Rare earth elements in gneiss regoliths in southern Minas Gerais, Brazil

Regolith characterization in its entirety is particularly difficult in gneissic regoliths due to the heterogeneity of their rock structure. Rare earth elements (REE) are a useful tool in helping understand the evolution of regoliths. This study relates the mineralogy and weathering indexes of three gneisses regoliths (P1-leucocratic, P2-mesocratic and P3-melanocratic gneisses) to the distribution of REE at depth. In soil, clay activity, iron and manganese oxides, CaO, SiO2, P2O5, TiO2, Fe2O3, and MgO showed high positive correlation with REE. The absolute content of REE was enriched in mafic minerals. At the interface between the soil and saprolite, the sum of absolute REE content was greater in soil than in saprolite in P1, while the opposite pattern was found in P2 and P3. The sums of absolute REE in the whole profiles did not overlap between P1, P2 and P3, and the absolute concentration of Gadolinium (Gd) differentiated the three gneisses in all and every horizon/layer of their regoliths without overlapping values. Normalized REE content was greater in the subsurface of P1 due to Eu content in plagioclase, and fractionation had less variation when estimated by Light REE / Heavy REE (LREE/HREE) than by La/Yb, since the variation in REE is great in gneisses (due to the segregation of minerals into bands), and had low levels of association with the Chemical Index of Alteration (CIA) and the Weathering Index of Parker (WIP).

Rare earth elements in gneiss regoliths in southern Minas Gerais, Brazil

Regolith characterization in its entirety is particularly difficult in gneissic regoliths due to the heterogeneity of their rock structure. Rare earth elements (REE) are a useful tool in helping understand the evolution of regoliths. This study relates the mineralogy and weathering indexes of three gneisses regoliths (P1-leucocratic, P2-mesocratic and P3-melanocratic gneisses) to the distribution of REE at depth. In soil, clay activity, iron and manganese oxides, CaO, SiO2, P2O5, TiO2, Fe2O3, and MgO showed high positive correlation with REE. The absolute content of REE was enriched in mafic minerals. At the interface between the soil and saprolite, the sum of absolute REE content was greater in soil than in saprolite in P1, while the opposite pattern was found in P2 and P3. The sums of absolute REE in the whole profiles did not overlap between P1, P2 and P3, and the absolute concentration of Gadolinium (Gd) differentiated the three gneisses in all and every horizon/layer of their regoliths without overlapping values. Normalized REE content was greater in the subsurface of P1 due to Eu content in plagioclase, and fractionation had less variation when estimated by Light REE / Heavy REE (LREE/HREE) than by La/Yb, since the variation in REE is great in gneisses (due to the segregation of minerals into bands), and had low levels of association with the Chemical Index of Alteration (CIA) and the Weathering Index of Parker (WIP).(AU)

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)

Relação solo-vegetação em remanescente da floresta estacional decidual na região central do Rio Grande do Sul / Soil-vegetation relationship in seasonal deciduous forest remnant in the central region of Rio Grande do Sul, Brazil

O presente trabalho objetivou caracterizar a relação solo-vegetação em remanescente da Floresta Estacional Decidual na Região Central do Rio Grande do Sul a partir da análise da relação entre atributos edáficos e dois grupos fitossociológicos (G1 e G2). Características químicas e o percentual de argila do solo foram submetidos à análise da variância e suas relações com G1 e G2 foram avaliadas por análise de componentes principais (ACP). Para tanto, G1 e G2 foram classificados em 3 intervalos de declividade: 1-14º; 15-34º e 35-45º. Foram identificados Neossolo Litólico nas áreas declivosas e Neossolo Quartzarênico nas áreas planas. G1 na declividade 35-45º e G2 em 1-14º foram mais sensíveis à variação da qualidade química do solo. A relação dos grupos fitossociológicos com a qualidade química do solo aumentou proporcionalmente ao aumento de declividade. Relevo declivoso, pedogênese incipiente e material de origem sedimentar ressaltaram a fragilidade da área, o que valoriza a presença da floresta para a manutenção de serviços ambientais.(AU)

