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ABSTRACT Serra da Saudade Formation corresponds to the upper part of the stratigraphic column of the Bambuí Group. Few studies have addressed the soil properties and pedogenesis of the pelitic rocks rich in potassium minerals of this formation. This study analyzed siltstone-derived soils, some of which are glauconitic (green siltstone; “verdete”), to understand the role of the main pedogenetic factors and processes in the landscape of the Central-West region of the Minas Gerais State, covered by Cerrado vegetation. Nine soil profiles were described, and their morphological, physical, chemical and mineralogical properties were analyzed. Soils were classified as Neossolos Litólicos (P1, P3, P6, P8 and P9), Cambissolos Háplicos (P2 and P5), Argissolo Vermelho-Amarelo (P4) and Argissolo Acinzentado (P7). The main active pedogenetic processes identified in the study area are melanization, goethization, argiluviation and elutriation. These are essentially controlled by the nature of the parent material and position of the soil in the relief. Soils are typically shallow, dystrophic, highly Al-saturated and contain essentially quartz and micas in the coarse fractions (sand and silt) and illite/glauconite and kaolinite in the clay fraction. In soil environments with siltstone and green siltstone under “dry forests”, the soil water pH was higher and high levels of exchangeable calcium and magnesium, a eutrophic character and high-activity clay were observed. Barium, chromium, lead and zinc contents were high in all studied soils. Green siltstone-derived soils have peculiar physical and chemical properties, divergent from those developed from other glauconitic rocks on the Earth surface. However, greenish tones in horizons are common in all these soils.

The lack of cover is one of the main accelerators of soil degradation. Without protection and exposed to rainfall, the soil breaks the particles, causing surface sealing, making infiltration difficult. This study characterizes surface sealing and hydraulic erosion in Ultisols of the Alto Ipanema Basin. Eight erosion plots were established under the treatments: bare soil and soil with Brachiaria decumbens mulch. Three rain events were simulated at 24-hour intervals, with an intensity of 54.63 mmh-1. After each simulation, the surface micromorphology and the amount of soil lost were investigated. The use of mulch reduced runoff by 42% and the loss of soil and the rate of disaggregation was reduced by 70% on average. Infiltration was increased by 242%. Mulch was effective in preserving soil porosity and microstructure for the first simulated rainfall event (0 h), but was not observed in the second (24 h) and third (48 h) rainfall events.

Nitisols are livelihood sources of agricultural and socio-economic development in several underdeveloped countries worldwide, including Brazil. Brazilian Nitisols are usually associated with basaltic rocks found in the Southern and Southeastern regions of the country. However, Nitisols derived from basalt also occur on the southern coast of Pernambuco state, a region under full urban, agricultural, and industrial development. Aiming to understand the relationship between climate and attributes of Nitisols from the southern coast of Pernambuco, we performed morphological descriptions, physical and chemical analyzes, iron selective extraction, and soil mineralogy (sand, silt, and clay) for three basaltic soil profiles along a land slope. The results suggest a strong weathering of the profiles due to climate conditions, besides a great loss of basic cations and xanthization process, resulting in the natural genesis of acric Nitisols with yellowish coloration, which has not been yet cataloged for this soil order in the Brazilian taxonomic system. In addition, there is a variation for physical attributes of Nitisols along the slope.

ABSTRACT On the southern coast of Pernambuco State (PE), Brazil, lithotypes of the Cabo Basin (volcanic and sedimentary rocks), in association with the relief, allow the determination of the dynamics of the formation of Nitossolos Háplicos (Nitisols), including those with high levels of exchangeable aluminum. The objective of this study was to evaluate the influence of lithological diversity (basalt and sedimentary siliciclastic rocks) on the morphological, physical, chemical, and mineralogical properties of Nitossolos Háplicos along a slope (P1-summit, P2-backslope, P3-footslope) on the southern coast of PE, in order to consider its genesis and the relation of soil properties to adjacent environments and to evaluate its framing within the Brazilian Soil Classification System (SiBCS). The interaction of lithology/soil permeability and climate indicate significant differences in the mineralogical composition and dynamics of soil chemical elements. The profiles P1 and P2 are subject to monosialitization, ferralitization, and alitization processes. All profiles showed high Fe contents (ferric soils) and clay fractions, consisting primarily of kaolinite, goethite, hematite, and gibbsite, as well as quartz and feldspar in the sand and silt fractions. However, smectite minerals (P3) are probably inherited from the sedimentary source material. In the conglomerate samples, under P3, biotite, muscovite, and plagioclase were identified. Allytic characteristics (P3) are probably associated with the weathering of aluminous smectite minerals. These properties distinguish these soils from adjacent Nitossolos and other Nitossolos in Brazil. For the classification of soils according to SiBCS, considering the high levels of Fe and Al, Nitossolo Háplico distroférrico (P1 and P2) and Nitossolo Háplico alitiférrico (P3) are suggested, and according to the World Reference Base of Soils (WRB), the soils are classified as Ferritic Nitisols.

ABSTRACT Archaeological Dark Earth (ADE) pedogenesis and pre-Columbian history are fundamental for understanding the biodiversity and pedodiversity of the Neotropical rainforest in the Amazon region. This study aimed to evaluate the morphological, physical, chemical, and mineralogical properties as well as NaOH-extractable organic matter [OM(NaOH)] in ADE and Mulatto Earth (ME) overlying volcanic rocks along a toposequence (four soil profiles) in western Amazonia, Brazil. The soil profiles show anthropic A horizons over an argic horizon (Bt) in the ADE (Humic, Pretic Luvisols) and Bi in the ME (Clayic, Dystric Cambisols). The soil-forming processes in all of the profiles are associated with organic matter accumulation, such as humification and melanization, besides the formation of organometallic complexes. Calcium, Mg, P, and organic carbon contents were higher in ADE compared to ME. High-activity clays are derived from parent volcanic material, distinguishing the soils studied from Amazonian soils (Tertiary Plateau, Terra Firme) and most Amazonian anthropic soils. The anthropic horizons generally have a large contribution from OM(NaOH), predominantly humin and humic acids associated with Ca, Mg, and poorly crystalline Al hydroxides. The results suggest that the anthropic driving-forces caused greater differences in pedogenesis than the soil location in the landscape.

