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Genesis and Classification of Nitisols from Volcano-Sedimentary Lithology in Northeastern Brazil

ABSTRACT

On the southern coast of Pernambuco State (PE), Brazil, lithotypes of the Cabo Basin (volcanic and sedimentary rocks), in association with the relief, allow the determination of the dynamics of the formation of Nitossolos Háplicos (Nitisols), including those with high levels of exchangeable aluminum. The objective of this study was to evaluate the influence of lithological diversity (basalt and sedimentary siliciclastic rocks) on the morphological, physical, chemical, and mineralogical properties of Nitossolos Háplicos along a slope (P1-summit, P2-backslope, P3-footslope) on the southern coast of PE, in order to consider its genesis and the relation of soil properties to adjacent environments and to evaluate its framing within the Brazilian Soil Classification System (SiBCS). The interaction of lithology/soil permeability and climate indicate significant differences in the mineralogical composition and dynamics of soil chemical elements. The profiles P1 and P2 are subject to monosialitization, ferralitization, and alitization processes. All profiles showed high Fe contents (ferric soils) and clay fractions, consisting primarily of kaolinite, goethite, hematite, and gibbsite, as well as quartz and feldspar in the sand and silt fractions. However, smectite minerals (P3) are probably inherited from the sedimentary source material. In the conglomerate samples, under P3, biotite, muscovite, and plagioclase were identified. Allytic characteristics (P3) are probably associated with the weathering of aluminous smectite minerals. These properties distinguish these soils from adjacent Nitossolos and other Nitossolos in Brazil. For the classification of soils according to SiBCS, considering the high levels of Fe and Al, Nitossolo Háplico distroférrico (P1 and P2) and Nitossolo Háplico alitiférrico (P3) are suggested, and according to the World Reference Base of Soils (WRB), the soils are classified as Ferritic Nitisols.

smectites; alitic soils; Nitossolo Háplico; Nitisols Ferritic

INTRODUCTION

The southern part of the Pernambuco coast is part of the Cabo volcanic-sedimentary basin, which is associated with the separation of the South American and the African continents during the Cretaceous. This tectonic event began in the Late Cretaceous, when the deposition of fluvio-deltaic sediments occurred. In the Upper Cretaceous, intense volcanic activity was responsible for the diversity of acid and alkaline rocks found in the basin (Lima Filho et al., 1996). Thus, volcanic rocks, such as basalt, andesite, trachyte, rhyolite, and ignimbrites, integrate the Ipojuca Formation, and the sedimentary rocks, particularly the Cabo Formation, are constituted essentially by conglomerates (originating from granite, gneiss, migmatite, and micaschist) associated with siltstone and argillite (Sial et al., 1987Sial AN, Long LE, Borba GS. Field trip guide excursion: cretaceous magmatic province of Cabo, Pernambuco, Northeast Brazil. Rev Bras Geoc. 1987;17:667-73.; Mabesoone and Alheiros, 1988Mabesoone JM, Alheiros MM. Origem da bacia sedimentar costeira Pernambuco-Paraíba. Rev Bras Geoci. 1988;18:476-82.; Alheiros and Ferreira, 1989Alheiros MM, Ferreira MGVX. Considerações sedimentológicas e estratigráficas sobre a Formação Cabo, Pernambuco. Rev Bras Geoc. 1989;19:17-24.; Nascimento et al., 2009Nascimento MAL, Souza ZS, Arnosio JM, Vasconcelos PMP. Ignimbrito do Engenho Saco, Ipojuca, PE - Registro de vulcanismo explosivo cretácico na província magmática do Cabo. In: Winge M, Schobbenhaus C, Souza CRG, Fernandes ACS, Queiroz ET, Berbert-Born M, Campos DA, editores. Sítios geológicos e paleontológicos do Brasil. Brasília, DF: CPRM; 2009. v. II. p. 1-13.).

According to the soil surveys carried out by Brasil (1972)Brasil. Ministério da Agricultura. Levantamento exploratório-reconhecimento de solos do Estado de Pernambuco. Escala 1:600.000. Recife: Sudene; 1972. (Boletim Técnico, 26). and Araújo Filho et al. (2000), the main orders of soils that occur along the southern coast of Pernambuco are Argissolos (Acrisols; Lixisols), Latossolos (Ferralsols), Nitossolos (Nitisols), and Gleissolos (Gleysols). Previously, studies have been performed in the abovementioned region with Nitossolos (Oliveira et al., 2004Oliveira LB, Ferreira MGVX, Marques FA. Characterization and classification of two soils derived from basic rocks in Pernambuco State Coast, Northeast Brazil. Sci Agric. 2004;61:615-25. https://doi.org/10.1590/S0103-90162004000600009
https://doi.org/10.1590/S0103-9016200400...
; Neves et al., 2018Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
https://doi.org/10.1590/1983-21252018v31...
), which are always formed from the basaltic alteration of the Ipojuca Formation, classified as Nitossolo Vermelho and Nitossolo Háplico, typically presenting a kaolinitic and oxidic mineralogy in addition to low levels of exchangeable Al3+.

The Nitossolos are composed of mineral material and have a nitic B horizon below the A horizon, with clay of low activity or allytic character in most of the B horizon within 1.50 m from the surface. These soils have a clayey to very clayey texture and a textural gradient equal to or inferior to 1.5. In addition, Nitossolos present no marked polychromy (color variation in depth) in the profile (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.).

