frequently asked questions about biochar _ international biochar initiative

8/15/2019 Frequently Asked Questions About Biochar _ International Biochar Initiative

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Biochar pot trials in the greenhouse. Photo courtesy of Edward Someus.

What is biochar?

Biochar is a solid material obtained from the carbonization thermochemical conversion of biomass in

an oxygen-limited environments. In more technical terms, biochar is produced by thermal

decomposition of organic material (biomass such as wood, manure or leaves) under limited supply of

oxygen (O ), and at relatively low temperatures (


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While the larger questions concerning overall biochar benefits to soils and climate have been

answered in the affirmative, significant questions remain, including the need for a better

understanding of some of the details of biochar production and characterization. Work is ongoing to

develop methods for matching different types of biochar to soils for the best results.

How can biochar help farmers?

Biochar provides a unique opportunity to improve soil fertility for the long term using locally available

materials. Used alone, or in combinations, compost, manure and/or agrochemicals are added at

certain rates every year to soils, in order to realize benefits. Application rates of these can be

reduced when nutrients are combined with biochar. Biochar remains in the soil, and single

applications can provide benefits over many years. Farmers can also receive an energy yield when

converting organic residues into biochar by capturing energy given off in the biochar production

process. In both industrialized and developing countries, soil loss and degradation is occurring at

unprecedented rates, with profound consequences for soil ecosystem properties. In many regions,

loss in soil productivity occurs despite intensive use of agrochemicals, concurrent with adverse

environmental impacts on soil and water resources. Biochar can play a major role in expanding

options for sustainable soil management by improving upon existing best management practices, not

only to improve soil productivity but also to decrease nutrient loss through leaching by percolating

water.

How does biochar affect soil biology?

Decades of research in Japan and recent studies in the U.S. have shown that biochar stimulates theactivity of a variety of agriculturally important soil microorganisms, and can greatly affect the

microbiological properties of soils. The pores in biochar provide a suitable habitat for many

microorganisms by protecting them from predation and drying while providing many of their diverse

carbon (C), energy and mineral nutrient needs. With the interest in using biochar for promoting soil

fertility, many scientific studies are being conducted to better understand how this affects the physical

and chemical properties of soil and its suitability as a microbial habitat. Since soil organisms provide a

myriad of ecosystem services, understanding how adding biochar to soil may affect soil ecology is

critical for assuring that soil quality and the integrity of the soil subsystem are maintained.

How does biochar affect soil properties like pH and CEC?

Biochar reduces soil acidity which decreases liming needs, but in most cases does not actually add

nutrients in any appreciable amount. Biochar made from manure and bones is the exception; it

retains a significant amount of nutrients from its source. Because biochar attracts and holds soil

nutrients, it potentially reduces fertilizer requirements. As a result, fertilization costs are minimized

and fertilizer (organic or chemical) is retained in the soil for longer. In most agricultural situations

worldwide, soil pH (a measure of acidity) is low (a pH below 7 means more acidic soil) and needs tobe increased. Biochar retains nutrients in soil directly through the negative charge that develops on

its surfaces, and this negative charge can buffer acidity in the soil, as does organic matter in general.


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CEC stands for Cation Exchange Capacity, and is one of many factors involved in soil fertility.

“Cations” are positively charged ions, in this case we refer specifically to plant nutrients such as

calcium (Ca2+), potassium (K+), magnesium (Mg2+) and others. These simple forms are those in

which plants take the nutrients up through their roots. Organic matter and some clays in soil hold on

to these positively charged nutrients because they have negatively charged sites on their surfaces,

and opposite charges attract. The soil can then “exchange” these nutrients with plant roots. If a soil

has a low cation exchange capacity, it is not able to retain such nutrients well, and the nutrients are

often washed out with water.

Can you add biochar to alkaline soils?

Most biochar trials have been done on acidic soils, where biochars with a high pH (e.g. 6 – 10) were

used. One study that compared the effect of adding biochar to an acidic and an alkaline soil found

greater benefits on crop growth in the acidic soil, while benefits on the alkaline soil were minor. In

another study, adding biochar to soil caused increases in pH which had a detrimental effect on yields,

because of micronutrient deficiencies which occur at high pH (>6). Care must be taken when adding

any material with a liming capacity to alkaline soils; however, it is possible to produce biochar that has

little or no liming capacity that is suitable for alkaline soils.

