Resumen La falta de cobertura es uno de los principales aceleradores de la degradación del suelo. Sin protección y expuesto a la lluvia, el suelo rompe las partículas, provocando el sellado de la superficie, dificultando la infiltración. Este estudio caracteriza el sellado superficial y la erosión hidráulica en Ultisoles de la Cuenca del Alto Ipanema. Se establecieron ocho parcelas de erosión bajo los tratamientos: suelo desnudo y suelo con mantillo de Brachiaria decumbens. Se simularon tres eventos de lluvia a intervalos de 24 horas, con una intensidad de 54,63 mmh-1. Después de cada simulación, se investigó la micromorfología de la superficie y la cantidad de suelo perdido. El uso de mantillo redujo la escorrentía en un 42% y la pérdida de suelo y la tasa de desagregación se redujo en un 70% en promedio. La infiltración se incrementó en un 242%. El mantillo fue eficaz para preservar la porosidad y la microestructura del suelo para el primer evento de lluvia simulado (0 h), pero no se observó en el segundo (24 h) y tercero (48 h) eventos de lluvia.

Abstract 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.

RESUMO Pequenas variações de relevo influenciam na drenagem e no escoamento superficial, contribuindo para a formação de horizontes superficiais arenosos e subsuperficiais endurecidos (fragipãs e, ou, duripãs) em solos dos Tabuleiros Costeiros. Este trabalho investigou a pedogênese em área de Tabuleiros Costeiros com baixa amplitude altimétrica no Estado da Paraíba; secundariamente, buscamos contribuir para o aprimoramento do Sistema Brasileiro de Classificação de Solos (SiBCS). Quatro perfis de solos foram descritos e coletados para a realização das análises físicas e químicas de rotina, extrações de Fe, Si e Al por digestão sulfúrica, por ditionito-citrato-bicarbonato de sódio, por oxalato ácido de amônio e por pirofosfato de sódio, e as análises mineralógicas das frações areia e argila por difratometria de raios X. A densidade ótica do extrato de oxalato (ODOE) também foi determinada; os resultados obtidos foram estatisticamente avaliados utilizando o programa R. As variações do microrrelevo condicionando fluxos diferenciados de água, juntamente com a textura arenosa dos horizontes superficiais (A e E) e a menor relação areia grossa/areia fina no horizonte subsuperficial, parece favorecer o acúmulo de argila em profundidade nos Espodossolos desenvolvidos no ambiente dos Tabuleiros Costeiros. Para esses solos, o caráter argissólico em nível de subgrupo do SiBCS deveria ser incorporado. Além disso, fases mineralógicas amorfas e, ou, de baixa cristalinidade de Al têm importante participação na formação de horizontes fortemente cimentados (duripãs) dos Espodossolos. Finalmente, a ODOE mostrou-se eficiente como indicador de solos sob processo de podzolização e poderia ser utilizada como critério taxonômico para classificação de Espodossolos pelo SiBCS.

ABSTRACT Small variations of relief may change drainage and runoff and hence promote the formation of sandy surface horizons and hardened subsurface horizons (fragipans and/or duripans) in Coastal Tablelands soils. This study aimed to investigate the pedogenesis on Coastal Tablelands area with low range altimetry in Paraíba state; secondly, we also sought to contribute to the improvement of the Brazilian Soil Classification System (BSCS). Four soil profiles ware described and collected to be submitted to routine physical and chemical analysis, determination of Fe, Al and Si extracted by sulfuric acid digestion, sodium citrate-bicarbonate-dithionite and acid ammonium oxalate, sodium pyrophosphate, and mineralogical analysis in the sand and clay fractions by X-ray diffractometry. Optical density of the oxalate extract (ODOE) was also determined; the results were statistically evaluated using the R software. Microrelief variations conditioning differentiated water flows, along with the sandy texture of the surface horizons (A and E) and the lower coarse sand/fine sand ratio in the subsurface horizon, seem to promote clay accumulation in depth in the Spodosols developed on Coastal Tablelands environments. For this soils, the argilluvic (argissólico) character at the subgroup level of the BSCS should be incorporated. In addition, Al amorphous mineral phases and/or poorly crystalline play an important role in the formation of strongly cemented horizons (duripans) of the Spodosols, as also reported by other authors. Finally, the ODOE showed to be an efficient indicator of soils under podzolization process, being possible its use as a taxonomic criterion for classification of Spodosols by the BSCS.

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 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.

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: 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.

