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ISSN 1064-2293, Eurasian Soil Science, 2008, Vol. 41, No. 10, pp. 1124–1134. © Pleiades Publishing, Ltd., 2008.Original Russian Text © N.P. Chizhikova, E.I. Godunova, S.K. Kubashev, 2008, published in Pochvovedenie, 2008, No. 10, pp. 1268–1278.

INTRODUCTION

Studies of the impact of various fertilizers and ame-liorants on soil properties are of great practical value;they also contribute to the theory of soil formation andto the solution of particular genetic problems, such asthe genesis of solonetzic soils, the effect of soil acidifi-cation on the development of podzolization, etc.

The methodological approaches to studying theessence of soil processes that take place under theimpact of fertilizers and ameliorants can be groupedinto several directions. The traditional approach isbased on the experimental study of the effect of differ-ent rates of solid fertilizers and ameliorants evenly dis-tributed in the soil mass on the particular soil proper-ties. Though the direct contacts of the applied sub-stances with the soil material are localized, the changesin the soil properties are estimated for the bulk soilmass. In this case, local effects are masked by the greatvolume of the soil material. Within the framework ofthis approach, it is difficult to judge the real character ofthe interaction of the applied substances with the soilmaterial and, particularly, with clay minerals.

Another approach suggests the study of the impactof various solutions on the soil mass. Interesting exper-imental data on the impact of different cations andanions applied to soils in solutions on the soil mass andon the soil minerals have been obtained. In particular,the impact of alkaline and alkali-earth cations on thesoil properties and the soil structure has been thor-oughly studied [2]. The processes of mineral destruc-tion and alteration of the physicochemical properties ofsoil materials under the impact of dissolved sodium,

magnesium, and calcium have been studied in specialexperiments [9, 10].

Considerable changes in the water-physical proper-ties of soils (soil swelling, a decrease in the infiltrationcapacity, and an increase in the amount of water-peptiz-able clay, and a lowering of the soil tolerance towardsalkaline hydrolysis) take place under the impact of saltsolutions. Mobilization of silicon, aluminum, and ironunder the impact of such solutions attest to the destruc-tion of soil minerals. The treatment of clayey materialswith solutions of calcium, magnesium, sodium, andpotassium chlorides changes the characteristics of theparticle-size distribution; in particular, the content ofthe clay fraction increases. The cations of salt solutionsact as clay dispersants. The degree of clay dispersionunder the impact of these cations can be quantitativelyestimated. Analogous experiments were performedwith acids [17, 19].

The behavior of clay minerals and their tolerancetowards substances of different natures were discussedduring the symposium “Clay Minerals and Acidifica-tion” within the framework of the XVI World Congressof Soil Science in Montpelier (1998). The importanceof adequate assessment of the soil response to acidifica-tion via the analysis of the behavior of clay mineralsand the rates of their weathering was stressed. It wasshown that the rate of weathering of clay minerals (asjudged from the release of major cations from theircrystalline lattices) should be taken into account indetermination of critical loads on soils [21]. Changes inclay minerals of soddy-podzolic soils under the impactof different rates and forms of mineral fertilizers were

MINERALOGY AND MICROMORPHOLOGY OF SOILS

Changes in Clay Minerals of Vertic Chernozems under the Impact of Different Ameliorants

in a Model Experiment

N. P. Chizhikova

a

, E. I. Godunova

b

, and S. K. Kubashev

b

a

Dokuchaev Soil Science Institute, per. Pyzhevskii 7, Moscow, 119017 Russia

b

Stavropol Research Institute of Agriculture, Mikhailovskoe, Stavropol region, Russia

Received July 24, 2007

Abstract

—The interaction of different ameliorants and fertilizers with the solid phase of clayey vertic cher-nozems was studied in a model experiment. Changes in the organization and properties of the mineral massfrom the plow horizon under the impact of ameliorants took place at several hierarchical levels. At the level ofsoil aggregates, both the disaggregation of the soil mass and the formation of agronomically valuable soil aggre-gates under the impact of different ameliorants were observed. The method of fractional peptization of the soilmass was applied to study the behavior of clay minerals. The specificity of the crystallochemistry of smectiticminerals and their changes under the impact of introduced substances were studied in different fractions of clay.

DOI:

10.1134/S1064229308100153

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analyzed. The assessment of critical loads on soils isone of the major challenges facing soil mineralogy.

There are many experimental works devoted to thedestruction of clay minerals under the impact of variousacids [18, 20]. An interesting aspect of such studies isthe effect of weathering products on soil aggregation.Active destruction of kaolinite, illite, and montmorillo-nite under the impact of relatively weak (0.1 and 0.5 M)solutions of phosphoric and nitrous acids has beenproved [20]. The kinetics of the release of aluminum,silicon, and iron from clay minerals have been ana-lyzed. The effect of phosphoric acid on clay minerals ismore significant than the effect of nitrous acid. Theproducts of the destruction are represented by X-rayamorphous particles 0.025

µ

m in diameter; these parti-cles have a negative charge and consist of hydroxyalu-minophosphate complexes and amorphous silica. Theproducts of the destruction of phyllosilicates favor theflocculation of clay particles and the development ofnew microaggregates. The use of transmission electronmicroscopy has made it possible to trace the changes inthe surface of phyllosilicates.

