Morphological and Physico-Chemical Characteristics and Classification of Vertisol Developed on Deltaic Plain

doi:10.4236/ojss.2012.21004

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Open Journal of Soil Science, 2012, 2, 20-27

http://dx.doi.org/10.4236/ojss.2012.21004 Published Online March 2012 (http://www.SciRP.org/journal/ojss)

Morphological and Physico-Chemical Characteristics and

Classification of Vertisol Developed on Deltaic Plain

Orhan Dengiz*, Mustafa Sağlam, F. Esra Sarioğlu, Fikret Saygin, Çağla Atasoy

Department of Soil Science and Plant Nutrition, Faculty of Agriculture, Ondokuz Mayıs University, Samsun, Turkey.

Email: *[email protected]

Received January 27th, 2012; revised February 24th, 2012; accepted March 8th, 2012

ABSTRACT

The name of Vertisol is derived from Latin “vertere” meaning to invert. This case restricts development of soil horizons

in profile. These soils have the cap acity to swell and sh rink, inducing cracks in the upp er parts of the soil and distinctiv e

soil structure througho u t the soil. Th e fo rmation of these speci fic features are caused by a heavy texture, a dominance of

swelling clay in the fine fraction and marked changes in moisture content. The swell-shrink behavior is attributed to the

wetting and drying of the soil mass. In this study, morphology, physico-chemical characteristics and classification of

vertisols that were formed on alluvial delta plains, were investigated. Those soils formed on the Bafra Plain found in the

Kızılırmak Delta and located in the central Black Sea region of Turkey. All studied Vertisols are characterised by a dark

colour in surface soil, a heavy clayey texture, hardpan formation under top soil (high bulk density a high compaction)

and very high COLE values. In addition, they have deep wide-opened desiccation cracks at the surface, slickensides at

the middle part of the profiles and a poor differentiation of their horizons. Physico-chemically, the studied soils are

slightly basic to very basic, non-saline and poor in organic matter, which is slightly higher in the surface horizon. In

addition, cation exchange capacity, sum of exchangeable bases and base saturation of soils are very high. On the basis

of morphological and physicochemical analysis, soil profiles were classified as Sodic Haplustert, Typic Calciaquert,

Sodic Calciustert according to Soil Taxonomy (Soil Survey Staff, 1975 and 1999) and as Sodic Vertisol and Calcic

Vertisol according to FAO/ISRIC (2006) classification systems.

Keywords: Vertisol; Soil Morphology; Soil Classification; Bafra Delta Plain

1. Introduction

The materials that form vertisols can be either alloch-

tonous or autochtonous in origin [1]. The former are geo-

graphically more extensive and generally occur in the lo-

wer parts of the landscape. Vertisols are known to de-

velop on a wide variety of parent materials such as ba-

salts in Australia [2], calcareous rocks in the West Indies

[1], gneisses and sandstones in India [3], deltaic deposits

in the United States of America [4], lacustrine deposits in

Trinidad [5], glacio-lacustrine in Saskatchewan [6], ma-

rine deposits in Guyana [7], and marls [8]. It is reported

that in all cases (except fo r the vertisols developed on la-

custrine deposits), the materials were recently deposited

and that soil formation was still at its early stages [9]. In

the case of vertisols developed from lacustrine deposits

in Trinidad, it is believed that extensive weathering and

clay-mineral synthesis had occurred prior to deposition

[10].

The name of vertisol is derived from Latin “vertere”

meaning to invert. This case restricts development of so il

horizons in profile [9]. These soils have the capacity to

swell and shrink, inducing cracks in the upper parts of

the soil and distinctive soil structure throughout the soil

[11]. The formation of these specific features are caused

by a heavy texture, a dominance of swelling clay in the

fine fraction and marked changes in moisture content [12].

The swell-shrink behaviour is attributed to the wetting

and drying of the soil mass. Vertisols exhibit cracks a

depth of 50 cm down that are at least 1 cm wide and ex-

tend upward to the surface or the base of the plough layer

or surface crust. These soils exhibit minimal horizon dif-

ferentiation as a result of pedoturbation. They are also

very plastic and sticky when wet [13]. Vertisols are de-

scribed by Glossary of Soil Science Terms [14] as “min-

eral soils that have 30% or more clay, deep wide cracks

when dry and either gilgai microrelief, intersecting slicken-

side or wedge-shaped structural aggregates tiled at an an-

gle from the horizon. It was added as an order in US sys-

tem of soil taxonomy.

