Changes in Chernozem Erosion Resistance Due to the Evolution of Clay Plasma in Western Ukrainian Region

The major problem of efficient agriculture in Ukraine is increasing rates of the water erosion in Chernozems. The aim of this research study is to describe the negative trends in the clay profile for evolution of various Chernozem sub-types, which lead to the reduction of erosion resistance. Cohesion strength between soil aggregates is determined dominating smectite minerals in clay plasma. Disturbing the stable balance between the organic and mineral matter are the main causes of soil disaggregation. Evolutionary changes of Chernozems clay plasma are studied using the methods of chemical and x-ray diffractometry analysis. The processes of de-humification have been destabilized the mineral colloidal complex and smectite-illit dynamic equilibrium in soils. From Haplic Chernozems to Greyzemic Chernozems, the substantial loss of highly dispersive smectite material is observed. The dominance of inactive illite clay in the arable layer of all Chernozems reduce the role of clay plasma in formatting of water-stable micro-and macrostructure. According to the anti-erosion properties of clay plasma, the Chernozems under study is found in the following order: Haplic Chernozem > Greyzemic Chernozem. These properties reduce themselves following the increase in soil hydromorphism stimulating argillification in the middle and lower horizons due to the processes of lessivage and inter-soil weathering. Anthropogenic evolution of Chernozems, when caused by the changes in the silicate fraction of soils, is basically of irreversible degrading nature.


Introduction
The total area of Ukraine territory is 60.3 million hectares.Chernozems1 cover 46.1% of its territory (27.8 million hectares).Agricultural land covers 41.8 million hectares, 61.8% (24.9 million hectares) of which lies on Chernozems.The Chernozem soils are the main factor behind the food security in Ukraine.These soils have experienced the strongest anthropogenic pressure in its entire history.Anthropogenic evolution of Chernozems, when caused by the changes in the silicate fraction of soils, is basically of irreversible degrading nature.
The dynamics of erosion losses of arable soils in the Ukraine has been disastrous for the last 50 years.According to Nosko (2006), its erosion was accelerated at the stage of intensive land use and led to the deterioration of physical, chemical and biological properties.Nowadays only 40-45% of Ukraine's territory has erosion-safe organization of land use, the rest of the territory is erosion prone (Polupan and Volkov, 2010).The total area of eroded soils is 9.7 million hectares, over 30% of which is eroded on slopy lands having over 3º slopes (Bulygin, 2005).
Erosion resistance of soils describes its ability to resist disaggregation of the surface soil layer caused by rain drops and washing out soil material by stream and between-stream surface slope waters.Quantitatively, it is measured by the erosive velocity of water flow, which is directly determined by the size of water-stable aggregates, and its cohesion with each other (Kuznyetsov and Glazunov, 2004).All other properties of soils, that determine water stability and soil structure, including the quality of soil plasma, indirectly influence the erosion resistance through the above listed parameters.Chernozems, unlike other soils have high erosion resistance, has been formed over centuries.It has different nature and various mechanisms of anti-erosion protection such as external, internal and basic.Vegetation and relief provide external protection to the Chernozems from erosion.The characteristics of highly dispersed soil plasmamull humus, a high content of physical clay with highly active smectite phase in its composition, soil-absorbing complex saturated with bases form the basic mechanisms.Interacting with each other, these soils form a complex of erosion resistant soil properties by which anti-erosion potential of Chernozems is determined.So, the internal mechanisms include substantial humus horizon (70-100 cm) with strong and water-stable macro-and microstructure, low density (1.0-1.2 g/cm 3 ) and high total porosity (50-60%), high water capacity and water conductivity, significant biological activity (Papish, 1997).Owing to these properties, Chernozems have high ecological potential and natural buffer to erosion.When basic mechanisms of the self-organisation of the soil matrix are harmonized with the newest approaches to ecologically safe organization of land use, then Chernozems serve as an example of inexhaustible resources of fertility and environmental sustainability.
During 1970s-1980s, studying the evolution of Chernozem clay minerals under the influence of irrigation and fertilization was particularly topical in Ukraine (Gogolev et al., 1977;Nosko and Philon, 1988;Pozniak, 1997).However, there are still only a few scientific papers on mineralogy of Chernozem clay fraction of Western Ukrainian region (Andruschenko et al., 1981).There are no scientific research of the Chernozems mineralogy in Western Ukraine region since the 1990s.The assessment of anti-erosion properties of the clay fraction in Chernozems are very relevant in conditions of dissected Podollian and Pre-Carpathian uplands.

Methodology Study Region and Field Sampling
In field practice, it often happens that no eroded Chernozems are found even on the slopes with high erosion potential (5-7°).At the same time, Chernozems can often be slightly eroded on the relatively declivous slopes (3-5°).That means that under the same climatic conditions the factor of relief is not necessarily determinant for Chernozems.The practice proves that relief can realize its erosion potential only in case of Chernozems weakened by irreversible changes in the organic and mineral components of soil plasma (Mirtshulava, 1970;Kuznyetsov and Glazunov, 2004;Smirnova et al., 2006).
