Particle size distribution and mineralogy of Brazilian Ferralsols: Significance for the structure and hydraulic properties.

The Cerrados Biome is one of the major regions of Brazil with 24% of the Brazilian territory (204.106 ha). It is mainly located in the center of Brazil and corresponds to the whole Central Plateau. About 49% of the soils are Ferralsols and approximately 79.106 ha of these soils are dedicated to agriculture. The main characteristics of Ferralsols are a poor horizonation, a weak development of the macrostructure, and a strong submillimetric granular microstructure

Hydraulic properties of the diagnostic horizon of Latosols of a regional toposequence across the Brazilian Central Plateau.

International audienceThe Brazilian Central Plateau covers about 40% of the Cerrados Biome and represents 24% of the Brazilian territory. The Latosols that correspond to about 40 % of the surface area of the Central Plateau are characterized by a poor horizonation, a weak macrostructure and a strong development of the fine granular structure composed of sub-rounded microaggregates 50 to 300 µm in size. In this study, we analyzed the hydraulic properties of a set of Latosols varying according to their clay content and mineralogy with respect to their location along a regional topossequence across the Brazilian Central Plateau. Ten Latosols (L) were selected on the South American Surface (L1 to L4) and Velhas Surface (L5 to L10) and we studied the properties of their diagnostic horizon (Bw). We measured their bulk density and particle density, and the soil-water retention properties at 1, 6, 10, 33, 300, and 1500 kPa by using the centrifugation method. We also determined the saturated hydraulic conductivity in the field using the Guelph permeameter procedure. Results showed that the total pore volume (Vp) ranged from 0.460 to 0.819 cm3 g-1 and 58.2 % of the variance was explained for by the clay content. According to Balbino et al. (2002), Vp was divided into a volume of intra-microaggregates pores (Vintra) and inter-microaggregates pores (Vinter). Results showed that Vintra ranged from 0.090 to 0.234 cm3 g-1 and Vinter from 0.305 to 0.585 cm3 g-1. Results showed also that Vp explained a proportion of the variance of the water retained that decreased with the water potential. On the other hand, the clay content explained a proportion of that variance that increases when the water potential decreased. The great proportion of variance (90.7 %) explained for by the clay content alone at 1500 kPa showed that there is little variability that can be attributed to clay mineralogy variation. The saturated hydraulic conductivity (Ks) was related to an effective porosity (Φe) defined as the volume proportion of pore with equivalent diameter > 300 µm. Finally, our results showed that water retention properties and saturated hydraulic conductivity varied mainly according to the clay content and development of large pores without any close link with the mineralogy of the clay fraction

Validity of the centrifuge method for determining the water retention properties of tropical soils

International audienceThis study aims at comparing the centrifuge and pressure plate methods when appropriate duration of run is adopted. Samples collected in tropical soils located in Brazil along a 10-km local hydrosequence across the Cerrado-Amazonia transition (set 1) and along a 350-km regional toposequence across the Cerrado region (set 2) were selected to compare and discuss statistically the similarity of the soil-water retention recorded by using the pressure plate and centrifuge methods. The results showed good agreement (R2 = 0.99) for the 1:1 comparison of measured point-wise soil-water content values (set 1) as well as for the fitted soil-water content curves by van Genuchten model using data points obtained with the two methods (set 2). Thus, the centrifuge method should be considered as an appropriate method for determining soil-water retention properties not only for the similar results with the pressure plate method but also for being much less time consuming

Comparação da perda de solo atual em relação ao ambiente natural na Bacia do Rio Jardim - DF

