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Changes in selected soil physical properties causedby sodicity of soil and irrigation waterN.I. Eltaif a , M.A. Gharaibeh a & Z.A. Ababneh aa Department of Natural Resources and the Environment, Faculty of Agriculture , JordanUniversity of Science and Technology , P.O. Box 3030, Irbid, 22110, JordanPublished online: 02 Feb 2011.

To cite this article: N.I. Eltaif , M.A. Gharaibeh & Z.A. Ababneh (2011) Changes in selected soil physical properties causedby sodicity of soil and irrigation water, Acta Agriculturae Scandinavica, Section B — Soil & Plant Science, 61:1, 84-91, DOI:10.1080/09064710903544193

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ORIGINAL ARTICLE

Changes in selected soil physical properties caused by sodicity of soiland irrigation water

N.I. ELTAIF, M.A. GHARAIBEH & Z.A. ABABNEH

Department of Natural Resources and the Environment, Faculty of Agriculture, Jordan University of Science and Technology,

P.O. Box 3030, Irbid 22110, Jordan

AbstractSodic water and spring water percolated through clay, clay loam, and sandy loam (SL) soils with exchangeable sodiumpercentages (ESPs) of 0, 10, 30, and 50. Reduction in saturated hydraulic conductivity and water stable aggregates recordedat higher ESPs. At ESP :30, application of sodic and spring water to clay soil (C) reduced saturated hydraulic conductivityfrom 1.2 to 3 mm hr�1, whereas in SL soil, the values were 2.8 and 6.2 mm hr�1, respectively. Results indicated that at anyESP and water source, the highest free swelling obtained was in the C soil. This study has practical importance to themanagement of irrigation water quality with respect to soil deterioration.

Keywords: Aggregate stability, hydraulic conductivity, sodicity, swelling, water quality.

Introduction

Irrigated soils in arid and semi arid lands often

experience declining soil quality as a result of

excessive exchangeable sodium content. High levels

of sodium cause slaking of aggregates, swelling/

dispersion of clay particles and this would decrease

hydraulic conductivity through reduction of soil

aggregate stability and plugging of soil pores by

dispersed clay particles (Mace & Amrheim, 2001).

Swelling reduces the sizes of the interaggregate pore

spaces in the soil and, therefore, produces a sub-

stantial reduction in the hydraulic conductivities of

soils. Swelling is particularly important in soils that

contain expandable clay minerals and have ex-

changeable sodium percentages (ESPs) of greater

than about 15.

Soil structure and permeability are very sensitive

to the type of exchangeable ions present in irrigation

water. Frequently, the nearby water may be the only

water available to overcome the limitation of sustain-

able supplies of renewable water resources. How-

ever, different water supplies in arid and semi arid

regions may be taken into consideration as one of the

limitations that imposes using low quality of irriga-

tion water.

Shainberg and Letey (1984) reported that ESP in

agricultural soils ranged from 1 to 30. However,

sodicity may be apparent at any ESP level and

should not confine to the traditional definitions

(Sumner, 1993). The deterioration in these soils

occurs through changes in the proportions of soil

solution and exchangeable ions that lead to osmotic

and specific ion effect together with imbalances in

plant nutrition (Qadir & Schubert, 2002). However,

the ESP boundary between stable and unstable

conditions varies from one soil to another (Pratt &

Suarez, 1990). The presence of swelling clay in soils

also increases the risks of dispersion as the soil comes

into contact with irrigation waters of high sodium

adsorption ratio (SAR). Pons et al. (2000) reported

that swelling is the primary physical process asso-

ciated with high sodium concentrations in soils. The

dispersive effect of Na� as it enters the soil promotes

the development of a thick diffuse double layer

around the colloid particle. This behavior is con-

sidered in relation to the operation of van der Waals

forces, hydration forces, and osmotic repulsive forces

Correspondence: N.I. Eltaif, Department of Natural Resources and the Environment, Faculty of Agriculture, Jordan University of Science and Technology,

P.O. Box 3030, Irbid 22110, Jordan. Tel: 096227201000. Fax: 096227201078. E-mail: nieltaif@just.edu.jo

Acta Agriculturae Scandinavica Section B � Soil and Plant Science, 2011; 61: 84�91

(Received 1 September 2009; accepted 9 December 2009)

