Miguel Cooper

Origin of microaggregates in soils with ferralic horizons

Microaggregates that characterize ferralic soils have been hypothesized to have physical, geochemical and/or biological origins. Despite of many studies, the hierarchy between these processes that form microaggregates has seldom been reported. The objective of this work was to study the genesis of microaggregates in a sequence of Ferralic Nitisols developed on Quaternary red clayey sediments and diabase in Piracicaba (SP), Brazil. This issue was tackled by combining optical microscopy, image analysis, scanning electron microscopy and elemental iron quantifications by X-ray fluorescence. Micromorphological investigations showed three different types of microaggregates: (i) oval microaggregates with well sorted quartz grains in their interior; (ii) oval microaggregates without or with poorly sorted quartz grains in their interior; and (iii) dense polyedric microaggregates. These morphological evidences, together with the elemental iron determinations and scanning electron microscopy, revealed the contribution of more than one process for microaggregate formation: (i) the mechanical action of the mesofauna would form the first type of microaggregates (ii) geochemical and biological processes would form the second type and (iii) the fissuration of the soil matrix by expansion and compression processes would form the third type.

Pedogênese em uma seqüência latossolo-podzólico na borda de um platô na depressão periférica paulista

A soil sequence (Oxisol → Ultisol → Alfisol) was studied on the border of a plateau, which is the oldest regional surface near the Piracicaba river valley (southeastern Brazil). Seven pits were identified, sampled and morphologically described under the different segments of the sequence (end of summit, shoulder, backslope and footslope). A bi-dimensional sketch of the soil horizons was drawn. Undeformed soil samples were taken for micromorphological studies, and mineralogical, chemical and granulometric analyses were performed. The very clayey Oxisols of the flat summit are developed on a neo-cenozoic cover and the Ultisols resulted from a lateral pedologic Latosol transformation gradually receiving at the end of the backslope a contribution from fresh siltites (Tatui formation, Permian). The genesis of the top Oxisol microaggregates is complex, but two processes became evident: the geochemical microstructure ant the zoogenetics. The Bw → Bt transition was attributed to the subsurface densification of the microaggregates due to the levelling and convexity of the original surface and to the lateral water flows growing influence downstream. Further mechanisms of argilluviation and clay destruction of the Bt horizon top by temporary hydromorphism will complete the transformation of Bw into Bt and of the latter into E, respectively.

Savanna woodland soil micromorphology related to water retention

The limiting factors of the Brazilian savanna physical environment have been largely discussed. Soil morphology is fundamental to understand the behavior of soil water flow, soil physical properties and soil-landscape relationships. The aim of this study is to relate soil micro and macromorphologic attributes to soil water retention on a toposequence under native savanna woodland (cerradao) in a permanent plot of 320 m ´ 320 m installed in Assis, SP, Brazil. Samples collected at five points within the toposequence were used to determine the soil macroporosity by means of image analyses, estimated total porosity, chemical analysis, particle size distribution analysis and soil water retention. From the summit down to the footslope, the soils were classified as Rhodic Haplustox, Typic Haplustox and Epiaquic Haplustult, presenting a gradual color transition and a sandy loam texture. In the surface horizons, the higher organic matter content and the high total macroporosity determined a lower soil bulk density and lower water retention. In the Oxisols, the high soil macroporosity results from the packing of microaggregates in the oxic horizon. In the Ultisol, the lower total porosity in the deeper horizons resulted in a higher water retention and an imperfect water drainage. The water retention conditions on the slope influenced the morphological differences in soil color and structure. The low water retention on the surface and oxic horizons, conditioned by the high total macroporosity, is one of the factors that may define the vegetal pattern of the savanna woodland within the permanent plot.

Dinâmica físico-hídrica de uma toposseqüência de solos sob Savana Florestada (Cerradão) em Assis, SP

The aim of this study was to characterize the morphological, physical and hydraulic soil properties in a toposequence under native plant cover in a permanent observation plot of 320 x 320 m installed in the Assis Ecological Station, Sao Paulo State, Brazil. The plot is covered by a remnant Savanna Woodland (Cerradao) vegetation of the southern border zone of the great Cerrado domain. The bi-dimensional geometry (horizontal and vertical) of the soil horizons in a toposequence provided details on the soil morphology. The soil water dynamics in the native plants environment was studied through determination of the soil-water retention curves as well as soil particle-size distribution, and saturated soil hydraulic conductivity using the Guelph permeameter. Soil moisture was measured in situ using a WCR sensor. Soil moisture and rainfall distribution were monitored from November 2003 to November 2004. The soils were classified, from the summit down to the footslope, as Rhodic Haplustox, Typic Haplustox and Epiaquic Haplustult. The high clay content in the subsurface horizon of the Epiaquic Haplustult, when compared to the Oxisols with greater sand content, determines less drainage, greater water retention and lower hydraulic conductivity. The soil moisture in this layer never attained the saturation during the study period. Soil water dynamics were influenced by relief conditions, as evidenced by the continuous lateral color transition, soil texture and structure, and by rainfall. At the soil surface, the soil moisture oscillation is closely related to the rain events. In the subsurface, this effect is less intense, and lagged in time. The water availability along the toposequence is limited in the dry season and in part of the wet season. The floristic characteristics of the forest formation and its mosaic distribution in the plot can be explained by the seasonal water availability.

