bio-char: uses of charcoal in soil

[alwyn]

This issue came up in another thread. I have been experimenting with bio-char (which is charcoal-from wood, not briquettes ) to aid in growing plants. Anecdotally, my corn is growing bigger over char. My theory is that, rather than acting as a fertilizer, the charcoal acts like a filter for toxins, as well as a spacer for the soil. It may also help the soil retain moisture.

This link to a cartoon explanation is from the school of forestry, at UM...it seems to back up my assertations, but there are still questions raised.
http://www.bioed.org/ecos/pubs/Presenta ... ations.pdf

from Wiki: Atmospheric carbon absorbtion

Biochar is a way for carbon to be drawn from the atmosphere and is a solution to reducing the global impact of farming (and in reducing the impact from all agricultural waste). Since biochar can sequester carbon in the soil for hundreds to thousands of years,[2] it has received considerable interest as a potential tool to slow global warming. The burning and natural decomposition of trees and agricultural matter contributes a large amount of CO2 released to the atmosphere. Biochar can store this carbon in the ground, potentially making a significant reduction in atmospheric GHG levels; at the same time its presence in the earth can improve water quality, increase soil fertility, raise agricultural productivity and reduce pressure on old-growth forests.[3]
Current biochar projects are small scale and make no significant impact on the overall global carbon budget, although expansion of this technique has been advocated as a geoengineering approach. As trees pull down carbon dioxide and release oxygen very efficiently they are already well suited to geoengineering. Further research is in progress, notably by the University of Georgia, which has a dedicated research unit.[4] Agrichar is produced by Best Industries in Australia.
The approach which favors applications that benefit the poorest is gaining traction: in May 2009, the Biochar Fund received a grant from the Congo Basin Forest Fund to implement its concept in Central Africa. In this concept, biochar is a tool used to simultaneously slow down deforestation, increase the food security of rural communities, provide renewable energy to them and sequester carbon.[5]
[edit]History

Pre-Columbian Amazonian natives are believed to have used biochar to enhance soil productivity and made it by smoldering agricultural waste.[6] European settlers called it Terra Preta de Indio.[7] Following observations and experiments by a research team working in French Guiana it has been hypothesized that the Amazonian earthworm Pontoscolex corethrurus was the main agent of fine powdering and incorporation of charcoal debris to the mineral soil.[8]
Biochar is a high-carbon, fine-grained residue which used to be produced using centuries-old techniques by smoldering biomass (i.e., covering burning biomass with soil and letting it smolder). Biochar is another word for charcoal. The ancient method for producing charcoal for native use as fuel (and accidentally as a soil additive) was the “pit” or “trench” method, which created terra preta, or dark soil after abandonment.[9]
[edit]Uses

