The boron content in soils of solonetzic complexes in the Irtysh Region of Omsk oblast and the boron resistance of plants

512

ISSN 1064-2293, Eurasian Soil Science, 2007, Vol. 40, No. 5, pp. 512–521. © Pleiades Publishing, Ltd., 2007.Original Russian Text © Yu.A. Azarenko, 2007, published in Pochvovedenie, 2007, No. 5, pp. 562–573.

INTRODUCTION

Microelements play an important physiological rolein the life of plants, animals, and people. The microele-mental composition of soils, soil forming rocks, surfacewaters, and groundwater is an important ecological fac-tor of the development of living organisms. Boronoccupies a special place among microelements and par-ticipates in vitally important physiological processes inorganisms [23].

All living organisms normally develop within a par-ticular range of boron concentrations. Both a deficit andan excess of this element in the nutrient medium resultin the disturbance of physiological functions, the devel-opment of diseases, and a drop in plant and animal pro-ductivity. It should be mentioned that boron is usuallyinvestigated in soils where its content is low, and thesestudies are mainly aimed at elaboration of applicationtechniques of boron fertilizers. The effect of high boronconcentrations on living organisms is less studied. Atthe same time, areas with a high boron content in theenvironment are rather numerous in Russia and abroad,including Central Asia, Kazakhstan, India, the UnitedStates, and China [6, 8, 16].

In the 1930s, Kovda pointed to the fact that boratesmay cause soil salinization [15]. Some investigatorsshowed that the plant productivity and quality decreasewhen the boron content in the soil is 5 mg/kg andhigher. On this basis, Alikhanova suggested that boron-saline soils should be distinguished as soils with amobile (available) boron content of 5–10 mg/kg andmore [1, 19].

A boron excess in soil may result in a high concen-tration of this element in plants and produce anadverse effect on animal health. Data by Koval’skiishowed that a high boron concentration in forage

plants and potable water causes endemic diseases inanimals in the northwestern Kazakhstan boron bio-geochemical province [14].

Il’in and Anikina [11] proved that there is a vast areaof boron salinization in the southern part of WesternSiberia and that borates are more toxic than sulfates,chlorides, and soda. A high boron content is typical ofthe soils of solonetzic complexes. Their area in WesternSiberia is 8.8 million ha, including 1.9 million ha inOmsk oblast; of this area, 1.3 million ha are occupiedby solonetzes proper. Solonetzes of the Irtysh region inOmsk oblast are characterized by an excessive boronaccumulation, which causes a drop in the productivityand quality of some crops [2, 3, 17]. Thus, the boronsalinization should be taken into consideration uponcrop growing in the areas with solonetzic soil com-plexes and for the general appreciation of the bio-geochemical conditions in the area.

Data on the boron salinization of soils and on theplant tolerance to boron are not numerous. The aim ofour investigations was to study the boron content anddistribution in the soils of solonetzic complexes in theIrtysh region of Omsk oblast and to appreciate theeffect of the boron salinization on plants.

OBJECTS AND METHODS

Omsk oblast is found in the southern part of thevast alluvial West Siberian Plain. It represents a greatdepression filled with marine and continental Meso-zoic and Cenozoic deposits underlain by Paleozoicbedrock [9]. The surface is undulating and has a slightnorthward inclination. Thick Quaternary alluvial andglaciofluvial deposits create a virtually flat surfacewith a sparse hydrographic network; the drainage

The Boron Content in Soils of Solonetzic Complexes in the Irtysh Region of Omsk Oblast and the Boron Resistance of Plants

Yu. A. Azarenko

Omsk State Agrarian University, Institutskaya pl. 2, Omsk, 644008 Russia E-mail: [email protected]

Received February 9, 2006

Abstract

—Data on the boron content in the main soil types of solonetzic complexes in the Irtysh Region ofOmsk oblast are given. They attest to the boron salinization of the soils. It is shown that there is a risk of exces-sive boron accumulation in natural plants and crops. The boron resistance of crops cultivated on the boron-saline soils has been examined in the field and in pot experiments. Approximate normal and toxic levels of theboron content in soils and in plants and the corresponding Ca-to-B ratios in the aboveground phytomass aresuggested. Amelioration of solonetzes with application of gypsum and phosphogypsum reduces the degree oftheir boron salinization and the boron uptake by plants.

DOI:

10.1134/S1064229307050067

SOILCHEMISTRY

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THE BORON CONTENT IN SOILS OF SOLONETZIC COMPLEXES 513

conditions are generally poor and nonuniform. Thesoil and vegetation zonality is well pronounced inOmsk oblast: the southern taiga, forest-steppe, andsteppe zones replace one another from the north to thesouth. The intrazonal factors—poor drainage, well-pronounced microtopography of the surface, wide-spread development of heavy-textured calcareous andsaline sediments, and relatively shallow groundwateroccurrence—also play an important role in the soilformation. All these factors result in a very complexsoil cover pattern with a great degree of participationof hydromorphic and saline soils.

The boron content in soils of solonetzic soil com-plexes was studied on the Ishim–Irtysh interfluve andwithin the Baraba Plain in the forest-steppe zone andthe Kurumbel Plain in the forest-steppe and steppezones. The obtained data were compared with data onthe boron content in zonal soils. The total boron contentwas determined in 14 pits; the mobile boron contentwas determined in 9 pits of zonal soils and in 26 pitsand 7 boreholes characterizing the soils of solonetziccomplexes. In addition, the boron content was deter-mined in 60 samples of groundwater and 50 samples ofnatural vegetation. Data on the boron content in theameliorated solonetzes were also obtained on experi-mental fields of the Laboratory of Agrotechnical andChemical Amelioration of Solonetzes of Omsk StateAgrarian University.

