fund. The UN declared 2008 the year of the Global Food Crisis (see [18] Food Without Fossil Fuels Now, SiS 39); food riots and fuel protests were rife. UK’s Environment Audit Committee joined the call for moratorium in January 2008 [19], and reiterated it in May 2008 [20].

Biochar is widely seen as the successor to biofuels on grounds that it will sequester carbon and improve soil fertility while also producing energy. Biochar is not just carbon neutral; it is “carbon negative”, according to its proponents, because buried biochar is stable for thousands, if not hundreds of thousands of years.

A lifecycle analysis published in 2008 [21] by John Gaunt and Johannes Lehmann, principal biochar proponent at Cornell University, New York, in the United States, considered both purpose grown bioenergy crops (BEC) and crop wastes (CW) as feedstock. The BEC scenario involves a change from growing winter wheat to miscanthus, switchgrass, and corn as bioenergy crops. The CW scenario considers both corn stover and winter wheat straw as feedstock. The energy balance is much more favourable than the production of biofuels such as ethanol from corn. The avoided emissions are between 2 and 5 times greater when biochar is applied to agricultural land than used solely for energy in fossil energy offsets. Some 41–64 percent of emission reductions are related to the retention of C in buried biochar (so the stability of biochar is important), the rest due to offsetting fossil fuel use for energy, fertilizer savings, and avoided soil emissions of N2O and CH4, as additional effects of biochar. Unfortunately, the analysis is largely based on assumptions. Biochar is now found to be not quite as stable as claimed and can speed up litter decomposition in the soil (see below). The energy balance of pyrolysis is taken as that reported by one company; and there is lack of conclusive evidence in support of the supposed significant N2O reduction for at least ten years [6, 11]..

Biochar is not ‘terra preta’

The biochar initiative was inspired by the discovery of ‘terra preta’ (black earth) in the Amazon basin [22, 23], at sites of pre-Columbian settlements (between 450BC and 950AD), made by adding charcoal, bone, and manure to the soil over many, many years (see Fig. 1). Besides charcoal, it contains abundant pottery shards, plant residues, animal faeces, fish and animal bones. The soil’s depth can reach 2 metres, and is reported capable of regenerating itself at the rate of about 1 cm a year. Similar sites are found in Benin and Liberia in West Africa, in the South African savannahs, and even in Roman Britain. According to local farmers in the Amazon, productivity on the terra preta is much higher than surrounding soils.

Figure 1. Terra preta left compared with surrounding soil right

Investigations in the laboratory revealed that terra preta soils are rich in nutrients such as nitrogen, phosphorus, calcium, zinc, and manganese, and have high levels of microbial activities. Terra preta contains up to 70 times more black carbon (BC) than the surrounding soils. Due to its polycyclic aromatic structure, black carbon is believed to be chemically and microbiologically inert (but see later) and persists in the soil for centuries, if not thousands of years. During this time, oxidation produces carboxylic groups increasing its nutrient-holding capacity. Bruno Glaser and colleagues at the University of Bayreuth concluded that [24] “black carbon can act as a significant carbon sink and is a key factor for sustainable and fertile soils, especially in the humid tropics.”

Similarly, BC derived from terra preta sites in central Amazon differing in age from 600 to 8 700 years were chemically, biologically and spectroscopically indistinguishable, as consistent with their “extremely slow” rate of decomposition [25].

However, BC collected from 11 historical charcoal blast furnace sites from Quebec Canada to Georgia USA, were quite different from BC newly produced using rebuilt historical kilns [26]. The historical BC samples were substantially oxidized after 130 years in soils compared to the new BC, or new BC incubated for one year at 30 C or 70 C. The major alterations were an increase in oxygen from 7.2 percent in new BC to 24.8 percent in historical BC; a decrease in carbon from 90.8 percent to 70.5 percent; formation of oxygen-containing function groups, particularly carboxylic acid and phenolic functional groups; and disappearance of surface positive charge, to be replaced entirely by negative charges. New BC incubated at 30 C or 70 C for 12 months increased in oxygen concentrations to 9.2 and 10.6 percent respectively; and also had complete replacement of surface positive charges by negative charges.

These findings show that BC is a substantial oxygen sink, and could deplete atmospheric O2 fairly rapidly if massive amounts are produced in a hurry!

The main factor accounting for the changes was mean annual temperature, which was highly correlated with degree of oxidation. BC oxidation was increased by 87 nmoles/kg C / degree Celsius increase in mean annual temperature. BC oxidation to carboxylic groups accounts for the high cation exchange capacity of natural BC in the soil that the authors suggest is the basis of the enhancement in soil fertility.

