Abstract
The Brazilian System of Soil Classification (SiBCS) is a taxonomic system, open and in permanent construction, as new knowledge on Brazilian soils is obtained. The objective of this study was to characterize the chemical, physical, morphological, micro-morphological and mineralogical properties of four pedons of Oxisols in a highland toposequence in the upper Jequitinhonha Valley, emphasizing aspects of their genesis, classification and landscape development. The pedons occupy the following slope positions: summit - Red Oxisol (LV), mid slope (upper third) - Yellow-Red Oxisol (LVA), lower slope (middle third)- Yellow Oxisol (LA) and bottom of the valley (lowest third) - "Gray Oxisol" ("LAC"). These pedons were described and sampled for characterization in chemical and physical routine analyses. The total Fe, Al and Mn contents were determined by sulfuric attack and the Fe, Al and Mn oxides in dithionite-citrate-bicarbonate and oxalate extraction. The mineralogy of silicate clays was identified by X ray diffraction and the Fe oxides were detected by differential X ray diffraction. Total Ti, Ga and Zr contents were determined by X ray fluorescence spectrometry. The "LAC" is gray-colored and contains significant fragments of structure units in the form of a dense paste, characteristic of a gleysoil, in the horizons A and BA. All pedons are very clayey, dystrophic and have low contents of available P and a pH of around 5. The soil color was related to the Fe oxide content, which decreased along the slope. The decrease of crystalline and low- crystalline Fe along the slope confirmed the loss of Fe from the "LAC". Total Si increased along the slope and total Al remained constant. The clay fraction in all pedons was dominated by kaolinite and gibbsite. Hematite and goethite were identified in LV, low-intensity hematite and goethite in LVA, goethite in LA. In the "LAC", no hematite peaks and goethite were detected by differential X ray diffraction. The micro-morphology indicated prevalence of granular microstructure and porosity with complex stacking patterns.. The soil properties in the toposequence converged to a single soil class, the Oxisols, derived from the same source material. The landscape evolution and genesis of Oxisols of the highlands in the upper Jequitinhonha Valley are related to the evolution of the drainage system and the activity of excavating fauna.
Highlights
The Brazilian System of Soil Classification – Sistema Brasileiro de Classificação de Solos (SiBCS) (Embrapa, 2006) comprises 13 soil orders, one of which are the Oxisols
The Oxisols sustain a large fraction of the agricultural, livestock and forestry production in Brazil, since their physical properties are highly suitable for mechanization and large-scale production
According to the current SiBCS (Embrapa, 2006), the pedons were classified along the slope as Red Oxisol (LV) – A prominent, very clayey texture
Summary
The Brazilian System of Soil Classification – SiBCS (Embrapa, 2006) comprises 13 soil orders, one of which are the Oxisols. In Brazil, such soils cover a total surface of about 331,637,200 ha, corresponding to approximately 39 % of the Brazilian territory (Espig et al, 2005) These soils are the most weathered of the Earth surface, and are found predominantly on the summit of plateaus and on slopes, in the region of the Cerrado (savanna-like vegetation in Brazil). They have been described as deep, nutrient-poor, practically without primary minerals (Gomes et al, 2004). The SiBCS is a taxonomic system, open and in permanent construction, as new knowledge on Brazilian soils is obtained
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