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Mineralogy, Micromorphology, and Genesis of Soils with Varying Drainage Along a Hillslope on Granitic Rocks of the Atlantic Forest Biome, Brazil

ABSTRACT

Although the physical environment of the Atlantic Forest realm is well known, studies on the soil-landform relationships are fundamental to improve the management of soil resources to facilitate sustainable development. The purpose of this study was to evaluate a representative topossequence on the “Mares de Morros” landscape of deeply weathered regolith on leucocratic granite rocks and demi-orange convex slopes. The soils varied along the topossequence according to drainage and were classified as Acrudox, Pseudogleysol, and Epiaquent. The clay fraction was composed by kaolinite, in association with gibbsite, goethite, hematite, and traces of vermiculite and hydroxy-Al interlayered vermiculite (HIV). The kaolinite crystallinity index obtained by different methods showed high structural disorder throughout the sequence, indicating that long-term pre-weathering has produced a homogenous regolith with little differences in terms of mineralogy, despite the changes in drainage. On the other hand, micromorphological features showed a complete change from the typical, well-developed microaggregate structure of upland, well-drained soils, to a massive, poorly developed structure downslope, consistent with the morphological description. Changes in microstructure development and micropedological features occurred both vertically and laterally along the topossequence and indicate that mineralogy alone cannot account for the microaggregate structure of kaolinitic Latossolos (Oxisols) well-drained with low Fe contents. Soils from the “Mares de Morros” landscape of the Alegre river basin on leucocratic granitic rocks highlight an inheritance of a deep pre-weathered regolith, showing subtle chemical and mineralogical changes, but marked morphological and physical differences along the topossequence, basically controlled by soil drainage in the past or present.

kaolinite crystallinity; pseudogleysol; “Mares de Morros” landscape; thermal analysis

INTRODUCTION

Atlantic Forest domain stretches from the northeastern to the southern regions of Brazil and to northern Argentina and southeastern Paraguay. The state of Espírito Santo, Brazil, is entirely comprised within this domain, with a typical physiography that changes from mountainous or hilly areas to coastal tablelands. In the southern part of the state, the Alegre river basin is representative of the dissected plateau and the demi-orange landscape known as “Mares de Morros”. It is characterized by hilly landforms forming a dissected plateau, originally covered by tropical rain forest on crystalline rocks, mainly gneiss and granite (Ab’Sáber, 1970Ab’Sáber AN. Províncias geológicas e domínios morfoclimaticos no Brasil. São Paulo: Geomorfologia; 1970., 2012Ab’Sáber A. Os domínios de natureza no Brasil: potencialidades paisagísticas. 7. ed. São Paulo: Ateliê Editorial; 2012.).

Morphogenesis of the “Mares de Morros” landscape involves a set of physiographic and ecological processes that resulted in the demi-orange, dome-like dissection on crystalline rocks with dominant convex slopes (Ab’Sáber, 1970Ab’Sáber AN. Províncias geológicas e domínios morfoclimaticos no Brasil. São Paulo: Geomorfologia; 1970., 2012Ab’Sáber A. Os domínios de natureza no Brasil: potencialidades paisagísticas. 7. ed. São Paulo: Ateliê Editorial; 2012.). This morphoclimatic area is characterized by humid to sub-humid tropical environments, associated with deep weathering and rainforest (IBGE, 2012Instituto Brasileiro de Geografia e Estatística - IBGE. Manual técnico da vegetação brasileira. 2. ed. rev. ampl. Rio de Janeiro: IBGE; 2012.). Such physiognomy and edaphoclimatic characteristics form a rather homogeneous landscape that favors the widespread formation of dome-like, convex slopes as well as deep soil mantles (Embrapa, 1978Empresa Brasileira de Pesquisa Agropecuária - Embrapa. Levantamento de reconhecimentos de solos do estado do Espírito Santo. Rio de Janeiro: Serviço Nacional de Levantamento e Conservação de Solos; 1978. (Boletim técnico, 45).).

The original semi-deciduous forest cover of the Alegre river basin is preserved in the form of small and scattered forest fragments due to intense deforestation in the late 19th century (Novaes, 1968Novaes MS. História do Espírito Santo. Vitória: Fundo Editorial do Espírito Santo; 1968.; Lani et al., 2008Lani JL, Resende M, Rezende SB, Feitoza LR. Atlas de ecossistemas do Espírito Santo. Vitória, ES: Governo do Estado do Espírito Santo, Secretaria Estadual de Meio Ambiente e Recursos Hídricos, Universidade Federal de Viçosa, Núcleo de Estudo de Planejamento e Uso da Terra; 2008.) for the establishment of coffee plantations and subsistence crops. Due to long-term soil nutrient exhaustion by coffee cultivation, the current land use type is mainly pasture, almost exclusively with Brachiaria sp. (SEAG, 2008Secretaria de Estado da Agricultura, Abastecimento, Aquicultura e Pesca - SEAG. Plano estratégico de desenvolvimento da agricultura: novo PEDEAG 2007-2025. Vitória: SEAG; 2008.), which is adapted to degraded soils.

The peculiar thick mantle of weathered materials (regolith), typical of the “Mares de Morros” landscape, can also be observed in the Alegre river basin. The thickness of the saprolite (C horizon) tends to be much greater than the thickness of the overlying solum (A and B horizons) (Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.; Lani et al., 2001Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61.; Ab’Sáber, 2012Ab’Sáber A. Os domínios de natureza no Brasil: potencialidades paisagísticas. 7. ed. São Paulo: Ateliê Editorial; 2012.), reaching more than 100 m in some places.

Most “Mares de Morros” landscapes on granite-gneiss rocks are associated with clayey, dystrophic Latossolo Vermelho-Amarelo (5YR) - Oxisol (Embrapa, 1978Empresa Brasileira de Pesquisa Agropecuária - Embrapa. Levantamento de reconhecimentos de solos do estado do Espírito Santo. Rio de Janeiro: Serviço Nacional de Levantamento e Conservação de Solos; 1978. (Boletim técnico, 45).; Rezende, 1980Rezende SB. Geomorphology, mineralogy and genesis of four soils on gneiss in southeastern Brazil [thesis]. West Lafayette: Purdue University; 1980.; Oliveira et al., 1983Oliveira V, Costa AMR, Azevedo WP, Camargo MN, Larach JOI. Levantamento exploratório de solos - folhas SF.23/24, Rio de Janeiro/Vitória. In: Brasil - MME. Secretaria Geral. Rio de Janeiro: Projeto Radambrasil; 1983. p. 385-552. (Levantamento de recursos naturais, 32).; Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.). However, Latossolos (Oxisols) originated from leucocratic granites have a yellowish color (7.5YR or higher) and are classified as Latossolo Amarelo, according to the Brazilian System of Soil Classification (Santos et al., 2013Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.). In this case, even when clayey, they do not exhibit the cohesive character of the Latossolos Amarelo from the coastal tableland areas (Gomes, 1976Gomes IA. Oxisols and Inceptisols from gneiss in a subtropical area of Espírito Santo State, Brazil [dissertation]. West Lafayette: Purdue University; 1976.; Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.; Ker, 1997Ker JC. Latossolos do Brasil: uma revisão. Geonomos. 1997;5:17-40. https://doi.org/10.18285/geonomos.v5i1.187
https://doi.org/10.18285/geonomos.v5i1.1...
; Lani et al., 2001Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61.).

In the Alegre river basin, the perennial drainage is composed of “V” valleys, with discontinuous terraces and floodplains, where Neossolos Flúvico (Fluvents), Gleissolos (Aquents), Argissolos (Ultisols), and Cambissolos (Inceptsols) occur (Oliveira et al., 1983Oliveira V, Costa AMR, Azevedo WP, Camargo MN, Larach JOI. Levantamento exploratório de solos - folhas SF.23/24, Rio de Janeiro/Vitória. In: Brasil - MME. Secretaria Geral. Rio de Janeiro: Projeto Radambrasil; 1983. p. 385-552. (Levantamento de recursos naturais, 32).; Ab’Sáber, 2012Ab’Sáber A. Os domínios de natureza no Brasil: potencialidades paisagísticas. 7. ed. São Paulo: Ateliê Editorial; 2012.). The structural control of the drainage is evident, as commonly observed everywhere on granitic rocks of the “Mares de Morros” landscape (Oliveira et al., 1983Oliveira V, Costa AMR, Azevedo WP, Camargo MN, Larach JOI. Levantamento exploratório de solos - folhas SF.23/24, Rio de Janeiro/Vitória. In: Brasil - MME. Secretaria Geral. Rio de Janeiro: Projeto Radambrasil; 1983. p. 385-552. (Levantamento de recursos naturais, 32).; CPRM, 2007; Varajão and Alkmim, 2015Varajão CAC, Alkmim FF. Pancas: the kingdom of bornhardts. In: Vieira BC, Salgado AAR, Santos LJC, editors. Landscapes and landforms of Brazil. Dordrecht: Springer; 2015. p. 381-8.).

Although the geology of the Alegre river basin is dominantly granitic-gneiss, variations in the mineralogical composition in these rocks may lead to different soils, depending on the performance of the other training factors and processes. Studies on crystalline rocks in various climatic conditions in southeastern Brazil have revealed kaolinite as the main secondary mineral, often associated with the alteration of feldspars (Meunier and Velde, 1976Meunier A, Velde B. Mineral reactions at grain contacts in early stages of granite weathering. Clay Miner. 1976;11:235-40. https://doi.org/10.1180/claymin.1976.011.3.05
https://doi.org/10.1180/claymin.1976.011...
; Melfi et al., 1983Melfi AJ, Cerri CC, Kronberg BI, Fyfe WS, McKinnon B. Granitic weathering: a Brazilian study. J Soil Sci. 1983;34:841-51. https://doi.org/10.1111/j.1365-2389.1983.tb01076.x
https://doi.org/10.1111/j.1365-2389.1983...
; Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.; Dixon, 1989Dixon JB. Kaolin and serpentine group minerals. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 467-525; Melo et al., 2001Melo VF, Singh B, Schaefer CEGR, Novais RF, Fontes MPF. Chemical and mineralogical properties of kaolinite-rich Brazilian soils. Soil Sci Soc Am J. 2001;65:1324-33. https://doi.org/10.2136/sssaj2001.6541324x
https://doi.org/10.2136/sssaj2001.654132...
). Most soil studies in the hilly landscapes of the “Mares de Morros” have been carried out on biotite gneiss, with little studies on leucogranites, normally associated with much-degraded pastures. In the first, a rejuvenation of some Latossolos is commonly observed, leading to a “cambic” character and enhanced nutrient status (Albuquerque Filho et al., 2008Albuquerque Filho MR, Muggler CC, Schaefer CEGR, Ker JC, Santos FC. Solos com morfologia latossólica e caráter câmbico na região de Governador Valadares, médio Rio Doce, Minas Gerais: gênese e micromorfologia. Rev Bras Cienc Solo. 2008;32:259-70. https://doi.org/10.1590/S0100-06832008000100025
https://doi.org/10.1590/S0100-0683200800...
).

Previous field observations allowed to distinguish two basic terrace systems in the Atlantic Forest zone: (1) one that has soils with gleying and evidence of Fe-losses, apparently associated with leucocratic basement rocks, and (2) terraces with high Fe contents, high chroma, and yellowish colors associated with basement rocks rich in biotite (Fe). The hypothesis is that periods of hydromorphism in Fe-poor sediments were capable of efficient Fe-removal, imposing paleogley features following drainage incision.

In this context, this study aimed to evaluate the soil formation on leucogranites along a topographic gradient, emphasizing chemical, physical, mineralogical, and micromorphological properties in relation to soil genesis. In addition, we investigated the effects of environmental/hydrological changes on soil properties.

MATERIALS AND METHODS

Description of the physical environment

This study was conducted in the Alegre river basin, a tributary of the Itapemirim river, south of the Espírito Santo State, Brazil (Figure 1), located between 41° 30’ and 41° 38’ S and between 20° 45’ and 20° 53’ W. According to the Kӧppen classification system, the climate is characterized as Cwa (mesothermal with dry winter), with the mean temperature of the coldest month lower than 18 °C and exceeding 22 °C in the warmest month (Alvares et al., 2013Alvares CA, Stape JL, Sentelhas PC, Gonçalves JLM, Sparovek G. Köppen’s climate classification map for Brazil. Meteorol Z. 2013;22:711-28. https://doi.org/10.1127/0941-2948/2013/0507
https://doi.org/10.1127/0941-2948/2013/0...
). The Alegre river basin is located between 100 to 1,200 m above sea level; this study was performed at a topossequence from 650 to 750 m (Figures 1 and 2). Annual average rainfall varies from 1,300 to 1,500 mm, with a rainy season from October to March and a dry season from April to September. The original vegetation was semideciduous Atlantic Forest (IBGE, 2012Instituto Brasileiro de Geografia e Estatística - IBGE. Manual técnico da vegetação brasileira. 2. ed. rev. ampl. Rio de Janeiro: IBGE; 2012.), now almost totally replaced by pastures.

Figure 1
Location of the Alegre river basin, Espírito Santo State, Brazil.

The regional geology is composed of Precambrian basement rocks of the Paraíba do Sul Complex, part of the Atlantic Mobile Belt (Oliveira et al., 1983Oliveira V, Costa AMR, Azevedo WP, Camargo MN, Larach JOI. Levantamento exploratório de solos - folhas SF.23/24, Rio de Janeiro/Vitória. In: Brasil - MME. Secretaria Geral. Rio de Janeiro: Projeto Radambrasil; 1983. p. 385-552. (Levantamento de recursos naturais, 32).). It mainly consists of granitic rocks (migmatized paragneiss) with a significant presence of quartz, feldspar, granite, and minor amphibole (CPRM, 2007). Rocks have an acid composition (70 % SiO2, 14 % Al2O3, and 2 % Fe2O3), with low amounts of Fe and Mn (CPRM, 2007).

The geomorphology of the Alegre river basin is defined as part of the stepped hillslopes of southern Espírito Santo, as a geomorphological unit (Oliveira et al., 1983Oliveira V, Costa AMR, Azevedo WP, Camargo MN, Larach JOI. Levantamento exploratório de solos - folhas SF.23/24, Rio de Janeiro/Vitória. In: Brasil - MME. Secretaria Geral. Rio de Janeiro: Projeto Radambrasil; 1983. p. 385-552. (Levantamento de recursos naturais, 32).). Hence, the hills are distributed in successive steps at different altitudinal levels (Ab’Sáber, 1970Ab’Sáber AN. Províncias geológicas e domínios morfoclimaticos no Brasil. São Paulo: Geomorfologia; 1970.; Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.). The structural control of the drainage is evident in the entire Alegre river basin (Figure 1).

Site selection and sample collection

The selected topossequence was identified through interpretation of a planialtimetric map at a 1:50,000 scale, a geological map at a 1:100,000 scale (Embrapa, 1978Empresa Brasileira de Pesquisa Agropecuária - Embrapa. Levantamento de reconhecimentos de solos do estado do Espírito Santo. Rio de Janeiro: Serviço Nacional de Levantamento e Conservação de Solos; 1978. (Boletim técnico, 45).; CPRM, 2007), and a soil map at a 1:50,000 scale (Pacheco, 2011Pacheco AA. Pedogênese e distribuição espacial dos solos da bacia hidrográfica do rio Alegre - ES [dissertação]. Viçosa, MG: Universidade Federal de Viçosa; 2011.), using aerial photographs at a scale of 1:15,000. A Digital Elevation Model (DEM) was prepared, using the ArcGIS 10.1 software. Four representative soil profiles (P1, P2, P3, and P4) were selected and collected along the topossequence (Figure 2).

