Biochar is a solid material produced by the thermal decomposition of biomass (such as wood, manure, or leaves) under limited supply of oxygen (O2) and at relatively low temperatures (<700°C). This process, called pyrolysis, is a fundamental part of biochar technology; biochar production is modeled after a process begun thousands of years ago in the Amazon Basin, where islands of rich, fertile soils called terra preta (“dark earth”) were created by Indigenous people. A primary application of biochar is its 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.

Sustainable biochar is a powerfully simple tool that can:

1. fight global warming
2. produce a soil enhancer that stores 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.

Hydrochar: Hydrochar is the solid product of hydrothermal carbonization (HTC) or liquefaction (sometimes referred to as HTC material), and is distinct from biochar due to its production process and properties. Hydrochar typically has higher H/C ratios and is less aromatic than biochar, as well as little or no fused aromatic ring structures.  Hydrochar is only occasionally discussed in comparison to biochar.

Soot: Soot is a secondary Pyrogenic Carbonaceous Material (PCM) and a condensation product.  Chars, charcoal, biochars, black carbons and, to a limited extent, also activated carbon) may contain soot, but soot can also be identified as a separate component resulting from gas condensation processes.

Ash: Ash is the operationally defined fraction of biomass or PCM (according to ASTM DI762-84) and typically includes inorganic oxides and carbonates (Enders et al, 2012).  The term does not describe the solid residue of combustion which commonly contains some residual organic C.

Not all biochar is the same. The key chemical and physical properties of biochar are based on the type of feedstock it’s made from and the conditions of how its made. For example, biochar made from manure will have a higher nutrient content than biochar made from wood cuttings. Different biochars will look similar but they will behave quite differently. Our Biochar Standards  provide more information on the unique characteristics of biochar.

Some biochar materials, for example those made from manures and bones, are mainly composed of ashes 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 like synthetic fertilizers. On the other hand, high mineral ash biochars have a low carbon content, so the long-term nutrient retention will be less.

Anyone implementing biochar should consider testing several rates of biochar application on a small scale before applying the product on large areas. Experiments have found that rates between 0.5 – 5 kg/m2 have been used successfully.

The characteristics of biochar depend on what feedstock it is made from and how it is made. For example, biochar made from manure will have a higher nutrient content than biochar made from wood cuttings. One unifying characteristic of different types of biochar, however, is that it mineralizes in soils much more slowly than its uncharred source material. Most biochars do have a small, easily decomposable fraction of carbon, but there is typically a much larger stable fraction –– this is why biochar is considered a scalable and immediate climate change solution. Scientists have shown that the estimated amount of time that biochar’s stored carbon will persist in soils ranges from decades to millennia.

Large amounts of forestry and agricultural waste material, alongside other biomass, are currently burned or left to decompose, effectively releasing carbon dioxide (CO2) and/or methane (CH4)—two main greenhouse gases—into the atmosphere. Biochar made from that same waste material is able to store carbon (in which the easily mineralized carbon compounds are converted into fused carbon ring structures). When biochar is placed in soils, that carbon can persist for hundreds to thousands of years. If gigatonnes of biomass were converted to biochar on a global scale, studies have shown that biochar has the potential to mitigate global climate change by drawing down atmospheric GHG concentrations (Woolf et al, 2010).

Studies have indicated that incorporating biochar into the world’s soils 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 carbon. While nitrous oxide has a global warming potential that is 310 times greater than carbon. Although the mechanisms for these impacts are not fully understood, it is likely that a combination of biotic and abiotic factors are involved that 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-carbon greenhouse gas emissions will promote biochar’s use in climate change mitigation strategies, and ultimately, its commercial availability and application.

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.