Resumo

Termites can create structures that alter the physical and chemical properties of soils. In this process, termites are selective about the soil constituents they will use to construct their mounds. Considering the common occurrence of termite mounds in Brazilian soils, this study aimed to investigate the selective action of termites in the mound building process. Samples were collected from six termite mounds and control soils (at a distance of 15 to 30 m from the termite mound) in different regions in Brazil to analyze the fine earth fraction. The content of clay fraction, organic C and Fe in pedogenic iron oxides increased in the mounds resulting in specific surface area increments. X-ray diffraction indicated a selectivity of termites by clay-sized particles such as kaolinite, gibbsite and iron oxides (hematite and goethite) rather than larger particles such as quartz. The proportion of low-crystalline iron oxides and the maghemite amount decreased in the mounds. The change of color parameters in the termite mounds was due to a combination of increase in clay fraction, organic carbon and iron oxides. The techniques used were sensitive, indicating changes and similarities between the control soils and the termite mounds.

Resumo

Termites can create structures that alter the physical and chemical properties of soils. In this process, termites are selective about the soil constituents they will use to construct their mounds. Considering the common occurrence of termite mounds in Brazilian soils, this study aimed to investigate the selective action of termites in the mound building process. Samples were collected from six termite mounds and control soils (at a distance of 15 to 30 m from the termite mound) in different regions in Brazil to analyze the fine earth fraction. The content of clay fraction, organic C and Fe in pedogenic iron oxides increased in the mounds resulting in specific surface area increments. X-ray diffraction indicated a selectivity of termites by clay-sized particles such as kaolinite, gibbsite and iron oxides (hematite and goethite) rather than larger particles such as quartz. The proportion of low-crystalline iron oxides and the maghemite amount decreased in the mounds. The change of color parameters in the termite mounds was due to a combination of increase in clay fraction, organic carbon and iron oxides. The techniques used were sensitive, indicating changes and similarities between the control soils and the termite mounds.(AU)

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Our goal was to analyze the impact of a multipractice soil conservationist system on coffee production in tropical soils (LATOSSOLO VERMELHO-AMARELO caulinítico/kaolinitic Haplustox and LATOSSOLO VERMELHO-gibbsítico/gibbsitic Acrustox) in Minas Gerais, Brazil. In the experimental area, the soil management involved a set of multiple conservationist practices during cultivation for more than 3.5 yrs. Soil samples were collected at 0-5, 10-15, and 20-25 cm depths at two positions: planting rows and between rows. The soil physical and mechanical properties were determined, with a focus mainly on the preconsolidation stress model (preconsolidation stress versus matric tension). For the purpose of analysis, a split-split plot experimental design was implemented. A linear mixed regression model (LMR) was fitted, and Wald's test was performed (P < 0.05). An improvement of soil physical quality for both Oxisols was observed at the planting row position. The effects of multipractice soil management after 3.5 yrs of cultivation in association with increased gibbsite content could promote new soil structure organization, as revealed by LMR, resulting in more resilient soils (between rows) and increasing the resistance to external pressures on gibbsitic Acrustox. Overall, the findings herein are in concordance with global trends towards conservationist practices that may alleviate soil compaction in agricultural systems to maintain environmental sustainability.(AU)

Nosso objetivo foi analisar o impacto de um sistema de manejo do solo com multi-práticas conservacionistas para o cultivo cafeeiro em solos tropicais (LATOSSOLO VERMELHO-AMARELO caulinítico/ kaolinitic Haplustox and LATOSSOLO VERMELHO gibbsítico/ gibbsitic Acrustox) em Minas Gerais, Brasil. Na área experimental, o manejo do solo incluiu um conjunto de multi-práticas conservacionistas por mais de 3,5 anos. Amostras de solo foram coletadas em 0-5; 10-15; e profundidades de 20 a 25 cm em duas posições: linha e entrelinha. As propriedades físicas e mecânicas do solo foram determinadas, concentrando-se principalmente na modelagem da compactação (estresse de pré-consolidação versus tensão matricial). Para fins de análise, foi considerado o delineamento experimental de parcelas subsubdivididas. Foi ajustado o modelo de regressão linear mista (RLM), bem como o teste F de Wald (P < 0,05). Melhorias na qualidade física do solo em ambos os Latossolos foi observada na linha de plantio. Os efeitos do sistema de manejo multipráticas usado após 3,5 anos de cultivo associado ao maior conteúdo de gibbsita podem promover uma nova organização da estrutura do solo revelada pelo RLM, que resulta em solos mais resilientes (na entrelinha), melhorando a resistência às pressões externas aplicadas ao Latossolo gibbsítico. No geral, os resultados aqui apresentadas estão de acordo com as tendências globais em direção a práticas conservacionistas que podem aliviar a compactação do solo em sistemas agrícolas e manter a sustentabilidade ambiental.(AU)

Resumo

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.