So charcoal is not the same as terra preta that has been created over thousands of years by human intervention and natural geochemistry. The claim that biochar is a “stable carbon pool” in the soil that does not degrade for thousands of years is not borne out by the study, nor by a number of other studies (see below).

Naturally occurring black carbon has a far more complex relationship with the soil and the earth as a whole, as recent research is revealing. Moreover, black carbon pollution from fossil fuel and biomass burning associated with deforestation contribute as much to global warming as CO2, and climate scientist are proposing a reduction of black carbon emissions as a way of cooling the planet [27] (see Black Carbon Warms the Planet Second Only to CO2, SiS 44). That’s another reason the biochar initiative will spoil the climate, by increasing BC emissions.

Biochar increases loss of organic carbon from humus

A ten-year trial in Swedish forests showed that buried charcoal appear to promote the breakdown of humus, the decomposing plant matter on the forest floor [28], thus completely offsetting the carbon sequestered in the charcoal.

David Wardle and colleagues at Umeå University started their experiment to investigate the effect of forest fires on soil ecology. They buried hundreds of litter bags containing humus, charcoal, or a 50–50 mixture of the two in several sites in the Swedish boreal forest.

Periodically, they weighed the bags and measured the concentration of carbon and nitrogen. After just one year, they began to see an unexpectedly large decrease in mass from the bags containing the humus–charcoal mixture: 17 percent (the expected was 9 percent), compared to 18 percent in the bags with only humus and 2.5 percent in the bags with only charcoal Over ten years, the bags with mixed humus and charcoal released just as much carbon as did those containing only humus (130 mg per g initial mass), instead of only half as much as would be expected if charcoal had no effect on the loss of carbon from humus. The bags with charcoal had lost a small amount of its carbon (less than 5 mg per g initial mass) but gained about the same in nitrogen and microbial activity. The mixture did not gain or lose any nitrogen while humus released 2 mg N per g initial mass.

The results show that burying charcoal can speed up the decomposition of forest humus during the first decade, thus offsetting nearly all of the carbon sequestered in the charcoal itself.

Biochar may not be a stable carbon pool

Caroline Masiello, marine chemist at Rice University Houston, Texas, in the United States, pointed to apparent discrepancy in the production and deposition of of BC on both sea sediment and on land [29]. BC production globally was previously estimated at 0.05 to 0.27 Gt/y [30], representing 1.4 to 1.7 percent carbon exposed to fire that’s converted to BC. The only documented loss process for BC is deposition in ocean sediments. However, the rate of total organic carbon deposited on the seafloor is only 0.16 Gt/y. Even assuming the lower end of the BC production rate, 0.05 Gt/y, would mean that BC should be 30 percent of ocean sediment organic carbon; but the actual measured amount is 3-10 percent.

Furthermore, isotope studies of highly refractory BC detected 14C graphite BC in sediment from the Northeast Pacific coastal transept. This was not a product of fossil fuel combustion but the result of erosion of very old graphite from rocks and deposited into the ocean, which is at least in part derived from petrogenic graphite. If BC deposited in ocean sediments comes both from biomass burning and from recycled petrogenic graphite, even less of the annually produced BC can be accounted for in ocean sediments. So where does the rest of the earth’s annually produced BC go?

The same applies to BC on land. If BC has been produced since the last glacial maximum from biomass burning at the same rate as it is now produced, and if it is as stable as assume, it should account for 25 – 125 percent of total soil organic carbon pool. Instead, only a few measurements of BC or soil organic carbon ever reach 25 percent. A study of BC production during Siberian boreal forest fires made clear that not enough BC remains even after 250 years to account for all the BC produced during a fire [31] - estimated at 0.7 -0.8 percent of organic carbon - due to a combination of in situ erosion and translocation within the soil profile, with in situ degradation being the most likely.

In a later study, the amount of BC in organic carbon was compared in soils of three Siberian Scots pine forests with frequent, moderately frequent, and infrequent fires [32]. The researchers concluded that BC did not significantly contribute to the storage of organic matter, most likely because it is consumed by intense fires. They found 99 percent of BC in the organic layer, with a maximum stock of 72 g/m2. Less intense fires consumed only parts of the organic layer and converted some organic matter to BC, whereas more intense fires consumed almost the entire organic layer.