The boron resistance of crops grown on the solo-netzic soil complexes was studied in a series of pot andfield experiments with a meadow-chernozemic soil.Boron was applied at a rate of 5–15 mg/kg in the formof borax (Na

2

B

4

O

7

·

10

H

2

O) or boric acid (H

3

BO

3

) tosimulate different levels of boron salinization. The ini-tial content of mobile boron in the soil comprised2.4

−

3.0 mg/kg. The average humus content in the soil(according to the Tyurin method) was 6.2–6.5%; theCEC value was 35 mg-equiv/100 g. The soil reactionwas neutral (pH 6.9). The contents of available phos-phorus and potassium extracted with 0.5 N

ëç

3

ëééç,

were high and comprised 150 and450 mg/kg, respectively. We performed twelve fieldand ten pot experiments with barley (

Hordeum vul-gare

), Sudan grass (

Sorghum sudanense

), bromegrass(

Bromus inermis

), lucerne (

Medicago sativa

), melilot(

Melilotus officinalis

), and vetch (

Vicia villosa

) in theperiod from 1991 to 2005.

The total and mobile boron contents in all the inves-tigated objects (soils, water, and plants) were deter-mined by the colorimetric method with azomethine-H.Mobile boron was extracted from the soil via its boilingwith a 0.1% solution of MgSO

4

. The total boron wasdetermined after alloying with soda at a temperature of

900°ë

. The boron concentration in the plants was deter-mined after dry ashing. The calcium concentration inthe plants was determined by a trilonometric methodwith fluorexone. The obtained data were treated withstandard statistical methods.

RESULTS AND DISCUSSION

The boron distribution in the soils of the studiedregion is controlled by natural conditions affecting thesoil-forming processes. Therefore, each soil type ischaracterized by its own content and distribution ofboron in the soil profile. The geochemical features ofthe boron distribution in the soil cover are mainly deter-mined by its rather high migration capacity in watersolutions, active biogenic sorption, and active adsorp-tion on highly dispersed mineral and organomineralsoil components. The diversity of the soil forming con-ditions results in a contrasting distribution pattern ofthe element in the soil cover. The total boron content inall the soils is considerably higher than the clarke value(12 mg/kg) [8]. The boron content in the soils of theIrtysh region within Omsk oblast generally increasesfrom the north to the south, which is explained bychanges in the water regime of the soils, the decrease inthe degree of leaching of the soil profile, and the higherintensity of the hydrogenic-accumulative and biogenic-accumulative processes.

Zonal soils. Soddy-podzolic soils of the southerntaiga zone are characterized by the lowest contents ofthe total and mobile boron among the zonal soils ofOmsk oblast (Table 1). A percolative water regime andan acid reaction result in the depletion of boron com-pounds from the soils. In soddy-calcareous and soddy-gley soils, the content of mobile boron compounds ishigher, especially in the humus horizon. The high con-tent of mobile boron (3.7–6.0 mg/kg) is also typical ofthe peat layer of low moors. The considerable accumu-lation of boron in the organic horizons is related to itsactive biogenic uptake.

In the forest-steppe soils with a periodically perco-lative water regime and a slightly acid or neutral reac-tion, the accumulation of boron compounds is greater.The average content of mobile boron in the humus hori-zons of gray forest soils is three times higher as com-pared with that in the soddy-podzolic soils, but itdecreases sharply in the middle and deep parts of thesoil profile.

Among the zonal soils of the forest-steppe zone, thehighest boron content is typical of chernozems andmeadow-chernozemic soils. The distribution of boronin the soil profiles depends on the soil subtype. Thehighest content of mobile boron is typical of the humushorizon of leached chernozems (2.1–2.2 mg/kg); itdrops considerably in the B, BC, and C horizons (to1.5–0.8 mg/kg). In ordinary chernozems, mobile boronis distributed rather evenly: its content varies from 1.5to 3.6 mg/kg. Similar values are typical of meadow-chernozemic soils (1.8–3.2 mg/kg). In southern steppechernozems, the mobile boron content varies from 1.7to 5.3 mg/kg with a maximum in the C horizon.

A weak degree of erosional dissection of the sur-face, well-pronounced microtopography, and poordrainage against the background deficit of atmosphericprecipitation favor the development of halogenesis, the

514

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AZARENKO

accumulation of soluble salts, and an increased contentof mobile boron compounds in the soil-forming rocks,soils, groundwater, and undrained surface water basins.Weathering of boron-bearing minerals is accompaniedby the release of mobile boron compounds. Minerals ofthis kind include salts of boric and polyboric acids, forexample, datolite (CaH

Ç

SiO

5

), hydroboracite(CaMgB

6

O

11

·

6 ç

2

é

), ascharite (

2

MgOB

2

O

3

·

3

H

2

O),boracite (Mg

3

B

7

O

13

Cl), and borax (Na

2

B

4

O

7

·

10

H

2

O).

The anions

Ç , Ç ,

and

Ç

4

are the main com-pounds of boron migration in the zone of supergenesis[7]. The intensity of the migration depends on the localconditions and the degree of mobility of boron com-pounds released in the course of weathering; the result-ing distribution of boron in the local soilscapes is rathercontrasting.

Our results show that, on average, the total andmobile boron contents in soils of solonetzic complexesare by two and four–ten times higher, respectively, thanthose in zonal soils (Tables 1 and 2).

Soils of solonetzic complexes are developed fromthe parent materials that are richer in boron than theparent materials of zonal soils. There is a reliable cor-relation (

r

= 0.68

±

0.13,

n

= 20) between the boron con-tents in the A and C horizons of the soils.

As noted by Il’in, the total boron content in the soil-forming rocks of Western Siberia is higher than that inthe mantle deposits of the European part of Russia. Thisis related to the specific geological structure and gene-sis of the soil-forming rocks in Western Siberia. For

O33– O2

2– O72–

example, the boron content in granitoid rocks of themountains surrounding the West Siberian Plain ishigher than the clarke value. Soil-forming rocks in thelowlands of Western Siberia were formed from thesaline and calcareous weathering products transportedto the valleys from the surrounding mountain systemsof Altai, Kazakhstan, and the Urals. Boron compoundsmigrated with them and were accumulated under con-ditions of a slightly dissected topography. The conti-nental and semidry climate in the southern part of West-ern Siberia favored the enrichment of soil-formingrocks with boron [5, 10, 13].

