Fragipan horizon degradation and bleached tongues formation in Albeluvisols of the Carpathian Foothills, Poland

Geoderma 167-168 (2011) 340–350

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Geoderma j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g e o d e r m a

Fragipan horizon degradation and bleached tongues formation in Albeluvisols of the Carpathian Foothills, Poland Wojciech Szymański a,⁎, Michał Skiba b, Stefan Skiba a a b

Jagiellonian University, Institute of Geography and Spatial Management, Department of Pedology and Soil Geography, Gronostajowa St. 7, 30-387 Cracow, Poland Jagiellonian University, Institute of Geological Sciences, Department of Mineralogy, Petrology and Geochemistry, Oleandry St. 2a, 30-063 Cracow, Poland

a r t i c l e

i n f o

Article history: Received 8 February 2011 Received in revised form 26 June 2011 Accepted 7 July 2011 Available online 14 September 2011 Keywords: Fragipan horizon Albeluvisols Quantitative X-ray diffraction Micromorphology The Carpathian Foothills

a b s t r a c t A fragipan horizon is defined as a natural, dense subsurface soil horizon, which restricts the infiltration of water and the penetration of roots. Most fragipans show evidence of degradation, which manifests itself in the formation of bleached tongues along vertical cracks. Despite the fact that fragipans have been extensively studied since the 1940s, the problem of their genesis, degradation and vertical tongues formation remains obscured. The main aim of the present study was to explain the genesis of bleached tongues in fragipan horizon using the example of Albeluvisols from the Carpathian Foothills in Poland. Undisturbed soil material was subjected to detailed micromorphological analysis using optical microscopy. Bulk soil material and soil clay fractions were analyzed quantitatively using X-ray diffraction. Basing on the obtained results, it is concluded that the formation of the vertical cracks is likely to be a result of seasonal drying, which promotes the opening of cracks. The prevalence of swelling clay minerals within illuvial horizons promotes periodic swelling and shrinking due to moisture changes. Once vertical cracks are formed, the next phase of fragipan degradation i.e. bleached tongues formation takes place. Tongues formation is most likely caused by the eluviation (microerosion) of weathering products. Eluviation is indicated by a lower concentration of clay minerals and iron oxides in material from vertical tongues when compared with material from prismatic clods and Btx horizon. In the studied soils, the formation of tongues due to the infilling of vertical cracks with material from an upper, eluvial horizon is also likely but only in the upper parts of the cracks. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Fragipan horizons have been extensively studied since the 1940s when Winters used this term for the first time to name dense soil horizons in loess and colluvium in Kentucky and Tennessee in the United States (Lindbo and Veneman, 1989). Previously, many different names had been assigned in the literature to horizons of this type, e.g. hardpans, siltpans, X-layers and indurated layers (Franzmeier et al., 1989). According to the literature (Ciolkosz et al., 1995; Lindbo et al., 1994; Witty and Knox, 1989), the fragipan horizon is defined as a natural, dense subsurface soil horizon, which restricts the infiltration of water and the penetration of roots. According to Witty and Knox (1989), the identification of fragipan horizons is possible only in the field basing on several criteria. According to Soil Survey Staff (2010), the criteria include: thickness N15 cm, coarse or very coarse prismatic structure, very hard consistence in the dry state and a more friable consistence in the moist state. In addition, fragipan horizons exhibit no cementation and air-dry clods should slake or rupture when placed

⁎ Corresponding author. Tel.: + 48 12 664 52 58; fax: + 48 12 664 53 85. E-mail address: [email protected] (W. Szymański). 0016-7061/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2011.07.007

in water (Soil Survey Staff, 2010). Fragipan horizons contain less than 0.5% organic carbon and do not contain carbonates. It shows evidence of pedogenesis in the form of clay coatings, clay infillings and iron– manganese nodules. Fragipan horizons are characterized by very low hydraulic conductivity resulting from close packing of grains. The physical properties of fragipan horizons make them a barrier to the infiltration of water and the penetration of roots (Ajmone-Marsan et al., 1994; Graveel et al., 2002; James et al., 1995; Lindbo et al., 1994, 1995; Miller et al., 1993). Fragipans are characteristic of mediumtextured soils from the middle latitudes and have been reported in the USA, Canada, New Zealand, the British Isles, the Czech Republic, Slovakia, Hungary, Romania, the Ukraine, France, Belgium, the Netherlands, Germany, Spain, Sweden, Italy and Poland (e.g. Ajmone-Marsan et al., 1994; Wilson et al., 2010; Witty and Knox, 1989). Most fragipans show evidence of degradation, which manifests itself in the formation of bleached tongues along vertical cracks (Payton, 1993b; Lindbo et al., 2000 and literature cited therein). In the horizontal section, bleached tongues are connected, forming a polygonal pattern (Aide and Marshaus, 2002; Ajmone-Marsan et al., 1994; Lindbo et al., 1995; Szymański et al., 2008). In the first stage of fragipan degradation, vertical fissures are formed. According to e.g. Van Vliet and Langohr (1981), Langohr and Sanders (1985),

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Payton (1993a), Van Vliet-Lanoё (1998) and Brahy et al. (2000), the formation of fissures is a result of the contraction of the soil material occurring in periglacial climate conditions. Grossman and Carlisle (1969), Ranney et al. (1975), Ciolkosz et al. (1995), Ciolkosz and Waltman (2000) and Weisenborn and Schaetzl (2005) state that fissures are formed due to seasonal drying taking place in moderately humid climates and causing the soil material to crack due to the dehydration of swelling clay minerals. The next phase of fragipan degradation and the processes that produce bleached tongues (glossic structures) are poorly understood. According to Carlisle (1954), Grossman and Carlisle (1969), Ranney et al. (1975), and Rampelberg et al. (1997), the formation of glossic structures is caused by the infilling of opened cracks with material from an overlying horizon. Such process may occur both in periglacial and moderately humid climates. Weisenborn and Schaetzl (2005) as well as Miller et al. (1993) believe that bleached tongues formation is a result of the microeluviation of weathering products caused by percolating water, which washes out clay minerals and iron oxides from the adjacent soil material. Lindbo et al. (1995, 2000), Ciolkosz et al. (1995), and Payton (1993b) suggest that in addition to water percolation, the presence of roots – a source of organic matter – promoting Fe 3+ reduction controls the translocation of weathering products along vertical cracks and controls the development of tongues. The main aim of the present study was to explain the genesis of bleached tongues in fragipan horizon using the example of Albeluvisols from the Carpathian Foothills in Poland. A combination of detailed micromorphological analysis and quantitative X-ray diffraction (QXRD) was applied. 2. Materials and methods 2.1. Study area The research was carried out in the Carpathian Foothills (i.e. the outermost part of the Carpathians) in Poland. The investigated area is built up of interstratified layers of sandstones and shales of turbiditic origin (so-called Carpathian flysch), which are covered by loess. In Poland, these deposits are called loess-like deposits. The loess was deposited during the Pleistocene — in the last phase (i.e. Vistulian) of glaciation (Klimaszewski, 1967), but it is somewhat different from typical loess because of a more sandy texture, lower porosity and higher content of angular grains (evidence of short transport). The source of such deposits was local material — weathered Carpathian flysch residue (Uziak, 1962). The loess forms virtually a continuous cover with thickness up to 20 m. The mean annual temperature in the area is 6 to 8 °C and the mean annual precipitation is 700–900 mm (Hess, 1965). Due to the favorable climate conditions, the Carpathian Foothills are an important agricultural region in Poland. 2.2. Field and laboratory methods Five soil profiles located between 200 and 310 m above sea level were studied. Each soil profile is formed entirely in loess. Four pits (i.e. Gaik-Brzezowa, Jedlicze, Łazy, and Pleśna) were excavated on gentle slopes (b5°) and one pit (Brzezie) on a footslope. The native vegetation in the study area was deciduous forest (Tilio-Carpinetum) with hornbeam (Carpinus betulus L.), lime (Tilia cordata Mill.), oak (Quercus sp.) and beech (Fagus sylvatica L.). All of the investigated soils were cultivated, with wheat (Triticum aestivum), rye (Secale cereale) and potatoes (Solanum tuberosum) being the most common crops. Soil samples were collected from every horizon in the excavated soil pits. Subsamples were taken from bleached tongues and prismatic clods (prisms) from fragipan horizon. All the soil samples