But appreciable degradation of BC can also occur in the absence of fires, by microbial action or photo-degradation. The stability of BC was investigated in a sandy savannah soil at Matopos in Zimbabwe, where some soil plots have been protected from fire for the past 50 years [33]. The abundance of BC in these plots was compared to plots that have continued to be burnt. The plots protected from fire had 2.0+5 mg/cm2 BC, about half of the 3.8+0.5 mg/cm2 found in plots burnt every 1-5 years. The half-life of BC at a depth of 0-5 cm of the soil protected from fire was estimated at < 100 years, and that of large particles <50 years. The results suggest that in well-aerated tropical soil environments, charcoal and other BC can be significantly degraded in decades to a hundred years.

BC is best understood as a continuum of combustion products, ranging from slightly charred, degradable biomass to highly condensed refractory soot [28]. All components of this continuum are high in carbon content, chemically heterogeneous and dominated by aromatic structures. The reactivity of BC also varies along the combustion continuum. Charcoal decomposes much more rapidly than soot when exposed to chemical oxidants, such as acid dichromate, in the lab [33].

The results are also complicated by the different ways of producing charcoal and different methods of quantifying BC [28]. In studies on the National Institute of Standards and Technology reference materials, the values varied by a factor of 500, depending only on the method used in quantification.

Research in the atmospheric chemistry community has shown that even soot, the most inert part of the combustion spectrum, can be chemically altered on a very short timescale through reaction with atmospheric oxidants. Reaction with ozone and other atmospheric oxidants create hydrophilic carboxylic acid groups on its exterior These reactions are so rapid that solubilisation of soot particles can occur in 30 min in the presence of 50 ppb (parts per billion) ozone, making it possible to dissolve soot in a solution of distilled water. Ozone concentration in rural air in the US ranges diurnally from 20 to 70 ppb. So soot can enter some of the Earth’s dissolved organic carbon pools.

BC has been measured by thermal techniques to be 5 to 12 percent of dissolved organic carbon in Chesapeake Bay, the Delaware Bay, and in adjacent Atlantic Margin. Another electrospray ionization with high resolution mass spectrometry applied to dissolved organic matter from a small stream in New Jersey and Rio Negro detected BC degradation products that were assigned chemical structures.

Biochar effects on soil fertility not always positive

Experiments carried out so far have yielded equivocal results on the ability of biochar to increase productivity. There have been positive effects claimed, at least in the short term, but also some negative impacts, at least partly due to nitrogen limitation [34]. In a small scale lab experiment, biochar appeared to increase nitrogen fixation by legumes, principally by increasing the availability of trace elements boron (B) and molybdenum (Mo), and to a lesser extent, K, Ca, and P, while lowering N availability and Al saturation. The results on productivity were not statistically significant, however.

A report published in 2007 presented results on crop yields over four seasons [35]. Researchers at the University of Bayreuth in Germany, and EMBRAPA Amazonia Occidental Manaus in Brazil carried out a field trial near Manaus on cleared secondary forest with 15 different amendment combinations of chicken manure (CM), compost (CO), forest litter, chemical fertilizer (F), and charcoal (CC) applied once on rice and sorghum, and followed over four cropping cycles (see Fig. 2).

Biochar and crop yields in combination with other amendments

Figure 2. Biochar and crop yields in combination with other amendments

Chicken manure gave by far the highest yield over the four cycles (12.4 tonne/ha). Compost application came second at about half the yield, but was still four times higher than chemical fertilizer. The control, leaf litter (burnt and fresh), and charcoal treatments gave no grain yields after the second season, and were discontinued.

In combination with compost, charcoal amendment decreased yield by about 40 percent compared to compost alone, and only improved yield in combination with chemical fertilizer. The charcoal was derived from secondary forest wood bought from a local distributor, and applied at the rate of 11 tonne/ha. This corresponded to the amount of charcoal C that could be produced by a single slash-and-char event in a typical secondary forest on the dry iron-rich soil of central Amazonia.

The highest yields for all treatments were obtained at the first harvest, and except for chicken manure, yields declined rather sharply by the second harvest.

A second fertilization with chemicals was applied after the second harvest to all remaining treatments, but that did not improve the yields.

Plants fertilized with chicken manure had the highest nutrient contents followed by plants that received compost and/or chemical fertilizer. Chicken manure significantly improved the K and P nutrition compared to all other treatments, while charcoal applications did not show a significant effect on nutrient levels. Most importantly, surface soil pH, phosphorus, calcium and magnesium were significantly enhanced by chicken manure. Plots fertilized by chicken manure had pH higher than 5.5 and increased cation exchange capacity.

These results are disappointing for those looking to promote ‘biochar’ as a means of improving the yield of crops at the same time as sequestering carbon, which also turns out to be illusory.