Depressions and level to undulating areas, mainly in

*Corresponding a uthor.

Morphological and Physico-Chemical Characteristics and Classification of Vertisol Developed on Deltaic Plain 21

tropical, semi arid to sub humid and Mediterranean cli-

mates with and alternation of district wet and dry season s.

An estimated 150 million hectares is potential crop land

[15]. According to a map called the Turkey Soil Zones

Map at the scale of 1:2,000,000 prepared from the results

of the Turkey Development Soil Maps Survey at a scale

of 1:100,000, vertisols comprise 598 ,693 hectar es or 0.86

percent of the land area of Turkey [16,17].

Vertisols are important agricultural soils in left side of

Bafra Delta Plain. Soils are mostly used for rice cultiva-

tion. The main ai ms of this research were to determine th e

morphological and some physico-chemical characteristics

of these soils and to classify the soils according to the

USDA Soil Taxonomy and FAO/ISRIC soil classifica-

tion systems.

2. Material and Methods

2.1. Description of the Study Area

This study was carried out in the left side of Bafra Plains

found in the Kızılırmak delta located in the central Black

Sea region of Turkey (Figure 1). The Bafra Delta Plain is

far 30 km from north of the Samsun province. The cur-

rent climate in the region is semi-humid. The summers

are warmer than winters (the average temperature in July

is 22.2 and in January is 6.9˚C). The mean annual tem-

perature, rainfall and evaporation are 13.6˚C, 764.3 mm

and 726.7 mm respectively. According to [18], soil tem-

perature regime is mesic and moisture regime is ustic in

the study area. The mean annual temperature, rainfall and

evaporation are 13.6˚C, 764.3 mm and 726.7 mm respec-

tively in Bafra plain that area is mainly flat and slightly

Figure 1. Location map of the study area.

Morphological and Physico-Chemical Characteristics and Classification of Vertisol Developed on Deltaic Plain

sloped (0% - 2.0%). The study area has been under in-

tensive agricultur al activities. Rice, wheat, maize, pepper,

watermelon, cucumber and tomato with sprinkler and

furrow irrigations in the summer, and cabbage and leek

in the winter have been produced in the study area.

2.2. Physical and Chemical Analysis

Four vertisol profiles formed on deltaic deposits were

selected for this study in left side of Bafra delta plains.

Morphological p roperties of these four soil pro files in the

field were identified and sampled by genetic horizons.

Nineteen soil samples were taken to investigate for their

physical and chemical properties at the laboratory. Dis-

turbed soil samples were dried under atmospheric condi-

tion and passed through a 2 mm sieve to prepare for la-

boratory analysis. In soil samples, particle size distribu-

tion was determined by the hydrometer method [1 9]. Dry

bulk density was determined by the core method [20].

Soil reaction (pH), electrical conductivity (EC) and CaCO3

content were determined by standard procedure [21]. Ex-

changeable cation s an d cation ex chang e cap acities (CEC)

were measured using a 1 N NH4OAc (pH 7) extraction

method [22]. Organic matter content was determined us-

ing the Walkley-Black wet digestion method [23]. Coef-

ficient of linear extensib ility (COLE) was determined ac-

cording to [18]. In addition, these four soil profiles were

classified according to [18-24].

3. Results and Discussions

3.1. Soil Morphology and Classification

Two main types of vertisols can be distinguished: Litho-

morphic vertisols and topomorph ic vertisols [24,25]. L itho -

morphic vertisols are formed on various parent rocks

whose weathering generates base-rich environments fa-

vourable for smectite synthesis, while topomorphic ver-

tisols are formed mainly in favour of low land scape posi-

tions which favour the accumulation of bases. In this study,

morphological characteristics of selected four soil profiles

formed on alluvial delta plains are presented in Table 1.