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were air dried, gently crushed using a wooden rolling pin, and screened through a 2 mm sieve. Soil properties were determined for the fine earth material (fraction b2 mm). Particle-size distribution was determined using a sieving and a hydrometer method (Gee and Bauder, 1986) for raw samples (i.e. without organic matter removal). Organic carbon content was determined using a modified Tyurin titrimetric technique (Nelson and Sommers, 1996) (digestion reagent: K2Cr2O7 and H2SO4; titrant: FeSO4 7H2O). Soil pH was measured in a 1:2.5 soil/distilled water ratio (w/w) (Thomas, 1996). In order to determine the amount of free and amorphous pedogenic Fe- and Al-oxides, citrate–bicarbonate–sodium dithionite (CBD) and ammonium oxalate (at pH 3) extracts were prepared according to the procedure given in Van Reeuwijk (2002). The CBD extracts were analyzed for Fe and Al using atomic absorption spectrometry (Schlichting and Blume, 1966). The oxalate extractable Fe and Al were measured using the colorimetric method with 1.10phenanthroline (Fe) and aluminon (Al). Bulk density and porosity were determined using the core method (Blake and Hartge, 1986). Soil color was described in the moist state using Munsell Color Soil Charts. Micromorphological analyses were carried out in thin sections (30 μm thick) prepared from undisturbed soil samples, which were first impregnated under vacuum with epoxy resin Araldite 2020. Micromorphological analyses were conducted for samples, which were collected from eluvial, fragipan and argillic horizons. Thin sections were described using terminology given by Stoops (2003). Quantitative and qualitative determinations of mineral composition were performed using X-ray diffraction (XRD). Bulk soil material (b2 mm fractions) and separated clay fractions (b0.2 μm) were analyzed. The bulk soil samples were air dried and 2.7 g of each sample was mixed with 0.3 g of Baker ZnO (catalog no. 1314-13-2) and ground in methanol using a McCrone micronizing mill for 5 min. The ground samples were passed through a 0.4 steel sieve and sideloaded to obtain random powder mounts according to the procedure given by Moore and Reynolds (1997). Clay fractions were separated from bulk samples by centrifugation. Prior to the separation, the bulk samples were treated with Na-acetic buffer, hydrogen peroxide, and Na-citrate–bicarbonate–dithionite (CBD) according to the procedure described by Jackson (1969). The separated fractions were split into two aliquots, which were saturated with K + and Mg 2+. Oriented mounts with a surface density of 10 mg/cm 2 were prepared from both K-saturated and Mgsaturated samples using a glass slide technique. For the XRD analyses, a Philips X'Pert diffractometer with a vertical goniometer PW3020 was used. The instrument was equipped with a 1° divergence slit, 0.2 mm receiving slit, incident- and diffracted-beam Soller slits, 1° anti-scatter slit and a graphite diffracted-beam monochromator. CuKα radiation was used with an applied voltage of 40 kV and a 30 mA current. Random mounts were scanned from 2 to 65°2θ at a counting speed of 0.02°/5 s. Oriented mounts were scanned from 2 to 52°2θ at a counting speed of 0.02°/2 s. K-saturated clays were analyzed in air dry condition and after heating for 1 h at 330 °C and at 550 °C. Mg-saturated clays were analyzed in air dry condition and after solvation with liquid glycerol. Relative air humidity was measured during every run. Quantitative analysis of the mineral composition of the bulk samples (b2 mm) was performed using the Rietveld AutoQuan/BGMN computer program (Taut et al., 1998). XRD data from a 15°2θ to 65°2θ range were used for calculation purposes. For the calculation of swelling minerals' content, a smectite structural model was used because the modeling of the XRD patterns recorded for the clay fractions indicated smectite rich mixed-layered minerals to be the main component of the fractions. Clay minerals were identified using operational definitions given by Środoń (2006). X-ray patterns were analyzed using the

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Fig. 1. Location of the study area and sampling sites within the Carpathian Foothills.

ClayLab computer program (Mystkowski, 1999). The modeling was performed for the pattern recorded under air-dry conditions and for the pattern recorded after solvation of the mount with ethylene

glycol. The Sybilla program – proprietary Chevron software – was used for the modeling. The program uses an algorithm originally developed by Drits and Sakharov (1976).