Figure 2
Topographic profile of the topossequence drawn from the digital elevation model and soil profile pictures.

The positions of the soil profiles were georeferenced, and morphological descriptions were made based to Santos et al. (2015Santos RD, Lemos RC, Santos HG, Ker JC, Anjos LHC. Manual de descrição e coleta de solo no campo. 5. ed. rev. ampl. Viçosa, MG: Sociedade Brasileira de Ciência do Solo; 2005.). Classification, to the categorical level of the subgroup, was based on the Brazilian System of Soil Classification (Santos et al., 2013Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.) and Soil Taxonomy (Soil Survey Staff, 1999Soil Survey Staff. Soil taxonomy: a basic system of soil classification for making and interpreting soil surveys. 2nd ed. Washington, DC: USA: United States Department of Agriculture, Natural Resources Conservation Service; 1999. (Agricultural Handbook, 436).).

Physical and chemical analyses

The pH in water and KCl 1 mol L-1 were determined at a ratio of 1:2.5 v/v; the potential acidity (H+Al) was extracted with Ca(OAc)2 0.5 mol L-1 buffered to pH 7.0 and quantified by titration with 0.0606 mol L-1 NaOH. Exchangeable Ca, Mg, and Al were extracted with KCl 1 mol L-1, and Na+ and K+ were extracted with Mehlich-1 solution (Donagema et al., 2011Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise de solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011.). The concentration of elements in the extracts were determined by atomic absorption (Ca2+, Mg2+, and Al3+), flame emission (Na+ and K+), and photocolorimetry (P). Effective cation exchange capacity (CECE) was calculated by the sum of cations (Ca2+, Mg2+, Na+, K+, and Al3+), and total cation exchange capacity (CECT) was estimated by the sum of bases (BS) and potential acidity. Base saturation (V%) and Al3+ saturation (m%) were calculated via the sum of bases, CECT, and Al3+ content (Donagema et al., 2011Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise de solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011.). The remaining P was determined according to Alvarez et al. (2000)Alvarez V VH, Novais RF, Dias LE, Oliveira JA. Determinação e uso do fósforo remanescente. Bol Inf Soc Bras Cienc Solo. 2000;25:27-32.. Soil texture analysis was performed by the pipette method (Ruiz, 2005Ruiz HA. Incremento da exatidão da análise granulométrica do solo por meio da coleta da suspenssão (silte + argila). Rev Bras Cienc Solo. 2005;29:297-300. https://doi.org/10.1590/S0100-06832005000200015
https://doi.org/10.1590/S0100-0683200500...
; Donagema et al., 2011Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise de solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011.); soil was divided into coarse sand, fine sand, silt, and clay. Total soil organic carbon (TOC) was determined according to the Walkley–Black titration method (Mebius, 1960Mebius LJ. A rapid method for the determination of organic carbon in soil. Anal Chim Acta. 1960;22:120-4. https://doi.org/10.1016/S0003-2670(00)88254-9
https://doi.org/10.1016/S0003-2670...
) by wet oxidation with K2Cr2O7 0.167 mol L-1 in the presence of sulfuric acid with external heating (Yeomans and Bremner, 1988Yeomans JC, Bremner JM. A rapid and precise method for routine determination of organic carbon in soil. Commun Soil Sci Plant. 1988;19:1467-76. https://doi.org/10.1080/00103628809368027
https://doi.org/10.1080/0010362880936802...
).

Total contents of Fe, Al, Si, and Ti were determined in dried soil by the “sulfuric attack” method (Donagema et al., 2011Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise de solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011.) and expressed as oxides. We used a digestion of sulfuric acid 9 mol L-1 at 180 °C for 1 h, and with NaOH (30 %) on a heating plate for 2 min. Based on these results, we calculated the weathering indices Ki = [(SiO2 × 1.70)/Al2O3] and Kr = {(SiO2 × 0.60)/[(Al2O3/1.02) + (Fe2O3/1.60)]} molar ratios. The Fe and Al contents in the clay fraction were quantified after five sequential extractions, using the dithionite-citrate-bicarbonate method (DCB) at pH 7.3 (Mehra and Jackson, 1958Mehra OP, Jackson ML. Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. Clay Clay Miner. 1958;7:317-27. https://doi.org/10.1016/B978-0-08-009235-5.50026-7
https://doi.org/10.1016/B978-0-08-009235...
) and after one extraction by the acid oxalate method (AOD) in darkness at pH 3.0 (McKeague and Day, 1966McKeague JA, Day JH. Dithionite- and oxalate-extractable Fe and Al as aids in differentiating various classes of soils. Can J Soil Sci. 1966;46:13-22. https://doi.org/10.4141/cjss66-003
https://doi.org/10.4141/cjss66-003...
). The molecular Feo/Fed and Fed/Fes ratios were calculated using the Fe contents extracted by ammonium oxalate (Feo), dithionite-citrate-bicarbonate (Fed), and sulfuric acid attack (Fes). These were used as an index for the crystallinity degree of Fe oxides and the interpretation of pedogenic processes and the intensity of weathering (Kampf and Curi, 2000Kämpf N, Curi N. Óxidos de ferro: Indicadores de ambientes pedogênicos e geoquímicos. Tópicos Cienc Solo. 2000;1:107-38.). The Al, Si, Fe, and Ti, extracted via sulfuric acid digestion, and Fe and Al, extracted via selective dissolution with DCB and AOD, were quantified by atomic absorption spectrophotometry.

Mineralogical analysis

X-ray diffraction (XRD) analyses were conducted on the clay-size fraction (<2 mm) from selected samples, using a Panalytical X’Pert PRO (CoKα radiation) at the Federal University of Viçosa. X-ray diffraction patterns were collected between 4 and 50 °2θ, at a scan speed of 1 °2θ min-1, with a potential 40 kV generator and a current generator of 40 mA. Crystalline and non- crystalline Fe oxides were removed using a sodium dithionite-citrate-bicarbonate (DCB) solution (Mehra and Jackson, 1958)Mehra OP, Jackson ML. Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. Clay Clay Miner. 1958;7:317-27. https://doi.org/10.1016/B978-0-08-009235-5.50026-7
https://doi.org/10.1016/B978-0-08-009235...
. The remaining phyllosilicate minerals, after the removal of Fe oxides, were analyzed in oriented and random powder clay minerals. The identification of 2:1 minerals present in the clay mineral fraction followed the methodology described by Whittig and Allardice (1986)Whittig LD, Allardice WR. X-ray diffraction techniques. In: Klute A, editor. Methods of soil analysis. Physical and mineralogical methods. 2nd ed. Madison: American Society of Agronomy; 1986. Pt 1. p. 331-62..

The degree of structural disorder of kaolinite of selected samples was determined by full-width at half-maximum (FWHM °2θ) for the position of the peaks 001 and 002 (Klug and Alexander, 1974Klug HP, Alexander LE. X-ray diflraction procedures for polycrystalline and amorphous materials. 2nd ed. New York: John Wiley & Sons; 1974.), the R2 crystallinity index (Liétard, 1977Liétard O. Contribution a l’etude des proprietes physicochimiques, cristallographiques et morphologiques des kaolins [thesis]. Nancy: University of Nancy; 1977.), and the HB index (Hughes and Brown, 1979Hughes JC, Brown G. A crystallinity index for soil kaolins and its relation to parent rock, climate and soil maturity. J Soil Sci. 1979;30:557-63. https://doi.org/10.1111/j.1365-2389.1979.tb01009.x
https://doi.org/10.1111/j.1365-2389.1979...
). Kaolinite standard samples obtained from the Source Clay Repository of the Clay Minerals Society at Purdue University, West Lafayette, USA, were used as references (Pruett and Webb, 1993Pruett RJ, Webb HL. Sampling and analysis of KGa-1B well-crystallized kaolin source clay. Clay Clay Miner. 1993;41:514-9. https://doi.org/10.1346/CCMN.1993.0410411
https://doi.org/10.1346/CCMN.1993.041041...
; Moll Jr, 2001Moll Jr WF. Baseline studies of the clay minerals society source clays: geological origin. Clay Clay Miner. 2001;49:374-80. https://doi.org/10.1346/ccmn.2001.0490503
https://doi.org/10.1346/ccmn.2001.049050...
). The standards used were KGa 2, with a high structural disorder, and KGa 1b, with a low structural disorder, together with the KAm with the lower structural disorder from Amazônia, Brazil.

Thermogravimetric (TGA) analysis was conducted using a Shimadzu TGA 50 at the Embrapa Cerrado Research Center. The samples of the clay-size fraction (Fe-free) were placed in an alumina cell with a thermobalance under a constant nitrogen flow. Analysis was performed in the temperature range from 25 to 800 °C, at a heating rate of 10 °C per minute. Mass losses of gibbsite and kaolinite were identified individually at temperature ranges in which the dehydroxylation of these minerals commonly occurs (Mackenzie, 1982Mackenzie RC. Thermoanalytical methods in clay studies. In: Fripiat JJ, editor. Advanced techniques for clay mineral analysis. Amsterdam: Elsevier; 1982. p. 5-29. https://doi.org/10.1016/S0070-4571(08)70014-1
https://doi.org/10.1016/S0070-4571...
; Stucki et al., 1990Stucki JW, Bish DL, Mumpton FA, editors. Thermal analysis in clay science. Boulder: Clay Minerals Society; 1990.).

Micromorphological analysis

Micromorphological investigations were performed on undisturbed samples of soil subsurface horizons. The thin sections were prepared according to Fitzpatrick (1984)Fitzpatrick EA. The micromorphology of soils. In: Fitzpatrick EA, editor. Micromorphology of soils. Dordrecht: Springer; 1984. p. 331-57.. The recommendations of Stoops (2003)Stoops G. Guidelines for analysis and description of soil and regolith thin sections. Madison: Soil Science Society of America; 2003. and Stoops et al. (2010)Stoops G, Marcelino V, Mees F. Interpretation of micromorphological features of soils and regoliths. Amsterdam: Elsevier; 2010. were used for micromorphological descriptions. Microstructures were described by the aggregates and porosity. Inside the aggregates or in the apedal microstructures, the coarse and fine materials of the groundmass were described. Finally, the pedofeatures were identified and characterized. A Zeiss® Trinocular Optical Microscope (Axiophot model) with polarized light and an integrated digital camera was used for the descriptions.

RESULTS

Morphological and physical properties

Soil color along the topographic sequence varied from yellowish at the top and mid-slope (P1 and P2) to grayish at the foot-slope and the toe-slope under past (P3) and current (P4) hydromorphic conditions (Table 1). The P3 presented hydromorphic properties that occurred in the past, since it showed grayish colors, but no more saturation by water in any period currently. Therefore, these pale colors are related to the nature of the parent material (Santos et al., 2010Santos AC, Pereira MG, Anjos LHC, Bernini TA, Cooper M, Nummer AR, Francelino MR. Gênese e classificação de solos numa topossequência no ambiente de Mar de Morros do Médio Vale do Paraíba do Sul, RJ. Rev Bras Cienc Solo. 2010;34:1297-314. https://doi.org/10.1590/s0100-06832010000400027
https://doi.org/10.1590/s0100-0683201000...
), with low Fe contents of leucocratic granites (CPRM, 2007). The slope gradients to P1, P2, P3, and P4 showed values of 7, 22, 15, and 6 %, respectively (Table 1).

Table 1
Physical and morphological characterization of soils

Based on the morphological properties of P1 and P2, they were classified (Santos et al., 2013Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.) as Latossolo Vermelho-Amarelo (P1) and Latossolo Amarelo (P2). According to the Soil Taxonomy (Soil Survey Staff, 1999Soil Survey Staff. Soil taxonomy: a basic system of soil classification for making and interpreting soil surveys. 2nd ed. Washington, DC: USA: United States Department of Agriculture, Natural Resources Conservation Service; 1999. (Agricultural Handbook, 436).), they were classified as Acrudox for both P1 and P2. Evaluating the colors at the subsurface horizon, Bw1 at P1 and P2 were 5YR 4/6 and 7.5YR 4/6, respectively (Table 1). All soils showed a silt/clay ratio lower than 0.50, indicating a high degree of weathering (Camargo et al., 1987Camargo MN, Klemt E, Kauffman JH. Classificação de solos usada em levantamento pedológico no Brasil. Bol Inf Soc Bras Cienc Solo. 1987;12:11-33.). Brazilian Latossolos (Oxisols) are typical soils of the “Mares de Morros” landscape, formed from leucocratic granitic-gneiss rocks (Lani et al., 2001Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61.; Resende et al., 2002Resende M, Lani JL, Rezende SB. Pedossistemas da Mata Atlântica: considerações pertinentes sobre a sustentabilidade. Rev Arvore. 2002;26:261-9. https://doi.org/10.1590/s0100-67622002000300001
https://doi.org/10.1590/s0100-6762200200...
; CPRM, 2007; Ab’Sáber, 2012Ab’Sáber A. Os domínios de natureza no Brasil: potencialidades paisagísticas. 7. ed. São Paulo: Ateliê Editorial; 2012.). The subsurface horizons (Bw) of upland Latossolos (P1 and P2) presented a moderate sub-angular block structure, turning into granular when moist and handled.

The terraces along the margins of the Alegre river basin display evidence of past hydromorphism processes, which resulted in efficient Fe mobility and losses (Table 1). Hence, grayish colors are common, and the soils are difficult to classify via the Brazilian System of Soil Classification (Santos et al., 2013Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.), the Soil Taxonomy (Soil Survey Staff, 1999Soil Survey Staff. Soil taxonomy: a basic system of soil classification for making and interpreting soil surveys. 2nd ed. Washington, DC: USA: United States Department of Agriculture, Natural Resources Conservation Service; 1999. (Agricultural Handbook, 436).), and the FAO guidelines (WRB, 2015IUSS Working Group WRB. World reference base for soil resources 2014, update 2015: International soil classification system for naming soils and creating legends for soil maps. Rome: Food and Agriculture Organization of the United Nations; 2015. (World Soil Resources Reports, 106).). The main difficulty is that the soil lacks sufficient plinthite to be classified as Plintossolo (Plinthic subgroup) and is not saturated by water to be classified as Gleissolo (Aquents) (Santos et al., 2013Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.). Hence, based on its features, the proposed nomenclature for soil P3 was “Pseudogleysol” (Blume, 1988Blume H-P. The fate of iron during soil formation in humid-temperate environments. In: Stucki JM, Goodman BA, Schwertmann U, editors. Iron soils clay minerals. Dordrecht: D. Reidel Publishing Company; 1988. p. 749-77. https://doi.org/10.1007/978-94-009-4007-9_21
https://doi.org/10.1007/978-94-009-4007-...
; Fanning and Fanning, 1989Fanning DS, Fanning MCB. Soil: morphology, genesis, and classification. New York: John Wiley and Sons Inc.; 1989.), although this term is not officially included in the soil classification systems.

Soil P4 was located in the lowest part of the floodplain, which is periodically water saturated, leading to the occurrence of Gleissolos (Aquents). Abundant mottling and soft plinthite are common in the horizon Cg, especially along root channels, where an aerobic rhizosphere environment allows the oxidation of Fe2+ into Fe3+, corroborated by the positive reaction with α, α’-dipyridyl (Childs, 1981Childs CW. Field tests for ferrous iron and ferric-organic complexes (on exchange sites or in water-soluble forms) in soils. Aust J Soil Res. 1981;19:175-80. https://doi.org/10.1071/SR9810175
https://doi.org/10.1071/SR9810175...
).

