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ῑ῏῎ῒΐῐ
No. 23, p. -ῌ+- ῍,**,῎Maximum Potentially Dispersible and Stabilizable
Clays under Cropping in Soils with Inherent
Textural Di#erences
Velu RASIAH*, ** and Tahei YAMAMOTO** Arid Land Research Center, Tottori University, Hamasaka, Tottori 02*ῌ***+,
Japan (Corresponding address)** Permanent address : Department of Natural Resources, PO Box +*/., Mareeba,
Qld. .22*. Australia
Abstract
Physical and mechanical stresses induced changes in clay dispersion is a major sustainability
and environmental issue, particularly in large-scale intensive agricultural production systems.
However, the dispersed clay may re-stabilize when the stresses are reduced or minimized/
removed. The objectives of this study are to (i) quantify the maximum potentially dispersible(DCmax) and stabilizable clay (SCmax) in soils with textural di#erences when the stresses wereintroduced and reduced, respectively, and (ii) identify the role of inherent soil variable(s) on DCmax
and SCmax. Dispersible clay measurements were conducted at monthly intervals for - years onseven soil types under di#erent cropping treatments. The cropping treatments used in this study
were conventionally tilled continuous corn (CTCC) and forages, which were established in +323 onplot that were previously under CTCC for more than +* years. The CTCC represents stress
imposed and the forages the stress reduced system. The DCmax in the stress imposed system acrosssoils ranged from -., to +0.0 ῌ compared to 0.. to --.2 ῌ, the total clay (TC) content. The DCmax
increased with increasing TC and decreasing soil organic matter (SOM) content. The SCmax in the
stress reduced system across soils ranged from +., to ../ ῌ and it increased with increasing TC and
SOM. Eleven to -1 ῌ of the DCmax was re-stabilized during the --year period under forages, i.e.
stress reduced system. The amount of SOM in the soil at the time of switchover from CTCC
played a signiﬁcant role in the re-stabilization of dispersed clay, particularly in soils with similar
TC. The results show the stabilization of dispersed clay under reduced stresses depended on
DCmax and SOM.
Key words : Dispersible clay, Stabilizable clay, Soil texture, Soil organic matter, Physical andmechanical stresses.

+.

Introduction

Dispersed clays in soils under cropping, canbe a major sustainability and environmental
issue, because of its association with runo# anderosion. In the highly mechanized intensive
agricultural production systems the physicaland mechanical stresses induced by multiple
tillage, heavy machinery wheel tra$c, andwater impact energy from over-head sprinklers
are, at least partially, responsible for increases
in clay dispersion. Number of environmental
factors, such as freezing and thawing (Rasiah
and Kay, +33.) and wetting and drying cycles
also play a role in clay dispersion (Caron andKay, +33,a & b). Weakening and breaking of‘ῌclay῍-ῌsoil organic matter (SOM)῍-ῌclay
῍’ bonds during SOM mineralization, removal

῏

4



of polyvalent cations, particularly Ca,, from‘clay-Ca,-clay’ bonds, and Ca,displacement by Na, under saline condition,
are examples of chemical stress induced clay
dispersion (Baldock and Oades, +33*).
Dispersed clays in soils have impact on soil
physical, chemical and biological processes.
Clay dispersion induced aggregate bondweakening enhances aggregate breakdown
when soils were subjected to further physicaland mechanical stresses (Rasiah and Kay, +33/a; Shanumuganathan and Oades, +32,). Clay dispersion increased sediment load in runo#(Rasiah and Kay, +33/b ; Isensee and Sadeghi,+320 ; Miller and Baharuddin, +320), decreased
water inﬁltration and conductivity in soil proﬁles (Collis-George and Greene, +313), and may
decrease the proportion of habitable pores for
microbes through pore clogging.
The dispersed clay (DC) in a given non-saline
soil under cropping increased with increasing
gravimetric soil water content (q) (Rasiah et al.,+33,). On the other hand, the DC in texturally
di#erent soils increased with increasing total
clay content (TC), soil pH, and q, and decreasing SOM (Rasiah et al., +33,). When q increased
to a potential maximum value, qmax, then potential existed for the dispersed clay to approach apotential maximum value, DCmax (Rasiah, +33.).
In texturally di#erent soils, the DCmax and qmax
depended on TC and SOM (Rasiah, +33.).
Though it is known that under ﬁeld conditions,at least a small proportion of DCmax may restabilize during soil drying, the major proportion would remain dispersed or weakly bonded(Caron and Kay, +33,a & b). The weakly
bonded sites are points of potential failurezones, which are responsible for aggregate
breakdown under physical and mechanicalstresses.
When the physical and mechanical stresses
inducing clay dispersion under conventional
corn were reduced, through switch over toforage-corn rotation, the dispersed clay restabilized during the forage phase (Rasiah andKay, +33.). Furthermore, inclusion of forages

23

,**,

in rotations or as legume covers increased
water inﬁltration (Cassman and Rains, +320),
improved porosity (Disparte, +321), and protected soil surface from rain and sprinkler drop
impact, thereby preventing crust formation(Disparte, +321). Though re-stabilization of dispersed clay might have had several beneﬁcial
e#ects on soil water processes, limited information, however, exists on maximum potentiallystabilizable clay (SCmax) under forages of cornforage rotation. Thus, quantitative information on physical and mechanical stresses induced clay dispersion under stressed systems
and that on stabilization under reduced
stresses are essential. Therefore, the objectivesof this study are to (i) to provide quantitative
information on DCmax and SCmax when the
stresses were imposed and reduced, respectively, in soils with textural di#erences and (ii)identify the role played by inherent soil variable(s) on DCmax and SCmax.
,.

Materials and methods+) General
The data used in this study is from crop
rotation and tillage experiments established in
1 sites (Table +) in Ontario province, Canada, in+323 and continued until +33+. Before +323, theexperimental sites, in farmers’ ﬁeld, were underconventionally tilled continuous corn (Zeamays L.), CTCC, for at least +* years. Conventional tillage involved plowing in the fall,
followed by secondary tillage in the spring.
The CTCC treatment represents the physicaland mechanical stresses imposed system, andthe forage phase in corn-forage rotation the
stress reduced system. Crop rotations at thesites included cereal-forage or soybean-forage
rotation. In this study, however, we will present the data relating to CTCC and corn-forage
rotation only. During the sampling period thecorn-forage rotation plots were in the forage
phase. The forages included in the rotation
were alfalfa (Medicago sativa L.) in soil .,bromegrass (Bromus inermis L.) in soils +, ,, -,and 0, and red clover (Trifolium pratense L.) in῎῍ : Maximum Potentially Dispersible and Stabilizable Clays under Cropping in Soils with Inherent Textural Di#erences

Table +

Soil description and selected properties

Soil description
Soil type

Series name
(US classiﬁcation)

5

Soil properties
Caly

Silt

Soil organic
matter

CaCO-

pH(ῌῌῌῌῌ g/ +** g soil ῌ or ῌ ῌῌῌῌῌ)+Brookston clay
(Typic Haplaquept)

--42

,14-

-4-

*4**

/411

,

Brookston clay
(Typic Haplaquept)

,+4+

.,4-

-4+

*413

14--

-

Tuscola silt loam
(Aquic Hapludalf)

+24/

/043

-43

*4+0

040*

.

Conestoga silt loam
(Aquic Eutrochrept)

+24-

/,4*

-43

+4/*

14,

/

Conestoga silt loam
(Aquic Eutrochrept)

+143

/-4.

-4.

,4*.

14+1

0

Wattford loamy sand(Arenic Hapludalf)

04.

+*4.

,43

*4**

04.*

1

Fox loamy sand(Arenic Hapludalf)

04.

+/41

,4,

*4+*

/42.

soil / and 1. The experimental design at eachsite was a randomized complete block withfour replications. Crop, fertilizer, weed, pest,
and disease managements were carried out according to the recommendations of the Ontario
Ministry of Food and Agriculture (+322a and b).
For further experimental details and other related information, the readers are referred to
Rasiah and Kay (+33. and +33/a, b) and Rasiah
et al. (+33,).
,) Soil sample collection and laboratory
analyses
Soil cores (1 cm diameter and 1 cm length)were collected from the surface * to 1-cm layer
at four randomly selected locations from each
replicate at monthly intervals from May
through September in +323, +33*, and +33+. The
soil cores from each replicate were thoroughly
mixed, and approximately one-quarter of themixed moist soil sieved, on a mechanicalshaker, using a nest of sieves with mesh openings of +*, ,, and + mm, respectively, and ashaking time of one minute. The aggregatesretained on the +-mm sieve, i.e. + to ,-mm aggregates, were used for the dispersible clay (DC)and ﬁeld soil water content (q g/g) determinations. The + to ,-mm aggregates from the +323
soil samples were also used for particle-size,
soil organic matter content, SOM, pH in a + : +soil : water mixture, and calcium carbonate
content (Page, +320) determinations.
The
results of the analyses are reported in Table +.
Dispersible clay measurements on the ﬁeld
moist + to ,-mm aggregates were conductedusing the procedure described by Pojasok andKay (+33*). In brief, three /-g subsamples of theﬁeld moist + to ,-mm aggregates from each
replicate were prewetted on a wetting table at+ cm suction for 3*-min using deionized water.
The prewetted sample was transferred to a /*-ml test tube using .*-ml of deionized water.
The suspension was shaken in a mechanicalshaker for +*-min and then transferred to a ,/*-ml conical ﬂask using another 2*-ml ofdeionized water. After a .*-min settling time
(calculated using Stakes Law), the DC in thesuspension was determined, using a colorimeter previously calibrated for each soil. The DC
is expressed as a percent of total oven-dry soil
mass. The q in the + to ,-mm aggregates was  23  ,**,

6

Table ,The maximum gravimetric soil water content (qmax) and the maximum potentially dispersible
clay (DCmax)
Soil type

Soil property
qmax(g/g soil)
DCmax (g/+** g soil)

Table -

+

,

-

.

/

0

1

*4.0
+040

*4..
+,42

*4.2
04*

*4./
/41

*4.*
142

*4-1
-4,

*4.*
/4.

The dispersible clay at average water content and that at maximum water content expressed
as a fraction of other variables
Dispersible clay type and its relationship with other variables

Soil type

DC (ῌ)

DCmax/TC[DCmaxDC (ῌ)]A

A/DCmax

A/TC

+
,
.
/
0
1

/420
/4+,
,403
,411
-4.*
,4*0
+4,,

*4/*
*40+
*4-*4-,
*4..
*4/+
*42.

+*411
140.
-4,2
,431
.4-2
+4+0
.4+3

*40/
*40*
*4//
*4/,
*4/1
*4-0
*413

*4-,
*4-1
*4+2
*4+1
*4,/
*4+2
*400

DC (ῌ)/DCmax DC (ῌ)/TC
*4-0
*4.+
*4./
*4.3
*4..
*40.
*4,,

*4+2
*4,.
*4+/
*4+0
*4+3
*4-*4+3

DC (ῌ)dispersible clay at average water content (ῌ), DCmaxmaximum potentially dispersible clay, TCtotal clay in soil.

determined gravimetrically and expressed as afraction of the oven-dry soil mass (g/g).
-) Computations
According to Rasiah et al. (+33,) the dispersed clay (DC) across soil types increased
with increasing soil-water content (q),DCipiqi qi

+where the subscript ‘i’ refers to a given soil.
When qi in Eq. [+] approaches a ﬁnite maximum
value (qmax), then clay dispersion is at its potential maximum and this is deﬁned as DCmax. The
DCmax was computed using Eq. [+], for qqmax,
and the computed values are provided in Table,. The qmax used in the DCmax computations arealso provided in Table ,. The values for pi andqi, for each soil, used in the computation of qmax
and DCmax are provided by Rasiah et al. (+33,)
in their table ,.
Rasiah and Kay (+33.) developed a model, topredict the net amount of clay re-stabilized byforages, in corn-forage rotation, and theydeﬁned this as SCnet,
SCnetpq qf+ektqcqcqf ,
where SCnet is the di#erence in DC between
that under CTCC and the corresponding forage
treatment. In Eq. [,] the p, q, k, and qc aremodel parameters, which were estimated using
experimental data. In Eq. [,] q is equal to thedi#erence between q of forage and corn andsimilarly for p. The subscript ‘c’ refers tocorn, ‘f’ to forage, the superscript ‘k’ a rate
constant, and ‘t’ is time, in months, after the
introduction of forages in corn-forage rotation.
The values for the parameters in Eq. [,] areprovided by Rasiah and Kay (+33.) in theirtable -. The amount of dispersed clay that canbe re-stabilized by forages, i.e. under reduced
stresses, as ‘t’ approaches inﬁnity has been
deﬁned by Rasiah and Kay (+33.) as maximum
potentially stabilizable clay SCmax and they῕῔ : Maximum Potentially Dispersible and Stabilizable Clays under Cropping in Soils with Inherent Textural Di#erences

Table .

7

The stabilized clay expressed as a fraction of dispersed clay
Stabilized clay and its relationship with dispersed clay types

Soil type

+
,
.
/
0
1

ῒ

ΐSC (ῌ)ΐSC(ῌ)/TC ΐSC(ῌ)/DC(ῌ) [DCΐSC(ῌ)/ΐSC(ῌ)/DCmax
maxῐDC(ῌ)]

.4/+
-4*,
+411
+42*
,4*3
+4+1
*4//

*4+.
*4+.
*4+*
*4+*
*4+,
*4+3
*4*3

*411
*4/3
*400
*40/
*40+
*4/1
*4.1

*4.,
*4.*
*4/.
*40+
*4.2
+4*+
*4+.

*4,2
*4,.
*4-*
*4-,
*4,1
*4-1
*4++

ῒ
ΐSC (ῌ)ῑstabilized clay at average water content (ῌ), DCmaxῑmaximum
potentially dispersible clay, TCῑtotal clay in soil, and ΐDC (ῌ)ῑstabilized clay at
average water content (ῌ).

showed, through appropriate re-arrangementof Eq. [,], that SCmax can be computed using thefollowing equation,
ΐSCῌq῍ῑῌΐpῐΐq q῍

῎-῏

where q is the average soil water content overthe growing season in a given soil. The ΐSC(q),computed using Eq. [-], for the 1 soils are provided in Table ..
-.