Table 1 Description of the studied soils. Horizon

Structure

Roots

Fe–Mn nodules

Clay coatings

Gaik-Brzezowa profile Cutani-Fragic Albeluvisol (Siltic) Ap 0–30 10YR 4/3 Btx1 30–90 10YR 5/4; 10YR 6/2 Btx2 90–140 10YR 5/4; 10YR 6/2 Btg 140–170 10YR 6/1

Depth (cm)

Color (moist)

Angular blocky Prismatic Prismatic Massive

++ Few Absence Absence

Absence +++ +++ ++

Absence +++ +++ +

Brzezie profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–25 10YR 5/3 AE1 25–40 10YR 5/4 AE2 40–58 10YR 5/3 Eg 58–70 10YR 7/2 Btx 70–95 10YR 6/8; 10YR 7/2 Btg1 95–115 10YR 6/6; 10YR 6/1 Btg2 115–180 10YR 6/6; 10YR 7/1

Angular blocky Angular blocky Angular blocky to granular Angular blocky to granular Prismatic Prismatic Prismatic

+++ ++ ++ + Few Absence Absence

Absence Absence Absence ++ +++ +++ ++

Absence Absence Absence Absence +++ +++ +++

Pleśna profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–35 10YR 4/3 Eg 35–45 10YR 5/3 Btx1 45–100 10YR 5/4; 10YR 6/3 Btx2 100–180 10YR 5/3; 10YR 6/3 Btg 180–245 10YR 5/2; 10YR 6/3 BCg 245–285 10YR 5/2

Angular blocky Angular blocky Prismatic Prismatic Massive Massive

+++ + Few Absence Absence Absence

Absence +++ +++ +++ + +

Absence Absence +++ +++ + +

Jedlicze profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–15 10YR 4/3 AE 15–30 10YR 4/3 Eg 30–50 10YR 4/3 to 5/3 Btx 50–100 10YR 4/4; 10YR 5/2 Btg 100–160 10YR 5/8; 10YR 5/3

Blocky Angular blocky Sub- to angular blocky Prismatic Massive

+++ + + Few Absence

Absence Absence Absence + ++

Absence Absence Absence +++ +

Łazy profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–35 10YR 3/3 Eg 35–50 10YR 4/3 Btx 50–70 10YR 5/6; 10YR 8/1 Btg 70–90 10YR 5/6 BC 90–110 10YR 5/4 C 110–150 10YR 5/4

Subangular blocky Ang- to subangular blocky Angular blocky Angular blocky Ang- to subangular blocky Massive

+++ + Few Absence Absence Absence

Absence Absence +++ Absence Absence Absence

Absence Absence +++ +++ + Absence

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3. Results and interpretation 3.1. Soil morphology and properties The location of the soils studied is shown in Fig. 1. Most of the soil pedons show a similar morphology: Ap-AE-Eg-Btx-Bt(g)-BC-C, and are classified as Fragic Albeluvisols according to WRB (IUSS Working Group WRB, 2006). The field description of the soil profiles is shown in Table 1. Four of the studied pedons (Brzezie, Pleśna, Jedlicze and Gaik-Brzezowa) contain thick fragipan horizon (Btx) with very distinctive vertical tongues, while one pedon (Łazy) is characterized by a thin fragipan horizon with very small tongues. The thickness of Ap horizons is 15–35 cm because of cultivation. Ap horizons show an angular blocky or sub-angular blocky structure and their color is dull yellowish brown (10YR 4/3 to 5/3) or dark brown (10YR 3/3). Within the Brzezie and Jedlicze profiles, underneath the Ap horizon, a transition horizon (AE) can be found. Lower parts of eluvial (E) horizons present in four of the profiles studied (Brzezie, Pleśna, Jedlicze and Łazy) exhibit a stagno-gleyic color pattern, which is due to a distinct change in permeability between upper horizons (Ap, E) and a deeper horizon (Btx). The thickness of E horizons is between 10 and 20 cm. In the case of the Gaik-Brzezowa profile, an eluvial horizon does not exist (probably due to erosion) and a secondary Ap horizon formed by cultivation is directly underlain by a fragipan horizon. In all of the investigated profiles, the fragipan horizon constitutes an upper part of an argillic horizon and is characterized by the occurrence of light grey tongues (10YR 6/2 to 8/2), which follow vertical cracks. The tongues are 1–10 cm wide and 10–180 cm long and form a polygonal network. In the Pleśna and the Gaik-Brzezowa profiles, reddish rims (7.5YR 5/6) were observed within the bleached tongues. The rims show very sharp contact with tongues and diffuse contact with prisms. The thickness of the hard and mottled fragipan horizon varies from 20 cm in the Łazy profile to 135 cm in the Pleśna profile. This is most likely related to variation in the erosion rate in the different soil profiles. A very coarse prismatic structure with thick clay coatings (argillans) on the faces of prisms was observed (visual inspection) within the fragipan horizon studied. The prism diameter is between 20 and 40 cm. The most common secondary structure in the fragipan is an angular blocky. The studied fragipan horizon shows extremely hard consistence and brittleness. Within the fragipan horizon, numerous black and rusty-black iron and iron–manganese nodules occur (especially in the upper part of the horizon) indicating seasonal variations in moisture conditions. The argillic horizon (Bt) exhibits a similar morphology to the fragipan. However, the prismatic structure is less developed and the consistence is not as hard as it is in the fragipan horizon. With increasing depth, the argillic horizon gradually transforms via a transition horizon (BC) into the parent material (C). In the Łazy profile, the C horizon shows very weak lamination. In the remaining profiles, the C horizon was not reached because of very deep (N3 m) illuviation of colloidal clay. The chemical and physical properties of the investigated soils are typical for Albeluvisols (IUSS Working Group WRB, 2006; Soil Survey Staff, 2010) and are summarized in Tables 2 and 3, respectively. The acidic or slightly acidic pH of the soils studied is a result of a lack of carbonates in the parent material and the effect of a moderately humid climate that promotes leaching. In the Gaik-Brzezowa and Łazy profiles, higher pH values were observed in the upper part of the soil profile, which is most likely the effect of liming treatments. Organic carbon content in the Ap horizons is rather low because of the strong activity of soil edaphone and very intensive agriculture. In the soils studied, the CBD-extractable Fe concentration is higher in fragipan and argillic horizons than in upper (i.e. Ap, E) horizons, which suggests the translocation of extractable Fe together with clay minerals due to lessivage (Table 2). However, the concentration of CBD-extractable iron is appreciably lower in vertical tongues in

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Table 2 Selected chemical properties and organic carbon content of the studied soils. Alod (%)

Fed– Feo

(Fed– Feo)/Fed

Feo/ Fed

Cutani-Fragic Albeluvisol (Siltic) 6.8 0.9 0.60 0.41 0.15 6.2 0.0 0.75 0.42 0.15 5.4 0.0 0.54 0.37 0.13 6.0 0.0 0.39 0.18 0.07 n.a.⁎ 0.0 0.06 0.04 0.07 n.a. 0.0 n.a. n.a. n.a.

0.20 0.32 0.18 0.21 0.02 n.a.

0.32 0.43 0.33 0.54 0.28 n.a.

0.68 0.57 0.67 0.46 0.72 n.a.

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

0.16 0.13 0.09 0.00 0.41 0.53 0.44 0.04

0.30 0.24 0.18 0.00 0.52 0.73 0.74 0.17

0.70 0.76 0.82 1.00 0.48 0.27 0.26 0.83

0.39 0.48 0.60 0.40 0.29 0.35 0.09 1.29

0.13 0.14 0.15 0.11 0.11 0.11 0.11 n.a.

