This paper presents a review on Latosols (oxisols) genesis, classification and use in tropical Brazil.Chemical, physical and mineralogical aspects are throughly discussed, as well as their relationship withsoil use and management. Some problems of definition are considered for all types of Latosols recognizedin the Brazilian System of Soil Classification. The role of clay minerals such as kaolinite, gibbsite and ironoxides (namely hematite, goethite, magnetite and maghemite) is discussed against the background of soilclassification and soil fertility aspects. The ammount of trace-elements and the relationship between theseelements (Mn, Cu, Zn, Co) and latosols genesis and classification is shown, illustrating the trend of highervalues for those soils developed from mafic rocks and alike. The geographic distribution of latosols classesin Brazil (namely Ferriferous, Dusky-Red, Dark-Red, Red-Yellow, Yellow, Brown, Humic, Una variationand Pallid) is given. Finnaly, a general view on phosphorous adsorption for the various types of latosols ispresented, illustrating the importance of the clay mineralogy as a primary factor of controlling P availabilityin these soils.
This review focuses on the clay mineralogy of the most important Brazilian soils: the Latosols, which cover >60% of the country by area, and occur in association with other soils. They are typically deep, highly-weathered soils, dominated by low-activity 1:1 clay minerals and Fe and Al oxyhydroxides, with varying proportions of these minerals, depending on parent material and weathering intensity. They are usually of low fertility, although eutric types also occur. Latosols are generally correlated with Oxisols (American soil taxonomy) and Ferralsols (WRB system). Clay mineralogy is typically monotonous: kaolinite, gibbsite, hematite, goethite, maghemite and Ti minerals (mainly ilmenite and anatase) are the prominent mineral phases in the clay fraction. Some Latosols developing on basalt from southern Brazil contain significant amounts of hydroxyl-interlayed vermiculite. Among the pedogenic oxides the most frequent are goethite (α-FeOOH), indicated by yellowish colours (2.5Y–10YR; in the absence of hematite), and hematite (α-Fe2O3), which imbues reddish colors (2.5YR–5R), even when present in very minor amounts. Maghemite (γ-Fe2O3) is less frequent; it imparts a reddish-brown colour (5YR–2.5YR) and magnetic properties. Both goethite and hematite show Al-substitution, with a greater relative proportion in soil goethites. Hence, in similar drainage conditions, goethite is less prone to dissolution than hematite. Most reddish Latosols also contain maghemite, due to partial or complete oxidation of magnetite, which generally occurs naturally or is fire-induced. Magnetite and/or maghemite are associated with trace elements which are important in plant nutrition, such as Cu, Zn and Co. The contents of gibbsite in Latosols are extremely variable, from a complete absence in brown Latosols, to 54% in red Latosols from mafic rocks. Relatively large amounts of gibbsite are found in the clay fraction of these soils and this mineral is important in P sorption in deeply weathered Latosols in association with goethite and hematite. Even though most Latosols are dystrophic, some are eutrophic, revealing an unusually large base saturation in areas under ustic regimes where the parent material is particularly rich in bases, such as basalts. This eutrophic nature is attributed to the protecting role of micro-aggregates in ferric red Latosols, which retard baseleaching from the inner aggregate. At the other extreme, some Brazilian Latosols are acric and positively-charged in sub-surface horizons, as revealed by the relationship pH KCl > pH H2O. These acric Latosols are the result of long-term weathering and intensive leaching, during which pH tends to increase to values close to the zero point charge of Fe and Al oxides (between 6 and 7), greatly increasing P adsorption, which is mainly attributed to gibbsite, goethite and hematite. Soil kaolinites in Brazilian Latosols are mostly of low crystallinity, with Hughes and Brown indexes of between 6 and 15. In this review we have discussed the role of these clay-fraction minerals in soil genesis and fertility, highlighting the marked role of inheritance from deeply-weathered parent material. Latosols typically retain large amounts of Fe oxides, some of which are magnetic, with spontaneous magnetization >1 J T–1 kg–1. In this regard, reddish Latosols developed from mafic rocks are the most representative magnetic soils, and cover as much as 3.9% of Brazil. An overview of magnetic soils on four representative examples of mafic lithologies is presented, together with some aspects of their Fe-oxide mineralogy and related field and laboratory technqiues.