How long does biochar persist in the soil?

Biochar is a spectrum of materials, and its characteristics vary depending upon what it is made from

and how it is made. One unifying characteristic of biochars, however, is that it mineralizes in soils

much more slowly than its uncharred precursor material (feedstock). Most biochars do have a smalllabile (easily decomposed) fraction of carbon but there is typically a much larger recalcitrant (stable)

fraction. Scientists have shown that the mean residence time (the estimated amount of time that

biochar carbon will persist in soils) of this recalcitrant fraction ranges from decades to millennia.

Why is biochar persistence in soils important?

The persistence of biochar when incorporated into soils is of fundamental importance in determining

the environmental benefits of biochar for two reasons: first, it determines how long carbon in biochar

will remain sequestered in soil and contribute to the mitigation of climate change; and second, it

determines how long biochar can provide benefits to soil and water quality.

Why does biochar persist in soils longer than the original biomass from which it

was made?

The carbon lattice structure made up of fused polyaromatic carbon rings is hypothesized to be the

key property that confers a resistance to mineralization (conversion from organic carbon to carbon

dioxide via respiration) by soil microbes that utilize organic matter i.e., hydrocarbons, as food

(Lehmann et al, 2015). The energy required by microbes to access the carbon in biochar appears to

be greater than that acquired when it is released. In contrast, carbon compounds in the original

biomass (feedstock) are a net positive energy sources and are more readily mineralized by soil


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microbes.

How is biochar carbon persistence measured?

The fused carbon ring structure of biochar can be measured in the laboratory using a range of

established techniques, some low cost and relatively easy to conduct, others more sophisticated and

requiring high-tech equipment that analyzes nano-structural properties. In combination with empirical

(measurement-based) modelling exercises which show how biochar carbon mineralizes over time

using field and laboratory incubation trials for validation, the degree of carbon aromaticity can be

used to predict how much biochar would remain in soils over discrete time periods, for example 100

years or 1,000 years. Persistence is then quantified as mean residence time (MRT)—the average

time that biochar is present in the soil

How can biochar mitigate climate change?

Large amounts of forestry and agricultural residues and other biomass are currently burned or left todecompose thereby releasing carbon dioxide (CO ) and/or methane (CH4)—two main greenhouse

gases (GHGs)—into the atmosphere. Under biochar conversion scenarios, easily mineralized carbon

compounds in biomass are converted into fused carbon ring structures in biochar and placed in soils

where they persist for hundreds or thousands of years. When deployed on a global scale through the

conversion of gigatonnes of biomass into biochar, studies have shown that biochar has the potential

to mitigate global climate change by drawing down atmospheric GHG concentrations (Woolf et al,

2010).

How much carbon can biochar potentially remove from the atmosphere?

According to one prominent study (Woolf et al, 2010), sustainable biochar implementation could

offset a maximum of 12% of anthropogenic GHG emissions on an annual basis. Over the course of

100 years, this amounts to a total of roughly 130 petagrams (106 metric tons) of CO -equivalents.

The study assessed the maximum sustainable technical potential utilizing globally available biomass

from agriculture and forestry. The study assumed no land clearance or conversion from food to

biomass-crops (though some dedicated biomass-crop production on degraded, abandoned

agricultural soils was included), no utilization of industrially treated waste biomass, and biomass

extraction rates that would not result in soil erosion.

How does biochar work to reduce emissions of greenhouse gases other than

CO ?

Recent studies have indicated that incorporating biochar into soil reduces nitrous oxide (N O)

emissions and increases methane (CH ) uptake from soil. Methane is over 20 times more effective in

trapping heat in the atmosphere than CO , while nitrous oxide has a global warming potential that is

310 times greater than CO . Although the mechanisms for these reductions are not fully understood,

it is likely that a combination of biotic and abiotic factors are involved, and these factors will vary

according to soil type, land use, climate and the characteristics of the biochar. An improved

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understanding of the role of biochar in reducing non-CO greenhouse gas (GHG) emissions will

promote its incorporation into climate change mitigation strategies, and ultimately, its commercial

availability and application.