Basic and intermediate rocks are widely documented as the parent lithology for soils with a nitic horizon (Cooper and Vidal-Torrado, 2000Cooper M, Vidal-Torrado P. Gênese de ferri-argilãs em horizontes B texturais de uma sequência de solos sobre diabásio em Piracicaba (SP). Sci Agric. 2000;57:745-50. https://doi.org/10.1590/S0103-90162000000400024
https://doi.org/10.1590/S0103-9016200000...
; Cooper et al., 2010Cooper M, Vidal-Torrado P, Grimaldi M. Soil structure transformations from ferralic to nitic horizons on a toposequence in southeastern Brazil. Rev Bras Cienc Solo. 2010;34:1685-99. https://doi.org/10.1590/S0100-06832010000500021
https://doi.org/10.1590/S0100-0683201000...
; Melo et al., 2010Melo VF, Schaefer CEGR, Uchôa SCP. Indian land use in the Raposa-Serra do Sol Reserve, Roraima, Amazonia, Brazil: physical and chemical attributes of a soil catena developed from mafic rocks under shifting cultivation. Catena. 2010;80:95-105. https://doi.org/10.1016/j.catena.2009.09.004
https://doi.org/10.1016/j.catena.2009.09...
; Soil Survey Staff, 2014Soil Survey Staff. Keys to soil taxonomy. 12th ed. Washington, DC: United States Department of Agriculture, Natural Resources Conservation Service; 2014.; De Wispelaere et al., 2015De Wispelaere L, Marcelino V, Regassa A, De Grave E, Dumon M, Mees F, Van Ranst E. Revisiting nitic horizon properties of Nitisols in SW Ethiopia. Geoderma. 2015;243-244:69-79. https://doi.org/10.1016/j.geoderma.2014.12.021
https://doi.org/10.1016/j.geoderma.2014....
). The Nitossolos developed from basalt throughout Brazil (Brasil, 1972Brasil. Ministério da Agricultura. Levantamento exploratório-reconhecimento de solos do Estado de Pernambuco. Escala 1:600.000. Recife: Sudene; 1972. (Boletim Técnico, 26).; Santos Filho et al., 1978; Araújo Filho et al., 2000; Tremocoldi, 2003Tremocoldi WA. Mineralogia dos silicatos e dos óxidos de ferro da fração argila de solos desenvolvidos de rochas básicas no Estado de São Paulo. Rev Bioci. 2003;9:15-22.; Oliveira et al., 2004Oliveira LB, Ferreira MGVX, Marques FA. Characterization and classification of two soils derived from basic rocks in Pernambuco State Coast, Northeast Brazil. Sci Agric. 2004;61:615-25. https://doi.org/10.1590/S0103-90162004000600009
https://doi.org/10.1590/S0103-9016200400...
; Neves et al., 2018Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
https://doi.org/10.1590/1983-21252018v31...
) generally present values of Fe2O3 (sulfuric digestion) above 18 % and are classified as Nitossolos Vermelhos or Brunos (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.). However, for Nitossolos Háplicos, neither the ferric nor the allytic character have been predicted to date (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.).

Due to the distinct lithotypes around the Cabo Basin (volcanic rocks and siliciclastic sedimentary rocks), studies have shown the occurrence of Argissolos with high levels of exchangeable Al (>4 cmolc kg-1) and high clay activity (smectite minerals in the clay fraction), that formed from the weathering of conglomerates (Costa, 2012)Costa EUC. Caracterização e gênese de Argissolos e Nitossolos na Bacia Cabo, Pernambuco [dissertação]. Recife: Universidade Federal Rural de Pernambuco; 2012.. Although soils with similar properties have been studied in several parts of Brazil (Cunha et al., 2014, 2Cunha GOM, Almeida JA, Barboza BB. Relação entre alumínio extraível com KCl e oxalato de amônio e a mineralogia da fração argila, em solos ácidos brasileiros. Rev Bras Cienc Solo. 2014;38:1387-401. https://doi.org/10.1590/S0100-06832014000500004
https://doi.org/10.1590/S0100-0683201400...
, 2015Cunha GOM, Almeida JA, Testoni SA, Barboza BB. Formas de alumínio em solos ácidos brasileiros com teores excepcionalmente altos de Al3+ extraível com KCl. Rev Bras Cienc Solo. 2015;39:1362-77. https://doi.org/10.1590/01000683rbcs20150017
https://doi.org/10.1590/01000683rbcs2015...
; Delarmelinda et al., 2017)Delarmelinda EA, Souza Júnior VS, Wadt PGS, Deng Y, Campos MCC, Câmara ERG. Soil-landscape relationship in a chronosequence of the middle Madeira River in southwestern Amazon, Brazil. Catena. 2017;149:199-208. https://doi.org/10.1016/j.catena.2016.09.021
https://doi.org/10.1016/j.catena.2016.09...
, previous pedological studies in the Cabo Basin do not cover the current knowledge of local geological diversity. The presence of smectites is also not common in the clay fraction of the Nitossolos in Brazil, probably due to the strong weathering involved in the formation of these soils, predominated by monosialitization and ferralitization processes (Cooper and Vidal-Torrado, 2005)Cooper M, Vidal-Torrado P. Caracterização morfológica, micromorfológica e físico-hídrica de solos com horizonte B nítico. Rev Bras Cienc Solo. 2005;29:581-95. https://doi.org/10.1590/S0100-06832005000400011
https://doi.org/10.1590/S0100-0683200500...
.

The southern coast of Pernambuco is inserted in areas of dissected plateaus. In addition to the close relationship between parent material and soil properties (Brilhante et al., 2017Brilhante SA, Santos JCBS, Souza Júnior VS, Araujo JKS, Ribeiro Filho MR, Corrêa MM. Weathering of rhyolites and soil formation in an Atlantic Forest fragment in northeastern Brazil. Rev Bras Cienc Solo. 2017;41:e0160558. https://doi.org/10.1590/18069657rbcs20160558
https://doi.org/10.1590/18069657rbcs2016...
; Neves et al., 2018Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
https://doi.org/10.1590/1983-21252018v31...
), the relief plays a key role in pedodiversity, since along the slopes, there may be mixtures of parent materials, conditioning the formation of soil with peculiar properties. It is possible to find the occurrence of Nitossolos distinct from those previously studied in other regions of Brazil (Cooper and Vidal-Torrado, 2000Cooper M, Vidal-Torrado P. Gênese de ferri-argilãs em horizontes B texturais de uma sequência de solos sobre diabásio em Piracicaba (SP). Sci Agric. 2000;57:745-50. https://doi.org/10.1590/S0103-90162000000400024
https://doi.org/10.1590/S0103-9016200000...
; Ferreira et al., 2003Ferreira BA, Fabris JD, Santana DP, Curi N. Óxidos de ferro das frações areia e silte de um Nitossolo desenvolvido de basalto. Rev Bras Cienc Solo. 2003;27:405-13. https://doi.org/10.1590/S0100-06832003000300002
https://doi.org/10.1590/S0100-0683200300...
; Silva et al., 2009Silva L, Emer AA, Bortolini CE, Arruda JH. Estudo de um Nitossolo Vermelho com evidência de caráter coeso da região sudoeste do Paraná. Synergismus Scyentifica UTFPR. 2009;4:301-4.; Melo et al., 2010Melo VF, Schaefer CEGR, Uchôa SCP. Indian land use in the Raposa-Serra do Sol Reserve, Roraima, Amazonia, Brazil: physical and chemical attributes of a soil catena developed from mafic rocks under shifting cultivation. Catena. 2010;80:95-105. https://doi.org/10.1016/j.catena.2009.09.004
https://doi.org/10.1016/j.catena.2009.09...
) and from those already studied in this region of Pernambuco (Araújo Filho et al., 2000; Oliveira et al., 2004Oliveira LB, Ferreira MGVX, Marques FA. Characterization and classification of two soils derived from basic rocks in Pernambuco State Coast, Northeast Brazil. Sci Agric. 2004;61:615-25. https://doi.org/10.1590/S0103-90162004000600009
https://doi.org/10.1590/S0103-9016200400...
; Neves et al., 2018Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
https://doi.org/10.1590/1983-21252018v31...
).