[edit]Carbon sink potential
See also: Geoengineering
Biochar can sequester carbon in the soil for hundreds to thousands of years, like coal.[2] Modern biochar is being developed using pyrolysis to heat biomass in the absence of oxygen in kilns.[10] However, to the difference of coal and/or petroleum charcoal, when incorporated to the soil in stable organo-mineral aggregates does not freely accumulate in an oxygen-free and abiotic environment. This allows it to be slowly oxygenated and transformed in physically stable but chemically reactive humus, thereby acquiring interesting chemical properties such as cation exchange capacity and buffering of soil acidification. Both are precious in nutrient- and clay-poor tropical soils.[11] Modern biochar production can be combined with biofuel production in a process that may produce 3 to 9 times more energy than invested, is carbon-negative (withdraws more carbon from the atmosphere than it releases) and rebuilds geological carbon sinks.[12] This technique is advocated by prominent scientists such as James Hansen, head of the NASA Goddard Institute for Space Studies,[13] and James Lovelock, creator of the Gaia hypothesis, for mitigation of global warming by greenhouse gas remediation.[14]
Biochar is a high-carbon, fine-grained residue which today is produced through modern pyrolysis processes. Pyrolysis is the direct thermal decomposition of biomass in the absence of oxygen to obtain an array of solid (biochar), liquid (bio-oil) and gas (syngas) products. The specific yield from the pyrolysis is dependent on process conditions, and can be optimized to produce either energy or biochar.[15] Even when optimized to produce char rather than energy, the energy produced per unit energy input is higher than for corn ethanol.[16]
[edit]Use as a carbon sink
Hypothetically, biochar can be used to sequester carbon on centurial or even millennial time scales. In the natural carbon cycle, plant matter decomposes rapidly after the plant dies, which emits CO2; the overall natural cycle is carbon neutral. Instead of allowing the plant matter to decompose, pyrolysis can be used to sequester some of the carbon in a much more stable form. Biochar thus removes circulating CO2 from the atmosphere and stores it in virtually permanent soil carbon pools, making it a carbon-negative process. In places like the Rocky Mountains, where beetles have been killing off vast swathes of pine trees, the utilization of pyrolysis to char the trees instead of letting them decompose into the atmosphere would offset substantial amounts of CO2 emissions.[17] Although some organic matter is necessary for agricultural soil to maintain its productivity, much of the agricultural waste can be turned directly into biochar, bio-oil, and syngas.[18] The use of pyrolysis also provides an opportunity for the processing of municipal waste into useful clean energy rather than increased problems with land space for storage.[19]
Biochar is believed to have long mean residence times in the soil. While the methods by which biochar mineralizes (turns into CO2) are not completely known,[20] evidence from soil samples in the Amazon shows large concentrations of black carbon (biochar) remaining after they were abandoned thousands of years ago.[21] The amount of time the biochar will remain in the soil depends on the feedstock material, how charred the material is, the surface:volume ratio of the particles, and the conditions of the soil the biochar is placed in.[22] Estimates for the residence time range from 100 to 10,000 yrs, with 5,000 being a common estimate.[23] Lab experiments confirm a decrease in carbon mineralization with increasing temperature, so carefully controlled charring of plant matter can increase the soil residence time of the biochar C.[24]
Under some circumstances, the addition of biochar to the soil has been found to accelerate the mineralization of the existing soil organic matter, probably from the excessive potash and increased pH from biochar[25] but this would only reduce and not suppress the net benefit gained by sequestering carbon in the soil by this method. Furthermore, the suggested soil conditions for the integration of biochar are in heavily degraded tropical soils used for agriculture, not organic matter-rich boreal forest soils (as tested in the above reference).
Johannes Lehmann, of Cornell University, estimates that pyrolysis can be cost-effective for a combination of sequestration and energy production when the cost of a CO2 ton reaches $37.[26] As of mid-February 2010, CO2 is trading at $16.82/ton on the European Climate Exchange (ECX), so using pyrolysis for bioenergy production may be feasible even if it is more expensive than fossil fuels.
The technology for biochar sequestration does not require a fundamental scientific advance. The underlying production technology is robust and simple, making it appropriate for many regions of the world.[27]
[edit]Positive and negative effects on soil
Biochar may be a substance mostly suited to severely weathered and deprived soils (low pH, absent potassium, low or no humus). Clearly, there is the real potential for carbon sequestration, simply because biochar is so stable and is not accessible to normal microbial decay. Soils require active carbon to maintain micro and macro populations, not the inactive form found in biochar.[28] Biochar can prevent the leaching of nutrients out of the soil, partly because it absorbs and immobilizes certain amounts of nutrients, however, too much immobilization can be harmful.[29][30] It has been reported to increase the available nutrients for plant growth, but also depress them [31][32] increase water retention,[33] and reduce the amount of fertilizer required. Additionally, it has been shown to decrease N2O (Nitrous oxide) and CH4 (methane) emissions from soil, thus further reducing GHG emissions.[34] Although it is far from a perfect solution in all economies, biochar can be utilized in many applications as a replacement for or co-terminous strategy with other bioenergy production strategies.[35]
[edit]Co-benefits for soil of pyrolysis
Biochar can be used as a soil amendment to affect plant growth yield, but only for plants that love high potash and elevated pH,[36] improve water quality, reduce soil emissions of GHGs, reduce leaching of nutrients, reduce soil acidity, and reduce irrigation and fertilizer requirements.[37]
These positive qualities are dependent on the properties of the biochar,[38] and may depend on regional conditions including soil type, condition (depleted or healthy), temperature, and humidity.[39] Modest additions of biochar to soil were found to reduce N2O emissions by up to 80% and completely suppress methane emissions.[40]
Pollutants such as metals and pesticides seep into the Earth's soil and contaminate the food supply. This pollution reduces the amount of land suitable for agricultural production and contributes to global food shortages. Studies have reported positive effects to crop production in highly degraded and nutrient poor soils.[41] Biochars can be designed to have specific qualities that can target distinct properties of soils.[42] Application of biochar reduces leaching of critical nutrients, creates a higher crop uptake of nutrients, while also providing greater soil availability of nutrients.[43] Biochar added at 10% levels reduced contaminant levels in plants by up to 80%, while reducing total chlordane and DDX content in the plants by 68 and 79%, respectively.[44]
[edit]Animal feed
Before incorporating biochar into the soil, it also has use as dietary supplement for animals, and traditionally as charcoal biscuits for humans. These reports are possibly dubious however, and a veterinary surgeon / veterinarian should be consulted before animals are exposed. The effects of this are to provide additional minerals, maintain a healthy digestive system, reduce flatulence (which is a source of methane), and reduce the odour of and ammonia emissions from slurry (i.e. sweeten the dung). However raising the pH of dung causes huge ammonia-N losses, so this practice is also dubious. Use of highly alkaline and especially high potash biochar in animal grazing systems could lead directly to grass tetany, a severe and sudden ailment that is often fatal to milking cows.
[edit]Slash and char
Switching from slash and burn to slash and char techniques in Brazil can decrease both deforestation of the Amazon and carbon dioxide emission, as well as increase the crop yield. Under the current method of slash and burn, only 3% of the carbon from the organic material is left in the soil.[45]
Switching to slash and char can sequester up to 50% of the carbon in a highly stable form.[46] Adding the biochar back into the soil rather than removing it all for energy production is necessary to avoid heavy increases in the cost and emissions from more required nitrogen fertilizers.[47] Additionally, by improving the soil tilth, fertility, and productivity, the biochar enhanced soils can sustain agricultural production, whereas non-amended soils quickly become depleted of nutrients, and the fields are abandoned, leading to a continuous slash and burn cycle and the continued loss of tropical rainforest. Using pyrolysis to produce bio-energy also has the added benefit of not requiring infrastructure changes the way processing biomass for cellulosic ethanol does. Additionally, the biochar produced can be applied by the currently used tillage machinery or equipment used to apply fertilizer.[48]

That'll do for a start.

[Joe Hillshoist]

Just quickly for now ...

I've been doing this for years. It was kind of serendipitous how I started.

I used to have a fire pit, its still there and I use it sometimes. Years ago we did a hungi. Burned shitloads of wood to get the temp up then sealed it to cook the food. This created charcoal in the pit, and I just started using it, originally for the potash.

I used the ash on its own and as it ran out the charcoal a bit as well, around the same time I was digging a garden and about 2 feet underground was the top of a burnt stump. Someone had tried to burn the stump out then buried it I assume. This bed was and still is very productive (well I haven't grown anything much in the garden since spring last year cos of the rain we have had, but for the decade beforehand it did well...)

I noticed that bed and the ones I added charcoal to performed better than the ones that just had ash added. I dug out the bed and put the potash and charcoal underneath the plants primarily, then top dressed a little later on. Dunno why.

The soil activity seemed better in the soil with charcoal.

I don't think its a matter of nutrients alone.

My theory is that, rather than acting as a fertilizer, the charcoal acts like a filter for toxins, as well as a spacer for the soil. It may also help the soil retain moisture.