A intensificação do uso do solo provoca um aumento nas taxas de erosão, causando diferentes impactos, tanto no ambiente quanto nos agroecossistemas. A Equação Universal de Perda de Solos (EUPS) é o método mais utilizado para descrever e predizer a ocorrência de erosão laminar. O presente trabalho possui como objetivo comparar a taxa de erosão laminar das condições atuais em relação a um cenário sem atividade antrópica. A área de estudo é a bacia do rio Jardim localizada no Distrito Federal. A metodologia adotada realiza uma comparação entre o cenário natural com ouso da terra atual, com a finalidade de avaliar os ambientes mais impactados dentro da bacia. Os resultados indicaram que houve um aumento de seis vezes da taxa de erosão com o uso e ocupação do solo. _________________________________________________________________________________ ABSTRACTSignificant land-use intensification causes an increase in erosion rates, causing different impacts, both for environment and agroecosystems. Equation Universal Soil Loss (EUPS) is the method most used to describe and predict the occurrence of laminar erosion. This article aims to compare the laminar erosion rate incurrent conditions in relation to a scenario without anthropogenic activity. The study area is the rio Jardim watershed located in the Federal District. The methodology adopted compares the natural landscape with the current land use, in order to evaluate the most impacted environments within the basin. The results indicated that there was a sixfoldin crease in the erosion rate with landuse

Carbono e nitrogênio do solo sob diferentes usos e posições na paisagem no Brasil central

In Central Brazil, plateaus, the most common geomorphologic form, have been undergoing intense conversion from native vegetation to pasture and agriculture in recent decades. We used carbon stable isotope ratios (δ13C) and nitrogen stable isotope ratios (δ15N) to assess possible changes in soil organic matter dynamics under such land use modifications. This study aimed to evaluate the differences in soil δ13C and δ15N and C and N stocks between native vegetation and agricultural or pasture areas in different locations of a plateau in the savannas of Central Brazil. We sampled soil up to 100 cm depth in pasture areas in the summit of the plateau and no-tillage and conventional tillage on the border of a plateau, as well as soils under native vegetation in both landscape locations. Both soil δ13C and δ15N, and C and N stocks showed no differences between land uses. The different relationships between δ15N and C/N ratio at different locations indicated distinct behavior of the soil organic matter between the summit and border of the plateau. Therefore, in addition to land-use, landscape location contributes to both δ13C and δ15N, and C and N stocks in the soil of the plateau.No Brasil Central, os planaltos são a forma geomorfológica mais comum e vêm sofrendo intensa conversão de vegetação nativa em pastagem e agricultura nas últimas décadas. Os isótopos estáveisde carbono (δ13C) e de nitrogênio (δ15N) foram usados neste estudo para acessar possíveis mudanças na dinâmica da matéria orgânica no solo nestas áreas convertidas. Este estudo teve como objetivo avaliar as diferenças no δ13C e no δ15N e nos estoques C e N do solo entre a vegetação nativa e áreas agrícolas ou de pastagem em diferentes posições de um planalto nas savanas do Brasil Central. Foram coletadas amostras de solo até 100 cm de profundidade em áreas de pastagem no topo e plantio direto e convencional na borda do planalto, bem como solos sob vegetação nativa em ambas as posições. O δ13C, o δ15N e os estoques de C e N não mostraram diferenças entre os usos da terra. As diferentes relações entre δ15N e a razão C/N em cada posição indicam um comportamento distinto da matéria orgânica do solo entre o topo e a borda do planalto. Portanto, além do uso da terra, a posição da paisagem contribui para os valores de δ13C e δ15N e os estoques de C e N no solo desse planalto

Modelling Bulk Density According to Structure Development: Toward an Indicator of Microstructure Development in Ferralsols.