The southern coastal region of Pernambuco, in addition to the estuarine environments, is formed by the Atlantic forest ecosystem, the natural vegetation of which is practically nonexistent. The area is mainly used for sugarcane cultivation, a large industrial park, and dense urban areas with a population of approximately 500,000 inhabitants (IBGE, 2010Instituto Brasileiro de Geografia e Estatística - IBGE. Censo demográfico de 2010. Rio de Janeiro: IBGE; 2010.). Considering the scarcity of pedological studies in the Cabo Basin region, detailed knowledge of soil diversity and its properties is fundamental for the ecological and socioeconomic sustainability and maintenance of the region. In this context, this study aimed to evaluate the influence of lithological diversity (basalts and siliciclastic sedimentary rocks) along a slope on the morphological, physical, chemical, and mineralogical properties of Nitossolos Háplicos in order to understand its genesis, its framing in the Brazilian Soil Classification System (SiBCS), and its enhancement in the SiBCS.

MATERIALS AND METHODS

Study area and sampling

The study area is located in the municipality of Cabo de Santo Agostinho at the southern coast of the state of Pernambuco (Figure 1). The local geology consists of Ipojuca Formation basalt with rare outcrops and conglomerates of the Cabo Formation, with significant outcrops along the area. In the Cabo Formation, besides conglomerates formed by fragments of granite and gneiss, there is also siltstone and argillite, often interspersed between the conglomeratic materials. The relief is predominantly convex and wave-like formed by hills linked to the so-called Mares de Morros geomorphology (Assis, 1999Assis HMB. Cartografia geomorfológica do Município do Cabo de Santo Agostinho/PE. Recife: CPRM/FIDEM; 1999. (Série Cartas Temáticas, 4).).

Figure 1
Location of the study area (Cabo Basin) on the southern coast of Pernambuco, Brazil.

The climate is hot and humid, type As’ (Köppen classification system), with average annual rainfall of 2,200 mm and average temperature of 25 °C (Assis, 1999Assis HMB. Cartografia geomorfológica do Município do Cabo de Santo Agostinho/PE. Recife: CPRM/FIDEM; 1999. (Série Cartas Temáticas, 4).). The native vegetation is predominantly subperenifolia forest, distributed in the Atlantic Forest ecosystem (Andrade-Lima, 1960Andrade-Lima D. Estudos fitogeográficos de Pernambuco. Arq Inst Pesq Agron. 1960;5:305-42.; Brasil, 1972Brasil. Ministério da Agricultura. Levantamento exploratório-reconhecimento de solos do Estado de Pernambuco. Escala 1:600.000. Recife: Sudene; 1972. (Boletim Técnico, 26).), which is practically deforested mainly for agricultural use (sugarcane), urban areas, and the port and industrial complex of Suape. Mangroves, hygrophilous fields of floodplains, and restingas occur in the vicinity (Andrade-Lima, 1960Andrade-Lima D. Estudos fitogeográficos de Pernambuco. Arq Inst Pesq Agron. 1960;5:305-42.).

The selection of the area was based on the geological map (CPRM, 2005Serviço Geológico do Brasil - CPRM. Projeto cadastro de fontes de abastecimento por água subterrânea. Diagnóstico do município de Cabo de Santo Agostinho, estado de Pernambuco. Recife: CPRM/PRODEEM; 2005.) and field evaluations, assuring the relationship of the soils with the parent material (basalt and conglomerates). In this way, three soil profiles were dug along a slope in an area without recent agricultural use (due to the scarcity of native vegetation). The P1 profile was located at the summit (8° 18’ 46” S e 35° 01’ 22” W), the P2 profile at the half-slope position of the backslope (8° 18’ 43” S e 35° 01’ 25” W), and the P3 profile was at the footslope (8° 18’ 43” S e 35° 01’ 28” W), with elevations of 55, 35, and 23 m a.s.l., respectively. The declivity in the three segments was 8 % (P1), 20 % (P2), and 40 % (P3), with 140 m between P1 and P3 and 110 m between P2 and P1.

The morphological descriptions of the profiles and the sample collection were performed according to Santos et al. (2015)Santos RD, Lemos RC, Santos HG, Ker JC, Anjos LHC, Shimizu SH. Manual de descrição e coleta de solo no campo. 7. ed. rev. ampl. Viçosa, MG: Sociedade Brasileira de Ciência do Solo; 2015.. Collected samples were undisturbed and deformed from all horizons for physical, chemical, and mineralogical analysis. For petrographic characterization, samples of rock fragments were collected in an area close to the location of the profiles. The basalt was collected in a cut made for civil construction at a depth of approximately 5 m from the soil surface. At the base of P3, a fragment of the altered parent material was collected (conglomerates), ensuring that the base of this profile has a lithology related to the Cabo Formation (sedimentary).

Analytical procedures

Physical analyses were performed according to Donagema et al. (2011)Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise do solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011., including soil bulk density (Bd) by the volumetric ring method, soil particle density (Pd) by the volumetric flask method, and particle size distribution analysis and water-dispersed clay (WDC) by the densimeter method after slow stirring with a Wagner-type rotary shaker at 50 rpm for 16 h (Mauri et al., 2011Mauri J, Ruiz HA, Fernandes RBA, Ker JC, Rezende LRM. Dispersantes químicos na análise granulométrica de Latossolos. Rev Bras Cienc Solo. 2011;35:1277-84. https://doi.org/10.1590/S0100-06832011000400021
https://doi.org/10.1590/S0100-0683201100...
).

Soil pH was measured in water [pH(H2O)] and in KCl 1 mol L-1 [pH(KCl)] using a potentiometer with a soil:liquid ratio of 1:2.5 (v/v). The Ca2+, Mg2+, and Al3+ were extracted with KCl 1 mol L-1, and determined using atomic absorption spectrophotometry. The K+, Na+, and available P were extracted with Mehlich-1 solution; K+ and Na+ were determined through flame spectrophotometry and available P through colorimetry. Potential acidity (H+Al) was extracted using 0.5 mol L-1 calcium acetate solution buffered at pH 7.0, and determined by titration with NaOH 0.025 mol L-1. Based on the chemical analyses, we calculated the sum of base (SB), cation exchange capacity (CEC), base saturation (V), aluminum saturation (m), and activity of the clay (CECa). The total organic carbon (TOC) was determined by wet combustion, using potassium dichromate as the oxidizing agent. All chemical analyses mentioned above were performed according to the proceedings of Donagema et al. (2011)Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise do solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011..

The Si, Fe, and Al extracted by sulfuric acid digestion were determined for the upper, middle, and lower horizons of each soil profile, using the fine earth fraction according to Donagema et al. (2011)Donagema GK, Campos DVB, Calderano SB, Teixeira WG, Viana JHM. Manual de métodos de análise do solo. 2. ed. rev. Rio de Janeiro: Embrapa Solos; 2011.. Measurements were recorded using atomic absorption spectrophotometry.

