Clay minerals in a denudation-accumulative soil catena

ISSN 1064�2293, Eurasian Soil Science, 2010, Vol. 43, No. 1, pp. 85–93. © Pleiades Publishing, Ltd., 2010.Original Russian Text © N.P. Chizhikova, N.P. Sorokina, N.B. Khitrov, A.A. Samsonova, 2010, published in Pochvovedenie, 2010, No. 1, pp. 97–105.

85

INTRODUCTION

The spatial distribution of the minerals in the finelydispersed soil component has remained poorly under�stood until now. At the same time, this information isessential for understanding the mechanisms of theinteraction and interference of the main soil compo�nents.

We previously assessed the variation of the compo�sition of the clay minerals within the soil profiles forsolving pedogenetic problems [18]. It was found thatthe coefficient of variation for the predominant clayminerals (kaolinite, montmorillonite, and illite) inthese objects varied from 5 to 173%.

Sokolova et al. [5] studied the spatial variation ofthe mineralogy and chemistry of the clay fractions sep�arated from the upper horizons of loamy virgin (Klindistrict, Moscow oblast) and arable (Solnechnogorskdistrict, Moscow oblast) podzolic soils. A correlationof the phyllosilicate proportions with the soil reaction,humus content, and the amount of potassium fertiliz�ers applied was revealed. The spatial variation of theclay minerals in the plow layer of soddy�podzolic soilson mantle loams was 6–7% for illite and kaolinite withchlorite and 112% for the minerals with labile struc�tures.

The study of the variation of the soil mineralogy atsmall distances showed that the empirical distributioncould be approximated by the normal law and that thevariation coefficient of the individual parameters wasno more than 10–15% in most cases and, rarely,increased to 30% for minor minerals [3, 10–12, 15].These studies were performed on clay loamy soddy�podzolic soils at the Dolgoprudnaya Experimental

Agricultural Station [10], a clay loamy leached cher�nozem at the Shatilovo Experimental AgriculturalStation [3, 11], and clay loamy alluvial soils in the OkaRiver floodplain in the region of Dedinovo [15]. Themoderate variation of the mineralogical parameterswithin the elementary soil areas suggested that thewider variation range of similar parameters previouslyobserved [5, 18] could be explained by including ofdifferent soils into the population analyzed.

This supposition was confirmed by the studies ofthe spatial distribution of the mineralogical parame�ters in the soil catenas of forest, forest�steppe, and dry�steppe zones [10–13, 17].

Of special interest is the analysis of the soil mineral�ogy in the study of the soil matter redistribution in theerosion�accumulative structures of the soil cover in thezone of chernozems. Studies of the runoff plots estab�lished in Fatezh district of Kursk oblast showed that theremoved material consisted of humus�enriched fineaggregates with the mineralogy of the clay fraction sim�ilar to that in the upper horizons of the eroded soils.However, they had a higher proportion of the smectitephase consisting of mica–smectite interstratified for�mations with a high content of smectite packets [10].

The lands on the slopes belong to the most dynamiclandscapes in the Central Chernozemic Zone [1]. Thesoil cover pattern of the plowed slopes is characterizedby complex erosion–linear combinations of cher�nozems differing in the degrees of erosion, alkalinity,salinity, and carbonate contents [1, 6]. The spatialvariation of the soil cover of the slopes is attributed tothe combined effect of many factors: the relief (theslope steepness and shape, and the hollow microre�

SOIL MINERALOGY AND MICROMORPHOLOGY

Clay Minerals in a Denudation–Accumulative Soil CatenaN. P. Chizhikova, N. P. Sorokina, N. B. Khitrov, and A. A. Samsonova

Dokuchaev Soil Science Institute, Russian Academy of Agricultural Sciences, per. Pyzhevskii 7, Moscow, 119017 Russia

E�mail: [email protected] March 30, 2009

Abstract—Chernozems and agrochernozems of the Kamennaya Steppe agroforest landscape have a silty clayor clay texture and similar associations of clay minerals. The plow horizons of the agrochernozems on a slopeof 2°–3° to the Talovaya Balka have an increased content of the smectite phase (50–70%) compared to theupper horizons of the chernozems on flat watersheds (30–50%) due to the lithological discontinuity of thesoil�forming material and the possible total removal of material on the slope by denudation. On slightlyeroded areas, the clay minerals display a more intense disturbance of their crystal lattice structures by pedo�genetic processes, which increase the degree of disorder in their layers and the accumulation of fine quartz inthe clay fraction. In the areas with more significant erosion of the humus horizon, the clay minerals are char�acterized by their perfect structure and clean reflections, which are indicative of the outcropping of lessweathered material from the middle part of the chernozem profile less transformed by pedogenesis.