The present study aimed to characterize the soil-vegetation relationship in Seasonal Deciduous Forest remnant at Central Region of Rio Grande do Sul, starting from the analysis of the relationship between soil attributes and two phytosociological groups (G1 and G2). Chemical soil characteristics and clay percentage were submitted to variance analysis and relations with G1 and G2 were evaluated by Principal Components Analysis (PCA). Therefore, it was classified G1 and G2 within 3 slope intervals: 1-14°, 15-34° and 35-45°. Leptosols have been identified in high slopes and Arenosols in the plan area. G1 in 35-45° and G2 in 1-14º were more sensitive to soil chemical quality. The phytosociological groups and soil quality relationship increased proportionally with the increase on slope. The declivous relief, recent pedogenesis and sedimentary parental material highlighted the fragility of the area, which emphasizes the forest presence for the environmental services maintenance.(AU)

Caracterização de plintitas e petroplintitas em solos da depressão central do Rio Grande do Sul

The presence, composition and distribution of ferruginous concretions in the soil, called plinthite and petroplinthites, are conditioned to the environmental characteristics of the region, attributing intrinsic properties to the soil. The objective of this study was to understand the composition of plinthite and petroplinthites, of soils at the Central Depression of Rio Grande do Sul state, Brazil, by the evaluation of chemical and mineralogical characteristics of these features. For this, chemical, morphological and particle size characterization of three soil profiles, was performed. The ferruginous concretions present in some horizons were separated from the soil matrix and submitted, separately to successive procedures for selective extraction of Fe and Al. The horizons of the soils showed a wide variation of textures and chemical attributes such as pH, S, V, m and MO. The levels of Feh, Feo and Fed followed the trend of the soil matrix plinthite petroplinthites. Among the oxides of Fe, there was higher incidence of hematite mineral in all samples.

A presença, composição e distribuição de concreções ferruginosas no solo, denominadas de plintitas e petroplintitas, é condicionada às características ambientais da região, atribuindo propriedades intrínsecas ao solo. O objetivo do estudo foi caracterizar plintitas e petroplintitas de solos da Depressão Central do Rio Grande do Sul através da avaliação de características químicas e mineralógicas dessas feições. Para tanto, procedeu-se à caracterização química, morfológica e granulométrica de três perfis de solo. As concreções ferruginosas presentes em alguns horizontes foram separadas da matriz do solo e submetidas, separadamente, a sucessivos procedimentos de extrações seletivas de Fe e Al. Os horizontes dos solos apresentaram ampla variação de textura e atributos químicos como pH, S, V, m e Matéria Orgânica. Os teores de Feh, Fed e Feo seguiram a tendência: matriz do solo plintitas petroplintitas. Dentre os óxidos de Fe, verificou-se predomínio do mineral hematita em todas as amostras avaliadas.

Caracterização de plintitas e petroplintitas em solos da depressão central do Rio Grande do Sul

The presence, composition and distribution of ferruginous concretions in the soil, called plinthite and petroplinthites, are conditioned to the environmental characteristics of the region, attributing intrinsic properties to the soil. The objective of this study was to understand the composition of plinthite and petroplinthites, of soils at the Central Depression of Rio Grande do Sul state, Brazil, by the evaluation of chemical and mineralogical characteristics of these features. For this, chemical, morphological and particle size characterization of three soil profiles, was performed. The ferruginous concretions present in some horizons were separated from the soil matrix and submitted, separately to successive procedures for selective extraction of Fe and Al. The horizons of the soils showed a wide variation of textures and chemical attributes such as pH, S, V, m and MO. The levels of Feh, Feo and Fed followed the trend of the soil matrix plinthite petroplinthites. Among the oxides of Fe, there was higher incidence of hematite mineral in all samples.

A presença, composição e distribuição de concreções ferruginosas no solo, denominadas de plintitas e petroplintitas, é condicionada às características ambientais da região, atribuindo propriedades intrínsecas ao solo. O objetivo do estudo foi caracterizar plintitas e petroplintitas de solos da Depressão Central do Rio Grande do Sul através da avaliação de características químicas e mineralógicas dessas feições. Para tanto, procedeu-se à caracterização química, morfológica e granulométrica de três perfis de solo. As concreções ferruginosas presentes em alguns horizontes foram separadas da matriz do solo e submetidas, separadamente, a sucessivos procedimentos de extrações seletivas de Fe e Al. Os horizontes dos solos apresentaram ampla variação de textura e atributos químicos como pH, S, V, m e Matéria Orgânica. Os teores de Feh, Fed e Feo seguiram a tendência: matriz do solo plintitas petroplintitas. Dentre os óxidos de Fe, verificou-se predomínio do mineral hematita em todas as amostras avaliadas.