The forms of low- and high-crystalline Fe (Fed) were extracted using dithionite-citrate-bicarbonate (DCB) (Mehra and Jackson, 1960Mehra OP, Jackson ML. Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. In: Swineford A, editor. Clays and Clay Minerals: proceedings of the seventh national conference on clays and clay minerals. London: Pergamon Press; 1960. p. 317-27.), and low-crystalline iron (Feo) was extracted by ammonium acid oxalate (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 amounts were measured through atomic absorption spectrophotometry. The Ki, Kr, Feo/Fed, and Fed/Fes ratios were calculated from the results of these analyses.

For mineralogical analyses, the organic matter in the samples was eliminated using 3 % H2O2 (v/v) (Jackson, 1975Jackson ML. Soil chemical analysis: advance course. 2nd ed. Madison: Parallel Press; 1975.). The sand, silt, and clay fractions were separated after dispersion with NaOH and slow stirring. Separation of the clay fraction was carried out by siphonation after decantation of the silt fraction and by wet sieving (coarse and fine sand). The samples of coarse sand, fine sand, and silt were analyzed by X-ray diffractometry (XRD) as non-oriented powders. The clay fraction was also analyzed as natural clay (non-oriented powder) and as oriented aggregates on glass slides after being submitted to iron oxide elimination pretreatments (Jackson, 1975Jackson ML. Soil chemical analysis: advance course. 2nd ed. Madison: Parallel Press; 1975.).

The scanning amplitude in the powder samples was 5 to 70° 2θ, while in the samples in the form of oriented aggregates it ranged from 3 to 35° 2θ, all at the recording speed of 1° 2θ min-1, using a Kα radiation of λ 0.15405 nm, produced by a copper tube, with a voltage of 40 kV and an amperage of 20 mA. The deferred clay fraction was saturated with KCl and analyzed at room temperature, 110, 300, and 550 °C (K25; K110; K300; and K550). Analysis was also performed by MgCl2 saturation for determination at room temperature and solvated with glycerol (Mg and Mg-Gly). The samples that showed smectite minerals were subjected to the Greene-Kelly test (Greene-Kelly, 1953) by saturation with LiCl 1 mol L-1, according to Lim and Jackson (1986)Lim CH, Jackson ML. Expandable phyllosilicate reactions with lithium on heating. Clay Clay Miner. 1986;34:346-52. https://doi.org/10.1346/CCMN.1986.0340316
https://doi.org/10.1346/CCMN.1986.034031...
. The criteria used to interpret the diffractograms and to identify the minerals were based on the interplanar spacing (d), according to Jackson (1975)Jackson ML. Soil chemical analysis: advance course. 2nd ed. Madison: Parallel Press; 1975. and Brown and to Brindley (1980).

Conglomerate and basalt samples were submitted to petrographic analysis of thin sections, according to the methodology proposed by Cesero et al. (1989)Cesero P, Mauro LM, Ros LF. Técnicas de preparação de lâminas petrográficas e de moldes de poros na Petrobrás. Rio de Janeiro: Petrobrás; 1989. p. 105-16. (Boletim de Geociências da Petrobrás, 3)..

RESULTS

Morphological and physical properties

The morphological description data is presented in table 1. The soils along the slope were very deep, with a brown color with no polychromy and only subtle variations in the color of the surface horizons due to the influence of organic matter.

Table 1
Morphological properties of Nitossolos Háplicos (Nitisol Ferritic) on the southern coast of PE (Cabo Basin), Brazil

Profile P1 is located at the summit of the slope, presenting an A, Bn, Bw1, and Bw2 horizon sequence (w stands for weathering according to 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 hue is 5YR, with values of 3 to 4, and the chroma value is 4, differing from the other profiles by the reddish color (red bruno). Profile P2 is located at the backslope, with an A, BA, Bn1, Bn2, and Bw horizonal sequence, and profile P3 is situated at the footslope, presenting an A, BA, Bn, B/C, and Cr sequence. Both have a hue of 7.5YR, with values of 3 to 4, and a chroma value of 3 to 5 in horizons A and B (dark bruno).

The soil has a very clayey to clayey texture (Table 1); consistent with the nature of the material of origin (basalt alteration), the texture is sandy loam clay except in the Cr of P3, where there is sedimentary rock participation. The overall increase in the clay content with depth is insufficient to characterize an argic B horizon (textural ratio was less than 1.2), associated with a lack of polychromy and the clayey to very clayey texture, unlike soils from the Argissolos (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 Bd values are higher in the upper horizons (Table 2). Mean Pd has approximately the same values (2.9 Mg m-3) in P1 and P2 and is lower in P3.

Table 2
Physical properties of Nitossolos Háplicos on the southern coast of PE (Cabo Basin), Brazil

Chemical properties

The pH(H2O) was acidic (4.7 to 5.1), and the pH(KCl) values were approximately one unit lower than pH(H2O), indicating a negative charge, although the CEC was low in profiles 1 and 2 (Table 3). The organic carbon content gradually decreased with depth from 20.2 to 1.7 g kg-1. The exchangeable cations were dominated by Ca2+ and Mg2+, being higher in P3. Also, P3 presented a higher sum of bases (1.4 to 6.3 cmolc kg-1) and a higher CEC (19.9 to 31.7 cmolc kg-1) in relation to the other profiles, which had values between 2.8 and 1.0 cmolc kg-1 for the sum of bases and 6.0 to 12.1 cmolc kg-1 for CEC; the same behavior was observed for clay activity. The potential acidity (H+Al) was lower in P1 and P2, ranging from 5.6 to 9.3 cmolc kg-1, whereas the exchangeable acidity ranged from 0.3 to 1.0 cmolc kg-1 in P1 and P2 and was very high in P3, mainly from the BA horizon, where values varied between 10.0 and 24.0 cmolc kg-1. The P levels tended to increase with depth, ranging from 9.2 to 14.7 mg kg-1 (Table 3).

Table 3
Chemical properties of Nitossolos Háplicos on the southern coast of PE (Cabo Basin), Brazil

The Ki index ranged from 1.7 to 2.2 in profiles 1 and 2 (Table 4). These data agree with the mineralogical composition of the clay fraction (Table 5 and Figure 2). In spite of the smectite minerals in P3, the Ki index was 2.0 and 2.1 in the Ap and Bn horizons, respectively, and 2.7 in Cr. The increasing values of Ki with depth at P3 were correlated with increases in the intensity of diffraction peaks related to the 1.4-nm interplanar distance (smectite minerals) and the decrease in peak intensity related to the 0.7-nm interplanar distance (kaolinite) (Figure 2), indicating coherence between the Ki values and the XRD results for the clay fraction of the studied soils.

