Caracterização mineralógica de um gleissolo sob cultivo de duas espécies de bambu por técnicas de espectroscopia e difração de raios X

Abstract

The soil is very important for life maintenance, either as a means of food production, residue filtration or simply for the support given to everyday human activities. It is a dynamic system, and modifications in the soil might result in environmental processes and impacts. However, environmental control measures, and through information from analysis of the soil conditions and changes, possible damage to the soil might be mitigated. This study is placed in a context where information is sought to identify variations or to understand the soil formation as well as possible anthropic influences that might occur. The study consists in the investigation of a soil collected from the experimental campus of the Federal University of Goiás Agriculture School (UFG) in Goiânia, GO. The soil was classified as a Gleysol based on physical aspects such as texture, topographic position and hydric conditions. Gleysols are hydromorphic soils that present a gley horizon within 150 cm of the soil surface due to the high frequency of inundation or long periods of water saturation. They might present greyish, blueish or greenish coloration, caused by the reduction in iron, with sandy to clay textures. Therefore, this study aimed at the mineralogical characterization of a Gleysol and investigation of possible mineralogical distinctions, since some factors were taken into consideration, namely, the fact that two species of bamboo were growing on it, Guadua angustifolia and Dendrocalamus asper; the samples were collected from two depths 0-10 cm and 10-20 cm around each species in two periods 2016 and 2018, and that between them several occurrences of fire were observed. The techniques employed in the characterization such as gas pycnometry allowed the observation that in both collections the particle density tended to increase with depth. The texture was obtained using the pipette method, which varied between Loam and Loam-clay-sandy. Both Energy Dispersive X-Ray Fluorescence and Wavelength Dispersive X-Ray Fluorescence were used and, in both collections, the predominant elements were Si, Al, Fe and Ti, constituting 97% of the total content, while Ca, Na, K, and Cl were found in lower amounts. In the Fourier transformed infrared spectroscopy and X-ray diffraction, the minerals identified were, Kaolinite, Montmorillonite, Quartz, Goethite, Rutile, Anatase, Calcite, Ilmenite, and Gibbsite, both in the 2016 and 2018 collections. The Rietveld Method assisted by the GSAS software enabled the quantification of the minerals in the 2016 collection. Since the ai- dried soil samples contained approximately 45% Kaolinite and 45% Quartz, the sand 17% Kaolinite and 75% Quartz, on average, the silt 22% Kaolinite and 70% Quartz, on average, and clay 80% Kaolinite, 9% Anatase, and 1.5% Quartz, on average. The refinement was repeated using two different functions for the background radiation: the first type Chebyschev polynomial, and the Fourier cosine series with a constant term, the results were similar and the quality indices were good and consistent with the literature, and both could be used for soil studies and analysis. Regarding the different types of vegetation, an increase in Kaolinite was noticed as well as a decrease in Rutile and Ilmenite in the soil with the bamboo Dendrocalamus asper.