The soil texture has a definite effect on the boroncontent. There is a reliable correlation between the totalboron content and the clay fraction content in the soil-forming rocks (

r

=

0.69

±

0.17,

n

= 20); for other genetichorizons, the corresponding correlation coefficient isequal to

0.67

±

0.08

(

n

= 48).

The genetic specificity of the soils of solonetzic com-plexes in the Irtysh region of Omsk oblast has affectedthe boron distribution patterns in their profiles. In thesesoils, the degree of humus accumulation has no positiverelationship with the boron content (

r

= – 0.46

±

0.21,

n

= 20). The boron content in these soils is mainlydetermined by the hydrogenic migration of boron com-pounds in landscapes and within the soil profile.

A considerable part of the total boron in salt-affected soils is represented by mobile compounds. Theportion of mobile boron is 0.4–5.0% of its total contentin the soddy-podzolic and gray forest soils, 1.1–8.7% in

Table 1.

Boron content (mobile boron is above the line and total boron is under the line, mg/kg) in zonal soils of Omsk oblast

Soils

Ap, A1, and A horizons B horizon C horizon

S

±

s

x

LimMobile B, % of the total B

S

±

s

x


S

±

s

x


Southern taiga

Soddy-podzolic 0.4–1.5 0.4–2.9 0.3–5.0

Soddy calcare-ous – – –

Soddy gley – – –

Forest steppe

Gray forest 2.1–2.2 – 0.9

Forest steppe and steppe

Chernozems, meadow-cher-nozemic

2.0–4.7 1.1–6.4 1–8.7

Note: Here and in other tables,

S

±

s

x

is the mean B content and error of the mean, Lim is the variation limits, and dashes signify the absenceof determination.

0.31 0.05±17.2 3.86±--------------------------- 0.22–0.38

13.3–21.0------------------------ 0.57 0.04±

34.0 1.00±--------------------------- 0.22–0.73

33.0–35.0------------------------ 1.23 0.51±

43.0--------------------------- 0.6–2.30

43.0---------------------

1.10 0.44±–

--------------------------- 0.61–1.49–

------------------------ 0.76 0.09±–

--------------------------- 0.67–0.93–

------------------------ 0.55–

---------- 0.55–

----------

2.60 0.40±–

--------------------------- 2.15–3.00–

------------------------ 1.11 0.11±–

--------------------------- 1.93–1.32–

------------------------ 0.39–

---------- 0.39–

----------

1.10 0.37±19.3 0.75±--------------------------- 0.25–1.80

18.5–20.0------------------------ 0.47 0.26±

–--------------------------- 0.18–0.98

–------------------------ 0.86 0.40±

34.0--------------------------- 0.46–1.27

34.0------------------------

2.24 0.22±43.8 2.66±--------------------------- 1.50–3.10

34.1–50.0------------------------ 2.12 0.32±

40.2 1.30±--------------------------- 0.96–3.60

36.0–45.0------------------------ 2.80 1.33±

30.7 4.52±--------------------------- 0.80–5.30

21.0–39.3------------------------

EURASIAN SOIL SCIENCE Vol. 40 No. 5 2007


the chernozemic and meadow-chernozemic soils, and7–30% in the salt-affected soils.

Each soil type is characterized by its particular con-tent and distribution of boron in the soil profile(Table 2).

Meadow-chernozemic and meadow soils are wide-spread in the soil cover of the forest-steppe and steppezones. The presence of salts in the relatively shallowgroundwater and in the soil-forming rocks results in thedevelopment of soil salinization and alkalization. Solo-netzic and solonchakous meadow-chernozemic soilsare often seen in association with solonetzes. The soil-forming rocks are represented by the Quaternary cal-careous loams and clays with a total boron content of57.5 ± 3.5 mg/kg. The boron distribution patterns in theprofiles of solonetzic and solonchakous soils are differ-ent (Figs. 1a and 1b; Table 2).

The total boron content in the meadow-chernozemicand meadow solonetzic soils is rather high and its dis-tribution in the soil profiles is even. Contrary to nonsa-line soils, solonetzic soils are richer in the mobile boroncompounds (7–15% of the total boron). The boron con-tent in the plow layer of these soils is high, and boronsalinization is sometimes registered in it. The boroncontent gradually increases in the middle part of the soilprofile in parallel to the increase in the content of solu-ble salts and reaches its maximum in the C horizon.

Boron accumulation in the solonchakous soils ismore intensive as compared with the solonetzic soils,

which is related to the greater degree of soil salinization(Table 2). The boron distribution in the solonchakoussoils is uneven (Fig. 1b). The contents of total andmobile boron in the top and middle parts of the soil pro-file are considerably higher than those in the soil-form-ing rocks. The humus horizons are usually boron-saline. The zones of maximum boron concentrationmay be found at different depths. The mobile boroncontent reaches 17.7–22 mg/kg. It should be mentionedthat the maximum contents of boron and soluble saltsare not always allocated to the same depths. Statisticalprocessing of the analytical data has shown that thecontent of mobile boron in the investigated soils isclosely related to the total boron content (r = 0.86 ± 0.08,n = 16). The correlation between the mobile boron andsoluble salts is much weaker (r = 0.59 ± 0.22, n = 16),which is explained by the different migration capacitiesof sodium, magnesium, and calcium borates; chlorides;sulfates; and soda.