Resumo

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.

Resumo

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.

Resumo

No Planalto Norte Catarinense são escassas as informações sobre a composição mineralógica dos solos e há poucos perfis de solo descritos e caracterizados para a região. O mapa de solos de Santa Catarina indica predominância de Cambissolos, Neossolos Litólicos e Latossolos, com Gleissolos ocupando áreas de várzeas. Esses solos ocorrem em relevo desde plano até forte ondulado, onde pequenos e médios proprietários rurais desenvolvem cultivos diversificados, com áreas expressivas de reflorestamentos com pinus. Este trabalho objetivou aprofundar o conhecimento sobre a mineralogia e as propriedades químicas de alguns desses solos, desenvolvidos de rochas sedimentares de distintas formações geológicas. Foram descritos e amostrados 5 (cinco) perfis de solo, sendo um Latossolo e quatro Cambissolos.  Na TFSA, foram feitas análises físicas (areia, silte, argila) e químicas de caracterização básica ( pH em água e sal, carbono orgânico, Ca, Mg, K, Na, Al, H+Al) e com base nesses parâmetros foi calculada a CTC efetiva, CTC pH7, Soma e Saturação por Bases. Análises mineralógicas foram conduzidas na fração argila do horizonte B de cada solo, utilizando-se difratometria de raios X. Todos os solos apresentaram reação muito ácida, com baixa soma e saturação por bases e teores elevados de carbono orgânico e Al trocável. A mineralogia da fração argila revelou predomínio de caulinitas em todos os solos, com quantidades consideráveis de illita, gibbsita e vermiculita com hidroxi-Al entrecamadas.

In the North Plateau of Santa Catarina state, Brazil, there is little information about the mineralogical composition of the soils and a few soil profiles were described and characterized in the region. The two generalized soil maps of Santa Catarina indicate predominance of Inceptisols, Entisols and Oxisols, with hydromorphic soils occupying areas of floodplains. These soils occur in relief from plane to strong wavy, where small and medium rural farmers develop diversified crops, with significant areas with pine reforestation. This work aimed to increase the knowledge of the mineralogical and chemical properties of some of these soils developed from sedimentary rocks of different geological formations. Five soil profiles were described and sampled, included one oxisol and four Inceptisols. In fine earth, physical (sand, silt, clay) and chemical analyzes were performed (pH in water, organic carbon, Ca2+, Mg, K, Na, Al, H + Al) and based on these attributes was calculated effective CEC, CEC at pH7, sum of bases and base saturation. Mineralogical analyzes were conducted in the clay fraction of the B horizon of each soil, using X-ray diffraction techniques. All soils showed very acid reaction, with low sum of bases and base saturation and high levels of organic carbon and exchangeable Al. The clay mineralogy revealed predominance of kaolinite in all soils, with considerable amounts of gibbsite, and vermiculite with hydroxy-Al interlayered.

Resumo

Lateritic crusts developed upon the Guiana Shield basement rocks (e.g. granites of the Água Branca Intrusive Suite) was recognized in the Vila Nova Colina region, located in south Roraima state. The objectives of this work were to study the mineral and geochemical characteristics of lateritic crusts and to evaluate the relationship between them and the rocks of the region, in order to understand the evolution of laterization and provide information about the economic potential. This study comprises petrography, mineralogy and litogeochemical investigations of the granites, the quartz-hornblende gabbro and the lateritic crusts formed from these rocks. The granites and the quartz-hornblende gabbro has developed, respectively, a specific type of lateritic crust: (i) the ferruginous vermiform one with high amounts of kaolinite, goethite, hematite, magnetite and anatase, higher concentration of Al2O3, Sc, Th e Zr and, (ii) the iron-titaniferous massive one with high amounts of magnetite, hematite, maghemite, goethite, kaolinite, anatase, gibbsite and ilmenite, and consequently in higher amounts of Fe2O3, TiO2, V e Cu. Each crust type indicates the effect of the lateritization in the south portion of Roraima and their topographic position. The higher topographic position of the massive crust (220 m), its mineral and geochemical composition, indicate the maturity (i.e. needed more time to be formed) and may represent a relict of an erosion phase in the region, probably associated with a subsidence of the Tacutu basin in the Miocene. Otherwise, the vermiform crust formed at a lower topographic position (140 m) with no gibbsite, suggests that it is younger than the massive one and represents the immature laterization of the Plio-Pleistocene.