RESUMO Neossolos Regolíticos no Agreste Meridional de Pernambuco são utilizados para diversas atividades agrícolas, com destaque para a produção de feijão. Há uma variação expressiva na produção dessa cultura, possivelmente associada à presença de lamelas, que conferem comportamento hídrico distinto entre esses solos. Objetivou-se analisar as características macromorfológicas, micromorfológicas e físicas de Neossolos Regolíticos localizados no Agreste Meridional de Pernambuco, com a finalidade de se entender o comportamento hídrico desses solos. Foram coletados e analisados dois perfis de solos localizados nos municípios de Paranatama (P1 - sem lamela) e de São João (P2 - com lamela). Os resultados mostraram que nos atributos morfológicos (cor, textura, estrutura e consistência) não foram observadas diferenças expressivas entre os dois perfis de solos; os atributos físicos (teor de argila, macroporosidade, microporosidade, capacidade de campo e ponto de murcha permanente) apresentaram diferença significativa entre os horizontes dos perfis estudados; a micromorfologia indicou que a maior retenção de água no P2 é consequência da presença de zonas com empacotamento mais denso de seus componentes (empacotamento aglomerático) e expressividade das pontes de argila; e sugere-se adoção do termo “lamélico” pelo atual Sistema Brasileiro de Classificação de Solos (em 4º nível categórico) para diferenciação dos perfis estudados.

In general, Latosols have low levels of available P, however, the influence of the parent material seems to be decisive in defining the pool and predominant form of P in these soils. This study evaluated P availability by extraction with Mehlich-1 (M-1) and Ion Exchange Resin (IER), from samples of B horizons of Ferric and Perferric Latosols developed from different parent materials. To this end, in addition to the physical and chemical characterization of soils, 10 sequential extractions were performed with M-1 and IER from samples of B horizons (depth between 0.8 and 1.0 m). Total contents of Ca, P, Fe, Al, and Ti were determined after digestion with nitric, hydrofluoric and perchloric acids. The effects of sequential P extractions on Fe oxides were also evaluated from the analyses of dithionite-citrate-bicarbonate and ammonium acid oxalate. The high similarity between contents of P accumulated after sequential extractions with M-1 and IER in soils developed on tuffite indicated a predominance of P-Ca. Higher contents of P after a single IER extraction show greater efficiency in P removal from highly weathered soils, as from the Latosols studied here. The P contents also show the high sensitivity of extractant M-1 in highly buffered soils. Furthermore, a single extraction with extractant M-1 or IER is not sufficient to estimate the amount of labile P in these soils.

Na unidade geomorfológica dos Tabuleiros Costeiros dominam os solos com horizontes coesos, e alguns deles têm a presença de horizontes cimentados comumente do tipo fragipã. Esses horizontes interferem na dinâmica da água, no crescimento de raízes e, consequentemente, na nutrição mineral de plantas. O objetivo deste trabalho foi avaliar, por meio da dissolução seletiva, a participação de formas de Fe, Si e, ou, Al na coesão e, ou, cimentação de fragipãs e horizontes coesos em Argissolos e Espodossolos da região dos Tabuleiros Costeiros do sul da Bahia e norte do Espírito Santo. Para isso, foram realizadas extrações seletivas de Fe, Si e Al por ditionito-citrato-bicarbonato de sódio (DCB) e oxalato ácido de amônio. Os maiores teores de Fe, Si e, principalmente, Al extraídos por oxalato de amônio nos fragipãs sugerem que, na gênese desses horizontes, formas de baixa cristalinidade desses elementos agem como cimentantes químicos. As dissoluções seletivas não evidenciaram a participação de formas de alta ou baixa cristalinidade de Fe, Si e, ou, Al na gênese dos horiozontes coesos em solos dos Tabuleiros Costeiros. Os Argissolos Amarelos apresentaram goethitas com alta substituição isomórfica de Fe por Al, condizente com o ambiente de forte intemperização, não redutivo e pH ácido onde esses solos se encontram nos Tabuleiros Costeiros. A substituição isomórfica de Fe por Al nos óxidos de Fe cristalinos apresentaram relação com o grau de cristalinidade e teor de Fe obtido na primeira extração com o DCB.

ABSTRACT Weathering and pedogenesis have been studied for a wide range of rocks and climates around the world. However, the eruption of rhyolitic magmas is a rare geological event, which leads to few studies associated with the rhyolite-soil-landscape relationship. In this context, this study evaluated the influence of rhyolite weathering on the properties of soils along a slope in an Atlantic Forest environment in the state of Pernambuco, northeastern Brazil. Four weathering profiles derived from rhyolites were classified and sampled for chemical, physical, mineralogical, micromorphological, differential thermal, and thermogravimetric analyses. The chemical properties reflect the original rock rich in felsic minerals, poor in bases, and the types of clay minerals. The clay fraction of the profiles consists mainly of 1:1 phyllosilicates and oxides, indicating intermediate weathering. However, variations in the degree of structure weathering were evidenced by the presence of partially preserved fragments of the original rock in the sand fraction of the soils. The tropical humid climate of the region influenced conversion of hematite to goethite through the xanthization process, and the subsurface drainage deficiency allowed the formation of halloysite in the lowest position of the landscape. Because it is an acid rock with an aphanitic texture and porphyritic relative size of crystals, rhyolite weathering resulted in the formation of dystrophic soils, with predominance of quartz in the silt fraction. From the top to the lower third of the slope, a Haplic Cambisol, an Abruptic Lixisol, and two Haplic Lixisols were formed.