Results and Discussion+) General
The total clay content (TC) in the soils
ranged from 0.. ῌ to --.2 ῌ, the texture fromloamy sand to silty clay, and the soil organic
matter content (SOM) from ,., to -.3 ῌ (Table+). The clay mineralogy is dominated by illite,with subordinate amounts of chlorite, vermiculite, and hydroxy-interlayered vermiculite(Baldock and Kay, +321 ; Evans and Cameron,+32-).
Depending on the length of time (t) after the
introduction of forages, in corn-forage rotation,soil moisture content (q) at sampling, and thesoil type the amount of dispersed clay (DC) inthe soils ranged from *.*/ ῌ to +, ῌ (Rasiah etal., +33, ; and Rasiah and Kay, +33.). In general,the DC was high in soils with high TC, suggesting that source strength played an importantrole on the amount of DC in soil under ﬁeld
conditions. The DC in the 1 soils increased

with increasing TC and q, but decreased withincreasing SOM and soil pH (Rasiah et al. +33,).
The DC in the 1 soils decreased with timeafter the introduction of forages and subsequent to change over from conventional tono-till system (Rasiah and Kay, +33.). Rasiah
and Kay (+33/b) showed that runo# and sediment load, from soil /, increased with increasing DC, regardless of the cropping treatment.
Though runo# simulations were not conducted at the other sites, we anticipate similar
trends from these sites. Indirect evidence forswelling, during wetting, induced structuraldestabilization and reduction in inﬁltration
rate was derived positive associations that existed between DC and runo# (Rasiah and Kay,
+33/b). From the foregoing, it is evident that
DC in the 1 soils played important roles insurface and subsurface soil water ﬂow, and thespatio-temporal changes in DC depended oninherent soil variables, q, and cropping andtillage management practices.
,) Maximum potentially dispersible clay
The maximum potentially dispersible clay
(DCmax) in the soils ranged from -., to +0.0-g
clay/+**-g soil (Table ,). Rasiah (+33.) showedthat DCmax increased with increasing TC anddecreasing SOM, but was determined largelyby the source strength, i.e. TC. The DCmax
estimates, computed using the equation provided by Raisah (+33., Eq. 1) show that +..+-g

8



clay/+**-g soil was potentially dispersible insoil +, at -./ ῍ SOM, and the estimated DCmax
increased to +/.0 g clay +** g+ soil when the
SOM decreased to -.* ῍. This suggests that +*῍ increase in clay dispersion was associatedwith *./ ῍ loss in SOM, possibly through Cmineralization. Similar estimations for soil 0
show that only 0 ῍ increase in clay dispersion
for *./ ῍ reduction in SOM, suggesting theimpact of C-mineralization on clay dispersion
was higher in clay soil than in loamy sand.
The clay dispersed at maximum soil watercontent (qmax) is also potentially available fortransport in surface and subsurface ﬂow (Table,). Because, the clay dispersed at qmax is freefrom soil aggregates, it can be transported in
inﬁltrating water and may clog soil pores
during soil drying. The soil water status favorable for maximum clay dispersion to occur
usually arises after rain or irrigation events.
Thus, in soils with high TC, potential existed
for large quantities of the clay to be dispersed
at qmax and transported in surface and subsurface ﬂow. In soil +, with --.2 ῍ TC, the DCmax
was +0.0 ῍, implying that ῌ /* ῍ of the TC was
potentially available for transport in ﬂow compared to ῌ2. ῍ of the TC in soil 1 (Tables ,and -). Even though the absolute amount of
the DCmax was higher in soil + than in soil 1, alarger proportion of it in relation to TC was
potentially available for transport in runo#
from soil 1. The least amount of DCmax was
found in soil - and . that are characterized byhigh SOM, indicating the importance of SOM
in decreasing clay dispersion at maximum soil
water content.
Even though Rasiah and Kay (+33/) showedthat runo# or sediment load and DC(q) was
positively correlated, in reality though it seems
that DCmax should have been correlated withruno# and sediment load.
During dry-spells that follow rain or irrigation events, the amount of dispersed clay insoils will decrease with decreasing q, i.e. a corollary of the positive empirical relation between
dispersed clay and q (Rasiah et al., +33,). Thus,

23

,**,

the obvious question now is what is the fate ofthis DCmax during soil drying? During soil
drying the DCmax, at least a small proportion of
it may re-stabilize, temporarily, through weak
clay-clay bonding or be deposited on
aggregate surfaces and/or pore walls. During
re-wetting the temporary bonds may break
and release free clay. Evidences for temporary
weak bonding and for the release of free clay
have been provided by Caron and Kay (+33,a).
Thus, we suggest the clay that is potentiallyavailable for re-stabilization through changes
in cropping and tillage practices is that present
at qmax, i.e. DCmax. On the other hand, Rasiah
and Kay (+33.) used the amount clay dispersed
at average ﬁeld water content [DC(q)] as thatavailable for re-stabilization through changes
in cropping and tillage systems.
Because, the qmax soil water status (Table ,) isshort lived, we computed DC(q), for each soil, asa fraction of DCmax [DC(q)/DCmax] and TC [DC(q)/TC] (Table -).
The di#erence between
DCmax and DC(q) is the amount that was dislodged from soil aggregates through saturation and is in a relatively dynamic or in an
un-aggregated state and readily available fortransport. Thirty six to 13 ῍ of the DCmax or +2
to 0/ ῍ of the TC was in dynamic or unaggregated state. Exclusive of the loamy sand
1, /, to 0/ ῍ of the DCmax in silt loam and clay
soils were in un-aggregated or dynamic state
and we suggest that this fraction of the DCmax
need immediate re-stabilization attention.
The DC(q) is the amount of dispersed claythat is in a weakly bonded state due to soil
drying, but may disperse or disaggregate
during saturation. When DC(q) was expressed
as a fraction of DCmax (Table -), it showed that,, to 0. ῍ of the DCmax was DC(q), suggestingthat soil drying played an important role in
reducing the amount of clay available fortransport in water. In clay and silt loam soils,-0 to .3 ῍ of the DCmax was DC(q), The highest
and lowest percents were associated withloamy sands, suggesting inherent soil variables
other TC playing a temporary role in the stabi- : Maximum Potentially Dispersible and Stabilizable Clays under Cropping in Soils with Inherent Textural Di#erences

lization of dispersed clay during soil drying.
The major emphasis on clay dispersion inthis paper is that induced by mechanical andphysical stresses and dynamics of the dispersed clay in relation to soil water status.
However, it is important to recognize here that
dispersion induced by salinity, particularlythat arising from saline water use, may be amajor issue in arid, semi-arid, and tropical environments. Several studies have shown theimpact of salinity on decreases in soil hydraulic conductivity through pore clogging by thedispersed clay (Sumner, +33-). Gypsum application was e#ective in restoring, at least partially, conductivity under saline condition.
This suggests, the pore clogging clay particles
were transported or translocated away frompore walls after gypsum application and were
probably re-stabilized in aggregates. Limited
quantitative information, however, exists on
the fate of dispersed clay under forages inforage-cereal rotations in saline soils.
-) Maximum potentially stabilizable clay
The amount of dispersed clay (DC) underforages in forage-corn rotations decreased withtime, during the - yr period, in the 1 soil types
and the DC under forages were always less thecorresponding continuous conventional corn
treatment (Rasiah and Kay, +33.). The aforementioned provides evidence for the foragephase induced stabilization of clay that was indispersed status under corn. As time approaches inﬁnity, the DC under forages may
decrease to near zero and the amount of clay
stabilized would be at its potential maximum,
SCmax. The SCmax at growing season averagewater content, q, is deﬁned as SC(q). The 
SC(q) is the di#erence in dispersed clay between the corn and forage treatment. During
the --year period, the SC(q) ranged from +.+1
g clay +** g+ soil to ../+ g clay +** g+ soil
(Table .). The SC(q) had been shown to increase with increasing TC, SOM, and soil pH(Rasiah and Kay, +33.).
The clay stabilized by forages ranged from 3
to +3 ῌ of TC (Table .). According Rasiah and9Kay (+33.), the fraction of the dispersed claythat was stabilized by forage is SC(q)/DC(q).
Thus, according to them .1 to 11 ῌ of the dispersed clay was stabilized by forages in - years(Table .).
However, in reality though, asmentioned elsewhere in the text, the total dispersed clay in a given soil is DCmax. Thus, SC(q) was expressed as a fraction of DCmax (Table.). This form of expression revealed that only++ to -1 ῌ of the DCmax was stabilized byforages. We also indicated elsewhere in the
text the di#erence between DCmax and DC(q) is
the amount that was in a relatively free ordynamic state. Therefore, we expressed  SC(q) as a fraction of this di#erence (Table .).
This computation indicated that +. to almost
all the so-called free state clay was stabilized
by forages. Ironically, the highest and lowest
stabilization of the clay in dynamic state
occurred in the loamy sands. The highest stabilization occurred in the loam with the highSOM and the lowest in the loam with low SOM.
This suggests the SOM present at the time of
introduction of forage probably played an important in enhancing the stabilization of theclay in dynamic state.
The maximum amount of clay that can bestabilized by forages depended on the dispersed clay pool and we have shown this poolis DCmax and not DC(q) as indicated by Rasiah
and Kay (+33.). The DCmax is a much larger poolthan DC(q) in a given soil (Tables , and -), andDC(q) is only ,, to 0. ῌ of DCmax. The DCmax
increased with increasing TC and decreasing
SOM (Rasiah, +33.). The SC(q) showed atrend to increase with increasing TC or DCmaxor DC(q) and/or SOM (Fig. + and Table .).
Therefore, we explored SC(q) as a function of
TC and SOM, or DCmax and SOM, or DC(q) and
SOM using the stepwise variable selection procedure. The analyses produced a signiﬁcantrelation only with DCmax and SOM independent
variables,SCq+1/*,/ DCmax*/0 SOM
R,*30 and P **+.



10

Fig. +

23,**,

The relationship between maximum potentially stabilizable, [ῌSC (ῌ)], or dispersible, [ῌDC(ῌ)], and total clay (TC).

Equation [.] indicates that SC(q) increased
with increasing DCmax and SOM. However, therole played by DCmax is di#erent from that ofSOM.
The amount of clay that can bestabilized by forages depends largely on thedispersed clay pool. This pool could be either
TC or DCmax or DC(q). The aforementioned
analyses, i.e. using TC or DC(q) or DCmax as
the clay pool, indicate that DCmax is the poolthat determined SC(q) and not TC or DC(q).
Equation [.] also indicates that SOM enhanced
clay stabilization when the dispersed pool was
not a limiting factor. For example, in the
loamy sands (soils 0 and 1) with 0.. ῌ clay
content, the inﬂuence of SOM on clay stabilization is higher in soil 0, with ,.3 ῌ SOM, than insoil 1, with ,., ῌ SOM. The SOM clay stabilization enhancement role was signiﬁcant only
when DCmax was used as the dispersed clay pooland not TC or DC(q). This provides further
support to our hypothesis that DCmax is poolthat determined the maximum potentiallystabilizable clay.
The enhanced e#ectiveness of SOM in clay
stabilization under forages, suggests the binding materials arising from short-term forages
were more e#ective under high initial SOM
and is consistent with the results reported byother workers (Nadler and Letey, +323 ; Swift,+33+). The results are also compatible with theobservation made by Baldock and Oades (+33*)
that Ca, addition during straw decomposition
resulted in increased structural stabilization
through synergistic e#ects.
We suggest that in soils with high DCmax theorganic binding materials produced by shortterm forages were more e#ectively utilized
during clay stabilization. This probably led tothe immobilization of the organic materials inthe stabilized aggregates, thereby leading togradual increases in SOM. The aforementioned
hypothesis is consistent with the ﬁndings of by
Dormaar and Foster (+33+).
As mentioned elsewhere in the text, quantitative information on the stabilization of dispersed clay in saline soils under forages is
scarce. Recently, however, Mitchell et al. (,***)
showed that soil aggregation under legume
winter cover crops, followed by summer
cereals using saline water for irrigation, washigher than without cover crop treatment.
Further, the stability of soil with gypsum treatment and saline water use was less than covercrop. However, surface soil salinity was higher
under winter cover than the gypsum treatment. Unfortunately, the changes in clay dispersion after saline water irrigation and wintercover crop treatment were not measured in῍ῌ : Maximum Potentially Dispersible and Stabilizable Clays under Cropping in Soils with Inherent Textural Di#erences

this study. Nevertheless, the results indirectly
show that clay dispersion might decreased
after the introduction of winter cover crops
according to Rasiah et al. (+33,), who showednegative correlations existed between aggregate stability and dispersed clay (Rasiah et al.
+33,).
Even though the forage phase in forage-cornrotation was e#ective in stabilizing dispersed
clay, the practical applicability of this rotation
is limited, because, such rotations may not be
economically feasible or acceptable. Further, if
animal husbandry is not incorporated in thefarming systems then e$cient utilization of
forages is limited. Thus, it seems winter covercropping or under-seeding green manurelegumes in cereals, particularly under corn,more appropriate than forage-corn rotations.
..

Conclusions

In previous studies, the dispersed clay at average ﬁeld water content [DC(q)] was considered amount that was available for stabilization when forages were introduced (unstressed
system) in forage-corn rotation. In this study,
we show the maximum potentially dispersible
clay (DCmax) is the pool that was available forstabilization when the forages were introduced. The DCmax is much larger than DC(q),which ranged from ,, to .3 ῌ of DCmax acrosssoil types. The DCmax under conventional corn(stressed system) ranged from -, to 2. ῌ of thetotal clay (TC) across soil types. This indicatesthat substantial quantities of TC were in dispersed state in the stressed system. When theimpact of the stresses were reduced, throughthe introduction of forages, the dispersed clay
re-stabilized and the amount stabilized ranged
from ++ to -1 ῌ of the DCmax across soil types.
The sources strength, the total clay content(TC), determined DCmax pool and consequently
SCmax. Soil organic matter (SOM) had opposing
e#ects on SCmax and DCmax. The SCmax increased
with increasing SOM in a given soil and acrosssoil types. Thus, we suggest SOM conservationand management not only enhances clay stabi

11

lization, it may contribute towards C-sequestration in soil, particularly under reduced tillage systems. C-sequestration in soil may help
in reducing the concentration of green housegases in atmosphere.
/.