The potential for an oxygen crisis is real

It is clear that biochar has not lived up to its promises as a stable C repository or enhancer of crop yields. On the other hand, the risk of oxygen depletion is real [1-3]. Biochar itself is an oxygen sink in the course of degrading in the soil [24. 32]; adding to the depletion of oxygen that cannot be regenerated because trees have been turned into biochar for burial. And worse, as in the biofuels boom that has already apparently speeded up deforestation and oxygen depletion since 2003 [2], if biochar is promoted under the Clean Development Mechanism, it will almost certainly further accelerate deforestation and destruction of other natural ecosystems (identified as ‘spare land’) for planting biochar feedstock, and swing the oxygen downtrend that much closer towards mass extinction.

Article first published 07/09/09


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susan rigali Comment left 5th October 2009 14:02:42
Baucus' 2008 campaign raised $11.6 million, only 13% of which came from Montana donors; the rest included millions from health care and other industries overseen by Finance and Baucus' other committees.[5] The overwhelming ratio of special interest and out-of-state dollars to donations from Montana donors have raised questions: So as Baucus and other lawmakers attempt to craft a bill that can smash through a virtual gridlock of interests, the awkward question lingers: To whom are they more attentive, their voting constituencies back home or the dollar constituencies who are at the Capitol every day?[5]

Dave Comment left 8th September 2009 01:01:42
Thank you for your fabulous work! It would be great to read your research on glacial rock dust and how it may relate to sustainable agriculture and carbon sequestering. Thanks for your consideration, Dave

Geoffrey Pedersen Northeast Biochar, LLC Comment left 31st October 2009 02:02:50
As the owner of Northeast Biochar, LLC a distributor of Biochar, I feel the article although interesting, is very misleading to anyone in the industry who may be interested in this fascinating theory with proven results. The key to manufacturing beneficial Biochar is in the pyrolysis process. Innoculation of char is one of the key ingredients. Biochar is designed for specific purposes and therefor not all "char" is alike. Used safely in both residential and commercial applications, the following benefits are achieved. Improved soil drainage, reduced soil compaction, increased nutrient cycling, greater retention of water in dry soils, improved germination, improved plant resistance to fungal disease, root feeding nematodes, and insect infestations. Biochar products have made numerous achievments in crop health and productivity. Great for the organic gardener who wants to restore soil damaged by chemical treatments. It is also a great turf supplement for golf greens and courses. Feel free to visit our website at: or email anytime with questions or to further chat about this great product. Our email address is: E with you soon! Geoffrey Pedersen, Owner Northeast Biochar,LLC

David Russell Comment left 8th September 2009 01:01:52
A few years ago I read a (Sci-Fi) novel called The Last Gasp by Trevor Hoyle. Written in 1983, it was a completely believable fictional story dealing with oxygen depletion set in the future. In the light of your article on biochar this book may be prophetic.

Rory Short Comment left 8th September 2009 05:05:24
As I see it the exploitative relationship with the rest of nature is the paradigm on which Western culture has operated up until now and it is the fundamental cause of our apparent success but that success is only in the short term as the current and looming environmental catastrophes are showing us. Biochar is founded on that destructive paradigm. Unless we have a paradigm shift and start trying to work in cooperation with the rest of nature we will inexorably forge the demise of our species.

jonathan Comstock Comment left 8th September 2009 14:02:22
I find the discussion of O2 depletion very misleading. Oxygen is released from split water in the creation of biomass. Burning, or decomposition reunites it with this oxygen. All that was described in this article was that the black carbon isn't as stable as might be wished, and that gradual oxydation was taking place, which moves it slowly back towards no net change in global oxygen when it reaches completion. As long as it lasts, its matching O2 from the time of growth is either contributed to the atmosphere as a net gain or reacting with something else.

Stuart Comment left 8th September 2009 14:02:14
Thank you for these informative articles.To me the depletion of O2 is more critical than the CO2 problem. SIS seems the only organisation aware of this.There are no web sites except your that gives any info about world O2 levels only rubbish about rocks breaking down to O2.

Sean K. Barry Comment left 8th September 2009 14:02:06
This article is only full of BAD PSEUDO-SCIENCE guessing and propaganda. The continued production and use of biochar requires annually grown biomass. Plants take up CO2 when they grow and give off OXYGEN. It's called photosynthesis and it is a very basic understanding of how plants grow and cyle both CO2 out of the atmpspjere and O2 into the atmosphere. Stadmimg carbon sinks in old growth forest will not be taken down and put into production of biochar. Biochar can, should, and will be made from waste biomass that decompaoses anyway. Oxygen depletion simply will not occur from conversion of otherwise decaying biomass into mineralized varbon (THAT DOES NOT DECOMPOSE!) and it is merely an immoral scare tactic to say otherwise.