0.15 0.14 0.14 0.34 0.16 0.31 0.04 0.44

0.28 0.23 0.19 0.46 0.36 0.47 0.31 0.25

0.72 0.77 0.81 0.54 0.64 0.53 0.69 0.75

Jedlicze profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–15 5.4 1.1 0.52 0.35 AE 15–30 5.5 0.7 0.50 0.38 Eg 30–50 6.0 0.4 0.61 0.52 Btx 50–100 6.5 0.0 0.91 0.33 Btg 100–160 6.8 0.0 0.94 0.28 Bleached tongues n.a. 0.3 0.43 0.30

0.14 0.14 0.17 0.15 0.09 0.13

0.17 0.12 0.09 0.59 0.65 0.13

0.33 0.24 0.15 0.64 0.70 0.30

0.67 0.76 0.85 0.36 0.30 0.70

Łazy profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–35 6.4 0.9 0.39 Eg 35–50 6.7 0.2 0.55 Btx 50–70 6.1 0.0 1.10 Btg 70–90 5.5 0.0 0.87 BC 90–110 5.7 0.0 0.68 C 110–150 5.6 0.0 0.53

0.14 0.12 0.17 0.14 0.11 0.10

0.14 0.26 0.83 0.60 0.39 0.27

0.36 0.47 0.75 0.69 0.57 0.50

0.64 0.53 0.25 0.31 0.43 0.50

Horizon

Depth (cm)

Gaik-Brzezowa profile Ap 0–30 Btx1 30–90 Btx2 90–140 Btg 140–170 Bleached tongues Prisms

pH (H2O)

SOCa (%)

Fedb (%)

Feoc (%)

Brzezie profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–25 5.3 1.1 0.53 0.37 AE1 25–40 5.4 0.7 0.55 0.42 AE2 40–58 5.4 0.7 0.52 0.43 Eg 58–70 5.4 0.2 0.33 0.33 Btx 70–95 5.1 0.0 0.79 0.38 Btg1 95–115 5.4 0.0 0.73 0.20 Btg2 115–180 6.0 0.0 0.59 0.15 Bleached tongues n.a. n.a. 0.24 0.20 Pleśna profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–35 5.1 0.8 0.54 Eg 35–45 5.6 0.4 0.63 Btx1 45–100 6.0 0.0 0.74 Btx2 100–180 5.4 0.0 0.74 Btg 180–245 5.2 0.0 0.45 BCg 245–285 5.7 0.0 0.66 Bleached tongues n.a. n.a. 0.13 Rusty rims of n.a. n.a. 1.73 tongues

0.25 0.29 0.28 0.27 0.29 0.27

a

Soil organic carbon. Extracted with Na-citrate/bicarbonate/dithionite. Extracted with ammonium oxalate. d Extracted with ammonium oxalate. ⁎ Not analyzed. b c

comparison with adjacent prismatic clods from the fragipan horizon and the upper eluvial horizon. Most likely such a distribution of extractable iron is a result of the infiltration of water along vertical cracks. Infiltration promotes the reduction and dislocation of iron. The concentration of ammonium oxalate-extractable Al and Fe is almost evenly distributed throughout the investigated pedons. The highest concentration of crystalline iron oxides (Fed–Feo) and the highest crystallinity of the oxides (Fed–Feo/Fed) occur in fragipan and argillic horizons (Table 2). This suggests the presence of conditions that favor iron oxide crystallization within these horizons. The occurrence of maximum Feo/Fed ratios above the studied fragipan horizon (Brzezie, Jedlicze and Łazy profiles) or in the upper part of the pan (Pleśna profile) indicates the formation of poorly crystalline iron oxides and hydroxides due to redox processes taking place within these horizons (Table 2). The fragipan has higher bulk density and lower porosity than the upper horizons, which significantly reduces the permeability and retention ability of the investigated Albeluvisols. All of the horizons of the studied soils have a silt loam texture, which has been inherited from the parent material. However, the fragipan and argillic horizons contain a larger amount of clay (b2 μm) than the

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Table 3 Particle-size distribution, bulk density and total porosity of the studied soils. Horizon

Dba

Pb

0.006–0.002

(Mg/m3)

(%)

26.2 25.3 24.1 26.8 23.8 25.0

7.1 5.0 6.0 4.9 3.6 6.3

1.51 1.57 1.63 1.66 n.a.⁎ n.a.

42.8 41.4 39.6 37.8 n.a. n.a.

46.4 49.3 48.4 51.7 52.3 58.5 55.0

26.0 29.9 28.7 22.0 23.6 22.5 19.5

10.9 9.8 12.3 7.8 10.7 6.1 6.3

1.55 1.50 1.45 1.41 1.68 1.67 1.70

40.8 43.8 45.3 46.6 37.5 38.1 36.3

15.9 14.2 16.0 12.4 16.1 13.1 13.9 16.5 14.3

49.6 48.6 47.1 51.6 52.8 50.0 52.9 49.4 50.6

26.0 27.4 26.6 30.9 26.0 28.6 29.1 27.8 31.2

8.5 9.8 10.3 5.1 5.1 8.3 4.1 6.3 3.9

1.54 1.57 1.63 1.62 1.61 n.a. n.a. n.a. n.a.

40.3 40.1 38.0 37.7 38.8 n.a. n.a. n.a. n.a.

15.0 14.0 16.0 21.0 20.0 15.5

24.7 24.4 24.4 21.5 26.3 23.1

44.7 43.0 43.5 43.7 45.0 43.8

24.7 23.3 23.8 23.4 18.8 23.1

5.9 9.3 8.3 11.4 10.0 10.1

1.36 1.48 1.51 1.62 1.65 n.a.

47.9 43.3 43.2 38.9 38.0 n.a.

8.5 11.0 22.5 17.5 13.0 13.3 9.3 23.0

23.0 23.6 19.4 21.8 18.6 21.0 23.4 21.4

49.7 52.8 53.5 55.2 55.5 54.8 52.4 54.9

21.3 18.0 20.0 16.4 18.7 19.0 17.1 15.8

6.0 5.6 7.1 6.7 7.1 5.2 7.2 7.8

1.27 1.53 1.61 1.56 1.56 1.65 n.a. n.a.

51.2 43.1 39.7 42.4 41.8 38.7 n.a. n.a.