The investigation on Chernozem erosion resistance requires answering the wide range of complicated questions, the main ones being as follows: What evolution changes in the soil matrix organization of different Chernozem subtypes stimulate the cultivated soil formation process?How do they affect the Chernozem erosion resistance?To answer these questions, the current state of the major components of Chernozem soil plasma of Western Ukrainian region has been analysed under conditions that exclude the direct impact of erosion processes.
Chemical and mineralogical, granulometric and microaggregate analyses of the soil samples were conducted.These soil samples were taken after the end of the crop growing season from the four representative profiles (Figure 1).Three soil samples were taken from the middle of each genetic horizon ( 21  A1 (0-20 cm)plough-treated layer, dark-grey colour, homogeneous, medium loam, soft soil packing, silt-grain-crumb of soil structure, coprolites, transition to lower layer is sudden and irregular.A2 (20-66 cm)under plough layer, dark-grey colour, inhomogeneous of soil packing, water-stable crumb-grain of soil structure (in plough pan is lumpiness), medium loam, coprolites, transition to lower horizon is gradual and regular.AB (66-80 cm)dark-grey with a touch of brown, homogeneous, medium loam, condensed, waterstable medium grain of soil structure, mole drains, and transition to lower horizon is gradual and regular.ABk (80-110 cm)dark-grey with a touch of brown, homogeneous, medium loam, condensed, waterstable coarse-grain of soil structure, alluvial-calcareous, carbonate mouldiness, mole drains, and transition to lower horizon is gradual and pocket.BCAk (110-136 cm)dark-brown a touch of grey, homogeneous, medium loam, weak-condensed due to the oversaturation of carbonate mouldiness and pseudomycelium, grain-crumb of soil structure, mole drains, transition to lower horizon is visible and wavy.Ck (136-170 cm)loess loam, light-brown, homogeneous, medium loam, packing, structure less, carbonate pseudomycelium, transition to lower horizon is visible.Ckg (170-200 cm)loess loam, light-brown a touch of red, homogeneous, medium loam, packing, structure less, carbonate pseudomycelium, gleization in form of spots and Fe-Mn concretions.
Greyzemic Chernozems cover extensive natural Pre-Carpathian region within the limits of the valley-terrace complexes of the Dniester and Prut rivers.They were formed in the thickness of gleied loess loam with light and medium granulometric composition.On the ancient Pliocene terraces of the Prut and Dnister rivers the fine-sand calcareousness alluvium underlies Greyzemic Chernozems.Their distinctive regional feature is profile gleization, intensity of which increases westwards.The Greyzemic Chernozems of Prut-Dnister Upland have distinct features of this particular Chernozem subtype and characterize the soils of high terrace levels with complex geological structure of the soil-subsoil thickness.In the north-western Pre-Carpathians within the Syan-Dnister Upland the most hydro-morphological Chernozem group is prevalent with intensive profile gleization and soil profile texture-differentiation.The morphological construction of Luvic Greyzemic Chernozem profile is following (soil profile 61): A (0-18 cm)plough-treated layer, dark-grey colour, homogeneous, light loam, soft soil packing, siltgrain-crumb of soil structure, coprolites, transition to lower layer is sudden and irregular.Ae (18-41 cm)under plough layer, dark-grey colour, inhomogeneous of soil packing, small graincrumb of soil structure (in plough pan is lumpiness), light loam, coprolites, cristobalites neoformation SiO2, transition to lower horizon is gradual and regular.ABe,g (41-70 cm)dark-grey with a touch of brown, homogeneous, light loam, condensed, coarsegrain-nut of soil structure, cristobalites neoformation SiO2, spots of gleization with depth 62 cm, transition to lower horizon is gradual and pocket.Bt,e,g (70-88 cm)dark-brown a touch of grey, inhomogeneous, light loam, condensed, fissuring, nutprism of soil structure, clay-humus cutans, cristobalites neoformation SiO2, spots of gleization, mole drains, transition to lower horizon is visible and wavy.BCt,g (88-120 cm)dark-brown, inhomogeneous, light loam, dense of soil packing, prism-lumpiness, fissuring, clay-humus cutans, mole drains, red spots of gleization, Fe-Mn concretions, transition to lower horizon is visible and wavy.
The described Chernozem soil profiles are typical within the Wet Atlantic facies of Ukraine.

Experimental Part
The individual soil samples selected from each genetic horizon of Chernozems and parent rock by the method adopted for large-scale soil mapping.The whole complex of general methods (granulometric and microaggregate analyses) and special methods for quantitative analysis of soil (X-ray diffractometry and gross chemical analysis) were employed.