Caracterização de plintitas e petroplintitas em solos da depressão central do Rio Grande do Sul

The presence, composition and distribution of ferruginous concretions in the soil, called plinthite and petroplinthites, are conditioned to the environmental characteristics of the region, attributing intrinsic properties to the soil. The objective of this study was to understand the composition of plinthite and petroplinthites, of soils at the Central Depression of Rio Grande do Sul state, Brazil, by the evaluation of chemical and mineralogical characteristics of these features. For this, chemical, morphological and particle size characterization of three soil profiles, was performed. The ferruginous concretions present in some horizons were separated from the soil matrix and submitted, separately to successive procedures for selective extraction of Fe and Al. The horizons of the soils showed a wide variation of textures and chemical attributes such as pH, S, V, m and MO. The levels of Feh, Feo and Fed followed the trend of the soil matrix plinthite petroplinthites. Among the oxides of Fe, there was higher incidence of hematite mineral in all samples.

A presença, composição e distribuição de concreções ferruginosas no solo, denominadas de plintitas e petroplintitas, é condicionada às características ambientais da região, atribuindo propriedades intrínsecas ao solo. O objetivo do estudo foi caracterizar plintitas e petroplintitas de solos da Depressão Central do Rio Grande do Sul através da avaliação de características químicas e mineralógicas dessas feições. Para tanto, procedeu-se à caracterização química, morfológica e granulométrica de três perfis de solo. As concreções ferruginosas presentes em alguns horizontes foram separadas da matriz do solo e submetidas, separadamente, a sucessivos procedimentos de extrações seletivas de Fe e Al. Os horizontes dos solos apresentaram ampla variação de textura e atributos químicos como pH, S, V, m e Matéria Orgânica. Os teores de Feh, Fed e Feo seguiram a tendência: matriz do solo plintitas petroplintitas. Dentre os óxidos de Fe, verificou-se predomínio do mineral hematita em todas as amostras avaliadas.

Alteração mineralógica de Neossolos em uma climo-litossequência no Planalto do Rio Grande do Sul

In the Rio Grande do Sul state (RS) Neossolos Litólicos (Leptosols) and Neossolos Regolíticos (Regosols) are soils that have been suffering strong use pressure, demanding better knowledge on their genesis and mineralogy than the existing one. The objective of this research was to determine the weathering degree of Neossolos Litólicos and Neossolos Regolíticos through the evaluation of the minerals alteration in profiles disposed in a climo-litossequence in the RS Plateau, using techniques of chemical dissolution and X rays diffraction. The authors identified two groups of soils with different alteration degree. The first one is composed by the profiles of the West portion of the climo-litossequence (P1, P2 and P3) which has the weathering degree between the bissialitization and the monossialitization, with high content of smectite with hidroxi-Al interlayers (EHE), caulinite and hematite in the clay fraction. The second one is represented by the profiles of the East portion (P4 and P5), with weathering degree between the monossialitization and the ferralitization, with high content of caulinite and goethite and presence of gibbsite and EHE in the clay. The results suggested an higher contribution of the climate on the weathering of the profiles. The ki and kr indexes were not efficient in representing the condition of secondary alteration of the profiles of Neossolos.

No Estado do Rio Grande do Sul (RS), os Neossolos Litólicos e Neossolos Regolíticos são solos que têm sofrido forte pressão de uso, demandando maior conhecimento sobre sua gênese e mineralogia. O objetivo deste trabalho foi determinar o grau de intemperismo de Neossolos Litólicos e Neossolos Regolíticos, avaliando-se a alteração dos minerais em perfis dispostos em uma climo-litossequência no Planalto do RS, através de técnicas de dissolução química e difração de raios X. Foram identificados dois grupos de solos com graus de alteração distintos. O primeiro é constituído pelos perfis da porção Oeste da climo-litossequência (P1, P2 e P3) e encontra-se no estádio entre a bissialitização e a monossialitização, com predomínio de esmectita com hidroxi-Al entrecamadas (EHE), caulinita e hematita na fração argila. O segundo é representado pelos perfis da porção Leste (P4 e P5), encontrando-se no estádio entre a monossialitização e a ferralitização, com predomínio de caulinita e goethita e presença de gibbsita e EHE na fração argila. Os resultados sugerem maior influência do clima na alteração dos perfis. Os índices ki e kr não foram eficientes em representar a condição de alteração secundária dos perfis de Neossolos.