CARACTERIZAÇÃO MORFOLÓGICA, MICROMORFOLÓGICA E FÍSICO-HÍDRICA DE SOLOS COM HORIZONTE B NÍTICO

Com o objetivo de fornecer dados que ajudem na discussao de problemas existentes na classificacao dos Nitossolos no Brasil, foram estudadas detalhadamente a estrutura, consistencia, porosidade, cerosidade, condutividade hidraulica e retencao de agua de solos com horizonte B nitico e solos com ambos, B nitico e B latossolico. O comportamento fisico-hidrico dos horizontes dos perfis estudados mostrou a intima relacao existente entre este e a forma e o grau de estrutura, bem como a abundância e intensidade da cerosidade. Os horizontes caracterizados como B nitico apresentaram blocos subangulares de grau forte ou moderado e cerosidade moderada e abundante e moderada e comum. Este conjunto de atributos determinou um comportamento fisico-hidrico influenciado por um menor desenvolvimento de poros estruturais (macroporos) e por um maior desenvolvimento de poros texturais (microporos), que favorecem os processos de retencao de agua (menor condutividade hidraulica). Por outro lado, foram classificados como B latossolicos os horizontes formados por blocos subangulares de grau moderado ou fraco, com ou sem presenca de estrutura microgranular, e nenhuma cerosidade ou cerosidade fraca e comum. Estes horizontes caracterizam-se por apresentar um maior desenvolvimento dos poros estruturais (macroporos), que favorecem os processos de conducao de agua (maior condutividade hidraulica), e menor desenvolvimento dos poros texturais (microporos), que diminuem a retencao de agua no horizonte.

Pore system changes of damaged Brazilian oxisols and nitosols induced by wet-dry cycles as seen in 2-D micromorphologic image analysis

Soil pore structure characterization using 2-D image analysis constitutes a simple method to obtain essential information related to soil porosity and pore size distribution (PSD). Such information is important to infer on soil quality, which is related to soil structure and transport processes inside the soil. Most of the time soils are submitted to wetting and drying cycles (W-D), which can cause important changes in soils with damaged structures. This report uses 2-D image analysis to evaluate possible modifications induced by W-D cycles on the structure of damaged soil samples. Samples of three tropical soils (Geric Ferralsol, GF; Eutric Nitosol, EN; and Rhodic Ferralsol, RF) were submitted to three treatments: 0WD, the control treatment in which samples were not submitted to any W-D cycle; 3WD and 9WD with samples submitted to 3 and 9 consecutive W-D cycles, respectively. It was observed that W-D cycles produced significant changes in large irregular pores of the GF and RF soils, and in rounded pores of the EN soil. Nevertheless, important changes in smaller pores (35, 75, and 150 μm) were also observed for all soils. As an overall consideration, it can be said that the use of image analysis helped to explain important changes in soil pore systems (shape, number, and size distribution) as consequence of W-D cycles.

Representatividade e potencial de utilização de um banco de dados de solos do Brasil