Thomas Shelley Comment left 8th September 2009 14:02:46
Biochar, like many other "innovations" that don't hold up under scientific scrutiny, fits the old adage "If it sounds like it's too good to be true, it probably is." I think it falls into the same category as Cold Fusion, except Cold Fusion was a more or less harmless misinterpretation of data and biochar may well not be harmless. Tom Shelley, Ithaca New York

Erich J.Knight Comment left 8th September 2009 14:02:38
The only illusory thing I see in this report is not looking at the full literature on biochar in Japan for the last 15 years ,in Oz the last 4 years and current work in the US and UK. There are dozens soil researchers on the subject now at USDA-ARS. and many studies at The up coming ASA-CSSA-SSSA joint meeting; There is real magic coming out of the Asian Biochar conference. 15 ear per stalk corn with 250% yield increase, Sacred Trees and chickens raised from near death Multiple confirmations of 80% - 90% reduction of soil GHG emissions The abstracts of the conference are at Another significant aspect of bichar and aerosols are the low cost ($3) Biomass cook stoves that produce char but no respiratory disease. and village level systems with the Congo Basin Forest Fund (CBFF). The Biochar Fund recently won $300K for these systems citing these priorities; (1) Hunger amongst the world's poorest people, the subsistence farmers of Sub-Saharan Africa, (2) Deforestation resulting from a reliance on slash-and-burn farming, (3) Energy poverty and a lack of access to clean, renewable energy, and (4) Climate change. Most recent studies out; Imperial College test, this work in temperate soils gives data from which one can calculate savings on fertilizer use, which is expected to be ongoing with no additional soil amending. The BlueLeaf Inc. and Dynamotive study are exciting results given how far north the site is,and the low application rates. I suspect, as we saw with the Imperial College test, the yield benefits seem to decrease the cooler the climate. The study showed infiltration rates for moisture are almost double. The full study at Dynomotives site;

Jochen Binikowski Comment left 8th September 2009 18:06:24
The above story does not correspond with the findings we made at our commercial BC-based plantings in the Philippines. Althought I am not a scientist, I can confirm that a soil mixture of Biochar, ashes, chicken manure and humus soil reduces the fertilizer consumption by 80-100% at most vegetable varieties. In that mixture many dangerous soil borne deseases like bacterial wilt does not occur and fungus problems are reduced. Regardless how long the charcoal is stored in the soil, this soil mixture is feassible anyway. With best regards from the tropical office, Jochen

David Miller Comment left 8th September 2009 21:09:26
It's worth noting that amidst the hand-waving about oxygen depletion being a "real problem" due to the biochar adsorbing oxygen that no numbers are given. Lets try a quick bit of math. 1 ppm of the atmosphere represents ~2.13 Gtons of Carbon. Assume that 2.13 Gton of biochar was produced and sequestered in soils around the world. Further, assume that each atom of carbon adsorbs two atoms of oxygen. I find it highly doubtful this would be the case with most of the carbon atoms not exposed at all and therefore not able to adsorb anything, but lets make the assumption to produce the most alarmist oxygen depletion scenario possible. Under these assumptions (2 gigatons carbon sequestered annually) we'd see a corresponding decrease in oxygen of 2 ppm. Given that the atmosphere is composed of something over 209 THOUSAND ppm of oxygen I'm just not going to see this as a problem.

Christoph Steiner Comment left 8th September 2009 23:11:40
The above cited article [35] compared different soil carbon additions. The application rates were based on equal amounts of carbon. It is not surprising that the chicken manure supplied a lot more nutrients than the biochar did. The chicken manure added a lot more nutrients than the mineral fertilizer. Biochar produced from low nutrient feedstock is not a fertilizer but it can improve the efficiency of fertilizers. This has been published in other papers, but they were ignored by this review. Biochar is produced out of dead biomass, which is otherwise decomposing or burned. If biomass burns or decomposes oxygen is added to the carbon (CO2). In this process each carbon takes two oxygen atoms from the atmosphere. Therefore fire accelerates the carbon cycle. Biochar is produced without oxygen. Carbon capture and storage as proposed by the coal industry intends to capture CO2 and store it underground. Burning (+ oxygen) fossil fuel takes 2 oxygen atoms per each carbon atom to form CO2. If this CO2 is than stored underground we remove 2 oxygen atoms for each carbon atom sequestered. Biochar stores the carbon in a solid form before it ever became CO2. This is a deceleration of the carbon cycle. Depletion of O2 is the result of fossil fuel burning not biochar formation.