Alteração mineralógica de Neossolos em uma climo-litossequência no Planalto do Rio Grande do Sul

In the Rio Grande do Sul state (RS) Neossolos Litólicos (Leptosols) and Neossolos Regolíticos (Regosols) are soils that have been suffering strong use pressure, demanding better knowledge on their genesis and mineralogy than the existing one. The objective of this research was to determine the weathering degree of Neossolos Litólicos and Neossolos Regolíticos through the evaluation of the minerals alteration in profiles disposed in a climo-litossequence in the RS Plateau, using techniques of chemical dissolution and X rays diffraction. The authors identified two groups of soils with different alteration degree. The first one is composed by the profiles of the West portion of the climo-litossequence (P1, P2 and P3) which has the weathering degree between the bissialitization and the monossialitization, with high content of smectite with hidroxi-Al interlayers (EHE), caulinite and hematite in the clay fraction. The second one is represented by the profiles of the East portion (P4 and P5), with weathering degree between the monossialitization and the ferralitization, with high content of caulinite and goethite and presence of gibbsite and EHE in the clay. The results suggested an higher contribution of the climate on the weathering of the profiles. The ki and kr indexes were not efficient in representing the condition of secondary alteration of the profiles of Neossolos.

No Estado do Rio Grande do Sul (RS), os Neossolos Litólicos e Neossolos Regolíticos são solos que têm sofrido forte pressão de uso, demandando maior conhecimento sobre sua gênese e mineralogia. O objetivo deste trabalho foi determinar o grau de intemperismo de Neossolos Litólicos e Neossolos Regolíticos, avaliando-se a alteração dos minerais em perfis dispostos em uma climo-litossequência no Planalto do RS, através de técnicas de dissolução química e difração de raios X. Foram identificados dois grupos de solos com graus de alteração distintos. O primeiro é constituído pelos perfis da porção Oeste da climo-litossequência (P1, P2 e P3) e encontra-se no estádio entre a bissialitização e a monossialitização, com predomínio de esmectita com hidroxi-Al entrecamadas (EHE), caulinita e hematita na fração argila. O segundo é representado pelos perfis da porção Leste (P4 e P5), encontrando-se no estádio entre a monossialitização e a ferralitização, com predomínio de caulinita e goethita e presença de gibbsita e EHE na fração argila. Os resultados sugerem maior influência do clima na alteração dos perfis. Os índices ki e kr não foram eficientes em representar a condição de alteração secundária dos perfis de Neossolos.

Extrapolação das relações solo-paisagem a partir de uma área de referência

The aim of this study was to apply an automated technique of soil mapping from predictive models developed at a reference area, into nearby areas of the same soil-landscape relationships. Generalized linear models were developed using nine terrain attributes derived from a digital elevation model as covariate predictors, with soil classes, obtained from a conventional soil survey, as dependent variables. The models were able to distinguish the three main forms of the local landscape. Soil classes with pedogenesis intimately tied to the predictive covariates obtained the best results. The soil maps generated, showed a reproducibility of 46.12% and an accuracy of 21.06%.

O objetivo deste estudo foi aplicar uma técnica automatizada de mapeamento de solos a partir de modelos preditivos ajustados em uma área de referência e, posteriormente, aplicados em áreas próximas de mesmas relações solo-paisagem. Modelos lineares generalizados foram desenvolvidos utilizando-se de nove atributos de terreno, derivados de um Modelo Digital de Elevação, como covariáveis preditoras e classes de solos, obtidas em um levantamento convencional, como variáveis dependentes. Os modelos foram capazes de distinguir as três principais formas da paisagem local. Classes de solos de pedogênese intimamente ligada às covariáveis preditoras obtiveram os melhores resultados. O mapa de solos gerado apresentou uma reprodutibilidade de 46,12% e uma exatidão de 21,06%.

