Soils and environments of the Ferriferous Quadrangle (MG) and forestry suitability of the Coastal Plains / Solos e ambientes do QuadrilÃtero FerrÃfero (MG) e aptidÃo silvicultural dos Tabuleiros Costeiros

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Two quite different Brazilian environments were approached in this work: the Ferriferous Quadrangle, located in the center-south portion of the State of Minas Gerais, and Coastal Plains, which extend in narrow strip along the coast from the State of Rio de Janeiro to AmapÃ. The first was studied in a more general context, with respect to the distribution of the soils in the landscape and their interrelations with the components of the physical environment, having as a base an area representative of the region, referring to the Ãrea de ProteÃÃo Ambiental da RegiÃo Metropolitana de Belo Horizonte (APA Sul RMBH), in which seven different pedoenvironments were recognized and characterized, as well as in a more specific context, addressed to the soil physical, chemical and mineralogical characterization, with special attention to the iron oxides (a general expression which includes oxides, oxihydroxides ande hydroxides) and the relationship among trace elements content and parent material, and taxonomy of high iron level soils, which are common in this environment. For this, the following were sampled in the Ferriferous Quadrangle area: soils resulting from the weathering of mainly three parent materials: itabirite, ferroan dolomite (from the Cauà and Gandarela formations respectively, both of the Itabira group) and serpentinites (from the CÃrrego dos Boiadeiros complex), to which collection it were included soils of other Brazilian areas, developed from different parent materials, with prominence for tuffite, basalt and basic-ultrabasic rocks. Besides the very high iron levels obtained by the sulphuric acid digestion, the soils studied are differentiated by the intense red color and expressive maghemite concentration (one of the highest in Brazilian soils), that besides hematite and goethite constitute the dominant minerals in the clay fraction, which makes the use of color as an exclusive criterion of taxonomic distinction at the suborder level, as adopted by the current Brazilian Soil Classification System questionable, a criterion that is based, in synthesis, on the proportion between goethite and hematite indicated by the hue. In view of that, it is suggested that the iron levels are considered together with color in the distinction of soils in second category level, similar to the criterion used previously for the differentiation of Latosols by the classification scheme formerly adopted in Brazil. In some soils developed from ferroan dolomite from the Gandarela formation, which stand out due to an especially darkened coloration, it was also registered the todorokite presence, manganese oxide whose identification in soils is very uncommon. It is worthy to mention that in some soils studied here, the amount of manganese oxides (whithout concentration pre-treatments) is one of the highest in our country. As for the total content of trace elements, a clear differentiation was observed between soils related to the itabirite and the ferroan dolomite, on one hand, with levels very inferior to those developed of tuffite and basalt, and those derived from sepentinite on the other hand, in which some of the analyzed elements, especially chrome and nickel, are in extremely high concentrations, indicating a pollutant potential. Values of the molecular relationship between the content of titanium and iron oxides (TiO2/Fe2O3) obtained from the sulphuric acid digestion inferior to 0.10 were shown appropriate for the distinction of the soils derived of tuffite and basalt from those related to ferriferous materials and basic-ultrabasic rocks. Another aspect of note refers to the abundance of ferruginous concretions (petroplinthite) in the coarse fraction (cobbles and pebbles) of some soils of the Ferriferous Quadrangle, which, according to the current criteria leads them to be Petric Plinthosols, in spite of the very different pedogenetic conditions in relation to the formation environment of plinthite, together with other differential morphologic characteristics. As such, the figure of the concrecionary horizon as a diagnostic horizon is questioned, as defined by the current Brazilian System of Soil Classification, in view of the incongruity with the morphogenetic character considered as a basic principle of soil classification. As for the ecosystem represented by the Coastal Plains, a system was elaborated for evaluation of the forestry suitability for eucalyptus, motivated by the strong expansion of this crop in areas of that unit of landscape and the absence of more specific criteria for evaluation of the use potentialities of their lands. It were adopted the basic concepts of the evaluation method of the agricultural suitability used by Embrapa, establishing parameters and unique symbolization for the evaluation of the forestry suitability, considering the eucalyptus crop in this specific environment, and two management levels (medium and high technological level). Based on the established criteria, a computerized system was elaborated in the Microsoft Excel program, which makes the automatic evaluation of the suitability for eucalyptus in the environment in question possible, which should evolve through validation tests and adjustments, with basis upon the eucalyptus clones productivity. The proposed system constitutes an important tool for evaluation of areas of restricted dimensions, as well as for land use planning and diverse zonings, and also as a substantial support for precision silviculture.

ASSUNTO(S)

solos ferruginosos, Ãxidos de ferro, elementos-traÃo, potencial de uso da terra ferruginous soils, iron oxides, trace elements, use land pontenciality ciencia do solo

ACESSO AO ARTIGO

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