The granulometric and microaggregate analyses were conducted according to the standard methodology introduced by Kachynskyi (1965), using pyrophosphate method to prepare the soil.Preparations of soil samples and allocating the clay fraction up to 1 µm out of Chernozems were made in accordance with Gorbunov's (1960) methodology at the Department of Soil Science and Soil Geography, Ivan Franko National University of Lviv.The gross chemical analysis of the Chernozem clay fraction was performed in the chemical laboratory of the Institute of Geology and Geochemistry of Combustible Minerals of NAS of Ukraine (Lviv, Ukraine).The X-ray diffractometric analysis of the soil samples was made in the laboratory of soil mineralogy, Jagiellonian University, Krakow, Poland.Oriented preparations were obtained by method of sedimentation of the fractions on cover lenses.X-ray survey performed by diffractometer PHILIPS X'Pert APD (generator PW 1870 and PW 3020 vertical goniometer) and used CuKά-rays.Analysis carried out in the corners 2º-52º 2Θ with a speed of 0.02º/1s.Analysis were performed by increasing voltage 40 kV and amperage of 30 mA.Oriented preparations subjected to analysis in air-dry conditions (Na-air) and after satiation it by vapour ethylene glycol (EG-sat).Graphical analysis of the diffractograms was carried out using software firm Philips and also program Clay Lab (Papish, 2022).Individual pure minerals were identified as its heir packages in the mixed-planar minerals.The latter minerals were identified at grounds by Rule Meringa.

Evolution of Nature Mechanisms Chernozems Protection from Erosion
Obviously, for the last 40-50 years, there has been significant extension of eroded soils, including Chernozems by 1.6 million hectares in Ukraine due to the non-eroded soils on gentle slopes (2-3°).Its antierosion potential has reduced because of intensive and irrational land use.Over the study period, it has been found that the non-eroded Chernozems in the structure of arable land on gentle and declivous slopes cover considerably larger area than slightly eroded soils.The first step to prevent further extension of the area of eroded Chernozems is to make the objective analyses of the basic natural mechanisms of forming erosion resistance by soils yet on the stage of non-eroded soils under conditions of watersheds and watershed slopes.Almost all external natural mechanisms, which ensure that landscapes with Chernozems are capable to resist geological erosion, have been modified and degraded to such an extent that they no longer perform their natural protective functions.
The vegetation of agroecosystem under intensive crop rotations is not the factor of anti-erosion soil protection as on wild lands but the concentration factor of the energy potential of stream and between stream erosion (clean-cultivated crop) (Polupan and Volkov, 2010).However, in agrarian landscapes there is no environmentally safer place for intensive crop rotations than flat watershed surfaces and gentle watershed slopes (1-3°) containing Chernozems.This objective reality is indisputable.Because of thick humus horizon, even slightly eroded Chernozem series have high fertility potential and will be used in intensive crop rotations in the future.In this case, we can choose the priorities of what to "cure"the consequences of the "disease" such as soil erosion by means of agrotechnology and soil engineering that are not always efficient and often safe, or the reasons of the "disease" such as weakened basic natural mechanisms through which the Chernozem erosion potential is effectively realized.
In case of medium and severely eroded Chernozems on the declivous and steep slopes (more than 5°) there is no choice.Having lost the most of humus horizon, its basic and internal mechanisms of anti-erosion protection, especially clay-humic material, became not merely degraded but irreversibly lost due to the erosion.Loose ploughing horizon of medium washed soils has, on average, less erosive velocity than noneroded soils because of the reduction of soil water resistance under the soil plasma erosion (Kuznyetsov and Glazunov, 2004).Unilateral efforts to restore it through the land use system of soil protective crop rotations are unsuccessful.In case of its further agricultural use, such Chernozems will need effective outer antierosion protection through the system of appropriate grassland rotation and slope zoning.This will create conditions for the stabilization of natural protective mechanisms and, thus, will prevent the soils from further accelerated degradation.
Chernozem is a natural and historical product of interaction between zonal factors and regional conditions.On the regional level of soil organization, there is a close spatial correlation between Chernozems and the relief.In conditions of humid forest-steppe, Chernozems are always confined to gently undulating plateaus with wide watershed surfaces, long gentle slopes or short retreating, convex slopes with the well-developed branched hollow-arroyo system.In conditions of Ukraine's open steppe of loess plateaus, Chernozem formation and relief formation processes have harmonized on the slopes.The natural uneven terrains like systems of micro-and nano-relief forms (papillae of runoff) were formed, through which stream and between-stream surface waters are distributed running into the basic erosion network (Polupan and Volkov, 2010).Having lost natural vegetation, they have become the only external instrument of natural anti-erosion protection of Chernozems.The traditional land organization, including field planning, levelling the soil surface, ploughing in one direction and spatial orientation of crops created anthropogenic network of papillae of runoff that reallocated surface runoff between the largest slope and linear uneven terrains.As a result, both the catchment area of between-stream runoff and its erosion potential expanded.This led to the degradation and permanent loss of the active part of the Chernozem soil plasma decreasing its erosion resistance.The anthropogenic impact on external natural mechanisms of Chernozem protection from erosion and the consequences are described in detail in Polupan's and Volkov's work (2010).