Dana Rose Comment left 9th September 2009 01:01:02
This article seems like fear mongering. Biochar can be done in an ethical way without deforestation or using up precious crop space. Just as organic farmers reject the mass, industrial, earth damaging methods, biochar makers can act with care. Why can't we make biochar out of things that were going to burn anyway? Here in southern Oregon the BLM pays people to fireproof the forests. When they are done they set slash piles ablaze. Yearly. Portable biochar stoves could improve the air quality near these burns and provide local farmers with water retaining, microbe harboring biochar. It is worrying to see big industrialists get interested in biochar and I think it is important to keep them from making char in harmful ways. It is more worrying to see people who care about the earth rejecting a solution that may actually help with our climate crisis. I would love to see this energy put in to demanding biochar be done ethically, organically and intelligently.

susan rigali Comment left 10th September 2009 23:11:49
I decided to put some of these comments to the test. Erich says: ". The study showed infiltration rates for moisture are almost double." My test showed that this is true, unfortunately the run-off using biochar was twice that of using only soil. Filtration would be the key word not absorbtion. David sees no problem but I doubt he has spent many hours with his hands in the soil. And Chris you make biochar sound as if it is a formation of nature, not another by-product of the energy industry. Last is a response that this paper is fear mongering. That is really amusing because those that use it almost certainly have something to gain by it.

Erich J. Knight Comment left 28th September 2009 15:03:51
I just received word that Senator Baucus co-sponsored a bill along with Senator Tester (D-MT) called WE CHAR. Water Efficiency via Carbon Harvesting and Restoration Act! It focuses on promoting biochar technology to address invasive species and forest biomass. It includes grants and loans for biochar market research and development, biochar characterization and environmental analysis. It directs USDI and USDA to provide loan guarantees for biochar technologies and on-the-ground production with an emphasis on biomass from public lands. And the USGS is to do biomass availability assessments We can track it here:

mae-Wan Ho Comment left 22nd October 2009 00:12:21
Sander and others, have you read the article? Biochar gets oxidised in the soil, ie, it takes up oxygen while in the soil, also, it often gets completely burnt up, and, it can hasten the oxidation of humus, all of which means using up oxygen. Can you people think more than one step at a time or join dots together?

Sander Bruun Comment left 22nd October 2009 00:12:49
As many others have commented above the suggestion that biochar will lead to oxygen depletion in the atmosphere is completely rediculous. Biochar can never take up more oxygen than was released when the plant material was produced. My first thought was that this must have been posted on the 1. of April. In the scientific literature we are peer-reviewing articles. This means that other scientists are checking that the most blatant mistakes are not published. If this article had been peer-reviewed I can asure you it would never have been published.

Josh Frye Comment left 1st December 2009 21:09:46
Not all biochars are good and I think those in the biochar world will agree... but some are excellent. I produce poultry biochar low temp, fixed bed gasification.I use the heat to offset my demand for propane and to provide a constant heated air exchange for the poultry providing a ideal environment to grow poultry thus improving the feed conversion. Plants produce o2 right? Healthier plants more o2. I have seen the results of the char I produce. The growth and hardiness is quite amazing even after three years and no there were no other commercial fertilizers applied. Have you considered the energy and o2 it takes to make commercial fertilizers? But what do I know, I'm just one of those guy's who has a real job of putting food on your table using the resources god has given me in the most efficient manner that I possibly can. I think your ignorant. Oh and Susan some biochars are super absorbents... check out Isabel Lima USDA ARS.

Ed Witt Comment left 7th August 2010 15:03:23
The properties of biochar greatly depend upon the pyrolysis temperature. pH, for example, at 200C the pH will be about 4, at 500C (considered optimum) pH is 8, whereas at 800C the resulting pH is 12. You need to check your pH and adjust as necessary to achieve the best results. By the way, pyrolysis temperature also effects cation exchange capacity as well as carbon recovery.

Chris Comment left 12th April 2010 01:01:26
Good info you put together but Still more research to do on Biochar. Some plants will do much better with Bio char then others. I noticed that web site is gone and sold for a few weeks now. That guy pumped up bio char last fall and now he is gone? I have some test plots growing now with bio-char. I planted 6 plots with bio char and 6 without. I made a mixture of bio char from wood chips(hard wood and soft) bio chared turkey fertilizer 4-6-4. First 6 plots that are growing with only composted soil and are starting to grow. The second has composted soil and about 10% bio char mix and are not growing yet. I also noticed that the plots with bio char the surface has dried and did not stay moist like the composted soil plots. I will give updated latter on the plots.

Mae-Wan Ho Comment left 12th April 2010 05:05:24
Chris, thanks for your comment. We look forward to seeing your results in full. Don't forget to take dated photographic records of your observations.

