Biochar

Biochar is a form of charcoal, sometimes modified, that is intended for organic use, as in soil. It is the lightweight black remnants remaining after the pyrolysis of biomass, consisting of carbon and ashes.^[1] Despite its name, biochar is sterile immediately after production and only gains biological life following assisted or incidental exposure to biota. 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, reduce soil acidity,^[4] and potentially increase the water content of coarse soils.^[5] Biochar application may increase soil fertility and agricultural productivity.^[4] However, when applied excessively or made from feedstock unsuitable for the soil type, biochar soil amendments 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, a process of 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.