ῐ
J. Jpn. Soc. Soil Phys.
ῐ῎῍ῑῒ῏
No. ++*, p. /-ῌ00 ῍,**2῎

Evaluation of Powdered Polyacrylamide Application
along with Source of Electrolytes inControlling Sodic Soil Erosion
Tahei YAMAMOTO*, Yutaka SHIMURA**, Taku NISHIMURA***, Henintsoa ANDRY*,
Shigeoki MORITANI* and Ahmed AL-BUSAIDI** Tottori University, Arid Land Research Center, +-3* Hamasaka, Tottori, 02*ῌ***+, Japan** Nishida Industry Co. Inc., +-+ῌ+ Koaza-inumaru, Aza-amada,
Hukuchiyama-shi, Kyoto, 0,*ῌ**.0, Japan*** University of Tokyo, Yayoi +ῌ+ῌ+, Bunkyo-ku, Tokyo ++-ῌ20/1, Japan
Abstract
The anionic polyacrylamide (PAM) is recently used to rehabilitate saline and sodic soils. It isalso applied to control soil erosion ; however, few researches have tested the e#ectiveness ofanionic PAM along with source of electrolytes application to control artiﬁcial sodic soil erosion.
An experiment was conducted to study the e#ects of anionic PAM with and without gypsum on
the erosion of sodic soils under saline rain water conditions. A clay loam soil was prepared toachieve three levels of exchangeable sodium percentage (ESP) ; *./, 3.3 and ,/./ with appropriate
salts solutions. Soil samples were air-dried and packed in the trays. Powdered PAM, gypsum ora mixture of both were applied to the salt treated soils. Soils were subjected to simulated rainstorm of .* mm hῌ+ by a ﬁxed rainfall simulator. Saline waters with di#erent levels of electricalconductivity (EC) ; *.+-, ,, /, and 2 dS mῌ+ were used for simulated rains during the study.
It seems that the artiﬁcial soil showed fairly similar soil erosion characteristics as that reported
on a natural sodic soil. It was found that the soil sodicity enhanced soil erosion under non-saline
water. It seems that the e#ects of electrolyte source on soil erosion were a#ected by the soil initial
electrical conductivity (ECe) rather than by the ESP level of soil. PAM amendment substantially
increased the surface runo# while at the same time controlled the soil losses. A reduction insurface runo# was found by applying gypsum or saline water on the soil treated with PAM.
However, it seems that the mixed addition of PAM with gypsum or salts enhanced detachmentsof soil particles by raindrop impact.
Key words : Gypsum, saline water, polyacrylamide (PAM), artiﬁcial sodic soil, soil erosion+.

Introduction

Soil sodicity occurs naturally and can beenhanced by human activities such as irrigation. In arid and semi-arid areas, sodic soils
exhibit poor soil-water and soil-air relation ;these properties adversely a#ect root growth
restricting plant production and making thesoils di$cult to work when wet or dry. The

total area, which has sodic soils, is estimated atabout +-/ million hectares ; but as the distribution of sodic soils is very scattered worldwide
the individual areas are often too small for
inclusion in overview soil maps at a world
scale (FAO-AGL, ,***).
Soil sodicity can a#ect many physicochemical reactions. Soil pH usually has a strong
relationship with exchangeable sodium per-

῏

54



centage (Tan, +33-). Problem of sodic soil iscaused by the presence of sodium attached toclay in soil. A soil is considered sodic when thesodium reaches a concentration where it starts
to a#ect soil structure. The sodium may
extend di#use double layer and thus weaken
the bonds between soil particles when wetted
resulting in the clay swelling and often dispersing. When this happens the clay particles
spread out or disperse making the soil water
turbid. The dispersed clay particles can thenmove through the soil and clog the pores. Bothswelling and dispersion reduce inﬁltration anddrainage. During irrigation and rainfall, such
soils tend to have more runo# and thus bevulnerable to water erosion (Shainberg et al.,+32.). Agassi et al. (+32+) reported a considerable runo# from dispersive non-calcareous sodic
soil induced by rainfall. Soil loss becomes more
severe under sprinkler systems with highspraying intensities and longer duration of surface irrigation. Runo# and eroded sediments
not only lead to deterioration of land productivity, but also contribute substantially towards non-point source contamination of surface water bodies (Tang and Rengel, ,**-).
The scarcity of good quality water forces
farmers world wide to use poorer quality wateror reuse drainage water for irrigation. In somearid areas, saline (electrical conductivity of , to/.2 dS m+) and sodic (sodium adsorption ratioof +, to ,0) water have been used for irrigation(Levy et al., +33/ ; Yamamoto et al., +32*). Irrigation with such water introduces sodium tothe exchange sites and leads to the buildup ofhigh ESP levels of the soil (Mantell et al., +32/).
When exposed to the impact energy of water
drops, aggregates with high ESP levels disintegrate more readily than those with low ESP
levels (Shainberg et al., +33,). Consequently, athigh ESP levels the soil erosion is signiﬁcantly
higher than that at low ESP levels (Shainberg
et al., +33,).
Reduction of soil erosion can be obtained by
improving soil structure and aggregate stability at the soil surface. Gypsum has been used to++*,**2