The Garanhuns Plateau in the Agreste region of the State of Pernambuco, Brazil is characterized by humid climatic conditions due to orographic rains, unlike the surrounding semiarid region. These soils are subjected to intense agricultural use and are extremely important for the regional economy. This study was carried out in the municipality of Brejão in the Agreste region with the aim of assessing changes in humic Haplustox soils subjected to different land uses. Four plots with different vegetation covers (native forest, secondary shrubby vegetation (capoeira), traditional cropping system, and planted pasture) were selected, and samples were taken from a soil profile and four small pits surrounding it at each site. Physical and chemical properties were assessed, including aggregate stability, humic organic fractions, and a microbiological evaluation through determination of basal respiration, microbial biomass carbon, and metabolic quotient. The soils under study showed physical and chemical properties typical of a Haplustox, such as low nutrient content, low cation exchange capacity, and high levels of acidity and Al saturation. The total organic carbon (TOC) contents were high regardless of the type of land use. Aggregates < 2 mm were dominant in all the conditions under study. The TOC content was higher in the soil under capoeira, 43.91 g kg-1 on the surface, while 34.36 and 33.43 g kg-1 of TOC were observed in the first layer of forest and pasture soils, respectively. While the microbial biomass C (MBC) was greater than 700 mg kg-1 in the forest and pasture areas (in the 0-5 cm layer), and 588 mg kg-1 in the soil under capoeira, these numbers were not statistically different. In the cultivated soil area, there was a reduction of around 28 % in TOC and MBC contents. Agricultural activity contributed to degradation of the humic horizon, as can be seen from a significant decrease in the TOC and changes in the relative distribution of the humic fractions. In contrast, aggregate stability was not altered as a function of the different land uses; the soil under planted pasture and capoeira were similar to the soil under native forest. Humin was the most important humified fraction for C reserves, contributing over 40 % of the TOC in these soils.

Estudos de caracterização de solos em regiões ainda pouco exploradas, além de disponibilizarem e ampliarem a base de informações sobre as mais distintas ordens de solos do território nacional, também permitem sistematizar informações sobre suas propriedades, que poderão servir de subsídio para o desenvolvimento de práticas de manejo e uso sustentável das terras. Entre os principais solos recorrentes na região semiárida pernambucana, destacam-se os Neossolos Regolíticos, os quais perfazem aproximadamente 27 % da superfície do Estado e recobrem importantes áreas voltadas à produção agrícola, especialmente à agricultura familiar. Considerando a possibilidade de ocorrência de Neossolos Regolíticos com distintas propriedades físicas, químicas ou mineralógicas, em razão da existência de distintos contextos geológicos e climáticos ao longo do Estado de Pernambuco, o presente trabalho teve como objetivo caracterizar física, química e mineralogicamente Neossolos Regolíticos ao longo da região semiárida do Estado de Pernambuco, bem como relacionar os solos com sua litologia. Para isso, foram selecionados cinco perfis de Neossolos Regolíticos em diversos municípios do Estado de Pernambuco (P1=São Caetano, P2=Lagoa do Ouro, P3=Caetés, P4=São João e P5=Parnamirim). Os perfis foram descritos morfologicamente, coletando-se amostras de todos os horizontes do solo e da rocha do embasamento. Foram realizadas análises físicas e químicas para fins de classificação de solos, análises mineralógicas das frações grossas (cascalho e areia) por microscopia óptica e das frações silte e argila por difração de raios X, além de análises petrográficas das amostras de rochas. De acordo com os resultados, observou-se a ocorrência de solos semelhantes e com pequeno grau de desenvolvimento pedogenético, variando de medianamente a muito profundos, com sequência de horizontes A-AC-C e Cr e textura arenosa a média. Dois perfis apresentaram caráter solódico em profundidade. Todos os solos apresentaram baixos teores de matéria orgânica e P disponível. Apesar dos baixos teores de cátions trocáveis, todos os perfis são eutróficos. A assembleia mineralógica das frações cascalho, areia e silte é constituída essencialmente por quartzo, seguido de feldspatos e mica, corroborando a constituição petrográfica analisada. A caulinita é o principal argilomineral da fração argila em todos os perfis e horizontes estudados, indicando um importante processo de monossialitização em solos autóctones, em clima caracteristicamente semiárido. No perfil P2, devido à posição mais baixa do solo na paisagem, ocorreram minerais esmectíticos com misturas de fases entre montmorilonita, beidelita ou nontronita, identificados pela análise de DRX, empregando o teste de Greene-Kelly.