DOI: 10.1134/S1064229310010114

86

EURASIAN SOIL SCIENCE Vol. 43 No. 1 2010

CHIZHIKOVA et al.

lief), the lithological continuity of the soil�formingrocks, and the level and salinity of the groundwater.Among these factors, the erosional microrelief and thegroundwater level are the most dynamic and thusresponsible for the agrogenic transformation of the soilcover.

The aim of this work was to study the spatial distri�bution of the minerals in the fine soil material devel�oped in the denudation–accumulative soil catena ofthe Kamennaya Steppe agroforest landscape.

EXPERIMENTAL

The fine fractions (<1, 1–5, and 5–10 µm) sepa�rated from the segregational agrochernozems (plowedordinary chernozems) with different degrees of ero�sion were studied. The key plot 30 ha in area with adenudation�accumulative soil catena was located tothe east of forest belt 131 on a slope of the TalovayaBalka within the Kamennaya Steppe agroforest land�scape (territory of the Dokuchaev AgriculturalResearch Institute of the Central Chernozemic Zone,Talovaya district, Voronezh oblast).

A detailed soil map of the plot on a scale of 1 : 2000was compiled in 1987–1988 [7]. The procedure andresults of soil the survey were reported in detail [6, 7].

The eroded soils occur on hollow slopes, and theaccumulation of the removed material can be observedat the periphery of the hollows. The hollow bottomsare characterized by the highest diversity of soils. Anentire range of erosion–accumulative (eroded–accu�mulative) soils, including those with high efferves�cence and leached ones, can be found depending onthe lithological conditions, incision depth, the trans�verse profile of the hollow, and the longitudinal profileof its bottom. Meadow solonchakous soils are devel�oped at the shallow occurrence of saline groundwater.

Repeated through studies performed 12 years later(in 1999) revealed the differentiating role of the hollowmicrorelief in the formation and agrogenic transfor�mation of the soil cover on the plowed slopes [8]. Onthe interhollow watersheds, the mechanical transloca�tion of soil material along the slope is accompanied by

the selective redeposition of different particle�sizefractions; normally thick and slightly eroded soils arepredominant. The bottoms of the hollows with therunoff along their bottoms and accumulation from thehollows' sides are occupied by diverse soils. On short(10–30 m) hollow slopes, the erosion–accumulationprocesses control the actual dynamics of the soil coverand of the microrelief. Changes in the transverse pro�file of the hollow were observed during the 12 years ofobservations, which indicate that the erosion pro�cesses occur at the present time. They are manifestedon slopes with a gradient above 2° and are activated withincreasing steepness. The deformation of the north�fac�ing slope due to the removal and accumulation of mate�rial was noted. The deepening of the bottom by 10 cm wasobserved at a steepness of more than 3° [8].

To study the spatial distribution of the soil mineral�ogy in the denudation–accumulative soil association,samples were taken from the arable (0� to 20�cm) layerof the soils on different microrelief elements along across slope transect established from north to south100 m to the east of forest belt 131. The sampling wasperformed in 1999. The arrangement of the samplingpoints is shown in the topographic profile along thetransect (Fig. 1).

The particle�size fractions (<1, 1–5, and 5–10 µm)were separated from the transect samples by the Gor�bunov sedimentation method [2]. The mineralogy ofthe fine fractions was studied using X�ray diffractionanalysis using an HZG�4a universal X�ray diffracto�meter. Oriented preparations were analyzed in threestates: (A) air�dry, (B) solvated with ethylene glycol for2 days, and (C) after ignition at 550°C for 2 h. Theminerals were identified using conventional proce�dures. The proportions of the main mineral phases inthe clay fraction were calculated by the Biscayemethod [16]. The degree of the structure disorder wasdetermined according to Reynolds [19].

To characterize the vertical distribution of the min�erals, a segregational (ordinary) chernozem under for�est belt 131 (profile 6 [4]) was chosen. The separationand X�ray diffraction analysis of the clay fraction fromthe soil samples (profile 6) were performed byA. Zotova, a student of the Faculty of Soil Science ofMoscow State University, at the Laboratory of SoilMineralogy and Micromorphology of the DokuchaevSoil Science Institute under the supervision ofN.P. Chizhikova.

RESULTS AND DISCUSSION

According to their particle�size distribution, 19 soilsamples had a medium clayey texture and 4 soil sam�ples were coarse silty�clayey light clays (Tables 1, 2).

The soils confined to different elements of the ero�sional relief (inclined watersheds between hollows,and hollow microslopes and bottoms) on the generaleast�facing slope had similar variation ranges andaverage values for the contents of the clay and fine and

120

80

40

сm

400 300 200 100 0

N

417.3

406.2

456.6

426.3

396.041

6.4376.0

445.942

6.0

435.9

386.3

395.5

406.8

405.5

446.1

406.3

467.2

456.9

395.9

365.9

395.7

442.2

305.5

S

m

Fig. 1. Topographical profile along the transect, the loca�tion of the sampling points, and the contents of clay (abovethe line) and humus (under the line) in the plow (0� to 20�cm)layer of the segregational agrochernozems (ordinary cher�nozems) with different degrees of erosion.