Ferralsols have a ferralic horizon at some depth between 30 and 200 cm that results from long and intense weathering. Their clay fraction is usually mainly low-activity clay consisting of kaolinite with hematite, goethite and gibbsite in different proportions. Ferralsols show little or no horizonation, and their macrostructure is absent to moderate. On the other hand, they have typically a strong microstructure consisting of microaggregates < 1 mm in size. Because of the lack or small development of macrostructure, porosity of Ferralsols is closely related to the development of microstructure and the assemblage of elementary particles within the microaggregates with a small contribution of large pores resulting from root development and macrofaunal activity. Their physical properties are then closely related to the development of this microstructure. However, there is still no model in the literature that predicts changes of microstructure of these soils using easily accessible soil properties when land-use is modified. The objective of this work was to relate microstructure development to the bulk density (Db) in Ferralsols and then to make possible the use of Db as an indicator of microstructure development

Relação solo-relevo em vertentes assimétricas no Parque Nacional da Serra dos Órgãos, RJ

O estudo foi realizado no Parque Nacional da Serra dos Órgãos (PARNASO), estado do Rio de Janeiro, no contexto da Serra doMar e com vegetação típica da Mata Atlântica. O objetivo foi relacionar a organização do solo na paisagem, integrando osfatores pedológicos, geomorfológicos e geológicos. Os solos mostram seqüências assimétricas entre a vertente continental,mais suave, em relação à oceânica, com ruptura brusca de relevo. Os solos mostram polaridade evolutiva crescente entre o topoe base das vertentes. A vertente continental apresenta a seguinte toposseqüência com continuidade pedológica evolutiva:afloramentos rochosos, Neossolos Litólicos, Cambissolos, Argissolos e Latossolos. Por outro lado, a vertente oceânica mostrauma toposseqüência truncada, também com polaridade evolutiva do topo para a base: Afloramentos Rochosos, Cambissolos,Argissolos e Latossolos. A assimetria das vertentes é marcada pela escarpa oceânica formada por uma importante zona de falhana direção NE-SW. Nos compartimentos de Planalto os Neossolos Litólicos são associados localmente a Gleissolos, afloramentos rochosos e Plintossolos Pétricos, desenvolvidos sobre granitos equigranulares e isotrópicos. No compartimento de PlanaltoDissecado os Cambissolos são associados localmente a Plintossolos e Neossolos Litólicos e ocorrem sobre relevos multiconvexosrelacionados com saprolitos de rochas gnáissicas ou de estrutura de fluxo ígneo. Os Argissolos são associados localmente aLatossolos e Chernossolos em depósitos formados em porções deprimidas de vales encaixados e formados por facetastrapezoidais. Estes ambientes refletem o contínuo processo de erosão por escorregamentos, movimentos de massa e quedas deblocos das porções mais elevadas e a intemperização destes materiais nas porções mais baixas. _________________________________________________________________________________ ABSTRACTThe research was developed in the National Park of Serra dos Órgãos (PARNASO), part of the Serra do Mar complex inside theAtlantic Rainforest located in Rio de Janeiro. The aim was to connect the soil organization in the landscape, integratingpedologic, geomorphologic and geologic factors. It is noted asymmetric soil sequences between smoother continental comparedto relief rupture oceanic hillsides. Besides that, the soils show a crescent evolutive polarity between the top and bottom hill side.The continental hillside presents the follow toposequence with continuous pedologic evolution: rock outcrops, Litholic Neosols,Cambisols, Argisols, and Latosols. Otherwise, the oceanic hillside presents truncated toposequence with the same evolutivepolarity: rock outcrops, Cambisols, Argisols and Latosols. The hillside asymmetry is pointed by oceanic escarpment made byan important NE-SW fault direction. The Plateau unit is characterized by Litholic Neosols locally associated to Gleysols, rockoutcrops and Petric Plinthosols developed on equigranular and isotropic granites. The Dissected Plateau unit is pointed byCambisols locally associated to Plinthosol and Litholic Neosol on multiconvex relief related to gneiss and igneous flux structu rerock saprolites. The Valleys unit is distinguished by Argisols associated to Latosols and Chernosols in valley depositsdepressions related to trapezoidal facets. These features reflect the process of erosion by landslides, debris flows and rock fallsfor higher portions, and subsequent sediment pedogenesis in lower landscapes

