Carlos Ernesto Gonçalves Reynaud Schaefer

Pedogenesis and pre-Colombian land use of “Terra Preta Anthrosols” (“Indian black earth”) of Western Amazonia

Abstract The “Terra Preta de Indio” (Indian black earth) or Terra Preta of Western Amazonia is a thick, dark-coloured, anthropic epipedon, usually rich in nutrients. It occurs mostly at the fringes of the Terra Firme, along the Amazon river banks, overlying deep strongly weathered soils. We studied selected chemical, physical and mineralogical properties of seven soils, ranging from the Tertiary Plateau down to the Amazon river floodplain in the Iranduba district, near Manaus, Amazonas, Brazil. Three Terra Preta soils were classified as anthropogenic (Anthropic Xanthic Kandiudult, Anthropic Xanthic Kandiudox and Anthropic Dystropepts). Chemical, mineralogical and micropedological attributes, such as high total and available P and mica flakes in pottery remains found in the Terra Preta, indicate that the origin of soil materials of these anthrosols is closely associated with neighbouring floodplain (varzea) soils and sediments. Amazon floodplain soils were the source of soil material for pottery, since 2:1 clay minerals are not found in the Tertiary Plateau (Terra Firme) sediments. Total and available P contents of Terra Preta are associated with microfragments of bone apatite with high P and Ca values. In the anthrosols under cultivation, these values are less, with increasing Al release suggesting acidification and losses of nutrients. Large amounts of Mn and Zn occur in the anthrosols and in high-fertility floodplain soils. It is unlikely that well-drained Tertiary Plateau (Terra Firme) area far away from lowland Amazon floodplain soils could develop high-fertility Terra Preta on the top of nutrient-poor Oxisols (Latosols). The suggested model of Terra Preta formation between the Tertiary Plateau and nutrient-rich Amazon floodplain does not extend to other nutrient-poor, smaller, floodplains draining the deep-weathered interfluves of the Brazilian Uplands. This raises reservations about estimates of precolonial human population densities for the Amazon basin as a whole, assuming the widespread occurrence of such anthrosols farther inland.

Soils associated with rock outcrops in the Brazilian mountain ranges Mantiqueira and Espinhaço

A Serra do Espinhaco e a Serra da Mantiqueira sao duas cadeias de grande importância para o Brasil. Nas partes mais altas destas serras encontramse ecossistemas com caracteristicas singulares, associados aos afloramentos rochosos, denominados Complexos Rupestres de Altitude. Esses ambientes apresentam caracteristicas do solo e da vegetacao distintas das areas adjacentes. Os solos sao em geral rasos, arenosos, com alta saturacao de aluminio e teores variados de materia orgânica. Neossolos Litolicos, Cambissolos e Organossolos sao as classes de solo dominantes, diretamente associadas aos afloramentos, formando um mosaico de solos. Alguns solos encontrados nestes ambientes sao endemicos, em funcao das caracteristicas peculiares da rocha matriz, da topografia e da vegetacao, e sua preservacao e estrategica por se tratar de solos raros e ameacados de extincao. A materia orgânica desses solos apresenta alto grau de humificacao, com grande quantidade de fracoes soluveis, e a presenca generalizada de fragmentos de carvao. Horizontes espodicos e rios negros estao tipicamente associados as areas de afloramento de arenito e quartzito, sendo formados pela iluviacao de compostos orgânicos, e sendo menos comuns nas areas de granito. O oligotrofismo destes solos, associado a outras limitacoes de ordem quimica e fisica, induzem o desenvolvimento de estrategias de adaptacao fisiologica e morfologica por parte da vegetacao. A maioria destes ecossistemas e instavel sob a condicao climatica atual, e a intervencao antropica e um fator de aceleracao do processo de degradacao. A descricao detalhada dos solos nestes ambientes e fundamental para um melhor entendimento do seu papel nos processos ecologicos e para o desenvolvimento de politicas de conservacao.

CLAY-SIZED MINERALS IN PERMAFROST-AFFECTED SOILS (CRYOSOLS) FROM KING GEORGE ISLAND, ANTARCTICA

Cryosols from Maritime Antarctica have been less studied than soils from continental areas of Antarctica. In this work X-ray diffraction, difference X-ray diffraction, differential thermal analysis, thermogravimetry, transmission electron microscopy/energy dispersive spectroscopy and selective chemical dissolution were used to characterize the clay fraction of basaltic, acid sulfate and ornithogenic Cryosols from ice-free areas of Admiralty Bay, King George Island. Non-crystalline phases are important soil components and reach >75% of the clay fraction for some ornithogenic soils. Randomly interstratified smectite-hydroxy-Al-interlayered smectite is the main clay mineral of basaltic soils. Kaolinite, chlorite and regularly interstratified illite-smectite predominate in acid sulfate soils. Jarosite is also an important component of the clay fraction in these soils. Crystalline Al and Fe phosphates occur in the clay at sites directly affected by penguin activity and the chemical characteristics of these ornithogenic sites are controlled by highly reactive, non-crystalline Al, Si, Fe and P phases. Chemical weathering is an active process in Cryosols in Maritime Antarctica and is enhanced by the presence of sulfides for some parent materials, and faunal activity.