CLAY MINERALS IN A DENUDATION–ACCUMULATIVE SOIL CATENA 87

medium silt (Table 2). This was related to the clay tex�ture and the weak vertical differentiation (or itsabsence) of the upper part of the chernozem profilesdeveloped on loess�like sediments.

At the same time, the general variation range of theclay (fraction <1 µm) along the transect equal to 15%suggested the appreciable spatial variation of the parti�cle sizes in the plow horizon of the studied key plot.This could be related either to the initial lithologicalheterogeneity or to the translocation of material on theslope due to erosion and accumulation.

Along with the analysis of the averaged data givenin Table 2, the spatial differentiation of the clay andhumus in relation to the microrelief was consideredwithin the microcatenas, which characterized thechanges in these parameter values when going fromthe microwatershed to the nearest hollow. In micro�catena 1 (20 to 60 m along the transect) (Fig. 1), thecontent of clay increased from the watershed (40.1%)down both slopes of the narrow crest rising above thelocal hollow to no more than 40 cm. A more compli�cated situation was observed in the 219� to 380�m seg�ment, which included an interhollow watershed 40 mwide with the northern (microcatena 3) and southern(microcatena 4) slopes to the hollows. Its elevationwas 40 cm over the northern hollow and 70 cm over thesouthern hollow. The highest content of clay (45%)was found in a microdepression (280 m) on the water�shed, compared to 39% on the crest and 37–44% onthe slopes. These data are indicative of active denuda�tion–accumulation processes related to the hollowmicrorelief. Our conclusions agree with the results ofthe altimetric surveys in 1987 and 1999, which showedchanges in the transverse profile of the hollow [8].

The content of humus in the studied profilerevealed a positive correlation (0.55) with the claycontent (Fig. 2). The topographic allocation of thesampling points (on the watersheds, in the hollows,and on the slopes to the hollows) are denoted in theplot. It can be seen that the watersheds and slopes forma general correlation field, but the contents of humusand clay on the slopes vary in a wider range than on thewatersheds; this is especially true for the lower values.Hollows occur beyond the correlation field of thewatersheds and slopes and increase the general scatter�ing of the points. After the exclusion of the hollowsfrom the sample set, the correlation coefficientincreased to 0.67. This deviation of the hollows fromthe general tendency is due to the discontinuousunsteady conditions of the accumulation and transit ofthe solid runoff from the interhollow watersheds andslopes and along the hollow bottom.

The mineralogy of the fraction <1 µm includes clayand attendant minerals typical for loess�like loams,their derivatives, and the soils developed on them [9].The monotypic association of clay minerals includescomplex irregular mica–smectite and chlorite–smec�tite interstratifications, di� and trioctahedral hydrom�

icas, imperfect kaolinite, and magnesium–iron chlo�rite.

In the chernozems of unmown steppes and forestbelts on flat watersheds, the content of the mineralphases in the clay fractions of the upper horizons var�ied from 30 to 50% for the smectite phase, from 40 to50% for the hydromicas, and was about 10% forkaolinite with chlorite [14]. A tendency was observedtoward the eluvial distribution of the smectite phasethroughout the soil profile and the relative accumula�tion of hydromicas in the surface horizons. A similarcomposition and profile distribution of the clay miner�als was observed in profile 6, which characterized thesegregational (ordinary) chernozem under forestbelt 131 [4]. In the plow horizons of the soils locateddownslope from forest belt 131, several types of com�plex irregular interstratifications with different con�tents of smectite, mica, and chlorite packets werepresent. All these structures (hereinafter, the smectitephase) made up 50 to 70%. Complex interstratifiedmica–smectites with a high content (more than 50%)of smectite packets, mica–smectites with a low con�

Table 1. Contents of the particle�size fractions and humus inthe arable (0� to 20�cm) horizon of the chernozems along thetransect (1999)

Dis�tance, m

Relief el�ement*

Clay Fine silt Medium silt Humus

%

20 3 44.6 14.6 9.7 6.930 2 46.1 15.3 9.8 7.240 1 40.1 16.5 8.2 6.350 2 40.5 18.7 8.5 5.860 3 43.8 16.9 7.7 6.163 3 40.4 16.6 10.4 5.5

120 2 39.3 18.6 9.5 5.5141 3 37.9 18.4 10.3 6.3160 2 43.0 16.0 10.8 5.9219 3 41.7 17.5 10.3 5.4240 2 44.3 15.6 7.2 5.9250 2 40.1 17.2 9.6 6.2270 1 41.8 16.7 10.4 6.3280 1 45.0 14.6 9.2 6.6300 1 38.6 16.5 10.1 6.0330 2 41.1 16.9 10.5 6.4360 2 37.1 17.8 9.2 6.0380 3 41.5 18.4 10.1 6.6400 1 30.2 22.5 9.7 5.5420 1 39.2 19.0 10.1 5.9437 3 39.0 17.5 9.8 5.7444 3 36.0 17.2 8.6 5.9450 2 43.9 15.8 9.5 6.2

* Relief elements: (1) watershed between hollows; (2) hollow slope;(3) hollow bottom.