Crostas lateríticas desenvolvidas sobre as rochas do embasamento do Escudo das Guianas (p.e. granitos da Suíte Intrusiva Água Branca) são reconhecidas na região de Vila Nova Colina, localizada ao sul do estado de Roraima. Os objetivos deste trabalho foram estudar as características minerais e geoquímicas dessas crostas lateríticas e avaliar a relação entre elas e as rochas da região, a fim de entender a evolução da lateritização e fornecer informações sobre seu potencial econômico. Este estudo compreende dados de petrografia, mineralogia e litogeoquímica de granitos, quartzo-hornblenda gabro e crostas lateríticas formadas a partir dessas rochas. Os granitos e o quartzo-hornblenda gabro desenvolveram, respectivamente, um tipo específico de crosta laterítica: (i) vermiforme ferruginosa com elevados teores de caulinita, goethita, hematita, magnetita e anatásio e maior concentração de Al2O3, Sc, Th, e Zr e, (ii) maciça ferro-titanífera com altos teores de magnetita, hematita, maghemita, goethita, caulinita, anatásio, gibbsita e ilmenita e de Fe2O3, TiO2, V e Cu. Cada tipo de crosta indica o efeito da lateritização na porção sul de Roraima e sua posição topográfica. O posicionamento topográfico mais elevado da crosta maciça (220 m) e sua composição mineralógica e geoquímica, indicam sua maturidade (isto é, precisou de mais tempo para ser formada) e, portanto relicto de uma fase erosiva na região, provavelmente associada a subsidência da bacia do Tacutu no Mioceno. Enquanto a crosta vermiforme em uma posição mais rebaixada (140 m) sem gibbsita, sugere que ela é mais jovem que a maciça e representa a lateritização imatura do Plio-Pleistoceno.

Resumo

Several methods exist for determining soil organic carbon, and each one has its own advantages and limitations. Consequently, a comparison of the experimental results obtained when these methods are employed is hampered, causing problems in the comparison of carbon stocks in soils. This study aimed at evaluating the analytical procedures used in the determination of carbon and their relationships with soil mineralogy and texture. Wet combustion methods, including Walkley-Black, Mebius and Colorimetric determination as well as dry combustion methods, such as Elemental and Gravimetric Analysis were used. Quantitative textural and mineralogical (kaolinite, goethite and gibbsite) analyses were also carried out. The wet digestion methods underestimated the concentration of organic carbon, while the gravimetric method overestimated. Soil mineralogy interfered with the determination of carbon, with emphasis on the gravimetric method that was greatly influenced by gibbsite.

Resumo

Studies analyzing the variability of clay minerals and magnetic susceptibility provide data for the delineation of site-specific management areas since many of their attributes are important to agronomy and the environment. This study aimed to evaluate the spatial variability of clay minerals, magnetic susceptibility, adsorbed phosphorus and physical attributes in Oxisols of sandstones in different geomorphic surfaces. For that purpose, soil samples were collected every 25 m along a transect located within the area where the geomorphic surfaces were identified and mapped. The transect occupied the central portion of 500 ha, where it was also sampled for density purposes with one sample per six hectares. Soil samples were collected at a depth of 0.0-0.2 m. The results of the physical, chemical, mineralogical and magnetic susceptibility analyses were subjected to statistical and geostatistical analyses. The nature of the clay minerals and magnetic susceptibility was dependent on the variation of the soil parent material. High values of magnetic susceptibility were associated with the presence of maghemite and magnetite of coarse size. The spatial variability of crystallinity and the content of Fe oxides, as well as magnetic susceptibility, were dependent on the age of the geomorphic surfaces. The youngest surface had greater spatial variability of these attributes. The iron (goethite and hematite) and aluminum (gibbsite) oxides in the youngest geomorphic surface influenced the low values of soil density and high values of total pore volume, micropores and P adsorption. The characterization of the spatial variability of Fe oxides and susceptibility allowed for the delineation of homogeneous areas.