IMO this is a sound theory. By "spacer" do you mean something that contributes to soil structure? Cos I reckon that is a big part of it. To me the most successful organic gardens seem dependent not on the nutrients etc etc but on a thriving soil biology. I guess the default assumption there is that if the soil ecosystems are healthy then the nutrients will automatically be available as waste products from the critters and fungi in the soil.

That seems to be where the real strength of biochar is. Not the additional nutrients but the facilitation of an environment that makes the nutrients available and easily accessible to the plants. It conmtributes to the overall health of the soil, and while this might not directly provide nutrients to the plants the environment it helps create does. I'm sure it provides some nutrients, but I wouldn't rely on it. Thats what compost is for.

And if you want you can add charcoal to your compost. It might require some tweaking but it seems to work just as well. (The charcoal doesn't break down, it still provides the structure.) But I haven't done this very often. It seems to work, but its hard to tell if it does anything really different.

[Iamwhomiam]

Well, alwyn, just couldn't wait a day or so for me to begin "The Fallacy of Biochar as a Beneficial Soil Amendment," could you. Just had to get your misinformation out there first, huh.

Ok, I hope you realize there are people wiser than you in their knowledge of biochemistry and that your wiki info is severely flawed and extremely biased.

About charcoal in soil being a beneficial atmospheric carbon sink:

First, the term “biochar” was invented by Peter Read (one of the most outspoken lobbyists for vast ‘biochar’ plantations) to describe charcoal used as a soil amendment for agriculture.

‘Biochar’, a new big threat to people, land, and ecosystems

Keep ‘biochar’ and soils out of carbon trading

Caution urged against proposals for large scale use of charcoal in soils for climate change mitigation and soil reclamation

Adding charcoal (‘biochar’) to the soil has been proposed as a ‘climate change mitigation’ strategy and as a means of regenerating degraded land. Some even claim that this could sequester so much carbon that the Earth could return to pre-industrial carbon dioxide levels, i.e. that all the global warming caused by fossil fuel burning and ecosystem destruction could be reversed. Such large-scale production of charcoal would require many hundreds of millions of hectares of land for biomass production (primarily tree plantations). This is an attempt to manipulate the biosphere and land use on a vast scale in order to alter the global climate, which makes it a form of ‘geo-engineering’.

As the unfolding disaster of agrofuels clearly demonstrates, such major land-conversion poses a major threat to biodiversity and ecosystems that play an essential role in stabilising and regulating the climate and are necessary to ensure food and water security. It threatens the livelihoods of many communities, including indigenous peoples.

‘Biochar’ and agrofuels are closely linked: Charcoal is a byproduct from a type of bioenergy production which can also be used to make second-generation agrofuels, i.e. liquid agrofuels from wood, straw, bagasse, palm kernel residues and other types of solid biomass.

Eleven African governments have called for agricultural soils in general and ‘biochar’ in particular to be included into carbon trading. Their submission indicates that they seek to increase “private sector financing” (and by implication corporate control) over rural areas in the South, and to link this to proposals for including forests in carbon trading (i.e. the mechanisms for Reducing Emissions from Deforestation and Degradation or REDD being negotiated at present). Those REDD proposals have met with opposition on the basis that they commodify forest ecosystems with dire implications for indigenous peoples and biodiversity. The inclusion of soils into those mechanisms would further extend such serious impacts.

Proposals for ‘climate change mitigation’ through large-scale adoption of ‘biochar’ are a dangerous form of geo-engineering based on unfounded claims.
A lobby group (the International Biochar Initiative) made up largely of startup ‘biochar’ and agrofuel companies and academics, many of them with related commercial interests, are behind the push for ‘biochar’. Their extremely bold claims are not founded in scientific understanding.

+ It is not yet known whether charcoal in soil represents a ‘carbon sink’ at all. Industrial charcoal is very different from Terra Preta, the highly fertile and carbon-rich soils found in Central Amazonia which were created by indigenous peoples hundreds and even thousands of years ago. ‘Biochar’ companies and researchers have not been able to recreate Terra Preta.

+ ‘Biochar’ advocates are promoting ‘targets’ which would require the use of 500 million hectares or more of land to be used for producing charcoal plus energy. Industrial monocultures of fast growing trees and other feedstocks for the pulp and paper industry and for agrofuels are already creating severe social and environmental impacts which worsen climate change. This very large new demand for ‘biochar’ would greatly exacerbate these problems.

+ There is a risk that ‘biochar’ could in future be used to promote the development of genetically engineered (GE) tree varieties specifically engineered for ‘biochar’ production or to try and extend the range of fast-growing trees, both of which could have very serious ecological impacts.

+ There is no consistent evidence that charcoal can be relied upon to make soil more fertile. Industrial charcoal production at the expense of organic matter needed for making humus could have the opposite results.

+ Combinations of charcoal with fossil fuel-based fertilisers made from scrubbing coal power plant flue gases are being promoted as ‘biochar’, and those will help to perpetuate fossil fuel burning as well as emissions of nitrous oxide, a powerful greenhouse gas.

+ The process for making charcoal and energy (pyrolysis) can result in dangerous soil and air pollution.

Turning soils into a commodity is profitable to industry but disastrous for the poor.
Several patent applications have been made for charcoal use in soil and for pyrolysis with charcoal production. If granted, those will ensure that any future profits from the technology will go to companies, not communities. Given that successful strategies for combining charcoal with diverse biomass in soils were developed by indigenous peoples, ‘biochar’ patenting raises serious concerns over biopiracy. The inclusion of soils in carbon markets, just like the inclusion forests in carbon trading will increase corporate control over vital resources and the exclusion of smallholder farmers, rural communities and indigenous peoples.

The Clean Development Mechanism (CDM) has perpetuated, rather than reduced fossil fuel burning by permitting industries to purchase “rights to pollute” and further delaying the social and economic changes which are essential for addressing climate change. The climate impacts of fossil fuel burning are irreversible, yet so-called ‘soil carbon sinks’ are highly uncertain and temporary.