Extrapolação das relações solo-paisagem a partir de uma área de referência

The aim of this study was to apply an automated technique of soil mapping from predictive models developed at a reference area, into nearby areas of the same soil-landscape relationships. Generalized linear models were developed using nine terrain attributes derived from a digital elevation model as covariate predictors, with soil classes, obtained from a conventional soil survey, as dependent variables. The models were able to distinguish the three main forms of the local landscape. Soil classes with pedogenesis intimately tied to the predictive covariates obtained the best results. The soil maps generated, showed a reproducibility of 46.12% and an accuracy of 21.06%.

O objetivo deste estudo foi aplicar uma técnica automatizada de mapeamento de solos a partir de modelos preditivos ajustados em uma área de referência e, posteriormente, aplicados em áreas próximas de mesmas relações solo-paisagem. Modelos lineares generalizados foram desenvolvidos utilizando-se de nove atributos de terreno, derivados de um Modelo Digital de Elevação, como covariáveis preditoras e classes de solos, obtidas em um levantamento convencional, como variáveis dependentes. Os modelos foram capazes de distinguir as três principais formas da paisagem local. Classes de solos de pedogênese intimamente ligada às covariáveis preditoras obtiveram os melhores resultados. O mapa de solos gerado apresentou uma reprodutibilidade de 46,12% e uma exatidão de 21,06%.

Causes of morphological discontinuities in soils of Depressão Central, Rio Grande do Sul State, Brazil

Morphological, particularly textural, discontinuities between horizons increase soil erodibility in Depressão Central, Rio Grande do Sul State (Brazil). Characterization of such discontinuities would help to understand landscape evolution and to model near-surface hydrology. The objective of this research was to explore the relationship between morphological discontinuity and deposition of transported materials during pedogenesis. Transported material was meant to be mineral particles found in the soil profile, transported probably by water or gravity, that were not present neither in the parent material nor derived from it. Five soils of this region (two Alfisols, two Ultisols and one Mollisol) were sampled and morphological, sand grain size statistics, chemical and mineralogical analyses were used to search for evidences of deposition of transported materials. Two soils had abrupt textural change but no evidence of deposition of transported materials, two soils had less contrasting morphology and some characteristics that are possibly related to deposition, and one soil had no morphological discontinuity, but had deposition of material enriched in magnetite-maghemite in the sand fraction of the A horizon. Therefore, there were no relationship between morphological discontinuity and deposition of transported materials for these profiles in the Depressão Central.

Contrastes morfológicos entre horizontes, e particularmente os contrastes texturais, aumentam a erodibilidade do solo na Depressão Central do Rio Grande do Sul (Brasil). A caracterização destes contrastes contribui para a compreensão da evolução da paisagem e para a modelagem da hidrologia de superfície. Cinco solos desta região foram amostrados e a morfologia, distribuição do tamanho de grãos da fração areia, análises químicas e mineralógicas foram usadas para tentativamente relacionar o contraste textural e morfológico com materiais transportados durante a pedogênese. Por materiais transportados entendem-se as partículas minerais presentes no perfil do solo, transportadas provavelmente por água ou gravidade, e que não estavam presentes nem no material de origem e nem foram derivadas deste. Dois solos apresentaram mudança textural abrupta sem evidências de deposição, dois solos apresentaram menor contraste morfológico e evidências que sustentam a possibilidade de deposição e um solo não apresentou contraste morfológico, porém as características indicam deposição de material rico em magnetita-maghemita na fração areia do horizonte A. Portanto, não foi encontrada relação entre descontinuidades morfológicas e deposição de materiais transportados, na Depressão Central.

Causes of morphological discontinuities in soils of Depressão Central, Rio Grande do Sul State, Brazil

Morphological, particularly textural, discontinuities between horizons increase soil erodibility in Depressão Central, Rio Grande do Sul State (Brazil). Characterization of such discontinuities would help to understand landscape evolution and to model near-surface hydrology. The objective of this research was to explore the relationship between morphological discontinuity and deposition of transported materials during pedogenesis. Transported material was meant to be mineral particles found in the soil profile, transported probably by water or gravity, that were not present neither in the parent material nor derived from it. Five soils of this region (two Alfisols, two Ultisols and one Mollisol) were sampled and morphological, sand grain size statistics, chemical and mineralogical analyses were used to search for evidences of deposition of transported materials. Two soils had abrupt textural change but no evidence of deposition of transported materials, two soils had less contrasting morphology and some characteristics that are possibly related to deposition, and one soil had no morphological discontinuity, but had deposition of material enriched in magnetite-maghemite in the sand fraction of the A horizon. Therefore, there were no relationship between morphological discontinuity and deposition of transported materials for these profiles in the Depressão Central.

