ABSTRACT Saprolite plays a central role into hydrologic and nutrient cycles. Despite that, saprolite research is scattered and uses heterogeneous, sometimes conflicting, methods and concepts. During field work, it is difficult to assign the boundary between soil and saprolite. This paper aimed to identify the subjacent logic that pedologists use to assign to a regolith volume its soil or saprolite nature. To achieve this goal, a tree algorithm was used to build a hierarchy of physical and chemical properties of a set of regolith profiles. Such hierarchization expose the inner, subjective criteria used by researchers during the assignment of a certain profile zone as saprolite or soil. The following variables were measured: total porosity (TP); bulk density (Bd); particle density (Pd); total Fe2O3, Al2O3, CaO, MgO, K2O, Na2O, P2O5, and TiO2; selective extraction of iron by ditionite-citrate-bicarbonate (FeDCB) and ammonium oxalate (FeOA); and the FeDCB/FeOA ratio. These measurements were done in a set of 25 regolith profiles (137 horizons and layers), located in the Southeast region and Northeast region of Brazil. The decision tree algorithm was applied using the recursive partition method to identify which of the measured property was most strongly associated with the field assignment of the pedologists to a certain profile zone as saprolite or soil. The Bd, FeDCB/FeOA, MgO, CaO, TP, and P2O5 explained 93 % of the pedologists choice, being Bd responsible for 81 %.

RESUMO A expansão da fronteira agrícola em diferentes ambientes geológicos no oeste do Estado do Pará, norte do Brasil, torna necessário conhecer a influência do material de origem sobre os atributos dos solos locais. Este estudo teve como objetivo avaliar a influência de diferentes materiais de origem sobre cinco perfis de solo ao longo de uma litosequência exposta pela rodovia BR-163, que vai de norte a sul pelo oeste do Pará. Os solos foram classificados, morfologicamente descritos e seus principais horizontes amostrados para análises físicas, mineralógicas e químicas, incluindo a determinação de micronutrientes, formas de fósforo e formas secundárias de ferro. Análises multivariadas foram usadas para agrupar as diferentes associações solo-material de origem. Os resultados demonstraram que a diversidade do material de origem foi determinante para os atributos do solo, sendo um fator condicionante para a formação de diferentes argilominerais. A análise multivariada agrupou os solos ao longo da litosequência em um grupo formado por perfis derivados de rochas ígneas básicas e intermediárias, e um segundo grupo constituído por perfis derivados de sedimentos e rochas sedimentares. O perfil derivado de rocha ígnea ácida apresentou maior similaridade com os perfis derivados de materiais sedimentares em comparação àqueles derivados de outras rochas ígneas.

ABSTRACT The expansion of the agricultural frontier into different geological environments in the west of the state of Pará, northern Brazil, makes it necessary to know the influence of the parent material on local soil attributes. This study aimed to evaluate the influence of different parent materials on five soil profiles along a lithosequence exposed by the BR-163 highway, which runs from north to south through western Pará. The soils were classified, morphologically described and their main horizons sampled for physical, mineralogical and chemical analyses, including the determination of micronutrients, forms of phosphorus and secondary forms of iron. Multivariate analysis was used to group the different soil-parent material associations. The results demonstrated that the diversity of the parent material was a determinant of soil attributes, and was a conditioning factor for the formation of different clay minerals. Multivariate analysis grouped the soils along the lithosequence into a group formed by profiles derived from basic and intermediate igneous rocks, and a second group consisting of profiles derived from sediments and sedimentary rocks. The profile derived from acidic igneous rock showed greater similarity with the profiles derived from sedimentary materials in comparison to those derived from other igneous rocks.

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 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.

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.