We strongly oppose the inclusion of soils in carbon trade and offset mechanisms, including in the Clean Development Mechanism.

The ‘biochar’ initiative fails to address the root causes of climate change: Fossil fuel burning and ecosystem destruction, including deforestation and the destruction of healthy soils through industrial agriculture.

Small-scale agro-ecological farming and protection of natural ecosystem are effective ways to mitigate the impacts of climate change. These proven alternatives should be fully supported, not risky, unfounded technologies promoted by vested commercial interests. Indigenous and peasant communities have developed many diverse means of caring for soils and biodiversity, and living sustainably. Those locally and culturally adapted methods depend on regional climate, soils, crops and biodiversity. Attempts to commodify soils and impose a “one-size-fits all” approach to soils and farming risks appropriating, undermining and destroying this knowledge and diversity just when it is most critically needed.

If your organization wishes to support this declaration, or for questions or comments please send an e-mail containing the name of your organization and country to biochar_concerns@yahoo.co.uk
The ‘biochar’ initiative fails to address the root causes of climate change: Fossil fuel burning and ecosystem destruction, including deforestation and the destruction of healthy soils through industrial agriculture.
hoo.co.uk


Signatures:

Biofuelwatch (UK)
CENSAT Agua Viva (Friends of the Earth Colombia)
Down to Earth (UK)
EcoNexus (UK)
Energy Justice Network (US)
ETC Group
Food First (US)
Friends of the Siberian Forest (Russia)
Global Justice Ecology Project (US)
Grupo de Reflexion Rural (Argentina)
NOAH (Friends of the Earth Denmark)
PIPEC
Rettet den Regenwald e.V. (Germany)
Salva la Selva
World Rainforest Movement

BACKGROUND NOTES

‘Biochar’ is a term used to describe charcoal (generally fine-grained charcoal) when it is applied to soils). It is produced through a process called biomass pyrolysis. This involves exposing biomass to high temperatures in the absence of oxygen. It produces two types of fuel (syngas and bio-oil) as well as charcoal as a byproduct.

‘Biochar’ proponents claim that the biomass which they use is carbon neutral – a claim which ignores the fact that it will primarily come from industrial agriculture and tree plantations, which are associated with very high greenhouse gas emissions from organic soil carbon losses, destruction of natural vegetation, energy and synthetic fertiliser use. They further claim that the carbon retained in the charcoal (usually 20-50% of the original carbon in the biomass) will, if the charcoal is added to soil, permanently remain there and that this makes the process ‘carbon negative’, allowing it to reduce concentrations of carbon dioxide in the atmosphere. They also claim that adding charcoal will make soils permanently more fertile. Each of these claims is highly questionable and none of them is scientifically proven.

1) Does charcoal represent a ‘carbon sink’?

‘Biochar’ proponents are suggesting that industrial charcoal can be compared with Terra Preta, highly fertile and carbon-rich soils found in Central Amazonia which were created by indigenous peoples hundreds and even thousands of years ago, through the use of charcoal combined with highly diverse biomass. The success of Terra Preta has not been replicated. Modern ‘biochar’ is highly variable and results vary greatly depending upon the type of soil, the type of material used for making charcoal, and other factors. In some cases, charcoal addition has been shown to increase soil carbon losses by stimulating microbial breakdown of non-charcoal organic matter. Some microbes also can breakdown charcoal. While some charcoal does remain in soil for long periods, this is not always the case. No (even remotely) long term studies of modern ‘biochar’ exist. The impacts of tilling large areas of soil in order to incorporate ‘biochar’ are not known either. ‘Biochar’ at or near the surface may increase ‘black soot’ in the atmosphere, which is a major contributor to global warming. To avoid this, the charcoal would need to be tilled deep into the soil. Yet this tilling would disrupt and alter soil structure and cause significant releases of CO2 into the atmosphere. Claims that ‘biochar’ in soils provide a “permanent carbon sink” are false.

2) What would the likely impacts be of growing sufficient quantities of feedstock for ‘biochar’ as a climate geoengineering strategy?

Advocates of ‘biochar’ suggest growing vast tree and crop plantations, (on the order of at least 500 million hectares) for conversion to charcoal. As the disastrous impacts of industrial plantations for pulp and paper and for agrofuels have already shown, land-conversion on this scale poses a major threat to biodiversity and ecosystems, displaces communities, interferes with food production and degrades soil and freshwater resources. The proposed use of ‘agricultural and forestry residues’ is based on unrealistic assessments of the availability of such materials, the removal of which deprives soils of nutrients and organic matter, encourages erosion, and reduces critical habitat for biodiversity.

3) What will the effects of charcoal addition be on soil?

Advocates for ‘biochar’ claim that it improves soil fertility, reducing the need for chemical fertilizers and improves water retention. Yet the small number of studies that have been done show varying results, including, in some cases the exact reverse, i.e. declines in productivity. Again, no long term studies exist. In fact, much of the ‘biochar’ research and development focuses on charcoal combined with synthetic fertilizer, and charcoal ‘enhanced’ with flue gases ‘scrubbed’ from coal power plants (ammonium bicarbonate). The impact of large-scale biochar application and the mechanical disturbances involved in tilling it into soils on soil microbial diversity are unknown, but are deeply concerning on such a massive scale.

4) What other impacts need to be considered?
Pyrolysis can result in air pollution and particulate emissions known to have serious impacts on human health. As with conventional incineration, toxins contained within feedstocks are emitted into the air or retained in ash or and charcoal Some biochar companies are already using a wide variety of “wastes” which can include treated wood, crop residues that have been sprayed with agrichemicals, plastics, used tyres or coal mixed with other biomass. The impact of adding large quantities of potentially toxin-laden charcoal into soils must be assessed, along with air emissions from pyrolysis.

Summary:

In the face of such major scientific uncertainties, policy support for commercialising and scaling up this technology is extremely risky and not justified. The risk of severely worsening rather than mitigating climate change exists if emissions from land use change, from soil disruption, or from unanticipated soil carbon or ‘biochar’ carbon losses occur.