Chris Comment left 15th April 2010 15:03:08
Good to see my post showed up and did not vanish into the net.

Eric Comment left 12th March 2011 10:10:13
Given the information I read in this article, I think that the experiment conducted by David Wardle and his team is incomplete. The hypothesis that the mixture of biochar and humus would lose half as much mass as the 100% humus bags seems to be based on simple mathematics rather than biological processes. Humus is broken down primarily by aerobic organisms and all three treatments would get similar amounts of oxygen as the bags were buried, dug up to weigh, reburied, etc. Since the biochar is essentially inert, the same amount of oxygen was available to breakdown the humus in both the 100% humus and 50/50 humus/biochar treatments. I do not find it surprising these treatments lost similar amounts of humus. I expect that if a fourth treatment containing 50/50 humus/perlite were added to the experiment, the humus loss would be the same as the humus/biochar mixture.

Stephen Poole Comment left 6th December 2011 20:08:20
What solution are you proposing? Continue burning fossil hydrocarbons and you have a much bigger oxygen sink! How do you imagine that Terra Preta soils have avoided being an oxygen sink? Biochar will not be implemented worldwide overnight. The way to discover if biochar is an oxygen sink is to apply it over a wide range of soil types and climates. Don't kill the goose that may lay the golden egg!

Maewan Ho Comment left 6th December 2011 20:08:16
The solution to global warming and alternatives to biochar are legion. Only the lack of political will and vested interests are preventing greater progress. We have published numerous articles on the subject. Begin with the special 180 page report: Green Energies Now, 100% Renewables by 2050.

Abe Connally Comment left 6th June 2012 15:03:21
When will this article be up for peer review? A lot of data and studies were excluded from this report, and it is a shame, because different conclusions could be drawn if all information was on the table. Claiming that biochar (charcoal + addition of composts, not just charcoal alone) depletes humus based on one study is irresponsible. Let's examine other studies that did not have the same results. And to the point of O2, let's see the numbers. Northern Pine forests are currently being devastated by the pine beetle. Allowing these forests to decompose will be a disaster in terms of CO2 production. Instead, converting these dead trees into soil amendments, like biochar, could pose an alternative solution. There are many sources of biomass for biochar that currently exist as CO2 emitters, mainly agricultural wastes. Returning these wastes to the soil in an effective manner to lock up that carbon is of great importance. The claim that biochar is bad because it will cause deforestation is not only misleading, it is grossly incorrect. The largest sources of biomass are not living plants, but waste materials currently decomposing and emitting large amounts of CO2 and consuming large amounts of O2.

Michael Comment left 9th July 2012 07:07:02
Has anyone "loaded" biochar with anaerobic digestate? What about using a beneficial microbial mix? I manufacture organic fertilizer from poultry litter and have considered adding biochar to my products. Any thoughts? Also, what about varying the pyrolosis temperature during the production of the biochar. Does that effect its effectiveness?

Luke Comment left 29th November 2012 20:08:28
Studies on mixing of biofertilisers such as compost teas (worm juice) into biochar, and then integrating into the soil below 5 cm, have a highly beneficial role in crop growth and long chain organic carbon growth. Biochar production methods, and integration with biological fertilisers is critical to the success of the biochar in achieving its intended goal - that is, sequestering soil carbon, provide a reservoir for beneficial microbes and fungi, and holding water in the soil for longer to assist plant growth. Not all biochars are equal, and the co-factors in biochar are very important, namely biofertilisers. Anaerobic digestate that is rich in nitrogen and anaerobic digester effluent after oxidising somewhat) that is rich in nitrogen is also suitable for soaking biochar in, and then integrating into the soil. If biochar is utilised in a holistic and sustainable manner, it can greatly assist sustaniable farm management and sequester organic carbon in the soil, provided it is not turned over. So it needs to be included in no-till farming systems, not intensive turn over the soil farming systems. Again, these are all clarifications and pre-requisites for successful and sustainable biochar use. If biochar is produced badly, and applied without co-factors, and turned over and exposed to atmosphere and photo-degradation, then of course it will have a negative impact. The argument should not be for or against biochar, it should be about how it is made, how it is applied with certain co-factors such as biofertilisers, and how it is kept in the soil with no-till systems.