Os brejos de altitude nordestinos constituem uma disjunção da mata atlântica, formando ilhas de floresta úmida em plena região semiárida, tendo uma condição climática bastante atípica, favorecida pela ocorrência de chuvas orográficas, com precipitação pluvial que pode atingir valores superiores a 1.200 mm por ano. No Estado de Pernambuco, a maioria dos estudos em brejos de altitude abrange os aspectos botânicos e faunísticos, sendo, portanto, importante a realização de estudos para caracterização dos recursos edáficos. Com intuito de estudar os solos de brejos de altitude no Sertão Pernambucano e avaliar a influência dos diversos fatores pedogenéticos na sua formação e evolução, foi feita a caracterização morfológica, física, química e mineralógica de três perfis no maciço de Triunfo, em diferentes altitudes, localizados nos municípios de Serra Talhada (P1), Santa Cruz da Baixa Verde (P2) e Triunfo (P3), formando uma topoclimossequência. Os perfis estudados apresentam características morfológicas similares, relacionadas com o pequeno grau de desenvolvimento pedogenético, principalmente nos perfis P3 (Triunfo) e P2 (Santa Cruz), classificados, respectivamente, como Cambissolo Háplico Tb Eutrófico latossólico e Cambissolo Háplico Tb Eutrófico típico. O perfil P1 (Serra Talhada), localizado no sopé, apresentou menor teor de argila e acentuado gradiente textural, resultante de descontinuidade litológica, sendo classificado como Argissolo Vermelho-Amarelo distrófico abrúptico (cambissólico). Todos os solos deste estudo são oriundos de rochas sieníticas, sendo, pelo menos em parte, influenciados pelo transporte e pela deposição de materiais oriundos da parte superior do relevo. O perfil de Triunfo, em local mais úmido, apresentou o maior grau de desenvolvimento em relação aos demais. O clima, atuando principalmente pela variação de umidade, não foi, entretanto, o único fator de formação responsável pela diferenciação dos solos ao longo da topoclimossequência, devendo-se ressaltar, também, a influência do material de origem e do relevo.Highland forests in mountains of Northeast Brazil are islands of humid Atlantic forest in the midst of the semi-arid region. The climatic conditions are rather atypical, improved by the occurrence of orographic rainfall, which can reach 1,200 mm per year. In the state of Pernambuco, most of the scientific studies in these humid highland forests are focused on botanical and zoological aspects only, with very little information about soils. Aiming to study the soils of the humid mountains in the semi-arid region and to evaluate the influence of the various soil-forming factors on formation and evolution, three soil profiles were characterized for morphological, physical, chemical, and mineralogical properties in the Triunfo mountain range, at different altitude levels. The soil profiles were located in the municipalities of Serra Talhada (P1), Santa Cruz da Baixa Verde (P2) and Triunfo (P3), along a moisture and altitude gradient (topo-climatic sequence). The soils were morphologically similar, due to the low development degree, mainly in the soil profiles P3 (Triunfo) and P2 (Santa Cruz), classified, respectively, as Oxic Haplustept and Typic Haplustept. In the lower part of profile P1 (Serra Tallhada), a low clay content and greater textural gradient classified the soil as Typic Haplustult. The results showed that all studied soils were developed from syenitic rocks, with influence of sediments from the upper part of the relief. The development degree of the soil of Triunfo, with the highest rainfall levels, was higher than of the others. Climate, acting mainly by the variation in moisture, was however not the only soil forming factor responsible for soil differentiation along the sequence, but parent material and relief were important as well.

O caráter coeso é um atributo característico de horizontes subsuperficiais que, quando secos, apresentam consistência muito dura e extremamente dura, passando a friável ou firme quando úmidos. A formação desses horizontes, entretanto, ainda é um assunto polêmico, não estando completamente esclarecida. O objetivo deste trabalho foi realizar uma caracterização química, mineralógica e micromorfológica de solos coesos, visando entender a sua gênese e definir características que possam complementar a definição do caráter coeso no Sistema Brasileiro de Classificação de Solos. Quatro perfis de solos foram coletados na região dos tabuleiros costeiros de Alagoas, envolvendo um Argissolo Amarelo, um Argissolo Acinzentado e dois Latossolos Amarelos. Os solos foram descritos morfologicamente, e as amostras dos horizontes coesos e não coesos foram coletadas para execução de análises químicas de Fe, Al e Si por extração com DCB, oxalato, CaCl2 e água quente, análises mineralógicas por DRX e caracterização micromorfológica. Os solos apresentaram baixos teores de Fe, com domínio das formas de baixa cristalinidade e predominância de caulinitas com moderado a alto grau de desordem estrutural em todos os horizontes. Não foi observada, nos horizontes coesos, tendência de aumento dos teores de Al e Si extraídos com DCB e oxalato, indicando que a sua gênese não se deve à presença de agentes cimentantes. Os resultados das análises mineralógicas e micromorfológicas sugerem que a gênese do caráter coeso apresenta duas fases distintas, sendo formado inicialmente pelo entupimento dos poros decorrente da iluviação de argila fina, havendo posteriormente uma perda de Fe na parte superior, que colapsa a estrutura e provoca um ajuste face a face da caulinita.The cohesive character is a property of subsurface soil horizons with hard to extremely hard consistency when dry, and friable or firm when wet. Despite the agricultural importance, the formation of these horizons has not been fully explained. The objective of this study was a chemical, mineralogical and micromorphological characterization of cohesive soils of the Coastal Tablelands in Northeast Brazil, to understand their pedogenesis and identify properties for the definition of the cohesive character by the Brazilian System of Soil Classification. The following four soil profiles were morphologically characterized: a Yellow Argisol (Ultisol), a Gray Argisol (Ultisol) and two Yellow Latosols (Oxisols). Samples from cohesive and non cohesive horizons were taken for chemical analysis of Fe, Al and Si extracted by DCD, oxalate, CaCl2 and hot water, mineralogy by X ray diffraction, and micromorphological characterization. The Fe contents in the soils were low and kaolinite with a moderate to high degree of structural disorder predominated in all studied soil horizons. No increase in Al and Si extracted by DCB and oxalate was observed in the cohesive horizons, indicating the absence of cementation in its genesis. Results of the mineralogical and micromorphological characterization suggest two distinct phases in the genesis of the cohesive character. The first step was determined by clay illuviation, clogging the soil pores, and later iron loss, destroying the soil structure and resulting in a direct adjustment with kaolinite particles.