improve soil physical properties such as soil
aggregation and permeability as a result ofproviding electrolyte into the rainwater andalso dissolved Ca ions into the soils as well
(Shainberg et al., +323). On the other hand,
Polyacrylamide (PAM) was found to improvesoil structure by reducing clay dispersion(Saybold, +33.). An anionic PAM having large
molecular weight has the ability to stabilize
soil structure, reduce runo# and soil loss
(Zhang and Miller, +330), when soil solution
cations can bridge negative charged clay particles with anionic PAM (Theng, +32.). For thisprocess carboxyl groups of PAM are attachingwith soil particles.
It was reported that the dissolution of PAM
encouraged soil aggregation and structuring(Al-Abed et al., ,**-). This phenomenon could
ensure reduction of soil loss by runo#. Beside,
Yu et al. (,**-) reported a decrease in inﬁltration rate after an anionic PAM application on
the soil. This was caused by clogging pores bylong chains of gel structured PAM. Also, small
molecular weight PAMs may prevent coagulation of clay particles by cancelling the particle
charges by adsorption (Heller and Keren, ,**, ;Shainberg and levy, +33. ; Shainberg et al.,+323).
Treating sodic soil with anionic PAM or
gypsum can improve soil structure (Shainberg
et al., +323 ; Al-Abed et al., ,**-) ; however, few
researches have tested the e#ectiveness ofanionic PAM along with gypsum application
on soil erosion (Tang et al., ,**0). The direct
relationship between soil structure, PAM andgypsum application on soil erosion is not veryclear. Moreover, the e#ect of anionic PAM on
soil erosion was not fully studied.
There is a limitation for basic research to be
conducted on a natural soil due to inherent
variability of the soil properties in the ﬁeld.
Controlling and measuring many physicochemical parameters under ﬁeld study withvariable conditions of sodic soils could lead to acomplexity and variation in measured values.
As a result, it is hard to determine which factor῔ΐ : Evaluation of Powdered Polyacrylamide Application along with Source of Electrolytes
in Controlling Sodic Soil Erosion

is more important and to predict where andwhen soil erosion events are going to takeplace in the ﬁeld. These problems have generated the need for controllable simulation,such as simulated rainfall as well as simulated
sodic soil. Rainfall simulation has been used
for decades to study basic erosion processes
that are di$cult to study in detail on the ﬁeld ;for example, surface sealing, soil aggregate stability, and raindrop detachment. Using artiﬁcial sodic soil may be a method for a basic
study on sodic soils induced by blackish water
irrigation. The current experiment was designed and carried out on the objective to analyze the e#ects of anionic PAM mixed with
gypsum or under saline rain water on artiﬁcial
sodic soil erosion. Therefore, conducting abasic study under laboratory condition will
give precise understanding on the response of
sodic soils to various amendments.
,.

Table +

55

Some characteristics of the studied
soil

Physicochemical properties

ValuesSand [ῑ*4*, mm] (ῌ)
Silt [*4*,ῌ*4**, mm] (ῌ)
Clay [ῐ*4**, mm] (ῌ)
Bulk density (g cm῍-)
Hydraulic conductivity (cm s῍+)
pH-H,* [+ : ,4/]ECe (dS m῍+)
CEC (cmolc kg῍+)

-340
-04*
,.4.
+4+,
043,῎+*῍/
/40+
*411
+14,

Clay minerals (ῌ)
Smectite
Chalcedony
Analcime
Plagioclase
CalciteDolomite
PyriteQuartz.0ῌ.3-1ῌ-2-4*ῌ-4/,41ῌ/4/,4+ῌ,40,4*ῌ,42*4/ῌ*41*4/ῌ*41

