The Privolzh’e irrigation system (Marks raion ofSaratov oblast) was designed and built more than50 years ago. For all this period, it has affected the soilformation conditions and soil cover in this territory.Irrigation for a long time period of time not onlyimproves the water balance in soil, but also affectsmicroclimate as a soil formation factor. The complexof hydroengineering meliorations has left a trace onthe structure of the soil cover (SSC) of the territory,having affected its heterogeneity.
The goal of this research is to ascertain the reasonsfor the formation of heterogeneities of soil cover in theterritory under investigation. The information obtainedcan be interpreted and used when working in similarareas.
From the practical and scientific standpoints, it isimportant to know what happens to soil cover underlong impact of irrigation and what processes becomeirreversible.
THE OBJECTS AND METHODS OF STUDIES
According to the soil geographic zoning, the terri�tory is located within the limits of the Central Russiansteppe province with typical and southern medium�thick chernozems. Solonetz and alkali soils, solonetzicand solonchak�like grassland�chernozems, and typi�cal solonetzic and southern chernozems also occurhere (Soils and Vegetation…, 1987).
The territory extends for 19 km from north to southand 17 km from west to east. In a photograph takenfrom space, this area looks very heterogeneous (Fig. 1):groups of agricultural fields are interrupted by ravine
and gully nets and channels of the heads of the SmallKaraman River, as well as areas with highly mixedcharacter.
SCHEME FOR DESCRIBING HETEROGENEITIES OF SOIL COVER
IN THE TERRITORY UNDER INVESTIGATION
We chose the group of methods corresponding tothe comparative�geographic approach of V.M. Frid�land as a basis. A study of elementary soil areas, soilcombinations, and structures of soil cover with differ�ent levels of complexity was conducted by formingcomplex soil geomorphologic profiles (catenas) andkey areas, as well as using soil maps and data obtainedfrom analyzing space photographs.
At the preliminary stage, the territory was analyzedusing a Landsat�7 space photograph as of August 102008. The soil geomorphologic profiles (Mel, Mel_N,Vol) and key area (Fig. 2) were formulation based onthe information and field recognition obtained.
The key area (target ground) was located on thesecond terrace of the Volga in a large (3.5 × 2.5 km)depression, the majority of which is occupied byuncultivated soils with a high degree of salinizationand alkalization; it is almost the entire center. In theeastern part of the target ground, there are irregularlyirrigated areas (irrigated last in 2006).
A working set (group) of signs, according to whichthe meso� and microheterogeneities of soil cover weresubsequently described, was suggested by us based onthe theoretical approaches of Fridland and with allow�ance for the properties of soil cover in the territoryunder investigation. These signs were reduced to work�ing diagnostic tables.
The Properties of Meso� and Microheterogeneitiesof Soil Cover in the Area of the Privolzh’e Irrigation System
T. E. ShcherbaDepartment of Soil Science, Moscow State University, Moscow, Russia
Abstract—The meso� and microheterogeneities of soil cover must be taken into account when designing andusing an irrigation system to support sustainable functioning of agroecosystems and optimize field cutting,irrigation conditions, and crop rotation. The studies were conducted on the Privolzh’e irrigation system.The reasons and conditions for the formation of heterogeneities of the soil cover in the territory were ascer�tained during the works. The information gained can be used when analyzing soil cover in similar areas.
Keywords: heterogeneity of soil cover, salinization, alkalinization, irrigation system.
DOI: 10.3103/S0147687412020081
GENESIS AND GEOGRAPHYOF SOILS
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SHCHERBA
Object of studies
Privolzh’e
P. 228
P. 158
Marks
Saratov
Engel’s
Anisovka
Pushkino
Tarkhany
Saratov oblast
Privolzh’e raion
irrigation system
Fig. 1. Object of studies (Marks raion of Saratov oblast).
MeI_N
MeI_N
MeIMeI
Vol
Vol
Keyarea.
Fig. 2. Scheme for forming the soil geomorphologic profiles and key area (target ground) (a photograph of Landsat 7; August 10,2008; a source of the USGS).
The presented table gives a general list of the signswe used when describing the mesoheterogeneities ofsoil cover in the territory under investigation.
Taxonomic signs are needed to compare soils at theclassification level; they are a basis for describing and
naming soil combinations and represent soil diversity(according to names and taxons).
Signs related to the soil formation conditions:
Relief is one of the most important signs for study�ing the heterogeneities of soil cover. It describes the
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THE PROPERTIES OF MESO� AND MICROHETEROGENEITIES 57
relative location of soils as elements of the SSC withrespect to each other and determines the direction ofthe geochemical flow.
