Mauro Resende

The magnetic soils of Brazil

Abstract Certain Brazilian latosols show a spontaneous magnetization of the clay size fraction in excess of 1 J/T kg: they can be picked up by a hand magnet. Magnetization is a good indicator of soil type, being greatest in those soils derived from mafic or itabiritic rocks which have been little influenced by xanthization (the soil yellowing process). The magnetic phase is fully-oxidized titanomaghemite which is inherited directly from weathered bedrock. Simple magnetic measurements are recommended as an aid in classifying tropical latosols.

Pedossistemas da Mata Atlântica: considerações pertinentes sobre a sustentabilidade

A pedological analysis was carried out on the ecologically important Atlantic Forest system, as a contribution to the study of its biodiversity. Focus is placed on some factors that can influence local diversity, such as soil depth, that varies within short distances. The reasons for prohibiting the cultivation of hilly soils by small farmers is also questioned. It is suggested that radiation, water and nutrient resources, should be emphasized, since they are essential to ecosystem functioning, instead of indirect variables. Based on pedological information, ten great environments in the Atlantic Forest were identified. Comments related to water and nutrients, and observations related to use, fragility and ecological importance are made about each stratified ecosystem. Two great ecosystems are indicated as potentially very important to diversity: shallow soil areas and rock outcrops and humic soil areas (a very important carbon sink), in the higher portions of the landscape.

Magnetic properties of iron-rich oxisols

Four occurrences of highly magnetic soil in Brazil have been analysed with a view to identifying the magnetic minerals and quantifying the soil magnetization. Techniques used include X-ray diffraction, X-ray fluorescence and Mössbauer spectroscopy. This approach leads us to identify several ways that these soils, which have spontaneous magnetization in the range 1<σs<35 J/T/kg, can come about.One soil, which forms on dolerite (19.6 wt% Fe2O3), is found to contain fully-oxidized titanomaghemite inherited from the parent rock. This oxide has a canted ferrimagnetic spin structure with σs=36 J/T/kg of sample. The three others, formed on very iron-rich rock (50–90 wt% Fe2O3), contain magnetite or maghemite as the magnetic species and in two cases the soil is more magnetic than the parent rock (largely composed of pure hematite).

Development of magnetic soil from ferroan dolomite

An occurrence of maghemitic soil in association with ferroan dolomite in Minas Gerais is characterized by X-ray diffraction, magnetization measurements and Mossbauer spectroscopy. Altered layers on outliers of dolomite, which has composition (Ca1.04Mg0.83Fe0.11Mn0.02)(CO3)2 indicate the weathering sequence: ferroan dolomite → calcite + poorly-crystallized ferric hydroxide → maghemite + hematite + goethite. The spontaneous magnetization of the maghemitic soil (65 wt% Fe2O3) is 8.8 JT−1kg−1; the magnetization of the soil maghemite itself is estimated to be 25±5 JT−1kg−1, which is greatly reduced from the value for pure maghemite because of isomorphous substitution.

57Fe Mössbauer studies of oxisols

Mössbauer spectroscopy is a valuable complement to the standard analytical techniques of soil science for characterizing the iron content of soils, and for studying the mineralogical transformations that occur during pedogenesis from the point of view of the iron. The uses and limitations of Mössbauer spectroscopy in this field are illustrated by five selected examples. In each case, the starting point is a different question relating to the soil colour, mineralogy, magnetization or mode of formation.

Mobilização do solo, erosão e produtividade de milho e feijão em um regossolo no agreste pernambucano

This study was conducted in Caruaru County, PE, Brazil, from 1970 to 1990, in an eutrophic Regosol 12% slope, to evaluate different soil tillage methods on soil and water losses and corn (Zea mays L.) and bean (Phaseolus vulgaris L.) productivity under natural rainfall conditions. Data were obtained from four 1,000 m 2 experimental plots equiped to collect eroded material from the following treatments: hoe (manual), plow and harrow, double plow and harrow, and only harrow. The mean annual soil and water losses was higher with plowing twice and harrowing and with plowing and harrowing treatments, but, in general, the losses were low in all treatments. This fact was attributed to the large amounts of gravel and coarse sand in the soil profile by reducing direct impact of rain drops and increasing permeability. The more intensive soil tillage methods, by placing richer layer in nutrients deeper, where more water is available, increase nutrient absorption resulting in higher productivity specially for corn. There was significant correlation between corn productivity and average P content from 9 to 14 cm, 10 to 19 cm and 14 to 22 cm depths.

Mössbauer analysis of Brazilian Oxisols

Three sets of Brazilian Oxisols have been analysed by Mössbauer spectroscopy at 290, 80 and 4.2 K. In most cases two resolved magnetic hyperfine patterns associated with aluminous goethite and hematite are resolved; their ratio is related to soil colour. Samples from a 3 m soil profile show that both oxides become decreasingly aluminium substituted and/or better crystallized with depth. Goethite from surface or deep layers is readily differentiated by its hyperfine parameters. As there is no significant alternate source of iron, the results suggest that both hematite and goethite undergo continuous neoformation throughout the profile in response to the changing pedogenic environment.

Cotas fluviométricas do rio Acre, suas causas e implicações na política de colonização

Historical and limnimetrical records of rivers in the state of Acre (Amazon Region), Brazil, and soil characteristics are used to predict an increase in flood and navigation hazards with farther colonization of the region. It is suggested that a colonization plan to explore and preserve the natural forest should be improved based on the ideyitification of the main problems by interviews with the old colonizers and a re-study of the present colonization model.