Materials and Methods,. + Soil preparation and analysis
The soil for the experiment was sampledfrom the paddy ﬁelds of Tottori prefecture,
Japan. Smectite is the dominant clay mineralin this soil. Textural class of the soil was determined as clay loam by pipette method (Gee and
Bauder, +320). The pH of the soil was measured
in + : ,./ soil-water suspensions. Electrical conductivity (ECe) was measured in saturation extract by electrical conductivity meter. Exchangeable cations are extracted by using sodium acetate solution and cation exchange capacity (CEC) was determined by quantifying
the adsorbed sodium cation following replacement of the cation by +N ammonium acetate
solution. Quantiﬁcation of cations was conducted by atomic absorption spectrophotometer. The selected properties of the soil are
given in Table +.
Soils were air-dried and passed through ,mm mesh sieve. The soil samples were treatedwith CaCl,, MgSO. and Na,CO- to attain thefollowing three levels of ESP : i) low ESP *./,
ii) medium ESP 0.00, and iii) high ESP ,/./

(Table ,).
,. , Soil erosion experiment
Steel boxes having a dimension of (+**῎/*῎+- cm) were used for this experiment. Boxes
were ﬁlled with 1 cm of sand overlain to - cm
thickness gravel layers. The treated soil was
air dried and then uniformly packed withthickness of - cm to the top of the sand box.
The boxes were placed at +*ῒ slope and .*mm h῍+ simulated rainfall was applied for ,hours. Rain water was prepared by mixing
salts of NaCl and CaCl, with tap water (EC῏*.*3 dS m῍+) to attain electrical conductivity(EC) levels of *.+-, ,, / and 2 dS m῍+. Thesesaline rain waters were prepared in order tosimulate the e#ect of saline water used insprinkler irrigation. The sodium adsorption
ratio (SAR) value of the rain water for every
level of EC was maintained as /. This SAR
value was selected based on the average SARof drainage water of irrigation reported in theprevious research of Yamamoto et al. (+32*) undertaken in Khuzestan areas of Iran. Moreover,this SAR value, which is classiﬁed to be higher



56

Table ,++*  ,**2

Selected chemical properties of the salt treated soils
Exchangeable cations (cmolc kg+)ESP levelof soil

pH-H,O(+ : ,./)ECe(dS m+)ESP

Low
MediumHigh/43//40+
04-1042/240134.,

34,3
+-4/.
,4,.

*4/
0400
,/4./

Fig. +

Soil erosion experimentin the USDA Agricultural Handbook Guideline(US Salinity Lab. Sta#, +3/-), was also selected
in order to analyze soil dispersion of the sodic
soil.
A drip-type rainfall simulator with raindrop
fall-height of +, m was used for the study (Fig.
+). Average rain drop size was , mm. Runo#
was collected by a ﬂume connected at thelower end of the tray during every / minutes
intervals. The sediments in the runo# were
determined gravimetrically after oven-drying
at +*/ for .2 hours.
The e#ect of gypsum, saline water andanionic PAM alone was determined by supplying of gypsum at the rate of *, +, and / Mg ha+,under saline rain water having EC values of*.+-, , and 2 dS m+, or dry PAM at the rate of *,

Na

Mg,

Ca,

*4*3
+4+.
.4-2

*4..
+4*3
*432

+*42/
+*4+,
04+.

,* and 2* kg ha+. The saline rain water of *.+dS m+, which is also referred as a non-salinerain water in the subsequent text, was used in
the case of dry gypsum and anionic PAM.
Prior to the simulated rainfall these chemical
amendments were uniformly spread on soil
surface.
In case of mixing experiment either dry PAM
mixed with gypsum or dry PAM subjected tosaline water, prior to the simulated rainfall, dry
gypsum was uniformly spread on the soil surface at the rate of *, +, ,, and / Mg ha+ whereas
the dry PAM was uniformly spread at the rateof *, ,* and 2* kg ha+. Application rate of thetwo chemical agents was arranged in a mannerthat the above two doses of the PAM weremixed with the three doses of gypsum to give a
total of six di#erent application conditions.
The powdered anionic PAM (AP2,/) used in
the experiment was manufactured by the DiaNitrix Co., Ltd, with a molecular weight of +.++*1 g mol+ and +1 to ,+ῌ hydrolysis.
,. - Soil intake rate study
Soils of highest ESP amended by anionic
PAM, gypsum and mixtures of both wereused in the intake rate study. Inﬁltration rateof the soil was measured using constructedsoil column. The study was done following
Bouwer (+30-). Soil with thickness of ,./ cm
was packed uniformly in columns of +* cm inheight and / cm in diameter. The soil column
was kept ponded with water depth of / cm.
Water supply rate was monitored until thesteady state condition. At the end, soil basic
intake rate at steady state condition was calculated (Table -). The inﬁltration experiment
was performed with , to - replicates and withῑῐ : Evaluation of Powdered Polyacrylamide Application along with Source of Electrolytes
in Controlling Sodic Soil Erosion