Acknowledgment

The authors gratefully acknowledge theﬁnancial support provided by the Japanese
Ministry of Education, Culture, Sports, Scienceand Technology to the ﬁrst author as a visiting
Professor to conduct research for one year at
the Arid Land Research Center of the Tottori
University, Japan.
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ΐ¼ : Maximum Potentially Dispersible and Stabilizable Clays under Cropping in Soils with Inherent Textural Di#erences

13

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J. Jpn. Soc. Soil Phys.
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No. 23, p. +/,. ,**,

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*ῌ **
Anisotropy of Drainable Macropores in Andosolsand Alluvial Soils
Yukiyoshi IWATA* and Hajime NARIOKA*** National Agricultural Research Center for Hokkaido Region,
Shinsei, Memuro-chou, Kasai-gun, Hokkaido *2,ῌ**1+, Japan** Faculty of Environmental Science and Technology, Okayama University,-ῌ+ῌ+ Tsushima-naka, Okayama 1**ῌ2/-*, Japan
Abstract
Since macropores signiﬁcantly inﬂuence the movement of water and air in the soil, it seems thatthe structure of macropores should determine the processes of drainage.

A study was conducted

to investigate the structure of macropores and the associated drainage process.

The drainage

characteristics of volcanic ash and paddy ﬁeld soils were investigated, and the following results
were obtained.
(i) The structure of entry pores depended on the direction of sampling. We constructed amodel of entry pore structure, and found that this phenomenon is thought to reﬂect the shape ofdrainage macropores, especially the joints of tubular pores that have di#erent diameters.
(ii) The results of drainage experiments using a +** cm- cylindrical sampler were thought tohave been greatly a#ected by the inner wall of the sampler.

Nevertheless, it could be said thatwall-a#ected results show soil drainage characteristics better than non-wall-a#ected results.

We

constructed a model of drainable macropores structure to explain this phenomenon. The shapesof pF-distribution curves were di#erent depending on the direction of sampling when soil was
sampled using a +** cm- cylindrical sampler.

This could be explained by assuming that large

tubular pores in the network of macropores were in a vertical direction and smaller tubular pores
were in a horizontal direction.
Key words : macropore structure, drainability, anisotropy, soft X-ray imaging method, sampling
scale

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20

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Fig. 3

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Fig. +*

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Fig. ++

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Fig. +,

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345"' 678
 ,AB 29 6:;<+=)*>?!9 @AB
.. +. ,  

CD E.. +. +F /G HIJ 2
3K+'  L *.- mm MN/
078OP!,-"  QRST

25"8UVWXQR  ,AB  Y$Z ῌ+.

pF #;f23>?!st

[*  \]=^_ V  
1

`

a

(b^

=^+ cdFig. +.

 ` a (b+'eL =^*5'+ X fgh Eijk῏++ +,F  QRSoil structure of samples which haveanisotropy in pF-distribution curve.

 lm* :;n+op^.. , $qr"[ "st5'+

+** cm- pF 

." L *.- mm MC=eL  E+3/,F pF  ;f(!'"

;f( pF #;f$u GHIJ

MC(,' QR/u

%&3'p^(" ." E+323F

st k῏+- EvF wxl!p^(L.G!p pF xp()L pF #

!Xy
ῌ



6=^[9 :  

;f($!(*!peL  Y'[* eL  "V"  +l m+',-!p^9 +w῍

69 : z \]=^+_ V
῎V pF #;fj!23.

 $¡[/¢st V+

6ῌeL %9 :   eL qr'+

+** cm- }%{£0¤¥¦§pV@w

@+ ['++l 2%5'O 
 

p

6  %"{p  eL =:;n+"#{p|[ }{z# $' $qr"[=~!5'=~!

ijk῏2 p { G pF #;f2STV¨1['+ $p©ª

["{"" pF #;f(

 2u ;f«3¬(,' © ª
23­(o" $%& $"#  eL %
)* =^=~[p %&' 
=^*,-
MC QR® ¯ °® a ±,AB²` a ±` ¯ °Bw,

"{
³pV5"ST eL "{p  eL  !=
"s    CDw pF #;f(© pF ´µ/u,(*!;fpV!¶ $" p2 VG" ;f2{p  =$qr"

3·z,-+ $p k῏+. w"s 5'+,-x,¸¹º(,-"4] : 9^*_º»¼N^_[ 545 w8&23

   
    !

" #   $% !
 

 &   '( &)*+,  / 0.!

( ! 1%  &!  pF 23 45$6(7&89:
;<!=%>? 145@ῌ+/ ijk¹M § \<Cd

AB X 3C

 DE῏+,F   G   *.+H*., mm IJ

Fig. +/

E#ect of sampler-wall to drainage
experiment.

% K  pF 23LMN pF +.-H+./
DOP *.+*H*.+/ mmFI"  X 3C !"I% !

! Q#R pF 23ST$U1J&8!VW( 41%XY& pF 23

45Z=.!':I!()[&8;<!=%I^_ ῌKῌB8a s@  R%5"  S( &8 P|%5L=<( I a%! ! P|S7 ¡¢1\]! ^_`a Y&4
51b +** cm- 

*8

pF 

Df£¤&81f 4I
 X¤w= I8AB¥=K" 1J `a+523,$Xc  Cdefg
;<!=%.. - &8! `""JJ&8

;<!=%8aY&%M!=% & !`a1S7¦$ G+** cm- 

b-5.O? 45h ij

+5%XY& .: &8;<!=%kljmnoMp/0(  D <q12 +31*!!  7/  N*O(; 9r ,***F%&8`a1>§¨¦$ &@`a DE῏+/ ῍F%  +5,$?   `Y&3sh

+5 45

N*+ - !`a1¨

8$6! I8 t8uv Iijkl& * PQf1"

jmnoMp/0 w8&+ x41( &81

5© .. +

J % 5y`a  +** cm-  (

5Iª$618;< % 1 `¤ .. , ;~(

 ` + +5 Cdefz[&8!

*%QRf1! `J&;<  ! {/0 w8&x46'5I

=1  !%  - ¬% ! |7,$(

D+** cm-  F '(+5}8;~%9 &C ? : ;<=5Q8  ;

Y'ST1% K

 X 3C &CABK" 5nn$6!C(DE῏+* ῎F% P| &Da S(I!`fE &8% ! ;F GHP|%5 4P|

pF 2

3 ­U8 &8`a  ® VW¯ IX
=(° [  ;
231% !`a    18>§¨r>=8: ?:@=f
1" AB&C1f1IJ % K«!

8& ±²³´MNY&>§Xc Yµ( 18;< %¶ +** cm-  ,$(ῌ

+5  E῏+/V`a '(  - %XY& D±²³´M
NY&F efYµ( % G·¸p «!
¶Z *[;+%J& *+'()  23 ¼ w,**,x24

  

X6YZῌP[\ῌ]^ w+32-x : Z

2022O+ 78_`y a!

     


!"

#$% &  #'  () 



*&  +** cm- "

'bDe /. : .3*ῌ.32yc]

d w+31*x : %

efghR2y a! 'bDe .+ : ++3ῌ+,*yi

jῌklῌW

mῌnop w+3/,x : :;< ' '7!D) y Gkqr B , : 31ῌ+,,y +, -"  Mori, Y., Iwama, K., Maruyama, T. and Mitsuno, T.

./01234$5%6  +7 (+333 a) : Discriminating the Inﬂuence of Soil

$8 

*9"

Texture and Management-Induced Changes in/ῌ ῍ ῐ ῏ ῎Macropore Flow Using Soft X-Rays. Soil Science,+0. : .01ῌ.2,.

!" :;<# +=>$% $& +**cm- ?@'()+=* X +AB$C D,) E*9 :;<#  FG-H 


 

(I

./



>$%  FG-0 J12K3L   ( 4
2K3L)

4$ME  +** cm-

Mori,Y., Maruyama, T. and Mitsuno, T. (+333 b) : Soft
X-ray Radiography of Drainage Patterns ofStructured Soils. Soil. Soc. Am. J., 0- : 1--ῌ1.*.

s

KNOP5$6%  >$%  pF ./012346"(VI*&WX9 ./01234
Y:; ($*&    Z[\]^<" _=`a"

()=

 w+33,x : ef

:;<

u+

¡v¢wD) g*9y FjGk etq . : -/ῌ.-ys  w+33-x :S8$TU  +S  'O/0ys+7 :;<# 42
778G+G+Q?@2K+7R

 w+323x :D) y FjGk etq  + : +ῌ'Q` Oy a!

'bDe 0. : 3*ῌ31ysῌ£%¤ῌlHIm w,***x : DF¥2^ g x¦+==y

Gk Wev">  ,*2 : 0-ῌ1+ys ῌlHIm w,*** ax : yzY{DF¥2^
L"2K|}  §_Ey Gk
Wev">  ,*2 : 33ῌ+*/ybc !">$  I7?d@ eABs ῌlHIm w,*** bx : ¨~ 

CfghiWD?@ =7EE 

DF¥2^ ©ª3 Py Gk

FjGk elHImhi:;< 'JKE noh`$p, q LrM Ns

)Wev">  ,+* : +3ῌ,1yo w+33/x : «'P4|}()¬ D) y ­%®/Gk¯er ,+ : +ῌ03yῑ ῔ ΐ ῒ%°\ w+30-x :Bouma, J (+32+) : Comment on “Micro-, Meso-, andMacroporosity of Soil”. Soil Sci. Soc. Am. J., ./ :'()OtuvP w+312x :'()Oy

p. ,1, QzR Fjy{|ST w,***x :'7G+}~%%U'()#78V$

D) *9y Gk Wev">  ,*3 : +ῌ+-y

²³gῌs¡|+,..ῌ+,./.

NOP efghDyGk W± 1 : -,ῌ-1y
ῌLBH° w+32.x :

+

´O

'P* X +6E*9y Gk Wev">  ++. : 0+ῌ1.y²³gῌoῌµ¶ῌ·f w+32/x : ¸% # gEy'() /+ : .3ῌ0,y¹º»a : ,**+  , » ,- a¹)»a : ,**+  +, » +- a῔
J. Jpn. Soc. Soil Phys.
./A*B'
No. 23, p. ,/῍-- ῎,**,῏  *ῌ **ῌ

**ῌ

**

Ion Concentration Prediction of the E%uent during the Sulfuric
Acid Solution Permeation into Volcanic Ash Soil.
Kouji KAMEYAMA*, Susumu MATSUKAWA**, Tomoyasu ISHIDA**
and Hidemasa KATO*** The United Graduate School of Agricultural Science, Tokyo Universityof Agriculture and Technology, Fuchu, Tokyo +2-ῌ2/*3, Japan** Faculty of Agriculture, Utsunomiya University, Utsunomiya -,+ῌ2/*/, Japan
Abstract
The prediction method of ion concentration in the e%uent during pH - sulfuric acid solution
permeation into the air-dried volcanic ash soil column was examined in this study.

The method

for prediction was composed of chemical reactions between acid solution and soil, and mixing cell
model.
The chemical reactions were composed of aluminum dissolution, cation exchange between
dissolved aluminum and basic cations, bicarbonate formation, sulfate ion adsorption, charge
valance and mass balance of sulfate ion and basic cations. Cation exchange between dissolved
aluminum ion and soil bases were lumped together with the mineral weathering as acid bu#ering
e#ect.

Mixing cell size depends on dispersivity and that value was determined by the break-through curve during KCl and pH - sulfuric acid solution permeation.
Characteristics of the variable charge on volcanic ash soil were considered in the simulation
model by applying the anion adsorption equation (Wada, +32+) in which adsorbed amount of
sulfate ion depends on pH and sulfate ion concentration.
The simulation results agreed well with the measured values of pH, aluminum ion concentration and cumulative release of basic cations in the e%uent.

These represent the most serious

e#ects of the acid deposition on the soil. Therefore, parameters used in this simulation model areuseful for predicting the main e#ect of the acid deposition on the Kanto loam subsoil.
However, it could not estimate basic cations concentration of the e%uent with good accuracy.
This discrepancy may reﬂect the assumptions that cation exchange treated as aluminum-divalent
basic cation exchange, the equilibrium constant was assumed and exchange between hydrogen
ion and cation was not included. Therefore, it is necessary to describe the cation exchange inmore detail.
Key words : acid deposition, volcanic ash soil, chemical equilibrium equation, Mixing Cell model,
simulation*  +2-ῌ2/*3  ! -ῌ/ῌ2** "#$ -,+ῌ2/*/ "# %! -/*ῐῌῒῌῑ : &'()*+ ,-./+ 0123456786+ 9:;<+ 20=>?2@3ΐ  26

ῌ+ µ]  ῌNQ:b+    

 

23 ¼ ,**,

Table +

 pH KCl
pH H,O     Bloom and Grigal, +32/ ; Reuss|rN ῍῎*+
CEC cmolc kg¦+῎*,
cd&'( cmolc kg¦+῎*,
Ca,¶
Mg,¶
K¶
Na¶
cdC&'( cmolc kg¦+῎*Cl¦
NO-¦
SO.,¦
[·

and Johnson, +320 ! "  #$%&'()*+,-./&'(0
Gaston et al. +33,

1 2345  ! 676 8 9:;<= =26 > ?@A BC&'(DE2FGHI J!
K L
 MN6JO P
NQ RS +33.    +333   Ishiguro and Nakajima, ,*** !N B82
T"I ! 8 > ,  0 X+,=-NQ.YZ=/ 01[2
]^9 

*40,
*41*4/1
*4+2

+40+
*401
.4*3

*¸¹(

# * : NC *º&»1*, : Shollenberger #*- : *.*+ M NaOH # , g : +/* ml l&'9 +332 b  ()ῌW* +332 1

!

.43/4-1
,4*2
,,4-0

+

U#V$ %" !

J3\ pH )&'(45!NPhysical and chemical properties of soil!

JK ?@A !<b= 

676  6 pH !N $%&'(J> pH 2&'(45!N1C&'(cdcNG 601 _[2JG27896 `!Nb=0! bP T# 326 aI ! bP \  # pH 2T&'(45!N1 T  6&'(cdJGNQ:

201 _[2=e\821 f>;\:J<g h,J2H9 !

