Black Carbon in Soils: Relevance, Analysis, Distribution

Black carbon (BC), a graphitic, particulate form of carbon that results from the incomplete combustion of organic material, is a significant part of the soil organic carbon (SOC) in soils worldwide. This article gives an overview on the sources and the behavior of soil BC, discusses the different analytical approaches for BC, and reviews literature on its distribution in soils. Black carbon is released by biomass and fossil fuel burning in the form of soot and char and charcoal. It is ubiquitous in the atmosphere and in soils. In soils, BC is more persistent and less reactive than other SOC constituents. It has turnover periods ranging from some decades to some thousands of years. Its stability, together with chemical and physical features such as high surface area and porosity, has important implications for nutrient storage, contaminant adsorption, and bulk SOC stability, as well as for global climate change mitigation. Biochar BC production and storage in soils are discussed as very promising carbon sequestration strategies. Because BC includes a continuum of materials, a wide array of analytical approaches has been developed for its investigation, including optical, chemical, and thermal methods. This makes it difficult to compare different studies and to draw a big picture of BC distribution. Black carbon assessment in soil survey would be valuable from a use and management perspective, might help identify the factors and processes affecting BC in soils, and possibly provide an important clue in understanding the global carbon cycle.