Table 4
Silicon, aluminum, and iron contents obtained by sulfur digestion, and Ki and Kr values, Fe contents extracted by DCB (Fed), and ammonium oxalate (Feo) and their respective relationships from the superficial, median, and lower horizons of Nitossolos Háplicos on the southern coast of PE (Cabo Basin), Brazil
Table 5
Qualitative mineralogical composition of the fine and coarse sand, silt, and clay (untreated) fractions of Nitossolos Háplicos on the southern coast of PE (Cabo Basin), Brazil

Figure 2
X-ray diffraction patterns of the treated clay fraction of the surface, median, and lower horizons. (a) P2 profile (similar to P1) and (b) P3. Sm = smectite; K = kaolinite.

The results of selective dissolution are given in table 4. The Fed content was higher in P1 (186.0 g kg-1) than in P2 (156.2 g kg-1), and P3 (86.8 g kg-1) at the subsurface horizon, consistent with the reddish colors (Table 1). These contents tended to increase with depth at P1 and P2, unlike P3, where the contents decreased with depth. Such values are considerably larger than the values of Feo. Thus, the soil sequence in the direction of P1 to P3 (from the summit to the footslope) showed a reduction in Fes (Table 4), an increase in the Feo/Fed ratio (<0.05), and a reduction in the Fed/Fes (Table 4).

Mineralogical properties

Based on XRD data, quartz was the main mineral in the sand fraction (fine and coarse) in all profiles, although feldspar was also present (Table 5). Mica was observed only in the subsurface horizons of P3. In the silt fraction of all horizons, quartz, feldspar, magnetite, and ilmenite were identified, except in the 2Cr horizon of P3 (Table 5). The constituent minerals in the clay fraction were kaolinite, goethite, hematite, and gibbsite in all profiles. Throughout P3, smectite minerals were observed, especially in the 2Cr horizon (Table 5). The Greene-Kelly test showed a complete peak expansion relative to the basal spacings of 1.0 to 1.68 nm. This behavior is attributed to smectite minerals with isomorphic substitution in the tetrahedral layer (Borchardt, 1989Borchardt G. Smectites. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 675-727.), that is, the clay fraction of P3 has beidellite and/or nontronite as smectite minerals (Figure 3), consistent with high Fe and Al values (Tables 3, 4, and 5).

Figure 3
X-ray diffraction patterns of the clay fraction submitted to the Greene Kelly test, from the superficial, median, and lower horizons of the P3 profile. B/N = Beidelite/Nontronite; K = kaolinite.

Petrographic analysis

In the basalt sample, plagioclase (slat form), clinopyroxene phenocrysts (augite), sanidine phenocrysts, opaque minerals (magnetite), and zeolite filling cavities were identified, while in the conglomerate sample, although reasonably altered, microcline, orthoclase, quartz, plagioclase, biotite, muscovite, epidote, and opaque minerals were identified.

DISCUSSION

Soil properties and their relation to pedogenesis

In general, the soils were in advanced stages of weathering, as indicated by the Ki index, the mineralogical composition, and the depth (Tables 2 and 5), in accordance with the humid tropical climate and the predominance of basic rocks (Buol et al., 1980Buol SW, Hole FD, Mccracken RJ. Soil genesis and classification. 2nd ed. Ames: Iowa State University Press; 1980.). However, there were important differences in soil general properties according to lithology, and to a certain extent, these differences were also attributed to the slope.

Profile P1 (summit), derived from basalt, seemed to favor a greater infiltration of water compared to the other toposequence profiles due to its flat top position in the landscape, resulting in a profile with greater depth (Table 1) and Fed content (Table 4) due to the greater advance in the action of chemical weathering and due to the low loss of materials (clay) for the lower parts of the relief. Similar to P1, P2 also had a good drainage, since no redoximorphic feature was observed in field analysis, contributing to a dystrophic soil (Table 3) and the strong pedogenetic development.

Regardless of the topographic gradient, all toposequence profiles had a similar mineralogical composition in the superficial horizons, except for the presence of smectites in the fraction smaller than 2 μm, as observed in P3 (footslope). This similarity indicates material of basic origin, and an important loss of silica, as well as a loss of Fe and Al, albeit to a lesser extent, are favored by the humid climate. In addition, there was good soil drainage, even in the lowest position of the landscape. This intense weathering was confirmed by the mineralogy dominated by kaolinite and oxidic clay minerals (goethite, hematite, and gibbsite) (Table 5 and Figure 2), common in tropical soils (Schaefer et al., 2008Schaefer CEGR, Fabris JD, Ker JC. Minerals in the clay fraction of Brazilian Latosols (Oxisols): a review. Clay Miner. 2008;43:137-54. https://doi.org/10.1180/claymin.2008.043.1.11
https://doi.org/10.1180/claymin.2008.043...
). The soil profiles located at the highest slope positions, P1 (summit) and P2 (backslope), were subject to monosialitization, ferralitization, and alitization processes, consistent with the climate of the region and the position of the soil in the landscape (Kämpf et al., 2009Kämpf N, Curi N, Marques JJ. Intemperismo e ocorrência de minerais no ambiente do solo. In: Melo VF, Alleoni LRF, editores. Química e mineralogia do solo. Viçosa, MG: Sociedade Brasileira de Ciência do Solo; 2009. Pt 1. p. 333-80.). However, P3 (footslope) also presented characteristics of moderate weathering in the presence of smectite.

Soils with a nitic horizon are predominantly derived from basic to intermediate rocks (Cooper and Vidal-Torrado, 2000Cooper M, Vidal-Torrado P. Gênese de ferri-argilãs em horizontes B texturais de uma sequência de solos sobre diabásio em Piracicaba (SP). Sci Agric. 2000;57:745-50. https://doi.org/10.1590/S0103-90162000000400024
https://doi.org/10.1590/S0103-9016200000...
, 2005Cooper M, Vidal-Torrado P. Caracterização morfológica, micromorfológica e físico-hídrica de solos com horizonte B nítico. Rev Bras Cienc Solo. 2005;29:581-95. https://doi.org/10.1590/S0100-06832005000400011
https://doi.org/10.1590/S0100-0683200500...
; Cooper et al., 2010Cooper M, Vidal-Torrado P, Grimaldi M. Soil structure transformations from ferralic to nitic horizons on a toposequence in southeastern Brazil. Rev Bras Cienc Solo. 2010;34:1685-99. https://doi.org/10.1590/S0100-06832010000500021
https://doi.org/10.1590/S0100-0683201000...
; 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.; Soil Survey Staff, 2014Soil Survey Staff. Keys to soil taxonomy. 12th ed. Washington, DC: United States Department of Agriculture, Natural Resources Conservation Service; 2014.; De Wispelaere et al., 2015De Wispelaere L, Marcelino V, Regassa A, De Grave E, Dumon M, Mees F, Van Ranst E. Revisiting nitic horizon properties of Nitisols in SW Ethiopia. Geoderma. 2015;243-244:69-79. https://doi.org/10.1016/j.geoderma.2014.12.021
https://doi.org/10.1016/j.geoderma.2014....
), including the Nitossolos of the Cabo Basin (Oliveira et al., 2004Oliveira LB, Ferreira MGVX, Marques FA. Characterization and classification of two soils derived from basic rocks in Pernambuco State Coast, Northeast Brazil. Sci Agric. 2004;61:615-25. https://doi.org/10.1590/S0103-90162004000600009
https://doi.org/10.1590/S0103-9016200400...
; Neves et al., 2018Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
https://doi.org/10.1590/1983-21252018v31...
;). In contrast to the studies mentioned and to P1 and P2 of the present study, the P3 profile (footslope), in addition to basalt, is formed from sedimentary rocks richer in SiO2, since the blocks and the matrix of the conglomerate package present a typical granitic composition (Alheiros and Ferreira, 1989Alheiros MM, Ferreira MGVX. Considerações sedimentológicas e estratigráficas sobre a Formação Cabo, Pernambuco. Rev Bras Geoc. 1989;19:17-24.), contributing to an unusual formation of Nitossolo associated with acidic and basic rocks.