The external natural mechanisms of Chernozem anti-erosion protection characterize erosion on the level of soil type or subtype.In this case, detailed field investigations indicate the high erosion resistance of Chernozems compared with other zonal soils such as grey forest soils (Luvisols), Kastanozems, etc.These parameters are rather illustrative, and they are of poor practical value.
Therefore, the external elements of erosion resistance of Chernozems should be supplemented by other parameters, including humus, granulometric composition and chemical and mineralogical composition, which are basic for the formation of their erosion resistance and react to external stimuli.
Forest-steppe Chernozems have been intensively used for more than 1,000 years.Naturally, anti-erosion resistance of Chernozems has changed due to the long land use.The main reason of this phenomenon is the degradation of soil properties that define anti-erosion resistance.First of all, these are the processes of total and deep de-humification of Chernozems, which were catastrophic in terms of the historic scope.Grinchenko et al. (1965Grinchenko et al. ( , 1970) ) described in detail the dynamics and effects of this phenomenon.
Ihor Papish, Halyna Ivanyuk, Viktor Ivaniuk Humus is an organic component of the matrix substance of soils.The two interrelated trends can be outlined in the age dynamics of Chernozem humus on the post-wild stage of soil evolution.Initially, the intensive mineralization of humus in the arable layer is followed by its intensively moving down the profile.The most mobile humus fractions, which are not connected with clay minerals migrate and indirectly affect its potential migration capacity.At the same time, the total reserves of humus in one-meter layer of Chernozems almost do not change.However, after 50 years of intensive land use the de-humification process has affected the whole soil profile and become irreversible.The same trend can be noticed on the fallow Chernozems but on the smaller scale and without the mobile humus fractions, which were lost due to the mineralization on the post-wild stage.Obviously, the dynamic equilibrium disturbance between the organic and mineral components of Chernozem matrix substance affects, to some extent, the stability of the latter.The highly active mineral part of the Chernozem clay materialvermiculite-smectite phaseis the first to respond to such changes.These are the first substantial changes in the matrix organization of Chernozems used on the slopes that will have profound environmental impacts.
With the reduction in the proportion of lightly mineralized humus in the composition of Chernozem organic substance the intensity of mineralization processes decreases and there comes a period of relative environmental quasi-equilibrium.Under conditions of traditional extensive land use this period can last indefinitely long.The duration of this equilibrium period gradually decreases as a result of changes in the mineral composition of the matrix substance of Chernozems.The relative conservativeness of clay plasma and its close contact with organic substance is a pledge of long-term recession in the humus mineralization and stability of the organic-mineral soil absorbing complex.
The transition of considerable areas of full-profile Chernozems into slightly eroded soil series occurred as a result of the intensive land use in grain-row crop rotations.Irreversible changes in the mineralogy of Chernozem clay material take place against the background of local changes in the hydrothermal regime of soils.
The acidification of an arable soil layer by adding the normalized doses of manure (10-12 t/ha) and applying physiologically acidic fertilizers (172 kg/ha of active substance; this level was reached in the late 1980s).The increase in temperatures of an arable soil layer occurs under conditions of the increased moisture losses due to evapotranspiration under sugar beets crops, which is the main row crop on the wet forest-steppe Chernozems.Organic fertilizers (manure), in which the detritus mass dominates, become humidified only by 25-30%, since the mineralization energy is much greater in the soils with strongly negative balance of organic substance than the humification.Therefore, permanent fertilizing of sugar beet optimizes the regime of nitrogen and biophilic elements in acidified environment, rather than it contributes to the stabilization of organic and mineral substances of Chernozems.
During the vegetative period Chernozems in grain-row crop rotations serve its function under the variable hydrothermal and water-salt regime.By the phase of the maximal projective cover of vegetation the humus horizon of Chernozems is permanently acidified because of the dominance of downward flows of soil moisture against the background of enhanced seasonal mineralization of the organic substance (humus and organic fertilizers), destruction of physiologically acidic mineral fertilizers, intensification of microbiological activity and seasonal leaching.During the period of vegetative mass growth (August -September) downward flows of soil moisture are replaced by upward ones.At this time, the intensive mobilization of soluble calcium bicarbonates occurs in the lower part of the soil profile as well as its gradual migration to the rhizosphere zone with upward flows of moisture.In the lower part of Chernozem humus horizon (50-100 cm) the processes of seasonal acidification change into the weak formation of carbonates in the alkaline environment.The crystallization of solid microcrystalline calcite in the lower and mid parts of soil profile has a positive impact on their erosion resistance (Kuznyetsov and Glazunov, 2004).In the arable soil layer, the formation of carbonates has an indirect impact owing to seasonal leaching.Over the last decades the process of carbonates formation in soil has become widespread and led to the degradation of Greyzemic Chernozems throughout Podollian (Papish and Pozniak, 2010).
