Mineralogical, chemical and electrochemical attributes of soils

A set of attributes endows the soils with distinctive characteristics and astute understanding is required in order to formulate suitable strategies for soil management. The aim of this study was to physically, chemically and mineralogically characterize samples of the main soil classes in Minas Gerais, Brazil, determine the point of zero salt effect (PZSE) and the point of zero charge (PZC), and ascertain the correlation between these factors and soil attributes. The soils evaluated presented different textural classes ranging from loamy sand (Entisol) to very clayey (some Oxisols and Ultisols). The soils differed substantially in terms of fertility, presenting a range from dystrophic (low fertility, base saturation < 50 %) to eutrophic character (fertility, base saturation >= 50 %), even within the same soil class, such as the Oxisols, which suggests the concurrence of the parent material. Highly weathered soils are predominant in Minas Gerais and these soils are composed predominantly of kaolinite, gibbsite, goethite and hematite. Traces of hydroxy-Al interlayered vermiculite and illite were also found in the Oxisols, Ultisols and Inceptisols. A correlation between the PZSE and the PZC in the A horizon was observed. A high degree of correlation was observed between the PZC and the exchangeable aluminum and the ratio of iron obtained by ammonium oxalate and dithionite-citrate (Feo/Fed) in both the A and B horizons of soil classes. The results obtained reinforce the importance of knowledge of soil attributes to the adoption of practices such as the management of phosphate fertilization in clayey soils and liming in soils rich in aluminum.(AU)

Adsorption and desorption of arsenic and its immobilization in soils

Arsenic (As) is a naturally occurring chemical element considered toxic and carcinogenic by health and environmental protection agencies. Studies of As adsorption/desorption behavior in soils are important to predictions of As’ potential mobility in natural systems. The aim of this study was to assess the adsorption of As(V) in soils from Minas Gerais, Brazil, and determine its immobilization rate in order to identify soils with characteristics more favorable to its deployment as an As geochemical barrier. The adsorption experiment was performed using different As concentrations and the data pertaining to the maximum adsorption capacity of As(V) (MACAs) were determined by Langmuir and Freundlich isoterms. The Oxisols, due to their more oxidic mineralogy, especially more gibbsitic, and clayey texture, showed the highest MACAs, followed by Ultisols, Inceptisols, and Entisols. In terms of the desorption of As the Inceptisols were the soils that showed the most As desorption. Both As desorption and mobility was lower in the more oxidic and clayey soils. In all soils, the total amount of As was desorbed in due course, but the As release ratio tended to decrease with the passage of time. In general, soils with higher MACAs did not necessarily show less As desorption. For use as a geochemical barrier, as important as a high adsorption capacity of As by the soil is a low As desorption rate. The increase in As mobility may increase the risks of contaminating the supplies of water. To be a good As geochemical barrier the soil has to be a clayey Oxisol, with relatively high amounts of Fe and Al oxides, especially gibbsite.

Mineralogical, chemical and electrochemical attributes of soils

A set of attributes endows the soils with distinctive characteristics and astute understanding is required in order to formulate suitable strategies for soil management. The aim of this study was to physically, chemically and mineralogically characterize samples of the main soil classes in Minas Gerais, Brazil, determine the point of zero salt effect (PZSE) and the point of zero charge (PZC), and ascertain the correlation between these factors and soil attributes. The soils evaluated presented different textural classes ranging from loamy sand (Entisol) to very clayey (some Oxisols and Ultisols). The soils differed substantially in terms of fertility, presenting a range from dystrophic (low fertility, base saturation = 50 %), even within the same soil class, such as the Oxisols, which suggests the concurrence of the parent material. Highly weathered soils are predominant in Minas Gerais and these soils are composed predominantly of kaolinite, gibbsite, goethite and hematite. Traces of hydroxy-Al interlayered vermiculite and illite were also found in the Oxisols, Ultisols and Inceptisols. A correlation between the PZSE and the PZC in the A horizon was observed. A high degree of correlation was observed between the PZC and the exchangeable aluminum and the ratio of iron obtained by ammonium oxalate and dithionite-citrate (Feo/Fed) in both the A and B horizons of soil classes. The results obtained reinforce the importance of knowledge of soil attributes to the adoption of practices such as the management of phosphate fertilization in clayey soils and liming in soils rich in aluminum.