Pedogenesis on the uplands of the Diamantina Plateau, Minas Gerais, Brazil: a chemical and micropedological study

Abstract Little is known about the soil distribution on quartzitic uplands of Brazil. The Diamantina Plateau, where deeply weathered oxisols (latosols) and shallow sandy soils occur side by side, represents part of the higher and oldest planation on the quartzitic uplands of Minas Gerais State. We studied representative soils from the Diamantina Plateau to help understand the pedogenesis and landscape evolution of this part of Minas Gerais. We found evidence of a lithological and tectonic control on the distribution of soils in the landscape. Polygenetic oxisols (Acrustox) occur at the top of the landscape at altitudes of 1300 m or more, resting uncomformably on quartzitic saprocks (Xanthic types) or mafic rocks (Rhodic types). They change downslope to in situ Quartzpsamments and Haplorthods. In the B horizon of the Xanthic Acrustox, quartz grains smaller than 0.3 mm are surrounded by gibbsitic plasma, forming subspherical microaggregates. Microaggregates in the Bw horizon of all upland oxisols display inherited features of intense biological activity regardless of the parent material or texture. The nutrient-poor catena of Xanthic Acrustox–Ustic Quartzpsamments–Oxyaquic Haplorthods represents a sequence of increasing hydromorphic conditions downwards, in which clay minerals are destroyed in low pH and ferrolysis. In the poorly drained soils downslope, low pH and eH induce the movement of reduced Fe 2+ and organic matter (OM)-bound Al and Fe both per descendum and through lateral flow downslope. In the bottom, micromorphological features and the chemistry of organic matter indicated that some Bsh horizons represent buried A horizons subjected to post-burial podzolization, corroborating morphological field data. This indicates the pertinence of the study of humic fractions in defining the Bhs (spodic) horizons of Brazilian spodosols.

POTASSIUM AND MAGNESIUM IN CLAY MINERALS OF SOME BRAZILIAN SOILS AS INDICATED BY A SEQUENTIAL EXTRACTION PROCEDURE

The total contents of potassium (K) and magnesium (Mg) in selected Brazilian soils (Oxisols, Ultisols, Inceptsols, and Alfisols) developed from different parent materials were investigated to estimate the contribution of clay minerals to K and Mg reserves. Total K and Mg contents in the Na-saturated clay were determined by HF total digestion. The contribution of each mineral species to the total contents of K and Mg, was estimated by a sequential mineral extraction procedure, following the order: Na-saturated clay—1) amorphous aluminum and iron oxides (ammonium oxalate); 2) crystalline iron oxides (dithionite–citrate–bicarbonate); 3) amorphous aluminosilicate and gibbsite (0.5 M NaOH); 4) kaolinite (5 M NaOH); 5) mica (NaHSO4), and 6) feldspar (HF total digestion). In order to monitor mineralogical changes, after each extraction, the samples were studied by x-ray diffraction (XRD), analytical transmission electron microscopy (ATEM), differential thermal analysis and thermo-gravimetric analysis. Total amounts of K and Mg in the clay of the strongly weathered soils were very low, indicating a low reserve of these nutrients. Due to the high proportion of kaolinite in the clay fraction of these strongly weathered soils, this mineral accounts for more than 50% of the total K and Mg. The relative proportion of kaolinite and its contribution to the K and Mg reserves increased with weathering. In strongly weathered soils, the contribution of micaceous minerals to the total K and Mg ranged from 17 to 75% and from 8 to 59%, respectively, whereas in the younger soils the range was between 51 and 83%, and 35 and 82%, respectively. Only after the removal of the iron oxides and of the kaolinite was the mica concentration in the clay fraction high enough to be detected by XRD in some of the strongly weathered soils. Dioctahedral illite was the dominant micaceous mineral due to its high resistance to weathering. Microanalysis of individual mica particles by EDAX–ATEM revealed K2O and MgO concentrations between 62 and 121 g kg−1, and between 5 and 10 g kg−1, respectively.

Spatial variability models of CO2 emissions from soils colonized by grass (Deschampsia antarctica) and moss (Sanionia uncinata) in Admiralty Bay, King George Island

Abstract Soil CO2 emission is an important part of the terrestrial carbon cycling and is influenced by several factors, such as type and distribution of vegetation. In this work we evaluated the spatial variability of soil CO2 emission in terrestrial ecosystems of maritime Antarctica, under two contrasting vegetation covers: 1) grass areas of Deschampsia antarctica Desv., and 2) moss carpets of Sanionia uncinata (Hedw.) Loeske. Highest mean emission was obtained for the Deschampsia (4.13 μmol m-2 s-1) developed on organic-rich soil with a strong penguin influence. The overall results indicate that soil temperature is not directly related to the spatial pattern of soil CO2 emission at the sites studied. Emission adjusted models were Gaussian and exponential with ranges varying from 1.3 to 2.8 m, depending on the studied site and vegetation cover.