RESUMO Os Nitossolos dão suporte ao desenvolvimento agrícola e socioeconômico de muitos países subdesenvolvidos do mundo, incluindo o Brasil. Os Nitossolos brasileiros estão geralmente associados às rochas basálticas das regiões Sul e Sudeste. Entretanto, Nitossolos derivado de basalto também ocorrem na costa sul de Pernambuco, uma região em pleno desenvolvimento urbano, agrícola e industrial. Objetivando compreender as relações entre o clima e os atributos dos Nitossolos da costa sul de Pernambuco, foram realizadas descrições morfológicas, análises físicas e químicas, extrações seletivas de ferro e a determinação da mineralogia das frações areia, silte e argila de três perfis derivados de basalto ao longo de uma vertente. Os resultados demonstram que o clima da região implica em forte intemperização dos perfis, em grande perda de bases e favorece o processo de xantização, resultando na singular gênese de Nitossolos com matizes amarelados e caráter ácrico, fato que até o momento ainda não foi catalogado para esta ordem no sistema taxonômico brasileiro. Os resultados também demonstram a variação dos atributos físicos dos Nitossolos ao longo da vertente.

ABSTRACT 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 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.

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.

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.

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.

ABSTRACT Regosols in the Agreste Meridional region of Pernambuco, Brazil, are used for various agricultural activities, and prominent among them is production of common bean. An expressive variation is perceived in common bean crop yield, possibly associated with the presence of lamellae, which make for distinct water fluxes among these soils. The objective was to analyze the macro- and micromorphological, and physical characteristics of the Regosols located in the Agreste Meridional region of Pernambuco to understand the water fluxes in these soils. Two soil profiles, located in the municipalities of Paranatama (P1 - absence of lamellae) and São João (P2 - presence of lamellae) were collected and analyzed. In the morphological properties (color, texture, structure, and consistency) no significant differences between the two soil profiles were observed; the physical properties (clay content, macro- and microporosity, field capacity, and wilting point) exhibited significant differences among the horizons of the profiles studied; micromorphology indicates that greater water retention in P2 is a consequence of the presence of areas with denser packing of their components (agglomerative packing), and expressiveness of clay bridges; and we suggest adoption of the term “lamellic” within the current Brazilian System of Soil Classification (in the 4th categorical level) for differentiation of the soil profiles studied.

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.

In the geomorphological unit of the Coastal Tablelands of Brazil there is a predominance of cohesive soil horizons and some with the presence of cemented horizons, commonly of the fragipan type. These horizons interfere with water dynamics, root growth, and, consequently, mineral nutrition of plants. The objective of this study was to use selective dissolution to evaluate the participation of forms of Fe, Si, or Al, or their combination, in the cohesion or cementation or both of fragipans and cohesive horizons in Ultisols and Spodosols in the Coastal Tablelands region of southern Bahia and northern Espírito Santo. We made selective extractions of Fe, Al, and Si by sodium citrate-bicarbonate-dithionite (CBD) and acid ammonium oxalate. The higher levels of Fe and Si, and especially Al, extracted by ammonium oxalate in the fragipans suggest that, in the genesis of these horizons, low crystalline forms of these elements act as chemical cementing agents. The selective dissolutions did not show the participation of high or low crystalline forms of Fe, Si, or Al, or their combination, in the genesis of the cohesive horizons in the soils of the Coastal Tablelands. The Yellow Ultisols have goethites with high isomorphic substitution of Fe for Al, matching the strong weathering, non-reductive, and acid pH environment where these soil are found in the Coastal Tablelands. The isomorphic substitution of Fe for Al in the crystalline iron oxides was related to the degree of crystallinity and Fe concentration obtained in the first extraction with the CBD.

Os Latossolos apresentam, de modo geral, baixos teores de P disponível; no entanto, a influência do material de origem parece ser decisiva na definição do estoque e da forma de P predominante nesses solos. O objetivo deste trabalho foi avaliar a disponibilidade de P, pelos extratores Mehlich-1 (M-1) e Resina de Troca Iônica (RTI), em amostras de horizontes B de Latossolos Férricos e Perférricos desenvolvidos a partir de diferentes materiais de origem. Para tanto, além da caracterização física e química dos solos, foram realizadas 10 extrações sequenciais com os extratores M-1 e RTI em amostras de horizonte B coletadas entre 0,8 e 1,0 m de profundidade. Os teores totais de Ca, P, Fe, Al e Ti foram determinados após digestão com os ácidos nítrico, fluorídrico e perclórico. Os efeitos das extrações sequenciais de P sobre os óxidos de Fe também foram avaliados a partir das análises com ditionito-citrato-bicarbonato e oxalato ácido de amônio. A maior semelhança observada entre os teores de P acumulado após as extrações sequenciais com M-1 e RTI nos solos desenvolvidos de tufito é indicativo da predominância de P-Ca. Os maiores teores de P extraídos pela RTI após uma única extração relevam sua maior eficiência na remoção de P em solos bastante intemperizados como os Latossolos estudados e, ainda, ressalta a elevada sensibilidade do extrator M-1 em solos altamente tamponados. Além disso, uma única extração com o extrator M-1 ou RTI não é suficiente para estimar o fator quantidade de P lábil nesses solos.