57

Table - Soil basic intake rate (IB in mm hῌ+) of high ESP soils
Water quality used in this test

Non-saline water

Saline water , dS m῍+

Saline water / dS m῍+Control
PAM ,* kg ha῍+ῌGypsum , Mg ha῍+
PAM ,* kg ha῍+ῌGypsum / Mg ha῍+
PAM 2* kg ha῍+ῌGypsum , Mg ha῍+
PAM ,* kg ha῍+
PAM 2* kg ha῍+

.41/
/4+0
/4/*
/4+0
-4,.
*4**

n/a῏
n/a
n/a
n/a
14*/
0430

n/a
n/a
n/a
n/a
14*2
14+2

῏

n/a : not available

either non-saline or saline water.
,. . Soil aggregate stability
The e#ect of PAM on soil aggregate stabilityof low and high ESP levels was tested under
deionizer water to assimilate the e#ect of natural rain. A -* g of the treated soil was spread onan aluminum plate (+, by +../ cm) to form amonolayer and then anionic PAM was appliedby spraying the / ml of dilute PAM solution ata concentration of -/* mg L῍+. The treated soils
were air-dried for .2 hours before analysis. Soilaggregate stability was done by a combinationof wet-sieving using two aperture meshes of ,and *.*1/ mm and then measured by hydrometer method. Distilled water was used for wetsieving.
-.
-. +Results and Discussion

E#ect of gypsum or saline water onsoil erosion
Gypsum is known as a dispersion-restricting
agent for sodic soils due to electrolyte concentration and cation exchange e#ects (Shainberg
et al., +323 ; Zhang and Miller, +330). The performance of gypsum depends on the soil waterelectrolyte and Ca concentrations that result
from gypsum dissolution, and on the e$ciencyof the Na-Ca soil exchange process (Keren andShainberg, +32+). The e#ects of gypsum andexchangeable sodium percentage (ESP) of thesoil on surface runo# and soil loss under nonsaline rain water are shown in Fig. ,. It was
found that the cumulative runo# of each treatment for , hours rainfall event did not clearly
di#er among the gypsum levels. The soil

which had highest ESP showed the highest
values of surface runo#, followed by low ESP,and medium ESP. This result was in contrast
with the initial ECe of the soil as cited in thefollowing order : high ESP soil῎low ESP soil῎medium ESP soil. Based on this ranking, it
seems that the e#ectiveness of gypsum on improving soil inﬁltration was a#ected by the
initial ECe of the soil. It is important to mention that as ECe was measured in saturation
extract, this ECe depends on the concentrationof total soluble salts in the solution. And sincesoil ESP and ECe are not linearly dependent, apossible decrease in ECe with increasing soil
ESP could be occurred such as seen in thisstudy and also reported by Yamada et al.,(,**,).
The soil loss was not clearly a#ected by
gypsum application rate ; however, it seems
that the e#ect of gypsum application varied
accordingly to the level of ESP in the soil.
Gypsum application reduces soil loss from high
ESP soil. The soil having low ESP showed thelowest values of soil loss among treated soils.
Gypsum helps clay particles to ﬂocculate that
may at least reduce seal formation on soil surface (Shainberg and Letey, +32.). During rainfall season, application of gypsum enhanced
deposition of sediments and reduced the transport of ﬁner particles by surface runo# (Warrington et al., +33* ; Yu et al., ,**-). The inconsistency of the results in this study as compared to those reported by previous researches
were partly due to the initial condition of the
low and medium ESP soils having high initial