Resumo

The capacity of soils to sequestrate carbon (C) is mainly related to the formation of organo-mineral complexes. In this study, we investigated the influence of soil management systems on the C retention capacity of soil with an emphasis on the silt and clay fractions of two subtropical soils with different mineralogy and climate. Samples from a Humic Hapludox and a Rhodic Hapludox, clayey soils cultivated for approximately 30 years under no-tillage (NT) and conventional tillage (CT) were collected from six layers distributed within 100-cm soil depth from each site and from an adjacent native forest. After the removal of particulate organic matter (POM), the suspension ( 53 µm) was sonicated, the silt and clay fractions were separated in accordance with Stokes' law and the carbon content of whole soil and physical fractions was determined. In the Humic Hapludox, the clay and silt fractions under NT showed a higher maximum C retention (72 and 52 g kg-1, respectively) in comparison to those under CT (54 and 38 g kg-1, respectively). Moreover, the C concentration increase in both fractions under NT occurred mainly in the topsoil (up to 5 cm). The C retention in physical fractions of Rhodic Hapludox varied from 25 to 32 g kg-1, and no difference was observed whether under an NT or a CT management system. The predominance of goethite and gibbsite in the Humic Hapludox, as well as its exposure to a colder climate, may have contributed to its greater C retention capacity. In addition to the organo-mineral interaction, a mechanism of organic matter self-assemblage, enhanced by longer periods of soil non-disturbance, seems to have contributed to the carbon stabilization in both soils.

Resumo

No Estado de Santa Catarina há Argissolos com horizonte subsuperficial escurecido com morfologia semelhante à dos horizontes sômbricos dos sistemas de classifi cação norteamericano (Soil Taxonomy - ST) e da FAO (World Reference Base – WRB), mas existem dúvidas quanto à possibilidade de serem horizontes A enterrados. O presente trabalho avaliou a composição mineralógica das frações silte e argila dos horizontes genéticos de três Argissolos (Vermelho, Amarelo e Bruno-Acinzentado) com horizontes diagnósticos subsuperficiais similares ao sômbrico, localizados na região leste catarinense, objetivando identificar possíveis descontinuidades litológicas influenciando a gênese desses horizontes escuros. As amostras dos Argissolos foram coletadas nos municípios de Içara, Rancho Queimado e Alfredo Wagner. Na fração TFSA procedeu-se à separação das frações silte e argila para análises por difratometria de raios-X (DRX), analisadas respectivamente em pó e em lâminas de argila orientada. Parte das amostras da fração argila, após eliminação da matéria orgânica e dos óxidos de ferro, foi saturada com magnésio e solvatada com etileno-glicol. Outra parte foi saturada com potássio e submetida a várias temperaturas. As análises por DRX indicaram haver descontinuidade litológica nos Argissolos Amarelo e Bruno-Acinzentado, sugerindo que nesses solos os horizontes subsuperfi ciais escuros sejam antigos A enterrados, e não horizontes sômbricos. O Argissolo Vermelho de Içara não apresentou evidências de descontinuidade na litologia entre os horizontes, podendo indicar um horizonte sômbrico, o que depende de maiores investigações. A mineralogia da fração argila revelou predominância de caulinita nos Argissolos, e quantidades expressivas de vermiculita com polímeros de hidróxi-alumínio nas entrecamadas, além de gibbsita, illita e quartzo. No silte, os difratogramas indicaram somente quartzo em quantidades detectáveis, demonstrando não haver reserva mineral nesses solos.

In the Santa Catarina state there occurs darkened subsurface horizon in Ultisols, whose morphology is similar to the sombric horizons of the Soil Taxonomy and FAO classifi cation systems. But there are doubts about the possibility of there being buried horizons. The present study aimed to identify lithologic discontinuities in mineralogy of the silt and clay fractions of three Ultisols (red, yellow and brown-gray) which exhibit similar morphology to sombric horizons, located in the eastern region of Santa Catarina state. Samples. were collected in the Ultisols from Içara, Rancho Queimado e Alfredo Wagner municipalities. In the samples TFSA proceeded to separate the silt and clay samples for analysis by X-ray diffraction (XRD) , respectively analyzed in powder and oriented clay slides . Part of the clay samples, after removal of organic matter and the iron oxides was saturated with magnesium and saturated with ethylene glycol. After being analyzed by X-ray diffraction the samples saturated with magnesium underwent saturation with thylene glycol. The samples that were saturated with potassium were heated to various temperatures. The results identifi ed discontinuity clay mineralogy in Yellow and Brown-Gray Ultisols. These soils do not have sombric horizons. The Red Ultisol showed no mineralogical discontinuity and depend on further studies to confi rm or not sombric horizon. The mineralogy of the clay sample indicated a predominance of kaolinite in all Ultisols, with signifi cant amounts of vermiculite with hydroxyaluminum interlayered, gibbsite, illite and quartz. The silt sample showed only quartz. The soils have no detectable mineral reserve for plants.