ISSN 0906-4710 print/ISSN 1651-1913 online # 2011 Taylor & Francis

DOI: 10.1080/09064710903544193

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arising from the development of diffuse double layers

on particle surfaces (Quirk, 1986). The generated

repulsive forces are strong enough to overcome the

van der Waals attractive forces and enhance colloid

dispersivity especially in soils with significant

amounts of 2:1 minerals (Pons et al., 2000). Swelling

also is one of the most important factors affecting

soil structure and its stability as well as its effects on

soil physical status. Numerous attempts made to

develop reliable methods for determining the swel-

ling properties of soils. Kariuki and Van der Meer

(2003) reported that swelling prediction depended

on factors related to clay minerals such as plasticity

index (PI), cation exchange capacity (CEC), colloid

content, and X-ray diffraction (XRD). Classification

of swelling soils usually relates swelling potential to

PI. Seed et al. (1962) suggested classification of soils

according to their swelling potential indices: low

(0.0�1.5); moderate (1.5�5.0); and high (5.0�25.0).

Moreover, understanding the behavior of sodic soils

with application of different water sources to main-

tain acceptable soil physical properties is an impor-

tant issue that should be studied and addressed in

arid and semi-arid regions.

The present study aimed to investigate the effect

of increasing soil sodicity on some physical proper-

ties of three soils varied in their clay contents using

two sources of irrigation water.

Materials and methods

Soil samples

Soil samples of different clay contents from cropped

fields: sandy loam (SL) collected from Az-Zarqa

vicinity located 30 km north east of Amman; clay

loam (CL) collected from Ramtha vicinity located

60 km north of Amman; and clay soil (C) collected

from Noaimeh vicinity located 65 km north west

of Amman. Soils classified as Typic Xerorthents,

Xerochreptic Calciorthids, and Haploxerolls, respec-

tively (JOSCIS, 1995). Scanning electron micro-

scope (SEM) observations and XRD method were

used to identify types of clay minerals. The clay

mineralogy of studied soils is dominated by kaolinite

and vermiculite.

Surface soil samples (0�20 cm) collected from

random locations. Sieved through a 2 mm opening

sieve and kept in plastic jars for analysis. Selected soil

physiochemical properties were determined using

standard methods of soil analysis: particle size

analysis using the pipette method as described by

Gee and Bauder (1986), and bulk density using the

clod method as described by Blake and Hartge

(1986). Soil pH measured in saturated paste extract

as described by McLean (1982), CEC as described by

Palemio and Rhoades (1977), ESP using ammonium

acetate method (Thomas, 1982), soil organic carbon

(SOC) using Walkley�Black methods as described by

Nelson and Sommers (1982), and electrical conduc-

tivity (EC) measured in saturated paste extract as

described by Rhoades (1982). Soil physical and

chemical properties are shown in Table I.

Treatment of Na � soil samples

Three lots of each soil were treated with sodium

bicarbonate (NaHCO3) solutions to obtain ESP’s

equivalent to 10, 30, and 50. The adopted procedure

was similar to that of Bains and Fireman (1964).

Each soil was spread in layers of 10 mm thick on a

polyethylene sheet and the proper amount of sodium

bicarbonate solution sprayed by means of special

sprayer. The treated soil covered for 2 days with

another polyethylene sheet to reduce evaporation

and to provide time for sodium bicarbonate solu-

tions to reach equilibrium with treated soils. Con-

trols treated with distilled water using the same

procedure. All treated soils mixed manually, allowed

drying slowly for several days with 3�4 mixings a day.

Table I. Selected physical and chemical properties of clay (C), clay loam (CL), and sandy loam (SL) used in study.

Texture

Property C CL SL

Sand (%) 28.0 44.7 74.5

Silt (%) 19.3 18.5 11.9

Clay (%) 52.7 36.8 13.6

OC (%) 0.80 0.81 1.59

CEC (cmole(�) kg�1) 30.62 27.21 11.80

BD (Mg m�3) 1.23 1.32 1.45

pH 8.13 8.12 8.08

EC (dS m�1) 0.36 0.63 0.95

Main clay mineral Vermiculite Vermiculite and kaolinite Vermiculite and kaolinite

Note: EC, electrical conductivity; BD, bulk density; CEC, cation exchange capacity; OC, organic carbon. (Average of three replications).

Changes in selected soil physical properties 85

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The EC and pH of targeted and obtained ESPs of

treated soils presented in Table II.

Chemical analysis of the two irrigation sources,

namely; sodic and spring water is presented in Table III.