Pedogeomorphological evolution model of Serra da Canastra, MG

A gibbsita e as formas de ferro em solos tropicais são preferencialmente controladas pela posição na paisagem e variação das condições hídricas ao longo das pedossequências. Normalmente, em escala regional, a gibbsita aumenta com a elevação do terreno e a idade da superfície, enquanto que, na escala local, decresce do topo para a base das vertentes. A razão entre o ferro oxalato e o ferro ditionito (Feo/Fed) em condições oxidantes e bem drenadas tendem a ser baixas ( 0,8 são geralmente observadas em Latossolos. O comportamento destes parâmetros na paisagem é decorrente do processo evolutivo das catenas. Este trabalho tem como objetivo descrever uma pedossequência na Serra da Canastra, caracterizada por uma polaridade inversa da gibbsita e razões de Fed/Fe2O3eFeo/Fed próprias de um ambiente redutor. A pedossequência possui Latossolo no topo e Gleissolo na base. Entre a alta e média vertentes ocorrem solos desenvolvidos in situ, com uma sequência apresentando Latossolo a montante e Cambissolo a jusante. Na baixa vertente, ocorrem solos desenvolvidos sobre rampas de colúvio, mostrando a sequência Latossolo- Gleissolo para jusante. Foram coletadas amostras dos horizontes diagnósticos em 10 trincheiras ao longo de uma pedossequência. As amostras foram submetidas às seguintes análises: ferro extraído com ditionito-citrato-bicarbonato (Fed) e oxalato de amônio (Feo), análise termogravimétrica para quantifi cação direta de gibbsita e caulinita e susceptibilidade magnética. O conjunto de dados foi processado por análise multivariada: Análise de Componentes Principais (ACP) e Análise de Grupos (AG). Observou-se que os solos mostram uma evolução lateral de transformação de Latossolos em Gleissolos, de forma progressiva e descontinuada na paisagem. O limite superior da vertente onde ocorrem depósitos coluvionares é marcado pela variação da susceptibilidade magnética, textura e cor do solo. As análises multivariadas (ACP e AG) e os estudos de campo indicam que a pedossequência é derivada de sucessivos solapamentos provocados por erosão subsuperfi cial e deposição de colúvio, com avanço de ambientes hidromórfi cos nestas porções relativamente rebaixadas da paisagem. _________________________________________________________________________________ ABSTRACTThe gibbsite and iron compounds in tropical soils are controlled by landscape position and variation of hydric conditions along the pedosequences. Typically, in the regional scale the gibbsite ratio decrease with increasing elevation and surface age, while in the local scale the ratio decrease from top to base in a pedosequence. The ratio of oxalate iron and dithionite iron (Feo/Fed) under oxidizing conditions and well-drained tend to be low ( 0.8 are observed in Oxisols, generally. The behavior of these parameters in the landscape is the result of the evolutionary process of catenas. This paper aims to describe a pedosequence in Serra da Canastra, characterized by an opposite polarity of gibbsite and iron forms that indicate a reducing environment. This pedosequence has Oxisol in the top and Gleysol on the base. Samples were collected of the soil diagnostic horizon in 10 trenches. The samples were submitted the following procedures: geochemical analyses (major elements), iron extractable with dithionite-citratebicarbonate (Fed) and ammonium oxalate (Feo), thermogravimetric analysis for gibbsite and kaolinite direct quantifi cation and magnetic susceptibility. The data set was processed by multivariate analysis: Principal Component Analysis and Cluster Analysis. Soil transformation through upstream water saturation occurs gradually and discontinued in the landscape. The upper limit of colluvial deposits is marked by magnetic susceptibility, texture and color variation. Principal Components Analysis and Cluster Analysis show physical, chemical and mineralogical trends in the pedosequence. The analyses indicate that the pedosequence is derived of successive sinks and colluviums and the advancement of these hydromorphic environments to the hollows portions of the landscape