Could biochar impact climate through changes in soil albedo?

After centuries of agriculture, soils globally have become depleted of carbon, compared to pre-

agricultural conditions. Agricultural development goals include restoring carbon to carbon-depleted

soils. Unavoidably, adding carbon to soils darkens them, changing their albedo (a measure of

sunlight reflectance). Fortunately, darker, carbon-rich soils are more fertile and will be more easily re-

vegetated. Vegetation has a lighter albedo, so the albedo problem is very temporary in nature and is

not a significant issue.

Could black dust from biochar have an impact on climate?

Small particles of black carbon are produced from the incomplete combustion of fossil and biomassfuels. When deposited on snow and ice, they are able to absorb heat and energy. The smallest black

carbon particles associated with biochar production and application are much larger, in the millimeter

range, than the particles associated with global warming, in the nanometer range. Thus application of

biochar would result in little opportunity for long-range transport and deposition into the sensitive

Arctic and mountain regions.

Does a successful biochar industry depend on carbon markets?

Biochar offers direct, present day benefits to farmers of all sizes in the form of greater crop

productivity as well as numerous other quantifiable environmental benefits, among them climate

change mitigation. While efforts are underway to develop mechanisms to quantify and monetize the

climate benefits of biochar—chiefly in the form of carbon offset methodologies—these would only add

to the existing financial incentives for farmers and other stakeholders to adopt biochar.

Is biochar production sustainable?

Biochar production and use comprises a complex system and its sustainability must be parsed out

into various components. Of all the key factors that will support the fastest commercialization of the

biochar industry, feedstock supply and sustainable yield issues are by far the most important, from

both a broad sustainability perspective and from the financial and commercial points of view. This will

require the sources of biomass selected for biochar production to be appropriate and be able to

withstand a comprehensive life cycle analysis. Biochar can and should be made from waste

materials. Large amounts of agricultural, municipal and forestry biomass are currently burned or left

to decompose and release CO and methane back into the atmosphere. These include crop residues

(both field residues and processing residues such as nut shells, fruit pits, etc), as well as yard, food

and forestry wastes, and animal manures. Making biochar from these materials will entail no

competition for land with any other land use option.

Biochar can be a tool for improving soils and sequestering carbon in soil. However, this technology as

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any other must be implemented in a way that respects the land rights of indigenous people and

supports the health of natural ecosystems. The goal of biochar technology as IBI envisions it is to

improve soil fertility and sequester carbon, taking into consideration the full life cycle analysis of the

technology. Properly implemented, biochar production and use should serve the interests of local

people and protect biodiversity.

What about human health concerns from dust created during biochar productionand application?

Dust is a certainly a concern with biochar application, but best practices require that biochar

applications be done during periods of low wind to prevent the blowing of fines. Agricultural

techniques already exist to apply powdered fertilizers and other amendments. Several techniques are

available to help keep wind losses to a minimum: biochar can be pelleted, prilled, mixed into a slurry

with water or other liquids, mixed with manure and/or compost, or banded in rows. The optimization

of biochar application to soil is important, and the farm technology and methods are available to do

the job.

Does IBI advocate adding carbon derived from coal, old tires or municipal solid

waste to soils?

No. Coal is not a renewable resource. Biochar refers specifically to materials made from present-day

biomass, not fossil carbon. Tires and other potentially toxic waste materials are not appropriate as

sources of biochar for soil improvement.

What are the costs and benefits of producing and using biochar?

The benefits that potentially flow from biochar production and use include waste reduction, energy

co-production, improved soil fertility and structure, and climate change mitigation. Not all of these

benefits are accounted for under current economic systems, but under the carbon constrained

economies of the future, the climate mitigation benefit is likely to be accounted for as an economic

benefit. Biochar benefits are partly offset by the costs of production, mainly hauling and processing

feedstocks. Profitability of biochar systems will be especially sensitive to prices for energy and for

greenhouse gas reductions and offsets.

Can biochar be patented?

While some biochar producers may be able to patent a specific biochar production process or

method, there exist a number of open-source, low-cost, clean technologies that can make biochar at

the home or village level, and more are being developed.