Such permanent seasonal changes against the background of the negative balance of organic substance affect differently the stability of mineral plasma of Greyzemic and Haplic Chernozems.Under the circumstances, the stabilizing or destabilizing factor of Chernozem erosion resistance is the nature of interrelation between its various components.In the wild steppe, this interrelation is optimal and balanced.One mass fraction of the highly dispersed humic organic substance accounts for approximately 2-3 mass fractions of the similarly active clay material.Having the distinctive zonal impact (the correlation between the humus content and physical clay), the character of this interrelation is the same for different Chernozem subtypes.The imbalance becomes the impetus for evolutionary changes in the silicate part of Chernozems.
The results of granulometric analysis of Chernozems of Western Ukrainian region show the correlative dependence between the humus content and physical clay (the matrix component of soil) (Table 1).The investigated Chernozems have been functioning for hundreds of years in the cultural soil formation process.Thereafter, the real impact of natural processes (podzolization and in certain cases leaching) which can significantly destabilize the organic and mineral soil absorbing complex should be ruled out.The consequence of long evolution of wet forest-steppe Chernozems is the formation of its typical clay profile (Alekseev, 1977).Greyzemic Chernozems have a distinctive eluvial-illuvial type of vertical distribution of the clay fraction (Table 1).By this parameter they belong to the genus of texture differentiated Chernozems.The Haplic Chernozems of wet forest-steppe are characterized by the even or weak eluvial-illuvial type of fraction distribution (less than 0.001 mm).On the background of one-ordinal parameters of the humus content (3.4-4.8%),Greyzemic Chernozems have twice less content of physical clay (the size of particles is less than 0.01 mm) than its typical analogues with four or five times less silt in its composition.From the two similar genetic soil types, greater erosion resistance has the soil heavier by its granulometric composition and it contains more silt capable of aggregation.The high content of a coarse loam fraction (0.05-0.01 mm) greatly reducing water resistance of the structure is particularly unfavourable.In Greyzemic Chernozems of Sian-Dnister upland, the content of this fraction is higher by 15-20% than in other soils.For objective and unrelated to cultivation reasons, Greyzemic Chernozems have much weaker internal mechanism of erosion protection defined by the granulometric composition.

Mineralogical Composition of Clay Plasma
The data on humus content and the granulometric composition do not allow to identify trends in the evolution of a silicate part of soil plasma of Haplic and Greyzemic Chernozems on the stage of its cultural evolution.Only the gross chemical and mineralogical analysis of the fraction less than 1 µm (for the sample free of humus and carbonate) will allow to reveal the nature and direction of these trends.Since the silt soil fraction included humus, this mineral phase is the fraction of fertility (Papish and Pozniak, 2010).Moreover, it defines and controls the behaviour of the whole soil system through reactions of sorption and desorption, fixation and exchange of cations and other particles, fixation of the number of organic components, reactions of hydration and dehydration, hydrolysis, etc. (Chizhikova et al., 2007).The main anti-erosion properties of soils depend on the composition and interrelation between the basic mineral phases of the clay minerals, particularly their water-retaining capacity, moisture capacity, water permeability, adhesiveness, plasticity, structure forming ability, adhesion force between the (Alekseev, 2012).The mineralogical composition of the fraction (<1 µm) of Greyzemic and Haplic Chernozems in Western Ukrainian region is not homogeneous within the profile (Table 2).
The upper part of the profile is clearly distinctive because it is high in clastogenic minerals such as quartz, plagioclases, microcline and hornblende.The banding silicates are present within the profile in the form of disordered mixed-planar mica-smectite formations with the high content (over 50%) of smectite packets (33-63%), hydromicas (33-52%), kaolinit together with chlorite (4-15%).They form the mineral part of the soil matrix substance which performs important regulatory functions, defining the character of soil processes and regimes.Various components of the clay material, which react appropriately on external stimuli and are the solid phase product of the biogeocenosis irreversible in its changes, are the memory of soil.Thus, they store information on ancient and modern conditions of soil functioning (Chizhikova and Gradusov, 1995;Chizhikova, Morozova and Panin ., 2007).
Erosion resistance of Chernozems like other water-physical properties is determined largely by the properties of colloid-dispersed materials which dominate in a silt fraction of virgin Chernozems (Kuznyetsov and Glazunov, 2004).Their clay plasma is in the state of dynamic quasi-equilibrium with organic substance.Sub-zonal and facies conditions have its impact on the character of profile distribution and correlation of different mineral phases of Chernozem clay material.Being the most dispersive and mobile among clay minerals, mica-smectite minerals are capable to redistribute in the Chernozem profile under certain conditions such as leaching, podzolization, lessivage, eluvial-gleied process or anthropogenically provoked conditions such as de-humification, acidification, destruction of soil structure, over condensation (Kuznyetsov and Glazunov, 2004).