Pouco se conhece sobre a diferenciação pedogenética no Alto Paranaíba (MG), quando são comparados materiais de composição química tão variada, como tufitos, rochas ígneas alcalinas e ultramáficas e carbonatitos, todos de ocorrência na região. Dessa forma, este trabalho teve como objetivo caracterizar física, química e mineralogicamente os solos representativos de três topolitossequências do Alto Paranaíba. Para isso, foram descritos e coletados 11 perfis de solos, entre os municípios de Serra do Salitre, Patrocínio e Coromandel, representando as variações litológicas na faixa do contato geológico entre os grupos Bambuí, rochas vulcânicas ultramáficas e Araxá. Nas amostras de solos foram realizadas análises físicas e químicas de rotina, além de determinações de Fe, Al e Si após extração por ataque sulfúrico; Fe por DCB e oxalato; Fe, Ca, Mg, K, P, Ti e outros metais pesados após digestão total (ataque triácido); e determinação dos diferentes componentes da fração argila por difratometria de raios X. Os Latossolos do Alto Paranaíba são extremamente intemperizados e com índices Ki e Kr muito baixos, indicativos de solos ricos em óxidos de Fe e de Al, não possuindo uma filiação definida com os materiais de origem subjacente, indicando intensa pedoturbação e provável mistura com materiais alóctones. As assinaturas geoquímicas indicativas da natureza ultramáfica são os teores elevados de Cr, Ni, Mn, Fe e Mg. A mineralogia da fração argila dos Latossolos indica a coexistência de vermiculita com hidroxi-Al entrecamadas, caulinita, gibbsita e anatásio, evidenciando uma gênese policíclica dos minerais da fração mais fina e o elevado grau de intemperismo. Nos Cambissolos, a rápida dessilificação atual conduz à coexistência de gibbsita e óxidos de Fe com esmectitas e illitas, em virtude da rápida ação do intemperismo nos substratos de rochas máficas ou ultramáficas-alcalinas, pobres em sílica.Little is known bout the pedogenetic differentiation in Alto Paranaíba, western Minas Gerais, Brazil, when materials with such a variety of chemical compositions as tufite, alkaline-ultramafic igneous rocks and carbonatites are compared, which are all found in this region. The purpose of this study was to characterize the physical, chemical and mineralogical properties of three representative soil topolitosequences of the Alto Paranaíba region. Therefore, 11 soil profiles were described and collected in the Serra do Salitre, Patrocínio and Coromandel counties, representing the influence of mafic-ultramafic bodies along the geological interface between Bambuí and Araxá groups. Soil samples were routinely analyzed for physical and chemical properties, besides determinations of Fe, Al and Si after sulfuric extraction; Fe after extraction by DCB and oxalate; Fe, Ca, Mg, K, P, Ti, and other heavy metals after total digestion (triacid attack); and determination of the different components in the clay fraction by DRX. The Latosols (Oxisols) of the Alto Paranaíba are extremely weathered and have very low Ki and Kr indexes, indicators of soils with high iron and aluminum oxides contents, with no defined relationship with the underlying parent materials, indicating intense pedoturbation and mixture with alloctonous materials. The geochemical signatures of the ultramafic nature are the unusual high content of Cr, Ni, Mn, Fe, and Mg. The clay fraction mineralogy of the Latosols shows the coexistence of VHE, kaolinite, gibbsite, and anatase, indicating a polycyclic genesis of the minerals from the finer fraction and the high weathering degree. In the Cambisols, the current rapid desilification indicates the coexistence of gibbsite and iron oxides with smectites and illite because of the fast weathering in the silicon-poor mafic or alkaline-ultramafic rock substrates.

O caráter coeso é um atributo característico de horizontes subsuperficiais de solos que apresentam consistência muito dura a extremamente dura, quando secos, passando a friável ou firme, quando umedecidos. A formação desses horizontes, entretanto, ainda é um assunto polêmico, não estando completamente esclarecida. Este trabalho objetivou caracterizar e identificar os possíveis mecanismos envolvidos na formação dos horizontes coesos de solos dos Tabuleiros Costeiros, buscando entender sua gênese e definir propriedades que possam complementar a definição do caráter coeso no Sistema Brasileiro de Classificação de Solos. Quatro perfis de solos da região dos Tabuleiros Costeiros de Alagoas foram estudados: um Argissolo Amarelo, um Argissolo Acinzentado e dois Latossolos Amarelos. Os solos foram descritos morfologicamente, e amostras dos horizontes coesos e não coesos foram coletadas para execução de análises físicas e químicas. A caracterização morfológica constatou a presença de horizontes com caráter coeso tanto nas áreas sob floresta quanto nas áreas sob cultivo, confirmando sua natureza pedogenética. A morfologia e a densidade do solo, aliadas à determinação da superfície específica, mostraram-se eficientes na identificação dos horizontes coesos dos solos estudados.The cohesive character is an attribute of subsurface soil horizons with hard to extremely hard consistency when dry, and friable or firm when wetted. Despite the agricultural importance, the formation of these horizons is not yet completely understood. The objective of this study was to characterize and assess the possible mechanisms involved in the formation of cohesive horizons in soils of the Coastal Tablelands of Northeast Brazil, in order to understand their pedogenesis and to identify physical and chemical parameters that can be used for the definition of the cohesive character in the Brazilian System of Soil Classification. Four soil profiles were morphologically characterized: a Yellow Argisol (Ultisol), a Gray Argisol (Ultisol) and two Yellow Latosols (Oxisols). Samples from cohesive and non-cohesive horizons were taken for physical and chemical analysis. The morphological description revealed the presence of the cohesive character both under forest as well as under cultivation, confirming its pedogenetic nature. Soil morphology and soil density, together with the specific surface area efficiently identified the cohesive character in the studied soils.