Table 1. Selected morphological characteristics of pedons.

Colors

Horizon Depth

(cm) Boundary Dry Moist

Structure Consistence Special features

Pedon I (Sodic Haplustert/Sodic Vertisol)

Ap 0 - 18 as 10YR3/2 10YR3/3 3mgr sh fi st pt cracks

Bss1 18 - 45 cw 10YR4/3 10YR4/3 3mab k h fi st pt cracks, slickenside

Bss2 45 - 70 dw 2.5YR6/2 2.5YR5/2 3mpr h fi st pt cracks, slickenside

Bss3 70 - 116 dw 2.5YR5 /3 2.5YR5/3 3cpr h fi st pt cracks, slickenside

C 116+ - 10YR5/3 10YR5/4 m h fi st pt -

Pedon II (Typic Calciaquert/Calcic Vertisol)

Ap 0 - 25 aw 2.5YR4/3 2.5YR4/4 3mgr h fi st pt cracks

Bss1 25 - 70 cw 5Y5/3 5Y5/2 3mpr h fi st pt cracks

Bss2 70 - 116 cs 5Y6/1 5Y6/2 3mpr h fi st pt slickenside

Ck 116+ - 2.5YR7/3 2.5YR6/3 sg so fr ss ps carbonate mycelium and nodules,

water table

Pedon III (Sodic Haplustert/Sodic Vertisol)

Ap 0 - 15 as 2.5YR4/3 2.5YR4/3 3mgr sh fi st pt cracks

Ad 15 - 44 gw 2.5YR5/3 2.5YR4/4 3msbk h fi st pt densitic layer

Bssg1 44 - 73 gw 10GY6/1 10GY5/1 3mpr h fi st pt slickenside, redoximorphic feature

Bssg2 73 - 108 dw 10GY6/1 10GY5/1 2mpr h fi st pt slickenside, redoximorphic feature

Cg 108+ - 2.5YR6/3 2.5YR6/3 m sh fi ss pt redoximorphic feature

Pedon IV (Sodic Calciustert/Sodic Vertisol)

Ap 0 - 18 as 10YR4/2 10YR3/2 3cgr sh fi st pt cracks

Ad 18 - 50 aw 10YR 4/3 10YR 3/4 3msbk sh fi st pt densitic layer

Bss 50 - 82 cw 2.5YR6/3 2.5YR6/3 3mpr sh fi st pt slickenside

Bssk 82 - 125 cw 2.5YR7/3 2.5YR6/3 3mpr si fi st pt slickenside, carbonate mycelium

and nodules

C 125+ - 2.5YR7/3 2.5YR6/3 sg so fr ss ps -

Abbreviations: Boundary: a = abrupt; c = clear; g = gradual; d = diffuse; s = smooth; w = wavy; i = irregular Structure: 1 = weak; 2 = moderate; 3= strong; sg

= single grain; m = massive; vf = very fine; f = fine; m =medium; c = coarse; gr = granular; pr = prismatic; abk = angular blocky; sbk = subangular blocky.

Consistance: (Dry) lo = loose; so = soft; sh = slightly hard; h = hard; (Moist) lo = loose; vfr = very friable; fr = friable; fi = firm; (Wet) so = nonsticky; ss =

slightly sticky; st = sticky; po = nonplastic; ps = slightly plastic; pt = plastic.

Morphological and Physico-Chemical Characteristics and Classification of Vertisol Developed on Deltaic Plain 23

[11,26,27] stated that many vertisols have deep and dark

topsoil. In addition, [28] reported the dark colour (low

chroma) could be related to the strong impregnation of

profile by organic matter during pedogenesis or to pro-

long waterlogging . In this research, colour of the all pro-

files in hue changed 10YR and 2.5Y, value was 3 - 4 (dry

and moisture conditions) in surface soils. Thus, the find-

ing was showed coherent with these researchers. On the

other hand, colo ur changed due to redoximorphic featur e

(10GY 6/1) in subsurface horizon in Profile III and car-

bonate accumulation (high value-2.5YR7/3) in Ck and

Bssk horizons of PII and PIV. Besides, carbonate nod-

ules and mycelium were also recognised in these pedons

within 120 cm depth due to calcification process.