88


CHIZHIKOVA et al.

tent (<50%) of smectite packets, and chlorite–smec�tites were identified. The hydromicas consisted of dio�ctahedral varieties, the content of which varied from27.5 to 39.7%. The total content of imperfect kaoliniteand magnesium–iron chlorite was no higher than 10%(Table 3).

The increased content of the smectite phase in thesamples of the arable soils from the slope, compared tothe upper horizons of the chernozems of the unmownsteppe on flat watersheds or under forest belts, attractsattention. The higher content of the smectite phase inthe soils under study was due to the lithological dis�continuity of the soil�forming rocks: yellow�brownloess�like clays at a depth of 1–1.5 m on this slope seg�ment were underlain by older brown calcareous Qua�ternary clays, which formed an aquiferous and, at thesame time, a relatively waterproof layer. In most cases,the brown clays were enriched with smectite.

The analysis of the surface distribution of the min�erals in the fraction of <1 µm from the plow horizonsof the soils on the slopes revealed some tendencies inthe structural state of the minerals and the proportionsof the main mineral phases depending on the positionof the soil in the hollow microrelief on the generaleast�facing slope. The following parameters were pro�posed to be used for determining the differences in thesoil mineralogy: (1) the intensity of the reflection atd0.01 = 1.4 nm (I1.4nm) characterizing the perfection ofthe smectite phase structure, (2) the quantitative con�tent of the smectite phase, (3) the degree of the struc�

tural disorder of the interstratifications according toReynolds [19], and (4) the presence of fine quartz inthe clay fraction. The degree of structural disorder ofthe interstratifications was qualitatively assessed fromthe changes in the crystal parameters of the interstrat�ifications observed in the XRD patterns in the regionof small angles after the solvation of the sample withethylene glycol compared to the spectra of the air�drysamples. When the isolation of the reflection at 1.7 nmwas observed at the swelling of packets after solvationwith ethylene glycol instead of the reflection at 1.4 nmin the air�dry sample, the structure of the smectitephase could be considered as highly ordered. As far asthe degree of disorder of the interstratificationsincreased, the reflection at 1.7 nm became less isolatedand formed a wide range of reflections in the rangeabove 1.9–2.2 nm.

The experimental data were analyzed for the sepa�rate transect fragments (microcatenas). The numbersof sampling points and their distances from the start�ing point of the transect are given in Table 3.

Microcatena 1 (points 15–20; S = 20–63 m; Fig. 1and Fig. 3, panel 1). The clay fractions of the samplestaken in the hollow forms of the microrelief had simi�lar mineralogies. The smectite phase was predomi�nant, which consisted of some interstratified struc�tures with the predominance of smectite packets.

The following tendency was observed in the spatialdistribution of the minerals in the fraction <1 µmwithin the first 60 m of the transect. The samples of

Table 2. Statistical parameters of the distributions of the particle�size fractions and humus in the plow (0� to 20�cm) horizonalong the transect (1999)

Parameter, % Relief element*Statistical parameter

minimum lower quartile median upper quartile maximum

Clay 1 30.2 38.8 39.7 41.4 45.0

2 37.1 40.1 41.1 43.9 46.1

3 36.0 38.7 41.0 42.2 44.6

4 30.2 39.1 40.5 43.4 46.1

Fine silt 1 14.6 16.5 16.6 18.4 22.5

2 15.3 15.8 16.9 17.8 18.7

3 14.6 16.8 17.4 17.7 18.4

4 14.6 16.3 16.9 18.1 22.5

Medium silt 1 8.2 9.3 9.9 10.1 10.4

2 7.2 9.2 9.5 9.8 10.8

3 7.7 9.4 10.0 10.3 10.4

4 7.2 9.2 9.7 10.2 10.8

Humus 1 5.5 5.9 6.2 6.3 6.6

2 5.5 5.9 6.0 6.2 7.2

3 5.4 5.7 6.0 6.4 6.9

4 5.4 5.9 6.0 6.3 7.2

* 4 – total relief elements.



soils from a shallow hollow on the gentle right (north�ern) slope (at 20 and 30 m) had low�intensity reflec�tions of the smectite phase (Table 3; Fig. 3, panel 1)and a significantly disordered structure. These param�eters approached the composition of the minerals andtheir crystallochemical characteristics to those in theplow horizons of chernozems.