Hydraulic conductivity test

Treated soil samples with ESP of 0, 10, 30, and 50

packed in Plexi-glass columns (5 cm ID and 8 cm

length). Two sources of irrigation water percolated

through soil columns at constant hydraulic head and

the flow rates were then measured. Hydraulic con-

ductivity (HC) at steady state is:

HCs�Q

ADt

L

(H2 � H1)

HCs is basic saturated hydraulic conductivity, Q is

the volume of the water that flows through the sample

of cross section area A in time Dt, and (H2�H1) is the

hydraulic head difference imposed across sample

length L.

Aggregate stability test

Aggregate size distribution of treated soils performed

using a wet-sieving method. Approximately, 40 g of

1�2 mm aggregates saturated slowly by capillarity

and placed on a 0.25 mm opening sieve using wet-

sieving apparatus (Kemper & Rosenau, 1986).

Samples immersed in water, raised and lowered

through a 1 cm vertical distance at 30 cycles per

minute for 5 minutes. Stable aggregate mass (SA)

calculated by measuring the oven-dried materials

remaining on the sieve after oscillation (Beare &

Bruce, 1993). The fraction remained on the 0.25

mm sieve immersed in NaOH solution to disperse

the soil particles and then oven dried at 1058C, and

reweighed to obtain sand mass (SM).

Water stable aggregates percentage (WSA) is

calculated as follows:

WSA��

(SA � SM)

(SOM � SM)

��100

WSA is the percentage of water stable aggregate

in the soil, SA is the stable aggregate mass in g,

SM is the sand mass in g, and SOM is soil original

mass in g.

Swelling test

Soil swelling is a term generally applied to the ability

of a soil to undergo large changes in volume due to

increased moisture content. Essentially, the swelling

indices predict whether sodium-induced dispersion

or salinity-induced flocculation will more greatly

affect soil physical properties. Several swelling po-

tential indices used to estimate the swelling potential

(Kariuki & Van der Meer, 2003). An empirical

model by Nayak and Christensen (1974) was applied

to evaluate the swelling potential in treated soils.

os�0:0761548 �Ip �C=wn�0:222854

os is the free swelling magnitude, Ip is the PI, C is the

clay content, and wn is the natural water content.

The PI defined as the numerical difference be-

tween the plastic limit and liquid limit of soil, and it

is an indirect index for free swelling.

The plastic limit is that moisture content of a soil

at which it becomes too dry to be plastic. Approxi-

mately 20 g of soil paste was prepared and a thread

of about 3 mm thickness was rolled uniformly with

equal pressure and then the moisture content was

determined. The liquid limit of a soil can be

Table II. Selected chemical properties of treated clay (C), clay loam (CL), and sandy loam (SL) soils at 0, 10, 30, and 50 exchangeable

sodium percentages (ESP).

Texture EC (dS m�1) pH ESPm SAR ET* (dS m�1) EC�ET

** (dS m�1)

C 0 0.36 8.13 0.90 0.6 0.09 �0.27

10 0.50 8.88 9.20 6.1 0.40 �0.10

30 0.75 9.80 22.9 15.1 0.91 �0.16

50 1.10 10.50 46.20 30.5 1.77 �0.67

CL

/ ES

P

0 0.63 8.12 0.50 0.3 0.08 �0.55

10 0.71 8.85 10.0 6.6 0.43 �0.28

30 1.0 9.65 34.2 22.6 1.32 �0.32

50 1.38 10.1 49.6 32.7 1.89 �0.51

SL 0 0.95 8.08 0.70 0.5 0.09 �0.86

10 1.20 8.70 9.60 6.3 0.41 �0.79

30 1.60 9.20 27.90 18.4 1.09 �0.51

50 1.82 9.9 47.7 31.5 1.82 0.00

Note: EC, electrical conductivity; ESPm, measured exchangeable sodium percentage; SAR, sodium adsorption ratio; ET* , minimum level of

electrolyte required to maintain the soil in permeable conditions in dS m�1. ET�0.056 SAR�0.06 (Quirk, 1986); EC�ET**, surplus of salts

in the minimum level of electrolyte concentration. (Average of three replications).

86 N.I. Eltaif et al.

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measured by the liquid limit apparatus; in which soil

samples of about 40 g were seated in the dish, mixed

with the different irrigation waters and soil in the cup

divided with a grooving tool, then the cup lifted and

dropped by turning the crank at a rate of approxi-

mately two revolutions per second until the two

halves of the soil pat come together along a distance

of about 13 mm. The moisture content at the

intersection of the flow curve and the 25 hits line is

the liquid limit (Guarnieri et al., 2005).