Textural analysis showed a heavy clay texture (FAO, 2006Food and Agriculture Organization of the United Nations - FAO. Guidelines for soil description. 4th ed. rev. Rome: FAO. 2006 [Accessed on May 1 2017]. Available at: http://www.fao.org/docrep/019/a0541e/a0541e.pdf
http://www.fao.org/docrep/019/a0541e/a05...
) for P1 and clay for P2 (Table 1). For soil P4, Gleissolo (Aquents), the texture was uniform (sandy clay loam) throughout the profile, whereas P3 (Pseudogleysol) showed a textural gradient between the sandy loam A horizon and the clayey C3 horizon (Table 1).

The soils were classified to the categorical level of the subgroup, according to the Brazilian System of Soil Classification (Santos et al., 2013Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.), as Latossolo Vermelho-Amarelo Distrófico típico (P1), Latossolo Amarelo Distrófico típico (P2), and Gleissolo Háplico Distrófico típico (P4). According to the Soil Taxonomy (Soil Survey Staff, 1999Soil Survey Staff. Soil taxonomy: a basic system of soil classification for making and interpreting soil surveys. 2nd ed. Washington, DC: USA: United States Department of Agriculture, Natural Resources Conservation Service; 1999. (Agricultural Handbook, 436).), they were defined as Typic Acrudox (P1), Typic Acrudox (P2), and Typic Epiaquent (P4). Soil P3 was maintained as Pseudogleysol because its features did not fit into the commonly used soil classification systems.

Chemical properties

The pH(H2O) values ranged from 4.8 to 5.6 (Table 2), common for soils from the “Mares de Morros” landscape (Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.; Lani et al., 2001Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61.; Nunes et al., 2001Nunes WAGA, Ker JC, Schaefer CEGR, Fernandes Filho EI, Gomes FH. Relação solo-paisagem-material de origem e genêse de alguns solos no domínio do “Mar de Morro”, Minas Gerais. Rev Bras Cienc Solo. 2001;25:341-54. https://doi.org/10.1590/S0100-06832001000200011
https://doi.org/10.1590/S0100-0683200100...
; Santos et al., 2010Santos AC, Pereira MG, Anjos LHC, Bernini TA, Cooper M, Nummer AR, Francelino MR. Gênese e classificação de solos numa topossequência no ambiente de Mar de Morros do Médio Vale do Paraíba do Sul, RJ. Rev Bras Cienc Solo. 2010;34:1297-314. https://doi.org/10.1590/s0100-06832010000400027
https://doi.org/10.1590/s0100-0683201000...
). The pH(H2O) were higher than pH(KCl), indicating weak acid reactions, which implies net negative charges, as inferred from the negative values of ΔpH = [pH(KCl) – pH(H2O)] (van Raij, 1973van Raij B. Determinação de cargas elétricas em solos. Bragantia. 1973;32:171-83. https://doi.org/10.1590/s0006-87051973000100007
https://doi.org/10.1590/s0006-8705197300...
). Contents of Ca2+, Mg2+, and K+ in surface and subsurface horizons of all soil classes studied ranged from very low to low, according to the criteria defined by Ribeiro et al. (1999)Ribeiro AC, Guimarães PTG, Alvarez V VH. Recomendação para o uso de corretivos e fertilizantes em Minas Gerais: 5a aproximação. Viçosa, MG: Comissão de Fertilidade do Solo do Estado de Minas Gerais; 1999., except for the horizon A1 of soil P3.

Table 2
Chemical characterization of soils

The soils are dystrophic (V% <50), with a base sum below 0.5 cmolc kg-1 and low CEC, generally less than 7.0 cmolc kg-1, resulting from the high degree of weathering and intense leaching (Table 2). Levels of Al3+ were high, ranging from 1 to 2 cmolc kg-1, but not high enough (<4.0 cmolc kg-1) to characterize them as aluminic (Santos et al., 2013)Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.. The clay activity values below 27 cmolc kg-1 (CECR), observed in all soils (Table 2), indicate a dominance of low-activity clays (Tb), consistent with the results presented by the XRD patterns and the weathering index (Ki) (Donagema et al., 2011)Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise de solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011..

Organic carbon contents ranged from low to medium (Ribeiro et al., 1999Ribeiro AC, Guimarães PTG, Alvarez V VH. Recomendação para o uso de corretivos e fertilizantes em Minas Gerais: 5a aproximação. Viçosa, MG: Comissão de Fertilidade do Solo do Estado de Minas Gerais; 1999.) in the surface horizons (Table 2). Values of CECT and H+Al were mostly dependent on organic carbon (OC), with a high positive correlation with OC values (Xu et al., 2016Xu R-k, Qafoku NP, Van Ranst E, Li J-y, Jiang J. Adsorption properties of subtropical and tropical variable charge soils: implications from climate change and biochar amendment. Adv Agron. 2016;135:1-58. https://doi.org/10.1016/bs.agron.2015.09.001
https://doi.org/10.1016/bs.agron.2015.09...
), since clays are of low activity. The available P content was very low (Ribeiro et al., 1999Ribeiro AC, Guimarães PTG, Alvarez V VH. Recomendação para o uso de corretivos e fertilizantes em Minas Gerais: 5a aproximação. Viçosa, MG: Comissão de Fertilidade do Solo do Estado de Minas Gerais; 1999.), ranging from 0.40 to 2.70 mg kg-1. The remaining P levels were negatively correlated (r = 0.99, p<0.01) with the clay contents in all soils. The Ki and Kr ratios (Donagema et al., 2011Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise de solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011.) ranged from 0.86 to 1.48 and 0.64 to 1.43, respectively, for the subsurface horizons and from 0.94 to 1.43 and 0.70 to 1.34, respectively, for the surface horizons (Table 3).

Table 3
Results of acid sulfuric attack, dithionite-citrate-bicarbonate (DCB), acid oxalate method at darkness (AOD), and molar ratios

The Fe2O3 content via sulfuric digestion (FeS) in P1, P2, P 3, and P4 ranged from 6.84 to 14.5, 1.33 to 1.77, and 0.95 to 1.46 dag kg-1, respectively (Table 3).

Mineralogical properties

The clay fraction identified via the XRD pattern was composed by kaolinite [(Al2Si2O5OH)4], gibbsite [γ-Al(OH)3], goethite (α-FeOOH), hematite (α-Fe2O3), and traces of vermiculite and hydroxy-Al interlayered vermiculite (HIV) (Figures 3 and 4). The presence of hematite and goethite was confirmed in the clay fraction via interplanar spacing (d) of 0.413 nm and 0.265 nm (Figure 3), with a marked presence in upslope soils (P1 and P2), but absent in the bottom (P3 and P4) under current or past hydromorphism processes. These Fe oxides have very close reflections (0.265 nm), but with different hkl directions, and (130) of goethite and (104) to hematite (Figure 3).

Figure 3
XRD patterns collected from clay mineral (oriented powder). P1 = Latossolo Vermelho-Amarelo Distrófico típico/Typic Acrudox; P2 = Latossolo Amarelo Distrófico típico/Typic Acrudox; P3 = Pseudogleysol; P4 = Gleissolo Háplico Distrófico típico/Typic Epiaquent; Vm = vermiculite; HIV = hydroxy-interlayered vermiculite; Ka = kaolinite; Gb = gibbsite; Gt = goethite; Hm = hematite.

Gibbsite was identified via interplanar spacing (d) of 0.485 and 0.437 nm (Figure 3) for the hkl directions 002 and 110 in all soils. This mineral indicates an intense weathering degree, which was confirmed by the low Ki ratio (Table 3). The TGA showed a much greater kaolinite content (Table 4), ranging from 75.4 to 94.42 dag kg-1, whereas gibbsite accounted for 5.86 to 14.86 dag kg-1 in the soils (Table 4).

Table 4
Kaolinite crystallinity index and Thermogravimetric analysis (TGA)

Presence of vermiculite and hydroxy-Al interlayered vermiculite (HIV) was confirmed by interplanar spacing (d) of 1.418 and 1.212 nm in the clay fraction (Figure 4). Further, treatments with Mg, Mg + Glycerol, K 25 °C, K 350 °C, and K 550 °C were performed in the clay-size fraction after Fe extraction (Whittig and Allardice, 1986Whittig LD, Allardice WR. X-ray diffraction techniques. In: Klute A, editor. Methods of soil analysis. Physical and mineralogical methods. 2nd ed. Madison: American Society of Agronomy; 1986. Pt 1. p. 331-62.). These minerals were only observed in the soils of the back-slope (P2) and the toe-slope (P3 and P4).

Figure 4
XRD patterns collected from Fe-free clay mineral (oriented powder) for identification of 2:1 minerals (Whittig and Allardice, 1986Whittig LD, Allardice WR. X-ray diffraction techniques. In: Klute A, editor. Methods of soil analysis. Physical and mineralogical methods. 2nd ed. Madison: American Society of Agronomy; 1986. Pt 1. p. 331-62.). (a) P2 - Hoz. Bw1; (b) P3 - Hoz. C2; (c) P3 - Hoz. C3; (d) P4 - Hoz. A. Vm = vermiculite; HIV = hydroxy-interlayered vermiculite; Ka = kaolinite; Gb = gibbsite.

Kaolinite was confirmed in XRD patterns by interplanar spacing (d) of high intensity in 0.718, 0.358, and 0.238 nm and low intensities in 0.446, 0.256, 0.249, 0.234, and 0.229 nm (Figures 3 and 4).

Kaolinite crystallinity index proposed by Liétard (1977)Liétard O. Contribution a l’etude des proprietes physicochimiques, cristallographiques et morphologiques des kaolins [thesis]. Nancy: University of Nancy; 1977. and Hughes and Brown (1979)Hughes JC, Brown G. A crystallinity index for soil kaolins and its relation to parent rock, climate and soil maturity. J Soil Sci. 1979;30:557-63. https://doi.org/10.1111/j.1365-2389.1979.tb01009.x
https://doi.org/10.1111/j.1365-2389.1979...
and full width at half maximum (FWHM) of the 001 and 002 directions of kaolinite (Klug and Alexander, 1974Klug HP, Alexander LE. X-ray diflraction procedures for polycrystalline and amorphous materials. 2nd ed. New York: John Wiley & Sons; 1974.) suggested a high structural disorder in all profiles (Table 4). This observation was confirmed by the crystallinity indices for kaolinite standards with high (KGA 2) and low (KGA 1b and KAm) structural disorder (Table 4). Several other useful indices are presented in the literature (Hinckley, 1962Hinckley DN. Variability in “crystallinity” values among the kaolin deposits of the coastal plain of Georgia and South Carolina. Clay Clay Miner. 1962;11:229-35.; Plançon et al., 1988Plançon A, Giese RF, Snyder R. The Hinckley index for kaolinites. Clay Miner. 1988;23:249-60. https://doi.org/10.1180/claymin.1988.023.3.02
https://doi.org/10.1180/claymin.1988.023...
; Aparicio et al., 2006Aparicio P, Galán E, Ferrell RE. A new kaolinite order index based on XRD profile fitting. Clay Miner. 2006;41:811-7. https://doi.org/10.1180/0009855064140220
https://doi.org/10.1180/0009855064140220...
), but are not applied to kaolinite with a high structural disorder, such as those highly weathered soils investigated in the present study. Since these indices using the peaks of kaolinite in the directions 020, 110, 111, 021, which are not identified by XRD in kaolinite with the high structural disorder (Figure 5).

Figure 5
XRD patterns collected from Fe-free clay mineral (random powder). KGa 2 = high structural disorder kaolinite standard; KGa 1b = low structural disorder kaolinite standard; KAm = low structural disorder kaolinite from Amazônia; Ka = kaolinite; Gb = gibbsite.

Micromorphological properties

Micromorphological properties varied both vertically and laterally along the topossequence, with varying degrees of microstructure development and micropedological features (Table 5). The upland Latosol (P1) has a typical isotropic micromass, with occasional anisotropic areas with weak pedality, consisting of composite sub-angular block peds, with strong medium granular at high magnification (Figure 6). The main micropedological features were channels and micro-galleries, currently filled with a secondary clay plasma, fecal pellets of termites ranging from 10 to 50 microns, and other indiscriminate excremental pellets of microarthropods.

Table 5
Micromorphological description of soils

Figure 6
Optical microscope photomicrographs (OMP) in parallel (left) and crossed polarized light (right) of the P1 profile, highlighting: A horizon = sub-angular blocky microstructure with groundmass composed by angular/sub-angular quartz and opaque grains (coarse materials) and brownish yellow micromass with undifferentiated or weak speckled b-fabric; Bw1 horizon = granular microstructure with enaulic relative distribution. The coarse materials of the groundmass are composed of angular/sub-angular quartz, hematite, and opaque grains, and the micromass is brownish yellow with a circular or crescent striated b-fabric; Bw2 horizon = medium granular and vughy microstructure, with the same coarse materials and micromass of the Bw1 horizon. The presence of large charcoal fragments inter-aggregates and very small fragments inside them is common. Qz = quartz; V = vughy; cpv = complex packing voids; hg = hematite grain; op = opaque grain; ch = channel. Some granular aggregates of Bw (1 and 2) horizon are highlighted with a dashed yellow line.

In general, P3 and P4 showed evidence of strong coalescence of microaggregates (Figure 7), accompanied by Fe oxyhydrate removal by reducing conditions, leading to a collapsing effect of the structure, turning it virtually apedal and massive, forming a homogeneous dotted micromass almost completely leached and pallid. No weatherable minerals were found in the coarse sand, which is formed basically by poorly sorted quartz (sub-rounded to sub-angular), with rare fragments of oriented clay, similar to the well-drained upland soils P1 and P2.

Figure 7
Optical microscope photomicrographs (OMP) in parallel (left) and crossed polarized light (right) of the P3 and P4 profiles, highlighting: P3A horizon = single grain microstructure with pellicular areas (chitonic relative distribution). Amorphous opaque organic materials and root tissues are common; P3C2 horizon = apedal horizon with massive microstructure. Coarse material in the groundmass is mainly composed of quartz, immersed in a clear micromass, with typical depletion features of an aquic syndrome. P4A horizon = single grain microstructure and apedal zones. Epiaquic syndrome features occur in the form of depletion zones and Fe-impregnating; P4Cg2 horizon = apedal horizon with massive microstructure, similar to the P3C2 horizon. Planar (fissures) voids and vughs are present. There are no evidences of bioturbation, but aquic features are common. Qz = quartz; om = amorphous opaque organic materials; V = vughy.