An increase in the reflection intensity at 1.4 nm wasobserved in the X�ray diffraction patterns of the soilsamples from the interhollow watershed (40 m); how�ever, the structure remained disordered. The contentof fine quartz decreased. The sample from the steepersouthern microslope was characterized by intensereflections of the smectite phase, its high content(68%), and a more significant decrease in the contentof fine quartz. Two samples taken in microhollows(at 60 m and 63 m) were identical and differed fromthe above samples by the higher reflection intensitiesand the absence of disorder, which was proved by theclear isolation of the reflection at d0.01 ~1.7 nm.

In other words, in the slightly eroded areas (a shal�low hollow, the right microslope, and a watershed) ofmicrocatena 1, the minerals of the clay fraction weresubjected to more intense reworking by pedogeneticprocesses and had the highest degree of disorder. Inthe deeper hollow, where the soil was more stronglyeroded, the clay minerals were characterized by theirperfect structure and clear reflections; this indicatedthe outcropping of less weathered materials less trans�formed by pedogenesis.

The next segment under study, microcatena 2 (sam�pling points 21–23; S = 120–160 m; Fig. 1 and Fig. 3,panel 2), represented the hollow fragment traversed bythe transect at marks of 120, 141, and 160 m. In thisarea, changes in the proportions of the main mineralphases and the reflection intensities at d0.01 = 1.4 nmwere noted. Sample 21 taken on the slope of a micro�hollow was characterized by low contents of the clayfraction (39.3%) and smectite phase (50.6%, or 19.9%of the total soil weight) and the lowest intensity of thereflection at d0.01 = 1.4 nm (Table 3; Fig. 3, panel 2).Sample 22 taken in the lowest part of the microcatenacontained clay materials with a higher content ofsmectite (66.5%, or 25.2% of the total soil weight) anda high intensity of the reflection at d0.01 = 1.4 nm(Table 3). A small admixture of fine quartz was found.Sample 23 taken from a gentle slope to the microhol�low was characterized by an increased content of clay(43.0%) and a high content of the smectite phase(65.8%, or 28.3% of the total soil weight). However,the intensity of the reflection at d0.01 = 1.4 nm waslower, and weak disorder of the mineral structure wasnoted. Thus, the tendency in the distribution of theclay minerals was repeated within the microcatena;i.e., the best crystallochemical parameters wereobserved for the samples taken from the deepest runoffhollows, in which erosion exposed the lower horizons.

The finely dispersed material of microcatena 3(samples 24–29, S = 219–300 m; Fig. 1 and Fig. 3,

panel 3) was characterized by similar tendencies in itsdistribution. In the samples from the plow horizons ofthe soils on the microcatena slopes and in the hollow,the content of the clay fraction was 41.7 and 44.3%,respectively. The smectite phase was predominant inthe clay fraction: 61.1 and 68.5%, or 25.5 and 30.3% ofthe total soil weight, respectively. A high intensity ofthe reflection at d0.01 = 1.4 nm was typical for thesmectite phase, and the mineral had a perfect struc�ture. A higher degree of structural disorder wasobserved in the sample from the slope. When going to thegentle slope and then to the watershed (sample 26), thestructural state of the minerals changed: the intensityof e reflections decreased (Table 3), the degree of thestructural disorder of the smectite phase increased, andfine quartz appeared. The samples from the plow hori�zons of the watershed in microcatena 3 (samples 27–29)were almost identical in their mineralogical parame�ters. They had a minimum intensity of the reflection atd0.01 = 1.4 nm (Table 3) and a significant degree ofstructural disorder of the smectite phase, and finequartz appeared.

Microcatena 4 (samples 30–33; Fig. 1 and Fig. 3,panel 4) was located in the transect segment between330 and 400 m; it characterized the slope positions(samples 30 and 31), the deepest runoff hollow alongthe transect (sample 32), and the transition to thewatershed of an adjacent hollow (sample 33). Thecontent of the clay fraction in the plow horizon variedfrom 30.2% on the watershed to 41.5% in the hollow.The composition of the minerals in the fraction wasidentical to that of the plow horizons of the abovemicrocatenas. The following tendency was noted for

7.5

7.0

6.5

6.0

5.5

5.05045403530

1

2

3

Clay, %

Hum

us,

%

Fig. 2. Humus content vs. the clay content. Erosional reliefelements on the general east�facing slope: (1) interhollowwatersheds; (2) hollow slopes; (3) hollow bottoms.

90


CHIZHIKOVA et al.

Table 3. Proportions of the main mineral phases in the fractions <1 µm separated from the plow horizons of the chernozems

Microcat�ena no.

Sam�pling point no.