Dinâmica da mobilização de elementos em solos da Amazônia submetidos à inundação

Significant part of Amazonia soils stays partially or completely waterlogged for varying periods of days to months, as result of widespread inundation or drainage deficiency in some areas, causing changes in chemical, physical and biological properties. In this work, we aimed to evaluate the dynamics of mobilization of Al, Ca, Fe, K, Mg, Mn, Na, Si, P in soils subjected to controlled six months inundation. Soil solution aliquots were collected periodically during the inundation period, determining all elements in solution. The inundation influenced the kinetics of elements, increasing their mobilization, notably in the first weeks. Levels of Fe in solution were higher in soils with greater amounts of amorphous Fe. In soils with low amorphous Fe and low organic matter contents, mobilization of Fe was very low. Levels of P in solution were influenced by all P forms, but Fe-P forms exerted the greatest influence on mobilized P. Levels of Ca, Mg, K and Na in solution were directly influenced by their exchangeable levels, as well by the Mn and Fe kinetics.

Gênese, química e mineralogia de solos derivados de sedimentos pliopleistocênicos e de rochas vulcânicas básicas em Roraima, Norte Amazônico

The influence of parent material, varying from Plio-Pleistocene sediments and basic volcanics, and topographic position, to soil genesis, was studied in a topolitossequence typical of savanna at the Cauame River catchment, Roraima. We aimed to describe the soil variability under savanna by means of chemical, physical and mineralogical attributes. Fourteen soil profiles were described and samples, allowing the identification of the following classes: Yellow Latosol, Red Latosol, Yellow and Red-Yellow Argisols, Plinthosols, Gleisols, Fluvic Neosols and Vertisols. The mineralogy was determined by DRX. The pedogenetical processes and soil characteristics were closely related with topographical-hydrological variation and underlying lithology. Soils derived from pre-weathered sediments of the Boa Vista Formation are generally of low fertility, with high acidity and kaolinite mineralogy and low Fe-oxides contents. Soils developed from Basalt or under the influence of alluvia with mafic contribution all showed high base saturation (eutric) and clay mineralogy with the presence of 2:1 clays, with varying amounts of kaolinite. The occurrence of Vertisols, degraded carbonatic nodules and eutric soils under savanna indicate Quaternary drier paleoclimates in this part of north Amazonia, during which carbonates were formed in the lower horizons of Vertisols, in closed depressions.

Soil-vegetation relationships on a banded ironstone 'island', Carajás Plateau, Brazilian Eastern Amazonia.

Vegetation and soil properties of an iron-rich canga (laterite) island on the largest outcrop of banded-iron formation in Serra de Carajás (eastern Amazonia, Brazil) were studied along a topographic gradient (738-762 m asl), and analyzed to test the hypothesis that soil chemical and physical attributes play a key role in the structure and floristic composition of these plant communities. Soil and vegetation were sampled in eight replicate plots within each of the four vegetation types. Surface (0-10 cm) soil samples from each plot were analyzed for basic cations, N, P and plant species density for all species was recorded. CCA ordination analysis showed a strong separation between forest and non-forest sites on the first axis, and between herbaceous and shrubby campo rupestre on the second axis. The four vegetation types shared few plant species, which was attributed to their distinctive soil environments and filtering of their constituent species by chemical, physical and hydrological constraints. Thus, we can infer that Edaphic (pedological) factors are crucial in explaining the types and distributions of campo rupestre vegetation associated with ferruginous ironstone uplands (Canga) in Carajás, eastern Amazonia, therefore the soil properties are the main drivers of vegetation composition and structure on these ironstone islands.

Pedogenesis and relict properties of soils with columnar structure from Roraima, north Amazonia

Abstract A toposequence of soils with columnar structure in the Paricarana catchment (Roraima State, north Amazonia) was studied. The soils occur within the driest part of tropical Amazonia. The two soils in the lower positions are magnesic, as well as sodic, displaying columnar structural peds. The upper slope position is calcium-saturated, associated with dry forest, whilst the the Mg/Na affected soils are associated with xerophytic savanna. The whole toposequence is being progressively acidified and leached (the solodization process), from the upper slope position to a maximum at the bottom of the toposequence. In spite of the high amounts of total Na,O in all three soils due to the presence of Na-plagioclase, the exchangeable level is concentrated in the lower slope positions, thus creating abrupt changes between the columnar Bt and the overlying A and E horizons. Morphologically, the resulting structural patterns of columnar peds are thought to reflect the effects of exchangeable magnesium plus sodium, more than sodium itself. The little variability in total amounts combined with large variability in the exchange levels suggest that differential redistribution of Na and Mg by overland-flow, throughflow and groundwater fluctuations is responsible for such Na/Mg accumulation in the bottom of the landscape. The present climatic regime, although seasonal, ought not to favour the presence of sodium/magnesium affected soils in this part of Amazonia. They possibly represent relict soils from former semiarid climates in north Amazonia, showing features of the degradation process currently underway.