Extensive swelling and shrinking upon wetting and

drying is the major characteristics of these soils. This re-

sults to pedoturbation or mixing of the soils and minimal

horizonation [9]. Shrinkage causes the formation of wide

deep cracks and washing of surface materials into these

cracks. Vertisols may exhibit open cracks, which are up

to 50 cm deep and at least 1 cm wide and extend upward

to the surface or the base of the plow layer or surface

crust [13]. Moreover, cracks are a unique feature in soils

with strong shrink–swell potential and are used as one of

the criteria in defining vertisols and vertic intergrades in

soil taxonomy [18]. Cracking takes place as a result of

seasonal fluctuation. The moisture regime influences the

duration and intensity of cracking. The degree and fre-

quency of changes in moisture content of the soil are per-

haps the most important parameters th at control cracking

intensity [6]. Cyclic cracking and swelling contribute to

the formation of slickensides. Most of the subsurface ho-

rizons (except for C horizons) of profiles were character-

ised by numerous smooth and shiny surfaces called

slickensides that separated different blocks and prismatic;

their diameters varied between 5 and 15 cm. While Ap

horizons of profiles have strong, medium and coarse granu-

lar structures, due to high clay content blocky and pris-

matic structures were determined in 100 cm of profiles.

Consistencies of all B horizon of profiles wer e very hard

when dry and plastic when wet conditions.

Due to the fact that main soil formation process and

other features such as slickenside, cracking, carbonate

accumulation and redoximorphic symptoms, four soil

profiles were classified as Sodic Haplustert, Typic Cal-

ciaquert, Sodic Calciustert by taking into consideration

of Soil Taxonomy [18]. In addition, these soils were

classified as Sodic Vertisol and Calcic Vertisol according

to FAO/ISRIC [24].

3.2. Physico-Chemical Characteristics

3.2.1. Chemical Properties

Vertisols are generally found on sedimentary plains as

the result of thousands of years eroding the clay content

out of the surrounding hills. They can also be found on

level land and in d epressions. [29] also reported that v er-

tisols are typically developed on alluvial material in flat

inland areas. The pedons selected for the present study, it

was found significantly vation in pH values among all

the soil layers. The pH values varied from 7.84 to 9.39.

The increase in pH with depth of pedons is a characteris-

tic feature of all pedons and could imply the proximity of

the horizons to the alluvial parent material that is rich in

alkaline earth cations (Ca and Mg) and water table fluc-

tuation due to sea effect that includes high sodium ion

concentration. In parallel, increasing of sodium concen-

tration with depth caused increasing of ESP values in all

pedons. [30] reported that high ESP values in vertisols

cause dispersion of fine particles, leading to blockade of

pore spaces. This ultimately rend ers the soils non-porou s

as reflected by low permeability. Poor drainage conditions

lower the rate of organic matter decomposition. The or-

ganic matter values varied from 3.2% to 4.8% in surface

horizons whereas, these ratios decreased with depth and

varied from 0.5% to 2.5%. The higher organic matter at

the surface could be linked to the continuous addition of

crop residues on the surface of cropped fields in the area.

The cation exchange capacity for all the studied soils

ranged between 32.6 and 80.7 cmol·kg–1 of soils (Table

2). It increased regularly with pro file depth. Calcium and

magnesium were the dominant exchangeable cations,

with contents ranging between 25.6 and 73.5 cmol·kg–1 of

soils. It was followed by sodium (3.0 to 12.2 cmol·kg–1),

while potassium showed more modest values (0.6 to 1.0

cmol·kg–1). The CaCO3 content of the soils increased with

depth and values varied from 1.4% to 34.7%. The highest

values were observed at the subsurface horizons in Pro-

file II and Profile IV due to calcium carbonate leaching

and accumulation process. [31] reported that pedogenic

carbonates accumulation in the Texas Gulf Coast Prairie

Vertisols form by leaching of detrital carbonate in the

fine earth fraction of the sediments to just below the ef-

fective meteoric infiltration.

