Feições redoximórficas, micromorfologia e endurecimento da plintita em solos da planície do rio Araguaia, Brasil

• Autor(a) principal: Santos, Djavan Pinheiro
• Data de Publicação: 2020
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFG
• dARK ID: ark:/38995/0013000006zs1
• Texto Completo: http://repositorio.bc.ufg.br/tede/handle/tede/11887
• topic: Hematita; Goethita; Planície de inundação; Óxidos de ferro; Hematite; Goethite; Floodplain; Iron oxides; CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

The soils of the Araguaia River plain have abundance in redoxymorphic features, especially plinthite. The predominant soils in this plain are plinthossols that are subjected to natural water table fluctuation and altered by the anthropic use nearby, by the flood irrigation project in Luiz Alves, São Miguel do Araguaia, state of Goiás. Thus, the objective was to evaluate the chemical and mineralogical composition of the redoxymorphic features, dynamics of the iron element present in the soils, formation mechanisms and possible causes or conditioning of the plintite hardening, as well as the morphological aspects (macro and micro) of this feature. Redoxymorphic features were collected in different positions of the soil profiles and submitted to all analytical procedures as recommended by the specialized manuals for each analysis, as well as specific equipment to obtain the data. The iron contents in all the studied forms determined are always higher in the plinthite feature, intermediate in the mottled feature and lower in the soil matrix feature. The iron present in secondary minerals (vermiculites, VHES and illites) reach values of the order of 64.60% in P1 and 58.02% in P2, while only part (around 35.40% in P1 and 41.98% in P2) is detected in the form of oxides such as goethite and hematite that would have the possibility of being formed in oxi-reduction processes. The mottled and plintite features present in these soils are not the product of the classic process of segregation, mobilization and accumulation of iron as a result of oxidation processes. They formed or appeared in them as a result of a relatively slow and constant decomposition process of their source material, which is being decomposed in an aqueous medium releasing much of its components, including iron and more mobile elements such as bases and silicon, which leave the system by draining water, and some small part of them can recombine to form new less complex minerals, such as kaolinites and oxides. The greater hardness of the plintite features of the soils is directly related to the content of ferric iron contained in its fine fraction. Iron oxides are the elements responsible for promoting and maintaining the hardening of features. The presence of the plintite feature, with the requirements of color and hardness fully satisfied, was established in the cases studied with a combination of the following factors: condition of seasonality of the water regime; absolute levels of Fed of at least 40 g kg-1 associated with a Fed / Fes ratio of at least 0.35 and Fes values equal to or greater than 100 g kg-1 , associated with a Fes/Fet ratio of at least 0.70. The accumulations of iron identified in these features by the micromorphological study are probably formed in earlier times, immediately after the release of iron from silicate structures and in a distinct moisture condition that allowed its recombination in the form of oxides, probably with less water movement.