Solonchaks. The meadow solonchaks of the Irtyshregion in Omsk oblast are characterized by high con-tents of total and mobile boron (Table 2). The borondistribution pattern in the profile of the solonchaks isuneven. The saline A and B horizons are mostlyenriched in boron, and its content in the soil-formingrock is considerably lower. Strong boron salinization isregistered in the top layer of the solonchaks; the portionof mobile boron in this layer may reach 18.9–22.6% ofthe total boron content. In the soil-forming rock, the

Table 2. Boron content (mobile boron is above the line and total boron is under the line, mg/kg) in soils of solonetzic com-plexes of the Irtysh region within Omsk oblast

Soils; number of determinations

A and A1 horizons B1 horizon B2–B4 horizons C horizon

S ± sx Lim S ± sx Lim S ± sx Lim S ± sx Lim

Meadow-cher-nozemic and mead-ow solonetzic (5–6)

Meadow-cher-nozemic and mead-ow solonchakous (3–7)

Solonchaks (3)

Deep solonetzes (3)

Shallow solonetz-es (4–5)

Crusty solonetzes (15–54)

Solods (3)

4.5 0.3±55.7 1.73±---------------------------

3.8–5.351.6–60.0------------------------ 5.3 0.6±

58.2 0.99±---------------------------

3.0–5.456.6–60.0------------------------ 6.4 0.4±

58.4 2.35±---------------------------

5.5–7.755.0–62.9------------------------ 9.6 1.9±

58.2 6.00±---------------------------

6.3–14.852.2–64.2------------------------

7.5 1.6±85.9 8.44±---------------------------

4.1–12.577.5–94.4------------------------ 12.2 2.2±

59.0------------------------

5.9–17.759.0

--------------------- 15.0 4.5±58.0

------------------------4.7–22.2

58.0--------------------- 7.5 1.6±

56.0---------------------

3.7–15.256.0

---------------------

17.4 5.0±80.3 16.9±---------------------------

7.4–22.063.4–97.2------------------------ 7.6 0.4±

61.0---------------------

7.4–7.8–

------------------ 6.3 0.1±53.8

---------------------6.2–6.4

53.8------------------ 6.5 0.4±

49.7---------------------

5.3–8.049.7

------------------

4.5 0.7±57.3 6.9±------------------------

3.2–6.050.4–64.2------------------------ 4.6 0.7±

56.6 2.9±------------------------

2.2–5.050.4–60.4------------------------ 15.8 6.9±

–------------------------

4.0–27.6–

--------------------- 10.1 1.1±55.1 2.9±------------------------

8.6–13.852.2–58.0------------------------

4.7 0.8±57.4

---------------------3.3–6.9

57.4------------------ 7.5 1.3±

67.7---------------------

2.9–10.667.7

--------------------- 10.7 2.2±57.2

------------------------4.6–15.3

57.2--------------------- 11.2 1.9±

78.3------------------------

5.3–16.278.3

---------------------

12.1 1.1±72.9 9.2±------------------------

4.4–23.757.3–126.1--------------------------- 20.2 1.4±

73.7 6.40±---------------------------

8.8–37.257.3–108.6--------------------------- 14.8 1.3±

87.9 5.48±---------------------------

8.6–25.062.3–130.3--------------------------- 11.3 0.6±

78.5 7.5±------------------------

3.8–18.464.0–118.3---------------------------

8.6 1.3±–

---------------------6.3–10.9

–--------------------- 1.5 0.5±

–---------------------

1.0–2.6–

------------------ 2.0 0.3±–

---------------------1.6–2.6

–------------------ 2.4 0.4±

–---------------------

1.6–3.0–

------------------

516


AZARENKO

portion of mobile boron compounds averages 10.7% ofthe total boron content. Mobile boron is accumulated insolonchaks on the evaporation geochemical barrierformed under conditions of the exudative type of soilwater regime.

Solonetzes are characterized by high contents oftotal and mobile boron, which exceed their contents inall the above-discussed soils (Table 2). The total boroncontent in the soil-forming material of solonetzes aver-ages 73.0 ± 6.7 mg/kg. Different kinds of solonetzesvary in the contents and distribution patterns of boron.The highest boron content is typical of crusty solo-netzes, and the lowest boron content is registered indeep solonetzes. In the crusty solonetzes, the totalboron content is 1.3–1.5 times higher in comparisonwith that in the deep solonetzes. The distribution pat-tern of boron is rather even in the deep solonetzes andis well differentiated by soil horizons in the crusty solo-netzes (Figs. 1c and 1d). Boron is accumulated in theilluvial horizons that work as physicochemical sorptionand mechanical barriers. Above the solonetzic horizonsand in the soil-forming rocks, the boron content islower.

A considerable part of the total boron in solonetzesis represented by soluble compounds, so that themobile boron content is high throughout the soil pro-file. The portion of mobile boron compounds in solo-netzes averages 13.6% of the total boron in theA1 horizon, 19.2% in the B horizon, and 14.7% in theC horizon. The distribution pattern of mobile boroncompounds in the profiles of solonetzes is similar tothat of the total boron. The maximum content ofmobile boron is seen in the illuvial horizons, whichcorresponds to a rise in the solubility of boron com-pounds in these horizons. The soil-forming rocks arecharacterized by a considerable boron salinizationwith the average content of mobile boron of about11 mg/kg. In the topsoil layer above the solonetzichorizon, the boron content is usually lower than thatin the soil-forming rock, which is explained by theeluvial-solonetzic process.

The content of mobile boron in solonetzes variesgreatly (the variation coefficient V = 27–64%) depend-ing on the soil properties. Statistical processing of ana-lytical data shows that different kinds of solonetzes areprovided with mobile boron compounds to a different

6 7 98 10(a)

020

4060

80100

Dep

th, c

m

0.1 0.3 0.70.5 0.9

10 30 7050 90

1 3 7 95

6 7 98 10(b)

0204060

80100

0.1 0.3 0.70.5 0.9

10 30 7050 90

2 4 86 10

6 7 98 10(c)

02040

60

80100

0.1 0.3 0.70.5 0.9

10 30 7050 90

4 1612 24208

6 7 98 10(d)

0

306090

120

150

0.1 0.3 0.70.5 0.9

10 30 7050 90

4 168 2412 20

1.1

110

12

pH

Totalsalts, %Total boron,

Mobilemg/kg

boron, mg/kg

1.1

110

1.1

110

12345

pH

Totalsalts, %Total boron,

Mobilemg/kg

boron, mg/kg

Distribution patterns of the (1) total and (2) mobile boron (mg/kg), (3) pH, (4) soluble salts (%), and (5) clay (%) in the (a) meadowchernozemic solonetzic soil (Izmailovskoe farm, Kalachinsk district), (b) meadow chernozemic solonchakous soil (Lyubimovskoefarm, Okoneshnikov district), (c) crusty solonetz (Izmailovskoe farm, Kalachinsk district), and (d) deep solonetz (Krasovskoe farm,Okoneshnikov district).



extent and thus characterized by different rates of boronsalinization. The highest content of mobile boron isregistered in crusty solonetzes and decreases in shal-low, medium, and deep solonetzes. In the C horizons ofdifferent solonetzes, the mobile boron content variesinsignificantly.