8b=34H > &'(DN2 pH
K&'(452=-Z d* +32+

i= j>@?@k#ABC? D
Elmn FM82OGI ! @B-H
El6

&'(DNO!N82 H9 !

DoIJK=pq2r0=e/6 T&'(DX+,=+N6!

LJ,   1 se65:MtJu=BMvw x?I
 > yz{, Mt! "  D
-D256 |rN OJ P)QRῌ, +  fghRijMQklA3

NOOJ2H9 ! 8 > S T}~

mn@ .*0* cm oI796

JG:X+, )ῌU +33, )cd$D=/ !

%X+, VI 
2H9 !
26 @BX>?@A  J ῌNQ:b=- -+ 6 ! JK  #-ῌ+ p¡=#P !

8   6 3\
Y/

W /*῍ =Y/D =Z6 !

<¢q Schoﬁeld =# rs +300 ¡£¤B ! J¥ HCl "  NH. OH  pH = -3
tu6*., mol L¦+ ¦NH. Cl # /* mL =]o -U#  2#2vB [JNQ.Y

g vP §w¨©xyª§z1{6 |}^#=

Z 2  _ [ 2 =   :  -  Mixing Cell   +«~¬= +* ­®16 +* ­|}^# pH

Appelo and Willemsen, +321 =/ ! "  \= 6 =.Y# pH 2^J6 ! ¯1 B°T#=oIJK=G6 ]o±^] *., mol L¦+ ¦KNO- #= /* mL ©

 /I #&'(45 2 7t²³79§z1{6 |}^#=´>

34579

~¬=®1! ´> |}^#=c26 86

U#2^_`=a6

 : 89:X016./5(6)%

27

 + ,Sst_.vE )%   !

(6#[T;5/. SO.,,, NO-,, Cl, )%UV$W.P5 O)%   ! pH #~f Al- Ca, Mg, K Na #=
Cl, NO-, SO.,, #./&   ! Mw $tXY[.K    Z[ \# *.03.j*.1*, cm- cm, + h^# .1.*3j.3.0+ cm- %- !


, -

7 ./51]^ _;5 O ``Z7-FG5'(  )cmolc kg,+*5a ; b.4GF7 C%
O ! c )+323* ./0 7 C%

ῌ+ ns 
Fig. +#

Electric charge of soil.



af )molc g  aC%7 d\e.M-

ῌ+ 

  !

,+ ,+

s *

E5!


B

(6 )% f  gA  h[FO h[a7 \PQ.iFj W.
! ;5Q DC7 C% O !

"# pH 0./ $%& pH 1 '( )CEC* +'( )AEC* #  /.0
cmolc kg,+ -.2 cmolc kg,+ %- !

, . 

01k # 016 ¡&lm¢£/&O !

, , 

Hd /* mL ¤n_ - ,.

Ishiguro and Nakajima ),**** ./0 123

 |U.

-/ mL

7V / gmUVo ! 

  + 4%516789:.

m[ p ¥ +2 PQp  ¤qr[ s;5< =7> ?@ .! 7

t¦6 vE ! st¦6vE[§¤n_.# pH"A5B 7#CD.EFG5! H  $I2J

 , - . .uv016-* mL m

1%.&';5 pH 167;5<# +2 PQp  ¤qr st¦6vE w {Q(6 pH ! @KL)%! MN¡&l ! st¦6# R{ -* mL ;5 O.*PQ7+ M5! B O¨ / mL,RS# 6 F T-UC )+33/*©&vE6# *../ mm ª«Kg 9

./

vE

xG j¨.~f  pH



  !

y= z¬ [ ./pH- 016 1  !

V234 5W XYZ 6 O 7V [ , mm 89\ :] - cm *E +- cm
^K_`.V2;% *./, g cm,-  +* cm aE.<ῌ Liu et al. )+33**#bcd. pH- 016

&01)%   !
H P01k#­3{DC®

a ! C* : m01)% )mol L,+* V* : m./ =_>?@A016 )L* CN : N {Sm[|¯01)e^fghi./& /*% )mol L,+* VN : N {Sm[`6 )L* VrN

j0* m h,+ )kKlBC ,.*,m+*,-j,.--m+*,- cm: N {Sst¦6vE[©  )L*s,+ .&'* no !

S01°}# )CN,+mVrN,+C*mV** ,CNF (6 lp

qrg )st_ + ,' &D ,* mL* uvE! Mw $t# ,-x yzF , {b- ! GH.#aE *.. cm |I}] +0*j,/* mm ~fKg J hi./&no 0167`K .;5/.LM !
N

3,,**j+*,*** mLO.PmVN OC B
)molc g,+*G;! N {V~ )g* zFk

F®a !

BFOCpH 01)%k±². k³ )? +32+*

01

%F#O !

, / 

Os[T;5 Mixing

Cell ´Kµ¶.IF

t_,Q7 .2*j/3* , OI M- ! B O s

·.4GF>*7¸¹%5!

t_ +* ,R.(6 pH st_ -* ,R.(6 >*

;5 O.# Qº|BC »¼

v*b » 23 ¼ ,**,

28<+ ij1*klmKῌ,Table ,

Chemical equilibrium equation, equilibrium constants and conditions used in ion
concentration prediction of the e%uents+¥  ¡ ¦§ L ¨©L Al-_..,30ª+*-H+. 3,+1
 Al-H, O_AlOH,H Al-,H, O_AlOH
, ,H

-
logK_9/.*, Wolt, +33.
logK_93.-* Wolt, +33.

,¥ $ 
 ,Al--ExCa_-Ca,,ExAl« Ca 2' Ex 2( ExCaExAl_+-¥ ¬ m CO,H, O_HHCO-9

logK H

logK_91.2, Wolt, +33.

.¥   FG  ­ FG SO.,9 _*.**2 ®SO.,9¯*.,0- ®H¯*.,/1
Al-SO.,9_AlSO.
/¥-
logK_-.,* Wolt, +33.

+ &kY
&kY Fw_3.2..ª+*9+, molc g9+ s9+-0¥ =>°bno

9 9
SC
i Zi _SCi Zi
1¥ I)±,9SO,9+°SO,9. mol : ²;³_²;´. AlSO. FGSO.  Camol : ²;³_²;´ +°CaFGCa²;´ ¹mol9²;³ ¹molµ¶no·¸_º*.**+²;³ ¹mol BreakthroughCurve BTC : - 

    !"# $%&'()#*

+, -./ BTC 0 12)34506 7
8 *.+ mol L9+ 9KCl

- + 

ij1*klmK m no3p0q+0, :; <+BC, 1r 3` s- btu1@v=>? 1@/ BTC 0AB 7

wx f y45, -.U z{C DEFG0H

|3*u}0*B ~1@~ !"IJ

KLML van

Genuchten and Wierenga +320 1DENOP

0QC R0AB ST@UAB/V5
WXYR1  K0C2B R

Z0[ Mixing Cell \]^1Q

88 D : R cm, s9+ a : RZ cmv : 5WXY cm s9+ 06 3` KClb Ca, Mg, { + f6

b K Na {0 b Ca, Mg, {!"+.2 # )#* 8B $ 2 %1 ,

D_av

2 3h

+,

$


0Hb$Mg  K  Na ;i
,

Al-

 Ca,

pH u 1 6 Ch 1 %B CEC 

pH b2$ 12  CEC 2

-./AB/VRZQab0c6

CUh q &k1@ !"

B pH - 2 b0T 0r6b$ +,

1d*C( KCl; 1 
CR0AB KCl+0*:

e0*+0, :;5WX

Y R f0gh

&kY molc g9+ s9+ ;ie0ij1*q /AB ¡LK¢£, -.1`¤ <+ ¡  BC : ¹º».¼+*'  *

Gaston et al.



29

 

+33,

   !
"# $%&'()  *+ !
+

Schnabel et al.

+33+

Khanna et al. +320 ,- 

+ ./+012

34 Gaston et al., +33,  52678&+9# 
 !"#: *+ !

;

Mixing Cell - ,<=:>?@ ABC=# ;; C=#B !+DEF#  GH+ !:IJ?@BKL, M NOPQ:RS ῌ,

pH- *'!8¤4

Fig. ,

E%uent pH and cumulative release ofbasic cations.

TU V3 W <=:XYZIJ Mixing Cell 012:;
B

Mixing Cell +[\+]! "^#_,Appelo and Willemsen+`:

+321

Mixing Cell +[\Ba#!bM ῍ #!C' a +- ῑ #:je+je+Cjic+dfCije+c*./ +ef Cie+
cCic+

ftd

῎

,a
fx

῏

fx
v

ῐ

fd+e

῎gῐ #+hiBWj

C : k2*mol

Le+

i : k2$i j : lm$i f : no@pq *rfr+

fx : k2% cm

ft : &slm' sv:

 k2%fx +':]!> W; ῏ # no@pq f
k2+(*

PostmaB+33-

Appeloand

a#+ J,y!PQ:|F:῎ #}o@; o@+(ῑ}~ fx +'B ῑ #:R>-;!
> 

!+<45/+wx:PQ>6;  + ¡:¢!+lmM6;

.B/"
.*+Z
NO-e CleUNO0,- ~ + SO.,e+PQB * + 12+)Z*+
SO.

Cl

e

!

:XY33

+PQBWj /+*e0-+*e- /+*e- mol Le+ ~ M O4B)ῒ+ +O Ca,c Mg,c Kc Nac +@-,.+* cmolc kge+ :PQ;33
- .





. + 

 *+O* !

74:£{T+:8¤;8¤4 pH +¥¦:§ῒ, ¨O Kc

Nac +4:93 /* lm©B!

ª,« ¬ }~ :Aa­;+<  Kc Nac
A- - 

e
-

:

(# NOPQ  !O*; Kc Nac 8¤4B /* lm )ῒ+ ¨;

a
+
r
fx
-

,e

:> ft lm+k2+.῎ #B AH+*9 fx +' W+ῐ # &slm'ft :]!>

PQ(# SO.,e NO-e Cle +mt(uv cm se+ :);
wxy!++, z{ pH O*O Ca

;V3, ®+O* ! Ca,c
Mg

,c

,c



K



+4:93 ¬,~,.- ¯°§ῒ, +!c

Mg,c Bc<v :

Na +<v BWj /.,3.

+*e+, molc ge+ se+ ~ }~..//*

+@- 3.2..+*e+, molc ge+ se+ )ῒ, ῌ # :<v
;
A 1±².³ =´#µ:<v :!;¶· +332 a  4 =´#µ>+ pH? ../ ,~l@Aa­;+<  ¸A W B k2

¸¹ºῐ » 23 ¼ ,**,#

30ῌ- ῒ'89῔·89"I῍
Fig. -

Empirical isotherm applied to sulfate
ion adsorption in batch experiments.

 ῌ/

pH - ῒ'ῌST+
BCD7PQD

Fig. /¡Jῌ¢ pH

Measured and predicted pH in the
e%uent from soil column.

_`<ῒ. =+ & a

pH - ῒ'ῌST1

Lῒ' BTC UV23 WXYZῑ7\];^:;bcdefg.h+ & i ῌjk"lmlnῌST1L BTC I῍+ _` op;^DA KCl ῌ@ +.,-+q+.,23 pH - ῒ'ῌ@+/+.0*-q+/0.*0, @r &῎ "I῍1) \]s a A *.// cm 723Vt?D Mixing Cell uvwC῍R & a,

xyz+ ῒ'ῌSTy{1)|Vt DA }~xfg.ht & e KCl ῌSTy{
UV23 \]sI῍A 7t &. . 

ῌ. WXYZῑ7\];^:;Fig. .

Relationship between average ﬂow
velocity and dispersion coe$cient.

\]s a  *.// cm @rLUV ῑ "1)x+.0/cm +tVR& a

x As+* cm Z\L῎rL@x, cm 7

C+ & e IJA x, cm a*.//ῌ pH  ../ 

 ῏ῌ῔

ῌ῏

῍ "# $% &῔ !ῒ, ῌ

cm ῍R ῏ "1) f*../ 7+ & i <ῒ. =+

1 ῒ'ῌSTy{WXYZῑ v A ,.3q-.-+*[- cm s[+ @r

& PQI῍LnSTy{

WXYZῑ v ttῐ" +. , 

ῒ'ῌ()*+,$+ -./01)23 45& t sA 0*0q03* s @r &6 ῒ'67ῒ'89῔:;. / 

<ῒ- =+ &>+ ?<@Aῒ'67

pH - ῒ'ῌST+t 23¡Jῌ¢ pH PQD

ῒ'89῔:; ῕=+ & BCDAEF

7BCDEF<ῒ/ =+ & PQA !ῒ, @£¤GΐH89"IJ+ <K"ῒ'891¥¦^@rL῏§¨Y©C^ logK# ªQG

L'MNOPQ῍R &«%KCl ῌST1L BTC UV23

ῌ¢ pH BCD7PQDIJbΐR

D¬­®01 & logK2 7+ ¡J pH. -WXYZῑ v

cm s[+# 7\];^ D cm, s[+# :;῎ "I῍+

PQDA

pH BCD7EFGΐH¤¯+

W²@ΐR³´=+° +** ±& ¤µ +,* ±W¶@ pH

 : lmnop* !"#%&"#3]

ῌ0pH - !"#$%&'()*+,-./
012 , 4567890123*

Fig. 0Measured and predicted concentrationof basic cations and aluminum ion in
the e%uent from soil column.

31ῌ2 +,-./012"* 
Fig. 2!012

Measured and predicted cumulative
release of basic cations and sulfate ion
adsorption.

=' +** ABHI   :;M

NJS' +** ABHU

 *.+@*., mmol L>+

VW
+,-./0123XY!0123* +** ABHUZY[\V]
*  ῌ /012^_  `ab clogKd $efb
' , g$h'+,-./012 456789
012 *^_ '[ijk[Y ῍ /012^_
 CEC $J h'[Z lmnop*qr
pH st.$uv'[YYw*xy*

uz

{
. 0 

ῌ1
Fig. 1pH - !"#$%&'()*
3* !012

Measured and predicted concentrationof Sulfate ion in the e%uent from soilcolumn.