Resumo -Com base em levantamento pedológico de reconhecimento de alta intensidade, foram investigadas relações pedogeomorfológicas em uma área do Planalto Central Brasileiro, com vistas à predição de atributos e distribuição dos solos em áreas vizinhas carentes de mapas pedológicos. Três superfícies geomórficas, com distintos padrões de espacialização de solos, foram identificadas. Na mais elevada, a distribuição dos solos é estreitamente relacionada à variação do regime hídrico ao longo das encostas. Ocorrem Latossolo Vermelho (LV), Latossolo Vermelho-Amarelo (LVA), Latossolo Amarelo (LA), Latossolo Amarelo plíntico, Latossolo Amarelo petroplíntico (concrecionário) e Plintossolo Háplico, todos muito argilosos, com teores de Fe 2 O 3 e TiO 2 relativamente homogêneos e índices Ki e Kr indicativos de mineralogia oxídica. Na segunda superfície, os solos apresentam maior variação quanto à textura e teores de Fe e Ti. Predominam LV e LV acriférrico, além de LVA e LA. Nos limites com as chapadas, observa-se a ocorrência de LVA e LA acriférricos endopetroplínticos. Na terceira superfície, que disseca as anteriores, predominam solos menos intemperizados, com atributos muito variáveis, como Cambissolo Háplico, Argissolos Vermelho e Vermelho-Amarelo, Nitossolo Vermelho eutroférrico, Neossolo Litólico e Neossolo Flúvico. O trabalho inclui a proposição de um modelo de evolução para a paisagem regional.Termos para indexação: cerrados, pedogênese, aspectos morfológicos do solo, geomorfologia. Soil-geomorphic surface relationships and landscape evolution in an area of the Brazilian Central PlateauAbstract -The soil-geomorphic surface relationships were investigated in an area of the Central Brazilian Plateau, based upon a high intensity reconnaissance pedological survey, aiming at the prevision of the soil attributes and their distribution in adjacent areas which don't have pedological maps. Three geomorphic surfaces, with distinctive soil distribution patterns, were identified. In the highest geomorphic surface, the soil distribution is highly related to the hydric regime variation along the hillsides, occurring Red Latosol (RL), Red-Yellow Latosol (RYL), Yellow Latosol (YL), Plinthic Yellow Latosol, Petroplinthic Yellow Latosol (PYL) (concretionary soil) and Haplic Plinthosol. These soils show very clayey texture, values of Fe 2 O 3 and TiO 2 relatively homogeneous, and Ki and Kr indexes indicatives of oxidic mineralogy. In the second surface, the soils show higher variation with respect to texture and iron and titanium contents. RL, Acricferric RL, RYL and YL are the dominant soils, with occurrence of Acriferric Endopetroplinthic RYL and YL near the borders of the high tablelands. In the third surface, that cuts the first and second ones, predominate less weathered soils, with high variable attributes, such as Haplic Cambisol, Red and Red-Yellow Argisols, Eutroferric Red Nitosol, Litholic Neosol and Fluvic Neosol. This work includes a proposition of a regional landscape evolution model. IntroduçãoAs informações a respeito ...