Resumo

A presença simultânea de gibbsita, caulinita, argilominerais 2:1 com polímeros de hidróxi- Al (2:1HE) e interestratificados em solos ácidos e dessaturados do Sul do Brasil pode ser considerada contraditória, mas não rara. Como a correta identificação destes argilominerais é de difícil execução, a evolução destes solos pode acabar sendo atribuída simplesmente a uma escala de intemperismo moderado. Para melhor compreender a gênese dos solos da região do Planalto Sul de Santa Catarina, foram desenvolvidos estudos mineralógicos da fração argila e das respectivas rochas matriz de sete perfis de solo ao longo de duas topossequências. As análises mineralógicas foram realizadas por difratometria de raios X (DRX), utilizando os pré-tratamentos usuais e um pré-tratamento com hidróxido de sódio (NaOH) a 3,5 mol L-1 a quente (250ºC). Os teores dos óxidos de Si, Al e Fe foram determinados após a digestão das amostras com ataque sulfúrico. As rochas apresentaram mineralogia similar, exceto nas quantidades de plagioclásios, piroxênios e quartzo. Todos os solos apresentaram caulinitas de baixa cristalinidade e resquícios de argilominerais 2:1 sob a forma de interestratificados e/ou 2:1HE, que permaneceram nos solos devido à intercalação dos polímeros de Al e/ou Fe nas entrecamadas. As diminutas proporções de gibbsita são decorrentes do efeito complexante da matéria orgânica do solo (MOS) sobre a cristalização dos hidróxidos de Al e também, devido ao ambiente lixiviante que não foi sufi cientemente severo a ponto de predominar os processos de alitização. Nos Nitossolos Vermelhos o principal processo de alteração do material originário foi a monossialitização, enquanto os Cambissolos Háplicos apresentaram processo de hidrólise tendendo para a alitização.

The simultaneous presence of gibbsite, kaolinite, 2:1 clay minerals with Al-hydroxy polymers and interstratified minerals in acid soils and desaturated in southern Brazil can be seen as contradictory, but not rare. How correct identification of these clay minerals is difficult to perform, the evolution of these soils may simply end up being attributed to a range of moderate weathering. To better understand the genesis of soils in southern highlands of Santa Catarina, studies were conducted of mineralogical clay rocks and their array of seven soil profiles along two topossequences. The mineralogical analyzes were performed by X-ray diffractometry (XRD) using the usual pretreatment and a pretreatment with hot (250°C) 3.5 mol L-1 solution. The levels of oxides of Si, Al and Fe were determined after dissolving the samples in sulfuric acid. The rocks show similar mineralogy, except in amounts of plagioclase, pyroxene and quartz. All soils had low crystallinity of kaolinite and traces of 2:1 clay minerals in the form of interstratifi ed and/or 2:1 clay minerals with Al-hydroxy polymers, that/ which remained in the soil due to intercalation of the polymers of Al and / or Fe in interlayers. The diminutive proportions of gibbsite are due to the complex effect of soil organic matter (SOM) on the crystallization of Al hydroxides and also due to the leaching environment was not suffi ciently severe as to dominate the processes of alitization. In Kandiudox the main process of changing the source material was monossialitization while Haplumbrept showed hydrolysis process tending to alitization.

Resumo

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.

Resumo

The mineralogical characterization through mineral quantification of Brazilian soils by X-ray diffraction data using the Rietveld Method is not common. A mineralogical quantification of an Acric Ferralsol from the Ponta Grossa region, state of Paraná, Brazil, was carried out using this Method with X-Ray Diffraction data to verify if this method was suitable for mineral quantification of a highly-weathered soil. The A, AB and B3 horizons were fractioned to separate the different particle sizes: clay, silt, fine sand (by Stokes Law) and coarse sand fractions (by sieving), with the procedure free of chemical treatments. X-ray Fluorescence, Inductively Coupled Plasma Atomic Emission Spectrometry, Infrared Spectroscopy and Mössbauer Spectroscopy were used in order to assist the mineral identification and quantification. The Rietveld Method enabled the quantification of the present minerals. In a general way, the quantitative mineralogical characterization by the Rietveld Method revealed that quartz, gibbsite, rutile, hematite, goethite, kaolinite and halloysite were present in the clay and silt fractions of all horizons. The silt fractions of the deeper horizons were different from the more superficial ones due to the presence of large amounts of quartz. The fine and the coarse sand fractions are constituted mainly by quartz. Therefore, a mineralogical quantification of the finer fraction (clay and silt) by the Rietveld Method was successful.