For further information and references see “Biochar for Climate Change Mitigation: Fact of Fiction?”, Almuth Ernsting and Rachel Smolker, http://www.biofuelwatch.org.uk/docs/biocharbriefing.pdf

[Iamwhomiam]

Below is a two-part article written by an expert in the field, an editor of BioCycle Magazine, Dr. Sally Brown. As you will see, it is the compost that provides the nutrients present in terra preta, but some ingnore this fact and believe it's mostly due to the carbon in the charcoal. As I've said, biochar is to soil as a vitamin pill is to a human; without food (compost), its benefit is severely diminished.

Dr. Brown's two-part article is educational and explains why biochar is unhealthy, a waste of money and energy and why compost is extremely beneficial and the better choice to use to replenish nutrient depleted solis. A healhy soil and the plants that thrive in it are far better at carbon sequestration than a depleted soil treated with biochar.

Both articles can be found here.

Pyrolysis For Char Part I

BioCycle February 2009, Vol. 50, No. 2, p. 44

Climate Change Connections

Sally Brown

THIS month, instead of simply ranting about one topic or another, I thought it might be a nice change of pace to actually provide some information. After you read the column and digest the information, you can decide for yourself if and how you would like to rant about it. What prompted this mature decision were about 20 references to biochar within a one-week period. If you recall, biochar is the carbon soil amendment that is all the rage in soil and organics circles. This is because biochar is seen as the source of fertility for the ancient Terra preta soils in Brazil . Arguments go, “If it was good enough for the Amazon, it is going to be great for us.” Production of char is being looked at as an alternative to landfilling, composting and a range of other organics management options.

This is a topic that gets me ranting very easily. In fact, I have already devoted a column to ranting about char (see “Use What Works? How Novel!” March 2008). During the one-week period that prompted this second column, I was at a Washington Organics Recycling Council meeting. When you say the WORC meeting in Washington , people say, “Oh the compost meeting.” In this particular case it should have been referred to as the char meeting, as three speakers in a row got up and talked about biochar. I got back from the meeting, checked my email and found several messages from the Seattle biochar worship association (that may not be the exact name, but you get the point).

So, now it is time for you make your own judgment about char — after this column and the next one. This month I’ll provide information on pyrolysis, the process that produces char. I’ll do this with some comparisons to anaerobic digestion. Next month I’ll sound more like a soil chemist (what I was actually trained to know in grad school) and talk about char for soil, with compost or materials from anaerobic digesters used as a basis for comparison.

SIMPLE DEFINITION

Pyrolysis is the combustion process used to produce char. Pyrolysis is one type of thermolysis, meaning a way to chemically alter things using heat. It is a term used for combustion with limited oxygen, generally under elevated temperature and pressure.

Pyrolysis is a process that we’ve all seen. When you burn wood and stare at the pretty fire, you are actually looking, in part, at a pyrolysis reaction. In a normal fire, like a wood stove, the carbon compounds in the wood are gradually turned into gas as the wood heats up. This gas consists mostly of shorter chain (simple) carbon compounds like phenols, aromatics, methane and carbon dioxide, whereas the wood consists of more complex, longer chain compounds like cellulose and lignin.

In a normal fire, the pyrolysis gas starts to burn the minute it gets enough oxygen to fully combust (i.e., to oxidize to CO2 and H2O). In a fireplace with a log, that happens just a few millimeters past the log, where you see the flame. When you look at the fire, you aren’t seeing the wood burn, you are seeing the pyrolysis gasses released from the wood burn. In a pyrolysis reactor, sufficient heat is present to alter the carbon compounds in the feedstock, however there isn’t enough oxygen to allow actual combustion with a flame.

Pyrolysis facilities don’t have to be high-tech. In our house we have a wood stove. To get it going, we keep the vents wide open. This lets plenty of oxygen in and the pyrolysis is followed rapidly by combustion. We get a pretty fire. At night before bed, we load up the stove and shut all of the vents to reduce the oxygen supply and slow the combustion process. This takes it to pyrolysis alone. Some mornings we come downstairs and find wood with some blackened edges. The fire wasn’t hot enough when we took away the oxygen and it just went out. However, many mornings, we come downstairs and find charcoal from incomplete combustion. This is the primary product you get if you have pyrolysis for extended times at low heat. This is char.

So the process of combustion is basically: 1) Fuel heats up; 2) Pyrolysis starts to happen, forming volatile gases; 3) Gas hits oxygen and combusts. If you control the reaction to eliminate step three, you have pyrolysis.

PYROLYSIS PRODUCTS

The pyrolysis process creates three products: gas, a liquid and char. The gas and liquid are each comprised of a variety of different carbon compounds. Both have use as fuel.

The gas is called syngas and is similar in many ways to natural gas. If the gas is allowed to cool before it contacts oxygen it will produce the liquid or tar. This liquid is often called “biocrude” and can be used like unrefined oil. In fact, pyrolysis is a process used in crude oil processing. You also get the char, which is basically concentrated carbon. The char can also be used as a fuel (think of mesquite grilled steaks or salmon). It can also be used as a soil amendment.

The amount of gas, liquid or char produced depends on a number of factors including feedstocks, time and temperature. Typical reaction temperatures for pyrolysis range from 200° to 600°C. At higher temperatures, often called flash pyrolysis, higher concentrations of gas are produced. At low temperatures and long periods of time, production of char is highest. Pyrolysis under these conditions can also be called carbonization and is the commonly used process to make charcoal. It doesn’t require fancy highly engineered systems. Burning waste under a soil cover is likely what produced the Terra preta soils in Brazil and would be considered a carbonization process.