S, m from the start�ing point

of the transect

Clay, %

In the fraction <1 µm, % In the whole soil, %

I1.4 nm, mm

Presence of quartzkaolinite–

chloritehydromi�

ca smectite kaolinite–chlorite

hydromi�ca smectite

1 15 20 44.6 5.7 29.5 64.8 2.5 13.3 28.9 98 +

16 30 46.1 8.0 32.0 60.0 3.7 14.8 27.7 95 +

17 40 40.1 7.3 34.0 58.7 2.9 13.6 23.5 142 +

18 50 40.5 7.8 29.0 68.2 3.2 11.8 27.6 170 –

19 60 43.8 7.9 30.5 61.6 3.5 13.4 26.1 185 –

20 63 40.4 6.9 29.1 64.0 2.8 11.8 25.9 186 –

2 21 120 39.3 10.2 39.2 50.6 4.0 15.4 19.9 95 +

22 140 37.9 5.6 27.9 66.5 2.1 10.6 25.2 230 –

23 160 43.0 6.7 27.5 65.8 2.9 11.8 28.3 147 –

3 24 219 41.7 8.9 30.0 61.1 3.7 12.5 25.5 146 –

25 240 44.3 7.4 24.1 68.5 3.3 10.7 30.4 165 –

26 250 40.1 6.0 30.5 63.5 2.4 12.2 25.5 135 +

27 270 41.8 5.5 31.7 62.8 2.3 13.3 26.3 116 +

28 280 45.0 5.2 29.4 65.4 2.3 13.2 29.4 124 +

29 300 38.6 6.8 33.0 60.2 2.6 12.7 23.2 131 +

4 30 330 41.1 7.9 33.4 58.7 3.3 13.7 24.1 144 –

31 360 37.1 6.9 28.1 64.0 2.6 10.4 23.7 143 +

32 380 41.5 7.4 31.8 60.8 3.1 13.2 25.2 160 +

33 400 30.2 8.5 32.0 59.5 2.6 9.7 17.1 195 +

5 34 420 39.2 7.4 32.5 60.1 2.9 12.7 23.4 175 +

35 437 39.0 5.9 23.2 70.9 2.3 9.1 27.8 240 –

36 444 36.0 7.7 29.0 69.4 2.8 10.4 24.1 155 –

37 450 43.9 9.7 39.7 50.6 4.3 17.4 22.2 176 +

Note: (+) present; (–) absent.

the proportions of the mineral phases and their crystalchemistry: an increase in the intensity of the reflectionat d0.01 = 1.4 nm when going from the top point (sam�ple 30) to the hollow (sample 32, Table 3). The degreeof the structural perfection and the content of thesmectite phase increased in the same direction (Table 3).At point 33 on the watershed, a decrease in the con�tents of clay (30.2%) and the smectite phase (only17.9% of the total soil weight) was observed, as well asignificant disorder of the mineral structure. Thus, thebehavior of the finely dispersed material showed thesame tendencies as in microcatenas 1, 2, and 3.

Microcatena 5 (sampling points 34–37; S = 400–500 m; Fig. 1 and Fig. 3, panel 5) characterized thelowest hypsometric position of the transect. It alsoincluded slopes, a hollow, and a watershed. The frac�tion <1 µm of the soil from the plow horizons had asimilar mineral composition. In sample 34 taken on alow watershed, the proportions of the mineral phasesand the crystal chemistry of the minerals suggested

that this microrelief position depended on the erosionof the plow horizon on the watershed, because freshmaterial non�re�worked by pedogenesis was involved.This was confirmed by the high intensity and thepointed peak of the reflection at d0.01 = 1.4 nm (Table 3),as well as the isolation of the reflection at 1.7 nm afterthe solvation of the sample with ethylene glycol. Thecontent of the smectite phase was 60.1%, which wasintermediate between those in the soil samples fromthe runoff hollows and watersheds. In this sample, finequartz was present in the clay fraction, as well as in thesamples from the other interhollow watersheds. In thehollow (point 35, 437 m from the starting point of thetransect), the smectite phase in the plow horizonshowed the highest intensity of the reflection at d0.01 =1.4 nm. It had a perfect structure. No fine quartz wasfound in the clay fraction. Thus, the crystallochemicalparameters of the minerals from the clay fraction werein good agreement with the relatively low intensity ofthe pedogenesis typical for the exposed horizons in the