The mobile boron content in solonetzes displaysclose correlation with the total boron content (r =0.71 ± 0.08, n = 37) and the soil pH (r = 0.73 ± 0.05,n = 106). In conditions of alkaline reaction, the mobil-ity of boron compounds increases.

Though boron migration is obviously related toother soluble salts, the dependence of the mobile boroncontent on the degree of salinization is weak for all thesolonetzes (r = 0.28 ± 0.09, n = 109). This is explainedby the geochemical properties of boron compounds. Onthe one hand, boron migrates easily with water and isaccumulated in soils together with soluble salts. Onthe other hand, boron is accumulated at sorption bar-riers formed by the highly dispersed mineral com-pounds: clay minerals and aluminum and iron oxides.This explains the high boron content in the illuvialhorizons of solonetzes, which are often slightly saline.It has also been revealed that boron accumulation isrelated to the soil reaction. Thus, the boron distribu-tion pattern in solonetzes is controlled by a number offactors and is not always related to the distributionpattern of soluble salts.

The mobile boron content depends considerably onthe type of salinization. It is significantly higher insoda–sulfate and sulfate–soda solonetzes as comparedwith the neutral chloride–sulfate and sulfate–chloridesolonetzes (Table 3). The average boron content in the0- to 1-m-thick solonetz layer with neutral salinizationis almost two times lower than that in solonetzes withsoda salinization. This is probably explained by thehigher solubility of boron compounds in more alkalinesoil medium.

Solods differ from the above mentioned soils in thecontent and distribution of boron in the soil profile(Table 2). The maximum content of mobile boron com-pounds is registered in the A0 and A1 horizons ofsolods, which is related to the intensive biogenic accu-mulation of boron and its hydrogenic migration todepressions where these soils are formed. In their elu-vial horizons, the boron content decreases sharply to0.4–2.2 mg/kg. Deeper, in the illuvial horizons and inthe soil-forming rocks, the boron content slightlyincreases.

Thus, the soils of solonetzic complexes in the Irtyshregion within Omsk oblast may be arranged in the fol-lowing sequence with respect to the contents of totaland mobile boron compounds: solods < meadow-cher-nozemic and meadow solonetzic soils < meadow-cher-nozemic and meadow solonchakous soils < deep solo-netzes < solonchaks, shallow solonetzes < crusty solo-netzes. As the critical boron content in the nutrientmedium is 5 mg/kg for most crops, almost all the soils

of the studied solonetzic complexes are boron-saline tosome extent (except for solods). This is one of the fac-tors of the low soil fertility in the region.

The soils of solonetzic complexes in the studiedregion are mainly semihydromorphic and hydromor-phic, so we determined the boron content in the ground-water of the area. The groundwater with differentdegrees and chemistry of salinization is characterizedby an increased boron content. It varies from 0.64 to1.0 mg/l (the average content is 0.84 ± 0.3 mg/l, n = 17)in the groundwater under solonetzic complexes on theIshim–Irtysh interfluve. In the groundwater of solo-netzic complexes in the Baraba Plain, the boron contentvaries from 0.26 to 1.2 mg/l and averages up to0.73 ± 0.4 mg/l (n = 43). In fresh waters of bogs and inwater of the Irtysh and Om rivers, the boron content isconsiderably lower (0.17–0.22 mg/l). According to eco-logical requirements, the boron content in irrigationwater should not exceed 0.5–0.7 mg/l [21]. Conse-quently, it may be concluded that there is an excessiveboron content in the groundwater of the solonetzicassociations in the region.

Boron resistance of plants. Soils of solonetzic asso-ciations with an excessive boron content are plowedand used for pasturing, so it is important to determinethe boron resistance of cultivated crops and their capac-ity for boron uptake. We have performed a number offield and pot experiments on meadow-chernozemicsoils subjected to different levels of boron salinizationrates via the application of boric acid or borax in orderto study the effect of high boron concentrations(5−15 mg/kg) on crop productivity and boron uptake byplants.

Crops are characterized by different levels of boronresistance and different capacities for boron accumula-tion in the biomass (Tables 4 and 5). In the case ofboron-saline soils, boron intensively gets into theaboveground phytomass, where its concentrations maybe very high. Boron uptake by crops depends on theirbiological features, development stage, and growingconditions.

The highest boron concentration has been found inplants grown under conditions of pot experiments withsimulated boron salinization of the substrate (Table 4).Upon optimum soil moistening, boron applied to thesoil is actively consumed by plants and transported to

Table 3. The content of mobile boron in the 0- to 100-cm-thick layer of solonetzes of different salinization types(t0.5 = 2.2; tf = 5.5)

Salinization type nBoron, mg/kg

V, %S ± sx Lim

Sulfate–chloride, chlo-ride–sulfate

28 9.5 ± 0.5 8.1–11.1 12.1

Soda–sulfate, sulfate–soda, soda

39 19.3 ± 1.7 11.2–23.6 23.2

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the aboveground phytomass. Cereals are characterizedby the highest capacity for boron accumulation. Independence on the degree of boron salinization of thesubstrate, the boron content increases by 7–34 times inbarley and by 4–32 times in Sudan grass as comparedwith the control. The high boron concentration in bar-ley is preserved throughout the growing period,because soluble boron compounds are readily absorbedby plant roots with water. In the variants with boronsalinization, plants have distinct features attesting tothe toxic effect of boron: burns on leaf edges and brown

color and drying of leaves. This leads to a drop in thecrop yield. It should be mentioned that the capacity ofcereals for boron accumulation was open to questionfor a long time. Koval’skii considered cereals to have aspecial protective mechanism against excessive boroncontent in their nutrient medium due to which they donot accumulate large quantities of the element. He con-cluded that boron geochemical provinces should beused for cereal growing [14]. Further investigations[12, 19] revealed an opposite regularity and pointed toa close correlation between the boron contents in cere-als and in the soil. The latter opinion has been con-firmed by our experiments. The results obtained sug-gest that, under conditions of the high boron content inthe soil and optimum moistening, the boron concentra-tion in the aboveground biomass of cereals becomesvery high. There is a significant correlation between theboron content in the soil and its concentration in thephytomass (r = 0.93 ± 0.11, n = 25 for barley, andr = 0.90 ± 0.22, n = 14 for Sudan grass).