Grande parte das propriedades e características dos solos estão relacionadas à quantidade e ao tipo de mineral na fração argila. Os objetivos deste trabalho foram caracterizar a fração argila e estudar as características cristalográficas das caulinitas de solos vermelhos e amarelos, visando ao entendimento das relações desse mineral com as características e propriedades dos solos dominantes na região dos Tabuleiros Costeiros e mais interioranos do Brasil. Para isso, determinou-se a relação argila grossa/argila fina e foram realizadas análises mineralógicas (qualitativa e quantitativa) por meio de DRX e aplicação do método Rietveld; caracterização espectral por ERD, para determinação da relação hematita/goethita; estimativa de propriedades cristalográficas (tamanho e microtensões), por DRX e utilizando modelos matemáticos; da superfície específica, por BET-N2; da fractalidade; do grau de desordem estrutural, por diversos índices; e análises de microscopia eletrônica de transmissão. Os resultados permitiram as seguintes conclusões: (a) a quantificação dos minerais de argila pelo método Rietveld revelou predomínio marcante das caulinitas em todos os solos estudados; (b) a análise dos espectros de DRX, aplicando-se o método Rietveld, sugere a coexistência de caulinitas triclínicas e caulinitas com caráter monoclínico; (c) as caulinitas menores que 0,2 µm de todos os solos foram similares em superfície específica BET-N2, dimensão média do cristalito no plano (001), grau de desordem estrutural e dimensão fractal, mas diferentes em sua morfologia, que se apresentou correlacionada com o material de origem.Soil properties and characteristics are related to the quantity and type of minerals in the clay fraction. The objective of this research was to characterize the clay fraction and study the crystallographic characteristics of kaolinites in red and yellow soils, in support of further research on the relationships of this mineral with the characteristics and properties of the dominant soils in coastal tablelands. The following evaluations were performed: determination of the coarse clay/fine clay ratio; mineralogical analyses (qualitative and quantitative) by DRX and by the Rietveld method; spectrum characterization by ERD to determine the hematite/goethite ratio; estimation of crystallographic properties (size and microtension) by DRX and mathematical models; the specific surface by BET-N2; fractal dimension; structural disorder degree by several indexes and analyses by electronic transmission microscopy. Results allow the following conclusions: (a) clay mineral quantification by the Rietveld method revealed the prevalence of kaolinites in all soils under study; (b) the Rietveld analysis of the DRX spectra suggests the coexistence of triclinic and monoclinic kaolinites; (c) the kaolinites < 0.2 µm in all soils were similar in terms of specific BET-N2 surfaces, mean size of the in-plan crystallite (001), structural disorder degree and fractal dimension, whereas the morphology, which was correlated with the parent material, was different.

O objetivo do presente trabalho foi avaliar física, química, mineralógica e micromorfologicamente solos vermelhos, amarelos e acinzentados coesos em três toposseqüências na região dos Tabuleiros Costeiros do sul da Bahia e norte do Espírito Santo, desenvolvidos a partir de sedimentos do Grupo Barreiras ou de rochas gnáissicas do Pré-Cambriano, assim como os possíveis mecanismos físicos e, ou, mineralógicos que promovem a coesão dos solos e formação de fragipãs. Para isso, foram realizadas análises físicas; determinadas a relação argila fina/argila grossa, superfícies específicas por BET-N2 e adsorção de vapor de água, susceptibilidade magnética; e analisados os constituintes por microscopia eletrônica de varredura e micromorfologia em lâminas delgadas. As análises físicas e micromorfológica indicam que a gênese dos horizontes coesos deve-se ao maior conteúdo de argilas muito finas, principalmente menores que 0,2 µm, translocadas entre horizontes ou dentro do mesmo horizonte como argila dispersa. A maior coesão observada para o Argissolo Amarelo localizado em clima mais seco, em relação àqueles em clima mais úmido, pode ser devido à sua granulometria menos argilosa e maior quantidade de feições de iluviação de argila.The objective of this study was to evaluate the physical, chemical, mineralogical and micromorphological characteristics of cohesive red, yellow and grayish soils in a toposequence of the Coastal Tablelands region in southern Bahia and northern Espirito Santo states. It was also sought to understand the mechanisms promoting their cohesion and fragipan formation. Therefore, the routine physical analyses, determination of the coarse clay/fine clay ratio, specific surface by BET-N2 and water vapor adsorption, magnetic susceptibility, scanning-electron microscopy analyses and the micromorphology of thin plates were carried out. Physical and micromorphological analyses indicated that the high content of very fine clays, especially those smaller than 0.2 µm, translocated among horizons or within a same horizon as dispersed clay, were responsible for the genesis of the cohesive horizons. The higher cohesion observed in the Yellow Argisol (Ultisol) found in a drier climate, compared to those in a more humid climate could be due to the less clayey granulometry and a larger amount of clay illuviation features.

Os ácidos orgânicos provenientes da decomposição da matéria orgânica, da exsudação radicular e do metabolismo de microrganismos, possuem importante papel na melhoria das condições físicas e químicas do solo. Entretanto, sua eficiência está relacionada à qualidade e à forma dos ácidos orgânicos e à sua interação com colóides do solo. Com o objetivo de avaliar o efeito dos ácidos orgânicos de alto e baixo peso molecular na alteração de propriedades físicas e químicas de solos, foram coletados materiais de horizontes B de quatro Latossolos e um Plintossolo, e C de Neossolo Quartzarênico. Para isso, foram utilizadas doses de ácidos cítricos e oxálicos de 0, 1, 3, 9 e 18 mmol L-1; e para os ácidos húmicos, doses de 0,0; 2,0; 4,0; 6,0 e 10,0 g kg-1, num delineamento experimental inteiramente casualizado seguindo um esquema fatorial de 6 x 3 x 5 (solo, ácido e dose), com três repetições. As doses utilizadas foram de 0, 1, 3, 9 e 18 mmol L-1 para os ácidos cítrico e oxálico e, para os ácidos húmicos, de 0,0; 2,0; 4,0; 6,0; e 10,0 g kg-1. As unidades experimentais foram compostas de 25 cm³ de TFSA, colocadas em cilindros de PVC (2,0 cm de altura por 4,0 cm de diâmetro). Estas foram mantidas em câmaras isotérmicas a 30 °C e submetidas a ciclos de umedecimento e secagem de três dias, por sete ciclos. Ao final do experimento foram determinados o teor de argila dispersa em água, a resistência à penetração e os teores de Fe e Al por oxalato ácido de amônio. Os resultados mostraram que o conteúdo de argila dispersa variou com o tipo e dose dos ácidos orgânicos, textura e mineralogia dos solos, indicando que aqueles goethíticos apresentaram maior resistência à dispersão que os hematíticos, e estes, por sua vez, maior resistência que os gibbsíticos. Com relação aos ácidos, foi observado que os de cadeia curta promoveram maior dispersão e resistência à penetração que os ácidos de cadeia longa, podendo-se estabelecer a seguinte ordem, de acordo com seu efeito: ácido cítrico > ácido oxálico > ácidos húmicos. O conteúdo de argila dispersa em água mostrou ser o principal fator responsável pelo aumento da resistência à penetração.The organic acids from the organic matter decomposition, root exudation and microbial activity, play an important role on physical and chemical soil conditions. However their efficiency is conditioned to the quality and kind of organic acids and interactions with the soil mineral surface. The aim of this study was to evaluate the effect of humic and organic acids of high and low molecular weight on the physical and chemical properties of B horizons of four Oxisols and one Plinthustult, and a C horizon of Quartzipsamment. A completely randomized 6x3x5 factorial design (soils x organic acids x dose) was used, with 3 replications. The following organic acid rates were applied: 0, 1, 3, 9 and 18 mM citric and oxalic acid and 0.0; 2.0; 4.0; 6.0 and 10.0 g kg-1 humic acids. The experimental units consisted of 25 cm³ of air-dried fine-earth fraction in PVC cylinders (2.0 cm height and 4.0 cm diameter), subjected to moistening and drying cycles in an isothermal chamber at 30 °C, for three days, in seven cycles. The water dispersible clay, penetration resistance and ammonium oxalate-extracted Fe and Al were determined. The contents of water dispersible clay were variable, related to the rate and type of organic acids, and also to soil texture and mineralogy. Thus, the dispersion resistance of the goethitic was higher than of the hematitic soils, which was in turn higher than of the gibbsitic soils. Moreover, organic acids of low molecular weight resulted in higher dispersion and penetration resistance than those of high molecular weight, in the following sequence: citric acid ³ oxalic acid > humic acid. The content of water dispersible clay proved to be an important factor in the increase of penetration resistance.