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.

O Planalto de Garanhuns, no Agreste de Pernambuco, destaca-se por apresentar características climáticas privilegiadas, favorecidas pelas chuvas orográficas, distinguindo-se da região semiárida circundante. Essas áreas mais úmidas são conhecidas como "brejos de altitude" e intensamente utilizadas e importantes para a economia regional. Este trabalho foi desenvolvido no município de Brejão, Agreste de Pernambuco, com o objetivo de identificar alterações nos atributos de Latossolos Amarelos Húmicos, submetidos às diferentes formas de uso do solo. Foram selecionados quatro tipos de utilização do solo (cultivo, capoeira, pastagem e vegetação nativa), sendo amostrados um perfil e quatro minitrincheiras em cada área. Foram avaliados atributos químicos e físicos, incluindo estabilidade dos agregados, composição da matéria orgânica humificada, além da avaliação microbiológica do solo, por meio da respiração basal, do carbono da biomassa microbiana e do quociente metabólico. Os solos estudados apresentaram características químicas e físicas típicas da classe dos Latossolos Amarelos, como baixa reserva de nutrientes, baixa capacidade de troca de cátions, acidez elevada e alta saturação por Al. Os teores de matéria orgânica do solo foram altos, independentemente do tipo de utilização. O teor de carbono orgânico total (COT) foi maior no solo sob capoeira, 43,91 g kg-1, superficialmente, enquanto 34,36 e 33,43 g kg-1 foram constatados nos solos sob floresta e pastagem, respectivamente. O teor de carbono microbiano (CBM) foi superior a 700 mg kg-1 nas áreas sob floresta e pastagem, na camada de 0-5 cm, e 588 mg kg-1 no solo sob capoeira; no entanto, não diferiram estatisticamente. Na área cultivada houve redução em torno de 28 % no teor de COT e CBM. Os agregados > 2 mm predominaram em todas as áreas. A atividade agrícola contribuiu para a degradação do horizonte húmico, evidenciada pela significativa perda de COT e alteração da distribuição relativa das frações humificadas. Já a estabilidade dos agregados não sofreu alterações em razão dos diversos tipos de uso do solo. Os solos sob pastagem e a capoeira foram semelhantes ao solo sob vegetação nativa. A humina representou a fração humificada mais importante para a reserva de C, contribuindo com mais de 40 % do COT nesses solos.

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.

Studies on soil characterization in unexplored regions, besides the generation of data banks for the soil classes of the country, also produce scientific information about soil properties, important for the development of good management practices and sustainable land use. One of the main soil classes in the semiarid region of Pernambuco State, the Regosols, cover about 27 % of the state area, and are used mainly for family agriculture. Due to different geological and climatic aspects Regosols with different chemical, physical and mineralogical properties are found in Pernambuco, which were characterized for the semiarid region of the State. Five Regosol profiles were selected in different regions of the State (P1=São Caetano; P2=Lagoa do Ouro; P3=Caetés; P4= São João; P5=Parnamirim). The soils were morphologically characterized and samples collected from all horizons and the bedrock. Routine physical and chemical analyses were carried out for soil classification of all samples and mineralogical analyses of the coarse fractions (gravel and sand) by optical microscopy and of the silt and clay fractions by X ray diffraction (XRD), as well as petrographic analyses of the rock samples. The results showed similarities between the soils, with a low degree of pedogenetic development, varying from medium to very deep, with the horizon sequence A-AC-C-Cr and a sandy to sandy loam texture. In the deeper layers of two profiles (P1 and P5), a solodic character was observed. Organic matter and available phosphorus content were low in all studied soils. Despite the low levels of exchangeable cations, all soil profiles showed high base saturation. The mineralogical composition of gravel, sand and silt fractions consisted, essentially, of quartz, followed by feldspars and mica, supporting the results of the petrographic analysis of the bedrock. Kaolinite was the main clay mineral in all studied profiles and horizons, indicating an important monosialitization process in autochthonous soils of a typical semiarid region. In soil profile P2, at a lower landscape position, smectite minerals were observed, with mixing phases of montmorillonite, beidelite or nontronite, indentified by the Greene-Kelly test in the DRX analysis.