The major principles and criteria for assessing theinteraction of ameliorants and fertilizers with the soilmass and the changes taking place in the latter underthe impact of introduced substances have been consid-ered in a number of works [4, 5, 11, 12]. Such an assess-ment can be based on a number of parameters, such asthe soil buffer capacity towards nutrients, the degree ofmanifestation of negative impacts of fertilizers, and thesoil capacity for restoring natural ion concentrations inthe soil solution.

The model experiment performed by us wasaimed at studying the contact zone of interactionbetween the soil mass and the added fertilizers andameliorants.

Changes in the organization of the soil mass at dif-ferent hierarchical levels and changes in the crystal-lochemical parameters of clay minerals were studied inthe vertic solonetzic chernozems of the Stavropolregion. The soil was treated with ameliorants and fertil-izers that are widely applied in farming practice in thisregion.

OBJECTS AND METHODS

Samples from the plow horizon of a solonetzic, low-humus, medium-deep, medium clayey vertic cher-nozem from the Stavropol region were used in a modelexperiment performed under natural conditions in thearea of the natural distribution of vertic chernozems [6].The samples were thoroughly mixed and placed intovessels. Ameliorants and fertilizers were applied ontothe soil surface in the vessels as a uniform layer with athickness of 2.5 cm. Then, the vessels were left in theopen air in the field for three years. The soil samplingfrom the vessels was performed every year in fourfoldreplicates from the uppermost soil horizon (0–3 cm).

The experiment included the following variants: (1) thecontrol (soil without fertilizers), (2) phosphogypsum,(3) lignin + ammonium nitrate, (4) biohumus from lignin,(5) biohumus from cattle manure, (6) manure, (7) super-phosphate, (8) ammonium nitrate, (9) nitroammophoska,(10) phosphogypsum + lignin + ammonium nitrate, (11)phosphogypsum + biohumus from lignin, (12) phospho-gypsum + manure, and (13) shell limestone + manure.

In this experiment, the contact zone between theadded ameliorants and fertilizers and the soil was imi-tated. The changes in the soil physicochemical proper-ties, the particle-size distribution (with the soil pretreat-ment using sodium pyrophosphate), the microaggre-gate-size distribution, the contents of different fractionsof clay obtained by the method of fractional peptiza-tion, and the mineralogical composition of the sepa-rated clay fractions were studied [1]. The total humuscontent was determined by the Turin method. Themethod of fractional peptization of clay was performedaccording to the method suggested by Gradusov withcoauthors [3]. The fractions (subfractions) of the water-peptizable clay (WPC), the loosely aggregated clay(AC-1), and the firmly aggregated clay (AC-2) wereseparated.

RESULTS AND DISCUSSION

Soil macroaggregation.

Certain changes in the soilmacrostructure took place after the first year of theinteraction between the ameliorants and fertilizers andthe soil mass [14]. With respect to the effect on the soilstructure, the studied substances could be subdividedinto three groups: (1) the organic substances (manure,biohumus from manure, and biohumus from lignin)favored the development of angular blocky–coarsegranular aggregates; (2) the ameliorants appliedtogether with the fertilizers (phosphogypsum ligninwith ammonium nitrate, phosphogypsum with ligninand ammonium nitrate, phosphogypsum with biohu-mus from lignin, phosphogypsum with manure, andshell limestone with manure) had a lower effect on thesoil aggregation, so the soil mass consisted of coarsegranular aggregates with an admixture of loose earthymaterial; and (3) the mineral fertilizers (ammoniumnitrate, nitroammophoska, and superphosphate) had anegative effect on the soil structure, so that the soilmass consisted of fine granular aggregates and a looseearthy mass. In the latter case, some bleaching of thesoil mass from the surface was observed.

Soil microaggregation.

In the initial (control) soil,microaggregates of the coarse silt size (0.05–0.01 mm)predominated (27.8%). Microaggregates of the finesand size (0.25–0.05) constituted 26.9%; of the fine siltsize (0.005–0.001 mm), 24.3%; and of the medium siltsize (0.01–0.005 mm), 13.6%. Under the impact ofameliorants such as phosphogypsum and lignin in dif-ferent combinations and manure with shell limestone,the content of microaggregates of the fine sand sizeincreased considerably (32.9–49.2%) in comparison

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with the control. The application of phosphogypsumresulted in a rise in the content of this fraction of micro-aggregates in parallel with a considerable decrease inthe contents of the finest microaggregates (<0.001 and0.005–0.001 mm) (Table 1).

The effect of lignin was somewhat different. Itfavored an increase in the content of microaggregatesof the fine sand size (0.25–0.05 mm) and the clay(<0.001 mm) size. It is probable that the addition ofammonium nitrate to lignin favored the partial disper-sion of the soil mass.

The application of organic ameliorants (biohumusfrom manure, biohumus from lignin, and manure)decreased the content of the finest (<0.001 mm) frac-tion of microaggregates and considerably increased (up

to 40–44%) the content of the fraction of 0.25–0.05 mm.