A caracterização mineralógica por meio da quantificação dos minerais presentes em solos brasileiros por difração de raios X usando o Método de Rietveld é, ainda, pouco comum. Neste trabalho foi realizada a quantificação mineralógica de um Latossolo Vermelho ácrico da região de Ponta Grossa, Paraná, Brasil, utilizando o Método de Rietveld com dados de Difração de Raios X e também verificado se o método foi adequado na quantificação mineral de um solo altamente intemperizado. Os horizontes A, AB e B3 foram separados fisicamente nas frações: argila, silte, areia fina (por meio da Lei de Stokes) e areia grossa (por peneiramento) sem qualquer tratamento químico. As técnicas de Fluorescência de raios X, Espectroscopia de Emissão Atômica com Fonte de Plasma Induzido, Espectroscopia de Infravermelho e Espectroscopia Mössbauer foram utilizadas para auxiliar na identificação e quantificação dos minerais. O Método de Rietveld possibilitou a quantificação dos minerais presentes nas frações argila e silte de todos os horizontes: quartzo, gibbsita, rutílio, hematita, goethita, caulinita e haloisita. Na fração silte os horizontes mais profundos são diferentes do mais superficial devido à presença de grandes quantidades de quartzo. As frações areia fina e grossa são constituídas principalmente de quartzo. Portanto, o Método de Rietveld foi adequado para quantificação dos minerais, principalmente, das frações mais finas (argila e silte).

Resumo

Hillslope curvatures are associated with specific environments that correlate to chemical and mineralogical attributes of soil, so determining specific management zones. Phosphorus is one of the main limiting factors to the development and longevity of sugarcane. The type and the mineralogical constitution of the clay fraction play an important role in the phosphorus (P) adsorption of soil. High proportion of gibbsite (Gb) in soil may be the major responsible for P adsorption. The relationships among spatial variability as a function of hillslope curvature, the proportion of kaolinite (Kt) and Gb, and phosphorus adsorption were evaluated in an Alfisol cultivated with sugarcane. Two plots of 1 ha of a concave and a convex hillslope area were selected and 121 samples were collected in each area. The maximum P adsorption was determined in six samples taken randomly in each area. Data were submitted to descriptive statistical and geostatistical analysis. The lowest average values of available phosphorus were found in the convex area. In this area, the proportion of gibbsite, expressed by the values of the ratio [Gb/(Gb + Ct)] and the values of maximum adsorption capacity of phosphorus were higher than in the concave area.

As curvaturas do relevo promovem pedoambientes específicos que condicionam os atributos químicos e mineralógicos do solo e podem auxiliar na definição de zonas específicas de manejo. O fósforo (P) é um dos principais elementos limitantes ao desenvolvimento e longevidade do canavial. O teor e a constituição mineralógica da fração argila assumem papel importante na disponibilidade do P, sendo que a gibbsita (Gb), quando presente em altas proporções no solo, pode ser a principal responsável pela sua adsorção e indisponibilidade. Investigaram-se as relações e a variabilidade espacial da adsorção de P e a ocorrência de caulinita (Ct) e gibbsita na fração argila de um Argissolo Vermelho-Amarelo eutrófico originado de rochas areníticas sob diferentes curvaturas do relevo em área sob cultivo de cana-de-açúcar. Duas malhas de 1 ha foram delimitadas numa área côncava e outra área convexa. Foram coletadas 121 amostras em cada área para realização das análises granulométricas, químicas e mineralógicas. A capacidade máxima de adsorção de P foi obtida em seis amostras escolhidas ao acaso em cada área. Os resultados foram submetidos às análises estatísticas descritiva e geoestatística. Os menores valores médios de P disponível encontraram-se na área convexa. Nesta área, a proporção de gibbsita, expressa pelos valores da razão [Gb/(Gb+Ct)] e os valores de capacidade máxima de adsorção de fósforo foram maiores do que na área côncava.

Resumo

Information about genesis and mineralogical composition of Santa Catarina soils are scarce. The objectives of this work were to characterize the morphology, chemical, physical and mineralogical attributes of representative soil profiles of the eastern coast mountains of this region, to identify soil mineralogical composition and its relation with soil physical and chemical properties. Seven profiles of Ultisols and Oxisols (Argisols and Latosols in the Brazilian Classification System, respectively), derived from different lithologies, were selected for this study. Morphology of soils and physical aspects of the environment were described. Physical and chemical routine analyses were performed in the fine earth. In the clay fraction, samples were saturated with K, Mg and Mg plus ethylene glycol and analyzed by X-ray diffractometry. Silt was analyzed in powder. All soil profiles were acid, with low organic carbon and low sum of basis and basis saturation, indicating lixiviated and highly weathered soils. Clay soil composition was very similar among the soils. Kaolinite was the dominant clay mineral, with minor proportions of illite, vermiculite with hidroxy-Al interlayers and interstratified illite-vermiculite. Aluminum oxide (gibbsite) and quartz, were also detected in some profiles. Despite the occurrence of 2:1 clay minerals in some soils, CEC of clay was low, probably because these clay minerals have high hidroxy-Al interlayers, which reduce soil CEC.