/012^_ J|}~* !012
!C ]*.$r +,-.
/012"

!012**:;$<῎2 =' Z +,-./012
" /012^_ J|}~*!C
 * * X
  pH-  *.- !"#$%&'()*+,-./0123 4567890123* *:;$<῎0 =' +,-./0123
  *.+ mmol L>+ ?

 0*@+** AB*CDEFG*<E{ +,-./012"*]Y[  X uz{+** ABHI*3

. 1

<῎3

T

!0123* *:;$<῎1!012  :;MNJS' !C J KL :;MNOP' JQ 45
67890123  NRJS$='

!012

012!C * * X
 pH -!"#$%& ,/ /* 1/ +**+/* AB\'A* pH 4567890123*$='* X9: 14 ¼ 23 ¸ ¥,**,¦

32

ῒῌ3 ¹º» pH,  !"#$%&0xyz
Fig. 3Proﬁles of predicted pH and concentration of aluminum ion at several elapsed times.

  pH  pH _`4e 0e-3
K 54&0"$1q

  !"#$%& '()*+, pH . F+-. /0,0 1234+ A 00\ 45 \¡ + ]¢1q£]\A /ῌ ῎ ῍ ῏45+A} {1q

6789:3;<=> ?@3B pH - +?@ῐ ῔ ΐ ῑC9:DE"FGH I#$%& ?+J/3

?Appelo, C.A. J and Willemsen, A. (+321) : Geochemical-

K 9: +LMNOPQ0RS

calculations and observation on salt water intru-+TUV Mixing Cell WX+Y/<ZH@

sions, I. Acombined geochemical/mixing cell+3 M[ 6789:\]^_`4 Mmodel. J. Hydrol., 3. : -+-῍--*.

Za pH #$%&Nb#$%cd Appelo, C.A. J. and Postma, D. (+33-) : Geochemistry,N4+e3B #$%fg hi#

groundwater and pollution. pp. -,1῍-3/, Balkema,$%& #$%&jk,0+fgQ+3
lm 45 9:=>+n

Rotterdam.
Bloom, P.R. and Grigal, D.F. (+32/) : Modeling soil

1o\pV1q pH r!"#$%

& stp4#$%uvwxyz0?{
zK|V}~ w" 945

response to acidic deposition in nonsulfate adsorbing soils. J. Environ. Qual., +. : .23῍.3/.
Gaston, L.A. Mansell, R.S. and Selim, H.M. (+33,) :Predicting removal of major soil cations andLM=> ?@ ME +{1anions during acid inﬁltration : Model evalua-

230e-3 3 NOPQ0 Mixing Cell Wtion. Soil Sci. Soc. Am. J., /0 : 3..῍3/*.

X+Y/<ZH@

RS+ ?

#$¤% ¥+333¦ : §ῌ9&¨ῌ ©ª'«0&¨  1q,0 !G-3   

pp. 33῍++0 (9:&¨ O¬) *+­ ®¯[stp4#$%&0#$%&xyz,°±- ¥+300¦ : ²³%[´6789:4

K?{z\ ?G- #$%cdF^

0#$%cd¯ .µ¶/· B+1 ¸ : +*1῍++-¯

°± : ²³%{´3Z[µ¶*+,Z·[de~Ishiguro, M. and Nakajima, T. (,***) : Hydraulic conductivity of an allophanic andisol leached with

pqr,sk33

:; 00 : ,+/ῌ,,*

Reuss, J.O. and Johnson, D.W. (+320) : Acid deposition

dilute acid solutions. Soil Sci. Soc. Am. J., 0. : 2+-

and the acidiﬁcation of soils and waters.,

ῌ2+2.

Springer-Verlag., New York.

 +323 : 

pp. 0ῌ+2 "@tῌuvwx +33, : %&'(yz*+,3
Ql-M%{|}~*,s 
Khanna, P.K., Wever, G.T. and Beese, F. (+320) : f +2 : 12ῌ3*

E#ects of Sulfate on ionic transport and balance

Schnabel, R.R., Potter, R.M. and Richie, E.B. (+33+) :in a slightly acidic forest soil. Soil Sci. Soc. Am.

Applying batch-determined retension properties

J., /* : 11*ῌ110.

to predict sulfate transport through soil col-ῌ

!ῌ"#$ +33/ : %&'()*+,-./012%3456789:; 00 : 0//ῌ00,
Liu, K.H., Mansell, R.S. and Rhue, R.A. (+33*) : Cation
removal during application of acid solutions into
air-dry soil column. Soil Sci. Soc. Am. J., /. : +1.1
ῌ+1/-.

<= >ῌ?@ABῌCDE +332 a : FGHIJ
% + KLMN*+,345O %MP
Q 2* : .+ῌ.1
<= >ῌ?@ABῌRSTUVῌWX Y +332 b :3QZ[\]^_`a?`bc%Z[defpH %MPQ 11 : ++ῌ+2

ghBi +33. : 3Qj .k3Ql-M*+mn%oumns. Soil Sci., +/, : ..*ῌ..1.

@ῌSx +332 : 3Q*+,%
Q*+,~kf%3Qyz{2*+, ¡k:; 03 : .11ῌ.21
van Genuchten, M.Th. and Wierenga, P. J. (+320) :Methods of soil analysys. Part +, p. +*--, Klute, A.
(ed.), Agronomy, USA.

¢S£¤ +32+ : %¥¦§ pp. /ῌ/1%:¨  ©ª« 
Wolt, J.D. (+33.) : Soil solution chemistry, pp. +/2ῌ+0+,John Wiley&Sons Inc., New York.
¬­®¯
¬P®¯

: ,**+ ® . ¯ ,/: ,**+ ® +, ¯ +-ῐJ. Jpn. Soc. Soil Phys.
῏῍ῌῐῑ῎
No. 23, p. -/ῌ., ῍,**,῎E#ect of Groundwater Level on Salinity Content
and Environmental Land Classiﬁcation
Chaiyanam DISSATAPORN*, Kane YACOUBA**, Machito MIHARA**
and Rokuro YASUTOMI*** Land Development Department, Thailand** Faculty of Regional Environment Science, Tokyo University of Agriculture
Abstract
Saline a#ected soil is in the northeast of Thailand, especially in the Khon Kaen Province. The
relation between the salinity accumulation in brackish groundwater and the groundwater levelfrom ground surface represents the progress state of soil salinization.
The practice for suitable land use against the salinization can be established when the main
conditions of salinization hazards are known. Based on this concept, the electric conductivity (EC)of groundwater and its level were measured with piezometers for three years in an experimentalﬁeld at Khon Kaen Province. The ﬁeld data showed that the groundwater level much a#ected bysalinity was less than one and half meters from ground surface in the investigated area, and it was
conﬁrmed that the saline soil was mainly caused by the capillary rise of brackish water and by theaccumulation of salt occurred at the soil surface.
Salt accumulation process was investigated by the change in groundwater level. The reducing
e#ect of salinization caused by capillary water rise became remarkable when the groundwaterlevel was lowered until ground surface soil was out of the dominant capillary water zone.
This indicates the reduction of groundwater level was very e#ective in reducing salinization.
Allowing for ﬁeld experimental results, a classiﬁcation map for environmental land use in saline
a#ected area was proposed.
Key words : salinization, capillary water, salt movement, land reclamation, land classiﬁcation+.

Introduction

The prevention of soil salinization is one of
the methods for environmental protection
against deterioration of water and land resources. Many of the agricultural lands in the
Khon Kaen Province, northeastern Thailand,
were cultivated from woodland and forest.
Some low-lying land gave rise to saline soils,
which occurred after the clearing of forest.
Sodic soils were also produced through capillary water rise induced by the high rate ofevapotranspiration, sometimes through ﬂoods.
A number of regions, arid and semi-arid, suchas the northeast of Thailand as well as Mauri-tania in West Africa and others are still being
a%icted with salinization problems and thedeterioration of land productivity.
To decrease the rate of salinization, leachingof the accumulated salts by ﬂooding or drip
irrigation have been found to be e#ective(Goldberg and Uzrad, +310). Farming systems
such as multi cropping or agroforestry are also
said to be e#ective. This idea is based on thefact that mixing fruit plants with cover crops
take up soil moisture e$ciently. The surface
soil moisture content is taken up by shallow
rooted plant such as grass, while the deeper
subsoil moisture is tapped by deep roots,
guaranteeing an e#ective moisture up-take.

῏  23

36

Thus, a reduction in salt accumulation will bepossible (Lovenstein et al., +323). This plantcultivation technique for soil salinity prevention is still empirical. Interruptions of rainfall
and the capillary water rise to the soil surface
using trees are one of the measures for preventing salinization hazards (Dissataporn et al.,,**+ a).
The ﬂuctuation of groundwater level varied
from season to season, and the annual change
in the level was large in the area. Accordingly,
it is not practical to set up a large scale (morethan +** ha for an example) land development
project in the saline area. A small scale project(several ha) is rather suitable for each farmer
because the degree of salinization changes byplaces so that multi cropping land use, andprivate land improvement will be beneﬁcial.
The hillside is usually used for orchard, eucalyptus and cassava cultivation, and the low
land for paddy ﬁelds. For making an environmental land classiﬁcation map for rehabilitation, ﬁeld observations of the ﬂuctuationof groundwater level and its salinity were conducted in this study.
,.

,**,

Fig. +

Topography of investigated ﬁeld with
contour lines above mean sea level andlocation of piezometers (P).

Fig. ,

Soil proﬁles in piezometer P+, P+, and P+-.

Materials and Methods

The ﬁeld experimental site, located ,/ km
southwest of Khon Kaen in the northeast of
Thailand, has an altitude ranging from +11 to+2. m above mean sea level. An annual rainfallof 3-/ mm and soil salinization are strikingly
damaging the area, especially in low land
which gets water logged during the rainyseason. However, the dry season brings abouthigh evaporation rates amounting to ,,*,* mmin a year. The surface soil texture in the area isclassiﬁed as sandy loam (SL) to loamy sand(LS) which belongs to a kind of the lateritic
soils (Wada, +332).
The low land area was much a#ected bysalinization, and ECe (electrical conductivity ofsaturate soil extract) of surface soil was generally over ,* dS/m. Values of more than -* dS/m appeared during the dry season in low land
where salt accumulation had badly damaged

the soil. In the hillside area, the ECe of thesurface soil on average was generally less than+* dS/m through the year.
The items of ﬁeld experiment consisted ofmonitoring of groundwater level ﬂuctuation inall seasons and of estimating the relationshipbetween groundwater level and salinization.
The groundwater level was deﬁned here as the
distance from ground surface to groundwaterlevel. Thirty seven spots were selected in thisstudy area included an area of *.1 km*.1 km
in view of the topography (Fig. +). Piezometers῏῎ : E#ect of Groundwater Level on Salinity Content and Environmental Land Classiﬁcation

Table +

37

Annual standard deviation of groundwater level and electric conductivity of groundwater
Year

+330

+331

+332

Standard deviation of groundwater level from ground surface (m)Standard deviation of electric conductivity of groundwater (dS/m)*41+.43.*

*4.0+
-40*/

*4,1+
,42.,

Table ,

Changes in groundwater level between rainy and dry season (Khon Kaen +330)

Maximum di#erence (m)Average di#erence (m)Low landIntermediate land

Hillside

,40*
*4.0

,4,/
*421

,4.0
-4+1

(P+ to P-1) were set up at each spot to monitor
the groundwater level and its salinity (EC).
Several piezometers did not work properly
after setting owing to breaking down or ﬂoods
so that actual measuring points were ,/ to ,1 in
number, depending on the year. All the depthof piezometers installed was 1 m.
The area investigated was practically divided into three areas based on the contour lines.
These are hillside (῍+2* m high from mean sea
level), low land (ῌ+12 m) and intermediate land
between +12 m and +2* m. The data from eachpiezometer were collected monthly for three
years from +330 to +332. The salinity of thesurface soil (ECe) was measured at several
points. The typical soil proﬁle P+ for the lowland, P+, for the intermediate land and P+- forthe hillside were shown in Fig. ,. The proﬁle ofthe hillside (P+-) is stratiﬁed by SL, while thatof the low land (P+) has ﬁner particles layers
like clay loam (CL) at the depth of *.2 m whichis rather impervious than LS. From these textures, the soil types of the area were classiﬁed
as SL in the surface soil.
-.

Results and Discussion

EC change of groundwater on annualbasis
The groundwater level during +331 and +332
was lower compared with that in +330, which
increased the intensive evapotranspiration
rate during the dry seasons. Standard deviations of the level showed that +330 was the year-. +of ﬂood and high level of groundwater (Table+). From the data, it can be seen that mostﬂuctuations in groundwater level and EC
values occurred in +330.
During +330, the di#erences between the
maximum and minimum groundwater level ofpiezometers indicated less than ,.0* m in low
land and ,..0 m in the hillside (Table ,). The
average groundwater level changes of the piezometers between the rainy and dry seasons
were *..0 m in the low land and -.+1 m in thehillside.
The EC values of groundwater were taken as
mean values of the ﬂuctuating groundwaterlevel for each three consecutive years (Fig. -).
The remarkable di#erences in the averagegroundwater level between the rainy and dry
seasons were observed at the hillside. The low
land and even hillside were often in ﬂood after
a heavy rainfall. The EC values of groundwater doubled from +330 to +331, especially inthe area where the groundwater level was lessthan , m (Fig. .). The increase in salinity ofgroundwater was more conspicuous in the low
land, while the groundwater deeper than , m
had no remarkable increase in salinity. There
was almost no general change in +332 compared to the previous year.
It was supposed that the soil surface wasenough covered in the reach of capillary risewhen the groundwater level was shallower
than + m from ground surface. In this case, thesoil surface was heavily damaged by the salt

38

Fig. -

Fig. .

  23,**,

Fig. /

Example of ﬂuctuation of groundwaterlevel from ground surface in period
during +330 to +332 in P+ piezometer.

Fig. 0

Example of ﬂuctuation of electric
conductivity of groundwater in period
during +330 to +332 in P+ piezometer.

Electric conductivity of groundwatertaken from piezometers for three years
observation (+330ῌ+332).