Superphosphate exerted the strongest effect on thesoil microaggregation: the portion of microaggregatesof the fine sand size increased up to 68.7%. It is knownthat the soils enriched in phosphorus compounds areusually well structured and have increased biologicalactivity [7]. The components of ammonium nitrateacted as dispersants, as the content of the finest(<0.001 mm) fraction of microaggregates increased upto 13% (the maximum value in the experimental vari-ants).

Thus, at this level of the soil mass arrangement(1

−

0.001 mm), the indices of the microaggregate-sizedistribution in the experimental variants can be grouped

Table 1.

Changes in the particle-size distribution (nominator) and microaggregate-size distribution (denominator) in verticchernozems under the impact of ameliorants and fertilizers, %

Treatment

Contents of particle-size and microaggregate-size fractions; fraction size, mm Coefficient

of structure dispersion1–0.25 0.25–0.05 0.05–0.01 0.01–

0.005 0.005–0.001 <0.001 <0.01

1. Control soil 14

2. Phosphogypsum 6

3. Lignin + ammonium nitrate 20

4. Biohumus from lignin 13

5. Biohumus from cattle ma-nure 3

6. Cattle manure 6

7. Superphosphate 7

8. Ammonium nitrate 26

9. Nitroammophoska 14

10. Phosphogypsum + lignin + ammonium nitrate 14

11. Phosphogypsum + biohu-mus from lignin 5

12. Phosphogypsum + manure 7

13. Shell limestone + manure 3

0.10.1------- 13.5

26.9---------- 9.5

27.8---------- 8.1

13.6---------- 18.6

24.3---------- 50.2

7.3---------- 76.9

45.2----------

0.20.4------- 14.6

46.7---------- 14.8

21.4---------- 10.9

12.8---------- 18.0

16.2---------- 41.5

2.5---------- 70.4

31.5----------

0.60.4------- 16.4

32.9---------- 7.9

22.0---------- 10.4

12.2---------- 17.4

23.0---------- 47.3

9.5---------- 75.1

44.7----------

2.01.1------- 16.4

40.0---------- 10.1

24.5---------- 9.9

12.4---------- 16.4

16.0---------- 45.5

6.0---------- 71.8

34.4----------

2.12.1------- 20.3

44.8---------- 13.7

27.6---------- 11.8

6.9---------- 10.3

17.2---------- 41.8

1.4---------- 63.9

25.5----------

1.31.0------- 22.4

44.1---------- 9.4

26.0---------- 8.6

7.1------- 19.2

19.5---------- 39.1

2.3---------- 66.9

28.9----------

0.50.7------- 22.2

68.8---------- 9.5

17.3---------- 17.8

1.5---------- 21.3

9.7---------- 28.7

2.0---------- 67.8

13.2----------

0.41.1------- 11.3

17.9---------- 14.2

34.2---------- 8.1

13.3---------- 16.8

20.5---------- 49.2

13.0---------- 74.1

46.8----------

0.40.5------- 9.7

49.2---------- 11.7

17.9---------- 4.9

13.1---------- 22.5

11.9---------- 50.8

7.4---------- 78.2

32.4----------

0.20.6------- 18.3

46.6---------- 6.7

18.9---------- 6.7

10.4---------- 25.2

17.5---------- 42.9

6.0---------- 74.8

33.9----------

0.10.5------- 8.9

44.3---------- 11.0

27.5---------- 6.6

6.2------- 23.6

18.8---------- 49.8

2.7---------- 80.0

27.7----------

0.60.9------- 16.7

46.4---------- 9.4

26.9---------- 3.9

10.8---------- 18.8

11.5---------- 50.6

3.5---------- 73.3

25.8----------

1.73.6------- 11.2

41.1---------- 9.0

30.5---------- 8.5

6.8------- 19.9

16.5---------- 50.1

1.5---------- 78.1

24.8----------

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as follows. In the variants with application of phospho-gypsum, microaggregates of the fine sand size (0.25–0.05 mm) predominate and the content of clay-sizemicroaggregates (<0.001 mm) is low. Similar resultshave been obtained in the variants with organic fertiliz-ers. The variants with ammonium nitrate are character-ized by a considerable rise in the content of clay-sizemicroaggregates (up to 13%). In the variants withsuperphosphate, the content of microaggregates of thefine sand size increased, whereas the content of micro-aggregates <0.01 mm decreased. With respect to thecontent of microaggregates of the fine sand size, theeffect of organic substances is close to the effect ofphosphogypsum. However, the application of organicsubstances also increased the content of microaggre-gates of the coarse silt size (0.05–0.01 mm).

As in the case with the soil macroaggregation, thevariants with application of mineral fertilizers (super-phosphate and nitroammophoska) have their own spec-ificity. At the level of microaggregates, the amount ofmicroaggregates of the fine sand size (0.25–0.05 mm)increased considerably in the contact zone of the soilmass with these fertilizers (up to 68 and 48%, respec-tively).

The initial (control) soil had a silty medium clayeytexture; the clay (<0.001 mm) content in it reached76.8%. Some changes in the particle-size distributiontook place under the impact of the added ameliorantsand fertilizers, mainly at the expense of the clay frac-tion. The minimum content of the clay fraction wasdetermined in the variant with superphosphate. Theorganic substances favored the preservation or somerise in the content of fine sand particles (0.25–0.05 mm)(16.4–22.4%). In the variants with superphosphate, thecontent of this particle-size fraction also reached22.4%. It can be supposed that new structural bondsappeared in the soil due to additional products of

weathering of smectitic minerals in the clay fractionunder the impact of the superphosphate [18–20].