DISCUSSION

In the Brazilian System of Soil Classification (Santos et al., 2013Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.), P3 could be classified as Argissolo Acinzentado or Cambissolo, since it now occurs in an environment no longer saturated with water. Therefore, a better definition of the classification criteria for this soil class is necessary, maybe as a Gleissolo variation. The interpretation is difficult when the Fe-poor soil has been subjected to several environmental cycles, causing an overlap of gley and pseudogley features (Buurman, 1980Buurman P. Palaeosols in the Reading Beds (Paleocene) of Alum Bay, Isle of Wight, U.K. Sedimentology. 1980;27:593-606. https://doi.org/10.1111/j.1365-3091.1980.tb01649.x
https://doi.org/10.1111/j.1365-3091.1980...
; Blume, 1988Blume H-P. The fate of iron during soil formation in humid-temperate environments. In: Stucki JM, Goodman BA, Schwertmann U, editors. Iron soils clay minerals. Dordrecht: D. Reidel Publishing Company; 1988. p. 749-77. https://doi.org/10.1007/978-94-009-4007-9_21
https://doi.org/10.1007/978-94-009-4007-...
). Since there are no well-defined characteristics for the classification of these soils, Pseudogleysols are generally recognized as Gleissolos (Rubinić et al., 2014Rubinić V, Durn G, Husnjak S, Tadej N. Composition, properties and formation of Pseudogley on loess along a precipitation gradient in the Pannonian region of Croatia. Catena. 2014;113:138-49. https://doi.org/10.1016/j.catena.2013.10.003
https://doi.org/10.1016/j.catena.2013.10...
; Ndjigui et al., 2015Ndjigui P-D, Abeng SAE, Ekomane E, Nzeukou AN, Mandeng FSN, Lindjeck MM. Mineralogy and geochemistry of pseudogley soils and recent alluvial clastic sediments in the Ngog-Lituba region, Southern Cameroon: an implication to their genesis. J Afr Earth Sci. 2015;108:1-14. https://doi.org/10.1016/j.jafrearsci.2015.03.023
https://doi.org/10.1016/j.jafrearsci.201...
), regardless of whether the hydromorphism process has occurred in the past or is currently occurring. Sometimes, these soils are recognized in the Soil Taxonomy (Soil Survey Staff, 1999Soil Survey Staff. Soil taxonomy: a basic system of soil classification for making and interpreting soil surveys. 2nd ed. Washington, DC: USA: United States Department of Agriculture, Natural Resources Conservation Service; 1999. (Agricultural Handbook, 436).) as the fragi great groups or as Albolls, Albaqualfs, Albaquults, Argialbolls, and Hapludults (Fanning and Fanning, 1989Fanning DS, Fanning MCB. Soil: morphology, genesis, and classification. New York: John Wiley and Sons Inc.; 1989.). However, there is no consensus regarding soils with such properties and their taxonomy in the Soil Taxonomy.

Pseudogleysols are soils that largely correlate with Stagnosols or Planosols, according to the FAO soil classification system (WRB, 2015) because of their stagnic properties and redoximorphic features. However, the P3 of the present study totally differed from the definition given by the FAO (WRB, 2015) since it has no more stagnic properties and the hydromorphism process has occurred in the past. This demonstrates the need for a better definition of the classification criteria for this soil class.

Morphology described for the upland Latossolos (P1 and P2) is consistent with their advanced weathering degree, confirmed by the dominance of kaolinite, with minor gibbsite, typical for this type of composed block/granular aggregation in such soils (Ker, 1997Ker JC. Latossolos do Brasil: uma revisão. Geonomos. 1997;5:17-40. https://doi.org/10.18285/geonomos.v5i1.187
https://doi.org/10.18285/geonomos.v5i1.1...
; Ferreira et al., 1999Ferreira MM, Fernandes B, Curi N. Mineralogia da fração argila e estrutura de Latossolos da região sudeste do Brasil. Rev Bras Cienc Solo. 1999;23:507-14. https://doi.org/10.1590/S0100-06831999000300003
https://doi.org/10.1590/S0100-0683199900...
; Nunes et al., 2001Nunes WAGA, Ker JC, Schaefer CEGR, Fernandes Filho EI, Gomes FH. Relação solo-paisagem-material de origem e genêse de alguns solos no domínio do “Mar de Morro”, Minas Gerais. Rev Bras Cienc Solo. 2001;25:341-54. https://doi.org/10.1590/S0100-06832001000200011
https://doi.org/10.1590/S0100-0683200100...
; Resende et al., 2002Resende M, Lani JL, Rezende SB. Pedossistemas da Mata Atlântica: considerações pertinentes sobre a sustentabilidade. Rev Arvore. 2002;26:261-9. https://doi.org/10.1590/s0100-67622002000300001
https://doi.org/10.1590/s0100-6762200200...
). Profiles P3 and P4 showed a massive structure with greyish colors in the subsurface (high value and low chroma), resulting from past or present hydromorphism processes (Table 1). Since P3 is no longer water-saturated, it showed a negative reaction in the alpha, alpha-dipyridyl field test for ferrous iron (Childs, 1981Childs CW. Field tests for ferrous iron and ferric-organic complexes (on exchange sites or in water-soluble forms) in soils. Aust J Soil Res. 1981;19:175-80. https://doi.org/10.1071/SR9810175
https://doi.org/10.1071/SR9810175...
), highlighting efficient Fe-removal after drainage incision.

Textural gradient found in P3 is consistent with that reported by Fanning and Fanning (1989)Fanning DS, Fanning MCB. Soil: morphology, genesis, and classification. New York: John Wiley and Sons Inc.; 1989., who described primary and secondary “Pseudogleysols”, depending on the genetic nature of the dense underlying horizon of these soils. The secondary type would have a thick clay layer formed by pedogenesis, representing a Bt horizon, while the primary one would have a dense layer inherited from the parent material, such as a dense shale bedrock underlying the soil. The P3 is a typical secondary “Pseudogleysol” with a texture gradient. Its position in the landscape, at the bottomland, favored clay translocation through leaching (Smeck and Runge, 1973Smeck NE, Runge ECA. Factors influencing profile development exhibited by some hy dromorphic soils in Illinois. In: Schlichting E, editor. Pseudogley and gley - genesis and use of hydromorphic soils: transactions of commissions V and VI of the International Society of Soil Science. Weinheim: Verlag Chemie; 1973. p. 169-79.; Blume, 1988Blume H-P. The fate of iron during soil formation in humid-temperate environments. In: Stucki JM, Goodman BA, Schwertmann U, editors. Iron soils clay minerals. Dordrecht: D. Reidel Publishing Company; 1988. p. 749-77. https://doi.org/10.1007/978-94-009-4007-9_21
https://doi.org/10.1007/978-94-009-4007-...
; Fanning and Fanning, 1989Fanning DS, Fanning MCB. Soil: morphology, genesis, and classification. New York: John Wiley and Sons Inc.; 1989.; Zaidel’man, 2007Zaidel’man FR. Lessivage and its relation to the hydrological regime of soils. Eurasian Soil Sci. 2007;40:115-25. https://doi.org/10.1134/S1064229307020019
https://doi.org/10.1134/S106422930702001...
; Rubinić et al., 2014Rubinić V, Durn G, Husnjak S, Tadej N. Composition, properties and formation of Pseudogley on loess along a precipitation gradient in the Pannonian region of Croatia. Catena. 2014;113:138-49. https://doi.org/10.1016/j.catena.2013.10.003
https://doi.org/10.1016/j.catena.2013.10...
).

Compared with previous studies of soils developed on similar basement rocks on the “Mares de Morros” region (Ab’Sáber, 1970Ab’Sáber AN. Províncias geológicas e domínios morfoclimaticos no Brasil. São Paulo: Geomorfologia; 1970.; Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.; Lani et al., 2001Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61.; Nunes et al., 2001Nunes WAGA, Ker JC, Schaefer CEGR, Fernandes Filho EI, Gomes FH. Relação solo-paisagem-material de origem e genêse de alguns solos no domínio do “Mar de Morro”, Minas Gerais. Rev Bras Cienc Solo. 2001;25:341-54. https://doi.org/10.1590/S0100-06832001000200011
https://doi.org/10.1590/S0100-0683200100...
; Santos et al., 2010Santos AC, Pereira MG, Anjos LHC, Bernini TA, Cooper M, Nummer AR, Francelino MR. Gênese e classificação de solos numa topossequência no ambiente de Mar de Morros do Médio Vale do Paraíba do Sul, RJ. Rev Bras Cienc Solo. 2010;34:1297-314. https://doi.org/10.1590/s0100-06832010000400027
https://doi.org/10.1590/s0100-0683201000...
), in our study, the Al3+ contents were greater and similar to values reported by Gomes (1976)Gomes IA. Oxisols and Inceptisols from gneiss in a subtropical area of Espírito Santo State, Brazil [dissertation]. West Lafayette: Purdue University; 1976. from southern Espírito Santo. These results are explained by the leucocratic nature of the rock and the hydrolysis of minerals such as kaolinite, identified in the XRD patterns, favoring desalination and intense weathering (Loughnan, 1969Loughnan FC. Chemical weathering of the silicate minerals. New York: Elsevier; 1969.; White and Buss, 2014White AF, Buss HL. Natural weathering rates of silicate minerals. In: Turekian K, Holland H, editors. Treatise on geochemistry. 2nd ed. Amsterdam: Elsevier; 2014. p. 115-55. https://doi.org/10.1016/B978-0-08-095975-7.00504-0
https://doi.org/10.1016/B978-0-08-095975...
).

The low TOC content of the samples with low-activity clay explains the positive correlation with CEC, mainly since the negative charges of organic matter derived from dissociation of carboxylic and phenolic H compounds at high pH values. Thus, soils with high organic carbon have a high CEC at pH 7.0; under the natural acid condition, they have a low CECe (Parfitt et al., 1995Parfitt RL, Giltrap DJ, Whitton JS. Contribution of organic matter and clay minerals to the cation exchange capacity of soils. Commun Soil Sci Plan. 1995;26:1343-55. https://doi.org/10.1080/00103629509369376
https://doi.org/10.1080/0010362950936937...
; Ciotta et al., 2003Ciotta MN, Bayer C, Fontoura SMV, Ernani PR, Albuquerque JA. Matéria orgânica e aumento da capacidade de troca de cátions em solo com argila de atividade baixa sob plantio direto. Cienc Rural. 2003;33:1161-4. https://doi.org/10.1590/S0103-84782003000600026
https://doi.org/10.1590/S0103-8478200300...
).

Extremely low P content is consistent with the nature of the leucogranite (CPRM 2007), corroborating previous studies (Ker, 1997Ker JC. Latossolos do Brasil: uma revisão. Geonomos. 1997;5:17-40. https://doi.org/10.18285/geonomos.v5i1.187
https://doi.org/10.18285/geonomos.v5i1.1...
; Lani et al., 2001Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61.; Santos et al., 2010Santos AC, Pereira MG, Anjos LHC, Bernini TA, Cooper M, Nummer AR, Francelino MR. Gênese e classificação de solos numa topossequência no ambiente de Mar de Morros do Médio Vale do Paraíba do Sul, RJ. Rev Bras Cienc Solo. 2010;34:1297-314. https://doi.org/10.1590/s0100-06832010000400027
https://doi.org/10.1590/s0100-0683201000...
). Higher values in the surface horizons are due to organic matter, reducing P adsorption sites in the mineral fraction and increasing P availability (Mesquita Filho and Torrent, 1993Mesquita Filho MV, Torrent J. Phosphate sorption as related to mineralogy of a hydrosequence of soils from the Cerrado region (Brazil). Geoderma. 1993;58:107-23. https://doi.org/10.1016/0016-7061(93)90088-3
https://doi.org/10.1016/0016-7061(93)900...
; Guppy et al., 2005Guppy CN, Menzies NW, Moody PW, Blamey FPC. Competitive sorption reactions between phosphorus and organic matter in soil: a review. Aust J Soil Res. 2005;43:189-202. https://doi.org/10.1071/SR04049
https://doi.org/10.1071/SR04049...
).

Regarding P3 and P4, the higher sand contents (>50 %) led to high P-rem and low adsorption capacity (Table 2). In the clay soils, the predominant clay mineral fraction has pH-dependent charges (van Raij, 1973van Raij B. Determinação de cargas elétricas em solos. Bragantia. 1973;32:171-83. https://doi.org/10.1590/s0006-87051973000100007
https://doi.org/10.1590/s0006-8705197300...
; Parfitt et al., 1995Parfitt RL, Giltrap DJ, Whitton JS. Contribution of organic matter and clay minerals to the cation exchange capacity of soils. Commun Soil Sci Plan. 1995;26:1343-55. https://doi.org/10.1080/00103629509369376
https://doi.org/10.1080/0010362950936937...
; Weber et al., 2005Weber OLS, Chitolina JC, Camargo OA, Alleoni LRF. Cargas elétricas estruturais e variáveis de solos tropicais altamente intemperizados. Rev Bras Cienc Solo. 2005;29:867-73. https://doi.org/10.1590/S0100-06832005000600004
https://doi.org/10.1590/S0100-0683200500...
; Zhu et al., 2016)Zhu X, Zhu Z, Lei X, Yan C. Defects in structure as the sources of the surface charges of kaolinite. Appl Clay Sci. 2016;124-125:127-36. https://doi.org/10.1016/j.clay.2016.01.033
https://doi.org/10.1016/j.clay.2016.01.0...
, enhancing P adsorption at low pH values.

The Ki and Kr ratios were low (Table 3). Similar values have been reported for soils from southern Espírito Santo (Gomes, 1976Gomes IA. Oxisols and Inceptisols from gneiss in a subtropical area of Espírito Santo State, Brazil [dissertation]. West Lafayette: Purdue University; 1976.; Lani et al., 2001Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61.), indicating a kaolinitic/oxidic mineralogical composition, typical of highly weathered soils on acid rocks (Ker, 1997Ker JC. Latossolos do Brasil: uma revisão. Geonomos. 1997;5:17-40. https://doi.org/10.18285/geonomos.v5i1.187
https://doi.org/10.18285/geonomos.v5i1.1...
; Melo et al., 2001Melo VF, Singh B, Schaefer CEGR, Novais RF, Fontes MPF. Chemical and mineralogical properties of kaolinite-rich Brazilian soils. Soil Sci Soc Am J. 2001;65:1324-33. https://doi.org/10.2136/sssaj2001.6541324x
https://doi.org/10.2136/sssaj2001.654132...
).

Soil P3 and P4 showed low levels of Fe2O3 due to current (P4) and past (P3) poor drainage. Although the Pseudogleysol is no longer subjected to waterlogging, its shows evidence of past hydromorphism, with inherited past greyish colors (Kampf and Curi, 2000Kämpf N, Curi N. Óxidos de ferro: Indicadores de ambientes pedogênicos e geoquímicos. Tópicos Cienc Solo. 2000;1:107-38.). The Al2O3/Fe2O3 molecular ratio was greater than 1.80 (Table 3), indicating low contents of Fe oxides in all soils and high Al contents in the parent material (CPRM, 2007).

The Fe2O3 content extracted by DCB (Fed) was consistent with the sulfuric acid data and decreased from the top to the bottom of the topossequence, highlighting that a changing soil moisture regime can lead to Fe losses downslope. These results are consistent with previous studies of topography influence on soil properties (Vidal-Torrado et al., 1999Vidal-Torrado P, Lepsch IF, Castro SS, Cooper M. Pedogênese em uma seqüência Latossolo-Podzólico na borda de um platô na Depressão Periférica Paulista. Rev Bras Cienc Solo. 1999;23:909-21. https://doi.org/10.1590/s0100-06831999000400018
https://doi.org/10.1590/s0100-0683199900...
; Silva et al., 2001Silva MB, Anjos LHC, Pereira MG, Nascimento RAM. Estudo de toposseqüência da baixada litorânea fluminense: efeitos do material de origem e posição topográfica. Rev Bras Cienc Solo. 2001;25:965-76. https://doi.org/10.1590/s0100-06832001000400019
https://doi.org/10.1590/s0100-0683200100...
; Ghidin et al., 2006Ghidin AA, Melo VF, Lima VC, Lima JMJC. Toposseqüência de Latossolos originados de rochas basálticas no Paraná: I. Mineralogia da fração argila. Rev Bras Cienc Solo. 2006;30:293-306. https://doi.org/10.1590/s0100-06832006000200010
https://doi.org/10.1590/s0100-0683200600...
).