The mica-smectite and hydromica phases of Chernozems under study have the contrary character of profile distribution.The clay profile of Greyzemic and Haplic Chernozems of wet forest-steppe is characterized by eluvial type of smectite phase distribution.Hydromicas especially kaolinite is accumulated in the humus horizon and have isoclay profile.This pattern is inherent not only to Chernozems of Ukrainian wet foreststeppe but also to Chernozems of Moldova steppe (Alekseev, 2012).Thus, Chernozem type of soil formation in forest-steppe with periodical leaching type of soil water regime is prone to redistribution of the smectite phase of clay material which is less resistant to weathering and mobile.
Chernozems have gone through long periods of the natural evolution (4-5 thousand years) as well as cultural evolution (0.8-1.5 thousand years).Each of these periods is equal to the formation of full-profile soil having quasi-equilibrium with the environment.Under conditions of wet forest-steppe, the natural and anthropogenic factors are unidirectional in forming the dispersion profile of Greyzemic and Haplic Chernozems (different intensity of di-flocculation and downward movement of smectite minerals in the profile).Therefore, we cannot clearly determine which of natural and anthropogenic factors have impact on the character of vertical distribution of the main mineral phases of clay material.However, taking into account the relative stability of hydromicas and high mobility and reactive capability of the mica-smectite phase, we can identify with high credibility the anthropogenic changes in its proportions.The virgin Chernozems formed on the Late Pleistocene loess are characterized by the dominance of disordered mixedlayered minerals with a predominance of smectite packets in its composition over the hydromica within the whole profile.The same proportions of the main mineral phases of clay material but on a smaller scale are inherent to leached Chernozems (Alekseev, 2012).
The scientifically proven fact is that not only clay minerals, but also primary soil minerals are affected by natural and anthropogenic factors (Pozniak, 1997;Egli et al., 2006, Egli, Mirabella and Sartori, 2000, 2008;Alekseev, 2012).The mineral profile of Chernozems is changing due to the processes of acid hydrolysis, lessivage, internal soil weathering, losses and neoformations of smectite, illitization.These processes cause the changes in soil properties that often have the negative effects.Such Chernozems on the slope lands are vulnerable to various forms of erosion.
The visual method of evaluating the mineralogical condition of Chernozem silicate part was used in order to assess the current soil processes, that is to determine its occurrence and evaluate to what extent they influence the formation of soil properties (Alekseev, 2012).Highly dispersive banding silicates are more resistant to destruction than organic matter and carbonates.For this reason, they record and store the changes in Chernozems more reliably.At the same time, as the unstable minerals of magmatic origin they are not able to reproduce under conditions of soil formation (normal temperature and pressure).Its content in the soil compared to the more stable minerals can only reduce.Among the two main mineral phases of Chernozem clay plasma (smectite and hydromica) that predominate in the composition of Chernozems, bioctahedral illite with the curve of isoclay profile distribution is the most resistant to weathering.It largely dominates in the composition of hydromica minerals of Chernozem humus horizon owing to the destruction of tri-octahedral hydromicas.This highly dispersive mineral can be accumulated due to the destruction and movement of less stable and more mobile smectites and tri-octahedral hydromicas.Within hydromicas the admixture of tri-octahedral illite cannot be taken into account because of its little amount is only possible.Probability of the processes of non-exchange sorption of potassium by highly charged smectite (illitization) in rainfed drylands and the deficit of potassium supply is very low (Alekseev and Valiev, 1992).This fact allows us to identify trends in the changes of Chernozem clay mineralogy under the intensive anthropogenic impact on the soils.The intensity of transformation changes in the fractions of Chernozem mineral profile (less than 1 µm) can be assessed by the index of intensity of weathering, illite/smectite (IIIS) in terms of the changes in illite/smectite correlation (Alekseev, 2012).This index is the ratio of the content of stable bi-octahedral illite (in percentage) to the content of unstable smectite in the fraction multiplied by 10 to get an integer number (Table 3).
The stress of mineral transformations in a series of changes of illite/smectite correlation throughout the profile can be evaluated by the index of weathering stress, illite/smectite (ISIS) which equals to the difference between IIIS of the top horizon and a rock (Alekseev, 2012).Since there is the correlation between these two indices, the ISIS index is appropriate to apply to the whole humus horizon.This will allow to identify in which part the highest stress of transformation changes is observed.
The research results of mineralogical composition of leached and Haplic Chernozem silicate part in Moldova have shown that, in leached Chernozems of wet forest-steppe, both layered silicates and field spars are being destructed.The rate of destruction of layered silicates is higher than of field spars (Alekseev, 2012).Therefore, the wetness conditions of Chernozem functioning, the more intensive is the process of mineral profile destruction.
Analyzing the data in table 3 indicates that Greyzemic and Haplic Chernozems of the Ukrainian wet foreststeppe have two silicate weathering crusts of different maturity.From Haplic Chernozems to Greyzemic Chernozems, the substantial loss of highly dispersive smectite material can be observed.Apart from theoretical and practical importance, this fact is of great value for paleo-geographical reconstructions.The deep transformation of Chernozem silicate part regardless of its current content of carbonates, can testify the paleo-geographical climate variability within the area under study.Such conclusions can be made due to irreversibility and preservation of transformation changes in the Chernozem silicate part.