Adsorption and desorption of arsenic and its immobilization in soils

Arsenic (As) is a naturally occurring chemical element considered toxic and carcinogenic by health and environmental protection agencies. Studies of As adsorption/desorption behavior in soils are important to predictions of As potential mobility in natural systems. The aim of this study was to assess the adsorption of As(V) in soils from Minas Gerais, Brazil, and determine its immobilization rate in order to identify soils with characteristics more favorable to its deployment as an As geochemical barrier. The adsorption experiment was performed using different As concentrations and the data pertaining to the maximum adsorption capacity of As(V) (MACAs) were determined by Langmuir and Freundlich isoterms. The Oxisols, due to their more oxidic mineralogy, especially more gibbsitic, and clayey texture, showed the highest MACAs, followed by Ultisols, Inceptisols, and Entisols. In terms of the desorption of As the Inceptisols were the soils that showed the most As desorption. Both As desorption and mobility was lower in the more oxidic and clayey soils. In all soils, the total amount of As was desorbed in due course, but the As release ratio tended to decrease with the passage of time. In general, soils with higher MACAs did not necessarily show less As desorption. For use as a geochemical barrier, as important as a high adsorption capacity of As by the soil is a low As desorption rate. The increase in As mobility may increase the risks of contaminating the supplies of water. To be a good As geochemical barrier the soil has to be a clayey Oxisol, with relatively high amounts of Fe and Al oxides, especially gibbsite.(AU)

Bioavailability of soil Cu, Fe, Mn and Zn from soil fractions / Biodisponibilidade de Cu, Fe, Mn, e Zn em frações do solo

Cationic micronutrients bioavailability depends on the chemical characteristics of soil fractions. Fourteen soils received individual doses of five micronutrients (Cu, Fe, Mn, Zn, B) arranged in seven treatments set according a Baconian Matrix. The soils incubated with treatments during 15 days had corn cultivated in greenhouse for 30 days, in three consecutive growth cycles. The cationic micronutrients were determined in the corn shoots after each growth cycle. Soil samples collected before the first and after each growth cycle had the available concentrations of Cu, Fe, Mn and Zn determined by single extractions (Mehlich-1 and DTPA-pH 7.3) and by sequential extraction. Correlation analysis was performed for the Cu, Fe, Mn and Zn concentrations determined in the corn shoots, the available concentrations of Cu, Fe, Mn and Zn in the soils (Mehlich-1 and DTPA) and the concentrations of Cu, Fe, Mn and Zn in the soil fractions (sequential extraction). The distribution of available metals forms in fractions reflected their affinity with soil components. Soil available Cu correlated with Cu bound to organic matter. The exchangeable fraction was the main source of soil available Mn and Zn. The Fe availability related mainly to the Mn oxides, Fe oxides, and exchangeable fractions. The plants absorbed Cu mainly from the Mn-oxides and organic matter fractions.(AU)

A biodisponibilidade dos micronutrientes catiônicos depende das características químicas das frações do solo. Quatorze solos receberam doses individuais de cinco micronutrientes (Cu, Fe, Mn, Zn, B) em sete tratamentos, estabelecidos conforme uma Matriz Baconiana. Os solos, com os tratamentos, foram incubados em vasos plásticos durante 15 dias, cultivando-se milho durante 30 dias, em três ciclos consecutivos. Amostras de solo e planta foram coletadas após cada ciclo de crescimento. Os metais foram determinados na parte aérea das plantas e correlacionados com sua disponibilidade no solo (DTPA/Mehlich-1) e concentrações nas frações do solo (extração sequencial). A distribuição dos metais disponíveis nas frações refletiu sua afinidade com os componentes do solo. O Cu disponível correlacionou-se com o ligado à matéria orgânica. Enquanto a fração trocável foi a principal fonte de Mn e Zn disponíveis, a disponibilidade de Fe esteve ligada às frações óxidos de Mn, óxidos de Fe, e fração trocável. As plantas absorveram o Cu, principalmente, das frações óxidos de Mn e matéria orgânica; o Mn das frações trocável e óxidos de Mn; e o Zn da fração trocável. As extrações com DTPA e Mehlich-1 se correlacionaram positivamente com Cu, Mn e Zn absorvidos pelas plantas(AU)