Contrastes morfológicos entre horizontes, e particularmente os contrastes texturais, aumentam a erodibilidade do solo na Depressão Central do Rio Grande do Sul (Brasil). A caracterização destes contrastes contribui para a compreensão da evolução da paisagem e para a modelagem da hidrologia de superfície. Cinco solos desta região foram amostrados e a morfologia, distribuição do tamanho de grãos da fração areia, análises químicas e mineralógicas foram usadas para tentativamente relacionar o contraste textural e morfológico com materiais transportados durante a pedogênese. Por materiais transportados entendem-se as partículas minerais presentes no perfil do solo, transportadas provavelmente por água ou gravidade, e que não estavam presentes nem no material de origem e nem foram derivadas deste. Dois solos apresentaram mudança textural abrupta sem evidências de deposição, dois solos apresentaram menor contraste morfológico e evidências que sustentam a possibilidade de deposição e um solo não apresentou contraste morfológico, porém as características indicam deposição de material rico em magnetita-maghemita na fração areia do horizonte A. Portanto, não foi encontrada relação entre descontinuidades morfológicas e deposição de materiais transportados, na Depressão Central.

Características de latossolos roxos desenvolvidos de rochas alcalinas e básicas de Jaboticabal, SP

A comparative study was carried out on chemical, physical and mineralogical characteristics of dusky red latosols originated from the weathering of alcaline (LRe) and basic eruptive rocks (LRd), of the Jaboticabal country Brazil The results showed that the LRe presented a younger development stage than LRd, while this soil showed a tendency to maturity. This trend was corraborated through the lower clay and total Fe2O3, contents and higher base saturation contents, Si2O/Al2O3 molecular ratio (Ki) and clay f ration CEC presented by LRe. It can be concluded that the occurrence of eutrophic dusky red latosols hi the UNESP-Jaboticabal campus may be due to the influence of alcaline rocks.

Comparou-se as características químicas, físicas e mineralógicas de Latossolos Roxos desenvolvidos de rocha alcalina (LRe) e de rocha eruptiva básica (LRd), da região de Jaboticabal, SP. Os resultados indicaram que o LRe apresenta-se num estádio de desenvolvimento, comparativamente, menos evoluído que o LRd, enquanto esse se apresenta com tendência para a maturidade. Os menores teores de argila e ferro total e maiores teores de saturação por bases, Ki e CTC da fração argila apresentados pelo LRe comprovam esta tendência. Conclui-se que a ocorrência de Latossolo Roxo eutrófico no campus da UNESP-Jaboticabal, pode estar associada a participação de rochas alcalinas na sua pedogênese.

Características de latossolos roxos desenvolvidos de rochas alcalinas e básicas de Jaboticabal, SP

A comparative study was carried out on chemical, physical and mineralogical characteristics of dusky red latosols originated from the weathering of alcaline (LRe) and basic eruptive rocks (LRd), of the Jaboticabal country Brazil The results showed that the LRe presented a younger development stage than LRd, while this soil showed a tendency to maturity. This trend was corraborated through the lower clay and total Fe2O3, contents and higher base saturation contents, Si2O/Al2O3 molecular ratio (Ki) and clay f ration CEC presented by LRe. It can be concluded that the occurrence of eutrophic dusky red latosols hi the UNESP-Jaboticabal campus may be due to the influence of alcaline rocks.

Comparou-se as características químicas, físicas e mineralógicas de Latossolos Roxos desenvolvidos de rocha alcalina (LRe) e de rocha eruptiva básica (LRd), da região de Jaboticabal, SP. Os resultados indicaram que o LRe apresenta-se num estádio de desenvolvimento, comparativamente, menos evoluído que o LRd, enquanto esse se apresenta com tendência para a maturidade. Os menores teores de argila e ferro total e maiores teores de saturação por bases, Ki e CTC da fração argila apresentados pelo LRe comprovam esta tendência. Conclui-se que a ocorrência de Latossolo Roxo eutrófico no campus da UNESP-Jaboticabal, pode estar associada a participação de rochas alcalinas na sua pedogênese.