The high indices of intensity and stress of mineral transformations enable us to diagnose the mineralogical condition of clay material of the Chernozems under study.The index of intensity of clay mineral transformation under the influence of weathering and soil formation processes (IIIS) in Greyzemic Chernozems is 10.2-14.2 in the humus horizon and 8.4-4.5 in the lower horizons.The same index for Haplic Chernozems is much lower and equals to 7.1-10.0and 3.1-5.2correspondingly.Moreover, in case of Greyzemic Chernozems, this index is high within the whole humus horizon (0-70 cm) with the highest value in under-plough layer (30-40 cm) where the maximum concentrations of highly dispersive amorphous silica are morphologically recorded.In case of Haplic Chernozems, this index is low almost throughout the profile except the arable layer (15.7 cm) of Upper Bug Upland soils.The nature of such abnormality distinctively correlates with the gross chemical analysis data and requires further investigation.There is the direct dependence between the intensity of transformation processes in Chernozems with the content and depth of calcium carbonates.Consequently, Greyzemic Chernozems are characterized by greater intensity and depth of transformation processes in the silicate part of the profile compared to Haplic Chernozems in which these processes take place mainly in the arable layer.As far as Pre-Carpathian Greyzemic Chernozems are concerned, the intensity of transformation processes is increasing with strengthening of soil hydromorphism.Finely crystalline calcite dispersed in the middle and lower parts of the profile is the source of the clay plasma stabilization only in Haplic Chernozems.
The index of the maximum stress of mineral transformations (ISIS) in Greyzemic Chernozems shifts into the under-plough horizon (5.8-6.9)whereas in Haplic Chernozems it falls on the arable layer (6.9-10.5).
The rise in the ISIS of Greyzemic Chernozems indicates the increasing loss of smectite compared to Haplic Chernozems.The high indices of ISIS for both Chernozem subtypes show the high intensity of weathering and soil formation impact on clay minerals and increasing stress of these processes upward the profile (Alekseev, 2012).
The relative share of bi-octahedral illite has increased dramatically due to the unbalanced loss of the smectite component in the composition of Greyzemic Chernozem clay minerals unlike Haplic Chernozems.Along with hydromica, the chemically inactive clastogenic minerals are accumulated in the silt fraction of Chernozem humus horizon.All in all, this shows that the silt of Greyzemic Chernozems amalgamates and reduces its activity due to the accumulation of rigid illite structures and clastogenic minerals.Such tendency has a long-lasting environmental importance since it directly predetermines the anti-erosion properties of soils (Alekseev, 2012).The dominance of inactive illite clay in the arable layer of all Chernozem subtypes, particularly Greyzemic Chernozems, in the whole humus horizon (0-70 cm) as well as the high content of kaolinite, reduces the role of clay plasma as the major stabilizer of organic matter and soil micro-structure along with the accelerated humus mineralization.Bi-octahedral illite and kaolinite, unlike smectite, reduce erosion resistance of arable Chernozem layer since they ensure poor adhesion of soil particles.Such changes lead to comminution of the soil macro-and micro-structure, reduction of its hardness and water resistance, boosting of lumpiness of the arable and under-plough layers, formation of the surface crust and underplough pan, condensation of the humus horizon, and reduction of moisture capacity and water permeability of Chernozems.Being the object of intensive use in grain-tilled crop rotations on the slopes, Chernozems with degraded clay plasma in the arable horizon are the favourable substrate for the development of erosion processes (Smirnova, Novykh and Pelekhotse, 2006;Alekseev, 2012).
The loss of the active smectite part of Chernozem mineral matrix and relative accumulation of bi-octahedral illite, kaolinite and clastogenic non-clay minerals in the clay of humus horizon correspond to the data of gross chemical analysis (Table 4).To see the real situation on the content of oxides in the mineral part of soil, all calculations have been conducted according to the standard techniques (Myakina and Arinushkina, 1979).
If the chemical composition of mineral part of the rock is to be compared with the composition of upper soil horizons, it can be noticed that the upper horizons lack silica with reduced level of sesquioxides.This fact indicates that the Chernozem mineral profile still has the high hardness potential.