Leguminous plants grown on boron-saline soilsaccumulate boron in smaller amounts as compared withcereals. Lucerne and vetch are characterized by ahigher physiological demand for boron. When grownon the meadow-chernozemic soil, they contain1.5−3.0 times more boron than barley and Sudan grass.In the variants with boron salinization, its concentrationin the aboveground phytomass of lucerne and vetchincreases considerably (by 3–14 and 4–8 times, respec-tively), but the degree of boron uptake by these plantsis smaller than that by cereals. The correlation coeffi-cients between the boron content in the soil and in theaboveground phytomass are r = 0.82 ± 0.33 (n = 14) forlucerne, and r = 0.90 ± 0.12, n = 20 for vetch.

The boron resistance of bromegrass and melilot hasbeen studied in field experiments (data are partially pre-sented in Tables 4 and 5). The accumulation of boron inthe biomass of plants under field conditions at naturalmoistening is generally lower than that in pot experi-ments with optimum moistening. As seen from theresults of our experiments, the protective mechanism ofbromegrass against excessive boron uptake is ratherweak and is similar to that of barley. Boron is mostintensively consumed by bromegrass during the firstyear. Its concentration in the aboveground phytomassmass at the stage of booting increases by 4–14 times onthe boron-saline soils in comparison with the control(Table 4). In the second year, at the heading stage, bro-megrass consumes considerably smaller amounts ofboron (up to 50 mg/kg at the maximum boron saliniza-tion rate). This is explained by the dilution of the ele-ment concentrations in the plants whose productivitybecomes higher as compared to that in the first year.

In conditions of boron salinization, boron uptake bymelilot plants during the first and second years is con-siderably lower. Its concentration increases by only1.3–1.6 times as compared with the control. There is areliable correlation between the boron content in the

Table 4. Crop productivity with respect to the boron contentin the soil, its concentration in plants, and the Ca-to-B ratioin the aboveground phytomass (generalized data)

Boron content, mg/kgCa/B A drop in pro-

ductivity, %soil aboveground phytomass

Barley, tillering stage, pot experiment2.1–2.7 29 167 06.0–8.0 216 13 6

12.5–13.1 567 9 1416.0–17.5 989 4 16

Barley, heading phase, pot experiment2.1–2.7 40 155 06.0–8.0 300 37 14

12.5–13.1 880 14 2016.0–17.5 1089 7 34

Sudan grass, phase of 4–5 leaves, pot experiment2.6–3.1 20.8 462 07.6–9.5 83.3 106 22

12.5–14.9 426 23 3217.5–20.3 669 12 39

Lucerne, tillering stage, pot experiment2.6–3.1 58.3 332 07.0–8.0 192 92 4

12.5–13.1 583 27 2317.5–18.9 800 19 31

Vetch, tillering stage, pot experiment2.6–2.9 59 195 06.0–8.0 224 50 6

12.5–13.1 357 39 7.516.0–17.5 462 25 18Brome of the first year, booting stage, field experiment

2.6–3.0 14.2 227 06.6 66.2 133 168.5 118 74 35

12.5 204 Not det. 54Melilot of the first year, booting stage, field experiment

2.6–3.0 39.0 310 06.6 40.4 287 48.5 45.8 275 5

12.5 56.2 251 19



soil and in the plant mass at various stages: r = 0.94 ±0.09, n = 130 for bromegrass; and r = 0.83 ± 0.16, n = 97for melilot.

We have also determined the boron concentrationsin barley, bromegrass, melilot, and lucerne grown infield experiments on solonetzes with a mobile boroncontent of 8–14 mg/kg. The highest boron concentra-tion is seen in the young plants. At the tillering stage,bromegrass contains up to 45 mg/kg of boron on thesolonetz and 14–16 mg/kg on the meadow-cher-nozemic soil. At the stage of harvesting, the boron con-centration in the plants is considerably lower:4−8 mg/kg in barley at the stage of full ripeness and12–20 mg/kg in bromegrass at the heading stage.A lower concentration of boron in the abovegroundphytomass of the crops grown on solonetzes in fieldconditions is explained by the insufficient moistening.In addition, the biomass of the adult plants is large, sothe boron concentration in it becomes lower. Theboron concentration in melilot and lucerne at the bud-ding and blossoming stages is considerably higher(40−65 mg/kg).

The high boron concentration in the phytomass ofthe plants grown on the boron-saline soils is accompa-nied by a disturbance of the Ca-to-B ratio in them. Thisis one of the reasons for the negative effect of boron(Table 4). It is known that plant development is normalat particular contents and ratio between these elements,and a relative decrease in the content of Ca exerts atoxic effect [22]. In the experimentally grown cereals,the calcium content is not high (0.27–0.28%) as com-pared with that in the leguminous plants (1.4–2.9%).Under conditions of boron salinization, the C-to-B ratio

in the cereals and leguminous plants becomes consider-ably lower, which results in the development of borontoxicosis. The Ca-to-B ratio in the plants grown on theboron-saline soils decreases most significantly in theaboveground phytomass of the cereals; its decrease inthe biomass of leguminous plants is somewhat lower.