Caracterização e gênese de uma topossequência latossolo amarelo-podzol originado de material da formação barreiras - estado de alagoas

Morphological, physical, chemical and mineralogical characteristics studies were carried out in a Yellow Latosol - Grey Podzol toposequence developed from the Barreiras Formation, in the so-called "Tabuleiro Region" in Maceió, Alagoas State, Brazil. The aim of this study was to help understanding the pedological differences among the soils in the toposequence. The observations suggested that the soil formation processes were controled by drainage conditions due to the position of the profiles in the landscape, with very good drainage and kaolinite/gibbsite mineralogy on one side, and in the other, were the Podzol occurs, prevail poor drainage and kaolinite/vermiculite-mica mineralogy. The Yellow Podzolic Latosol, Yellow Podzolic and Gray Podzolic soils occur interposed in the landscape and the soil formation process is drainage dependent. The an fragipan, duripan and the iron concentration are also drainage related.

Características morfológicas, físicas, químicas e mineralógicas foram determinadas em 5 perfis ao longo de uma topossequência numa depressão fechada de Latossolo Amarelo até Podzol em tabuleiro a 60 km de Maceió, Estado de Alagoas, no sentido de elucidar os principais processos envolvidos na formação dos solos. A formação dos solos está diretamente relacionada às condições de drenagem devido as posições que eles ocupam no relevo. O Latossolo Amarelo ocupa a posição de transição tabuleiro-encosta, o que permite uma boa drenagem e intenso intemperismo, enquanto que no outro extremo menos intemperizado ocorre o Podzol, ocupando posições de depressão no relevo, de drenagem imperfeita. Os solos Podzólico Amarelo Latossólico, Podzólico Amarelo com fragipãs e Podzólico Acinzentado, ocupam posições intermediárias no relevo com mineralogia essencialmente caulinítica. As formações especiais, fragipã, duripã e lamelas de concentração de ferro são também relevo (drenagem) dependente, aumentando seu desenvolvimento a medida que a drenagem tende a ficar mais imperfeita.

CARACTERIZAÇÃO E GÊNESE DE UMA TOPOSSEQUÊNCIA LATOSSOLO AMARELO-PODZOL ORIGINADO DE MATERIAL DA FORMAÇÃO BARREIRAS - ESTADO DE ALAGOAS

Morphological, physical, chemical and mineralogical characteristics studies were carried out in a Yellow Latosol - Grey Podzol toposequence developed from the Barreiras Formation, in the so-called "Tabuleiro Region" in Maceió, Alagoas State, Brazil. The aim of this study was to help understanding the pedological differences among the soils in the toposequence. The observations suggested that the soil formation processes were controled by drainage conditions due to the position of the profiles in the landscape, with very good drainage and kaolinite/gibbsite mineralogy on one side, and in the other, were the Podzol occurs, prevail poor drainage and kaolinite/vermiculite-mica mineralogy. The Yellow Podzolic Latosol, Yellow Podzolic and Gray Podzolic soils occur interposed in the landscape and the soil formation process is drainage dependent. The an fragipan, duripan and the iron concentration are also drainage related.

Características morfológicas, físicas, químicas e mineralógicas foram determinadas em 5 perfis ao longo de uma topossequência numa depressão fechada de Latossolo Amarelo até Podzol em tabuleiro a 60 km de Maceió, Estado de Alagoas, no sentido de elucidar os principais processos envolvidos na formação dos solos. A formação dos solos está diretamente relacionada às condições de drenagem devido as posições que eles ocupam no relevo. O Latossolo Amarelo ocupa a posição de transição tabuleiro-encosta, o que permite uma boa drenagem e intenso intemperismo, enquanto que no outro extremo menos intemperizado ocorre o Podzol, ocupando posições de depressão no relevo, de drenagem imperfeita. Os solos Podzólico Amarelo Latossólico, Podzólico Amarelo com fragipãs e Podzólico Acinzentado, ocupam posições intermediárias no relevo com mineralogia essencialmente caulinítica. As formações especiais, fragipã, duripã e lamelas de concentração de ferro são também relevo (drenagem) dependente, aumentando seu desenvolvimento a medida que a drenagem tende a ficar mais imperfeita.