Ratio of Fed/Fes can be a proxy for the soil development degree, being higher in weathered soils (Pereira and Anjos, 1999Pereira MG, Anjos LHC. Formas extraíveis de ferro em solos do estado do Rio de Janeiro. Rev Bras Cienc Solo. 1999;23:371-82. https://doi.org/10.1590/s0100-06831999000200020
https://doi.org/10.1590/s0100-0683199900...
; Cornell and Schwertmann, 2003Cornell RM, Schwertmann U. The iron oxides: structure, properties, reactions, occurrences and uses. 2nd ed. Weinheim: Wiley-VHC Verlag GmbH and Co. KGaA; 2003.). It showed a negative correlation with the Feo/Fed ratio (r = 0.70, p<0.01), since Fe-oxides are good pedogenetic indicators (Kampf and Curi, 2000Kämpf N, Curi N. Óxidos de ferro: Indicadores de ambientes pedogênicos e geoquímicos. Tópicos Cienc Solo. 2000;1:107-38.). The Feo/Fed ratio decreased with depth for P3 and P4, which can be explained by the resistance of Al-rich goethites to dissolution upon reduction (Torrent et al., 1987)Torrent J, Schwertmann U, Barron V. The reductive dissolution of synthetic goethite and hematite in dithionite. Clay Miner. 1987;22:329-37. https://doi.org/10.1180/claymin.1987.022.3.07
https://doi.org/10.1180/claymin.1987.022...
. Also, part of the Fe can be assigned to Fe in kaolinite or as Fe-oxides in the coarse fractions (sand and silt), determined by sulfuric acid digestion (Resende et al., 2011)Resende M, Curi N, Ker JC, Rezende SB. Mineralogia de solos brasileiros: interpretação e aplicações. Lavras: Editora UFLA; 2011..

Iron contents extracted by Feo were higher in the surface horizons, indicating the inhibitory effect to Fe-oxide crystallinity exerted by soil organic matter (Schwertmann and Taylor, 1989Schwertmann U, Taylor RM. Iron oxides. In: Dixon JB, Weed SB, editors. Mineral soil environments. 2nd ed. Madison: SSSA Book Series; 1989. p. 379-438.). In addition, the increasing trend in Feo/Fed along the topossequence corroborates the decreasing amount of crystalline Fe oxides (P1 > P2 > P3 > P4) (Table 3), suggesting that increasing hydromorphism downslope accounts for higher contents of low-crystalline Fe oxides, such as ferrihydrite (Vidal-Torrado et al., 1999Vidal-Torrado P, Lepsch IF, Castro SS, Cooper M. Pedogênese em uma seqüência Latossolo-Podzólico na borda de um platô na Depressão Periférica Paulista. Rev Bras Cienc Solo. 1999;23:909-21. https://doi.org/10.1590/s0100-06831999000400018
https://doi.org/10.1590/s0100-0683199900...
; Silva et al., 2001Silva MB, Anjos LHC, Pereira MG, Nascimento RAM. Estudo de toposseqüência da baixada litorânea fluminense: efeitos do material de origem e posição topográfica. Rev Bras Cienc Solo. 2001;25:965-76. https://doi.org/10.1590/s0100-06832001000400019
https://doi.org/10.1590/s0100-0683200100...
; Park and Burt, 2002Park SJ, Burt TP. Identification and characterization of pedogeomorphological processes on a hillslope. Soil Sci Soc Am J. 2002;66:1897-910. https://doi.org/10.2136/sssaj2002.1897
https://doi.org/10.2136/sssaj2002.1897...
; Ghidin et al., 2006)Ghidin AA, Melo VF, Lima VC, Lima JMJC. Toposseqüência de Latossolos originados de rochas basálticas no Paraná: I. Mineralogia da fração argila. Rev Bras Cienc Solo. 2006;30:293-306. https://doi.org/10.1590/s0100-06832006000200010
https://doi.org/10.1590/s0100-0683200600...
.

The Feo/Fed ratio was lower in P3 (Pseudogleysol) compared to P4 (Gleissolo), showing that the signs of past hydromorphism process are retained in the well-drained terraces (Table 3). Since the Gleissolo is subject to redox conditions that lead to the formation of low-crystallinity and/or amorphous Fe-phases (Schwertmann, 1985Schwertmann U. The effect of pedogenic environments on iron oxide minerals. In: Stewart BA, editor. Advances in soil science. New York: Springer-Verlag; 1985. v. 1. p. 171-200.; McBride, 1994McBride MB. Environmental chemistry of soils. New York: Oxford University Press; 1994.), these values decreased towards the soil bottom, near the water table (Table 3).

The overall mineralogy (>> Ka >> Gb, Gt, Hm, and HIV) is in agreement with most soil sequences so far studied in the Atlantic Forest (Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.; Anjos et al., 1988Anjos LH, Fernandes MR, Pereira MG, Franzmeier DP. Landscape and pedogenesis of an Oxisol-Inceptisol-Ultisol sequence in southeastern Brazil. Soil Sci Soc Am J. 1988;62:1651-8. https://doi.org/10.2136/sssaj1998.03615995006200060024x
https://doi.org/10.2136/sssaj1998.036159...
; Nunes et al., 2000)Nunes WAGA, Schaefer CER, Ker JC, Fernandes Filho EI. Caracterização micropedológica de alguns solos da Zona da Mata Mineira. Rev Bras Cienc Solo. 2000;24:103-15. https://doi.org/10.1590/S0100-06832000000100013
https://doi.org/10.1590/S0100-0683200000...
. Gomes (1976)Gomes IA. Oxisols and Inceptisols from gneiss in a subtropical area of Espírito Santo State, Brazil [dissertation]. West Lafayette: Purdue University; 1976. and Lani et al. (2001)Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61. also found the same secondary minerals in soils developed from leucogranites, from southern Espírito Santo, basically composed of quartz, K-feldspars, plagioclase, and minor amounts of biotite and amphibole (CPRM, 2007).

Compared to P2, the well-drained P1 soil at the summit has a more uniform water retention profile and greater moisture levels, suggested by yellowish colors, indicating the dominance of goethite (Curi and Franzmeier, 1987Curi N, Franzmeier DP. Effect of parent rocks on chemical and mineralogical properties of some Oxisols in Brazil. Soil Sci Soc Am J. 1987;51:153-8. https://doi.org/10.2136/sssaj1987.03615995005100010033x
https://doi.org/10.2136/sssaj1987.036159...
; Kampf and Curi, 2000Kämpf N, Curi N. Óxidos de ferro: Indicadores de ambientes pedogênicos e geoquímicos. Tópicos Cienc Solo. 2000;1:107-38.; Corrêa et al., 2008aCorrêa MM, Ker JC, Barrón V, Fontes MPF, Torrent J, Curi N. Caracterização de óxidos de ferro de solos do ambiente tabuleiros costeiros. Rev Bras Cienc Solo. 2008a;32:1017-31. https://doi.org/10.1590/s0100-06832008000300011
https://doi.org/10.1590/s0100-0683200800...
). This evidence may be noticed by the increased intensity relative to the directions 110 and 130 of goethite (Figure 3) and more yellowish colors in P1 (7.5YR) than P2 (Table 1) in all diagnostic horizons evaluated.

The formation of hematite and goethite is consistent with humid climate conditions and low amounts of Fe in the parent material (leucogranite), as indicated by Fes and Fed values (Table 3). The Feo/Fed ratio and Kr (Table 3) along the topographic gradient were lower in soils at the summit (P1) in relation to the soil of the back-slope (P2), so that poorly crystallized Fe oxides increased downslope (Schwertmann and Kämpf, 1983Schwertmann U, Kämpf N. Óxidos de ferro jovens em ambientes pedogenéticos brasileiros. Rev Bras Cienc Solo. 1983;7:251-5.; Curi and Franzmeier, 1987Curi N, Franzmeier DP. Effect of parent rocks on chemical and mineralogical properties of some Oxisols in Brazil. Soil Sci Soc Am J. 1987;51:153-8. https://doi.org/10.2136/sssaj1987.03615995005100010033x
https://doi.org/10.2136/sssaj1987.036159...
; Kampf and Curi, 2000Kämpf N, Curi N. Óxidos de ferro: Indicadores de ambientes pedogênicos e geoquímicos. Tópicos Cienc Solo. 2000;1:107-38.), as corroborated by the lower intensities of hematite and goethite peaks in P2 relative to P1 (Figure 3). The Fed/Fes ratio was higher than 0.69 in all horizons of P1 and P2, corroborating the deep weathered nature of these soils (Schwertmann and Kämpf, 1983Schwertmann U, Kämpf N. Óxidos de ferro jovens em ambientes pedogenéticos brasileiros. Rev Bras Cienc Solo. 1983;7:251-5.; Cunha et al., 2005Cunha P, Marques Júnior J, Curi N, Pereira GT, Lepsch IF. Superfícies geomórficas e atributos de Latossolos em uma seqüência arenítico-basáltica da região de Jaboticabal (SP). Rev Bras Cienc Solo. 2005;29:81-90. https://doi.org/10.1590/S0100-06832005000100009
https://doi.org/10.1590/S0100-0683200500...
). In both soils, with evidence of current or past hydromorphism (P3 and P4), the Fed/Fes ratio decreased with depth (Table 3).

On the other hand, the presence of 2:1 minerals (vermiculite/HIV) in the lower parts of the landscape indicates moderate drainage, maintaining a high Si activity in the soil solution (Dixon, 1989Dixon JB. Kaolin and serpentine group minerals. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 467-525), despite the low Ki values (Table 3 ). Also, these 2:1 minerals (vermiculite and HIV) can be formed via chemical weathering of feldspars in the silt fraction, as suggested by Vidal-Torrado et al. (1999Vidal-Torrado P, Lepsch IF, Castro SS, Cooper M. Pedogênese em uma seqüência Latossolo-Podzólico na borda de um platô na Depressão Periférica Paulista. Rev Bras Cienc Solo. 1999;23:909-21. https://doi.org/10.1590/s0100-06831999000400018
https://doi.org/10.1590/s0100-0683199900...
a,b). The occurrence of vermiculite and HIV in highly weathered soils has also been observed by Gomes (1976)Gomes IA. Oxisols and Inceptisols from gneiss in a subtropical area of Espírito Santo State, Brazil [dissertation]. West Lafayette: Purdue University; 1976. and Lani et al. (2001)Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61. in soils from southern Espírito Santo as well as from elsewhere in Brazil (Moura Filho, 1970Moura Filho W. Studies of a Latosol Roxo (Eutrustox) in Brazil : clay mineralogy, micromorphology effect on ion release, and phosphate reactions [Thesis]. Raleigh: North Caroline State University; 1970.; Alleoni and Camargo, 1995Alleoni LRF, Camargo OA. Óxidos de ferro e de alumínio e a mineralogia da fração argila desferrificada de Latossolos ácricos. Sci Agric. 1995;52:416-21. https://doi.org/10.1590/s0103-90161995000300002
https://doi.org/10.1590/s0103-9016199500...
).

Increasing kaolinite and decreasing gibbsite (Table 4) downslope the topographic gradient are controlled by local soil drainage (Curi and Franzmeier, 1987Curi N, Franzmeier DP. Effect of parent rocks on chemical and mineralogical properties of some Oxisols in Brazil. Soil Sci Soc Am J. 1987;51:153-8. https://doi.org/10.2136/sssaj1987.03615995005100010033x
https://doi.org/10.2136/sssaj1987.036159...
; Kampf and Curi, 2000Kämpf N, Curi N. Óxidos de ferro: Indicadores de ambientes pedogênicos e geoquímicos. Tópicos Cienc Solo. 2000;1:107-38.; Corrêa et al., 2008 a,b). Higher leaching at the upland soil (P1) reduces Si activity in the solution, leading to the formation of gibbsite (Norfleet et al., 1993Norfleet ML, Karathanasis AD, Smith BR. Soil solution composition relative to mineral distribution in Blue Ridge Mountain soils. Soil Sci Soc Am J. 1993;57:1375-80. https://doi.org/10.2136/sssaj1993.03615995005700050035x
https://doi.org/10.2136/sssaj1993.036159...
; Sommer et al., 2006Sommer M, Kaczorek D, Kuzyakov Y, Breuer J. Silicon pools and fluxes in soils and landscapes - a review. J Plant Nutr Soil Sci. 2006;169:310-29. https://doi.org/10.1002/jpln.200521981
https://doi.org/10.1002/jpln.200521981...
; Buol et al., 2011Buol SW, Southard RJ, Graham RC, McDaniel PA. Soil genesis and classification. 6th ed. John Wiley & Sons; 2011.), whereas some Si mobility and accumulation in the lower parts of the topossequence helps the maintenance, or neoformation, of kaolinite (Curi and Franzmeier, 1987Curi N, Franzmeier DP. Effect of parent rocks on chemical and mineralogical properties of some Oxisols in Brazil. Soil Sci Soc Am J. 1987;51:153-8. https://doi.org/10.2136/sssaj1987.03615995005100010033x
https://doi.org/10.2136/sssaj1987.036159...
; Dixon, 1989Dixon JB. Kaolin and serpentine group minerals. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 467-525). The TGA analysis indicated its abundance at the summit and back-slope profiles - with 83.78 and 75.40 dag kg-1, respectively (Table 4). Soils at lower parts of the landscape (P3 and P4) had contents of up to 94.42 dag kg-1, due to the low Fe oxides contents caused by hydromorphism in this sector. This fact is corroborated by the high values of the Feo/Fed ratio at P3 and P4, indicating the formation of low-crystallinity Fe oxides (Kampf and Curi, 2000Kämpf N, Curi N. Óxidos de ferro: Indicadores de ambientes pedogênicos e geoquímicos. Tópicos Cienc Solo. 2000;1:107-38.).

Evaluating the HB index (Hughes and Brown, 1979Hughes JC, Brown G. A crystallinity index for soil kaolins and its relation to parent rock, climate and soil maturity. J Soil Sci. 1979;30:557-63. https://doi.org/10.1111/j.1365-2389.1979.tb01009.x
https://doi.org/10.1111/j.1365-2389.1979...
) along the topographic gradient, decreasing values, P1 < P2 < P3 < P4 were observed (Table 4), indicating that the structural disorder of kaolinite decreases towards the bottom. If we compare this with standards values, these range from 28.7 to KGA 2 with the high structural disorder to very high values, symbolized by the infinity symbol (Table 4), for KGA 1b and KAm having a lower structural disorder. Therefore, the lower crystallinity index indicates materials with a high structural disorder. The values reported are consistent with those observed by several other authors (Ker, 1995Ker JC. Mineralogia, sorção e dessorção de fosfato, magnetização e elementos traços de Latossolos do Brasil [tese]. Viçosa: Universidade Federal de Viçosa; 1995.; Melo et al., 2002Melo VF, Schaefer CEGR, Singh B, Novais RF, Fontes MPF. Propriedades químicas e cristalográficas da caulinita e dos óxidos de ferro em sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo. Rev Bras Cienc Solo. 2002;26:53-64. https://doi.org/10.1590/s0100-06832002000100006
https://doi.org/10.1590/s0100-0683200200...
; Corrêa et al., 2008bCorrêa MM, Ker JC, Barrón V, Torrent J, Fontes MPF, Curi N. Propriedades cristalográficas de caulinitas de solos do ambiente Tabuleiros Costeiros, Amazônia e Recôncavo Baiano. Rev Bras Cienc Solo. 2008b;32:1857-72. https://doi.org/10.1590/s0100-06832008000500007
https://doi.org/10.1590/s0100-0683200800...
) in kaolinites of Latossolos related of Brazilian soils, as well as by Hughes and Brown (1979)Hughes JC, Brown G. A crystallinity index for soil kaolins and its relation to parent rock, climate and soil maturity. J Soil Sci. 1979;30:557-63. https://doi.org/10.1111/j.1365-2389.1979.tb01009.x
https://doi.org/10.1111/j.1365-2389.1979...
and Singh and Gilkes (1992)Singh B, Gilkes RJ. Properties of soil kaolinites from south-western Australia. J Soil Sci. 1992;43:645-67. https://doi.org/10.1111/j.1365-2389.1992.tb00165.x
https://doi.org/10.1111/j.1365-2389.1992...
for humid tropical regions worldwide.