3.2.2. Physical Properties

The soils selected for the present study belong to verti-

sols and their intergrades. Logically, the sand, silt and

clay content should be within the range to qualify them

as Vertisols [18]. The contents of sand, silt and clay vary

as shown in Table 3. The clay content of all studied pe-

dons varies from 52.2% to 85.7% except for C horizons

of pedons while, sand content changes between 5.3% -

17.6% in pedogenetic horizons. While the clay contents

were the highest in Pedon IV and ranged between 80.1%

and 85.7% within 80 cm depth, the highest sand content

(20.0%) was observed in Pedon II. The representation of

various grain size fractions on [32] Jamagne’s textural

diagram showed that the all soils layers of pedons had a

heavy clayey texture (Figure 2).

Morphological and Physico-Chemical Characteristics and Classification of Vertisol Developed on Deltaic Plain

Table 2. Some chemical properties of pedons.

Exchangeable cations (cmol·kg–1)

Horizon Depth (cm) pH EC (dS m–1) CaCO3 (%)O.M (%)CEC (cmol·kg–1) ESP (%) Na+ K

+ Ca++ + Mg++

Pedon I—Coordinate: North: 4,6 1 6,083 m - East: 73 7,858 m (UTM) (Sodic Haplustert/Sodic Vertisol)

Ap 0 - 18 7.89 0.88 9.1 3.9 64.2 4.7 3.0 0.9 62.1

Bss1 18 - 45 8.39 0.51 13.4 2.3 60.6 5.9 3.6 0.8 57.6

Bss2 45 - 70 8.60 0.73 12.5 1.8 56.3 8.2 4.6 0.8 52.5

Bss3 70 - 1 16 9.04 0.45 9.1 1.6 59.8 14.2 8.5 0.9 52.7

C 116+ 9.15 0.70 12.4 1.1 53.5 17.4 9.3 0.9 46.0

Pedon II—Coordinate: North: 4,616,541 m - East: 737,542 m (UTM) (Typic Calciaquert/Calcic Vertisol)

Ap 0 - 25 8.30 0.73 1.4 3.2 65.4 5.0 3.3 0.9 62.9

Bss1 25 - 70 8.52 1.99 6.3 2.5 6 1.7 12.8 7.9 0.8 55.3

Bss2 70 - 1 16 8.86 0.91 6.6 1.2 53.7 17.7 9.5 0.8 46.0

Ck 116+ 9.39 0.48 34.7 0.5 33.9 13.6 4.6 0.6 30.6

Pedon III—Coordinate: North: 4,617,456 m - East: 736,809 m (UTM) (Sodic Haplustert/Sodic Vertisol)

Ap 0 - 15 7.84 1.36 11.6 4.6 80.7 7.2 5.8 1.0 72.8

Ad 15 - 44 8.49 1.25 13.7 2.4 73.9 12.3 9.1 0.8 70.4

Bss1 44 - 73 8.97 1.24 14.1 2.0 54.2 17.9 9.7 0.8 50.8

Bss2 73 - 108 9.07 0.68 11.0 1.7 58.0 15.0 8.7 0.7 53.2

C 108+ 8.94 0.82 21.6 1.3 56.0 16.8 9.4 0.7 50.1

Pedon IV—Coordi nate: North: 4,618,055 m - East: 736,735 m (UTM) (Sodic Calciustert/Sodic Vertisol)

Ap 0 - 18 7.92 1.15 11.7 4.8 78.7 9.0 7.1 1.0 73.5

Ad 18 - 50 8.78 0.36 15.0 2.3 71.0 13.0 9.2 0.8 67.8

Bss 5 0 - 82 8.89 0.71 10.9 1.9 63.6 18.2 11.6 0.9 58.3

Bssk 82 - 125 9.22 0.54 28.3 1.9 62.8 19.4 12.2 0.8 56.4

C 125+ 8.26 2.92 6.7 0.9 32.6 30.1 9.8 0.6 25.6

EC: Electrical conductivity; CEC: Cation exchange capacity; O.M: Organic matter; ESP: Exchangeable sodium percentage.

Table 3. Some physical properties of pedons.