The experiment was conducted using completely

randomized design (CRD). Each treatment was

replicated three times. Significance was tested using

one-way ANOVA between treatments with subse-

quent mean separation by student’s least significant

difference (LSD) test using the John Macintosh

Product (JMP) 5.1.2 (SAS 2003) program.

Results and discussion

A detailed analysis of the effects of soil sodicity

expressed by ESP on HCs with respect to water

source indicated that HCs for each soil decreased

linearly with increasing soil sodicity. McIntyre

(1979) noticed that the decrease in HC associated

with an increase in the ESP, and the decrease in the

total electrolyte concentration of soil solution.

A regression analysis of the effects of ESP on soil

HCs showed a linear decrease with increasing soil

sodicity (Table V). It is clear that ESP significantly

decreased HCs in all treated samples for both

irrigation water sources. The rate of reduction in

HCs with increased sodicity depended on soil

texture and source of irrigation water.

Water source impact on hydraulic conductivity of sodic

soils

The basic hydraulic conductivity (HCs) of different

soil textures as affected by two water sources

percolated through each soil is shown in Figure 1.

In the two water sources, a reduction in HCs was in

all soils at different ESP values. For example, at ESP

of 30, the HCs values in SL, CL, and C were about

6.2, 2.3, and 3.0 mm hr�1 with spring water and

2.8, 1.2, and 1.2 mm hr�1 with sodic water.

The amount of electrolyte required to prevent the

deterioration in soil structure is the threshold con-

centration (ET). The threshold concentration con-

cept simply expresses the minimum level of

electrolyte required to maintain the soil in a perme-

able condition for a given degree of sodium satura-

tion of the soil colloids. Quirk (1986) indicated that

the decreases in HCs at electrolyte concentrations

below the threshold concentration are usually occa-

sioned by extensive development of diffuse double

layers which give rise to enhanced swelling. Mechan-

ical failure associates with this swelling and defloc-

culation of clay particles. The higher values of HCs

in SL soil could be attributed to the surplus of salts

in the ET of electrolyte concentration in treated soil

especially at the higher ESP, i.e. 30 and 50 compar-

ing with other two soils (Table II). The data showed

that although EC of treated soils increased with

increasing ESP; the values of EC were not high

enough (below 2 dS m�1) to be effective in reducing

the deteriorating effect of high sodicity.

Results indicated that if the sodicity of applied

water (i.e. sodic water) was high relative to soil

sodicity; swelling of clay particles would occur and

consequently a decrease in soil HCs. In contrast,

application of irrigation water (i.e. spring water) with

low sodicity and salt concentration above the thresh-

old level (ET) tends to cause relatively high HCs

(Table III). The average depths of applied water to

soil textures at different ESP levels presented in

Table IV. It appears that with increasing soil ESP the

average depth decreased for both water sources.

Table III. Chemical properties of sodic and spring irrigation water used in experiment.

Water sample pH EC (dS m�1) Na� (meq L�1) Ca2��Mg2� (meq L�1) SAR ET

Sodic 8.1 2.8 18.7 0.4 41.8 2.4

Spring 7.8 0.63 0.9 1.2 1.2 0.13

Note: EC, electrical conductivity; SAR, sodium adsorption ratio; ET* , minimum level of electrolyte required to maintain the soil in

permeable conditions in dS m�1. ET�0.056 SAR�0.06 (Quirk, 1986). (Average of three replications).

0

5

10

15

20

0 10 30 500 10 30 500 10 30 50ESP

HC

S

Sodic water Spring water

C CL SL

Figure 1. Saturated hydraulic conductivity (HCs) in clay (C), clay

loam (CL), and sandy loam (SL) at 0, 10, 30, and 50 exchange-

able sodium percentages (ESP) with application of sodic and

spring water. (Average of three replications).

Changes in selected soil physical properties 87

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At ESP :50 the average depth was almost the same

in both water sources, indicating that swelling was at

maximum. Moreover, at ESP �30 the average

depth of applied water decreased sharply in all soil

textures and for both water sources. It is worthwhile

to notice that the absolute values of the slopes which

represent the rate of reduction in HCs values with

increasing ESPs of soils were generally higher in

spring water treatments as compared with sodic

water. Table V shows that SL soil gave 0.28 and

0.11 as a rate of decrease in HCs with spring water

and sodic water, respectively. Moreover, in all runs,

no particles in effluent were observed indicating a

limited particle mobility within our soil system. It

seems that clay swelling governed the process of

irrigation of sodic soils, and caused clay particles to

plug soil pores and reduce HCs.