Fractional composition of the clay.

The amelio-rants and fertilizers also affect the clay fraction, whichis seen from the data on the different subfractions ofclay determined by the method of fractional peptization(Table 2). The most considerable peptizing effect isseen in the variant with ammonium nitrate (Fig. 1).Nearly 44% of the total amount of clay in this casebelongs to the subfraction of the water-peptizable clay(WPC). Such an increase in the WPC content attests tothe poor stability of the soil structure. The soil loses itsaggregation and its hydraulic conductivity drasticallydecreases (the latter effect was noted in the second yearof the experiment). In the control soil, the WPC contentreaches only 5.2% of the total clay. The available dataon the fractional peptization of clay in the samples ofvirgin chernozems from the European part of Russia[13, 14, 16] suggest that the amount of WPC in them isvery low. It increases under the impact of plowing; i.e.,some part of the aggregated clay is transformed into theWPC. The strongest peptizing effect was noted uponirrigation of the chernozems with soda-containingwater of poor quality. The increase in the WPC contentupon the anthropogenic loads on the soils is a serioussignal attesting to deterioration of the soil agrophysicalproperties, including “fusion” of the soil mass.

In our experiment, no peptization of clay wasobserved in the variant with superphosphate: the WPCcontent comprised just 1.1% of the total clay, or 0.04%of the bulk soil mass. In the variants with phosphogyp-sum, phosphogypsum + lignin + ammonium nitrate,and nitroammophoska, the WPC contents were alsolow (2.5, 2.3, and 2.9% of the total clay, respectively, orfrom 1.2 to 1.3% of the bulk soil mass (Table 2)). In thevariants with organic ameliorants and fertilizers (biohu-mus from lignin, biohumus from manure, phosphogyp-sum + manure, and shell limestone + manure), the WPC

Table 2.

Contents of clay subfractions obtained by the method of fractional peptization of vertic chernozems from the modelexperiment (nominator, % of the soil; denominator, % of the sum of the clay subfractions)

Treatment WPC AC-1 AC-2 Sum

1. Control soi 2.2/5.2 25.9/60.9 14.4/33.9 42.52. Phosphogypsum 1.3/2.5 37.2/71.1 13.8/26.4 52.33. Lignin + ammonium nitrate 1.4/3.6 36.5/94.3 0.8/2.1 38.74. Biohumus from lignin 2.1/4.3 40.7/83.7 5.8/11.9 48.65. Biohumus from cattle manure 2.3/6.1 30.6/80.7 5.0/13.2 37.96. Cattle manure 3.0/6.8 30.1/68.7 10.7/24.4 43.87. Superphosphate 0.4/1.1 9.6/27.1 25.4/71.8 35.48. Ammonium nitrate 23.2/44.0 21.1/40.0 8.4/15.9 52.79. Nitroammophoska 1.2/2.3 28.8/55.6 21.8/42.1 51.810. Phosphogypsum + lignin + ammonium nitrate 1.2/2.9 30.6/75.0 9.0/22.1 40.811. Phosphogypsum + biohumus from lignin 2.0/3.7 34.4/63.7 17.6/32.6 54.012. Phosphogypsum + manure 2.9/6.1 21.4/44.8 23.5/49.2 47.813. Shell limestone + manure 2.5/5.4 24.5/52.7 19.5/41.9 46.5

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contents were relatively close to the control value(5.2%): 4.3, 6.1, 6.8, 6.1, and 5.4%, respectively.

Mineralogical composition of the water-peptiz-able clay.

In the vertic chernozems, the WPC consistsof the dominant smectitic minerals (40.8–80.8%) withdi- and trioctahedral hydromica, kaolinite, and chloriteas subdominant minerals. Fine-dispersed quartz andfeldspars may be present in the WPC as admixtures.The smectitic minerals are represented by individualsmectite of the montmorillonite–beidellite type andmixed-layered minerals of the mica–smectitic andchlorite–smectitic types with a high content of smec-titic layers (Fig. 2).

The following regularities in the mineralogical com-position of the WPC should be noted. First, the higherthe portion of the WPC in the total clay, the closer themineralogical composition and properties of the WPCto the mineralogical composition and properties of thetotal clay. Second, the lower the portion of the WPC inthe total clay, the more specific the mineralogical com-position of the WPC as compared with the mineralogi-cal composition of the total clay. The crystallochemicalparameters of the WPC become different from those ofthe total clay; the ratio of phyllosilicates to the fine-dis-persed quartz and feldspars changes, and the degree ofcrystallization of the dominant (smectitic) componentchanges.

The different ameliorants and fertilizers exerted dif-ferent effects on the mineralogical composition andcrystallochemical properties of the WPC.