Bioavailability of soil Cu, Fe, Mn and Zn from soil fractions / Biodisponibilidade de Cu, Fe, Mn, e Zn em frações do solo

Cationic micronutrients bioavailability depends on the chemical characteristics of soil fractions. Fourteen soils received individual doses of five micronutrients (Cu, Fe, Mn, Zn, B) arranged in seven treatments set according a Baconian Matrix. The soils incubated with treatments during 15 days had corn cultivated in greenhouse for 30 days, in three consecutive growth cycles. The cationic micronutrients were determined in the corn shoots after each growth cycle. Soil samples collected before the first and after each growth cycle had the available concentrations of Cu, Fe, Mn and Zn determined by single extractions (Mehlich-1 and DTPA-pH 7.3) and by sequential extraction. Correlation analysis was performed for the Cu, Fe, Mn and Zn concentrations determined in the corn shoots, the available concentrations of Cu, Fe, Mn and Zn in the soils (Mehlich-1 and DTPA) and the concentrations of Cu, Fe, Mn and Zn in the soil fractions (sequential extraction). The distribution of available metals forms in fractions reflected their affinity with soil components. Soil available Cu correlated with Cu bound to organic matter. The exchangeable fraction was the main source of soil available Mn and Zn. The Fe availability related mainly to the Mn oxides, Fe oxides, and exchangeable fractions. The plants absorbed Cu mainly from the Mn-oxides and organic matter fractions.

A biodisponibilidade dos micronutrientes catiônicos depende das características químicas das frações do solo. Quatorze solos receberam doses individuais de cinco micronutrientes (Cu, Fe, Mn, Zn, B) em sete tratamentos, estabelecidos conforme uma Matriz Baconiana. Os solos, com os tratamentos, foram incubados em vasos plásticos durante 15 dias, cultivando-se milho durante 30 dias, em três ciclos consecutivos. Amostras de solo e planta foram coletadas após cada ciclo de crescimento. Os metais foram determinados na parte aérea das plantas e correlacionados com sua disponibilidade no solo (DTPA/Mehlich-1) e concentrações nas frações do solo (extração sequencial). A distribuição dos metais disponíveis nas frações refletiu sua afinidade com os componentes do solo. O Cu disponível correlacionou-se com o ligado à matéria orgânica. Enquanto a fração trocável foi a principal fonte de Mn e Zn disponíveis, a disponibilidade de Fe esteve ligada às frações óxidos de Mn, óxidos de Fe, e fração trocável. As plantas absorveram o Cu, principalmente, das frações óxidos de Mn e matéria orgânica; o Mn das frações trocável e óxidos de Mn; e o Zn da fração trocável. As extrações com DTPA e Mehlich-1 se correlacionaram positivamente com Cu, Mn e Zn absorvidos pelas plantas

Mineralogical and chemical attributes of soils from the Brazilian Atlantic Forest domain

The Atlantic Forest is one of the most important and yet the most devastated Brazilian biome, occupying in the past the majority of the East Atlantic Coast. Therefore, a detailed knowledge of the soils near the coastal line influenced by this biome is essential for land use and management of these environments. The aim of this study was to acquire a deeper knowledge of the chemistry, mineralogy and genesis of soils in two micro-watersheds of the Atlantic Forest Biome. Eight soil profiles were sampled and described along one transect. Both young and more developed soils exhibit low fertility and low Fe2O3 content. The Oxic Dystrudepts are less dystrophic than the other soils studied and exhibit greater availability of K+, due to the mixing of weathered material and primary minerals. Transitions from shallow to deep soils are more common in rejuvenated landscapes. All soils are kaolinitic (Kt), with low levels of goethite (Gt) and hematite (Hm), and contain secondary 2:1 minerals such as mica (Mi) and, in the youngest soils, hydroxy-interlayered vermiculite (HIV) and interstratified mica-hydroxy-interlayered vermiculite (Mi-HIV). The widespread presence of gibbsite (Gb) in soils, including the Lithic Udifolist, indicates high rates of both pedogenesis and morphogenesis. The gibbsite showed good crystallinity suggesting that climate, terrain and good drainage favored its formation and stability.