Excessive boron accumulation and a drop in the Ca-to-B ratio in the aboveground phytomass at the boronsalinization of the soil cause a decrease in the cropyields (Table 4). Approximate normal and toxic boronlevels in soils and plants and the Ca-to-B ratio values inthe crops are given in Table 5. The characteristics atwhich the crop productivity decreases considerably aretaken as toxic ones. The averaged data show that barley,Sudan grass, and bromegrass are characterized by thelowest boron resistance among the studied crops: theirproductivity drops when the mobile boron content inthe soil reaches 6–7 mg/kg and more. The boron resis-tance of lucerne, vetch, and melilot is higher. Their pro-ductivity drops considerably at a boron content in thesoil equal to 12.5–15 mg/kg. The higher resistance ofleguminous plants to excessive boron concentration inthe soil is explained by the high calcium content in theirtissues and their capacity to maintain the Ca-to-B ratioat a relatively stable level. Thus, boron salinization ofthe soil exerts an adverse effect on the productivity andquality of crops. In this connection, crops grown onsolonetzic soil complexes should be chosen with dueconsideration for their boron resistance and the boroncontent in the soil.

Plants are the source of boron in food chains. There-fore, we have studied the boron concentrations in natu-ral vegetation of hayfields and pastures on various soils

Table 5. Normal and toxic boron concentrations in soils and plants and the Ca-to-B ratio in the aboveground phytomass (gen-eralized data, 1991–2005)

Stage

Boron, mg/kgCa/B

soil, 0–20 cm aboveground phytomass

normal toxic normal toxic normal toxic

BarleyTillering 2.1–2.7 >6.0 29 >200 167 <25Heading 2.1–2.7 >6.0 40 >250 155 <40

Sudan grass4–5 leaves 2.7–3.1 >7.0 20.8 >80 462 <100

Bromegrass, first yearTillering 2.6–3.0 >6.6 14.0 >40 227 <120Booting 2.6–3.0 >6.6 16.0 >50 420 <130Heading 2.6–3.0 >8.5 14.0 >50 – –

Lucerne, first yearTillering 2.7–3.1 >13.0 58.3 >500 330 <30

VetchTillering 2.6–2.9 >15.0 59.0 >350 195 <30

Melilot, first yearTillering 2.6–3.2 >12.5 50.0 >80 536 <370Blossoming 2.6–3.2 >12.5 48.6 >60 310 <290

520


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with different boron contents [4]. It has been revealedthat the boron concentration in forbs is 1.4–2.8 timeshigher on soils with boron salinization as comparedwith forbs grown on nonsaline soils. The boron concen-tration in cereals at the heading stage is not high(3−15 mg/kg). In plants of other families (Compositae,Cruciferae, Labiatae, and Leguminosae), the boronconcentration at the blossoming stage is rather high(34–58 mg/kg). According to Koval’skii, the state of thehealth of animals consuming plants containing morethan 65 mg B/kg of dry phytomass worsens [14]. Ourdata show that the average boron content in adult plantsgrown on the soils of solonetzic complexes is lowerthan this critical value. Nevertheless, excessive boronaccumulation in forage plants may occur in particularconditions. Young plants growing on the boron-salinesoils under favorable moistening may be hazardous foranimals. We suppose that the ratios of boron to otherelements should be taken into consideration togetherwith the boron concentration in the plants. Thus, unfa-vorable Ca-to-B ratios are typical of the plants growingon the soils of solonetzic complexes. Published datashow that the ratios between boron, copper, and molyb-denum concentrations in plants of hayfields and pas-tures on saline soils of the Ishim–Irtysh Plain are unfa-vorable [5]. Hence, the soil–groundwater–plant sys-tems in landscapes of solonetzic complexes arecharacterized by the specific geochemical regime ofboron and other elements.

Boron-saline soils require special measures todecrease the toxic effect of boron on living organisms.Some investigations into this problem have been per-formed in our country and abroad. Soil washing is sug-gested as one of the measures against boron salinizationof soils, and there are data on a decrease in the borontoxicity under the impact of zinc salts and gypsum[1, 6, 24, 25].

In Western Siberia, chemical amelioration of solo-netzes with the use of gypsum and phosphogypsum isone of the basic methods to improve their properties.The effect of ameliorants on the boron content in crustyand shallow semihydromorphic and hydromorphicsolonetzes and in the crops grown on them has beenstudied at the experimental fields of the Laboratory ofSolonetz Amelioration of Omsk State Agrarian Univer-sity [18, 20].

Our data show that gypsum and phosphogypsumapplication at a rate of 25–60 t/ha decreases the boronsalinization of solonetzes. The content of mobile boronin the upper 20 cm of the ameliorated soils drops by26−61% in different experiments. It should be men-tioned that, in the case of a strong boron salinization ofsolonetzes, the use of these ameliorants somewhatdecreases the negative effect of boron on the plants butdoes not eliminate it completely. The content of mobileboron in the ameliorated solonetzes may decrease dueto the improvement of their infiltration properties andthe leaching of borates from the topsoil. A decrease in

the content of mobile boron compounds may also beexplained by more a intensive boron adsorption by clayminerals in the reclaimed solonetzes under the effect ofcalcium ions.

Boron uptake by plants on the ameliorated solo-netzes also decreases, and its toxic effect on the plantsweakens. The most pronounced decrease in the boronconcentration takes place in cereals: by 1.7–1.9 times inthe grain and straw of barley, by 1.3–2.0 times in thegrain and straw of wheat, by 1.6–2.1 in the above-ground phytomass of bromegrass, and by 1.4 times inthe aboveground phytomass of millet. For melilot witha high boron resistance, a drop in the microelementconcentration is insignificant. Thus, a decrease in thecontent of mobile boron in the solonetzes and in itsuptake by plants is one of the ways to increase crop pro-ductivity on the ameliorated solonetzes.

CONCLUSIONS

Soils of solonetzic complexes in the Irtysh regionwithin Omsk oblast are boron-saline: they are character-ized by high contents of both the total (50.4−126 mg/kg)and mobile (3.8–37 mg/kg) boron. The boron content isthe highest in crusty solonetzes and is also excessive(up to 1.2 mg/l) in the groundwater of solonetzic com-plexes. Boron salinization of soils and groundwater isone of the factors causing a drop in crop productivityand quality. In conditions of boron salinization of soils,this microelement is intensively absorbed by the above-ground phytomass and causes a considerable decreasein the Ca-to-B ratio in it and a drop in the plant produc-tivity. Cereals are less resistant to a high boron contentin the soil in comparison with leguminous plants. Bar-ley, bromegrass, and Sudan grass should be cultivatedon soils with a boron content of less than 8 mg/kg. At ahigher boron content, lucerne, melilot, and vetch can becultivated. The amelioration of solonetzes via applica-tion of gypsum and phosphogypsum reduces the degreeof boron salinization and the negative effect of boron onthe plants. The boron content in natural vegetation ofhayfields and pastures on the soils of solonetzic com-plexes is considerably higher than that in zonal soilswith low boron content. This circumstance poses a dan-ger of a high boron concentration in forage plants. Cropgrowing on the soils of solonetzic complexes should beperformed with due account for the boron content in thesoils, the boron resistance of the plants, and control ofthe boron concentration in the crops.

