Humic acid composition and soil fertility of soils near an ancient charcoal kiln: are they similar to Terra Preta de Índios soils?

6 páginas.-- 5 figuras.-- 1 tabla.-- 31 referenciasPurpose: Charcoal production during the nineteenth century transformed landscapes in the Brazilian Atlantic Forests in Rio de Janeiro city. These paleo-territories were studied to improve our understanding of how this activity altered soil properties. By comparing their humic acids (HA) with those extracted from a Terra Preta de Índios (TPI) site, we showed that the aging of charcoal in soils alone is sufficient to generate recalcitrant organic material with high cation exchange capacity (CEC). Materials and methods: The soils were sampled: at the center of the area affected by the ancient charcoal kiln (center of the kiln—CK), at the dump site (D—local deposition of charcoal residues not used for marketing, downstream of the ancient charcoal kiln), and from the surrounding soil, upstream of the kiln, as a control (natural soil—NS). Elemental analysis and fertility characterization of the soil samples were performed. Solid-state 13C nuclear magnetic resonance (NMR) spectra were obtained from their humic acids (HA). These spectra were compared against HA data on TPI. Results and discussion: As shown by solid-state 13C NMR spectroscopy, the soil organic matter (SOM) fraction which is high in charged functional groups (the so-called humic acids—HA) was extracted from areas rich in ancient charcoal and dominated by recalcitrant carboxylated aromatic structures (aged charcoal). This peculiar SOM explains the observed high cation exchange capacity (CEC). It yields a fertile soil with a high resistance against degradation by potential intensive use. Comparable results are described in the literature for SOM of TPI. Conclusions: The high structural similarity between the HA from the soils under the paleo-charcoal kilns and from TPI supports the hypothesis that just the natural weathering and biochemical reworking of charcoal in soils, together with ash input, is sufficient to generate fertile and resilient soils with peculiar SOM and properties commonly associated with the high fertility and C sequestration potential of TPIThis study was financially supported by the Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq)Peer reviewe