Caracterização e gênese de uma topossequência de solos do município de Sena Madureira - Acre

Abstract

In order to study the properties, genesis and distribution of the soils of a toposequence in Sena Madureira, State of Acre, four profiles were selected at altitudes ranging from 195 to 266 meters, along BR 364. The soils were morphologically characterized and deformed samples were collected and undeformed for physical, chemical, mineralogical and micromorphological analyzes. Based on the results obtained, the soils, in the descending direction in the toposequence, were classified as DYLOSOLUS YELLOW Argisolic Dystrophic, ARGISOLO RED-YELLOW Typical Dystrophic, ALYSOL CHROMIC Argilúvico Typical and PLINTOSOLO ARGILÚVICO Alumínico alumínico. Argissolo and Alissolo are represented by very similar morphologically profiles, being distinguished only based on the aluminum character, without any correlation with the presence or absence of attributes that can be identified in the field, as recommended by the System. This finding supports the suggestion of merging the two classes at the level of order and subsequent separation of the aluminum character at the third level. The soils in the sequence are divided into two groups: the first, with well-drained soils, low-activity clay, with loss of exchangeable bases, dominance of strongly acidic, acidic conditions, with a predominance of highly stable minerals such as quartz, kaolinite and vermiculite with interlayered hydroxy-Al (HEV); the second, constituted exclusively by the Plinthossol, at the lower level of the sequence, has a marked drainage deficiency, which influences the lower leaching of the profile bases, with Mg ++ as the predominant basic cation, aluminum character, strongly acid reaction, and differentiated mineralogy, with presence of smectite and illite in greater quantity, in addition to the mineralogical components of the soils of the upper part. In the micromorphological analysis, the Latassolo presents intermediate characteristics between Iatosols and argisols, which is denoted by the incipient micropedic structure and the evidence of clay illuviation. The Argisol and Alisol are micromorphologically similar, presenting a significant concentration of iluvial clay in the Bt horizons, and a greater presence of more expansive clay minerals in the direction of the lower horizons. In the Plintossolo there are areas of iron depletion due to the alternating processes of oxireduction to which it is subjected. The biotite present in the thicker fractions, when weathered, results in the formation "in situ" of clays. The Oxisol in the most extensive tabular interfluvium, followed by the Argisol and Alisol in smaller flat tops, located in areas of wavy regional relief, and the Plinthossol , in contact with the plain, express geomorphological control in the distribution of soils in the studied area.