Comparing the R2 crystallinity index (Liétard, 1977Liétard O. Contribution a l’etude des proprietes physicochimiques, cristallographiques et morphologiques des kaolins [thesis]. Nancy: University of Nancy; 1977.) and FWHM (Klug and Alexander, 1974Klug HP, Alexander LE. X-ray diflraction procedures for polycrystalline and amorphous materials. 2nd ed. New York: John Wiley & Sons; 1974.) (Table 4) with the values obtained from kaolinite standards, all soils contained kaolinites with a high structural disorder (Figure 5). The HB index and the FWHM were highly correlated (r = 0.95; p<0.01), indicating a reduction in structural disorder downwards the topossequence (Table 4). This correlation was not observed for the R2 index, indicating the low sensitivity of this index for kaolinite from deeply weathered soils, with a high degree of structural disorder.

The HB index was negatively correlated with of Fes (r = 0.91, p<0.01) and Fed amounts r = 0.92, p<0.01) and positively with the FWHM (r = 0.84 and 0.86, p<0.01). This suggests that higher Fe contents are associated with an increasing structural disorder of kaolinite (Mestdagh et al., 1980Mestdagh MM, Vielvoye L, Herbillon AJ. Iron in kaolinite: II. The relationship between kaolinite crystallinity and iron content. Clay Miner. 1980;15:1-13. https://doi.org/10.1180/claymin.1980.015.1.01
https://doi.org/10.1180/claymin.1980.015...
; Fysh, 1983Fysh SA, Cashion JD, Clark PE. Mössbauer effect studies of iron in kaolin: I. Structural iron. Clay Clay Miner. 1983;31:285-92. https://doi.org/10.1346/CCMN.1983.0310406
https://doi.org/10.1346/CCMN.1983.031040...
; Brindley and Kao, 1986Brindley GW, Kao C-C, Harrison JL, Lipsicar M, Raythatha R. Relation between structural disorder and other characteristics of kaolinites and dickites. Clay Clay Miner. 1986;34:239-49. https://doi.org/10.1346/ccmn.1986.0340303
https://doi.org/10.1346/ccmn.1986.034030...
; Melo et al., 2002Melo VF, Schaefer CEGR, Singh B, Novais RF, Fontes MPF. Propriedades químicas e cristalográficas da caulinita e dos óxidos de ferro em sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo. Rev Bras Cienc Solo. 2002;26:53-64. https://doi.org/10.1590/s0100-06832002000100006
https://doi.org/10.1590/s0100-0683200200...
; Iriarte et al., 2005Iriarte I, Petit S, Huertas FJ, Fiore S, Grauby O, Decarreau A, Linares J. Synthesis of kaolinite with a high level of Fe3+ for A1 substitution. Clay Clay Miner. 2005;53:1-10. https://doi.org/10.1346/CCMN.2005.0530101
https://doi.org/10.1346/CCMN.2005.053010...
; Ghidin et al., 2006)Ghidin AA, Melo VF, Lima VC, Lima JMJC. Toposseqüência de Latossolos originados de rochas basálticas no Paraná: I. Mineralogia da fração argila. Rev Bras Cienc Solo. 2006;30:293-306. https://doi.org/10.1590/s0100-06832006000200010
https://doi.org/10.1590/s0100-0683200600...
. This in further corroborated by the Fed contents in standard kaolinite (KGa 2, KGa 1b, and Kam equal to 0.12, 0.03, and 0.02 dag kg-1, respectively), with a progressively greater structural disorder with increasing Fed amounts (Table 4); this finding agrees with the previous observation of Singh and Gilkes (1992)Singh B, Gilkes RJ. Properties of soil kaolinites from south-western Australia. J Soil Sci. 1992;43:645-67. https://doi.org/10.1111/j.1365-2389.1992.tb00165.x
https://doi.org/10.1111/j.1365-2389.1992...
in Australian soils.

Structural disorder of kaolinite showed no correlation with soil chemical and physical properties. This contrasts with reports of Murray and Lyons (1959)Murray HH, Lyons SC. Further correlations of kaolinite crystallinity with chemical and physical properties. Clay Clay Miner. 1959;8:11-7. https://doi.org/10.1016/B978-0-08-009351-2.50008-8
https://doi.org/10.1016/B978-0-08-009351...
and (Singh and Gilkes, 1992Singh B, Gilkes RJ. Properties of soil kaolinites from south-western Australia. J Soil Sci. 1992;43:645-67. https://doi.org/10.1111/j.1365-2389.1992.tb00165.x
https://doi.org/10.1111/j.1365-2389.1992...
), who showed higher CEC for kaolinites with a higher structural disorder. This may be explained by methodological differences for CEC determination; previous studies used the clay fraction for CEC determination, whereas in our study, the CEC was calculated for the <2 mm soil (fine earth).

Maximum dehydroxylation temperature of kaolinite (Table 4) for all soils was positively correlated with the HB crystallinity index (r = 0.98, p<0.01) and negatively with the FWHM (r = 0.97, p<0.01). This fact is attributed to the small crystal size and the high structural disorder of kaolinite (Melo et al., 2001Melo VF, Singh B, Schaefer CEGR, Novais RF, Fontes MPF. Chemical and mineralogical properties of kaolinite-rich Brazilian soils. Soil Sci Soc Am J. 2001;65:1324-33. https://doi.org/10.2136/sssaj2001.6541324x
https://doi.org/10.2136/sssaj2001.654132...
; Ghidin et al., 2006)Ghidin AA, Melo VF, Lima VC, Lima JMJC. Toposseqüência de Latossolos originados de rochas basálticas no Paraná: I. Mineralogia da fração argila. Rev Bras Cienc Solo. 2006;30:293-306. https://doi.org/10.1590/s0100-06832006000200010
https://doi.org/10.1590/s0100-0683200600...
, consistent with negative correlations with Fes (r = 0.97; p<0.01) and Fed (r = 0.99, p<0.01). The presence of structural Fe promotes the structural disorder and reduces the crystal size, resulting in a lower temperature for kaolinite dehydroxylation (Singh and Gilkes, 1992)Singh B, Gilkes RJ. Properties of soil kaolinites from south-western Australia. J Soil Sci. 1992;43:645-67. https://doi.org/10.1111/j.1365-2389.1992.tb00165.x
https://doi.org/10.1111/j.1365-2389.1992...
because the thermal stability of Fe-structural OH groups is lower than that of the Al-OH groups in the octahedral sheet of kaolinite.

The described microstructure agrees with the morphological description of the structure at field scale and represents the common micropedological syndrome of most Latossolos Vermelho-Amarelo developed on crystalline rocks of the “Mares de Morros” landscape in southeastern Brazil (Corrêa, 1984Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.; Carvalho Filho, 1989Carvalho Filho A. Caracterização mineralógica, química e física de solos de duas unidades da paisagem do planalto de Viçosa [dissertação]. Viçosa: Universidade Federal de Viçosa; 1989.; Nunes et al., 2001Nunes WAGA, Ker JC, Schaefer CEGR, Fernandes Filho EI, Gomes FH. Relação solo-paisagem-material de origem e genêse de alguns solos no domínio do “Mar de Morro”, Minas Gerais. Rev Bras Cienc Solo. 2001;25:341-54. https://doi.org/10.1590/S0100-06832001000200011
https://doi.org/10.1590/S0100-0683200100...
; Schaefer, 2001Schaefer CER. Brazilian Latosols and their B horizon microstructure as long-term biotic constructs. Aust J Soil Res. 2001;39:909-26. https://doi.org/10.1071/SR00093
https://doi.org/10.1071/SR00093...
). Microped structure, the b-fabric, and most pedofeatures are fully consistent with the “oxic syndrome” of Buol and Eswaran (1978)Buol SW, Eswaran H. The micromorphological of Oxisols. In: Proceedings of the 5th International Working Meeting on Soil Micromorphology, Granada, Spain, 1977. Granada; 1978. p. 325-47., further corroborated by Stoops and Buol (1985)Stoops GJ, Buol SW. Micromorphology of Oxisols. In: Douglas LA, Thompson ML, editors. Soil micromorphology and soil classification. Madison: Soil Science Society of America; 1985. p. 105-19., suggesting a polycyclic genesis on colluvial parent material (Muggler and Buurman, 1997Muggler CC, Buurman P. Micromorphological aspects of polygenetic soils developed on phyllitic rocks in Minas Gerais, Brazil. In: Shoba S, Gerasimova M, Miedema R, editors. Soil micromorphology: studies on soil diversity, diagnostics and dynamics. Wageningem, International Society of Soil Science; 1997. p. 129-38.).

In subsurface Bw horizons of P1 and P2 (Figure 6), the pedality degree was enhanced, with a strong medium-sized granular microstructure, typical of B horizons of Brazilian Latossolos. Recently, different studies have investigated the origin of the granular structure of Latossolos, either emphasizing a basic physicochemical interaction between kaolinite and Fe and Al oxi-hydroxides under extreme Si leaching conditions (Eswaran and Daud, 1980Eswaran H, Daud N. A Scanning electron microscopy evaluation of the fabric and mineralogy of some soils from Malaysia. Soil Sci Soc Am J. 1980;44:855-61. https://doi.org/10.2136/sssaj1980.03615995004400040040x
https://doi.org/10.2136/sssaj1980.036159...
; Santos et al., 1989Santos MCD, Ribeiro MR, Mermut AR. Submicroscopy of clay microaggregates in an Oxisol from Pernambuco, Brazil. Soil Sci Soc Am J. 1989;53:1895-901. https://doi.org/10.2136/sssaj1989.03615995005300060047x
https://doi.org/10.2136/sssaj1989.036159...
) or intense, long-term biological activity, especially by termites (Rezende, 1980Rezende SB. Geomorphology, mineralogy and genesis of four soils on gneiss in southeastern Brazil [thesis]. West Lafayette: Purdue University; 1980.; Schaefer, 2001Schaefer CER. Brazilian Latosols and their B horizon microstructure as long-term biotic constructs. Aust J Soil Res. 2001;39:909-26. https://doi.org/10.1071/SR00093
https://doi.org/10.1071/SR00093...
). The presence of abundant termite fecal pellets with high porosity, contributing to the intense desilication of these soils, suggest microstructure formation, as reported by Lani et al. (2001)Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61. in soils from southern Espírito Santo.

In both Bw horizons, minute Fe concretions, charcoal particles, reddish hematite fragments, and fecal pellets were dispersed in the clay micromass, where easily weatherable primary minerals were completely absent. Titanium minerals (ilmenite), gibbsite nodules, Fe-impregnated lithorelics, and abundant biological channels were observed in the Bw2 horizon of P2. All features above support the observed desilication of these upland soils, favoring the formation of gibbsite (Hsu, 1989Hsu PH. Aluminum hydroxides and oxyhydroxides. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 331-78.).

The A2 and C2 horizons of P3 and A and Cg2 of P4 (Figure 7) had a coarse fraction dominated by fractured quartz grains, without Fe-coatings or infillings along fractures and with many poorly connected voids and weak to absent pedality. The single grain structure at P2 is associated with the complete absence of easily weatherable primary minerals, with rare charcoal micro-fragments and ferruginized roots remaining. A general bleaching process was clearly observed in the two profiles (P3 and P4), forming depleting, reducing zones with a greyish clayey micromass (10YR) at the pedoplasmation front, where the soil forming process is active (Stoops and Schaefer, 2010Stoops G, Schaefer CEGR. Pedoplasmation: formation of soil material. In: Stoops G, Marcelino V, Mees F, editors. Interpretation of micromorphological features of soils and regoliths. Amsterdam: Elsevier; 2010. p. 69-79.). This corresponds to a monic (c/f) related distribution pattern.

Pedogenesis under hydromorphic conditions at P3 and P4 profiles has led to the massive and compact structure at all scales. This is consistent with the macro-morphological description at the field scale, as postulated by previous studies (Curmi et al., 1993aCurmi P, Soulier A, Trolard F. Forms of iron oxides in acid hydromorphic soil environments. Morphology and characterization by selective dissolution. In: Ringrose-Voase AJ, Humphreys GS, editors. Soil micromorpohlogy: studies in management and genesis. Amsterdam: Elsevier; 1993. p. 141-8.,bCurmi P, Widiatmaka, Pellerin J, Ruellan A. Saprolite influence on formation of well-drained and hydromorphic horizons in an acid soil system as determined by structural analysis. In: Ringrose-Voase AJ, Humphreys GS, editors. Soil micromorpohlogy: studies in management and genesis. Amsterdam: Elsevier; 1993. p. 133-40.; 1993bCurmi P, Widiatmaka, Pellerin J, Ruellan A. Saprolite influence on formation of well-drained and hydromorphic horizons in an acid soil system as determined by structural analysis. In: Ringrose-Voase AJ, Humphreys GS, editors. Soil micromorpohlogy: studies in management and genesis. Amsterdam: Elsevier; 1993. p. 133-40.; Vepraskas et al., 1993Vepraskas MJ, Wilding LP, Drees LR. Aquic conditions for Soil Taxonomy: concepts, soil morphology and micromorphology. In: Ringrose-Voase AJ, Humphreys GS, editors. Soil micromorpohlogy: studies in management and genesis. Amsterdam: Elsevier; 1993. p. 117-31.).

CONCLUSIONS

Soils from the hilly Atlantic Forest zone of the Alegre river basin developed from leucogranites indicate that they were formed from homogeneous pre-weathered saprolite. Soils on past or present floodplain/terraces are, despite the depositional environment, highly weathered regardless of past or present hydromorphism. This highlights that erosion and sedimentation acted upon a deeply weathered regolith mantle, with limited contribution of fresh, little-weathered materials, so that Quaternary floodplains are also nutrient-depleted, having a similar source.

Clay mineralogy is composed of mixed kaolinite (dominant) and gibbsite in all soils, with minor contents of Fe oxides (hematite and goethite), only present in the upland Latossolos (Acrudox) (P1 and P2), controlled by the dynamics of Si and Al in the system. Traces of 2:1 minerals (vermiculite and HIV) were identified in the back-slope (P2) and low-lying soils at the toe-slope/lower part of the landscape (P3 and P4), possibly due to resilication downslope.

Kaolinite of all soils had a high structural disorder, influenced by the weathering degree conditions of this tropical environment, neoformation, and the possible presence of structural Fe, to be confirmed by further studies.

The micromorphological properties indicate a strong composite micro-granular (microped) microstructure in a weak sub-angular blocky structure, with no evidences of illuviation, at the well-drained upland Latossolo (Oxisol) domain. It changes into the lowland “hydromorphic” domain, with redoximorphic degradation features such as Fe-impregnating hypocoatings, clay/Fe depletions (bleached zones, albans), and reduced matrices (low chroma). Hence, the “oxic” (Latosolic) microped structure is not related to changes in clay mineralogy and closely associated with aged soils of well-drained slopes.