Depth

Sand

Silt

Clay

Clay-free basis (%)

(cm)

2.0–0.05

0.05–0.002

b0.002

2.0–0.05

0.05–0.02

0.02–0.006

Gaik-Brzezowa profile Cutani-Fragic Albeluvisol (Siltic) Ap 0-30 12.0 72.0 Btx1 30–90 12.0 67.0 Btx2 90–140 13.0 70.0 Btg 140–170 13.0 69.0 Bleached tongues 12.0 72.0 Prisms 12.0 68.0

16.0 21.0 17.0 18.0 16.0 20.0

14.3 15.2 15.7 15.9 14.3 15.0

52.4 54.4 54.2 52.4 58.3 53.8

Brzezie profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–25 14.3 AE1 25–40 9.3 AE2 40–58 9.0 Eg 58–70 16.6 Btx 70–95 10.5 Btg1 95–115 10.3 Btg2 115–180 16.1

71.4 75.3 75.7 73.5 67.2 68.9 67.6

14.3 15.4 15.3 9.9 22.3 20.8 16.3

16.7 11.0 10.6 18.4 13.5 13.0 19.2

Pleśna profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–35 13.6 Eg 35–45 12.1 Btx1 45–100 12.9 Btx2 100–180 10.2 Btg 180–245 13.2 BCg 245–285 11.0 Bleached tongues 11.1 Rusty rims of tongues 13.0 Prisms 11.0

72.1 72.9 67.8 71.8 68.8 73.0 68.9 66.0 66.0

14.3 15.0 19.3 18.0 18.0 16.0 20.0 21.0 23.0

Jedlicze profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–15 21.0 AE 15–30 21.0 Eg 30–50 20.5 Btx 50–100 17.0 Btg 100–160 21.0 Bleached tongues 19.5

64.0 65.0 63.5 62.0 59.0 65.0

Łazy profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–35 21.0 Eg 35–50 21.0 Btx 50–70 15.0 Btg 70–90 18.0 BC 90–110 16.2 C 110–150 18.2 Bleached tongues 21.2 Prisms 16.5

70.5 68.0 62.5 64.5 70.8 68.5 69.5 60.5

a

Bulk density Total porosity ⁎ Not analyzed b

upper parts of the studied soil profiles (Table 3). A similar texture found throughout the entire profile when taken into consideration without the clay fraction (clay-free basis) in all of the soils studied indicates that all of the soils are formed entirely within one formation of loess (Table 3). A higher content of clay particles and higher bulk density of the fragipan and argillic horizons in comparison with the upper genetic horizons is most likely a result of lessivage. However, the high bulk density of the fragipan horizon may also have been inherited from the parent material, which may become more dense due to hydroconsolidation before pedogenesis. 3.2. Micromorphological properties In most of the studied soils, the eluvial horizon shows a massive, channel and chamber microstructure. The diameter of voids is about 200–500 μm. The coarse material consists of rough and subangular grains of quartz, plagioclases (albite), K-feldspars (microcline) and flakes of muscovite. In addition, small subangular aggregates of glauconite (most likely inherited from the parent material) occur. The eluvial horizon is almost completely free of clay coatings and clay

infillings. A small number of such structures are visible only in the lower part, along the contact with the fragipan horizon. The color of the horizon is light grey (almost white) with very characteristic rusty and rusty-black iron and iron–manganese nodules (Fig. 2A and B). The nodules occur especially along the contact with the fragipan horizon. Both disorthic nodules with very sharp boundaries and orthic nodules, which show diffuse boundaries, are observed. The nodules show an undifferentiated fabric and reach 400–500 μm in diameter. The studied fragipan horizon has a very coarse prismatic structure with the presence of several clay coatings and clay infillings. The central parts of prisms are characterized by a massive or channel microstructure (Fig. 3A and B). The diameter of the channels reaches 200–500 μm. Vertical fissures (planes) occur between structural units. Rough and subangular grains of quartz, plagioclase, K-feldspar and flakes of muscovite constitute the coarse material of the groundmass. In addition, strongly weathered lithic grains (i.e. shales and cherts) and subangular aggregates of glauconite are observed. The lithic grains are 100–400 μm in diameter. The micromass is composed of yellowish brown structures of anisotropic clay, which are oriented around channels forming porostriated b-fabric or

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Fig. 2. Fe-nodules in eluvial horizon, Pleśna profile (A, B); central part of bleached tongue with clay coatings (arrows) in the fragipan horizon, Pleśna profile (C, D).

around coarse grains forming granostriated b-fabric with the granostriated b-fabric being less common. Clay coatings and clay infillings are enriched with iron oxides (ferriargillans according to Brewer (1964)). In addition, numerous compound pedofeatures (i.e. iron nodules coated with clay cutans) occur. Clay coatings are concentrated on prism faces and around channels. Fragments of deformed clay coatings (i.e. papules according to Brewer (1964)), which serve as evidence of mechanical deformations (i.e. swelling and shrinking) of soil material, also occur. Numerous microlaminated clay infillings with a very distinctive orientation of clay domains are present within the fragipan horizon. In addition to clay coatings, clay domains, which were formed in situ (most likely by weathering), are observed. Clay domains surround highly weathered flakes of muscovite (showing pellicular and parallel linear patterns). Numerous iron–manganese nodules are visible in the upper part of the fragipan horizon. Common vertical cracks (1–2 mm wide) surrounded with light grey material (10YR 8/2) also occur (Fig. 3C and D). The light grey material shows a massive microstructure and is depleted of clay coatings and iron oxides. In other words, it forms a depletion zone (Fig. 3E and F). The content of illuvial clay is lower in the central parts of tongues in comparison with their peripheral parts. Bleached tongues are almost completely lacking in iron–clay cutans (Fig. 2C and D). The lower parts of vertical fissures are plugged with clay particles. The argillic horizon (Bt or Btg) shows very similar features to those observed in the fragipan horizon (Btx). However, the argillic horizon is characterized by a lack of vertical cracks. It has a massive and channel microstructure. The groundmass is composed of rough and subangular grains of quartz, plagioclase, K-feldspar, flakes of muscovite, subangular aggregates of glauconite and highly weathered lithic grains (shales and cherts) belonging to the silt or fine sand fractions. The orientation of the micromass is mainly porostriated b-fabric. Numerous argillans occur within the illuvial horizon. The argillans concentrate on the faces of peds and in channels forming linings. In addition, large clay infillings with distinctive mechanical deformations (cracks) and iron and iron–manganese nodules are also present.