The formation of Nitossolos under the influence of sedimentary rocks (P3) seems to have experienced pedoturbation acting in the mixture of materials (acids and basic), mainly in the more superficial horizons, which was suggested based on the reduced magnetic attraction in depth. In addition, the absence of polychromy and a textural gradient (Tables 1 and 2), despite a clear change in the parent material (product of the conglomerate change), suggests biological activity (bioturbation) (Hole, 1961Hole FD. A classification of pedoturbations and some other processes and factors of soil formation in relation to isotropism and anisotropism. Soil Sci. 1961;91:375-7.; Johnson et al., 1987Johnson DL, Watson-Stegner D, Johnson DN, Schaetzl RJ. Proisotropic and proa-nisotropic processes of pedoturbation. Soil Sci. 1987;143:278-92.) in this profile. Evidence of this process was clearly observed in the other profiles of the present study, indicated by the homogeneity of the soil color and the low textural gradient along the profile, mainly in P1, where crotovins were observed (Borst, 1968Borst G. The occurrence of crotovinas in some southern Californian soils. Transactions of the 9th International Congress of Soil Science; 1968; Adelaide. Sydney: Angus & Robertson; 1968. p. 19-27.). This is consistent with De Wispelaere et al. (2015)De Wispelaere L, Marcelino V, Regassa A, De Grave E, Dumon M, Mees F, Van Ranst E. Revisiting nitic horizon properties of Nitisols in SW Ethiopia. Geoderma. 2015;243-244:69-79. https://doi.org/10.1016/j.geoderma.2014.12.021
https://doi.org/10.1016/j.geoderma.2014....
, who considered biological activity important in Nitossolos, particularly in those developed under continued surface deposition of volcanic ash.

The smectite in P3 may be related to complex conglomerates, since they may be intercalated with argillites and shales of the Cabo Basin (Mabesoone and Alheiros, 1988Mabesoone JM, Alheiros MM. Origem da bacia sedimentar costeira Pernambuco-Paraíba. Rev Bras Geoci. 1988;18:476-82.; Alheiros and Ferreira, 1989Alheiros MM, Ferreira MGVX. Considerações sedimentológicas e estratigráficas sobre a Formação Cabo, Pernambuco. Rev Bras Geoc. 1989;19:17-24.). Thus, this profile of Nitossolo differs from those studied by Oliveira et al. (2004)Oliveira LB, Ferreira MGVX, Marques FA. Characterization and classification of two soils derived from basic rocks in Pernambuco State Coast, Northeast Brazil. Sci Agric. 2004;61:615-25. https://doi.org/10.1590/S0103-90162004000600009
https://doi.org/10.1590/S0103-9016200400...
and Neves et al. (2018)Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
https://doi.org/10.1590/1983-21252018v31...
for not identifying 2:1 minerals in the clay fraction.

Smectic soils that formed in a Cretaceous sedimentary environment under a tropical humid climate have also been identified by Ribeiro et al. (1990)Ribeiro LP, Volkoff B, Melfi AJ. Evolução mineralógica das argilas em solos vérticos do recôncavo baiano. Rev Bras Cienc Solo. 1990;14:263-8.. The inference that smectite minerals are inherited from sedimentary rock is subsidized because there are no redoximorphic features indicating poor drainage under field conditions, and this could be sufficient for a current bisialitization process in these soils. Moreover, the neoformation of smectites in this environment is not excluded, although unlikely, and may constitute relics of a dry paleoclimate (Ribeiro et al., 1990Ribeiro LP, Volkoff B, Melfi AJ. Evolução mineralógica das argilas em solos vérticos do recôncavo baiano. Rev Bras Cienc Solo. 1990;14:263-8.; Ab’Sáber, 2000Ab’sáber AN. The natural organization of brazilian inter-and subtropical landscapes. Rev Inst Geol. 2000;21:57-70. https://doi.org/10.5935/0100-929X.20000005
https://doi.org/10.5935/0100-929X.200000...
). Even under the current climatic conditions (hot and humid), there is probably still no time for total hydrolysis of these minerals.

Nitossolos commonly presents low clay fraction activity (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 a consequence of the kaolinitic and oxidic mineralogical composition (Ferreira et al., 2003Ferreira BA, Fabris JD, Santana DP, Curi N. Óxidos de ferro das frações areia e silte de um Nitossolo desenvolvido de basalto. Rev Bras Cienc Solo. 2003;27:405-13. https://doi.org/10.1590/S0100-06832003000300002
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). However, the high activity identified along P3 is related to the smectites (Table 5 and Figure 2). The presence of 2:1 phyllosilicates also increased the ΔpH and CEC in P3 (Table 3) and may have contributed to the high levels of WDC in the surface horizon (Table 2), reaching high values for humid tropical soils. Smectic minerals associated with lower Fe oxyhydroxide contents reduced the Pd values in this profile (Table 2), whereas the highest Pd (above 2.8 kg dm-3), observed in P1 and P2, is common in soils derived from rocks rich in ferromagnesian minerals, such as basalt (Ghidin et al., 2006Ghidin AA, Melo VF, Lima VC, Lima JMJC. Topossequência 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
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).