1

hollow

hollow

hollow watershedleft (steeper) right slope40 m

0.334

hollow

hollow30 m 20 m50 m60 m63 m

0.3550.3550.334

0.3340.334

0.3340.334

0.3550.355 0.355 0.355

0.3550.355 0.355

0.334

0.3340.334

0.50.7

1.01.7

0.474

~1.8

0.50.5 0.5

0.7 0.7

0.70.7

1.0 1.01.0 1.0

1.0

1.0

1.0

0.474 0.474

0.4740.474

~1.8

1.8

~1.8~1.9

1.7

1.47

1.48 1.44 1.441.43

1.43

1.48

left slope left slopehollow

0.5 0.5 0.50.5 0.50.7

0.7 0.7

160 m 141 m 120 m

0.7

hollowright sloperight slope

slope

0.3550.3340.334

0.3340.355

0.355

0.355 0.355 0.3550.334 0.334

0.334

0.7 0.7 0.70.50.50.50.5

0.50.7 0.7

1.0 1.01.0

1.0

1.0

0.474

0.474

0.474 0.474

watershedwatershed

1.471.47

~1.9

~1.9

~1.9~1.9

1.431.45

~1.8 0.5

widewatershed

300 m 280 m 270 m 250 m 240 m 219 m

watershed

0.5 0.50.5

0.5

0.474 0.474 0.4740.474

0.7

0.7

1.0

1.01.0

1.0

0.720.72

0.3340.334

0.334

0.3340.358

0.3580.358

0.353

0.3570.353

1.47

400 m 380 m 360 m 330 mleft slope left slope

1.43

1.7~1.9

1.0

1.471.51

hollow

0.3550.355

0.3530.357

0.334

0.3340.334

0.3341.0

1.0

1.01.0

0.7

0.7

0.7

0.7

0.5

0.5

0.50.5

0.4740.474

0.426

1.43

1.44

1.44

1.71.7

1.7

1.53450 m 444 m 437 m 420 mlow

watershedleft slope А

B

C

А

B

C

А

0.7

B

C

1.7

1.43

А

B

C

А

B

C

1.0

1.9

1.43

2

3

4

5

1.45

1.47

Fig. 3. X�ray diffraction patterns of the fractions <1 µm separated from the plow horizons of the chernozems: (A) air�dry sample;(B) sample after solvation with ethylene glycol; (C) sample after ignition at 550°C for 2 h; (1)–(5) catena numbers.

92


CHIZHIKOVA et al.

middle part of the profile, which outcropped in thehollow bottoms because of the soil loss from the sur�face horizons by erosion.

In the hollow at the 444 m mark (point 36), theintensity of the reflection at d0.01 = 1.4 nm decreasedabruptly (Table 3; Fig. 3, panel 5), and some degree ofstructural disorder of the minerals was observed,which indicated the effect of pedogenetic processes.Eroded–accumulated material could be present. Inthe soil on the slope (point 37), the content of claymaterial was 43.9%. It had a relatively low content ofthe smectite phase (50.6%). However, the high inten�sity of the reflection at d0.01 = 1.4 nm pointed to amedium degree of the structural disorder of the clayminerals.

CONCLUSIONS

(1) The studied chernozems and agrochernozemswith different degrees of erosion on flat watershedsand in denudation–accumulative soil combinationson a slope of 2°−3° in the Kamennaya Steppe agrofor�est landscape have a silty clay or clay texture and amonotypic association of clay minerals. The latterincludes intricate irregular mica–smectite and chlo�rite–smectite interstratifications (30 to 70% in the clayfraction), di� and trioctahedral hydromicas (25–60%),imperfect kaolinite, and magnesium–iron chlorite(4 to 12% in total).

(2) The plow horizons of the agrochernozems onthe slope of 2°−3° toward the Talovaya Ravine to theeast of forest belt 131 have an increased content of thesmectite phase (50–70%) compared to the upper hori�zons of the chernozems on an unmown steppe, on flatwatersheds, or of the soils under forest belts (30–50%).The higher content of the smectite phase in the studiedsoils is due to the lithological discontinuity of the soil�forming rocks and the total removal of material fromthe slope by denudation.

(3) The conventional statistical analysis of the par�ticle�size fractions and the clay minerals in the clayfraction revealed no differences among the plow hori�zons of the segregational agrochernozems (ordinarychernozems) on different elements of the erosionalmicrorelief (the watershed, slope, and hollow bottom)on the general slope with a gradient of 2°−3°.

(4) The tendencies of the status of the clay mineralsin the plow horizons of the soils studied as dependingon the erosion intensity were revealed by means of thefollowing parameters: (1) the intensity of the reflec�tion at d0.01 = 1.4 nm (I1.4 ) characterizing the structuralperfection of the smectite phase, (2) the content of thesmectite phase, (3) the degree of structural disorder ofthe interstratifications according to Reynolds [19],and (4) the presence of fine quartz in the clay fraction.

(5) In the slightly eroded areas mostly confined tothe watersheds between hollows and gentle hollowmicroslopes, the minerals of the clay fraction are sub�jected to more intense disturbances of the crystal

structure by pedogenesis, which results in an increasein the degree of disorder of the intricate irregularmica–smectite interstratifications and the accumula�tion of fine quartz in the clay fraction. In the areas sub�jected to stronger erosion of the humus horizon, whichmore frequently occur on the bottoms of deep hollowsand relatively steep hollow microslopes, the clay min�erals are characterized by a perfect structure and clearreflections, which is indicative of the outcropping ofless weathered material from the middle horizons ofthe chernozems less reworked by pedogenesis.

ACKNOWLEDGMENTS

This work was supported in part by the RussianFoundation for Basic Research, project no. 06�04�08323 ofi.