3.3. Mineral composition of the investigated soils All of the investigated soils have a very similar mineral composition. The dominating non-clay minerals are: quartz, K-feldspars (microcline and sanidine), plagioclases (albite and oligoclase) and dioctahedral mica (muscovite) (Fig. 4). Clay minerals are represented by mica, kaolinite, chlorite and swelling minerals (Fig. 5). In addition, traces of goethite were found. Given that all of the studied clay fractions produced very similar XRD patterns, one sample (from the fragipan horizon from the Łazy profile) was selected for detailed analysis including XRD trace modeling. A best but far from perfect fit was achieved for a rather complex mixture of smectite, mica– vermiculite, chlorite–vermiculite, mica–smectite, and mica–vermiculite– smectite mixed layered minerals (Fig. 6). Quantitative analysis of the mineral composition shows distinct differences in the content of clay and non-clay minerals between genetic horizons (Table 4). Quartz is a dominant mineral and its mean content across all genetic horizons is similar. Distinct differences in the mean content of quartz between prisms of the fragipan horizon (57.3%) and bleached tongues (65.3%) are evidence of the depletion of the latter in colloidal particles. In general, K-feldspars and plagioclases occur in smaller amounts than quartz. The mean feldspar content is similar in all the studied horizons. However, K-feldspars prevail over plagioclases in upper soil horizons. This is most likely caused by the higher resistance of K-feldspars to weathering. Dioctahedral mica (muscovite/illite and glauconite) content increases with depth. The increase is most likely a result of weathering (mica vermiculitization), which takes place near the soil surface. Lessivage may also be responsible. The lower content of di-micas in bleached tongues (average 4.3%) than in prisms (average 5.9%) indicates that pedological processes (mainly lessivage) are more intensive along vertical cracks. The prism interior is protected from weathering and translocation of clay particles because of the close packing of mineral grains and thick clay coatings on faces. Swelling minerals (represented in Table 4 by smectite) are the most abundant clay minerals present in the studied soils. Swelling clays are most concentrated in

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Fig. 3. Channel microstructure and clay coatings in the fragipan horizon, Łazy profile (A, B); clay and iron depletion zone along vertical fissure in the fragipan horizon, Pleśna profile (C, D); contact of the bleached tongue (right side) with reddish rim (left side) and orthic Fe-nodule in the fragipan horizon, Pleśna profile (E, F).

the fragipan horizon, where their mean content reaches 14.0%. The translocation of clay minerals (lessivage) resulted in a decrease in the content of swelling minerals in the upper Ap, AE and E horizons (mean content: 8.1%, 7.9% and 6.4%, respectively) when compared with illuvial horizons (mean for Btx and Bt: 14.0% and 11.8%,

respectively). The significant difference in the amount of swelling clay minerals between prisms (mean: 14.7%) and glossic structures (mean: 8.0%) indicates that translocation of colloidal clay (lessivage) proceeds mainly along vertical cracks. The translocation is most likely caused by the preferential flow of infiltrating water along cracks

Fig. 4. XRD pattern of raw sample (b 2 mm) with internal standard (zincite) from the fragipan horizon, Łazy profile.

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347

Fig. 5. XRD patterns of clay fraction (b0.2 μm) oriented mounts from the fragipan horizon, Łazy profile.

(because of the low porosity of the prisms). Chlorite and kaolinite exhibit a very similar trend as swelling clay minerals with the maximum concentration in illuvial horizons. The occurrence of the maximum content of swelling clay minerals, kaolinite and chlorite in the fragipan horizon, is related to lessivage occurring in the studied soils. Kaolinite is characterized by a somewhat higher concentration than chlorite, especially in the upper horizons where chlorite undergoes weathering. In the case of chlorite, and particularly in the case of kaolinite, a clear difference in the mean content between prisms (1.9% for chlorite and 1.5% for kaolinite) and bleached tongues (1.6% for chlorite and 0.9% for kaolinite) is observed. The lower content of chlorite and kaolinite in upper horizons and in vertical tongues is a result of lessivage.

4. Discussion The occurrence of the fragipan horizon is typical of soils in the Carpathian Foothills in Poland. The pan meets all the diagnostic criteria defined for fragic horizon in the World Reference Base for Soil Resources (IUSS Working Group WRB, 2006) and in Soil Taxonomy (Soil Survey Staff, 2010). The presence of albeluvic tonguing is a characteristic and common feature, which indicates that the fragipan horizon has undergone degradation. In order to explain the origin of bleached tongues in the studied fragipan, first the origin of the vertical cracks needs to be discussed. According to the literature (Brahy et al., 2000; Ciolkosz et al., 1995; Grossman and Carlisle, 1969; Langohr and Sanders, 1985; Van Vliet and Langohr,

Fig. 6. Comparison of the experimental (black) and the SYBILLA modeled (grey) XRD patterns of the Mg saturated, air dried, oriented clay fraction from the fragipan horizon, Łazy profile.

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Table 4 Quantitative mineral composition of bulk samples (b2 mm) of the studied soils. Horizon

Depth

Quartz

(cm)

(%)

Plagioclases

Di-micas

Chlorite

Kaolinite

Smectite

Goethite

Amorphous

Gaik-Brzezowa profile Cutani-Fragic Albeluvisol (Siltic) Ap 0–30 62.2 10.7 Btx1 30–90 58.2 9.6 Btx2 90–140 60.4 10.2 Btg 140–170 58.2 9.6 Bleached tongues 65.6 9.6 Prisms 56.4 10.7

8.6 8.3 9.0 10.6 9.1 8.6

5.6 3.9 5.0 5.3 4.6 5.8

0.7 1.7 1.1 2.2 1.2 1.7

1.6 1.8 1.5 0.8 0.0 1.7

10.2 16.5 12.7 13.0 9.9 15.0

0.1 0.0 0.1 0.0 0.0 0.1

0.3 0.0 0.0 0.3 0.0 0.0

Brzezie profile Stagni-Fragic Albeluvisol Ap 0–25 AE1 25–40 AE2 40–58 Eg 58–70 Btx 70–95 Btg1 95–115 Btg2 115–180 Bleached tongues 75.4