Electric conductivity of groundwater
against groundwater level from groundsurface.

accumulation. In these circumstances, if thecapillary rise was controlled or reduced, thesalinization hazards could be minimized using
plants, and a new soil improvement practicewill be established (Dissataporn et al., ,**+ b).
-. , Measurement of soil salinity andgroundwater level
It is assumed that the soil salinization process is a function of groundwater level, watersalinity of groundwater and evapotranspiration. The data of site P+ is shown as an example in Fig. / and Fig. 0. The salinity of surface
soil was remarkably a#ected by going up ofgroundwater level. In Figs. /, 0 for an example
of P+, when ﬂoods covered the surface, EC
values of surface soil increased sharply. There
were many ﬂoods in the low land, a discharge
area of groundwater where the salinity waseasily condensed, while the hillside is a re-charge area of groundwater by percolation
through the soil.
The salinity of surface soil was increasing
when the groundwater was shallow. As an
example shown in Fig. 1, the ECe values of
surface soil (*ῌ,* cm in soil depth) were between ,* dS/m and ,2 dS/m.
When thegroundwater level was lower than + m from thesurface during the dry season in +331, ECe ofsoil in P+ was lower than ,* dS/m. The soil,
during the rainy season in +330 and dry season
in +330, had higher salinization than thatduring the dry season in +331, because groundwater levels during the rainy season in +330
and dry season in +330 were *.*0 m deep and*.0- m deep from the surface, respectively. This
indicates that the groundwater deeper than + m
did not give much impact on salinization of thesurface (Fig. 2).
Using the estimate equation of capillary riseH1//d, where capillary height H mm andaverage particle diameter d mm, and another῍ῌ : E#ect of Groundwater Level on Salinity Content and Environmental Land Classiﬁcation

Fig. 1

Changes in electric conductivity ofsaturated soil extract with soil depth inP+ piezomter.

Fig. 2

Relation between groundwater leveland electric conductivity of soil in P+
piezometer.

experimental equations (Scott, +30-, Tabuchi,+31+), the capillary rise was calculated in between 3* cm and ++* cm for the soil proﬁlesgiven in Fig. ,. As the capillary height calculated for P+ fell within 32 cm to +** cm, a critical value for capillary rise may be at about + m
deep from ground surface (Yacouba, ,**+).
Groundwater makes it possible that capillarywater from shallow groundwater level is easily
connected to the surface soil. When the severe
evaporation of the water at soil surface urges
the movement of capillary water, the salt accumulation of water soluble salt contained incapillary water occurs in the low land.
Based on the data obtained in Iran(Matsumoto, +33/), the concentration ofsalinized soil was extremely high at a groundwater level of about 1* cm from ground surface, but if the groundwater level was as deep

39

as , m, the salinization was outstandingly restricted in the case of salt a#ected area.
According to the report by Watanabe et al.
(+332), the upward movement of water consistsof two types, one is liquid water movement by
capillary, the other is by vapor which did notconvey the salinity. From these experimental
investigations, it could be guessed that the lesssaline a#ected soil depends mainly on the typeof vapor movement, and much saline a#ectedsoil on that of the liquid water movement.
Therefore the reducing e#ect of salinization
by capillary water will be remarkable when the
groundwater level is lowered until the surface
soil is out of the dominant capillary water zone.
From above discussion, it can be proposedthat much a#ected area of salt is classiﬁed asvulnerable area A where the top capillary rise(H) situates above ground surface, and lessa#ected area as safer area B where the top of
capillary rise situates below ground surface,respectively.
-. - Salinity based soil classiﬁcation forland use
It can be possibly taken for granted thatsalinization proceeds in the case of the experimental ﬁeld when the capillary water range issituated between * and +./ m, rain water caneasily leaches down the accumulated salts tocondense the groundwater salinity.
The
percolating front of rainwater will induce thecapillary front to go up when they are connected. Then groundwater comes up again to thesurface during the seasons. On the other hand
there is no rapid increase in the soil salinity inthe range deeper than , m where capillarywater rise does not arrive quickly at the
ground surface, though the salinization may
proceed gradually for a long time if no rain.
Reducing the capillary water movement isdecisively important for the prevention of soil
salinization. The up and down movement in allseasons will condense the groundwater salinity
in the ﬁeld. This type of ﬂow will also get thesurface salinization to increase.
On the basis of Fig. ., it became clear that the40ΐῐ῎῔῕ῑ ῒ 23 ῏ ῌ,**,῍

critical level between the area A (much a#ected capillary zone) and the area B (less a#ectedcapillary zone) in the ﬁeld site may be situatedbetween +./ m and , m. The level more than ,m shows that the water quality of groundwater will be useful, if the quality limit of EC
for irrigation is - dS/m (Ayer and Westcot,+310) because over which the relative land productivity decreases remarkably though it
depends on a variety of crops. When the soil
salinization increases up to +* dS/m in ECe, theyield may be drastically damaged (Carter,+32+). The quality of groundwater EC observedin the ﬁeld was about / dS/m, so that it will be
useful for irrigation if it is diluted by fresh
water.
Accordingly, it may be useful for minimizing
the salt accumulation to provide a map showing as follows. The area A is vulnerable to becontaminated by brackish water (less than +./m level from ground surface), the area B is noteasily contaminated by the water (deeper than
, m from ground surface) if well managed, andthe area C is in between both areas. Based onthese standards, the areas with salinization
problem can be classiﬁed as shown in the map(Fig. 3).
The map may o#er a useful data for landdevelopment as well as land conservation andrehabilitation planning in the region with salt
problems. For the area A, reducing groundwater level will be e#ective to reduce the salinity. The irrigation water for leaching will beobtainable from the groundwater in the area B.
The agroforestry cultivation system toreduce the evapotranspiration and to reducegroundwater level will be expected applying
high water use and fast growing trees as
Eucaliptus to the recharge area of groundwater, in particular reforestation may be e#ective in the area B, because the area A and B are
linked with groundwater. If a quick and inexpensive method to identify the salinity in the
ground is applied, the map will be delineatedeasily (Dissataporn et al., +330).

Fig. 3

Land classiﬁcation map of soil a#ectedby salinity using annual averagegroundwater level from ground surface(counter lines fo groundwater level).

..

Conclusion

Capillary rise of groundwater was one of themain causes of salinization. Therefore themost important practice for salinization prevention is to interrupt capillary water rise, andto reduce the groundwater level. In the case of
the site investigated, salinization proceeded
quickly in the area where the annual averageof groundwater level was shallower than +./ mfrom ground surface.
When the surface is out of the much a#ectedzone by capillary rise, the application possibility of plant root system and agroforestry toabsorb the salinity will be worth considering.
A practical way of improving the soil in thearea A is to lower the groundwater level bydrainage to the depth of more than +./ m fromground surface. The leaching with ﬂood irrigation using the groundwater from the area B῍ῌ : E#ect of Groundwater Level on Salinity Content and Environmental Land Classiﬁcation

and C to area A will be useful. The applicationof an agroforestry system in the area B and thearea C may be useful as a practice of the soil
improvement by reducing water supply to thearea A.
Acknowledgements
I would like to thank Prof. Dr. ANASE, M. for
his advices during the course of this work.
Thanks are also due to Mr. Yamclee, P. and his
sta# of Soil Salinity Research Section, Land
Development Department for their assistancein carring out the observation in this study.
References
Ayer, R.S. and Westcot, D.W. (+310) : Water quality
for agriculture. FAO Report.
Carter, D.L. (+32+) : Salinity and plant productivity.
Chemical Rubber Co., Handbook Series in Nutrition and Food.
Dissataporn, C., Arunin, S., Narioka, H. and Anase,
M. (+330) : Groundwater hydrology in thepolder system in northeast Thailand. In : Rehabilitation and developmnt of upland andhighland ecosystem. (Anase, M. Mandang, T.
and Lasco, R. eds), pp. ,+3ῌ,,2. Tokyo University of Agriculture Press, Japan.
Dissataporn, C., Yamclee. P. and Narioka, H. (,**+ a): Application of electromagnetic technique toidentify recharge and discharge area forreforestation in northeast Thailand. J. of Japanese Soc. of Soil Physics (in press).
Dissataporn, C. Narioka, H., Yamclee, P. andArunin, S. (,**+ b) : Application of electromag-

41

netic induction terrain conductivity metro salinity assessment, Soil map in northeastern
Thailand. J. of Japanese Soc. of Soil Physics (inpress).
Goldberg, D. and Uzrad, M. (+310) : Strip cultivationof the area wetted by drip-irrigation in the
Arava desert. Hort. Sci., ++(,) : +-0ῌ+-2.
Lovenstein, H.M., Berliner, P.R. and van Keulen H.
(+323) : Runo# agroforestry in arid lands. Conference on Agroforestry, Principles and Practice, Edinburgh.
Matsumoto, S. (+33/) : Recent problems on the
global environment with an example of desertiﬁcation and some fundamental technologies
for the prevention of desertiﬁcation in Japan.
In : Soil Moisture Control, (Anase, M. andYasutomi, R. eds), pp. +/ῌ,1. Tokyo Universityof Agriculture Press, Japan.
Scott, R.F. (+30-) : Principles of soil mechanics.
Addison-Wesley Pub. Co. Inc.
Tabuchi, T. (+31+) : Inﬁltration and capillarity inthe particle packing. Rec. Land Reclam. Res.,+3 : +ῌ+,+.
Wada, H. (+332) : Techniques and strategies toameliorate salt-a#ected lands in Northeast
Thailand. JARQ, -, : 13ῌ2/.
Watanabe, M., Horino, H. and Maruyama, T. (+33/) :A technique for controlling Salinity bystratifying soils. In : Soil Moisture Control,(Anase, M. and Yasutomi, R. eds), pp. +*/ῌ+*3.
Tokyo University of Agriculture Press, Japan.
Yacouba, K. (,**,) : Soil classiﬁcation method forland development in arid and semi-arid zones
with regard to soil salinization through capillary action, Doctoral dissertation, Tokyo University of Agriculture.

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ῐ῎῍ῑῒ῏
No. 23, p. .-῍/- ῎,**,῏Application of Electromagnetic Induction Terrain
Conductivity Meter to salinity assessment
in salt-a#ected soils
ῌRegional salt-a#ected soils map in northeastern Thailandῌ
Chaiyanam DISSATAPORN*, Hajime NARIOKA**, Pramot YAMCLEE*
and Somsri ARUNIN** Land Development Department, Phahon Yo Thin Road, Chatuchak,Bangkok +*3**, Thailand** Okayama University, -ῌ+ῌ+ Tsushima-naka, Okayama 1**ῌ2/-*, Japan
Abstract
The electromagnetic induction terrain conductivity meter, “EITCM”, has been used for thesalinity assessment in salt-a#ected soils in northeastern Thailand. This paper brieﬂy discusses
the applicability of the electromagnetic method for delineating the salt distribution within thelandscape and determining the salt content in soil at the depth up to -* m. This information
together with hydrological data and present landuse is useful for the base of the salinity
management in northeastern Thailand. A case study presented the results of the use of theelectromagnetic terrain conductivity meter in some major salt-a#ected soils of Nakhonratchasima province. The results of the investigation revealed that the source of salt in theprocess of soil salinization underlies the salt-a#ected soils. High-elevated areas play an importantrole for the water supply in the process of soil salinization. Variations of the reading might be dueto the salt content, moisture content and soil type. Accuracy of the reading must be carefully
considered when the survey for soil proﬁles is carried out in the areas where high clay content andlow moisture content.
Key words : Electromagnetic induction terrain conductivity meter, electrical conductivity, salta#ected soils map, northeastern Thailand

Introduction
Salt-a#ected soils in the northeastern Thailand spatially spread in low-lying paddy ﬁelds.
The a#ected areas were estimated of seventeen
percent of the region or ,.2/ million ha (Department of Land Development, +323). The majorsoluble salt is NaCl in the soil solution and in
the groundwater resulting in the adverse
e#ects to soils and plants as well as environments. The salt derives from rock salt of theMahasarakram Formation underlying salta#ected lands and contaminates to shallow

groundwater (Williamson, et al. +322). The further extension of salt-a#ected soils is due todeforestation in recharge area, salt making, theconstruction of reservoirs and the mismanagement of irrigation (Arunin, +32.). Salt-a#ectedsoil map was developed through the interpretation of aerial photos, satellite imagery,hydrogeological maps and soil survey. Field
checks were done by collected some soil samples for laboratory analysis. Mapping units
were classiﬁed by degree of salinity into /classes as very strongly, strongly, moderately,slightly and non salt-a#ected areas and poten-44  23

tial salt-source areas (Department of Land Development, +33+).
Counter measures for the salinity control in
the northeastern Thailand are based on the
mapping units of the salt-a#ected soil map.
Agronomic practices and soil amendments including organic and inorganic substance aswell as green manuring are recommended forincreasing rice yields in slightly and moderately salt-a#ected soils, while salt tolerant trees
and halophytic grasses are cultivated in verystrongly and strongly salt-a#ected soils.
Reforestation with trees of salt tolerance, fastgrowing, and high water use is recommended
for preventing the secondary salinization in
potential salt-a#ected soils (Arunin, +33,).
The salinity assessment is essential to ensurethat recommendations for the management ofsalt-a#ected soils is fruitful. Mismanagement
may cause further expansion of salt-a#ectedsoils. Further more, it will be laborious topersuade farmers to acquire new technology(Abrol and Fireman, +311).
Various methods or techniques can be used
for assessing salt-a#ected soils. Extent of salt
patches, native halophytes in landscapes andcertain symptoms of crops as a result of stressimpound by salt are simple characteristics ofsalt a#ected-soils (Arunin, +32.).
But thedegree of salinity can only be speciﬁed byanalyzing soil samples for the concentration ofsoluble salts as electrical conductivity of thesaturation paste extract (Ece, dS/m) (Soil Science Society of America, +313). Sources of salt
underlie salt-a#ected soils. Subsurface conditions can be investigated at the shallow depth
which a hand auger can be drilled. Poweraugurs or drilling equipment can not be
employed. Subsurface conditions can be partly
obtained from one hydrogeological map at + :/**,*** scale which is only suitable for broad
scale purposes (Piancharaen, +31-). Cores drilling for salt, petroleum and groundwater exploitations are available in many places(Krairapanond, et al., +33, ; Japakasetr and
Suwanich, +32.). Groundwater hydrology is,**,investigated with the installation of piezometers in many major salt-a#ected soils in thenortheastern Thailand in order to investigating the relationship between groundwater andsalinity hazards in the region (Dissataporn etal., +33-).
As salt-a#ected soils are dynamic, more replication of sampling are required especially inlarge-scale mapping. Rapid, portable, nondestructive and surface applied method forassessing the soil electrical conductivity andlocating the spatial distribution of salt withinsoil proﬁles as well as within a landscape arerecommended. The recent commercial fourelectrode and electromagnetic technique are
accepted as the practical procedure for immediate assessing salt-a#ected soils (Rhoades, +33,).
The four-electrode resistivity techniquemeasures the average soil electrical conductivity by sending the electrical current into a soil
proﬁle through current electrodes while potential electrodes read the voltage di#erences.
The depth of reading depends on the spacing
between current and potential electrodes. A
regression model for converting the bulk soil
electrical conductivity to the laboratory value
was developed (Department of Land Development, +323)
The electromagnetic terrain conductivity
technique is a simple and rapid method fordelineating the distribution of average soluble
salt in a soil proﬁle from the soil surface to thedepth of 1./, +/ and -* m when the coil spacingof +*, ,* and .* meters, respectively (McNeil,+32*). The technique is widely used for quantify the soil salinity (Cameron et al., +32+ ;McFarlane, et al., +321 ; Williams and Hoey,+321 ; Dixon, +323 ; Cannon, et al., +33.). The
advantage of this instrument is rapidness but
there are various factors which a#ect the terrain conductivity (McNeill et al., +33,) Linear
regressions between the soil electrical conductivity and the terrain conductivity at each
depth of sounding were developed (Cook andWalk, +33,). The low conductivity on the
upland corresponds to the recharge area while῎ῌ῍ : Application of Electromagnetic Induction Terrain Conductivity Meter to salinity assessment in salt-a#ected soils

