Solid-state 13C nuclear magnetic resonance characterisation of humic acids extracted from Amazonian Dark Earths (Terra Preta de Índio)

Abstract

The environmental organic matter is the link between the biosphere, geosphere, hydrosphere and atmosphere and is fundamental for ecosystem sustainability. Estimates of the total mass of organic carbon in soils are in the range of 1.22 × 1018g (Sombroek et al. 1993) to 2.456 × 1018 g (Batjes 1996). This reservoir is at least three times greater than all organic materials above the earth's surface, and the way the soil sequestered carbon is managed can have significant influences the levels of atmospheric CO2. Estimates of the amounts of fossil organic carbon (gas, oil, coal etc.) are considerably greater, of the order of 4 × 1018 g (Falkowski et al. 2000; Janzen 2004). An increase of carbon improves the fertility of soil, especially in tropical conditions, and thus increases the vegetal biomass that this soil can support. The soil carbon stock represents a continuous process of deposition (5.67 × 1016g C year-1), in the form of vegetal and animal residues, and decomposition (with emissions of 5.50 × 1016 g C year -1). The deposition and decomposition fluxes are not equal because of the inputs of fossil fuel carbon (5 × 1015 g C year -1). However, fossil fuel carbon emissions are one order of magnitude less than that due to the decomposition of natural soil organic matter (United States 1999). © Springer Science + Business Media B.V. 2009.