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Maintaining an appropriate level of soil organic matter and biological cycling of nutrients is crucial to the success of any soil management in the humid tropics. Cover crops, mulches, compost, or manure additions have been used successfully, supplying nutrients to crops, supporting rapid nutrient cycling through microbial biomass, and helping to retain applied mineral fertilizers better (Goyal et al., 1999; Trujillo, 2002). The benefits of such amendments are, however, often short-lived, especially in the tropics, since decomposition rates are high (Jenkinson and Ayanaba, 1977) and the added organic matter is usually mineralized to CO2 within only a few cropping seasons (Bol et al., 2000). Organic amendments therefore have to be applied each year to sustain soil productivity. Management of black carbon (C) ? increasingly referred to as bio-char ? may overcome some of those limitations and provide an additional soil management option. This is a highly aromatic form of organic matter that is present in most soils to varying extents (Schmidt and Noack, 2000; Skjemstad et al., 2002). Interest in and application of biomass-derived black carbon ? using incompletely combusted organic matter such as charcoal (Glaser et al., 2002) ? was prompted by studies of soils found in the Amazon Basin, referred to as Terra Preta de Indio (Lehmann et al., 2003c). These Amazonian Dark Earths are anthropic soils that were created by Amerindian populations between 500 and 2500 years ago. They have maintained high amounts of organic carbon, and their high fertility, even several thousand years after they were abandoned by the indigenouspopulation, contrasts distinctly with the low fertility of the adjacent acid upland soils (Lehmann et al., 2003b). The reasons for these soils? high fertility are multiple, but the source of the large amounts of organic matter and their high nutrient retention has been attributed to the extraordinarily high proportions of black carbon (Glaser et al., 2001). Such large amounts of black carbon can only originate from incompletely combusted biomass carbon, such as wood from kitchen fires or possibly from in-field burning (Smith, 1980; Hecht, 2003). This chapter considers the beneficial effects of this bio-char soil management system and discusses opportunities for applying such management within a sustainable system that can be called ?slash-and-char,? as well as within other smallholder agricultural systems.

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