In any version of this process, a certain amount of the energy contained in the feedstocks is required to generate the heat required to maintain this process. If you are running a crude facility with the goal of producing charcoal, you won’t need to completely dry the feedstocks before you start. Material just has to be dry enough to burn on its own and suck all of the oxygen out of the system with sufficient heat remaining to continue to transform. This would be a solids content of 40 to 60 percent, I’d guess. For more highly controlled facilities where you want more than just char, drying feedstocks is required, as the water vapor in the gas will be a contaminant that will lessen the value of the syngas and biocrude.

A review paper by S. Yaman (2003) gives a very long list of different feedstocks that have been processed with pyrolysis. Reaction products vary with the conditions and you can alter conditions to maximize production of one of the three products. With wood, the volatile content is about 70 to 90 percent of the total dry weight. After complete pyrolysis, the remaining char would be about 10 to 30 percent of the original dry solids.

Renewable Energy Resources (Twidell & Weir, 2006, 2nd ed.) puts maximum char yield at 25 to 35 percent of dry biomass input.

In addition to chemically altering the carbon, pyrolysis changes the chemical forms of other ions in the feedstocks. At the temperatures used in pyrolysis, all of the nitrogen in the feedstocks will volatilize and be lost to the system. Other nutrients will likely form oxides like calcium oxide or potassium oxide. Just as wood ash makes a good fertilizer for certain ions, there is a potential that char would also provide plant nutrients — except for nitrogen that is.

COMPARISON WITH ANAEROBIC DIGESTION

So that is pyrolysis. How is it different from anaerobic digestion (AD), which also produces chemical changes in the carbon in the feedstocks? With AD, these changes are brought about by microbes rather than by heat. AD is a feeding frenzy for methanogenic bacteria. These creatures can eat carbon, just like we do, but they can do it without oxygen. Electrons released from the carbon they eat get stuffed onto other carbon compounds and produce methane. So if a microbe wanted to eat a good pound of carbohydrates, a portion of that pound would be converted into microbial biomass (think of a microbe with a big gut). Another portion would evolve into CO2 and methane (CH4), with a little bit left over as an indigestible carbon compound.

This process requires heat, as the microbes are hungrier and more active in a mesophillic environment (about 30°C). It also requires moisture, with wet (traditional) anaerobic digesters operating at about 2 to 7 percent solids and dry digesters operating at a solids content greater than 15 percent. Not all types of carbon compounds can decompose under anaerobic conditions. Lignin, for example, doesn’t change a whole bunch.

AD also takes some time. Retention time in digesters for food waste generally averages 10 to 15 days. In wastewater treatment, longer retention times are common, sometimes in excess of 30 days. Another thing about AD is that the nutrients don’t go anywhere. As it is a microbial transformation, rather than a purely abiotic one, the only nitrogen that is lost to gas is the stuff that was initially present as nitrate to begin with. Most of the nitrogen in these systems is present as organic nitrogen and is conserved in the digestion process. So is the phosphorus and the micronutrients.

So much for Part I. Stay tuned for Part II.