Substâncias orgânicas podem favorecer o aumento da estabilidade de agregados, reduzindo, de acordo com seu grau de hidrofobicidade, a velocidade de infiltração de água nos agregados. Este trabalho teve como objetivo estudar a formação e estabilização de agregados de um Latossolo Vermelho-Amarelo distrófico em virtude da adição de compostos orgânicos com características hidrofóbicas e hidrofílicas distintas. Foram incubados 100 g de TFSA do horizonte A e do B com diferentes doses de três compostos orgânicos: ácido esteárico P.A., amido P.A. e ácido húmico purificado de acordo com a Sociedade Internacional de Substâncias Húmicas. O experimento foi realizado com os tratamentos gerados de acordo com a matriz Plan-Puebla III modificada, com as doses do espaço experimental variando de -0,55 a 10,45 g kg-1. Após o período de 160 dias de incubação, avaliaram-se: o índice de estabilidade de agregados, o diâmetro médio ponderado e o diâmetro médio geométrico dos agregados formados. Os resultados indicaram que compostos orgânicos com caráter hidrofílico dominante não têm influência na formação e estabilização de agregados do solo, principalmente quando se usam doses até 9,9 g kg-1. Observou-se, também, que a aplicação de moléculas orgânicas com acentuado caráter hidrofóbico e hidrofílico na sua estrutura, como os ácidos húmicos, é capaz de melhorar a agregação de solos com grau de intemperismo avançado.According to their hydrophobicity degree, organic substances can increase the aggregate stability, reducing the rate of water infiltration into the aggregates. Our study investigated the aggregate genesis and stabilization in a Red-Yellow Latosol under organic compound addition with distinct hydrophobic and hydrophilic characteristics. Air-dried samples from the A and B horizons were incubated with different doses of three organic compounds: estearic acid, amid and humic acid purified in accordance to the International Humic Substances Society. The experiment was organized with the treatments according to the modified Plan-Puebla III matrix, using doses varying from -0.55 to 10.45 g kg-1 in the experimental range. After 160 days of incubation, the aggregate stability index, mean weight diameter, and the mean geometric diameter of the aggregates formed were measured. Results indicate that the addition of organic compounds with dominant hydrophilic character does not influence the soil aggregate genesis and stabilization, mainly in doses up to 9.90 g kg-1. The addition of organic molecules with a hydrophobic and hydrophilic structure character, such as humic acids, is able to improve aggregation in soils with a high weathering degree.

A adição de compostos orgânicos e os ciclos de umedecimento e secagem do solo têm influência marcante na agregação do solo. Este trabalho objetivou estudar o efeito do tempo de incubação e a influência dos ciclos de umedecimento e secagem sobre a ação de compostos orgânicos com características hidrofóbicas e hidrofílicas na agregação de um Latossolo Vermelho-Amarelo distrófico. Os tratamentos dos experimentos de períodos de incubação e de ciclos de umedecimento e secagem seguiram esquema fatorial incompleto 2 x 3[(4-1) + (4-1)]. Os fatores foram: TFSA de dois horizontes (A e B), três períodos de incubação (40, 80 e 160 dias), três compostos orgânicos (amido, ácido esteárico e ácido húmico), em combinações de ausência e presença de amido e ácido húmico (Am e AH), (4-1) e de ácido esteárico e ácido húmico (E e AH), (4-1). Todas as unidades experimentais foram mantidas em incubadora de DBO a 25 ºC e em ambiente natural, quando foram submetidas a 5, 11 e 22 ciclos de umedecimento e secagem, de acordo com os períodos de incubação. Após incubação, as amostras de agregados foram analisadas quanto ao diâmetro médio ponderado, diâmetro médio geométrico, índice de estabilidade de agregados e grau de repelência à água. Os resultados indicaram que a aplicação, mesmo em longos períodos de incubação, de compostos orgânicos com caráter hidrofóbico acentuado mostrou efeito marcante na melhoria da estabilidade em água do agregados, sendo sua melhor resposta na dose de 5,5 g kg-1. Para melhorar a agregação, a aplicação de compostos orgânicos hidrofílicos deve ser contínua e com períodos de incubação de no máximo 40 dias. Os ciclos de umedecimento e secagem reduziram os efeitos dos compostos orgânicos adicionados sobre a agregação.The input of organic compounds in agriculture and the soil wetting and drying cycles have a strong influence on soil aggregation. This study investigated the effect of incubation periods and the influence of wetting and drying cycles with the addition of organic compounds of distinct hydrophobic and hydrophilic characteristics on the aggregation of a Red-Yellow Latosol. The experiments were arranged in an incomplete factorial design 2 x 3[(4-1) + (4-1)]. The factors were: air-dried soil of A and B horizons, three incubation periods (40, 80 and 160 days), three organic compounds (amid, estearic acid, and humic acid), the combination of presence and absence of amid/acid humic (Am + AH), (4-1) and estearic acid/humic acid (E + AH), (4 + 1). All experimental units were kept in a BOD incubator at 25 ºC and in natural environment, where they underwent 5, 11 and 22 wetting and drying cycles. After the incubation period, the aggregate samples were analyzed for aggregate stability index, mean weight diameter, mean geometric diameter, and water repellence degree. Results indicated that even in the long term the application of organic compounds with strong hydrophobic character contributes considerably to the improvement of water aggregate stability. The 5.5 g kg-1 dose achieved best results. To improve the aggregation, the application of hydrophilic organic compounds should be continuous in intervals of up to 40 days. Soil wetting and drying cycles reduced the effect of organic compounds on aggregation.