Paul Taylor Comment left 29th April 2014 20:08:55
Even if the C was fully oxidised in the soil it would not significantly deplete O2. We are unlikely to sequester a lot more atmospheric C than the current excess in the atmosphere, currently about 250bt or 120ppm. The 120ppm of O2 that would be required for full oxidation of the sequestered C stands against 200,000ppm of O2, so the O2 depletion if the C reoxydises in the soil is only 0.06%. As well if the C fully reoxydised it would just be taking up the O2 released when it was reduced by photosynthesis to form the biomass the C was made from, for zero net effect. Currently O2 is depleting at order of the 0.1% level, perhaps because there are O2 sinks that are not being balanced by an overall reduced net biomass activity on earth due tropical rainforest and marine plankton loss. I researched this once when another madman brought up alarm about the supposed O2 depletion issue – but will leave it to Google to supply the details. If ALL the biomass in the world, about 560b tons (twice the above figure) was oxydised and NOT REGROWN it would deplete 1,500 Bt of O2. That is only 0.125% (again twice the above figure) of the 1.2 million billion tons of O2 in the atmosphere. (As well it would add 2000 Bt of CO2, increasing CO2 by 1000ppm. Without something like biochar we may well accomplish this since it looks like much of the boreal and tropical forests will go up in smoke and much C will release from the soil.) However, the very essence of biochar is to regrow the biomass and even to grow more biomass! If more C from CO2 in the atmosphere ends up in more biomass, then more O2 ends up in the atmosphere. In fact the biochar system (pyrolysis followed by sequestration and only long term degradation) doesn’t stop, but rather dramatically slows down, the natural return of C to the atmosphere. Its other promise is to speed up the photosynthesis cycle through boosting plant growth, so the net result is to remove CO2 and increase O2. So in this respect this “biologist” is barking up the wrong tree. Paul Paul Taylor, PhD Ed/Author: The Biochar Revolution Transforming Agriculture and the Environment

Adrian Hepworth Comment left 12th August 2014 01:01:57
A fascinating article which seems to have ignited (no pun intended) some anger amongst those posting comments. Dismissing it with words like ridiculous, madman and ignorant only shows an inability to express yourself. You loose any argument by being abusive. That said I still understand all the points made. However there still seems to be basic misunderstanding of the words biochar, charcoal and compost. The British Biochar Foundation, when asked what biochar was, described it as charcoal with a mission but is basically exactly the same as charcoal. The only difference is that it has been 'activated'. I used to think that activating meant adding the compost or compost tea. I think this is how most reading this report and blog believe best defines biochar. However I've more recently learnt that activated charcoal is simply grinding it to a fine dust. Very different to charcoal as it come out of the kiln/retort and very difficult to handle and incorporate in to a compost mix. The British Biochar website shows biochar made into pellets. I think most people think of charcoal in the form most often seen and used on barbeques. This is NOT biochar although chemically it is identical. There is no mention in the text above about the activation of charcoal. The size of finished particle would also add to the numerous variables that effect the efficiency of biochar. In itself biochar is benign, it does not contribute to plant growth. It only offers a better medium on which the mycorrhizae fungi can live. These fungi are essential for plant growth as they move any nutrients from the soil to the plant roots. As mentioned in several of the above comments, there still needs to be more research done and done with an open mind. I fear for its future when big business gets involved. Is the trouble that it can be made by anyone so big business is needed. If anyone can produce a simple stove from recycled materials, that uses wood as it fuel, gasifies the timber so burns cleanly and so reduces respiratory diseases in developing countries and at the same time produces small amounts of biochar that will slowly improve the moisture holding qualities in the immediate neighbourhood the benefit goes direct to the user rather than the shareholders of big businesses. The debate about incorporating biochar into the soil over time cannot be answered until time travel has been made possible. Then we can return to the Amazon basin and watch how it was made. My own belief is that it is a blend of deliberate additions of charcoal, the residues from accidental forest fires and the simple addition of carbon over time from the roots of harvested plant material. After all any plant materials will allow roots to die back if the top growth has been removed. This will then decompose and release it carbon content. A no till agriculture on the same plot over centuries would produce the ideal loam for the next seasons growth. That how they did it millennia ago and how we should be doing it now.

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john msson Comment left 16th September 2015 05:05:35
Seems like before its done a mass scale more research would be good.The PH and temperature of burn+ size of biochar when activated before mixing with soil is important,etc. The article+responses are vinteresting,I still to use coppiced-waste wood in occasional campfires.Only after reading this I aim to get the temperature around 350c for a PH of 6 and look more into the optimum size to grind biochar.

Chris Weston Comment left 7th October 2015 00:12:10
You should worry more about CO2-induced ocean acidosis and its effects on phytoplankton populations. 50% of our breathable oxygen comes marine phytoplankton. I feel that the argument still needs to be centered on CO2 emissions, because CO2 is driving ocean acidosis.