The organic substances affected the mineralogicalcomposition of the WPC in the following way: (1) anincrease in the portion of X-ray-amorphous substances,(2) the presence of sharply pronounced characteristicpeaks of micas and hydromicas, kaolinite, and quartzon the diffraction curves (such peaks attest to the clasticnature of these minerals), (3) an increased content offine-dispersed quartz (probably, the effect of phytolithsand/or the effect of a strongly acid medium formedunder the impact of the human load), and (4) the disor-

dered mineral structure and the superdispersed state ofsmectitic minerals.

Phosphogypsum and phosphogypsum in combina-tions with other ameliorants and fertilizers affected themineralogical composition of the WPC in a somewhatdifferent away. In all the experimental variants, the pre-dominance of smectitic minerals was determined. Invariant 11 (phosphogypsum + lignin + ammoniumnitrate), as well as in variant 12 (phosphogypsum + bio-humus from lignin), the effect of lignin is considerable.In this case, the mineralogical parameters of the WPCare similar to those in the variants with application oforganic substances.

The most significant impact on the mineralogicalcomposition of the WPC is exerted by mineral fertiliz-ers. The WPC in the variant with ammonium nitrateconsists of phyllosilicates with X-ray diffraction pat-terns very similar to those of the bulk clay. The super-phosphate facilitated the coagulation of the WPC, asthe WPC content in this variant decreased to about 1%.The roentgen-amorphous phase and clastic forms ofminerals predominate in the WPC. The smectitic min-erals are highly disordered and occur in the superdis-persed state.

Impact of ameliorants on aggregated clay.

Themajor mass (60.9%) of clay in the control sample is inthe aggregated state (Figs. 3, 4). In all the variants of theexperiment, the subfractions of loosely and firmlyaggregated clay predominate; their total content variesfrom 44.8 to 94.3%. Such a wide range attests to theconsiderable reorganization of the clayey material inthe soil under the impact of the ameliorants and, espe-cially, fertilizers. In the experiments with ammoniumnitrate, the loosely bound subfraction of aggregatedclay (AC-1) constitutes just 40% of the total clay, as alarger part of the total clay is represented by the WPC.On the contrary, the application of superphosphatefavored the transformation of a considerable portion ofthe clay material into the firmly aggregated state

%454035302520151050

1 2 3 4 5 6 7 8 9 10 11 12 13WPC

Fig. 1.

Changes in the content of water-peptizable clay in vertic chernozems under the impact of ameliorants and fertilizers. Hereand in Figs. 2–4: (

1

) control soil, (

2

) phosphogypsum, (

3

) lignin + ammonium nitrate, (

4

) biohumus from lignin, (

5

) biohumus fromcattle manure, (

6

) manure, (

7

) superphosphate, (

8

) ammonium nitrate, (

9

) nitroammophoska, (

10

) phosphogypsum + lignin +ammonium nitrate, (

11

) phosphogypsum + biohumus from lignin, (

12

) phosphogypsum + manure, and (

13

) shell limestone +manure.

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(AC-2), whereas the content of the AC-1 subfractiondecreased to 27.1%.

As shown earlier [13], the disturbance of the bondsof clay particles and their transition from the firmly toloosely aggregated state is a factor that predeterminesthe further transition of clayey substances into thewater-peptizable state.

In our experiment, this was observed in the variantwith lignin and ammonium nitrate. In this variant, theAI-1 subfraction comprised 94.3% of the total clay. Ahigh percent of the AI-1 subfraction was also recordedin the variants with biohumus from lignin (83.7%) andwith manure. The AC-1 subfraction is dominated (49–68%) by the smectitic phase (mixed-layered mica–

0.333

0.357

0.4260.470.51

0.711.0

1.41.6

0.318

0.333

0.357

0.4250.47

0.442

0.500.71

1.0

1.41.6

0.318

0.334

0.357

0.430.44

0.50.7 1.0

1.6

0.118

0.120

0.333

0.357

0.426

0.475

0.500.7 1.0

1.41.6

0.334

0.357

0.4260.44

0.50.71.0

2.0

0.334

0.318

0.357

0.426

0.44

0.50.7 1.0

1.41.6

0.334

0.3550.42

0.440.50.7

0.741.0

2.0 0.3340.357

0.4260.474

0.7 1.0

1.47

0.5

0.3340.357

0.4260.5

0.7

1.0

1.9

0.334

0.3550.420.5

0.70.74

1.0

2.0

0.334

0.356

0.426

0.44

0.50.700.74

1.0

1.8 0.334

0.333

0.42

0.44

0.470.5

0.71.0

1.5

0.333

0.357

0.4260.47

0.51

0.711.0

1.41.6

1 2 3 4

5 6 7 8

9 10 11 12

13

Fig. 2.

X-ray diffraction curves obtained for water-peptizable clay from vertic chernozems of the model experiment (air-dry sam-ples; the interplanar distances are given in nm).