8.0 8.0 10.1 9.4 8.7 8.9 8.5 7.8

6.5 6.4 6.9 6.8 6.8 7.8 8.3 2.5

3.3 2.9 5.3 3.3 5.1 4.8 4.5 1.6

1.4 1.0 1.0 1.4 1.8 1.7 1.4 0.4

1.4 1.3 2.1 0.6 2.5 1.8 1.0 2.7

7.0 7.7 9.7 5.7 15.3 11.9 9.9 0.0

0.0 0.0 0.0 0.0 0.5 0.1 0.1 0.3

10.9 8.0 1.5 5.3 1.8 0.8 4.0

8.4 8.8 9.5 9.6 8.5 8.9 9.5 10.0 10.0

8.2 7.6 8.4 8.9 9.3 9.7 8.4 8.4 7.7

3.4 4.3 6.5 5.4 5.3 6.4 5.6 6.3 5.3

0.6 1.1 1.2 1.9 2.0 2.0 1.9 1.0 2.1

1.4 1.6 2.2 2.0 1.8 1.3 2.2 2.4 2.1

9.7 6.4 15.0 11.9 11.4 12.5 12.1 13.7 15.5

0.1 0.0 0.0 0.2 0.0 0.0 0.0 0.2 0.2

10.1 10.7 0.0 1.6 2.9 0.0 3.1 0.0 0.0

10.2 8.8 9.0 8.4 8.2 8.7

10.1 10.0 9.7 8.8 9.4 9.9

4.6 4.0 4.9 6.9 7.3 5.3

0.9 1.7 1.6 1.7 2.2 2.1

1.3 0.7 1.1 2.0 1.9 2.0

8.4 6.4 6.2 11.4 14.0 9.3

0.0 0.0 0.0 0.2 0.3 0.0

1.8 3.6 3.5 6.9 1.6 4.8

8.8 9.3 5.8 8.4 8.5 9.1 9.1 8.0

7.7 7.4 6.7 8.3 7.9 8.2 8.7 7.0

3.2 4.1 5.5 5.6 4.9 4.1 3.5 6.5

1.4 1.2 2.1 1.7 1.3 1.4 1.3 1.8

0.3 1.8 1.4 2.2 1.8 2.0 0.0 0.7

5.0 7.1 15.1 11.8 11.0 10.1 6.0 13.5

0.0 0.0 0.3 0.2 0.1 0.0 0.0 0.4

7.1 5.8 6.0 0.4 4.4 3.3 1.2 3.6

Pleśna profile Stagni-Fragic Albeluvisol Ap 0–35 Eg 35–45 Btx1 45–100 Btx2 100–180 Btg 180–245 BCg 245–285 Bleached tongues Rusty rims of tongues Prisms

(Siltic) 61.5 64.7 63.4 67.5 57.5 62.2 62.3 9.3

(Siltic) 58.1 59.5 57.2 58.5 58.8 59.2 57.2 58.0 57.1

Jedlicze profile Stagni-Fragic Albeluvisol Ap 0–15 AE 15–30 Eg 30–50 Btx 50–100 Btg 100–160 Bleached tongues

(Siltic) 62.7 64.8 64.0 53.7 55.1 57.9

Łazy profile Stagni-Fragic Albeluvisol (Siltic) Ap 0–35 66.5 Eg 35–50 63.3 Btx 50–70 57.1 Btg 70–90 61.4 BC 90–110 60.1 C 110–150 61.8 Bleached tongues 70.2 Prisms 58.5

K-feldspars

1981, and Weisenborn and Schaetzl, 2005), vertical cracks can form in periglacial or moderate climate conditions, and both possible origins need to be taken into consideration. The degradation of the studied fragipan horizon in periglacial conditions due to contraction and the development of vertical cracks are unlikely, as the studied Albeluvisols were formed from loess, which was deposited during the last phase of glaciation (Klimaszewski, 1967). Thus, when periglacial conditions prevailed in the investigated area, the studied soils were in their initial phase of formation. At that time, solifluction processes were dominant and most likely the soil material had undergone densification due to hydroconsolidation (Assalay et al., 1998; Bryant, 1989). The lack of periglacial microstructures within the fragipan horizon (e.g. vesicle voids, platy or lenticular microstructure and banded fabric) also indicates that the pan must have been formed under different (i.e. non-periglacial) conditions. Platy microstructures in the fragipan horizon in Albeluvisols of the Carpathian Foothills were found in other places by other researchers (Drewnik and Żyła, 2010, personal communication), however, Ciolkosz et al. (1995) and Certini et al. (2007) reported that platy microstructures can be formed in fragipans developed in areas, which had never experienced periglacial conditions. Thus, the occurrence of platy microstructures without other

frost structures (i.e. banded fabric, vesicles) cannot be interpreted as a result of freezing processes. The degradation process of fragipan horizon in Albeluvisols of the Carpathian Foothills in Poland could have started at least after the last glaciation (i.e. moderate climate). Thus, the formation of vertical cracks is likely to be a result of seasonal drying, which promotes the opening of cracks. Wetting and drying are indicated by the presence of numerous iron and iron–manganese nodules, which are formed due to redox fluctuations (Lindbo et al., 2000; Rhoton et al., 1993). In addition, compound pedofeatures (iron nodules coated with clay cutans) and iron–clay cutans were observed in the studied fragipan horizon. The pedofeatures suggest simultaneous lessivage and gleyic processes (Zasoński, 1983, 1992). The existence of numerous and well-developed clay and iron–clay coatings in the studied fragipan indicates that lessivage is an ongoing process and allows to classify the fragipan horizon as an argillic horizon (Lindbo and Veneman, 1993). In addition, the opening of cracks is favored by the mineral composition of the studied soils' clay fraction. The predominance of swelling clay minerals within illuvial horizons promotes periodic swelling and shrinking due to moisture changes. The presence of swelling

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minerals in the fragipan showing glossic structures was reported previously by several researchers (Aide and Marshaus, 2002; Scalenghe et al., 2004; Tremocoldi et al., 1994). Thus, it seems very likely that the abundance of swelling clay minerals in the soil material is necessary for fragipan degradation (i.e. vertical cracks formation and bleached tongues development). Ritchie et al. (1974) and Ransom et al. (1987) reported that 30% content of the clay fraction in fragipans is a threshold value for degradation (because of swelling and shrinking) to occur. However, it is worth noting that the actual threshold value is expected to be dependent on the qualitative mineral composition of the clay fraction. A high content of swelling minerals will reduce the threshold value. On the contrary, the predominance of non-swelling clay minerals such as kaolinite and illite will raise the threshold value (James et al., 1995). Therefore, it appears that a clay fraction content between 17.0% and 22.5% is sufficient for degradation to occur in the investigated fragipan horizon, which is rich in swelling mineral phases. Once vertical cracks are formed, the next phase of fragipan degradation (i.e. the bleached tongues formation) takes place. Tongues formation is most likely caused by the eluviation and microerosion of weathering products. Eluviation is indicated by a lower concentration of clay minerals and iron oxides in material collected from vertical tongues compared with material collected from prismatic clods and the Btx horizon. Microerosion and eluviation along vertical cracks in the fragipan horizon was previously reported by Ciolkosz et al. (1995), Weisenborn and Schaetzl (2005) in the United States and Payton (1993b) in England. According to Ajmone-Marsan et al. (1994) and Lindbo et al. (2000), the migration of iron and manganese is favored by reduction because of periodic water saturation of the soil material over the fragipan horizon and between structural units (prisms). The reduced forms of iron and manganese are leached out from bleached tongues and are accumulated as nodules or Fe-staining rim at the tongue-prism interface. The presence of a rusty rim within the bleached tongues and Fe nodules in the studied soils confirms the migration of Fe with water. The occurrence of clay coatings and clay infillings within material from bleached tongues and a lack or merely trace amounts of such structures in the Eg horizon indicate that the bleached material between prisms is rather a remnant of a fragipan horizon, which was depleted of Fe and clay minerals to a lesser extent than the material from overlaying horizons. This is in agreement with the observation presented by James et al. (1995), who also reported gray seams (glossic structures) containing illuvial clay in fragipan soils in Missouri. Lindbo and Veneman (1993) also reported that bleached prism faces in Massachusetts fragipan soils contained clay coatings (argillans) but in smaller amounts than the interiors of prisms. In turn, Tornes et al. (2000), who studied soils with fractured parent material in Ohio, observed the reduction and removal of free iron oxides along fractures and formation of gray seams. In the studied soils, the formation of tongues due to the infilling of vertical cracks with material from the upper, eluvial horizon, which was previously proposed by Carlisle (1954), Grossman and Carlisle (1969), Ranney et al. (1975) and Rampelberg et al. (1997), is also likely but only in the upper parts of cracks. 5. Conclusions 1 The degradation of the fragipan horizon in periglacial conditions due to contraction, which promotes the development of vertical cracks, is unlikely. 2 The degradation of the fragipan horizon in Albeluvisols of the Carpathian Foothills has been taking place since at least the last glaciation in a moderate climate. 3 The formation of vertical cracks is most likely a result of seasonal drying and it is favored by the abundance of swelling clay minerals in a fragipan.