45

the high conductivity indicates discharge area
(Bullock and Williams, +321). Williams andArunin (+33*) identiﬁed the recharge and discharge area from the average ratio of the electromagnetic terrain conductivity of -* m depth
to ,* m depth, -* m depth to 1./ m depth and +/m depth to 1./ m depth of sounding at Nakorn
Ratchasima in northeastern Thailand. The
ratio greater or less than unity indicates recharge and discharge area, respectively.
The objective of this paper is to describe theuse of the electromagnetic technique for salinity assessment and to determine the accuracyof this technique in identify the soil and watersalinity of the salt-a#ected soils in northeastern Thailand.
Principle of operation and instrumentation
The EITCM measures the average apparent
electromagnetic terrain conductivity (Eca) of
the soluble salt concentration in a soil proﬁle in
mS/m. The terrain conductivity of +.* mS/m isequal to ,/ ppm of NaCl concentration. The
instrument consists of the transmitter and receiver meters connected with the magnetictransmitter and receiver coils, respectively.
The conﬁgurations of coils can be applied inhorizontal and vertical dipole mode which provide the depth of sounding of *.1/ and +./ timesof the distance between two magnetic coils,
respectively. Surveying the soil conductivity
can be done at the coil spacing of +*, ,* and .*m (Fig. +).
The transmitter coil with an alternating current generates time-varying magnetic ﬁelds at
frequency of 0,.**, +,0** and .** Hz to the soil
proﬁle, respectively. They induce small currents in the soil proﬁle, and they produce secondary magnetic ﬁelds. The magnitude of thesecondary magnetic ﬁeld depends on the concentration of soluble salt, moisture content andclay content. The receiver coil determines theprimary and secondary magnetic ﬁeld, and calculates the ratio between primary and secondary magnetic ﬁelds, which yield the bulk apparent electrical conductivity of the soil

Fig. +

Electromagnetic induction terrain conductivity meter, EITCM, in horizontal
dipole mode and vertical dipole mode.

proﬁle. The depth of reading depends on the
primary electromagnetic current frequency, on
the distance between the transmitter and receiver coil and on the coil conﬁguration. The
coils in horizontal dipole mode with the coilseparation of +*, ,* and .* m and primary electromagnetic currents at frequency of 0,.**,+,0** and .** Hz provide the depth of soundingof 1./, +/ and -* m from the soil surface, whilethat in vertical dipole mode conﬁguration provides depth of sounding of +/, -* and 0* m fromthe soil surface, respectively. Survey of terrain
conductivity by the EITCM is commonly usedin horizontal dipole mode as the reading invertical dipole mode is sensitive to low conductivity materials and geologic structure, fractures while the reading in horizontal dipole
mode is insensitive to those of materials. From
this reason, the accurate conductivity can beobtained from the horizontal dipole mode. Further more, alignment of coils in vertical dipole
mode is very di$cult to adjust (McNeil, +32-).
Operating procedure
Two persons are needed for operating the
EITCM. The instrument needs to set up inorder to cut down the magnetic ﬁeld of earth46  23

and air before starting survey. This set upprocedure is repeated during the survey wherever encounter low terrain conductivity area.
The transmitter coil in horizontal dipole modeis placed vertically to the soil surface where
subsurface features are interested. Electromagnetic currents are sent from the transmitter coil in the horizontal direction. The cable,.* m long, is connected between the transmitter and receiver coil. The coil and frequency
current switch are ﬁrstly set at .* m distance.
Receiver coil is moved forward and backward
upon the coil separation meter in order to ﬁx
the coil separation at .* m apart. Digital bulk
apparent electromagnetic conductivity in ms/
m from the soil surface to the depth of -* m isrecorded as well as landuse, landform and salt
patches. The coil separation and frequency
current are set to ,* and +* m, respectively.
The receiver coil is moved forward to transmitter coil to ,* and +* m spacing, respectively.
Repeatedly procedure is done in order to measure bulk salt concentration at the depth of +/and 1./ m. Vertical dipole mode can be done ashorizontal dipole mode by laying down bothcoils on the soil surface. Electromagnetic currents are sent from the transmitter coil in vertical direction. As the EITCM is sensitive to
any metallic material, the measurement should
escape from fences and electricity cables.
Survey technique
The electromagnetic induction survey using
the EITCM have been carried out investigatedin salt-a#ected areas of northeastern Thailand
since +33,. The horizontal dipole mode withthe coil separation of +*, ,* and .* m was usedat the spacing of one-kilometer grid basis. Topographic maps at scale of + : /*,*** and aerial
photos were used for locating the geographic
position. Later on, Global Positioning System(GPS) was employed for rapid locating. Bulk
apparent electromagnetic terrain conductivity,.2,02- records, at depths of 1./, +/ and -* m fromsoil surface with global coordinates were obtained and recorded in database. Further more,when close spacing need to be surveyed and,**,Fig. ,

Salinity assessment
Thailand.

in

northeastern

the geographic position can not be accurately
located by GPS. Sites are marked on aerial
photos and later geographic positions are readby computer program (Fig. ,).
Interpretation
The salinity data have not yet been converted into standard soil salinity because ofunavailable instruments for collecting soil
samples. The computer software Surfer for
Windows was used for contouring the apparent electromagnetic conductivity of the soil
proﬁle at depths of 1./, +/ and -* m from the soil
surface, respectively. Contours are producedby kriging method which is a useful geostatistical gridding method (Surfer for Windows,+330). Salinity is classed by adverse symptomsof plant and soil due to salinity into / classes as
non-salt-a#ected soils (*ῌ2* mS/m), slightly
salt-a#ected soils (2*ῌ+,* mS/m), moderately
salt-a#ected soils (+,*ῌ+0* mS/m), severely salta#ected soils (+0*ῌ,** mS/m) and very severely
salt-a#ected soil (,** mS/m).
Isoconduc-ῑῌῐ : Application of Electromagnetic Induction Terrain Conductivity Meter to salinity assessment in salt-a#ected soils

tivity in Surfer format was exported in to DXF
interchange ﬁles. They were read into digitalformat of Arc info. Digital map of salt-a#ectedsoils covering the whole salt-a#ected soils ofnortheast Thailand is being developed.
Case study
Site characterization
The study area is in Nakhonratchasima province where salinity is major problem of theKorat basin. Soils are spread on the geologic
Mahasarakram formation that is believed tothe source of salt for the process of salinization(Phiancharoen, +31-). A topographic map ispresented in Fig. - a with the +* m contour andmain drainage. A height above mean sea levelof the area ranges from +2* to ,.* meter. Mostof the area is in low terrace and slightly undulating. Lam Chiang Krai and Lam Khang
Phlu, which is tributary of Chi River, are themain drain of the area. The average rainfall
and evapotranspiration is +,+*2 and +,21- mm
per year, respectively. According to the soil
salinity map of the northeastern Thailand at
the scale of + : +**,***, salt-a#ected soil spreads
in the lowest elevation and along the river.
The degree of salinization is in scale of very
severely, severely and moderately salt a#ectedsoil (Department of Land Development, +33+).
Methodology
Salt-a#ected soils of Nakhonratchasima province were surveyed by the EITCM in horizontal dipole mode with the coil spacing of +*, ,*and .* meters. The average apparent terrain
conductivity, ,3- records, at the depth of 1./, +/and -* m from soil surface were recorded including present landuse, landform and salt
patches. Groundwater salinity from nested piezometers at the depth +/ m from the soil surface were collected. The statistic package,
SPSS for Windows, was used for analyzing thecharacteristic of the terrain conductivity andthe linear relationship between the terrain conductivity and the depth of reading. The salinity distribution at each depth of reading andgroundwater salinity was contoured by com-47

puter program, Surfer for Windows. EXCEL
drew the salinity distribution by depth andposition of site of reading from mean sea level
along cross section A-B.
Result of measurement
The terrain conductivity from the soil surface to the depth of 1./, +/ and -* m from thesoil surface ranged from +3ῌ-**, -+ῌ-** and .,ῌ
-** mS/m, respectively. The means values ofterrain conductivity at the three depths ofreading were +-2, +/, and +1, mS/m, respectively. The standard deviation of the terrain
conductivity at the depth of 1./, +/ and -* mvaried from 0/, 0, and 0* mS/m, respectively.
The high correlations were found among thethree depths of reading of 1./ῌ+/, 1./ῌ-* and +/ῌ
-* with the correlation coe$cient of *.3/., *.2++and *.22*, respectively. It was observed fromthe frequency distribution of the terrain conductivity that there were +0 stations where theterrain conductivity at the three depth of reading were -** mS/m, which is the maximum
reading of this instrument. The regression
analysis between the terrain conductivity ofthe three depths was developed in order toclarify the salt distribution within the soil
proﬁle. Linear regression equations between
the terrain conductivity at the depth of 1./, +/and -* m are as follow :V (1./ m)῏῎+0.,11῍+.**2 V (+/ m), R,῏*.3+*
V (1./ m)῏῎+-.,10῍*.211V (-* m), R,῏*.0/1
V (+/ m)῏῎,.-**῍*.3*+ V (-* m), R,῏*.1..
where V (1./ m) : Average conductivity of soil
proﬁle to 1./ m depth
V (+/ m) : Average conductivity of soil
proﬁle to +/ m depth
V (-* m) : Average conductivity of soil
proﬁle to -* m depth
The coe$cient of determination (R,) of thethree regression equations were 3+, 0/.1 and
1...ῌ, respectively.
The linear regression
models can be explained 3+, 00 and 1.ῌ of thevariation of the dependent terrain conductivity, respectively. From the three regression
equations, it can be explained that when V (1./m) and V (+/ m) is equal to +, V (-* m) is greater

48ΐῐ῎῔῕ῑ ῒ 23 ῏ ῌ,**,῍than V (+/ m) and V (1./ m), while V (+/ m) is as
well greater than V (1./ m). Thus, the averageterrain conductivity of soil proﬁle increases
from soil surface to the maximum depth ofreading. Further more, the terrain conductivity at the depth of +/ and -* m from the soil
surface can be estimated from the terrain conductivity at 1./ m with these regression equations.
Salt distribution maps at the depth of 1./, +/and -* m from the soil surface with map units
and the topographic map of the study area
were shown in Fig. -. The magnitude of apparent terrain conductivities were classed into
non, slightly, moderately, severely and very
severely salt-a#ected soils in order to characterize the distribution of the salt concentration
within a soil proﬁle and within a landscape.
Fig. - a and -b indicated that there was anaccumulation of salt in soil proﬁle from the soil
surface to the depth of 1./ m. Very severely
salt-a#ected soils spatially spread in the alluvium plain of the main drainage of the study
area. It occurred mostly in the areas where theelevation is less than ,** m. Non salt-a#ectedsoils where the terrain conductivity is less than
2* mS/m were situated at the elevation greaterthan ,+* m. Isoconductivity maps of the soil
proﬁles at the depth of +/ and -* m from soil
surface showed that the areas of very severely
salt-a#ected soils increased with the depth ofsounding. Further more, the area of non salta#ected soils decreased with the depths ofsounding, indicating the increase of the soluble
salt content with the depth under non-salt
a#ected soils at the depth more than 1./ m fromthe soil surface (Fig. - c and - d). The result ofcross-section AB showed that the degree ofsalinity in the high elevation areas was low
and gradually increases further down slope.
Low salinity could be detected in the undulating area. Salinity sharply increased with depth
in alluvium plain while in the high elevation
area there were little change in the terrain
conductivity with depth (Fig. - f).
Groundwater salinity from the nested pie-zometer at the depth of +/ m from the soil
surface was shown in Fig. - e. Groundwatersalinity ranges from less than + to ./ dS/m. It
was found that low salinity groundwater islocated in the high elevation area while very
high salinity is located in the ﬂood plain.
Discussion
The EITCM was employed for the salinity
assessment in northeastern Thailand. It has
been proved that this technique can provide
reliable data on the salinity distribution withina landscape and within a soil proﬁle. The
technique is easy for application, as no soil
samples are taken. Further more, it is thesurface treatment without inserting electrodes
as Four-probe resistivity. The receiver coils
can be adjusted from the coil separation metercomparing to four-probes resistivity meter,
which need to adjust electrode spacing by tapemeasuring. Two persons are minimum requirement for operating electromagnetic terrain conductivity.
As the instrument can detect an average terrain conductivity of a soil proﬁle from the soil
surface to the depth of 1./, +/ and -* m, it not
only enables to locate the salt concentration
within the landscape but also within the soil
proﬁle which can not be observed by aerial
photos or satellite imagery. Data collectedfrom the study area can indicate that salta#ected soils occur in the ﬂood plain of thethree main drain of the study area. The sourceof salt can be situated at the depth of +/ and -*m from the soil surface in the salt-a#ected soils.
Further more, the terrain conductivity of asoil proﬁle, greater than +,* mS/m, can befound at the depth of -* m from the soil surface
in the high-elevated areas. The salt content
situated at the depth more than -* m from thesoil surface may be higher than +,* mS/m if
the instrument can operate at depth more thanthat of from soil surface. From this reason it
can be shown that salt underlies Korat Basineven in the high-elevated area that were classiﬁed as non salt-a#ected soils (Piancharoen,῎ῌ῍ : Application of Electromagnetic Induction Terrain Conductivity Meter to salinity assessment in salt-a#ected soils

Fig. -

49

Topographic map (a), isoconductivity maps (mS/m) at depth 1./, +/ and -* m (b, c, d)groundwater salinity (dS/m) at depth +/ m (e) and cross section of terrain conductivity andheight from mean sea level (MSL) (f).