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smectitic and chlorite–smectitic minerals with someadmixture of individual smectites of the montmorillo-nite–beidellite type); hydromica, kaolinite, and chloriteare also present in the AC-1 subfraction. However, incontrast to the WPC subfraction, fine-dispersed quartzand feldspars are absent. The following changes in themineralogical composition of the clay materials takeplace upon changes in the degree of their aggregation.With a decrease in the portion of the AC-1 subfraction,the content of smectite in it also decreases. For exam-ple, in the variant with superphosphate favoring theaggregation of clay, the content of the AC-1 subfractiondecreased to 27%. The smectite content in this subfrac-tion decreased to 49.1%. The intensity of the peaksfrom all the minerals is relatively low. The applicationof organic substances also lowered the intensity of thepeaks on the X-ray diffraction curve, which is seenespecially well in the variant with biohumus andmanure. The absence of fine-dispersed quartz in theAC-1 subfraction (particularly, in the variants withorganic fertilizers) should be noted. The application ofphosphogypsum has affected the heights of the peakson the X-ray diffraction curves. In the variants withphosphogypsum, the percentage of the AC-1 subfrac-tion is considerable, and the minerals in this subfractionhave very distinct and high peaks. At the same time, theproportion between the main mineral phases in theAC-1 in the variant with phosphogypsum is analogousto that in the control.

The firmly aggregated clay (the AC-2 subfraction) ismore diverse in its mineralogical composition than theAC-1 subfraction. In the AC-2 subfraction, trioctahe-

dral hydromica predominates among the hydromica. Inthe WPC and AC-1 subfractions, the degree of perfec-tion of the mineral structures increases with an increasein the contents of these subfractions; this regularity isnot observed in the case of the AC-2 subfraction.

Some ameliorants such as lignin and its derivatives,favored the transition of clay from the AC-2 to the AC-1 subfractions. Among the remaining 2% of the clay inthe AC-2 subfraction, hydromica, mica, kaolinite, andchlorite predominate, whereas the mixed-layeredmica–smectitic minerals occupy a subdominant posi-tion. The biohumus from lignin also considerablyaffects the components of the clay. In this case, the por-tion of mica–smectitic minerals with a low content ofsmectite layers is much higher than in the variant withlignin. The effect of the biohumus from cattle manureis less significant: the portion of the AC-1 subfractionreaches 79.9%, which means that only about 19% of theclay particles were transformed from the firmly aggre-gated to loosely aggregated state; the AC-2 contentreaches 13%. This subfraction consists of the poorlyordered mixed-layered mica–smectitic minerals with ahigh content of smectite layers; the second type of thisgroup of minerals (with a low content of smectite lay-ers) is absent. Cattle manure favors the preservation ofthe initial organization of the clay materials in the soilmass. In this variant, the AC-2 content is 24.4%; i.e., itis relatively close to the control.

In the variant with superphosphate, the content ofthe AC-2 subfraction increased up to 71.7%. Thus, alarger part of the clay is in the firmly aggregated state.The mineralogical composition of this subfraction is

%100

80

60

40

20

0

1 2 3 4 5 6 7 8 9 10 11 12 13

80

70

60

50

40

30

20

10

0

(a)

(b)

Fig. 3.

Changes in the contents of (a) aggregated clay 1 and (b) aggregated clay 2 in vertic chernozems under the impact of amelio-rants and fertilizers.

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CHANGES IN CLAY MINERALS OF VERTIC CHERNOZEMS 1131

also specific: the content of mixed-layered mica–smec-titic minerals is lower than that in the control, and thepeaks of phyllosilicates are less pronounced than thosein the control. It can be supposed that dissolved calciumfrom the superphosphate favors the coagulation and

firm aggregation of the clay minerals. At the same time,the phosphoric acid affects the mineral structure and,particularly, the structure of smectites. Though the con-tent of these minerals remains high, their peaks on theX-ray diffraction curve become less pronounced.

0.3340.356

0.4260.5

0.71.0

1.47

0.3340.356

0.474

0.5

0.71.0

1.47

0.3340.356

0.47

0.5

0.71.0

1.48

0.33 0.356

0.47

0.5

0.71.0

1.48

0.334 0.356

0.4740.5

0.71.0

1.530.33

0.356

0.470.5

0.71.0

1.47

0.3340.355

0.440.50.7 1.0

1.90.334 0.356

0.470.71.0

1.4

1.9

0.5

0.334 0.354

0.474 0.50.7

1.0

1.53

0.330.357

0.5

0.71.0

1.47

0.334 0.357

0.470.5

0.71.0

1.51

0.334 0.357

0.470.5

0.71.0

1.51

0.334 0.357

0.470.5

0.71.0

1.43

1 2 3 4

56 7 8

9 1011

12

13

(a)

Fig. 4.

X-ray diffraction curves obtained for (a) aggregated clay 1 and (b) aggregated clay 2 separated from vertic chernozems ofthe model experiment (air-dry samples; the interplanar distances are given in nm).

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CHIZHIKOVA et al.

In the variants with ammonium nitrate and nitroam-mophoska, the main mass of clay was disaggregatedand transferred into the WPC subfraction; the portionof the AC-2 subfraction decreased to 15.9%. The con-tent of smectitic minerals in this subfraction alsodecreased; mica–smectitic minerals with a low content

of smectitic layers were absent. Trioctahedral hydrom-ica predominated.