Moisture conditions describe the water regimen ofsoils with the following parameters for its character�ization: irrigation (presence/absence), degree ofhydromorphism, and gleying (if it is present, what newformations represent it). The presence or absence ofirrigation points to the quantity of moisture comingfrom the surface. The groundwater level determinesthe degree of soil hydromorphism. The process ofgleying takes place only if there are reconstructionconditions, which may be caused in the soils underinvestigation by poor drainage, including a local one.
A lithological sign shows how the heterogeneity ofsoil cover changes depending on an underlying rock.
THE CHARACTERISTIC SIGNS OF SOILS:
The granulometric structure of horizon B: it is notaccidental that this horizon was taken as a diagnosticone. The territory under investigation has been in agri�cultural use for more than a decade, and the upper soilhorizons have undergone more significant anthropo�genic impact. Using the granulometric structure ofhorizon B, one can obtain the idea of the character ofilluvial accumulation, which may be indirect evidencefor alkalinization in a profile (presence, absence) andindicate the change or stability of a soil�forming rock.
The value of EC (quantity of salts). The degree ofsalinization of the soils was analyzed by us (conducto�metrically). A pattern, in which the value of electricconductivity (EC, mSm) was determined, was taken
from each horizon. This indicator was used as a char�acteristic sign for a depth of 20 cm, which is enoughwhen estimating surface salinization. The category ofsoil salinization was determined according to the scaledeveloped by the US Soil Service (Soil Survey Staff,1993).
The carbonate content is determined by the upperlimit of violent HCl effervescence, as well as forms ofrelease of new carbonate formations.
The thickness of a humus horizon is an indicator sig�nificantly changed by people by plowing, agrogenicerosion, fertilization, performance of such a culturaland technical process as planning, etc. This indicatorgives an indirect idea of the degree of erosion andthickness of accumulation.
The degree of alkalinization was determined basedon the combination and degree of manifestation ofsuch morphological signs as the presence of clayeyhumus cutans along the boundaries of structural rifts,the structure and density of illuvial horizons, etc.(Kust, 1994).
RESULTS AND DISCUSSION
The following meso� and microcombinations weredistinguished in the areas under investigation.
MesocombinationsVariations(1) Southern chernozems of usual types, weakly
solonetzic and medium�solonetzic chernozems (alongthe Mel_N1�Mel_N4 profile).
Signs describing mesoheterogeneities based on field descriptions of soil geomorphologic profiles and soils
Group of signs Sign for describing heterogeneity Variants of heterogeneities(method for description)
Taxonomic Field name of soils Combinations, variations; mosaics, soil combination
Soil formation conditions Relief Uplands, depressions, transit areas
Moisture conditions (gleying ESP) By hydromorphism (automorphic, hydromorphic, polihydromorphic); Presence or absence of artificial irrigation; Degree of gleying
Lithologica Name of rock
Characteristic signs of soils Granulometric composition of hor. B By gradations of the granulometric composition
Value of EC (quantity of salts) for upper 20 cm (salinization ESP)
Degree of salinization, mSm
Carbonate content Depth of violent effervescence, cm; form of distin�guishing a new formation
Thickness of the humus horizon (humus accumulation ESP)
Thickness of upper humus horizons is measured,A + AB, cm
Signs of alkalinization (alkaliniza�tion ESP)
By the degree of the morphological evidence of the alkalinization process (no; weak, medium, strong, solonetz soils)
* An ESP is an elementary soil process.** EC is electric conductivity.
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SHCHERBA
solonetzic chernozems (along the Mel_1�Mel_7 pro�file).
and southern chernozems (soil cover along the Vol_4�Vol_4 profile).
(2) Southern chernozems, southern chernozemswith a different degree of alkalinity, weakly alkalinesolonetz chernozems (along the Vol_5�Vol_8 profile).
MicrocombinationsSpottinesses(1) Southern chernozems with a different degree of
alkalinity (along the Mel_N1�Mel_N4 profile).(2) Southern chernozems and southern cher�
nozems with a different degree of alkalinity (along theMel_1�Mel_7 profile).
(3) Surface and deep�profile, takyr and discolored,medium�loamy grassland alkali soils (soil cover of thekey area).
(4) Medium�thick medium�loamy grassland�cher�nozem solonchak�like (60%) and grassland�cher�nozem saline (40%) soils (soil cover of the key area).
(5) Deep�profile and surface, discolored and dis�colored�crusted, medium�loamy marsh alkali soils(3%) and grassland alkali soils (97%) (soil cover of thekey area).
(6) Solonchak�like and weakly solonetzic grasslandchernozems (80%) and their washed analogues (20%)(soil cover of the key area).
(7) Weakly and medium�solonetzic medium�loamy medium�washed southern chernozems (soilcover of the key area).