The high levels of potassium oxide and aluminium oxide and the low levels of magnesium oxide in the Chernozem humus horizon, especially in Greyzemic Chernozems, are the indirect evidence of relative accumulation of bi-octahedral illite resistance to weathering in the upper horizons and destruction of its iron-magnesium tri-octahedral structures.Along with the high content of sodium, oxide also reveals the presence of highly dispersive potassium field spars in clay material.The invariance of molar ratios SiO2:Al2O3 for clay profile of all Chernozem subtypes regardless the environmental conditions of its formation, proves the relative resistance of bi-octahedral illite in the Chernozem profile of Ukrainian wet forest-steppe.The soils which contain iron hydroxide and solid macro-and microcrystalline calcite have the greatest erosion resistance (Kuznyetsov and Glazunov, 2004).Modern trends and the role of carbonates in this process were discussed above.Since the most of non-silicate iron in soil is in close coordinating bond with clay minerals (smectite, tri-octahedral illite), there is direct dependence between them.The unbalanced loss of colloidal clay in the Chernozem humus horizon, which is confirmed by the data of granulometric and mineralogical analysis, is followed by the same loss of iron oxide.This tendency is supported by the character of profile distribution of molar ratios SiO2:Fe2O3.The most distinct correlative link between these two indices can be observed in Greyzemic Chernozems of Sian-Dnister Upland forming the wet facial Chernozem subtype of Western Ukrainian region.Obviously, the main processes of destruction and movement of the smectite phase of Chernozem clay material in wet forest-steppe is leaching and lessivage.However, in Greyzemic Chernozems of Pre-Carpathians region the unbalanced loss of highly dispersive clay and non-silicate iron is additionally stimulated by the iron-gley process.This is proved by the results of morphological observations.
In Chernozems, which are the soils with poor adhesion, soil plasma is the main mechanism in the formation of water-resistant structure.Indirect indices of soil plasma capability to form water resistant aggregates correlate with erosion resistance of soils (Table 5).
The closest is the inverse correlation between erosion resistance and the coefficient of dispersion by Kachynskiy (1965).This correlation was used in the formula (Equation 1) of the erosion resistance coefficient introduced by Kuznyetsov and Glazunov (2004): . = .× 100  , (1) where Ks.resthe index of erosion resistance; Kgr.stthe granulometric index of structuring by Vadyunina and Korchagina (1986), that is the ratio of the content of the particles sized < 0.001 mm to the total content of coarser fractions (under the granulometric analysis of soils by Kachynskiy, 1965); Kdisthe coefficient of dispersion by Kachynskiy (1965), which is the ratio of the fraction <0.001mm under microaggregate analysis to the fraction of the same size under granulometric analysis.The low indexes Ks.res within the profile of Greyzemic Chernozems of Sian-Dnister Upland strictly correlate with the index of high intensity of transformation changes (IIIS) and index of stress of mineral transformations (ISIS).This indicates the weakening the role of Greyzemic Chernozem clay plasma in the formation of water resistant macro-and microstructure (Table 6).
Substantial increase of indices of Кs.res within the limits of profile of Chernozems clearly correlates with the indices of greatest intensity of weathering (IIIS) and weathering stress (ISIS).These circumstances specify on weakening of role of the soil plasma, in this part of profile, to form water-stable macro-and microstructure of soils.Offer comparisons are correct within the limits of soil profile and it can be used for research of dynamics and evolution of erosion resistance of soils.

Conclusions
The results of the chemical and mineralogical analysis aimed at evaluation of the condition and erosion resistance of soils have proved to be very effective.Different behaviour of the main components of clay plasma in Greyzemic and Haplic Chernozems in different environmental conditions of their functioning suggests the great value of this method for paleogeographical reconstructions, genetic and classification analysis and applied research of soil erosion.
Natural processes under long and intensive agricultural use of Chernozems of the Wet Atlantic facie have caused the disruption of its humus-mineral equilibrium.De-humification and other destructive soil processes have caused the destabilization of clay plasma and changes in smectite-illite dynamic equilibrium within clay plasma.The most intensive and profound changes in fine-grained silicate part of soils are evident in clay-differentiated Chernozems of the north-western Pre-Carpathian region.
Due to the irrational land use, the modern tendencies in the evolution of highly dispersive silicate part of Chernozems indicate the degradation of its mineral profile and loss of very important ecological functions.
According to the anti-erosion properties of clay plasma, the soils under study can be placed in the following order: Haplic Chernozems of Pre-Dnister Upland > Haplic Chernozems of Upper Bug Upland > Greyzemic Chernozems of Prut-Dnister Upland > Greyzemic Gleyic Chernozems of Sian-Dnister Upland.Chernozems of one sub-type with similar content and reserves of humus have its erosion resistance reduced following the increase in soil hydromorphism stimulating clay formation in the middle horizons due to the processes of lessivage and inter-soil weathering.

Table 1 :
Content of humus and carbonates, granulometric composition in Chernozems

Table 3 :
Quantitative estimation of intensity of weathering (IIIS) and weathering stress (ISIS) of clay plasma in Chernozems

Table 4 :
Gross chemical composition in fraction <1 µm, by selected with Chernozems

Table 6 :
Index of erosion resistance (Кs.res) of Chernozems Greyzemic Chernozem on the loess loam, underlined from the depth of 180 cm by thin sand alluvium of the Pliocene terrace of Prut River on the Prut-Dnister Upland (soil profile №91)