Texture impact on hydraulic conductivity of sodic

conditions

The rates of decrease in HCs with increasing sodicity

were characteristically distinct for unlike soil tex-

tures. The reduction in HCs occurred in all soil

textures but certainly in different ratios according to

soil sodicity, irrigation water source, and clay con-

tent and mineralogy. Irrespective to the water

source, HCs values decreased with increasing ESP

in all studied soils (Figure 1).

In general, the comparison between all soil tex-

tures revealed that SL soil had been distinguished

among the other two soil textures by higher values of

HCs. The lowest HCs values obtained in C soil

especially with spring water application as shown in

Figure 1. Soils with coarser textured soil like SL

contain relatively large number of macropores which

allow for relatively rapid flow of water through the

soil. When swelling induced by application of irriga-

tion water particularly sodic water, this attenuates

soil structure and reduce HCs.

Both C and CL soils showed a noticeable low

values in HCs presumably due to the nature of

expanding clay mineral in these soils (vermiculite).

Furthermore, our results showed that reductions of

HCs in soils containing expanding clay were more

severe at ESP :30 or higher depending on irrigation

water source (Figure 1). Shainberg and Letey (1984)

indicated that swelling and dispersion could cause

plugging of conducting pores with dispersed clay

particles which in this case could be the main cause

of HCs decline. Since clay swelling and pore plug-

ging were responsible for the decrease in HCs, one

would expect that soils with greater proportion of

macropores (i.e. SL soil) to be less susceptible than

soils with finer pore size distribution (CL and C

soils). On the other hand, narrower conducting

pores can significantly decrease the hydraulic con-

ductivity of any soil, because they are more likely to

trap dispersed particles (if any) leading to pore

clogging.

Levy et al. (2003) reported that the higher organic

matter content through the sandy matrix of a poorly

aggregated soil minimized the effect of aggregate

slaking responsible for the decrease in HC in most

cases. SL soil has higher organic matter than C or

CL soils and this may also explain the relatively high

values of HCs for SL soil. Clayey soil with vermicu-

lite clay mineral of specific surface (600�800 m2g�1)

characterized by interlayer water and the ability to

expand experienced noticeable swelling which con-

tributed in HC’s reduction. On the other hand,

kaolinite of specific surface (7�30 m2g�1) which has

no tendency to expand existed in SL soil in

considerable amounts (Table I) and played a role

Table V. Regression equation and coefficient of determination (R2) for saturated hydraulic conductivity (HCs) as related to exchangeable

sodium percentage (ESP) and water source.

Texture Spring water Sodic water

C HCs��0.18 ESP�8.12, R2�0.760 HCs��0.07 ESP�3.71, R2�0.842

CL HCs��0.13 ESP�7.22, R2�0.982 HCs��0.11 ESP�5.21, R2�0.983

SL HCs��0.28 ESP�16.25, R2�0.923 HCs��0.11 ESP�5.66, R2�0.997

Note: Average of three replications.

Table IV. Average depths of applied water to clay (C), clay loam

(CL), and sandy loam (SL) soils related to exchangeable sodium

percentage (ESP) and water source.

Water source

Texture Spring water Sodic water

C 0 74 54

10 62 40

30 40 30

50 8 7

CL

/ ES

P 0 84 64

10 62 55

30 42 38

50 9 7

SL 0 94 72

10 70 67

30 47 37

50 15 14

Note: Average of three replications.

88 N.I. Eltaif et al.

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in restricting major swelling effects in this soil

texture. In general, HCs decreased with increasing

sodicity of soils; however, the rate of decrease

depends on many factors such as soil texture, clay

content, and the organic matter content (Lado et al.

2004).

Effect of sodicity on aggregate stability

Results of this work indicated that the water stability

of aggregate (WSA) varied according to many factors

such as soil type, ESP level, and source of used

water.

In general, a conspicuous reduction in aggregate

stability observed in the course of using different

water sources with increasing ESP (Figure 2). The

differences in aggregation among the three soil

textures may pertain to many factors, e.g. total clay

content, clay type, and organic matter content. Since

the mineral compositions were not similar for soils;

clay mineralogy was probably the most important

factor affecting soil aggregate stability since the

mineral compositions were not similar for soils

(Table I). Previous study by Barzegar et al. (1977)

showed that soils with high shrink swell potential

associated with high aggregation. However, in sodic

conditions WSA was relatively low in studied soils

and probably this was due to swell and breakdown of

clay domains.

