Determinação dos estoques de carbono e nitrogênio nas frações físicas da matéria orgânica em solos antrópicos (terra preta de índio) e não antrópicos da Amazônia Central

Abstract

The soil organic matter, as the Amazonian Dark Earths, have functional compartments with different characteristics concerning composition and dynamics and these fractions can be evaluated using physical fractionation, in which the fractions are separated by densimetric and granulometric methods. In the Amazon region, studies involving physical fractionation are scarce. This work aimed to identify the compartments and their carbon and nitrogen stocks, the effect of fallow time, and to evaluate the use of these fractions as indicators of soil quality, in soils collected in areas of Amazonian Dark Earths and non-anthropic soils. Physical fractionation of organic matter was carried out in soil samples from Amazonian Dark Earths and non-anthropic soils, with forest cover. The carbon and nitrogen contents in each fraction were determined, and their stocks. The fallow time influenced the dynamics of organic matter in the Amazonian Dark Earths. The light‑free fraction proved to be a sensitive diagnostic attribute in the superficial layers. Fallow or the conversion of intensely cultivated Amazon areas to secondary forests can be a sustainable practice for mitigating carbon and nitrogen losses in the soil, especially in the most labile and reactive fractions present in the most superficial layers of the soil.