Particle size distribution (%)

Horizon Depth (cm) COLE Clay Silt Sand Class

(gr·cm–3)

Pedon I (Sodic Haplustert/Sodic Vertisol)

Ap 0 - 18 0.221 68.1 24. 2 7. 8 C 1.15

Bss1 18 - 45 0.274 66.0 23.4 10.6 C 1.21

Bss2 45 - 70 0.264 65.1 21.8 13.0 C 1.23

Bss3 70 - 116 0.285 79.4 13.2 7.4 C 1.29

C 116+ 0.225 72.9 13.7 13.5 C 1.34

Pedon II (Typic Calciaquert/Calcic Vertisol)

Ap 0 - 25 0.211 68.1 17.4 14.5 C 1.24

Bss1 25 - 70 0.281 72.1 15.7 12.2 C 1.22

Bss2 70 - 116 0.191 61.5 17.5 21.0 C 1.27

Ck 116+ 0.025 28.9 35.3 35.8 L 1.35

Pedon III (Sodic Haplustert/Sodic Vertisol)

Ap 0 - 15 0.280 79.7 13.3 7.0 C 1.23

Ad 15 - 44 0198 80.4 9.1 10.5 C 1.48

Bss1 44 - 73 0.190 55.1 29.4 15.4 C 1.27

Bss2 73 - 108 0.191 52.2 34.9 13.0 C 1.30

C 108+ 0.111 40.5 10.7 48.8 C 1.50

Pedon IV (Sodic Calciustert/Sodic Vertisol)

Ap 0 - 18 0.269 80.5 11.0 8.5 C 1.20

Ad 18 - 50 0.219 85.7 9.0 5.3 C 1.57

Bss 50 - 82 0.231 80.1 2.3 17.6 C 1.31

Bssk 82 - 125 0.174 62.5 25.9 11.6 C 1.35

C 125+ 0.021 23.5 53.6 22.9 SiL 1.55

COLE: Coefficient of linear extensibility; BD: Dry bulk density; C: Clay, SiL: Silty loam; L: Loam

Morphological and Physico-Chemical Characteristics and Classification of Vertisol Developed on Deltaic Plain 25

Figure 2. Soil textural classes with reference to Jamagne’s triangle (1967).

Bulk density (BD) indicates the weight of all the or-

ganic and inorganic materials of a given volume of soil.

Higher organic matter lowers BD. High clay content and

introduction of farm machinery causes compaction of sub-

surface layer, which increases the BD. Bulk density also

varies with the content of coarser fragments in soils. There

is a growing acceptance of the view that BD changes due

to change in land use pattern [33]. A study was conducted

with soil profil es from arable area used for field crop (rice)

and vegetables for 30 - 40 years. The highest BDs were

determined in parent materials of all pedons including

high sand content. On the other hand, BD of pedogenetic

horizons ranges between 1.15 and 1.35 g·cm–3 except for

Ad horizons of Pedon III and IV that soils have particu-

larly used for rice cultivation. Due to heavy tillage sys-

tem and field traffic on these soils leading to hard pan

formation, BD increased 1.57 g·cm–3. Similar results were

reported by [34] that over the years, continuous tillage

practices resulted bulk density increased from 1.22 g·cm–3

to 1.38 g·cm–3 in a tropical forest ecosystem of Bangla-

desh. In additio n, due to compression caused by ov erbur-

den weight, the BD values usually increase with soil depth

in all pedons. It has been reported that vertisols may have

BD values as high as 2.1 g·cm–3 [35]. It has been also

shown that at the swelling limit, the gravimetric water con -

tent decreases and BD values increase with depth [36].

Coefficient of linear ex tensibility (COLE) helps to p re-

dict the potential of a so il to shrink and swell. The LE of

a soil layer is the product of the thickness in cen timetres,

multiplied by the COLE of the layer in question. The

COLE of a soil is the sum of these products for all soil

horizons [18]. According to soil taxonomy, a soil should

be qualified for vertic subgroups if the COLE value is

more or equal to 6 between the mineral soil surface and

either a depth of 100 cm or a lithic contact, whichever is

shallower. In case of vertisols slickensides, cracks and

higher COLE values are mutually inclusive. Since higher

COLE values indicate the presence of more shrink-swell

minerals, namely smectite, a positive correlation between

COLE and smectite content can exist [37]. According to

COLE classification given in Table 4, it was also found

that high COLE values should have a positive relation

with vertic characteristic properties of shrink-swell soils

and cracking and vary from 0.174 to 0.281 in pedoge-

netic horizons of all pedons in Table 3.