Dados sobre a composição mineralógica dos solos das serras litorâneas do sul de Santa Catarina são escassos. Este trabalho objetivou caracterizar, do ponto de vista morfológico, físico e químico, perfis de solo representativos desta região, bem como identificar os componentes mineralógicos desses solos e suas relações com as propriedades físicas e químicas. Selecionaram-se sete perfis de Argissolos e Latossolos, contemplando materiais de origem diferenciados. Os perfis foram descritos quanto à morfologia e aspectos do meio físico. Na argila fezse pré-tratamentos de saturação com K, Mg e Mg + etileno glicol para análises mineralógicas por difratometria de raios X. O silte foi analisado na forma de pó. A maioria dos perfis apresentou reação ácida, médios a baixos teores de carbono orgânico e baixos valores de soma e saturação por bases, indicando tratar-se de solos lixiviados e muito intemperizados. A mineralogia da fração argila revelou-se bastante similar entre os perfis, com caulinita como argilomineral dominante, seguida de proporções baixas de illita, vermiculita com polímeros de Al entrecamadas e interestratificados illita-vermiculita. Óxidos de alumínio do tipo gibbsita, bem como quartzo, também foram constatados em alguns perfis. Apesar da proporção expressiva de argilominerais 2:1 em vários solos, a CTC da fração argila dos solos foi baixa, provavelmente porque os referidos argilominerais apresentam forte intercalação com polímeros de hidroxi-Al entrecamadas, que reduzem a CTC dos mesmos.

Resumo

Because weathering of minerals releases chemical elements into the biogeochemical cycle, characterization of their weathering products helps to better model groundwater quality, formation of secondary minerals and nutrient flux through the trophic chain. Based on microscopic and elemental analyses, weathering of riodacite from Serra Geral formation was characterized and weathering paths proposed. Three weathering paths of plagioclase phenocrystals were identified: plagioclase to gibbsite (Pg1); plagioclase to gels and gibbsite (Pg2); and plagioclase to gels, gibbsite and kaolinite (Pg3). Pyroxenes weathered to smectite and goethite (Py1), or to goethite and gibbsite (Py2), and magnetite weathered directly into iron oxides. Rock matrix comprises 90% of rock volume, and weathered to kaolinite and gibbsite, which explains why these minerals were the most abundant in the weathering products of these saprolites.

O intemperismo de minerais primários disponibiliza elementos químicos no ciclo biogeoquímico, que por sua vez influencia a qualidade da água subterrânea, formação de minerais secundários e o fluxo de nutrientes na cadeia trófica. Com base na análise microscópica e elemental, o intemperismo de riodacito da formação Serra Geral foi caracterizado e mecanismos de intemperismo propostos. Três processos principais de intemperismo de fenocristais de plagioclásios foram identificados: plagioclásio para gibbsita (Pg1); plagioclásio para gel e gibbsita (Pg2), e plagioclásio para gel, gibbsita e caulinita (Pg3). Piroxênios intemperizaram-se para esmectita e goetita (Py1), ou para goethita e gibbsita (Py2), e magnetita intemperizou-se para óxidos de ferro. A matriz da rocha compõe 90% do volume total, e intemperiza-se para caulinita e gibbsita, o que explica a abundância destes minerais nos produtos de intemperismo destes saprolitos.

Resumo

A estabilidade de complexos organo-minerais é uma característica importante quanto à química e física de solos tropicais e subtropicais. O objetivo deste estudo foi identificar variáveis relacionadas à estabilidade de complexos organo-minerais, avaliada pela energia de ultra-som necessária para a dispersão total do solo em partículas primárias, em seis solos das regiões Sul e Centro-Oeste do Brasil com textura e mineralogia distintas. A energia de ultra-som necessária para dispersão total dos solos variou de 239 a 2.389J mL-1, sendo diretamente relacionada aos teores de carbono orgânico (R²=0,799, P<0,05). A mineralogia da fração argila teve um papel determinante na estabilidade dos complexos organo-minerais, a qual foi relacionada aos teores de óxidos de ferro de baixa cristalinidade (R²=0,586, P<0,10), mas não teve relação com os teores totais de óxido de ferro pedogênicos. A análise qualitativa da fração argila, realizada por difratometria de raios-X, demonstrou que a estabilidade dos complexos organo-minerais variou positivamente em função das proporções de gibbsita e de goethita na fração argila, o que reforça o papel desses minerais na proteção física e estabilidade coloidal da matéria orgânica em solos tropicais e subtropicais.