The presence of well-preserved, inactive redoximorphic features in the Pseudogleysol, now well-drained, suggests that paleogleying is not reverted to a re-oxidized matrix when the soil parent material has low Fe contents. Destruction or coalescence of microaggregates are associated with this intense Fe removal, corroborating a degradation process leading to the degradation and collapse of the “Latosolic” microstructure and resulting in massive structure development.

REFERENCES

  • Ab’Sáber A. Os domínios de natureza no Brasil: potencialidades paisagísticas. 7. ed. São Paulo: Ateliê Editorial; 2012.
  • Ab’Sáber AN. Províncias geológicas e domínios morfoclimaticos no Brasil. São Paulo: Geomorfologia; 1970.
  • Albuquerque Filho MR, Muggler CC, Schaefer CEGR, Ker JC, Santos FC. Solos com morfologia latossólica e caráter câmbico na região de Governador Valadares, médio Rio Doce, Minas Gerais: gênese e micromorfologia. Rev Bras Cienc Solo. 2008;32:259-70. https://doi.org/10.1590/S0100-06832008000100025
    » https://doi.org/10.1590/S0100-06832008000100025
  • Alleoni LRF, Camargo OA. Óxidos de ferro e de alumínio e a mineralogia da fração argila desferrificada de Latossolos ácricos. Sci Agric. 1995;52:416-21. https://doi.org/10.1590/s0103-90161995000300002
    » https://doi.org/10.1590/s0103-90161995000300002
  • Alvares CA, Stape JL, Sentelhas PC, Gonçalves JLM, Sparovek G. Köppen’s climate classification map for Brazil. Meteorol Z. 2013;22:711-28. https://doi.org/10.1127/0941-2948/2013/0507
    » https://doi.org/10.1127/0941-2948/2013/0507
  • Alvarez V VH, Novais RF, Dias LE, Oliveira JA. Determinação e uso do fósforo remanescente. Bol Inf Soc Bras Cienc Solo. 2000;25:27-32.
  • Anjos LH, Fernandes MR, Pereira MG, Franzmeier DP. Landscape and pedogenesis of an Oxisol-Inceptisol-Ultisol sequence in southeastern Brazil. Soil Sci Soc Am J. 1988;62:1651-8. https://doi.org/10.2136/sssaj1998.03615995006200060024x
    » https://doi.org/10.2136/sssaj1998.03615995006200060024x
  • Aparicio P, Galán E, Ferrell RE. A new kaolinite order index based on XRD profile fitting. Clay Miner. 2006;41:811-7. https://doi.org/10.1180/0009855064140220
    » https://doi.org/10.1180/0009855064140220
  • Blume H-P. The fate of iron during soil formation in humid-temperate environments. In: Stucki JM, Goodman BA, Schwertmann U, editors. Iron soils clay minerals. Dordrecht: D. Reidel Publishing Company; 1988. p. 749-77. https://doi.org/10.1007/978-94-009-4007-9_21
    » https://doi.org/10.1007/978-94-009-4007-9_21
  • Brindley GW, Kao C-C, Harrison JL, Lipsicar M, Raythatha R. Relation between structural disorder and other characteristics of kaolinites and dickites. Clay Clay Miner. 1986;34:239-49. https://doi.org/10.1346/ccmn.1986.0340303
    » https://doi.org/10.1346/ccmn.1986.0340303
  • Buol SW, Eswaran H. The micromorphological of Oxisols. In: Proceedings of the 5th International Working Meeting on Soil Micromorphology, Granada, Spain, 1977. Granada; 1978. p. 325-47.
  • Buol SW, Southard RJ, Graham RC, McDaniel PA. Soil genesis and classification. 6th ed. John Wiley & Sons; 2011.
  • Buurman P. Palaeosols in the Reading Beds (Paleocene) of Alum Bay, Isle of Wight, U.K. Sedimentology. 1980;27:593-606. https://doi.org/10.1111/j.1365-3091.1980.tb01649.x
    » https://doi.org/10.1111/j.1365-3091.1980.tb01649.x
  • Camargo MN, Klemt E, Kauffman JH. Classificação de solos usada em levantamento pedológico no Brasil. Bol Inf Soc Bras Cienc Solo. 1987;12:11-33.
  • Carvalho Filho A. Caracterização mineralógica, química e física de solos de duas unidades da paisagem do planalto de Viçosa [dissertação]. Viçosa: Universidade Federal de Viçosa; 1989.
  • Childs CW. Field tests for ferrous iron and ferric-organic complexes (on exchange sites or in water-soluble forms) in soils. Aust J Soil Res. 1981;19:175-80. https://doi.org/10.1071/SR9810175
    » https://doi.org/10.1071/SR9810175
  • Ciotta MN, Bayer C, Fontoura SMV, Ernani PR, Albuquerque JA. Matéria orgânica e aumento da capacidade de troca de cátions em solo com argila de atividade baixa sob plantio direto. Cienc Rural. 2003;33:1161-4. https://doi.org/10.1590/S0103-84782003000600026
    » https://doi.org/10.1590/S0103-84782003000600026
  • Cornell RM, Schwertmann U. The iron oxides: structure, properties, reactions, occurrences and uses. 2nd ed. Weinheim: Wiley-VHC Verlag GmbH and Co. KGaA; 2003.
  • Corrêa GF. Modelo de evolução e mineralogia da fração argila de solos do planalto de Viçosa, MG [dissertação]. Viçosa: Universidade Federal de Viçosa; 1984.
  • Corrêa MM, Ker JC, Barrón V, Fontes MPF, Torrent J, Curi N. Caracterização de óxidos de ferro de solos do ambiente tabuleiros costeiros. Rev Bras Cienc Solo. 2008a;32:1017-31. https://doi.org/10.1590/s0100-06832008000300011
    » https://doi.org/10.1590/s0100-06832008000300011
  • Corrêa MM, Ker JC, Barrón V, Torrent J, Fontes MPF, Curi N. Propriedades cristalográficas de caulinitas de solos do ambiente Tabuleiros Costeiros, Amazônia e Recôncavo Baiano. Rev Bras Cienc Solo. 2008b;32:1857-72. https://doi.org/10.1590/s0100-06832008000500007
    » https://doi.org/10.1590/s0100-06832008000500007
  • Cunha P, Marques Júnior J, Curi N, Pereira GT, Lepsch IF. Superfícies geomórficas e atributos de Latossolos em uma seqüência arenítico-basáltica da região de Jaboticabal (SP). Rev Bras Cienc Solo. 2005;29:81-90. https://doi.org/10.1590/S0100-06832005000100009
    » https://doi.org/10.1590/S0100-06832005000100009
  • Curi N, Franzmeier DP. Effect of parent rocks on chemical and mineralogical properties of some Oxisols in Brazil. Soil Sci Soc Am J. 1987;51:153-8. https://doi.org/10.2136/sssaj1987.03615995005100010033x
    » https://doi.org/10.2136/sssaj1987.03615995005100010033x
  • Curmi P, Soulier A, Trolard F. Forms of iron oxides in acid hydromorphic soil environments. Morphology and characterization by selective dissolution. In: Ringrose-Voase AJ, Humphreys GS, editors. Soil micromorpohlogy: studies in management and genesis. Amsterdam: Elsevier; 1993. p. 141-8.
  • Curmi P, Widiatmaka, Pellerin J, Ruellan A. Saprolite influence on formation of well-drained and hydromorphic horizons in an acid soil system as determined by structural analysis. In: Ringrose-Voase AJ, Humphreys GS, editors. Soil micromorpohlogy: studies in management and genesis. Amsterdam: Elsevier; 1993. p. 133-40.
  • Dixon JB. Kaolin and serpentine group minerals. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 467-525
  • Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise de solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011.
  • Empresa Brasileira de Pesquisa Agropecuária - Embrapa. Levantamento de reconhecimentos de solos do estado do Espírito Santo. Rio de Janeiro: Serviço Nacional de Levantamento e Conservação de Solos; 1978. (Boletim técnico, 45).
  • Eswaran H, Daud N. A Scanning electron microscopy evaluation of the fabric and mineralogy of some soils from Malaysia. Soil Sci Soc Am J. 1980;44:855-61. https://doi.org/10.2136/sssaj1980.03615995004400040040x
    » https://doi.org/10.2136/sssaj1980.03615995004400040040x
  • Fanning DS, Fanning MCB. Soil: morphology, genesis, and classification. New York: John Wiley and Sons Inc.; 1989.
  • Ferreira MM, Fernandes B, Curi N. Mineralogia da fração argila e estrutura de Latossolos da região sudeste do Brasil. Rev Bras Cienc Solo. 1999;23:507-14. https://doi.org/10.1590/S0100-06831999000300003
    » https://doi.org/10.1590/S0100-06831999000300003
  • Fitzpatrick EA. The micromorphology of soils. In: Fitzpatrick EA, editor. Micromorphology of soils. Dordrecht: Springer; 1984. p. 331-57.
  • Food and Agriculture Organization of the United Nations - FAO. Guidelines for soil description. 4th ed. rev. Rome: FAO. 2006 [Accessed on May 1 2017]. Available at: http://www.fao.org/docrep/019/a0541e/a0541e.pdf
    » http://www.fao.org/docrep/019/a0541e/a0541e.pdf
  • Fysh SA, Cashion JD, Clark PE. Mössbauer effect studies of iron in kaolin: I. Structural iron. Clay Clay Miner. 1983;31:285-92. https://doi.org/10.1346/CCMN.1983.0310406
    » https://doi.org/10.1346/CCMN.1983.0310406
  • Ghidin AA, Melo VF, Lima VC, Lima JMJC. Toposseqüência de Latossolos originados de rochas basálticas no Paraná: I. Mineralogia da fração argila. Rev Bras Cienc Solo. 2006;30:293-306. https://doi.org/10.1590/s0100-06832006000200010
    » https://doi.org/10.1590/s0100-06832006000200010
  • Gomes IA. Oxisols and Inceptisols from gneiss in a subtropical area of Espírito Santo State, Brazil [dissertation]. West Lafayette: Purdue University; 1976.
  • Guppy CN, Menzies NW, Moody PW, Blamey FPC. Competitive sorption reactions between phosphorus and organic matter in soil: a review. Aust J Soil Res. 2005;43:189-202. https://doi.org/10.1071/SR04049
    » https://doi.org/10.1071/SR04049
  • Hinckley DN. Variability in “crystallinity” values among the kaolin deposits of the coastal plain of Georgia and South Carolina. Clay Clay Miner. 1962;11:229-35.
  • Horn AH. Geologia da Folha Espera Feliz, SF.24-V-A-IV, escala 1:100.000: nota explicativa. MG/ES/RJ: Universidade Federal de Minas Gerais/Companhia de Pesquisa de Recursos Minerais; 2007.
  • Hsu PH. Aluminum hydroxides and oxyhydroxides. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 331-78.
  • Hughes JC, Brown G. A crystallinity index for soil kaolins and its relation to parent rock, climate and soil maturity. J Soil Sci. 1979;30:557-63. https://doi.org/10.1111/j.1365-2389.1979.tb01009.x
    » https://doi.org/10.1111/j.1365-2389.1979.tb01009.x
  • Instituto Brasileiro de Geografia e Estatística - IBGE. Manual técnico da vegetação brasileira. 2. ed. rev. ampl. Rio de Janeiro: IBGE; 2012.
  • Iriarte I, Petit S, Huertas FJ, Fiore S, Grauby O, Decarreau A, Linares J. Synthesis of kaolinite with a high level of Fe3+ for A1 substitution. Clay Clay Miner. 2005;53:1-10. https://doi.org/10.1346/CCMN.2005.0530101
    » https://doi.org/10.1346/CCMN.2005.0530101
  • IUSS Working Group WRB. World reference base for soil resources 2014, update 2015: International soil classification system for naming soils and creating legends for soil maps. Rome: Food and Agriculture Organization of the United Nations; 2015. (World Soil Resources Reports, 106).
  • Kämpf N, Curi N. Óxidos de ferro: Indicadores de ambientes pedogênicos e geoquímicos. Tópicos Cienc Solo. 2000;1:107-38.
  • Ker JC. Latossolos do Brasil: uma revisão. Geonomos. 1997;5:17-40. https://doi.org/10.18285/geonomos.v5i1.187
    » https://doi.org/10.18285/geonomos.v5i1.187
  • Ker JC. Mineralogia, sorção e dessorção de fosfato, magnetização e elementos traços de Latossolos do Brasil [tese]. Viçosa: Universidade Federal de Viçosa; 1995.
  • Klug HP, Alexander LE. X-ray diflraction procedures for polycrystalline and amorphous materials. 2nd ed. New York: John Wiley & Sons; 1974.
  • Lani JL, Resende M, Rezende SB, Feitoza LR. Atlas de ecossistemas do Espírito Santo. Vitória, ES: Governo do Estado do Espírito Santo, Secretaria Estadual de Meio Ambiente e Recursos Hídricos, Universidade Federal de Viçosa, Núcleo de Estudo de Planejamento e Uso da Terra; 2008.
  • Lani JL, Rezende SB, Resende M. Estratificação de ambientes com base nas classes de solos e outros atributos na bacia do rio Itapemirim, Espírito Santo. Rev Ceres. 2001;48:239-61.
  • Liétard O. Contribution a l’etude des proprietes physicochimiques, cristallographiques et morphologiques des kaolins [thesis]. Nancy: University of Nancy; 1977.
  • Loughnan FC. Chemical weathering of the silicate minerals. New York: Elsevier; 1969.
  • Mackenzie RC. Thermoanalytical methods in clay studies. In: Fripiat JJ, editor. Advanced techniques for clay mineral analysis. Amsterdam: Elsevier; 1982. p. 5-29. https://doi.org/10.1016/S0070-4571(08)70014-1
    » https://doi.org/10.1016/S0070-4571
  • McBride MB. Environmental chemistry of soils. New York: Oxford University Press; 1994.
  • McKeague JA, Day JH. Dithionite- and oxalate-extractable Fe and Al as aids in differentiating various classes of soils. Can J Soil Sci. 1966;46:13-22. https://doi.org/10.4141/cjss66-003
    » https://doi.org/10.4141/cjss66-003
  • Mebius LJ. A rapid method for the determination of organic carbon in soil. Anal Chim Acta. 1960;22:120-4. https://doi.org/10.1016/S0003-2670(00)88254-9
    » https://doi.org/10.1016/S0003-2670
  • Mehra OP, Jackson ML. Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. Clay Clay Miner. 1958;7:317-27. https://doi.org/10.1016/B978-0-08-009235-5.50026-7
    » https://doi.org/10.1016/B978-0-08-009235-5.50026-7
  • Melfi AJ, Cerri CC, Kronberg BI, Fyfe WS, McKinnon B. Granitic weathering: a Brazilian study. J Soil Sci. 1983;34:841-51. https://doi.org/10.1111/j.1365-2389.1983.tb01076.x
    » https://doi.org/10.1111/j.1365-2389.1983.tb01076.x
  • Melo VF, Schaefer CEGR, Singh B, Novais RF, Fontes MPF. Propriedades químicas e cristalográficas da caulinita e dos óxidos de ferro em sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo. Rev Bras Cienc Solo. 2002;26:53-64. https://doi.org/10.1590/s0100-06832002000100006
    » https://doi.org/10.1590/s0100-06832002000100006