O Brasil ocupa uma posicao de destaque em estudos de solos tropicais, em razao do enorme volume de informacoes levantadas sobre os solos do pais. Entretanto, a disponibilizacao dessas informacoes tem-se mostrado pouco eficiente. Com o intuito de ampliar as possibilidades de utilizacao de uma base de dados de solos de abrangencia nacional, elaborada a partir de levantamentos pedologicos de grande amplitude, procedeu-se a sua reestruturacao, atualizando a classificacao dos perfis de solo que a constituem, seguida de uma avaliacao quanto a sua representatividade e potencial para analises qualitativas. Para isso, os dados foram organizados em formato de banco de dados e a classificacao pedologica atualizada de acordo com a versao mais recente do Sistema Brasileiro de Classificacao de Solos, ate o quarto nivel categorico. Essa atualizacao foi, em geral, bastante satisfatoria, sobretudo nos tres primeiros niveis hierarquicos, com maiores restricoes no subgrupo, conforme a analise dos graus de confiabilidade adotados para expressar a exatidao no ajuste do enquadramento taxonomico. Desse modo, ao suprir a carencia de uma nomenclatura unificada e ajustada aos criterios atuais que regem a classificacao de solos no Brasil, constituiu-se um banco de dados comparavel qualitativamente com variaveis externas, como distribuicao geografica, altitude e tipos climaticos. As avaliacoes realizadas a partir dessa base evidenciaram uma boa representatividade da distribuicao dos perfis na grande maioria dos estados da federacao, assim como em relacao as condicoes ambientais representadas por zonas e tipos climaticos da classificacao de Koppen. Entretanto, nao foram constatadas correlacoes estreitas entre estas variaveis e as classes de solo em nivel de ordem, embora algumas tendencias gerais tenham sido observadas, como uma significativa proporcao de perfis de Vertissolos e Luvissolos sob clima semi-arido (BS). De forma semelhante, a altitude de onde ocorrem as classes de solos foi tambem muito variavel, mas os valores de quartis e mediana indicaram algumas faixas preferenciais. Assim, Cambissolos e Latossolos tendem a ocupar os niveis mais altos da paisagem brasileira, ao passo que 75 % dos perfis de Espodossolos e de Plintossolos situam-se em cotas inferiores a 200 m. Alem das potencialidades de uso evidenciadas, a estruturacao atual da base de dados permite outras aplicacoes para atender necessidades especificas de estudo, inclusive no que tange a investigacoes relacionadas ao sistema de classificacao de solos que vem sendo desenvolvido no pais.

Environmental impact of the Brazilian agrarian reform process from 1985 to 2001

During the past 20 years, most settlements of the Brazilian Agrarian Reform (AR) have been established in or near better-preserved natural ecosystems, where environmental impact is likely to be negative and contribute to natural resources degradation. The objective of this work is providing a first, comprehensive insight of the impacts related to the environmental quality of these settlements, based on the primary survey of 4,340 AR settlements installed between 1985 and 2001. An index was calculated to integrate different aspects of environmental impacts in one single number. The index showed significant regional variation, with lower values (low environmental quality) for the North and Northeast of Brazil, intermediate values for the Central-west and Southeast, and high values for the South. Environmental impacts resulting from AR and settlement creation are slowly decreasing with time, but are still very high in absolute values. The lack of protection of riparian areas, cultivation of legal reserves, and deforestation, are the main concerns related to environmental impacts.

Soil structure transformations from ferralic to nitic horizons on a toposequence in southeastern Brazil

The soil structure transformation from ferralic to nitic horizons was studied in a toposequence on quaternary red clayey sediments and diabase in Piracicaba (SP), Brazil. Morphological and micromorphological studies, image analysis, soil water characteristic curves and monitoring of (total) soil water potential head were used. The presence of polyconcave vughs, clayskins and planar voids shows that the vertical and lateral transition and structural transformation from ferralic to nitic horizons is given by the coalescence of the microaggregates, probably due to tensions created in a drier period in the past. Changes to a more humid climate with a defined dry season and alternate drying and wetting cycles resulted in the fissuration of the previously coalesced material, forming polyhedral aggregates and microaggregates. Simultaneously, clay illuviation filled the voids and together with the compacting action of the biological activity of these soils contributed to the coalescence of microaggregates.

Controlled traffic and soil physical quality of an Oxisol under sugarcane cultivation

Machinery traffic in sugarcane ( Saccharum sp.) plantations reduces soil physical quality, and hinders both root development and crop yield. We evaluated the physical quality of an Oxisol and the development of sugarcane roots under controlled traffic. The treatments assessed were: without controlled machinery traffic (WCT), controlled traffic by adjusting the tractor and infield wagons to a 3.0 m track width with the operator guiding the machinery (CT1) and the previous treatment using real time kinematic / global positioning system (RTK / GPS) precision auto steer (CT2). Soil samples were collected from the planting rows, seedbed and inter-row center to determine the least limiting water range (LLWR) and soil porosity from scanned 2-D images. The root dry mass was sampled from monoliths, separated from the soil by washing through a 2-mm sieve and dried in an oven. A higher LLWR was observed in the planting row under CT1 and CT2 than under WCT. The planting row had a predominance of complex pores with a diameter > 500 µm in the 0.15-0.27 m depth layer under CT1 and CT2. In the planting rows under WCT, the root dry mass was only 44 % of that measured under CT2. Benefits regarding soil physical quality and growth roots were observed when the tractor-wagon track width was adjusted based on the sugarcane spacing using either precision auto steering or manual operation of the machinery.