• 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 (O2), and at relatively low temperatures (<700°C). This process mirrors the production of charcoal, which is perhaps the most ancient industrial technology developed by humankind. Biochar can be distinguished from charcoal—used mainly as a fuel—in that a primary application is use as a soil amendment with the intention to improve soil functions and to reduce emissions from biomass that would otherwise naturally degrade to greenhouse gases.

  • What can biochar do?

    Sustainable biochar is a powerfully simple tool that can 1) fight global warming; 2) produce a soil enhancer that holds carbon and makes soil more fertile; 3) reduce agricultural waste; and 4) produce clean, renewable energy. In some biochar systems all four objectives can be met, while in others a combination of two or more objectives will be obtained.

  • How do we know that biochar helps increase crop yields?

    There is a large body of peer-reviewed literature quantifying and describing the crop yield benefits of biochar-amended soil. Field trials using biochar have been conducted in the tropics over the past several years. Most show positive results on yields when biochar was applied to field soils and nutrients were managed appropriately.

    There is also evidence from thousands of years of traditional use of charcoal in soils. The most well-known example is the fertile Terra Pretasoils in Brazil, but Japan also has a long tradition of using charcoal in soil, a tradition that is being revived and has been exported over the past 20 years to countries such as Costa Rica. The Brazilian and Japanese traditions together provide long-term evidence of positive biochar impact on soils.

    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 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 small labile (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 microbes.

  • How can biochar mitigate climate change?

    Large amounts of forestry and agricultural residues and other biomass are currently burned or left to decompose thereby releasing carbon dioxide (CO2) 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 CO2-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 CO2?

    Recent studies have indicated that incorporating biochar into soil reduces nitrous oxide (N2O) emissions and increases methane (CH4) uptake from soil. Methane is over 20 times more effective in trapping heat in the atmosphere than CO2, while nitrous oxide has a global warming potential that is 310 times greater than CO2. 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 understanding of the role of biochar in reducing non-CO2 greenhouse gas (GHG) emissions will promote its incorporation into climate change mitigation strategies, and ultimately, its commercial availability and application.

  • Could black dust from biochar have an impact on climate?

    Small particles of black carbon are produced from the incomplete combustion of fossil and biomass fuels. 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 CO2 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 any other must be implemented in a way that respects the land rights of indigenous people and supports the health of natural ecosystems. Properly implemented, biochar production and use should serve the interests of local people and protect biodiversity.

  • 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 and how much should you add?

    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 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.

    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.