REFERENCES

1. O. I. Alikhanova, “Toxic Effect of Boron on Plants,”Agrokhimiya, No. 7, 98–102 (1980).

2. Yu. A. Azarenko, “Geochemistry of Boron in Soils of theSolonetzic Complex, Omsk Oblast,” in Ecological Sta-tus of Soils and Plants in Western Siberia and Problemsof Their Quality: Proceedings of Omsk State AgrarianUniversity (Omsk, 1997), pp. 19–27 [in Russian].



3. Yu. A. Azarenko and E. D. Orlova, “Boron Uptake byPlants and the Yield of Smooth Brome and MelilotDepending on the Boron Salinization of Soil,”Agrokhimiya, No. 11, 14–20 (2000).

4. Yu. A. Azarenko, “Boron Uptake by Plants on Soils withDifferent Boron Content,” Vestn. Omsk. Gos. Agrar.Univ., No. 3, 56–60 (2004).

5. V. K. Bakhnov, “Practical Significance of SchematicMaps of Microelements in the Soil Cover,” in Sketcheson the Biochemistry and Agrochemistry of BiophilousElements (Nauka, Novosibirsk, 1977) [in Russian].

6. V. M. Borovskii, Development of Saline Soils andHalochemical Provinces of Kazakhstan (Nauka, Alma-Ata, 1982) [in Russian].

7. M. G. Valyashko, “Geochemistry of Boron,” in Boron,Its Compounds, and Alloys (Akad. Nauk USSR, Kiev,1960), pp. 7–25 [in Russian].

8. A. P. Vinogradov, Geochemistry of Rare and DispersedChemical Elements in Soils (Akad. Nauk SSSR, Mos-cow, 1957) [in Russian].

9. The West-Siberian Plain, Ed. by S. A. Arkhipov,V. V. Vdovin, B. V. Mizerov, and V. A. Nikolaev (Nauka,Moscow, 1970) [in Russian].

10. V. B. Il’in, Biogeochemistry and Agrochemistry ofMicroelements (ån, Cu, Mo, and B) in Southern Regionsof Western Siberia (Nauka, Novosibirsk, 1973) [in Rus-sian].

11. V. B. Il’in and A. P. Anikina, “Boron Salinization ofSoils,” Pochvovedenie, No. 1, 102–108 (1974).

12. V. B. Il’in and A. P. Anikina, “Regions of Boron Salin-ization in Siberia,” in Sketches on the Biogeochemistryand Agrochemistry of Biophilic Elements (Nauka,Novosibirsk, 1977) [in Russian].

13. V. B. Il’in and A. I. Syso, Microelements and Heavy Met-als in Soils and Plants of Novosibirsk Oblast (Ross.Akad. Nauk, Novosibirsk, 2001) [in Russian].

14. V. V. Koval’skii, Geochemical Ecology (Nauka, Mos-cow, 1974) [in Russian].

15. V. A. Kovda, Solonchaks and Solonetzes (Akad. NaukSSSR, Moscow, 1937) [in Russian].

16. V. A. Kovda, Biogeochemistry of Soil Cover (Nauka,Moscow, 1985) [in Russian].

17. A. A. Neupokoev, E. D. Orlova, and T. B. Degtyareva,“Boron Content in Soils of the Solonetzic Complex ofOmsk Oblast,” in Saline Soils of Western Siberia, TheirProperties, and Methods of Improvement: Proceedingsof the Omsk Agricultural Institute (Omsk, 1984),pp. 65−69 [in Russian].

18. E. D. Orlova and A. A. Neupokoev, “Effect of Gypsum-ing on the Content of Exchangeable Boron in Solonetzesof Omsk Oblast,” in Reclamation of Solonetz-SolonchakSoils of Western Siberia: Proceedings of the Omsk Agri-cultural Institute (Omsk, 1986), pp. 60–67 [in Russian].

19. E. D. Orlova and A. A. Neupokoev, “Effect of ElevatedBoron Concentrations on the Yielding Capacity andChemical Composition of Plants,” Agrokhimiya, No. 12,44–52 (1990).

20. E. D. Orlova, Yu. A. Azarenko, and A. A. Klippert,“Boron in Plants on Soils with Different Boron Con-tents,” in Changes in Properties of Soils of the Cher-nozemic–Solonetzic Complex of Western Siberia underReclamation Development Conditions: Proceedings ofOmsk Agricultural Institute (Omsk, 1992), pp. 9–14[in Russian].

21. E. I. Pankova and I. P. Aidarov, “Ecological Require-ments to the Quality of Irrigation Water,” Pochvovede-nie, No. 7, 870–878 (1995).

22. I. A. Chernavina, Physiology and Biochemistry of Micro-elements (Vysshaya Shkola, Moscow, 1970) [in Rus-sian].

23. M. Ya. Shkol’nik, Microelements in the Life of Plants(Nauka, Leningrad, 1974) [in Russian].

24. M. S. Bajwa and H. C. Sharma, “Effectiveness of Gyp-sum and Sulfuric Acid in Reclaiming Boron-Rich Soil,”J. Indian Soc. Soil Sci. 38 (2), 355–357 (1990).

25. Singh Joginder and N. S. Randhawa, “Boron Leachingand Regeneration Capacity in Saline Sodic Soils,”J. Indian Soc. Soil Sci. 28 (3), 307–311 (1980).

Documents

The boron content in soils of solonetzic complexes in the Irtysh Region of Omsk oblast and the boron resistance of plants