REFERENCES

1. B. P. Akhtyrtsev, “Soils and Their Changes under theInfluence of Shelterbelts,” Kamennaya Steppe: Agrofor�est Landscapes (Izd. Voronezh. Gos. Univ., Voronezh,1992), pp. 94–115 [in Russian].

2. N. I. Gorbunov, “Methods of Soil Preparation for Min�eralogical Analyses,” in Methods of Soil Mineralogy andMicromorphology (Nauka, Moscow, 1971), pp. 5–15 [inRussian].

3. M. B. Motyashov, Extended Abstract of Candidate’s Dis�sertation in Geography (Pochv. Inst. im. V.V. Dokuchaeva,Moscow, 1999).

4. Yu. N. Zborishchuk, V. T. Rymar’, and Yu. I. Chever�din, The State of Ordinary Chernozems in the Kamen�naya Steppe (Moscow, 2007), 160 pp. [in Russian].

5. T. A. Sokolova, A. V. Lazarev, V. A. Pitryuk, andI. P. Kuibysheva, “Spatial Variability in the Mineralogicaland Chemical Compositions of the Clay Fraction of Pod�zolic Soils,” Pochvovedenie, No. 7, 82–91 (1990).

6. N. P. Sorokina, “Factors of the Differentiation andAgrogenic Transformation of the Soil Cover on PlowedSlopes in the Kamennaya Steppe,” in KamennayaSteppe: Problems of Studying the Soil Cover (Moscow,2007), pp. 97–120 [in Russian].

7. N. P. Sorokina, A. M. Ivanov, and V. I. Remezov,“Application of Detailed Agroecological Maps for theDevelopment of Regional Models of Soil Fertility,” inGeography and Cartography of Soils (Nauka, Moscow,1993), pp. 262–269 [in Russian].

8. N. P. Sorokina, N. B. Khitrov, N. P. Chizhikova, andA. A. Samsonova, “The Role of Hollow Microtopogra�phy in the Agrogenic Transformation of the Soil Coverof Plowed Slopes in the Kamennaya Steppe,” in SoilDiversity in the Kamennaya Steppe (Pochv. Inst. im.V.V. Dokuchaeva, Moscow, 2009), pp. 136–157 [inRussian].

9. N. P. Chizhikova, “Mineralogical Composition of ClayFractions in Chernozems,” in Chernozems of the SovietUnion (Kolos, Moscow, 1974), Vol. 1 pp. 178–186 [inRussian].

10. N. P. Chizhikova, Doctoral Dissertation in Agriculture(Pochv. Inst. im. V.V. Dokuchaeva, Moscow, 1992).



11. N. P. Chizhikova, “Spatial Differentiation of the Min�eralogical Composition of Soils in Relation to the SoilCover Pattern” (Pochv. Inst. im. V.V. Dokuchaeva,Moscow, 2000), pp. 182–196 [in Russian].

12. N. P. Chizhikova, “Mineralogical Composition of Soilsand Pedodiversity,” in Materials on the Study of RussianSoils (S.�Peterb. Gos. Univ., St. Petersburg, 2003),No. 4(31), pp. 91–99 [in Russian].

13. N. P. Chizhikova and V. S. Stolbovoi, “Spatial Distribu�tion of Clay Minerals in Soils of the Central TurgaiDepression,” Byull. Pochv. Inst. im. V.V. Dokuchaeva,No. 58, 21–32 (2006).

14. N. P. Chizhikova and A. A. Samsonova, “MineralogicalComposition of Fine�Dispersed Fractions in Cher�nozems of the Kamennaya Steppe,” in KamennayaSteppe: Problems of Studying the Soil Cover (Moscow,2007), pp. 97–120 [in Russian].

15. S. A. Shishov, Extended Abstract of Candidate’s Disserta�tion in Agriculture (Pochv. Inst. im. V.V. Dokuchaeva,Moscow, 2007).

16. R. E. Biscaye, “Mineralogy and Sedimentation ofRecent Deep Sea Clay in the Atlantic Ocean and Adja�cent Seas and Oceans,” Geol. Soc. Am. Bull. 76, 803–832 (1965).

17. N. P. Chizhikova, “Mineralogical Composition ofChernozems as Related to the Soil Cover Structure inthe Central European Part of Russia,” in Materials ofthe Intern. Symp. Soil Cover Pattern (Moscow, 1993),pp. 42–45.

18. A. D. Karathanasis, “Mineralogical Variability withinClayey Soil Control Sections and Family MineralogyPlacement,” Soil Sci. Soc. Am. J. 49 (3), 691–695(1985).

19. R. C. Reynolds, “Interstratified f Clays Systems: Cal�culation of the Total One�Dimensional DiffractionFunction,” Am. Mineral. 62 (5−6) (1967).

Documents

Clay minerals in a denudation-accumulative soil catena