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4 The development of bleached tongues is caused by percolating water, which infiltrates along vertical cracks and washes out clay minerals and iron oxides from the adjacent soil material. Acknowledgments This study was supported by the Polish State Committee for Scientific Research via Grant No. NN305 120934. The authors would like to thank Adam Michalski and Michał Dąbrowski from the Department of Pedology at Nicolaus Copernicus University in Toruń for their iron and aluminum oxide laboratory data. The authors would also like to thank Michael J. Vepraskas (Editor) and the two anonymous reviewers for their helpful suggestions. The authors further wish to acknowledge Chevron ETC and Dougal McCarty for permission to use the proprietary SYBILLA software. Finally, language editing was done by Grzegorz Zębik. References Aide, M., Marshaus, A., 2002. Fragipan genesis in two Alfisols in east central Missouri. Soil Science 167 (7), 453–464. Ajmone-Marsan, F., Pagliai, M., Pini, R., 1994. Identification and properties of fragipan soils in the Piemonte Region of Italy. Soil Sci. Soc. Am. J. 58, 891–900 (Madison, Wisconsin). Assalay, A.M., Jefferson, I., Rogers, C.D.F., Smalley, I.J., 1998. Fragipan formation in loess soils: development of the Bryant hydroconsolidation hypothesis. Geoderma 83, 1–16. Blake, G.R., Hartge, K.H., 1986. Bulk density, In: Klute, A. (Ed.), Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods, 2nd edition. : Agronomy Monograph, vol. 9. ASA-SSSA, Madison, Wisconsin, pp. 363–375. Brahy, V., Deckers, J., Delvaux, B., 2000. Estimation of soil weathering stage and acid neutralizing capacity in a toposequence Luvisol–Cambisol on loess under deciduous forest in Belgium. European J. of Soil Sci. 51, 1–13. Brewer, R., 1964. Fabric and Mineral Analysis of Soils. John Wiley & Sons, New York. Bryant, R.B., 1989. Physical processes of fragipan formation. In: Smeck, N.E., Ciolkosz, E.J. (Eds.), Fragipans: their occurrence, classification and genesis. : SSSA Spec. Publ., 24. SSSA, Madison, Wisconsin, pp. 141–150. Carlisle, F.J., 1954. Characteristics of soils with fragipans in a Podzol region. Ph.D. diss. Cornell Univ., Ithaca, NY (Diss. Abstr. 14, 1861–1862). Certini, G., Ugolini, F.C., Taina, I., Bolla, G., Corti, G., Tescari, F., 2007. Clues of the genesis of a discontinuously distributed fragipan in the northern Apennines, Italy. Catena 69, 161–169. Ciolkosz, E.J., Waltman, W.J., 2000. Pennsylvania's fragipans. Agronomy Series 147, 1–14. Ciolkosz, E.J., Waltman, W.J., Thurman, N.C., 1995. Fragipans in Pennsylvania soils. Soil Survey Horizons 36, 5–20. Drits, V.A., Sakharov, B.A., 1976. X-ray Analysis of Mixed-Layer Minerals. Nauka, Moscow. in Russian. Franzmeier, D.P., Norton, L.D., Steinhardt, G.C., 1989. Fragipan formation in loess of the Midwestern United States. In: Smeck, N.E., Ciolkosz, E.J. (Eds.), Fragipans: their occurrence, classification and genesis. : SSSA Spec. Publ., 24. SSSA, Madison, Wisconsin, pp. 69–97. Gee, G.W., Bauder, J.W., 1986. Particle-size analysis, In: Klute, A. (Ed.), Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods, 2nd edition. : Agronomy Monograph, vol. 9. ASA-SSSA, Madison, Wisconsin, pp. 427–445. Graveel, J.G., Tyler, D.D., Jones, J.R., McFee, W.W., 2002. Crop yield and rooting as affected by fragipan depth in loess soils in the southeast USA. Soil and Tillage Research 68 (2), 153–161. Grossman, R.B., Carlisle, F.J., 1969. Fragipan soils of the eastern United States. Adv. Agron. 29, 237–279. Hess, M., 1965. Altitudinal climatic zones in the Polish Western Carpathians. Zeszyty Naukowe UJ: Prace Geogr., 11 (in Polish). IUSS Working Group WRB, 2006. World reference Base for Soil Resources 2006. World Soil Resources Reports No. 103, FAO, Rome. Jackson, M.L., 1969. Soil Chemical Analysis: Advanced Course. Published by the author 2nd ed. Dept. of Soil Science, Univ. of Wisconsin, Madison, Wisconsin. James, H.R., Ransom, M.D., Miles, R.J., 1995. Fragipan genesis in polygenetic soils on the Springfield Plateau of Missouri. Soil Sci. Soc. Am. J. 59, 151–160 (Madison, Wisconsin). Klimaszewski, M., 1967. The Polish Western Carpathians in Quaternary period. In: Galon, R., Dylik, J. (Eds.), Quaternary of Poland. PWN, Warszawa, pp. 431–497. Langohr, R., Sanders, J., 1985. The Belgian loess belt in the last 20 000 years. Evolution of soils and relief in the Zoniёn forest. In: Boardman, J. (Ed.), Soils and Quaternary Landscape Evolution. John Wiley & Sons, pp. 359–371. Lindbo, D.L., Veneman, P.L.M., 1989. Fragipans in the Northeastern United States. In: Smeck, N.E., Ciolkosz, E.J. (Eds.), Fragipans: their occurrence, classification and genesis. : SSSA Spec. Publ., 24. SSSA, Madison, Wisconsin, pp. 11–31. Lindbo, D.L., Veneman, P.L.M., 1993. Morphological and physical properties of selected fragipan soils in Massachusetts. Soil Sci. Soc. Am. J. 57, 429–436 (Madison, Wisconsin).

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