Among the dioctahedral smectites identified by the Greene-Kelly test (Figure 3), the dominance of beidelite is more likely to be considered as an aluminous smectite mineral (Borchardt, 1989Borchardt G. Smectites. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 675-727.). This mineral contains the octahedral sheet consisting of Al hydroxide (Borchardt, 1989Borchardt G. Smectites. In: Dixon JB, Weed SB, editors. Minerals in soil environments. 2nd ed. Madison: Soil Science Society of America; 1989. p. 675-727.), and its geochemical destabilization can be an important source for the high exchangeable Al contents found in P3 (Table 3), as discussed in Ribeiro et al. (1990)Ribeiro LP, Volkoff B, Melfi AJ. Evolução mineralógica das argilas em solos vérticos do recôncavo baiano. Rev Bras Cienc Solo. 1990;14:263-8. and Cunha et al. (2014Cunha GOM, Almeida JA, Barboza BB. Relação entre alumínio extraível com KCl e oxalato de amônio e a mineralogia da fração argila, em solos ácidos brasileiros. Rev Bras Cienc Solo. 2014;38:1387-401. https://doi.org/10.1590/S0100-06832014000500004
https://doi.org/10.1590/S0100-0683201400...
, 2015Cunha GOM, Almeida JA, Testoni SA, Barboza BB. Formas de alumínio em solos ácidos brasileiros com teores excepcionalmente altos de Al3+ extraível com KCl. Rev Bras Cienc Solo. 2015;39:1362-77. https://doi.org/10.1590/01000683rbcs20150017
https://doi.org/10.1590/01000683rbcs2015...
).

Profile P3 (footslope) receives material from the upper portions, but due to its undulating relief and local slope (≈20 %), this profile seems to lose more material than it receives, resulting in less depth between toposequence soils. In addition, the contribution of conglomerate material may impede weathering compared to the basic material (poorer in SiO2), resulting in a shallower soil. The conglomerates may also explain the lower clay content in P3 (Table 2). The position of this profile in the landscape is subject to lateral water flow from the above areas, leaving it closer to the water table, resulting in moderate drainage and less leaching. Thus, it has higher Ca2+, Mg2+, and K+ values in the superficial horizons due to the accumulation of material from the higher parts of the landscape (Table 3). The higher content of Mg2+, in relation to Ca2+, in the 2Cr horizon of P3 may be associated with biotite in the fragments of rocks that constitute the conglomerates (Mabesoone and Alheiros, 1988Mabesoone JM, Alheiros MM. Origem da bacia sedimentar costeira Pernambuco-Paraíba. Rev Bras Geoci. 1988;18:476-82.). Additionally, the destabilization of smectite (as discussed above) can be a source of Mg2+ (Kämpf et al., 2009Kämpf N, Curi N, Marques JJ. Intemperismo e ocorrência de minerais no ambiente do solo. In: Melo VF, Alleoni LRF, editores. Química e mineralogia do solo. Viçosa, MG: Sociedade Brasileira de Ciência do Solo; 2009. Pt 1. p. 333-80.).

Taxonomic considerations

All profiles were classified according to the criteria established by the SiBCS (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 Nitossolos Háplicos and, according to the World Reference Base of Soils (WRB) (IUSS Working Group 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).), as Ferritic Nitisols. The profiles presented a dystrophic character and a high Fe content (ferric soils). In addition, P3 had an allytic character. Thus, a coherent soil classification requires a framework into new classes, related to the suborder of Nitossolos Háplicos. For that, it is suggested that profiles P1 and P2 are classified as Nitossolos Háplicos distroférricos, which is one of the classes already existing for Nitossolos Vermelhos and Brunos, while P3 is classified as Nitossolo Háplico alitiférrico, as a suggestion to improve the third categorical level of the order of the Nitossolos in the SiBCS (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 complete classification of the profiles was performed according to the SiBCS criteria (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 addition to the suggestions discussed above: P1 - Nitossolo Háplico distroférrico latossólico, a moderate, very clayey texture, with subperenifolia forest phase and undulating relief; P2 - Nitossolo Háplico distroférrico latossólico, a moderate, very clayey texture, with subperenifolia forest phase and undulating relief; P3 - Nitossolo Háplico alitiférrico típico, a moderate, very clayey texture, with subperforfolia forest phase and undulating relief.

Relation of soil to the adjacent environment

The comparison of the studied soils with other basalt-derived Nitossolos (Cabo Basin) under a humid tropical climate in the south coast of PE (Nascimento et al., 2009Nascimento MAL, Souza ZS, Arnosio JM, Vasconcelos PMP. Ignimbrito do Engenho Saco, Ipojuca, PE - Registro de vulcanismo explosivo cretácico na província magmática do Cabo. In: Winge M, Schobbenhaus C, Souza CRG, Fernandes ACS, Queiroz ET, Berbert-Born M, Campos DA, editores. Sítios geológicos e paleontológicos do Brasil. Brasília, DF: CPRM; 2009. v. II. p. 1-13.) suggests that the processes of monosialitization and ferralitization are more active in adjacent Nitossolos [Nitossolos Vermelhos - Oliveira et al. (2004)Oliveira LB, Ferreira MGVX, Marques FA. Characterization and classification of two soils derived from basic rocks in Pernambuco State Coast, Northeast Brazil. Sci Agric. 2004;61:615-25. https://doi.org/10.1590/S0103-90162004000600009
https://doi.org/10.1590/S0103-9016200400...
, and Nitossolos ácricos - Neves et al. (2018)Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
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], regardless of the position of the soil in the landscape. The lowest degree of evolution for the studied soils is indicated by the presence of easily weathered minerals (feldspars) in the sand and silt fractions of all toposequence profiles (Table 5). In addition, the occurrence of smectites in P3, which is under the influence of sedimentary rocks, increases the contrast between the Nitossolos studied in the present work and other Nitossolos of the Cabo Basin.

Other soils with Bt horizons are common in this region (Brasil, 1972Brasil. Ministério da Agricultura. Levantamento exploratório-reconhecimento de solos do Estado de Pernambuco. Escala 1:600.000. Recife: Sudene; 1972. (Boletim Técnico, 26).) with chemical and mineralogical properties similar to those of the studied soils, such as the Argissolos Vermelho-Amarelos developed from the Cabo Basin rhyolites (Brilhante et al., 2017Brilhante SA, Santos JCBS, Souza Júnior VS, Araujo JKS, Ribeiro Filho MR, Corrêa MM. Weathering of rhyolites and soil formation in an Atlantic Forest fragment in northeastern Brazil. Rev Bras Cienc Solo. 2017;41:e0160558. https://doi.org/10.1590/18069657rbcs20160558
https://doi.org/10.1590/18069657rbcs2016...
); these authors also described Cambissolo in this region. Argissolos Vermelho-Amarelos is typical of the PE coastal humid region in an area of pre-Cambrian rocks corresponding to the crystalline basement (Lima et al., 2008Lima JGC, Schulze SMBB, Ribeiro MR, Barreto SB. Mineralogia de um Argissolo Vermelho-Amarelo da zona úmida costeira do estado de Pernambuco. Rev Bras Cienc Solo. 2008;32:881-92. https://doi.org/10.1590/S0100-06832008000200042
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) and presents properties similar to those observed in the present study (mainly P1 and P2), such as base poverty, a clay fraction consisting mainly of 1:1 phyllosilicates and oxides, and being practically devoid of mineral reserves to release plant nutrients. In contrast to the studied soils (in the case of P3), the adjacent soils, including Nitossolos (Oliveira et al., 2004Oliveira LB, Ferreira MGVX, Marques FA. Characterization and classification of two soils derived from basic rocks in Pernambuco State Coast, Northeast Brazil. Sci Agric. 2004;61:615-25. https://doi.org/10.1590/S0103-90162004000600009
https://doi.org/10.1590/S0103-9016200400...
; Neves et al., 2018Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
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), present low levels of exchangeable Al3+.