Sally Brown — Research Associate Professor at the University of Washington in Seattle — is a member of BioCycle’s Editorial Board, and authors this regular column on the connections of composting, organics recycling and renewable energy to climate change. E-mail Dr. Brown at slb@u.washington.edu.

~~~~~~~~~~~~~~~~~~~~~~~~~~

The Char And Compost Face-Off, Part II

BioCycle March 2009, Vol. 50, No. 3, p. 44

Climate Change Connections

Sally Brown

I ENDED Part I of this column in the February issue drawing distinctions between pyrolysis and anaerobic digestion, setting the stage for this month’s comparison of the end products from each process — char versus digestate, or more generally, char versus compost (which can be produced from digestate). As it turns out, Part II is really a discussion about soils, and what each by-product brings to the table in terms of soil benefits.

Both pyrolysis and anaerobic digestion produce a high carbon residual that can be used as a soil amendment. So in both cases, if you add the char from pyrolysis or the digestate (straight or composted) to soils you are adding carbon to the soil, which is always a good thing. Carbon in soils has a wide range of functions and adding carbon has beneficial effects on almost every soil property you can name — chemical, physical and biological.

These cover things like soil tilth, nutrient availability, water holding capacity, cation exchange capacity, bulk density, aggregation and the list goes on. In some cases, these properties are all connected, like the hipbone being connected to the knee bone. In other cases, they can function independently.

But all carbon is not created equal. The same way that all potatoes are not created equal. Comparing a naked baked potato to one mashed with heavy cream and lots of butter and salt is a way to explain differences in potatoes. Maybe a good way to explain differences in soil is to go through some major soil properties that carbon can influence, and explain how char might work in comparison to compost.

NUTRIENTS FIRST

Nutrients are a fine place to start. Both char and compost are likely to provide a fraction of necessary plant nutrient requirements with one major exception. All of the nitrogen in the feedstocks that undergo pyrolysis is lost; it turns into nitrogen gas when the temperature gets high. For anaerobic digestion, nitrogen is conserved and is generally added as organic N to soils. If you compost digestate before land application, a fraction of the nitrogen can be lost when it gets transformed from organic nitrogen into ammonia.

However, a very large portion of the nitrogen stays put as organic N. In fact, compost is often used as the only nitrogen source for a crop. When that organic carbon with the nitrogen seasoning is added to the soil, soil microbes begin to feast, and as they eat this organic matter, they release nitrogen that is taken up by plants, which then return the N back to the soil as organic nitrogen and the cycle begins again. This same type of cycle goes on with all of the other nutrients in compost-amended soils.

Compost also holds onto nutrients in the soil because of its high surface area and internal charge, like a sponge with magnets. With these magnets (the technical term for these is cation exchange capacity), the carbon in the compost can hold nutrients and prevent them from leaching out of the soil. On a recent soil sampling field trip in California , we saw that compost increased plant available phosphorus, zinc, copper, iron and sometimes manganese and magnesium in soils. So with compost or digestate application, you get nutrients via the slow release breakdown of organics, increased microbial activity to recycle those nutrients, and magnets to hold onto those nutrients that are just waiting around.

Char also adds these other nutrients, but holds them via this cation exchange capacity rather than as part of the organic compounds. In other words, you just get the magnets and none of the cycling stuff. It’s like getting your nutrients from vitamins instead of a feast. Char is not in the least bit appetizing to soil microorganisms. The carbon in the char is very difficult to digest. The nutrients that don’t volatilize from the feedstock are added to the soil with the char, most likely as oxides. As these oxides dissolve, the magnets in the char can hold onto the nutrients and make them plant available. Char does nothing for nutrient cycling via microbial decomposition. So for char, nutrients are all the vitamins, with no calories and no flavor.

SOIL WATER HOLDING CAPACITY

Next up in the comparison is soil water holding capacity. The amount of water that falls on top of the soil — and actually goes into the soil and stays there — determines how drought resistant a soil is, how efficiently it can supply water to plants and how much water is needed for plants to prosper. This is a function of many factors. For example, how much water infiltrates into the soil depends on the bulk density of the soil. Soils are made mostly of different types of ground up/weathered rocks (clay, silt and sand particles) and pore space. If the soil only consisted of the rocks and no pore space, each cubic centimeter of soil would weigh 2.6 grams. Because of the pore space, a much more common weight is 1.5 g. Now, depending on how the clay, silt and sand particles are held together, that bulk density can get down below 1 g per cm3. The less dense the soil, the more room there is for water and the faster the water can flow into the soil.

The glue that holds the particles together and helps reduce bulk density is organic matter. As bacteria eat the organic matter, they produce waste and the waste carbon works like a glue to cement particles of soil together. This is what gives you good tilth in soil. This same type of action is one of the things that makes earthworm castes so desirable. As the carbon in compost is very tasty, compost addition to soils supplies plenty of that glue action. It also doesn’t hurt that the weight of organic matter is pretty low, usually about .25 g per cm3. Better yet, the organic carbon itself can hold an order of magnitude more than its weight in water, and then some. Just like a sponge.

Now you probably have guessed this, but I am going to tell you anyway. Compost gives you the glue and the water holding capacity. Char just gives you the water holding capacity, not the structure and tilth. Water holding capacity is good, don’t get me wrong.

It just helps if the water can get into the soil first so that the soil can store water instead of just letting it run off of the surface. In other words, the glue (aka organic matter) holds the particles together, making the soil porous so that the water can flow in.

AND THEN THERE’S CARBON STORAGE

You may be catching on to a pattern here: The compost serves up all the benefits, whereas the char supplies a minor helping. Well how about carbon storage in soils? Char is often touted as a wonderful means to sequester carbon in soils. Soil carbon storage is great, a fast and largely underappreciated way to store carbon. And when you put char in the soil it stays there a very long time. Why? Well who would want it, that is the main reason. Because it is unavailable to microbes and other soil biota, char sits there.

As I’ve made abundantly clear, compost is tasty and is eaten up. Of course, compost isn’t nearly as tasty as fresh plant residues or even digestate because the carbon in the compost has already gone through several digestive cycles, making it more recalcitrant than fresh organic matter. But it is a whole lot better to eat than char. So the carbon in compost gets eaten. A portion of what gets eaten volatilizes as CO2; another portion gets returned to soil as more recalcitrant organic matter, and humic and fulvic acids. But here’s the deal: While that piece of compost may get eaten and some of it may volatilize, that meal makes the soil a happier and better functioning environment. So plants grow better, and deposit even more carbon, and more of that gets eaten and some of that stays behind. And the cycle continues, building soil tilth, recycling nutrients and increasing soil carbon reserves.

Those biochar-enriched Terra preta soils in Brazil that I mentioned in Part I are vastly improved over their neighbors. But their neighbors are in very bad shape. It may be that the improved ability of the Terra preta soils to hold onto nutrients and water was enough to get that improved growth and cycling going. Our soils, while depleted, are nowhere near as weathered and nutrient poor as the Brazilian soils. So while our soils are almost definitely going to respond to compost addition, there is a good chance that char application to soils will get them as excited as a naked baked potato.

Sally Brown — Research Associate Professor at the University of Washington in Seattle — is a member of BioCycle’s Editorial Board, and authors this regular column on the connections of composting, organics recycling and renewable energy to climate change.

E-mail Dr. Brown at slb@u.washington.edu. Andrew Trlica, who is working with Sally Brown on his Masters of Science, provided much of the basics on pyrolysis for Part I.

~~~~~~~~~~~~~~~~~~~

Another important 110 page report on the benefits of composting would be Beyond Recycling ~ Composting food scraps and soiled paper which can be found here.

[Joe Hillshoist]

I'd just point out there is a massive difference between what I'm talking about and the wholescale industrial production of "biochar" as described in your post Iamwhoiam.

Research on biochar is clearly indicating that there simply is no “one-size-fits-all” biochar
solution, that many critically important issues remain poorly understood, and that there are
likely to be serious and unpredictable negative impacts if this technology is adopted on a large
scale.

Thats too true tho. Using anything on your soil has to be a matter of whats appropriate for local conditions. Note the S American thing ... a particular species of earthworm is associated with the production of terra preta. That seems to imply that adding charcoal on its own isn't enough to achieve the results we are hoping for. Its the charcoal in a particular situation with an environment that can take advantage of it.

From the post you put in while I was typing this:

The compost serves up all the benefits, whereas the char supplies a minor helping.

I wouldn't argue with that. i think its spot on. I think the two complement each other here tho.

Anyway:

http://www.abc.net.au/rn/scienceshow/stories/2011/3198213.htm

[alwyn]

Well, alwyn, just couldn't wait a day or so for me to begin "The Fallacy of Biochar as a Beneficial Soil Amendment," could you. Just had to get your misinformation out there first, huh.

Sorry. Was I supposed to wait with baited breath for you to grace me with your wisdom? You said you were busy.

Ok, I hope you realize there are people wiser than you in their knowledge of biochemistry and that your wiki info is severely flawed and extremely biased.

