Biochar

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Biochar is the lightweight black residue, consisting of carbon and ashes, remaining after the pyrolysis of biomass, and is a form of charcoal.^[1] Biochar is defined by the International Biochar Initiative as the "solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment".^[2]

Biochar is mainly used in soils to increase soil aeration, reduce soil emissions of greenhouse gases^[3], reduce nutrient leaching and reduce soil acidity^[4] and can increase soil water content in coarse soils.^[5] Biochar application may increase soil fertility and agricultural productivity.^[4] Biochar soil amendments, when applied at excessive rates or with unsuitable soil type and biochar feedstock combinations, also have the potential for negative effects, including harming soil biota, reducing available water content, altering soil pH and increasing salinity.^[6]

Beyond soil application, biochar can be used for slash-and-char farming, for water retention in soil, and as an additive for animal fodder. There is an increasing focus on the potential role of biochar application in global climate change mitigation. Due to its refractory stability, biochar can stay in soils or other environments for thousands of years.^[7] This has given rise to the concept of Biochar Carbon Removal, i.e. carbon sequestration in the form of biochar.^[7] Carbon removal can be achieved when high-quality biochar is applied to soils, or added as a substitute material to construction materials such as concrete and tar.