Vertisols are important agricultural soils in left side of

Bafra Delta Plain. However, vertisols are difficult to work,

they are of very hard consistence when dry and very plas-

tic and sticky when wet. Therefore, th e workability of th e

soil is often limited to very short period s of medium (op-

timal) water status. Vertisols are imperfectly to poorly

drained, leaching of soluble weathering products is lim-

ited, the contents of available sodium, calcium and mag-

nesium are high and the pH is usually above 7.5. Once

they have reached their field capacity, practically no wa-

ter movement occurs, this is due to the very low hydrau-

lic conductivity of a vertisol. In addition, flooding lead-

ing to crop damage can be a major problem in areas with

higher rainfall.

Morphological and Physico-Chemical Characteristics and Classification of Vertisol Developed on Deltaic Plain

Table 4. Coefficient of linear extensibility (COLE) classifi-

cation.

Class COLE

Low <0.03

Moderate 0.03 - 0.06

High 0.06 - 0.09

Very high >0.09

4. Conclusion

In this study, it was aimed at investigating the morpo-

logical and analytical characteristics of vertisols formed

on fluvial land in Bafra Deltaic Plain, in order to high-

light their particularities as well as to envisage their prac-

tical uses and management. From the morphological and

physical point of view, the vertisols of the Bafra Deltaic

Plain region are characterised by a dark colour, a heavy

clayey texture, hardpan formation under top soil (high bulk

density a high compaction) and very high COLE value,

deep wide-opened desiccation cracks at the surface,

slickensides at the middle part of the profiles and a poor

differentiation of their horizons. Physico-chemically, the

studied soils are slightly basic to very basic, non-saline

and poor in organic matter, which is slightly higher in the

surface horizon. Cation exchange capacity, sum of ex-

changeable bases and base saturation are very high. Ove-

rall, considering their characteristics in majority similar

to those of a majority of world deltaic vertisols, those

soils are still unused or are used only for extensive graz-

ing, wood chopping, charcoal burning and the like [24].

In agriculture, optimum yields could be attained if ap-

propriate management techniques are set up for a more

efficient exploitation, protection and conservation of these

soils. The comparatively good ch emical fertility and their

occurrence on extensive level plains where reclamation

and mechanical cultivation can be envisaged are assets of

vertisols. Their physical soil characteristics and, notably,

their difficult water management cause problems. The

physical properties and the soil moisture regime of verti-

sols represent serious management constraints. The heavy

soil texture and domination of expanding clay minerals

result in a narrow soil moisture range between moisture

stress and water excess. Tillage is hindered by stickiness

when the soil is wet and hardness when it is d ry. The su s-

ceptibility of vertisols to waterlogging may be the single

most important factor that reduces the actual growing

period. Especially due to those properties, these vertisol

soils have been generally used for rice cultivation in the

study area. On the other hand, this case is not suitable

other plants. Particularly, due to their very high of COLE

values, namely, very high shrink-swell potential plant

roots can be damaged from this soil activity. Zero till is

commonly advocated as a preferred cropping system to

conventional, multicultivation practices. Zero till is par-

ticularly attractive on clay soils to minimize compaction

and induce natural structure formation [17]. In particular,

the soil stru cture of vertisols h as strong potential to attain

optimal conditions for plant growth through activation of

their inbuilt resiliency via shrink-swell cycles [38,39]. It

is accepted that the major purposes of tillage are to re-

duce bulk density and soil strength and to control pests

and diseases [40,41]. However, soil cultivation affects

soil quality in various ways. With high clay content, cul-

tivation may lead to the formation of a hard pan below

the plough layer that restricts root penetration and down-

ward movement of water [42]. Therefore, many resear-

chers strongly recommend that close attention should be

taken into account for the soil cultivation, irrigation sys-

tem and time depending on the these soil types.

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