ABSTRACT: 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.

ABSTRACT The micromorphology of deeply weathered soils (Ferralsols/ Latossolos ) from the Central Plateau of Brazil remains little studied, and its affiliation to different parent materials, poorly known. To clarify the processes of soil formation of these acric, gibbsitic, Fe-oxide rich Ferralsols, three lithotoposequences on local ultrabasic to basic intrusive rocks were studied. The influences of mixing and pedobioturbation are evident in all soils, and Ferralsols of the Central Plateau of Brazil are polygenetic, based on the coarse mineral composition, with ultrabasic and metapelitic rock contributions. The typical oxic microstructure with stable microaggregates encompasses a gibbsite/Fe rich micromass with random inclusions of charcoal, allochthonous quartz, Ti-magnetite, and perovskite grains. Shallow Cambisols ( Cambissolos ) on tuffites also display a similar “oxic” microstructure, but a much lower degree of weathering. These Cambisols possesses apatite, and mafic and pelitic minerals as residuals minerals grains, indicating the polygenetic colluvia mixture of different substrates. The common occurrence of perovskite (CaTiO3) as a residual grain in deep-weathered, acric Ferralsols on ultrabasic rocks, not yet reported in the literature, shows an unusual resistant Ca reserve in oxic soils, though nothing is known about its implications to soil fertility.

ABSTRACT Despite the considerable amount of information on the mineralogical characteristics of pedogenic Fe oxides in Brazilian soils, there are few studies on Fe-rich soils developed from mafic rocks with taxonomic identities at lower categorical levels. This study evaluated the mineralogical characteristics of pedogenic Fe oxides in B horizons (Bw) of Fe-rich Oxisols developed from several mafic rocks in the state of Minas Gerais, Brazil. The Bw horizons were sampled at a 0.8-1.0 m depth in 13 Ferric and Perferric Rhodic Oxisols along with a Mesoferric Typic Oxisol originating from basalt, gabbro, tuffite, amphibolite and itabirite in Minas Gerais. The selected soils have taxonomic identities up to the fourth categorical level of the Brazilian System of Soil Classification. In the laboratory, the following analyses were made: a) powder X ray diffraction (XRD) of the clay fraction before and after selective concentration of Fe oxides by silicate alkaline dissolution (5 mol L-1 NaOH); b) selective chemical dissolution of the clay fraction by citrate-bicarbonate-dithionite (CBD), acid ammonium oxalate (AAO), and sulfuric acid (H2SO4 1.8 mol L-1); c) quantitative estimation of minerals in the clay fraction through allocation of phases from the XRD patterns, magnetic susceptibility of the clay fraction, and quantification of elements after sulfuric acid digestion (H2SO4 1:1) of the air-dried fine earth and treatment of the clay fraction with CBD; and d) estimation of the mean crystal size (MCS), specific surface area (SSA), and isomorphic Al-substitution (IS) of hematite, goethite, and maghemite from the XRD patterns obtained from concentrates of Fe oxides. The results showed that estimation of Fe content of maghemite by selective dissolution with 1.8 mol L-1 H2SO4 may not be accurate enough to realistically reflect the maghemite contents in the soil sample. The Al content extracted may also be influenced by other minerals that are sources of this element. Hematite crystals were predominantly placoid in shape in all Rhodic Oxisols and had smaller SSA compared to goethite, which showed both isodimensional and asymmetric habit. Higher crystallinity of maghemite and the IS values generally lower than those of hematite and goethite suggest that in well-drained soils derived from mafic rocks, the IS phenomenon in maghemites seems to result from pedogenetic advancement after its formation from magnetite oxidation.

ABSTRACT Ferrimagnetic Fe-oxides are important soil components, which are present in most of the agricultural soils of Brazil. Distinction, origin, and assessment of the influence of these minerals on magnetism and geochemistry is a challenge for mineralogists. This study aimed to characterize mineralogically Fe-rich Rhodic Oxisols ( Latossolos Vermelhos ) originating from several mafic rocks in Brazil, and assess the implications on their magnetic and geochemical properties. We present results on magnetic measurements, chemical dissolutions, X-ray diffractometry, Rietveld refinement, Raman, and Mössbauer spectroscopies of Fe-rich Rhodic Oxisols originating from several mafic rocks. They show that magnetite is inherited from the parent material, and its oxidation leads to the formation of maghemite. In the coarse fractions (sand and silt), magnetite and maghemite coexist and are interstratified with hematite, confirmed by Raman spectroscopy. This limited the distinction between magnetite and maghemite by Mössbauer spectroscopy. Maghemite represents the only ferrimagnetic Fe oxide in the clay fraction. The influence of both ferrimagnetic minerals, magnetite and maghemite, on magnetic susceptibility and total content of trace elements is determined by the pedogenic development, even among highly weathered soils. In general, the coarse fractions contribute with most of the total trace element contents, while the clay fraction contributes to trace elements availability and magnetic susceptibility of soils.