Elen Alvarenga Silva

Morphology, mineralogy and micromorphology of soils associated to summit depressions of the Northeastern Brazilian Coastal Plains

The scarcity of comprehensive characterizations of soils associated to gentle summit depressions of the Northeastern Brazilian Coastal Plains justifies this work, which had as objective to provide basic information for the more diverse agricultural and non-agricultural uses. For that, representative soils (Spodosols or similar soils) from these environments were selected in Alagoas, Sergipe and Bahia states. This approach included characterization of morphological, mineralogical and micromorphological properties of the soil profiles, employing standard procedures. The morphological characterization corroborated the effect of the podzolization process during the formation of these soils. The mineralogy of the clay fraction of these soils was basically composed of kaolinite and quartz, which, associated to the very sandy texture, helped in the understanding of the obtained data. The soil micromorphological study, besides confirming the field morphology, mainly in regard to the strong cementation, aggregated value to the work in terms of the secure identification of the clay illuviation process (non-identified in the field), in association with the dominant podzolization process.

Frações de carbono em topossequências de solos sob eucalipto com diferentes históricos de uso

In Brazil, most forest stands have been planted on soils with some degree of physical, chemical or biological degradation. The protection of the trees for the soil, depending on the litter deposition, is a driving force of the restoration process of degraded areas. Since organic matter is related to many of the physical, chemical and biological soil properties, it is characterized as a key factor for the maintenance of the environmental quality of forest systems. The purpose of this study was to characterize organic matter fractions in soils with eucalyptus under minimum tillage from positions in the landscape with different histories of soil use. The study was conducted in three forest stands (FST): Terra Dura, Canafistula and Sanga das Pedras with eucalyptus in the State of Rio Grande do Sul. The soils were sampled in the layers 0-5, 5-20 and 20-40 cm. In the 0-5 cm layer of the Ultisols, most FST studied had a higher organic carbon (OC) content than in adjacent native forest. In cultivated areas, the OC storage was greatest in FST Canafistula, with, in general, lower OC levels in the footslope in relation to the other toposequence positions. In general, the humification index was greater in forests than in the crop areas, but it varied according to the soil depth, the sampled toposequence position and the FST. In the 0-5 and 5-20 cm layer, the natural abundance of 13C in FSTs was similar to the native forests, however, the 13C levels were higher in the deepest layer of the cultivated soils, indicating the contribution to soil organic matter (SOM) of C derived from the pastures that preceded eucalyptus.

Tropical soils characterization at low cost and time using portable X-ray fluorescence spectrometer (pXRF): Effects of different sample preparation methods

Portable X-ray fluorescence spectrometer (pXRF) has been recently adopted by the Soil Science community for uses in both field and laboratory, obtaining the total content of several chemical elements in a few seconds. Sulfuric acid digestion is an expensive and time-consuming laboratory analysis that provides contents of Fe2O3, Al2O3, SiO2, TiO2 and P2O5, important for soil studies. Due to few pXRF studies in tropical soils, this work aimed to compare contents of Fe2O3, Al2O3, SiO2, TiO2 and P2O5 obtained by pXRF with sulfuric acid digestion results, and to evaluate the effects of varying forms of preparing soil samples and scanning with pXRF on the resulting values in Brazilian soils. Soils were scanned in five conditions in-field (in situ) and in laboratory, evaluating varying sample preparation methods, particle sizes and soil moisture. Four pXRF scanning operational modes were tested. Linear regressions were adjusted between results of pXRF and sulfuric acid digestion. Equations were validated with an independent set of samples. Statistical analyses compared the methods of preparing the samples. Adequate linear models reached R2 of 0.99 and 0.89 for Fe2O3 and TiO2, respectively. Validation promoted R 2 greater than 0.97 and RMSE and ME close to zero for both oxides. Statistical differences of pXRF results were found among the methods of preparing samples. pXRF spectrometer has great potential to obtain Fe2O3 and TiO2 content rapidly and economically with high correspondence with laboratory results of sulfuric acid digestion analysis. Varying methods of preparing the samples promote differences in the results of pXRF.

MACRO simulator (version 5.0) for predicting atrazine herbicide behavior in brazilian latosols

The knowledge of pesticides behavior is fundamental for understanding the environmental impact caused by these products. However, related field experiments are time consuming and expensive. The MACRO® simulator allows to predicting the leaching of pesticides through the soil profile and the possible environmental contamination. The objective of this work was to study the percolate behavior and the atrazine leaching in two contrasting Latosols using the MACRO® simulator. The MACRO® simulator was adequate to predict atrazine behavior under the studied conditions and it can be used for the risk evaluation of atrazine contamination in surface and underground waters.