What kind of biochar should you add to your soil, how much should you add, and

where can you buy biochar?

It is important to note that not all biochar is the same. Biochar is made by pyrolysing biomass—

pyrolysis bakes the biomass in the absence of oxygen, driving off volatile gases and leaving behind

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charcoal. The key chemical and physical properties of biochar are greatly affected by the type of

feedstock being heated and the conditions of the pyrolysis process. For example, biochar made from

manure will have a higher nutrient content than biochar made from wood cuttings. However, the

biochar from the wood cuttings may have a greater degree of persistence over time. The two

different biochars will look similar but will behave quite differently. The IBI Biochar Standards provide

more clarity on the characteristics of biochar.

Some biochar materials, for example those made from manures and bones, are mainly composed of

ashes (so-called “high mineral ash biochars”), and thus can supply considerable amounts of nutrients

to crops. Keep in mind that this fertilizer effect will likely be immediate and short-lived, just as is the

case with synthetic fertilizers. Conversely, the carbon content of high mineral ash biochars is low (e.g.

< 10%), and thus longer-term nutrient retention functions will be less for a given amount of material.

Given the variability in biochar materials and soils, users of biochar should consider testing several

rates of biochar application on a small scale before setting out to apply it on large areas. Experiments

have found that rates between 5 – 50 t/ha (0.5 – 5 kg/m2) have often been used successfully.

The biochar market is still in its infancy, but there are sellers of the product. You may be able to find a

biochar seller in your area by searching the IBI Business Member Directory. Additionally, IBI is

working to provide more information on the biochar industry through the annual State of the Industry

Report .

Can I use biochar immediately after producing it?

Biochar straight out of the pyrolysis unit might take some time to reach its full potential in soil,

because it needs it's surfaces to "open up", or "weather". This happens naturally in soil, but the

process can be sped up by mixing biochar with compost, for example. Nutrient retention with biochar

is thought to improve with time, along with crop benefits. Mixing biochar with compost is a great idea,

since apart from the ash (and there might only be small amounts of it in biochar), biochar is not a

fertilizer in itself so the compost can provide nutrients which the biochar can help retain.

Is it true that most of the biochar added to soils is exported to rivers and oceans?

A study published in the April 19, 2013 issue of Science magazine titled “Global Charcoal Mobilization

from Soils via Dissolution and Riverine Transport to the Oceans” examined the proportion of benzene

polycarboxylic acids (BPCA) as a proxy for black (pyrogenic) carbon (BC) in dissolved organic carbon

(DOC) of a number of rivers. While the paper makes an important contribution to the global

knowledge base on DOC fluxes in the environment, IBI believes there are a number of clarifications

needed to reduce the propagation of erroneous conclusions about biochar behavior in soil.

We concur with the finding that the export of BC to terrestrial ecosystems via rivers is significant. This

should not be interpreted, however, as being greater than the export of uncharred material. In fact,

the export of BC is only 10% of the total export of organic carbon, which is on the same order of

magnitude or even smaller than the proportions that the authors cite for BC contents in soils of 5 -

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40%. Therefore, BC in soil is not preferentially exported from watersheds.

Based on citations the authors conclude that production rates of BC exceed decomposition rates and

thus “a relatively labile BC pool must exist, allowing for considerable losses from soils.” However, the

studies cited acknowledge high uncertainty in the rates of BC production, and, in the case of BC

degradation, do not support inferences about BC degradation via microbial metabolization—rather

just total losses from soil, be it via erosion, leaching or mineralization. Based on uncertainty in bothproduction and decomposition of BC, we believe that further research is warranted to understand BC

fluxes in the environment.

Finally, the article concludes by implying that use of biochar may reduce DOC bioavailability with

cascading effects on microbial and aquatic food webs. This, however, would only be correct if all

biochar were made from biomass where the baseline scenario is accumulation in soil. In fact, most

biochar proponents—including IBI—advocate for use of biomass feedstocks that are currently burnt,

land filled or disposed of in ways other than returning them to soils. Furthermore, even aggressive

scenarios of biochar addition would still only be a fraction of total annual biomass residues that are

already returned to soils and the impact on DOC bioavailability would thus be small.

frequently asked questions about biochar _ international biochar initiative

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