50ΐῐ῎῔῕ῑ ῒ 23 ῏ ῌ,**,῍+31-). Salt in the deeper proﬁles can not be
observed because of the limitation of the instrument. In addition, salinization in this area
can not occur because these areas are in thehigh elevation, and salt at the depth more than-* m can not move up to the soil surface andleaching by rainfall is normally dominant inthese areas. On the other hand, the result of theelectromagnetic survey indicates that salt in
the high-elevated areas is not situated at thedepth where it can be a source of salt in theprocess of soil salinization, ie, saline seep
(Sinanuwong and Takaya, +31.). Further more,
the high-elevated areas in the salt-a#ected soils
are the areas where they might supply waterfrom the rainfall for the process of salinization.
This local recharge should be aware of water
management for salinity control (Dissataporn
et al., +33-).
The distribution of the terrain conductivity
in the soil proﬁle at each depth can be used for
identifying the recharge and discharge area.
As in the recharge area salt is leached down thesoil proﬁle by water and accumulated in the
deeper proﬁle. While in the discharge area salt
moves up to soil the surface by the capillaryrise from the shallow saline groundwater andaccumulated in the upper soil proﬁle (Williams
and Arunin, +330). But the terrain conductivity
in the discharge areas increases with the depthof reading. This can clarify that the source ofsalt situates in the salt-a#ected soils and themagnitude of the accumulation of salt is much
more than the accumulation of salt in theupper surface by the process of the capillaryrise and the evaporation soil surface.
It is observed that sixteen sites in the very
severely salt-a#ected soils class comprised of-** mS/m for the whole depth of reading,which is the maximum reading of the instrument. Salinity in these sites may be greaterthan -** mS/m if the digital model, which canmeasures more than -** mS/m, is used (McNeil,+32*).
The distribution of the terrain conductivity
at the depth of +/ m from the soil surface partly

coincided with the groundwater salinity at thesame depth (Fig. - c and - e). It can be seenfrom this comparison that the terrain conductivity might be used for identifying soluble salt
in soil proﬁles. The variation of these two data
may be due to the di#erence in the sample
densities. Simple nonlinear regression equations of the terrain conductivity at the depth of
1./, +/ and -* m from the soil surface and theelectrical conductivity of the groundwater at
the same depth were developed (Yamclee et al.,+330). It was found that the regression equation of the terrain conductivity could explain
about 22, 11 and 2+ῌ of the variation of thegroundwater salinity at the depth of 1./, +/ and-* m from the soil surface, respectively. From
this study it can be seen that variations of theterrain conductivity may be caused by otherfactors about +,, ,- and +3ῌ, respectively.
The low terrain conductivity in the highelevated areas may be due to the low salt concentration and moisture content.
As thegroundwater level in these areas is always situated at the depth more than / m from the soil
surface. Thus, the terrain conductivity of thesoil proﬁle measured in such places may be
confounded by moisture content especiallyreading at the depth of 1./ m from the soil
surface. While in the salt-a#ected soils, thegroundwater table is always at the depth of ,ῌ
- m from soil surface. The di#erence in moisture contents can be ignored in the salta#ected soils. On the other hand, as salta#ected soils in northeast occur mostly insandy soils which clay contents are not the
major constitutes of these soil types. Thus, thevariations of the terrain conductivity in the
sandy soils are not due to clay content. The
high terrain conductivity found in the ﬂooded
plain areas of the main drain may be interferedby the clay content in the soil proﬁle (Williams
and Hoey, +321 ; McNill et al., +33,).
These variations could be accepted for thesalinity assessment in the regional scale.
Anyhow, the anomaly of the terrain conductivity and electrical conductivity of soils should῎ῌ῍ : Application of Electromagnetic Induction Terrain Conductivity Meter to salinity assessment in salt-a#ected soils

be further investigated, as the terrain conductivity is relying on not only soluble salt but
also clay and moisture. It is necessary to develop the regression equation for converting theterrain conductivity to the electrical conductivity of the saturation paste especially in theclayey soil proﬁle and in the high elevation
areas where clay content and moisture content
could interfere the terrain conductivity ; respectively. The calibration can be done for the
1./ m reading as a hand auger can be drilled.
Soil samples from the soil surface to the depthof 1./ m must be collected and mixed together.
Saturation extract of soil paste is used formeasurement of the soil electrical conductivity. Regression of the average terrain conductivity and soil electrical conductivity can be
developed. This ﬁnding will be useful forassessing the soil salinity in standard unit. As
the salinity at the shallow soil proﬁle is themain purpose for salinity assessment in agriculture production.
Since the terrain conductivity is used directly for classifying salt-a#ected soils and the
responses of the terrain conductivity for eachsoil types and landscape are not the same. The
terrain conductivity for each map unit should
be classed for each catchment area. Surveyors
can class the terrain conductivity for each map
units from salt patches and native halophytes
as well as symptom of plants.
In addition, the electromagnetic terrain conductivity meter measuring in the vertical
dipole mode is sensitive to geologic structure,faults. Salinity survey should not only measure in horizontal dipole mode for the terrain
conductivity but also in vertical dipole mode.
As faults were claimed to be a channel of the
deep saline groundwater which contacts with
the Mahasarakram Formation. This saline
groundwater leak through these channels andcontaminate to the shallow groundwateraquifer (Imaizumi et al., +330). This information is useful for considering the salinity control.
Electromagnetic terrain conductivity with51

the short intercoil spacing and the single current frequency has been useful for the salinity
assessment in the agricultural production area
as it is portable, one man operate, rapid, rootzone reading and can be related to laboratory
analysis (Dissataporn et al., +33-).
The information from the electromagnetic
technique can be considered in planning theland-use strategy for the salinity control. It
can be a basis data for reducing the cost ofhydrological study which need to install expensive piezometers.
Further more, Salta#ected soils map in GIS format can be usedwith other map layers, land use, elevation, hydrology, for predicting areas risk for salta#ected soils.
Conclusion
The EITCM was used for salinity assessing
in northeastern Thailand. This technique issurface application, non-destructive, rapid andeasy to operate. It immediately locates the salt
concentration with in a landscape and within asoil proﬁle. The results of mapping indicatedthat sources of salt in the process of the soil
salinization is underlie the salt-a#ected soil.
The deviation of the bulk conductivity withina landscape and within a soil proﬁle may comefrom the di#erence in moisture content andclay content. Subsurface conditions can beinvestigated in more details by this technique.
Anomaly of the terrain conductivity from theelectrical conductivity of soil paste must be
found out even for the shallow depth of reading.
Reference
Arbol, I.P. and M. Fireman (+311) : Alkali and saline
soil identiﬁcation and improvement for crop
production. Central Soil Salinity Research Institute.
Arunin, S. (+32.) : Characteristics and managementof salt a#ected soil in the Northeast of Thailand. --0ῌ-/+. In Ecology and management ofproblem soils in Asia. Food and Fertilizer
Technology Center for the Asian and Paciﬁc
Region. Taipei, Rep. of China.
Arunin, S. (+33,) : Strategies for utilizing salt

52ΐῐ῎῔῕ῑ ῒ 23 ῏ ῌ,**,῍

a#ected lands in Thailand. Proceeding of theInternational Symposium on Strategies for
Utilization Salt A#ected Lands. pp. +1ῌ+/, February +33,, Central Plaza, Bangkok, Thailand.
Cameron, D.R., de Jong, E., Read, D.W.L. andOosterveld, M. (+32+) : Mapping salinity using
resistivity and electromagnetic inductive techniques. Canadian Journal of Soil Science. 0+ :01ῌ12.
Cannon, M.E., Mckenzie, R.C. and Lachapelle, G.
(+33.) : Soil salinity mapping with electromagnetic induction and satellite-based navigation
methods. Canadian Journal of Soil Science. ,. :--/ῌ-.-.
Cook, P.G. and Walk, G.R. (+33,) : Depth proﬁle ofelectrical conductivity from linear combination of electromagnetic induction measures.
Journal of Soil Science Society of America. /0: +*+/ῌ+*,..
Department of Land Development (+323) : Annual
report of Department of Land Development,
Ministry of Agriculture, Bangkok, Thailand. p.
+30 (in Thai).
Department of Land Development (+33+) : Distribution of salt a#ected soil s in Northeast region. +: /**,*** map.
Dissataporn C., Tokotkla, A. and Arunin, S. (+33-) :Salt tolerance of kallar grass Leptochloa fusca(L.) Kunth. Workshop on Research Activities
of ADRC Contributed to Agricultural Development in Northeast Thailand. pp. +ῌ-, Sep +33-.
ADRC, Khon Kaen, Thailand.
Dixon, P. (+323) : Dryland salinity in a subcatchment at Glenthompson, Victoria. Australia Geographer. ,* : +..ῌ+/,.
Imaizumi, M., Wichaidit, P., Sukchan, S. and Srisuk,
K. (+330) : Mechanism of salinization ofgroundwater in Phrayuen area, northeast
Thailand. Proceeding of Seminar on Geophysical prospective for groundwater development
and hazard prevention. +, December +330.
Chareonthani H
Japakasetr, T. and Suwanich, P. (+32.) : Potash androck salt in Thailand. Mineral Bulletin no. ,.
Department of Mineral Resources. Thailand.
Krairapanond, N., Krairapanond, A., Sinthuwanich,D. and Junpet, T. (+33,) : Environmental
impact of rock salt mining operations on land
and water resources of Northeast Thailand.
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February pp. +1ῌ,/, +33,, Bangkok, Thailand.

-*3ῌ-,,.
McFarlane, D. J., Engel, R. and Ryder, A.T. (+321) :Investigation of a saline valley on Allandale
Research Farm. Technical report Western
Australia Department of Agriculture. No. /2 :+0.
McNeil, J.D. (+32*) : Electromagnetic terrain conductivity measurement at low induction numbers. Tech. Note TN 0. Geonics Ltd.
McNeil, J.D., Topp, G.C., Topp, W.D. and Reynolds,
W.D. (+33,) : Rapid, accurate mapping of soil
salinity by electromagnetic ground conductivity meters. SSSA Special Publication -* : ,*3ῌ,,3.
Piancharoen, C. (+31-) : Hydrogeological map ofnortheastern Thailand (Scale + : /** /**). Department of Mineral Resources. Thailand.
Rhodes J.D. (+33,) : Recent advances in the methodology for measuring and mapping soil salinity. Proceeding of the International Symposium on Strategies for Utilization Salt A#ected
Lands. pp. +/ῌ+1, February +33,, Central Plaza,
Bangkok, Thailand.
Sinanuwong, S. and Takaya, Y. (+31.) : Saline soil
in northeast Thailand. Their possible origin as
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Williams B.G. and Baker, G.G. (+32,) : An electromagnetic induction technique for reconnaissance survey for salinity hazards. Aust. J. Soil
Res. ,* : +*1ῌ+2.
Williams B.G. and Hoey, D. (+321) : The use of electromagnetic induction to detect the spatial
variability of the salt and clay contents ofsoils. Australian Journal of Soil Research. ,/ :,+ῌ,1.
Williams, B.G. and Arunin, S. (+33*) : Inferring recharge/discharge areas from multifrequency
electromagnetic induction method. Technical
Memorandum 3*/++. CSIRO.
Williamson D.R., Turner, J.V., Peck, A. J. andArunin, S. (+323) : Groundwater hydrology andsalinity in a valley in Northeast Thailand. In
Groundwater Contamination. IAHS. Pub. No.
+2/.
Yamclee, P., Dissataporn, C., Pongwichian, P. andArunin, S. (+330) : Prediction of groundwatersalinity by geonic technique. Soil and Water
Conservation Journal. 0 : ./ῌ/0.

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Journal of the Japanese Societyof
Soil Physics
January ῍ῌῌ῍

No. 23
Contents

Foreword ῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍M. OKAZAKI῍ +Original Papers
Maximum Potentially Dispersible and Stabilizable Clays under Cropping in Soils with
Inherent Textural Di#erences῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍V. RASIAH and T. YAMAMOTO῍ Anisotropy of Drainable Macropores in Andosols and Alluvial Soils
῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍Y. IWATA and H. NARIOKA῍+/
Ion Concentration Prediction of the E%uent during the Sulfuric Acid Solution
Permeation into Volcanic Ash Soil῍῍῍῍῍῍῍῍῍῍῍῍῍῍K. KAMEYAMA, S. MATSUKAWA, T. ISHIDA and H. KATO῍,/
E#ect of Groundwater Level on Salinity Content and Environmental LandClassiﬁcation῍῍῍῍῍῍῍῍῍῍῍C. DISSATAPORN, K. YACOUBA, M. MIHARA and R. YASUTOMI῍-/
NoteApplication of Electromagnetic Induction Terrain Conductivity Meter to salinity
assessment in salt-a#ected soils
ῌRegional salt-a#ected soils map in northeastern Thailandῌ῍῍῍῍῍῍῍῍῍῍῍῍῍C. DISSATAPORN, H. NARIOKA, P. YAMCLEE and S. ARUNIN῍.Announcements ῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍//Editor’s Postscript ῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍῍0+Japanese Society of Soil Physics
Department Biological and Environmental Engineering
Graduate School of Agricultural and Life Sciences, The University of Tokyo+ῌ+ῌ+ Yayoi Bunkyooku, Tokyo ++-ῌ20/1, Japan