Irrespective to soil texture, results showed that

with application of spring water (at ESP�30) WSA

was 27%, 12%, and 11% in SL, CL, and C soils,

respectively. While application of sodic water (at the

same ESP level), WSA was 24, 10, and 9%.

It seems that some internal swelling was likely to

occur to an extent which can be determined by the

ionic concentration of the percolating solutions

(SAR). Water source affected WSA significantly,

however, if the ESP level increased, the WSA would

decrease more steeply in SL soil by using spring

water (Figure 2).

The C and CL soils are both characterized by high

clay content and of about the same organic matter

(OM) content (0.8%). Both soils had lower WSA

compared to SL soil and could be attributed to

breakdown of soil aggregates by differential swelling

which could enhance by high clay content. Aggre-

gate resistance to slaking was more probable with the

increase in clay content especially in soils containing

�30% clay (Nayak & Christensen, 1974; Emdad

et al., 2004). Barzegar et al. (1997) explained that

aggregate strength influenced by many soil proper-

ties such as exchangeable cations, clay content, clay

type, and the amount of dispersible clay. Rahimi

et al. (2000) added that when clay particles floccu-

lated and aggregated by calcium ions and organic

matter, they might not extensively involve in binding

or cementing other particles. Therefore, total clay

content may not reflect the stability of soil aggre-

gates, and the increase in aggregation may not be

significantly affected by the clay type.

Results indicated that when sodic water applied,

WSA of soils decreased with increasing ESP. The

lowest value of 7.5% observed in the CL soil at ESP

of 30 compared to 8.6% in C soil and 14.3% in SL

soil (Figure 2). Barzegar et al. (1997) stated that the

proportion of water stable macroaggregates (�250

mm) in soils increased with increasing the organic

matter content and decreased with increasing sodi-

city. The aggregate stability in SL soil was the

highest among studied soils due to the high organic

content as reported earlier. Organic matter content

of soil may play an important role in physical and

chemical binding of primary soil particles and thus

increases the soil stability and its resistance to

dispersion and swelling (Lado et al., 2004). The

relatively high WSA observed in SL soil at different

ESP levels could be due to (1) the high organic

matter content (1.59%) which may act strongly to

bind soil particles or (2) due to the low content of

expanding clays that may reduce dispersion of soil

aggregates. Caravaca et al. (2001) suggested that

total clay content and organic matter were more

important in soil aggregation. Our results indicated

that aggregate stability could be affected mainly by

soil texture (clay content, type), OM content, ESP of

soil, and SAR of water source.

Sodic water

0

5

10

15

20

25

30

35

40

WSA

- ε

s

Swelling Potential WSAC

CL

SL

Spring water

0

5

10

15

20

25

30

35

40

ESP

WSA

- ε

s

Swelling Potential WSA

C

CL

SL

0 10 30 500 10 30 500 10 30 50

0 10 30 500 10 30 500 10 30 50

Figure 2. Water stable aggregates (WSA) and swelling potential

(os) in clay (C), clay loam (CL), and sandy loam (SL) at 0, 10, 30,

and 50 exchangeable sodium percentages (ESP) with application

of sodic and spring water. (Average of three replications).

Changes in selected soil physical properties 89

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Swelling determination

Swelling of soils can be determined in different

techniques, but most of these are rather expensive

and provide little information about the parameters

controlling the swelling process. In C soil, swelling

potential os was 10 in the control and ranged from 14

to 22 in other treatments regardless of the water

source (Figure 2). According to Seed et al. (1962)

classification, the resultant (os) values were above 5

in all treatments, and this classified as a high swelling

value. In CL soil, application of spring water

increased os from 10 to 18 at ESP :10 and 50,

respectively (Figure 2). On the other hand, applica-

tion of sodic water had little effect on os regardless of

the ESP value.

When spring water applied to SL soil, the os

increased from 13 to 14.3, and with sodic water

from 14 to 16 at ESP :10 and 50, respectively. In

general, C soil experienced the highest free swelling

levels possibly due to the amount and type of clay.

Vermiculite as the dominant mineral in such soils has

ability to expand freely in the presence of sodium

ions in waters especially in sodic water.

This work concluded that if soil sodicity combined

with the used marginal water quality, this could lead

to low permeability, clay swelling, and eventually to

land deterioration. However, further research and

more data are needed to delineate more clearly the

interrelationship between surface charge density and

swelling of clay minerals which could then be

correlated with forces that could cause problems to

physical properties of soils.

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