Mineralogical and chemical attributes of soils from the Brazilian Atlantic Forest domain

The Atlantic Forest is one of the most important and yet the most devastated Brazilian biome, occupying in the past the majority of the East Atlantic Coast. Therefore, a detailed knowledge of the soils near the coastal line influenced by this biome is essential for land use and management of these environments. The aim of this study was to acquire a deeper knowledge of the chemistry, mineralogy and genesis of soils in two micro-watersheds of the Atlantic Forest Biome. Eight soil profiles were sampled and described along one transect. Both young and more developed soils exhibit low fertility and low Fe2O3 content. The Oxic Dystrudepts are less dystrophic than the other soils studied and exhibit greater availability of K+, due to the mixing of weathered material and primary minerals. Transitions from shallow to deep soils are more common in rejuvenated landscapes. All soils are kaolinitic (Kt), with low levels of goethite (Gt) and hematite (Hm), and contain secondary 2:1 minerals such as mica (Mi) and, in the youngest soils, hydroxy-interlayered vermiculite (HIV) and interstratified mica-hydroxy-interlayered vermiculite (Mi-HIV). The widespread presence of gibbsite (Gb) in soils, including the Lithic Udifolist, indicates high rates of both pedogenesis and morphogenesis. The gibbsite showed good crystallinity suggesting that climate, terrain and good drainage favored its formation and stability.(AU)

Mineralogy, magnetic susceptibility and geochemistry of Fe-rich Oxisols developed from several parent materials

Fe-rich Oxisols on mafic rocks in Brazil generally have high magnetic susceptibility with high contents of some trace elements. These are taxonomically similar soils; however, differences in magnetic and geochemical properties may affect agricultural or environmental usability and subsequent management. This study investigated the pedogenesis of Fe-rich Oxisols from various parent materials and evaluated the lithogenetic influence on magnetic susceptibility and trace elements contents. Soil samples were collected from Bw horizons in 13 Rhodic Oxisols and a Typic Oxisol developed from several parent materials in Minas Gerais State, Brazil. Soils were analyzed by X-ray diffractometry (XRD) and magnetometry. Soil chemical analyses consisted of sulfuric and total (tri-acid) digestions and selective Fe oxides dissolutions and statistical correlations were determined. Fe-rich Oxisols presented a typical mineralogical composition of highly weathered soils with structural stability. The results confirm the difficulty to identify accurately magnetic minerals in different grain sizes using XRD. However, coarse fractions still exert dominant influence on the magnetic properties of the Fe-rich Rhodic Oxisols. In addition, coarse fractions probably contribute to the enrichment of superparamagnetic particles for the clay fraction. Although highly weathered, Fe-rich Oxisols may have their geochemical attributes still controlled by the parent material, where trace elements seem to be correlated with the magnetic minerals in the coarse fractions. Thus, the natural replacement of some trace elements from soil-solution equilibrium reactions during plant development could be more effective in soils with higher magnetic particles concentrations in the coarse fractions.

Mineralogy, magnetic susceptibility and geochemistry of Fe-rich Oxisols developed from several parent materials

Fe-rich Oxisols on mafic rocks in Brazil generally have high magnetic susceptibility with high contents of some trace elements. These are taxonomically similar soils; however, differences in magnetic and geochemical properties may affect agricultural or environmental usability and subsequent management. This study investigated the pedogenesis of Fe-rich Oxisols from various parent materials and evaluated the lithogenetic influence on magnetic susceptibility and trace elements contents. Soil samples were collected from Bw horizons in 13 Rhodic Oxisols and a Typic Oxisol developed from several parent materials in Minas Gerais State, Brazil. Soils were analyzed by X-ray diffractometry (XRD) and magnetometry. Soil chemical analyses consisted of sulfuric and total (tri-acid) digestions and selective Fe oxides dissolutions and statistical correlations were determined. Fe-rich Oxisols presented a typical mineralogical composition of highly weathered soils with structural stability. The results confirm the difficulty to identify accurately magnetic minerals in different grain sizes using XRD. However, coarse fractions still exert dominant influence on the magnetic properties of the Fe-rich Rhodic Oxisols. In addition, coarse fractions probably contribute to the enrichment of superparamagnetic particles for the clay fraction. Although highly weathered, Fe-rich Oxisols may have their geochemical attributes still controlled by the parent material, where trace elements seem to be correlated with the magnetic minerals in the coarse fractions. Thus, the natural replacement of some trace elements from soil-solution equilibrium reactions during plant development could be more effective in soils with higher magnetic particles concentrations in the coarse fractions.(AU)