The amount of the AC-2 subfraction did not changein comparison with the control in the variants withphosphogypsum, phosphogypsum with biohumus fromlignin, phosphogypsum with cattle manure, and shell

0.334 0.355

0.470.5

0.71.0

1.47

0.33 0.357

0.470.5

0.71.0

1.43

0.3340.353

0.3570.470.5

0.7 1.01.41 0.334

0.3550.474 0.5 0.7 1.0

1.4

0.334 0.357

0.470.5

0.7

1.0

1.51

0.334 0.355

0.470.5

0.71.0

1.47

0.334 0.355 0.5

0.71.0

1.9

0.3340.335

0.470.5

0.71.0

1.4–1.9

0.334 0.355

0.470.5

0.71.0

1.4–1.5

0.334 0.3550.5

0.71.0

1.5

0.3340.356

0.5

0.71.0

1.5

0.3340.356

0.470.5

0.7 1.0

1.5

0.334 0.356

0.470.5

0.71.0

1.5

1 2 3 4

5 6 7 8

9 10 11 12

13

(b)

Fig. 4. (Contd.).

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CHANGES IN CLAY MINERALS OF VERTIC CHERNOZEMS 1133

limestone with manure. The changes in the mineralog-ical composition of the AC-2 fraction in these variantswere relatively small; the amount of smectitic mineralssomewhat decreased, and the peaks of all the phyllosil-icates became less pronounced.

CONCLUSIONS

(1) The clay fraction of the vertic chernozem has apolymineral nature with a predominance of the smec-titic phase (52.1–58.3%), di- and trioctahedral hydrom-ica (25.6–33.2%), and kaolinite and chlorite (in total,14.7–16.1%). It also contains an admixture of fine-dis-persed quartz. The smectitic phase consists of complexmixed-layered minerals of several types: (a) mixed-lay-ered mica–smectites with the predominance of smectitelayers, (b) mixed-layered mica–smectites with a lowcontent of smectite layers, (c) chlorite–smectites, and(d) individual smectite of the montmorillonite–beidel-lite type.

(2) Ameliorants and fertilizers applied onto thesoil surface have induced some reorganization of thesoil mass that can be registered at several hierarchi-cal levels.

(a) The morphology of the soil aggregates in theuppermost soil layer changed after a year. The sub-stances applied can be subdivided into three groupswith respect to their effect on the soil macroaggrega-tion. The organic substances favored the developmentof an agronomically valuable coarse granular and angu-lar blocky structure. The phosphogypsum, lignin withammonium nitrate, phosphogypsum with biohumusfrom lignin, phosphogypsum with cattle manure, andshell limestone with cattle manure had a low effect onthe soil aggregation. The mineral fertilizers (superphos-phate, ammonium nitrate, and nitroammophoska)partly destroyed the natural soil aggregates to the silt-size fraction.

(b) The aggregation of the soil mass at the level ofmeso- and microaggregates (<1 mm) as determinedduring the particle-size and microaggregate-size distri-bution analyses also changed. Superphosphate had themost pronounced effect on the formation of microag-gregates of the fine sand size (0.25–0.05 mm). Theircontent in the variant with superphosphate was higherthan that in the variants with the organic fertilizers. Inthe variants with ammonium nitrate and ammoniumnitrate + lignin, the portion of clay-size (<0.001 mm)microaggregates increased considerably; the coeffi-cient of the soil structure dispersion in these variantsreaches 26 and 20, respectively. In the variants withphosphogypsum, biohumus from lignin, biohumusfrom cattle manure, cattle manure, phosphogypsumwith biohumus from lignin, phosphogypsum with cattlemanure, and shell limestone with cattle manure, theamount of clay-size microaggregates decreased bytwo–three times.

(c) The degree of aggregation of the clay particles asdetermined by the method of the fractional peptizationof clay changed under the impact of the ameliorants andfertilizers. Ammonium nitrate had the most significanteffect on the clay peptization: the amount of water-pep-tizable clay reached more than 40% of the total clay.The lignin, biohumus from lignin, and biohumus frommanure partly prevented the clay peptization. At thesame time, the portion of loosely aggregated clayincreased. The phosphogypsum together with biohu-mus and the shell limestone together with manurefavored a considerable increase in the portion of firmlyaggregated clay.

(3) The mineralogical composition of the total clayfraction did not changed much under the impact of thefertilizers and ameliorants. However, considerablechanges took place in the portions of particular miner-als within the subfractions of water-peptizable, looselyaggregated, and firmly aggregated clay. The most sig-nificant changes took place in the subfraction of water-peptizable clay. This subfraction is characterized by thesuperdispersed state of the smectitic minerals, the con-siderable variability in the proportions between the dif-ferent mineral phases, and by the presence of fine-dis-persed quartz and feldspars. The mineral fertilizers hadthe most pronounced effect on the mineralogical com-position of this subfraction. The subfraction of looselyaggregated clay (AC-1) is the predominant subfraction.Its mineralogical composition is very similar to themineralogical composition of the total clay fraction,and the changes in the mineralogy of this subfractionunder the impact of the fertilizers and ameliorants areless pronounced than those in the subfraction of water-peptizable clay. Superphosphate exerts the most signif-icant effect on the mineralogical composition of theloosely aggregated clay.

The subfraction of firmly aggregated clay (AC-2) israther diverse with respect to its mineralogical compo-sition. Trioctahedral hydromica predominates amongthe hydromica in this subfraction. Considerablechanges in the mixed-layered mica–smectitic mineralstook place in the variants with ammonium nitrate, lig-nin with ammonium nitrate, biohumus from lignin, andsuperphosphate.