  • Melo VF, Singh B, Schaefer CEGR, Novais RF, Fontes MPF. Chemical and mineralogical properties of kaolinite-rich Brazilian soils. Soil Sci Soc Am J. 2001;65:1324-33. https://doi.org/10.2136/sssaj2001.6541324x
    » https://doi.org/10.2136/sssaj2001.6541324x
  • Mesquita Filho MV, Torrent J. Phosphate sorption as related to mineralogy of a hydrosequence of soils from the Cerrado region (Brazil). Geoderma. 1993;58:107-23. https://doi.org/10.1016/0016-7061(93)90088-3
    » https://doi.org/10.1016/0016-7061(93)90088-3
  • Mestdagh MM, Vielvoye L, Herbillon AJ. Iron in kaolinite: II. The relationship between kaolinite crystallinity and iron content. Clay Miner. 1980;15:1-13. https://doi.org/10.1180/claymin.1980.015.1.01
    » https://doi.org/10.1180/claymin.1980.015.1.01
  • Meunier A, Velde B. Mineral reactions at grain contacts in early stages of granite weathering. Clay Miner. 1976;11:235-40. https://doi.org/10.1180/claymin.1976.011.3.05
    » https://doi.org/10.1180/claymin.1976.011.3.05
  • Moll Jr WF. Baseline studies of the clay minerals society source clays: geological origin. Clay Clay Miner. 2001;49:374-80. https://doi.org/10.1346/ccmn.2001.0490503
    » https://doi.org/10.1346/ccmn.2001.0490503
  • Moura Filho W. Studies of a Latosol Roxo (Eutrustox) in Brazil : clay mineralogy, micromorphology effect on ion release, and phosphate reactions [Thesis]. Raleigh: North Caroline State University; 1970.
  • Muggler CC, Buurman P. Micromorphological aspects of polygenetic soils developed on phyllitic rocks in Minas Gerais, Brazil. In: Shoba S, Gerasimova M, Miedema R, editors. Soil micromorphology: studies on soil diversity, diagnostics and dynamics. Wageningem, International Society of Soil Science; 1997. p. 129-38.
  • Murray HH, Lyons SC. Further correlations of kaolinite crystallinity with chemical and physical properties. Clay Clay Miner. 1959;8:11-7. https://doi.org/10.1016/B978-0-08-009351-2.50008-8
    » https://doi.org/10.1016/B978-0-08-009351-2.50008-8
  • Ndjigui P-D, Abeng SAE, Ekomane E, Nzeukou AN, Mandeng FSN, Lindjeck MM. Mineralogy and geochemistry of pseudogley soils and recent alluvial clastic sediments in the Ngog-Lituba region, Southern Cameroon: an implication to their genesis. J Afr Earth Sci. 2015;108:1-14. https://doi.org/10.1016/j.jafrearsci.2015.03.023
    » https://doi.org/10.1016/j.jafrearsci.2015.03.023
  • Norfleet ML, Karathanasis AD, Smith BR. Soil solution composition relative to mineral distribution in Blue Ridge Mountain soils. Soil Sci Soc Am J. 1993;57:1375-80. https://doi.org/10.2136/sssaj1993.03615995005700050035x
    » https://doi.org/10.2136/sssaj1993.03615995005700050035x
  • Novaes MS. História do Espírito Santo. Vitória: Fundo Editorial do Espírito Santo; 1968.
  • Nunes WAGA, Ker JC, Schaefer CEGR, Fernandes Filho EI, Gomes FH. Relação solo-paisagem-material de origem e genêse de alguns solos no domínio do “Mar de Morro”, Minas Gerais. Rev Bras Cienc Solo. 2001;25:341-54. https://doi.org/10.1590/S0100-06832001000200011
    » https://doi.org/10.1590/S0100-06832001000200011
  • Nunes WAGA, Schaefer CER, Ker JC, Fernandes Filho EI. Caracterização micropedológica de alguns solos da Zona da Mata Mineira. Rev Bras Cienc Solo. 2000;24:103-15. https://doi.org/10.1590/S0100-06832000000100013
    » https://doi.org/10.1590/S0100-06832000000100013
  • Oliveira V, Costa AMR, Azevedo WP, Camargo MN, Larach JOI. Levantamento exploratório de solos - folhas SF.23/24, Rio de Janeiro/Vitória. In: Brasil - MME. Secretaria Geral. Rio de Janeiro: Projeto Radambrasil; 1983. p. 385-552. (Levantamento de recursos naturais, 32).
  • Pacheco AA. Pedogênese e distribuição espacial dos solos da bacia hidrográfica do rio Alegre - ES [dissertação]. Viçosa, MG: Universidade Federal de Viçosa; 2011.
  • Parfitt RL, Giltrap DJ, Whitton JS. Contribution of organic matter and clay minerals to the cation exchange capacity of soils. Commun Soil Sci Plan. 1995;26:1343-55. https://doi.org/10.1080/00103629509369376
    » https://doi.org/10.1080/00103629509369376
  • Park SJ, Burt TP. Identification and characterization of pedogeomorphological processes on a hillslope. Soil Sci Soc Am J. 2002;66:1897-910. https://doi.org/10.2136/sssaj2002.1897
    » https://doi.org/10.2136/sssaj2002.1897
  • Pereira MG, Anjos LHC. Formas extraíveis de ferro em solos do estado do Rio de Janeiro. Rev Bras Cienc Solo. 1999;23:371-82. https://doi.org/10.1590/s0100-06831999000200020
    » https://doi.org/10.1590/s0100-06831999000200020
  • Plançon A, Giese RF, Snyder R. The Hinckley index for kaolinites. Clay Miner. 1988;23:249-60. https://doi.org/10.1180/claymin.1988.023.3.02
    » https://doi.org/10.1180/claymin.1988.023.3.02
  • Pruett RJ, Webb HL. Sampling and analysis of KGa-1B well-crystallized kaolin source clay. Clay Clay Miner. 1993;41:514-9. https://doi.org/10.1346/CCMN.1993.0410411
    » https://doi.org/10.1346/CCMN.1993.0410411
  • Resende M, Curi N, Ker JC, Rezende SB. Mineralogia de solos brasileiros: interpretação e aplicações. Lavras: Editora UFLA; 2011.
  • Resende M, Lani JL, Rezende SB. Pedossistemas da Mata Atlântica: considerações pertinentes sobre a sustentabilidade. Rev Arvore. 2002;26:261-9. https://doi.org/10.1590/s0100-67622002000300001
    » https://doi.org/10.1590/s0100-67622002000300001
  • Rezende SB. Geomorphology, mineralogy and genesis of four soils on gneiss in southeastern Brazil [thesis]. West Lafayette: Purdue University; 1980.
  • Ribeiro AC, Guimarães PTG, Alvarez V VH. Recomendação para o uso de corretivos e fertilizantes em Minas Gerais: 5a aproximação. Viçosa, MG: Comissão de Fertilidade do Solo do Estado de Minas Gerais; 1999.
  • Rubinić V, Durn G, Husnjak S, Tadej N. Composition, properties and formation of Pseudogley on loess along a precipitation gradient in the Pannonian region of Croatia. Catena. 2014;113:138-49. https://doi.org/10.1016/j.catena.2013.10.003
    » https://doi.org/10.1016/j.catena.2013.10.003
  • Ruiz HA. Incremento da exatidão da análise granulométrica do solo por meio da coleta da suspenssão (silte + argila). Rev Bras Cienc Solo. 2005;29:297-300. https://doi.org/10.1590/S0100-06832005000200015
    » https://doi.org/10.1590/S0100-06832005000200015
  • Santos AC, Pereira MG, Anjos LHC, Bernini TA, Cooper M, Nummer AR, Francelino MR. Gênese e classificação de solos numa topossequência no ambiente de Mar de Morros do Médio Vale do Paraíba do Sul, RJ. Rev Bras Cienc Solo. 2010;34:1297-314. https://doi.org/10.1590/s0100-06832010000400027
    » https://doi.org/10.1590/s0100-06832010000400027
  • Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.
  • Santos MCD, Ribeiro MR, Mermut AR. Submicroscopy of clay microaggregates in an Oxisol from Pernambuco, Brazil. Soil Sci Soc Am J. 1989;53:1895-901. https://doi.org/10.2136/sssaj1989.03615995005300060047x
    » https://doi.org/10.2136/sssaj1989.03615995005300060047x
  • Santos RD, Lemos RC, Santos HG, Ker JC, Anjos LHC. Manual de descrição e coleta de solo no campo. 5. ed. rev. ampl. Viçosa, MG: Sociedade Brasileira de Ciência do Solo; 2005.
  • Schaefer CER. Brazilian Latosols and their B horizon microstructure as long-term biotic constructs. Aust J Soil Res. 2001;39:909-26. https://doi.org/10.1071/SR00093
    » https://doi.org/10.1071/SR00093
  • Schwertmann U. The effect of pedogenic environments on iron oxide minerals. In: Stewart BA, editor. Advances in soil science. New York: Springer-Verlag; 1985. v. 1. p. 171-200.
  • Schwertmann U, Kämpf N. Óxidos de ferro jovens em ambientes pedogenéticos brasileiros. Rev Bras Cienc Solo. 1983;7:251-5.
  • Schwertmann U, Taylor RM. Iron oxides. In: Dixon JB, Weed SB, editors. Mineral soil environments. 2nd ed. Madison: SSSA Book Series; 1989. p. 379-438.
  • Secretaria de Estado da Agricultura, Abastecimento, Aquicultura e Pesca - SEAG. Plano estratégico de desenvolvimento da agricultura: novo PEDEAG 2007-2025. Vitória: SEAG; 2008.
  • Silva MB, Anjos LHC, Pereira MG, Nascimento RAM. Estudo de toposseqüência da baixada litorânea fluminense: efeitos do material de origem e posição topográfica. Rev Bras Cienc Solo. 2001;25:965-76. https://doi.org/10.1590/s0100-06832001000400019
    » https://doi.org/10.1590/s0100-06832001000400019
  • Singh B, Gilkes RJ. Properties of soil kaolinites from south-western Australia. J Soil Sci. 1992;43:645-67. https://doi.org/10.1111/j.1365-2389.1992.tb00165.x
    » https://doi.org/10.1111/j.1365-2389.1992.tb00165.x
  • Smeck NE, Runge ECA. Factors influencing profile development exhibited by some hy dromorphic soils in Illinois. In: Schlichting E, editor. Pseudogley and gley - genesis and use of hydromorphic soils: transactions of commissions V and VI of the International Society of Soil Science. Weinheim: Verlag Chemie; 1973. p. 169-79.
  • Soil Survey Staff. Soil taxonomy: a basic system of soil classification for making and interpreting soil surveys. 2nd ed. Washington, DC: USA: United States Department of Agriculture, Natural Resources Conservation Service; 1999. (Agricultural Handbook, 436).
  • Sommer M, Kaczorek D, Kuzyakov Y, Breuer J. Silicon pools and fluxes in soils and landscapes - a review. J Plant Nutr Soil Sci. 2006;169:310-29. https://doi.org/10.1002/jpln.200521981
    » https://doi.org/10.1002/jpln.200521981
  • Stoops G. Guidelines for analysis and description of soil and regolith thin sections. Madison: Soil Science Society of America; 2003.
  • Stoops G, Marcelino V, Mees F. Interpretation of micromorphological features of soils and regoliths. Amsterdam: Elsevier; 2010.
  • Stoops G, Schaefer CEGR. Pedoplasmation: formation of soil material. In: Stoops G, Marcelino V, Mees F, editors. Interpretation of micromorphological features of soils and regoliths. Amsterdam: Elsevier; 2010. p. 69-79.
  • Stoops GJ, Buol SW. Micromorphology of Oxisols. In: Douglas LA, Thompson ML, editors. Soil micromorphology and soil classification. Madison: Soil Science Society of America; 1985. p. 105-19.
  • Stucki JW, Bish DL, Mumpton FA, editors. Thermal analysis in clay science. Boulder: Clay Minerals Society; 1990.
  • Torrent J, Schwertmann U, Barron V. The reductive dissolution of synthetic goethite and hematite in dithionite. Clay Miner. 1987;22:329-37. https://doi.org/10.1180/claymin.1987.022.3.07
    » https://doi.org/10.1180/claymin.1987.022.3.07
  • van Raij B. Determinação de cargas elétricas em solos. Bragantia. 1973;32:171-83. https://doi.org/10.1590/s0006-87051973000100007
    » https://doi.org/10.1590/s0006-87051973000100007
  • Varajão CAC, Alkmim FF. Pancas: the kingdom of bornhardts. In: Vieira BC, Salgado AAR, Santos LJC, editors. Landscapes and landforms of Brazil. Dordrecht: Springer; 2015. p. 381-8.
  • Vepraskas MJ, Wilding LP, Drees LR. Aquic conditions for Soil Taxonomy: concepts, soil morphology and micromorphology. In: Ringrose-Voase AJ, Humphreys GS, editors. Soil micromorpohlogy: studies in management and genesis. Amsterdam: Elsevier; 1993. p. 117-31.
  • Vidal-Torrado P, Lepsch IF, Castro SS, Cooper M. Pedogênese em uma seqüência Latossolo-Podzólico na borda de um platô na Depressão Periférica Paulista. Rev Bras Cienc Solo. 1999;23:909-21. https://doi.org/10.1590/s0100-06831999000400018
    » https://doi.org/10.1590/s0100-06831999000400018
  • Weber OLS, Chitolina JC, Camargo OA, Alleoni LRF. Cargas elétricas estruturais e variáveis de solos tropicais altamente intemperizados. Rev Bras Cienc Solo. 2005;29:867-73. https://doi.org/10.1590/S0100-06832005000600004
    » https://doi.org/10.1590/S0100-06832005000600004
  • White AF, Buss HL. Natural weathering rates of silicate minerals. In: Turekian K, Holland H, editors. Treatise on geochemistry. 2nd ed. Amsterdam: Elsevier; 2014. p. 115-55. https://doi.org/10.1016/B978-0-08-095975-7.00504-0
    » https://doi.org/10.1016/B978-0-08-095975-7.00504-0
  • Whittig LD, Allardice WR. X-ray diffraction techniques. In: Klute A, editor. Methods of soil analysis. Physical and mineralogical methods. 2nd ed. Madison: American Society of Agronomy; 1986. Pt 1. p. 331-62.
  • Xu R-k, Qafoku NP, Van Ranst E, Li J-y, Jiang J. Adsorption properties of subtropical and tropical variable charge soils: implications from climate change and biochar amendment. Adv Agron. 2016;135:1-58. https://doi.org/10.1016/bs.agron.2015.09.001
    » https://doi.org/10.1016/bs.agron.2015.09.001
  • Yeomans JC, Bremner JM. A rapid and precise method for routine determination of organic carbon in soil. Commun Soil Sci Plant. 1988;19:1467-76. https://doi.org/10.1080/00103628809368027
    » https://doi.org/10.1080/00103628809368027
  • Zaidel’man FR. Lessivage and its relation to the hydrological regime of soils. Eurasian Soil Sci. 2007;40:115-25. https://doi.org/10.1134/S1064229307020019
    » https://doi.org/10.1134/S1064229307020019
  • Zhu X, Zhu Z, Lei X, Yan C. Defects in structure as the sources of the surface charges of kaolinite. Appl Clay Sci. 2016;124-125:127-36. https://doi.org/10.1016/j.clay.2016.01.033
    » https://doi.org/10.1016/j.clay.2016.01.033

Publication Dates

  • Publication in this collection
    16 July 2018
  • Date of issue
    2018

History

  • Received
    2 Sept 2017
  • Accepted
    23 Jan 2018
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