However, the results show that the studied soils presented properties (greater sum of bases, CEC, available P) that compare favorably with other Nitossolos of the Cabo Basin (Oliveira et al., 2004Oliveira LB, Ferreira MGVX, Marques FA. Characterization and classification of two soils derived from basic rocks in Pernambuco State Coast, Northeast Brazil. Sci Agric. 2004;61:615-25. https://doi.org/10.1590/S0103-90162004000600009
https://doi.org/10.1590/S0103-9016200400...
; Neves et al., 2018Neves LVMW, Santos JCB, Souza Júnior VS, Corrêa MM, Araújo Filho JC. Associations between attributes of Nitisols and the climate of the Southern coast of Pernambuco. Rev Caatinga. 2018;31:255-63. https://doi.org/10.1590/1983-21252018v31n130rc
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) and other soils of this basin, mainly represented by Latossolos and Argissolos (Brasil, 1972Brasil. Ministério da Agricultura. Levantamento exploratório-reconhecimento de solos do Estado de Pernambuco. Escala 1:600.000. Recife: Sudene; 1972. (Boletim Técnico, 26).; Araújo Filho et al., 2000). This highlights the great agricultural potential of these soils surrounded by a variety of highly weathered soils, in contrast to floodplain soils such as Gleissolos Háplicos and Gleissolos Tiomórficos (Lemos, 2013Lemos JO. Caracterização de Gleissolos com e sem tiomorfismo da região litorânea do estado de Pernambuco [dissertação]. Recife: Universidade Federal Rural de Pernambuco; 2013.), with limitations due to hydromorphic conditions.

Although quartz is present in soils of the toposequence and predominates in adjacent soils (Lima et al., 2008Lima JGC, Schulze SMBB, Ribeiro MR, Barreto SB. Mineralogia de um Argissolo Vermelho-Amarelo da zona úmida costeira do estado de Pernambuco. Rev Bras Cienc Solo. 2008;32:881-92. https://doi.org/10.1590/S0100-06832008000200042
https://doi.org/10.1590/S0100-0683200800...
), especially those originated from felsic rocks (much of the Cabo Basin); the soils studied presented considerable amounts of minerals (feldspar) in the sand and silt fractions and mica in the sand fraction of P3, helping to maintain a high relative soil fertility through the release of nutrients. The occurrence of mica and smectite in Nitossolos, in addition to providing nutrients to plants (mainly K and Mg) by the chemical weathering of micaceous minerals, is a key factor in soil sorption properties under humid tropical conditions; such as relatively high CEC values (19.9 to 31.7 cmolc kg-1).

Minerals 2:1 in certain environments can contribute significantly to soil acidity, releasing high amounts of Al3+ (extracted by KCl 1 mol L-1) by weathering (Cunha et al., 2014Cunha GOM, Almeida JA, Barboza BB. Relação entre alumínio extraível com KCl e oxalato de amônio e a mineralogia da fração argila, em solos ácidos brasileiros. Rev Bras Cienc Solo. 2014;38:1387-401. https://doi.org/10.1590/S0100-06832014000500004
https://doi.org/10.1590/S0100-0683201400...
), as observed in P3 (Table 3). These minerals can be transported by erosion to associated environments (Navarre-Sitchler et al., 2011Navarre-Sitchler A, Steefel CI, Sak PB, Brantley SL. A reactive-transport model for weathering rind formation on basalt. Geochim Cosmochim Ac. 2011;75:7644-67. https://doi.org/10.1016/j.gca.2011.09.033
https://doi.org/10.1016/j.gca.2011.09.03...
), causing damage to both natural vegetation not adapted to high levels of exchangeable Al3+ and to commercial crops. In associated environments, the mineralogy of the hydromorphic soils has been strongly influenced by the geology of the basin that surrounds the coastal floodplains along the coast of PE cultivated with sugarcane (Lemos, 2013Lemos JO. Caracterização de Gleissolos com e sem tiomorfismo da região litorânea do estado de Pernambuco [dissertação]. Recife: Universidade Federal Rural de Pernambuco; 2013.). The transport of clay by erosion can be favored by the rolling relief of the Mares and Morros and the high rainfall, in addition to the intensive use of the soil (Tabarelli et al., 2006Tabarelli M, Melo MDVC, Lira OC. A Mata Atlântica do Nordeste. Rio de Janeiro: MMA; 2006.).

The high levels of Fe (ferric soils) in toposequence soils indicates a high phosphate-binding capacity (Almeida et al., 2003Almeida JA, Torrent J, Barrón V. Cor de solo, formas do fósforo e adsorção de fosfatos em Latossolos desenvolvidos de basalto do extremo-sul do Brasil. Rev Bras Cienc Solo. 2003;27:985-1002. http://dx.doi.org/10.1590/S0100-06832003000600003
http://dx.doi.org/10.1590/S0100-06832003...
), suggesting a high potential reserve of this nutrient. However, the low available P content can be quickly exhausted under intense agricultural activity, requiring the application of fertilizers at a high economic cost.

CONCLUSIONS

Nitossolo Háplicos (Ferritic Nitisols) in the southern coastal region of Pernambuco are formed from basalts and conglomerates, with the solum registering a marked influence of sedimentary material and soil topographic-hydrological conditions, presenting a high exchangeable aluminum content and the outstanding presence of smectite minerals.

The high levels of exchangeable aluminum are probably associated with the weathering of smectite minerals in addition to the possible presence of low-crystalline alumina forms.

The taxonomic classification of the studied soils requires improvement to the order of Nitossolos Háplicos in the SiBCS, contemplating the simultaneous occurrence of high levels of iron and aluminum, suggesting the following classes up to the third categorical level: Nitossolo Háplico distroférrico and Nitossolo Háplico alitiférrico.

ACKNOWLEDGMENTS

We thank our colleagues Mateus Rosas Ribeiro (In Memoriam), Orlando Augusto de Figueiro Filho, and José Fernando W. F. Lima for their cooperation in the design and performance of field work. We also thank Facepe through the Pronex-Facepe/CNPq Document (Process: APQ 0144-5.01/13), to CNPq (Processes: 552174/2011-4 and 486419/2013-4), and to the Coordination for the Improvement of Higher Education Personnel (CAPES) for scholarships.

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Publication Dates

  • Publication in this collection
    14 Feb 2019
  • Date of issue
    2019

History

  • Received
    1 May 2018
  • Accepted
    11 Sept 2018
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