(4) It is established that fertilizers and ameliorantsexert diverse and, often, oppositely directed impacts onthe aggregation of the soil mass and the mineralogy ofthe different subfractions of clay. From the ecologicalviewpoint, application of organic fertilizers (biohumus)seems to be the most feasible way of amelioration ofvertic chernozems.

REFERENCES

1. A. I. Vadyunina and Z. A. Korchagina, Methods of Study-ing the Physical Properties of Soils (Agropromizdat,Moscow, 1986) [in Russian].

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2. K. K. Gedroits, Selected Works, Vol. 1: Soil Colloids andthe Adsorbing Capacity of Soils (Sel’khozgiz, Moscow,1955) [in Russian].

3. B. P. Gradusov, N. P. Chizhikova, O. A. Ivanova, andL. A. Aidabekova, USSR Inventor’s Certificate no. 1 441 310(1985).

4. Yu. A. Dukhanin, V. I. Savich, A. G. Zamoraev, et al.,Ecological Assessment of Interaction of Fertilizers andAmeliorants with the Soil (Rosinformagrotekh, Moscow,2005) [in Russian].

5. Yu. A. Dukhanin, V. I. Savich, B. N. Batanov, andK. V. Savich, Information Assessment of Soil Fertility(Rosinformagrotekh, Moscow, 2006) [in Russian].

6. S. K. Kubashev, Extended Abstract of Candidate’s Dis-sertation in Biology (Moscow, 2005).

7. V. D. Mukha, N. I. Kartamyshev, I. S. Kochetov, et al.,Agro-Soil Science (1994).

8. K. P. Pak and I. G. Tsyurupa, “Effect of Salt Solutions onthe Properties of Clays and Finely Dispersed Materials,”in Weathering Crust (Nauka, Moscow, 1974), pp. 240–246 [in Russian].

9. N. P. Panov and N. A. Goncharova, “Genesis Features ofLow-Sodium Soils in the Volgograd Oblast,” Izv.Timiryazevsk. S–Kh. Akad., No. 5 (1969).

10. N. P. Panov and N. A. Goncharova, “Factors Determin-ing the Unfavorable Properties of Low-Sodium Solo-netzes,” in Reclamation of Solonetzes (VASKhNIL,Moscow, 1972), Vol. 1 [in Russian].

11. V. I. Savich, “Physicochemical Fundamentals of SoilFertility,” in Current Problems of Agricultural Chemis-try and Ecology (MSKhA, Moscow, 2004), pp. 144–182[in Russian].

12. T. A. Sokolova and T. Ya. Dronova, Changes in Soilsunder the Effect of Acid Precipitation (Mosk. Gos. Univ.,Moscow, 1993) [in Russian].

13. N. P. Chizhikova, “Mineralogy Changes in Typical Cher-nozems under Irrigation Conditions,” Pochvovedenie,No. 2, 65–81 (1991).

14. N. P. Chizhikova, V. A. Baranovskaya, and B. P. Gra-dusov, “Mineralogy and Peptizability of Rainfed andIrrigated Light Chestnut Soils in the Transvolga Region,”in Physical Chemistry of Soils and Fertility: Proceed-ings of the Dokuchaev Soil Science Institute (Moscow,1988), pp. 64–70 [in Russian].

15. N. P. Chizhikova, E. I. Godunova, and S. K. Kubashev,“Effect of Ameliorants and Fertilizers on the Propertiesand Composition of Vertic Chernozem,” in Proceedingsof the International Ecological Forum: “Conserve theEarth Planet,” St. Petersburg, Russia, 2004 (St. Peters-burg, 2004), pp. 305–309 [in Russian].

16. N. P. Chizhikova, P. M. Sapozhnikov, and D. Yu. Ivanov,“Effect of Fertilizers and Fallowing on the Fine SoilFraction,” Pochvovedenie, No. 12, 93–105 (1992).

17. C. W. Correns, “Experiments on the Decompositions ofSilicates and the Discussion on Chemical Weathering,”'lays Clay Miner. 10, 443–459 (1961).

18. D. J. Greenland and J. M. Oades, “Iron Hydroxides andClay Surfaces,” in Transactions of the 9th InternationalCongress of Soil Science, Adelaide, Australia, 1986(Elsevier, New York, 1968), Vol. 1, pp. 657–668.

19. G. J. Ross, “Acid Dissolution of Chlorites: Release ofMagnesium, Iron, and Aluminum and Mode of AcidAttack,” 'lays Clay Miner. 17, 347–354 (1969).

20. N. S. Yeoh and J. M. Oades, “Properties of Soils andClays after Acid Treatment: Clay Minerals,” Austr. J.Soil Res. 19 (147–158) (1981).

21. M. J. Wilson, “Acid Deposition, Critical Loads, and SoilMinerals: a Historical Review with Some CautionaryComments,” in The XVI World Congress of Soil Science:Introductory Paper to Symposium No. 24 on “Soils Min-erals and Acidification,” Montpellier, France, 1998(Montpellier, 1998).