RESUMOCom o intuito de avaliar diferenças de comportamento entre solos das superfícies geomórficas Sul-Americana e Velhas da região dos Cerrados, todos sob uso atual de cobertura vegetal nativa, foram realizadas caracterizações físicas, químicas e mineralógicas, bem como feitas análises de componentes principais desses atributos. Com os solos referenciados por sub-região e pela superfície geomórfica que representam, três agrupamentos foram constituídos: Grupo 1: solos de textura argilosa a muito argilosa e hipo a mesoférricos; Grupo 2: solos de textura média a arenosa e hipoférricos; e Grupo 3: solos de textura argilosa a muito argilosa e férricos. A retenção de água dos horizontes superficiais dos solos estudados foi positivamente correlacionada com os teores de argila e carbono orgânico. Os solos do Grupo 3 apresentaram a maior oferta de bases trocáveis dos horizontes superficiais, o que foi relacionado, em grande parte, com a maior reciclagem imposta pela formação florestal local, quando comparada à da formação de cerrado, presente em 31 dos 33 perfis de solos dos Grupos 1 e 2. O Grupo 3, diferenciado pelos elevados teores de Fe herdados do material de origem, é o grupo mais homogêneo em termos mineralógicos, com todos os perfis hematíticos. Os Grupos 1 e 2 apresentam sobreposição de composição mineralógica, sendo o Grupo 1, em termos médios, mais gibbsítico do que o Grupo 2. A maior eficácia do Sistema Brasileiro de Classificação de
(4) RESUMO A gênese de horizontes coesos em solos tem explicações não consistentes e, em muitos casos, contraditórias. Objetivou-se avaliar, em solos dos tabuleiros costeiros, os possíveis mecanismos físicos, químicos e mineralógicos que ocasionam o endurecimento em horizonte coeso, fragipã e duripã. Para isso, coletaram-se amostras de solos em duas toposseqüências. Na primeira, foram reconhecidas as classes Latossolo Vermelho eutrófico argissólico e Argissolo Amarelo distrófico latossólico e, na segunda, Argissolos Amarelo abrúptico e típico, e Espodossolo Cárbico órtico dúrico. As análises químicas consistiram da extração de Fe, Si e Al com ditionito-citrato-bicarbonato de sódio e oxalato ácido de amônio. A mineralogia da fração argila foi avaliada por difratometria de raios-X. Os teores de Fe, Si e Al recuperados com o ditionito e com o oxalato foram bastante baixos nos solos com presença de horizonte coeso. Por outro lado, no solo com fragipã e duripã, os teores de Si e Al do oxalato foram elevados, indicando a participação desses elementos como agentes cimentantes. A fração argila dos Argissolos é predominantemente caulinítica, sendo registrada a gibbsita apenas nos horizontes Bt 1 , Bt 2 e Bw do Argissolo Amarelo latossólico. Para o solo com fragipã e duripã (Espodossolo Cárbico órtico dúrico), identificou-se a presença de gibbsita, e, apesar de ser a gibbsita considerada como desorganizadora do ajuste entre as lâminas de caulinita, a manifestação de endurecimento foi mantida. Assim, os mecanismos de endurecimento parecem distintos para horizonte coeso, fragipã e duripã.Termos de indexação: camadas endurecidas, agente cimentante, sílica, aluminosilicato.(1) Parte da Tese de Doutorado do primeiro autor, apresentada à Universidade Federal de Viçosa -UFV. Realizada com apoio financeiro da FAPEMIG e VERACEL Celulose. Recebido para publicação em maio de 2004 e aprovado em novembro de 2006.
SUMMARYMorphologically differentiated Spodosols usually occur in the Coastal Plain of the South of Bahia and North of Espírito Santo. They are found in profiles known as "muçungas", i.e. sandy soils that accumulate water. In these areas, two kinds of Spodosols, different from those in the Restinga area, can be found: Spodosols with E albic horizon (white muçunungas) and without this horizon (black muçunungas). Eight soil profiles with spodic characteristics were collected and described in order to evaluate differences in the formation process of Barreiras and Restinga Spodosols in the South of Bahia. The soil profiles were also characterized chemically, physically and mineralogically. Additionally, texture and chemical analysis, Fe and Al extraction by sodium dithionite-citrate-bicarbonate (DBC), acid ammonium oxalate and sodium pyrophosphate, ammonium oxalate extract optic density (DOox), sulphuric acid attack, and X ray difractometry of the clay fraction were performed. In the Spodosols of the Barreiras area, fragipan was found the spodic layers. Cemented B spodic horizon were observed in the white muçunungas, and granular structure and dark color from the surface in the black muçunungas. There was no fragipan or hard spodic horizon in the Restinga Spodosol. This soil is acid, dystrophic and alic, with sandy texture and high clay percentages in the spodic horizons. The CEC, based on H + Al, is predominantly represented by the organic matter. The most representative components of the mineral phase of the clay fraction are kaolinite and possibly vermiculite traces with interlayered hydroxy.
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