Chemical fractionation of organic matter and physical characterization of amazonian dark earth
Abstract
The anthropogenic soil called ‘Terra Preta de Indio’ - Amazonian Dark Earth (‘TPI’, from Portuguese) is characterized by its high content of organic matter and fertility, but its physical characteristics are unknown. Thus, the purpose of this study was to analyze the physical-hydric behavior and chemical fractionation of organic matter in ‘Terra Preta de Indio’- Amazonian Dark Earth, in the State of Para. To this end, three areas were selected in the municipality of Melgaço: 1) ‘Sitio Mina I’, secondary forest; 2) ‘Sitio Mina II’, secondary vegetation; and 3) ‘Sitio Manduquinha’, secondary vegetation, classified as anthropogenic Oxisol, where the chemical analyzes were performed to characterize fertility and organic matter fractionation. The physical characterization was determined by soil texture, determination of soil water retention curve, available water capacity, distribution of pore space, curve of penetration resistance (PR) and bulk density (BD). Chemical analysis proved the high fertility of ‘TPI’ soil in Caxiuana. Regarding the humic fractions, it was
possible to observe higher contents of humin and humic acids and lower content of fulvic acid. Physical analysis indicated that ‘TPI’ present texture ranging from sandy loam to sandy clay loam, low BD, with more water available found in ‘Sitio Mina II’. Of the three areas studied, ‘Sitio Mina II’ and ‘Sitio Manduquinha’ showed PR values above 2.5 MPa; howeve.
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