Determination of carbon stocks of humic substances and vulnerability to emissions in archaeological and non-archaeological soils of the Central Amazon

The Amazon Region has archaeological soils called Amazonian Dark Earths (Terras Pretas de Indio) which are very efficient in retaining a large amount of highly stable organic matter when compared to typical non-archaeological soils in the region. The objective of this study was to determine the distribution, in depth, of the carbon concentrations and stocks contained in Humic Acids, Fulvic Acids, and Humine from Amazonian Dark Earths and Acrisols typical of Central Amazonia under secondary forests with a different fallow. The chemical fractionation of humic substances was performed using the method of sequential extraction by the difference in solubility. The Amazonian Dark Earths areas showed higher concentrations of total carbon but behaved differently to non-archaeological soils. There carbon stock's C_FA fraction was a predominance for the P01 soil and C_H fraction for the P02 soil, while for the non-archaeological soils, the carbon stock's C_HA fraction was predominant (100%). The relationships commonly used in studies on the distribution of humic substances (C_HA/C_FA and C_AE/C_H) are not appropriate for evaluating the stabilization mechanisms of organic matter in the Amazonian Dark Earths. (author)