Sure I know that. But I know about farming my vegetables, 'cause I've been feeding my family for 15 years that way. I only put the Wiki link up to get the conversation rolling.

It is unfortunate that this culture subscribes to "if a little of something must be good for you, then more must be better". If bio-char means wholesale destruction and industrial applications, then I want a different word. 'Cause the charcoal under my rows makes the beds perform better.

I started out using compost and organic amendments. The charcoal was an experiment after reading about the Tierra Preta. Plus, I had dead trees to burn. So, what am I going to believe? My lying eyes? Or another scientific report?

I know I grow damn good vegetables! And I had beds with charcoal side by side with beds without it. The char beds outperformed the beds lacking in it. I never said nuthin 'bout only using char, ever.

Joe, there is a theory out there that carbon is conductive, (can't remember which site right now, sorry) and that there is an advantage in an increased electrical charge available to the plants that helps them grow.

[Iamwhomiam]

Believe what you will and follow whichever practice you prefer... makes little difference to me what you do or don't do, alwyn. If you believe that making charcoal is better for your environment than letting nature take its due course, well, I would just say that I think it's wrong-minded and factually incorrect.

You believe the carbon you put in your garden is beneficial; I don't, at least not to the degree you do. It just doesn't hold water... or nutrients. I believe compost is much more beneficial and more closely mimics nature, is nutrient rich, provides a hospitable environment for beneficial bacteria and insects and holds water more effectively.

I won't argue the point further. I only wanted to offer a better understanding of the inefficiencies of biochar. I've done that.

Hey, some people are convinced Nuclear Energy is safe...

Joe, small or large scale, biochar, charcoal as a soil amendment, is really not all that helpful to the health of one's garden or fields or the environment. The naturally decaying organic matter in compost provides the most beneficial environment for the insects and bacteria that are necessary to further break-down the material to form a nutrient rich soil and it also sequesters carbon much more effectively and releases it slowly over time in a form that plants can and do absorb. Do as you will.

I wish you both well.

[Nordic]

Does charcoal count as ash? Because I've always read that ash (like potash) is good for a garden due to the potassium that's freed up in it.

I used to mix in a few shovelfuls of ashes from my fireplace to my compost. The results seemed pretty great, but who knows how much the ash had to do with it? I sure don't.

[Joe Hillshoist]

Nah thats potash.

Heaps of potassium in it. Its great for the compost.

[wintler2]

Charcoal is carbon, nearly pure carbon, so of course it is not going to provide any nitrogen, potassium, phosphorous, or any other macro or micro nutrient.
But its not meant to, and nobody claims that the charcoal itself provides nutrients - thats simply impossible.

What charcoal does do is provide a very very large surface area per volume, and that surface area is handily subdivided into fissures and slots of every conceivable tiny size and shape, and is hydrophilic and biologically benign. This provides a superb space to act as a reserve both of nutrients ('stored'/adhering when in abundance) and of soil biota, the latter benefiting greatly from the never-dry properties of the smallest fissures in a a charcoal fragment (water tension is unmovable at v.small scales). Think of it as like incised rainforest gorges that preserve species as drought scorches the plain above.

To actually get beneficial soil organisms into charcoal to really benefit soils requires post-fire composting, and that is what most researchers are doing. Charcoal appears able to absorb both biota and nutrients and deliver these to plants, rather than just dumping them in the soil as chemical ag and alot of plain composting does. Compost is nearly all labile/rapidly decomposed, and so growers are forced to add new at least every few years, and resign themselves to much of the benefit being washes thru the soil. Charcoal buffers the nutrient flow. Not all charcoal is the same, Dept Primary Industries NSW apparently have over 50 classes of char depending on origin and firing. They're doing a little work on it..

http://www.dpi.nsw.gov.au/research/topics/biochar
NSW DPI is running the world's largest demonstration of biochar, with over 150 field plots under management. ..

See link for vid & links, published papers, contacts for researchers etc.

I first tried it myself 4 years ago, have increased the bed area incorporating charcoal each year since. We put char in with compost and chook poo in raised wicking beds, easily 50% better growth than my best just-compost soil.

[wintler2]

Iamwhoiam, I found Sally Browns article disingenuous in the sense that it criticised charcoal for not being compost, without mentioning composts weaknesses. On the southern half of my continent, compost can fry out of soils (suffer accelerated decomposition from high soil temp) is a week, whereas charcoal will persist. And, i know its ad-hom but old habits die hard, did you know SB has form on not being the most impartial observer.

[Alaya]

Well, alwyn, just couldn't wait a day or so for me to begin "The Fallacy of Biochar as a Beneficial Soil Amendment," could you. Just had to get your misinformation out there first, huh.

Sorry. Was I supposed to wait with baited breath for you to grace me with your wisdom? You said you were busy.

Ok, I hope you realize there are people wiser than you in their knowledge of biochemistry and that your wiki info is severely flawed and extremely biased.

Sure I know that. But I know about farming my vegetables, 'cause I've been feeding my family for 15 years that way. I only put the Wiki link up to get the conversation rolling.

It is unfortunate that this culture subscribes to "if a little of something must be good for you, then more must be better". If bio-char means wholesale destruction and industrial applications, then I want a different word. 'Cause the charcoal under my rows makes the beds perform better.

I started out using compost and organic amendments. The charcoal was an experiment after reading about the Tierra Preta. Plus, I had dead trees to burn. So, what am I going to believe? My lying eyes? Or another scientific report?

I know I grow damn good vegetables! And I had beds with charcoal side by side with beds without it. The char beds outperformed the beds lacking in it. I never said nuthin 'bout only using char, ever.

Joe, there is a theory out there that carbon is conductive, (can't remember which site right now, sorry) and that there is an advantage in an increased electrical charge available to the plants that helps them grow.

Hear, hear! I also use it also, along together with horse, cow, buffalo manure and bat guano. Experienced gardeners sense the proper balance of how much of soil enhancers to use.