Caracterização Química e Mineralogia de Solos Antrópicos da Amazônia (Terras Pretas de índio) entre Coari-Manaus,AM.

Abstract

Anthopogenic Dark Earths (Terras Pretas de Indio) are soil horizons of dark color with high fertility and organic matter content. They could be found about different types of soils on the Amazon landscape, being more frequently next to water courses, presenting as a typical characteristic an anthropic horizon A, containing in its mass ceramic fragments, lithic material and charcoal. Understanding of its chemical characteristics and mineralogical composition could improve comprehension of it genesis, richness and sustainability. The present study was realized with the purpose of the evaluate the main chemical characteristics and mineralogical composition of clay and sand fractions of six soils in archeological sites with horizon A localized at the Sedimentary Basin of the Amazon and Solimões, between Coari-Manaus intervals, being those; Ena site, Comunidade S.J. Batista, Lago do Limão, Lauro Sodré, Jacuruxi and Pilão. Samples were collected prepared and submitted to granularymetric and chemical analysis realized at soil chemistry laboratories at UFAM and EMBRAPA, and mineralogical analysis at X-ray diffraction (XRD) UFAM laboratory. Results from chemical characterization has shown that in evaluated soils of archeological sites the pH in water varied between 5.1 and 7.05, displaying in most samples a moderate acidity; elements contents available and changeable as well presented high contents of P and Ca2+ and low potassium (K+) and aluminum Ca2+ contents. Meanwhile, in this study, soil from Jacuruxi site presented lower Ca2+ contents, high acidity, and high Al3+ contents, meantime, observed available P contents (mehlich-1) were high, varying from 42 to 113 mg kg-1 mineralogical soil composition evaluated by DXR has shown that argile from upland (terra firme) localized sites,(Comunidade S.J.Batista, ENA, Lago do Limão, Jacuruxi, and Pilão) are Kaolinite prevailed, wich is normally observed in soils of same geomorphologic surface in the Amazon. Anyhow, mineralogy of clay fraction at localized soil floodplain (várzea) ecosystem at Lauro Sodré, has shown a more heterogeneous mineral composition , composed by Kaolinite, goethite and type 2:1 minerals, enhancing current materials less intemperate in such environment. On the sand fraction there was a total predominance of quartz mineral in all evaluated soils independent of environment characteristic, meanwhile through mineral separation by dense liquid means in this fraction of two soils (Comunidade S.J. Batista and Jacuruxi), it was detected the appearance of hematite, rutile, anatase, ilmenite, zircon and maghemite ,and through magnetic separation , also on this fraction, in two soils (Comunidade S.J. Batista and Pilão) the analysis detected hematite (Hm) and maghemite (Mh) contents. The sulfuric acid attack done on evaluated samples has shown low iron contents, mainly at Jacuruxi site localized at hidromorphosis incidental area, that represents a removal environment of ferolise. The contents of P-total has shown the concentration magnitude of this elements on the anthropic soils horizons of archeological sites already evaluated, outstanding the floodplain site (Lauro sodré) with anthropic Horizon A beneath disposal layers of neo-soil at depth of 160 cm , achieving contents of 8840 mg kg-1 of P-total at this depth.