Complexes(1) Southern medium�solonetzic chernozems and
solonetz chernozems (along the Mel_N1�Mel_N4profile).
(2) Southern chernozems with a different degree ofalkalinity (70%) and medium�loamy grassland solo�netz chernozems with a different degree of salinity(30%) (soil cover of the key area).
(3) Medium�loamy saline weakly solonetzic grass�land chernozems (95%) and damaged soils (5%) (soilcover of the key area).
REASONS FOR FORMATIONOF HETEROGENEITIES OF SOIL COVER
ALONG SOIL GEOMORPHOLOGIC PROFILES OF THE TERRITORY UNDER
INVESTIGATION
MesoheterogeneitiesVariations are predominately located in the slope
areas with relatively small height amplitudes. Theseare naturally or artificially irrigated automorphic soils.Insignificant changes in the granulometric structure ofsoil�forming rocks are observed in their series (theMel, Mel_N profiles are examples).
Combinations occur on steeper slopes or slopes withlow absolute heights near groundwater. Contrast arisesboth at the boundary of hydromorphic and automor�phic soils and under the conditions of steep slopes; theformation of combinations is affected by the heteroge�neity of soil�forming rocks (example: the Vol soil geo�morphologic profile).
Microheterogeneities*Spottinesses are caused by the differences in the
conditions of moisture (irrigated, nonirrigated) andproperties of microrelief. They are related to thecleaning of natural soils by irrigative waters; to theirrelease from highly soluble salts and dealkalinizationwith the simultaneous conservation; and, possibly, tothe growth in the signs of alkalinization and surfacesalinization at the periphery of irrigated territories inthe immediate proximity of irrigation cirques (repre�sented in the areas of the Mel and Mel_N soil geomor�phologic profiles).
Complexes. It is worth noting that the mechanism oftheir formation is almost identical to the mechanismof formation of spottinesses. To all appearances, thecomplexes are characterized by more intense pro�cesses of moisture redistribution over microrelief and agreater duration of this process.
REASONS FOR FORMATIONOF HETEROGENEITIES OF SOIL COVER
IN THE KEY AREA.
The first reason is the general situation of the areaunder investigation in a bowl�shaped depression andthe proximity of groundwater on its “bottom.” Theground salinization of soils takes place under the con�ditions of the exudative water regimen; the closer isgroundwater, the higher is the degree of salinization.Another factor affecting heterogeneity is moistureredistribution over microrelief and microdepressions,which are also predominantly saline due to both thesurface income of saline waters and influence ofgroundwater. Correspondingly, the reasons for the for�mation of spottinesses and complexes in the key areahave a similar genesis and differ only in the degree ofevidence of these conditions.
CONCLUSIONS
At the mesolevel, the soil cover of the territoryunder investigation is equally represented by the vari�ations and combinations. The variations are predomi�nately widespread in the north and northeast of theterritory, being situated on flat slopes of the second andthird terraces of the Volga. In the southern part of theobject under investigation, the combinations arelocated on steeper slopes of the third terrace of theVolga and fourth terrace of the Big Karaman River.
* Investigation of microheterogeneities for the Vol profile was notcarried out.
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THE PROPERTIES OF MESO� AND MICROHETEROGENEITIES 59
The formation of the combinations is also related to adifferent degree of hydromorphism for the soils form�ing this combination.
At the microlevel, the majority of the soil cover isformed by spottinesses. They are especially pro�nounced at the boundaries of irrigated and nonirri�gated fields, as well as soils of the key area. Desaliniza�tion of solonetzic soils by irrigation with alkalinizationof peripheral areas and/or redistribution of salts withinthe limits of microrelief are the major processes takingplace at the microlevel.
Despite the fact that there is no artificial system ofdrainage facilities, the soil cover of the majority of theobject under investigation has been in a satisfactorystate for a long period of the existence of the irrigationsystem. On the whole, the territory does not have anabundance of heterogeneities that hinder agricultural
activity. The soils of the key area characterized by highindicators of complexity and contrast are the excep�tion.
REFERENCES
1. Afanas’eva, T.V., Balabko, P.N., Vostokova, L.B., et al.,Pochvy i rastitel’nost’ prirodnykh zon SSSR: prakt. ruk�vo po ucheb. zonal’noi prakt. po marshrutu (Soils andFlora of the USSR Natural Zones: Practical Guide toWork Zone Experience on the Route), Moscow, 1987.
2. Kust, G.S., On Posthydromorphous Evolution of SoilCover of Water–Accumulative Plains of Arid Territo�ries, Pochvovedenie, 1994, no. 2.
3. Soil Survey Staff. Soil Survey Manual, Washington:United States Department of Agriculture, 1993, Hnbk,no. 18.
