Lehmann, Johannes (Cornell University, 909 Bradfield Hall, Ithaca, NY, 14853, Phone: 607-254-1236; Fax: 607-254-1236; Email: CL273@cornell.edu)


Black Carbon Sequestration in Soil A New Frontier


J. Lehmann*, J. Gaunt, M. Rondon


Options to increase C stores in soil are limited under natural vegetation and virtually absent in agricultural systems, although soil C represents an important pool of C on a global scale. This study explores the potential to increase soil C stocks through management of bio-char (biomass-derived black C). Inspired by remnants of anthropogenic soil manipulation in Amazonia originating from pre-Colombian times, bio-char management was found to significantly increase crop productivity and decrease leaching losses of nutrients in an otherwise infertile soilscape. Bio-char sequestration provides an opportunity to exploit natural C stabilization mechanisms since bio-char is a highly stable form of organic matter that has shown to exhibit greater radiocarbon ages than the oldest organic matter fractions in soil. At the same time, bio-char is present in most soils in measurable quantities of up to 40% of organic C and therefore does not constitute an alien substance. Its primary incentive for application is increasing crop yields by up to 220% and decreasing nutrient losses by leaching. The production of bio-char can be integrated in various land-based production systems but must not compromise ecosystem services. Changing slash-and-burn to slash-and-char systems have the potential to sequester 0.2 Pg C yr-1 globally, and agricultural wastes add an additional 0.2 Pg C yr-1. Renewable fuels are becoming a viable alternative to fossil fuel and gasification of biomass and its partial use for bio-char production have proven to yield 48% bio-char of the added C while still producing 68% of the energy that would be produced under complete combustion. With an estimate of 180-310 EJ yr-1 of renewable energy in 2100, 9.5 Pg C yr-1 can be stored in soils annually. A combination of feasible approaches could sequester 0.6 Pg C yr-1 already today. At the end of this century, up to 10 Pg C yr-1 could be drawn from the atmosphere, helping to offset anthropogenic emissions that today amount to 5.4 Pg C yr-1.