The stability of organo-mineral complexes is an important characteristic related to the soil chemistry and physics of tropical and subtropical soils. This study was aimed at identifing the variables related to the stability of organo-mineral complexes, evaluated by ultrasonic energy necessary to complete soil dispersion, of six soils from South and West-Center regions of Brazil with distint texture and mineralogy. The ultrasonic energy to complete soil dispersion varied from 239 a 2389J mL-1, and was positively related to the soil organic carbon concentrations (R²=0.799, P<0.05). The clay mineralogy had an important role to the stability of organo-mineral complexes, which were related to the content of low cristalinity iron oxides (R²=0.586, P<0.10), but did not had relationship with the total pedogenic iron oxides. The qualitative analysis of the clay mineralogy, by X-ray diffraction, evidenced that gibbsite and goethite are the main clay minerals related to the stability of organo-mineral complexes, reinforcing the importance of these minerals on the physical protection and coloidal stability of the soil organic matter in the tropical and subtropical soils.

Resumo

Summary In the region of Manaus, the low sedimentary plateaux (Terciary formations of the Barreiras Group) are dominated by clayey yellow latosols with a very low base saturation (Acrorthox and Haplorthox according to the Soil Survey Staff). These soils present in general a fairly homogeneous profile particularly considering the colour, the texture (very clayey) and the structure (very weakly developed). But in the edge of the plateau, near the axes of drainage, the soils change lateraly and gradualy into a soil more differenciated with a B22Cn containing white and violescent red nodules. Microscopic and mineralogical analysis show at the first, the large dominance of a kaolinitic plasma with argillasepic fabric, showing no recognizable agregates norvoids, enclosing nothing but isolated quartz grains and white and violescent red micronodules. The abondance of the micronodules increases strongly in the neighbourhood and in the Interior of the microagregated filling of "aggrotubules" of biologic origin, which contains most of the interconnected voids. It is exactly in theese "bioturbed" volumes that appear and developp lateraly in the edge of the plateaux, the nodules of a centimetric size and whitisch colour (containing gibbsite, kaolinite and quartz) and/or violescent red colour (centaining hematite, gibbsite, kaolinite and quartz). The observation under S.E.M. together with the microprobe analyse show that the plasma of the S. matrix consists essencially of packing of very fine particles of kaolinite ( 0,2) forming the cryptovoids. The S. matrix of the white nodules consists of finely crystallised gibbsite and kaolinite, while in the red ones, besides these constituents a high concentration of iron oxydes (55% in weight) is present. The walls of the intranodular voids are coated with gibbsite crystal ("crystal chambers") or with iron cutans ("ferrans") The results of dispersion test and chemical and physico-chemical analysis show particularly the weak colloidal characteristic of the soil clay as well as their aptitude to retain strongly the cations under a non exchangeable form. Finally, as a conclusion, it can be said that the results shown out a group of characteristics, some of them being common to the latosols in general, and some other more peculiar to the studied soils: Bimodal distribution of the voids radius: cryptovoids ( 0,1) and meso or macrovoids (>30). The cryptovoids are situated within the plasmic structure of the S. matrix, while most of the others are enclosed In the "aggrotubules". Retention of high water content in the field capacity in the cryptovoids (30-40% in volume). Rapid drainage of excedent of water by the packing porosity of aggrutubules. Preservation of kaolinite and small content of quartz in the S. matrix, submited to slow movement of the soil solution. Strong desilicification and formation (or conservation) of gibbsite in the aggrotubules where strong leaching condition is present. Very weak colloidal activity of the clay fraction and strong fixation of cations under a nearly non exchangeable form, as considering the state of the absorption complex and the presence of a microporosity limiting the exchange possibilities.

Resumo Os latossolos argilosos são dominantes ao Norte e Este de Manaus, desenvolvendo-se sobre os baixos platôs sedimentares (Formação Barreiras). A sua evolução depende do clima úmido megatérmico e da cobertura florestal equatorial densa. Visando o estudo da dinâmica nestes solos, foram efetuadas análises microscópicas, químicas e mineralógicas em cerca de 50 amostras coletadas em toposseqüências selecionadas nas bacias hidrográficas estudadas pelo INPA. Os resultados mostraram que a circulação da água nestes latossolos se efetua por uma rede de vazios largos, contida nos setores "bioturbados". No seu Interior observa-se dessilicificação intensa e neoformação de gibbsita. O complexo sortivo é globalmente muito desaturado, mas constata-se também uma retenção muito forte da cátions sob forma não trocável. Estas características estão de acordo com a idéia de circulação da água pelo "by pass" sugerida pelos hidrólogos. Esta dinâmica seria dependente das ações da fauna e do flora.