58

Fig. ,++*

,**2

E#ect of gypsum on soil erosion at di#erent ESP subjected to non-saline water

ECe, 3.,3 and +-./. dS m+, respectively. The
electrolyte concentration exceeded the cationexchange e#ect in soil.
Without gypsum application, the surface
runo# from soils subjected to saline rain water
decreased with increasing the electrolyte concentration of rain (Fig. -). This result could be
explained by the improvement of soil inﬁltration by restricting clay dispersion (Shainberg
et al., +323 ; Zhang and Miller, +330) of thewhole soil layer. It was found that saline rainwater with EC value , dS m+ enhanced soil
loss of the medium and low ESP soils as compared to the non-saline rain water of *.+- dS
m+. However, the soil loss from the soil
having high ESP decreased signiﬁcantly withincreasing the electrolyte concentration in rain
(Fig. -). For the low and medium ESP soils hadhigh ECe at the beginning of rainfall event.
Combination of lower electrolyte concentration and rain drop impact of the saline water
rainfall exceeded ion exchange e#ect following
to apply saline water (SAR /) rainfall. En-

hance in dispersion due to raindrop impact
under dilluter electrolyte concentration could
happen at soil surface during saline water rainfall event. This caused more soil loss under ,dS m+ rainfall without drop in inﬁtration rate.
Then, soil loss decreased with higher EC salinerain water with the same SAR.
For both gypsum and saline water treatment, surface runo# and soil loss were varied
and inconsistence since those might be highly
a#ected by both ESP, SAR and the initial ECeof the soil. Hereby, the interactive e#ect of ECe,
ESP, gypsum and saline water treatment wasamong the main reasons for di#erentiatedranking order of soil loss and surface runo#
among all treatments as shown in Fig. , andFig. -.
-. , E#ect of PAM on temporal change ofsoil erosion under non-saline rainwater
The temporal changes of runo# and soil loss
during , hours simulated rainfall was a#ectedby PAM application (Fig. .). Runo# was great-ῐ῏ : Evaluation of Powdered Polyacrylamide Application along with Source of Electrolytes
in Controlling Sodic Soil Erosion

59

Fig. - Characteristics of soil erosion at di#erent ESP without gypsum application subjected tosaline waterer with higher dose of anionic PAM. This could
happen due to the long chain of the PAM
which clogged soil pores, prevented inﬁltrationand enhanced surface runo#. This is supported to some extent by the soil basic intake
rate test on the soil having high ESP (Table -),showing that the water intake increased asfollows : PAM 2* kg haῌ+῍PAM ,* kg haῌ+῍control. Soil loss decreased by higher amountof PAM incorporation in the following order :control῎,* kg haῌ+῎2* kg haῌ+ PAM. Yu et al.
(,**-) and Al-abed et al. (,**-) reported thatanionic PAM e#ectively reduced soil loss andenhanced surface runo# water. The long chainof the ionic PAM polymer in the soil surface
exposed to non-saline rain water could be apossible reason of reduction in soil loss. As Yu
et al. (,**-) explained that the chain length of
the PAM polymer in diluted solutions mightreach to a certain length and the polymer absorbed on external surfaces of aggregates andbound soil particles together, thereby developing higher resistance to the impacts of raindrops.
This result in Fig. . seems consistent withthe e#ects of PAM on the stability of soil aggregate of the low and high ESP levels as given
in Fig. /. The stability of the aggregate having, to *.*1/ mm was enhanced by anionic PAM
application. This is probably due to the anionic PAM incorporation with soil particles andreduction of sediment formation. PAM is anadhesive agent which is combining small particles into from large ones that can resist soil
erosion. The large fraction (῎*.*1/ mm) was
reported as an appropriate range to assess theability of soils to withstand rain impacts(Rasiah and Kay, +33/). Furthermore, as fraction of the largest aggregate increased, the formation of small particles decreased (Berthes◊
and Roose, ,**,). The results in general indicate that PAM stabilized the larger size frac-60ΐῐ῎῔῕ῑ ῒ ++* ῏ ῌ,**2῍Fig. . E#ect of PAM on surface runo# and soil loss at di#erent ESP subjected to non-saline watertions, suggesting that soil erosion from soil
treated with PAM would be less than that fromcontrol and this result is consistent with
reports by other workers (Berthes◊ and Roose,,**,).
-. - E#ect of PAM mixed with gypsum on
soil erosion under non-saline rain water
As shown in previous sections, the cumulative runo# and cumulative soil loss were notclearly a#ected by gypsum application rate or
by ESP level (Fig. ,). While, PAM application
alone was found enhancing surface runo# anddecreasing soil loss (Fig. .). As shown in Fig. 0,
mixing PAM with gypsum decreased surface
runo# compared to the soil treated with PAM
alone. Higher dose of gypsum application
caused generally a slight decrease in surface
runo#. It seems that the low rate of PAM
application mixed with gypsum is more e#ec-῎῍ : Evaluation of Powdered Polyacrylamide Application along with Source of Electrolytes
in Controlling Sodic Soil Erosion

Fig. /

61

E#ect of PAM on soil aggregate stability at two di#erent soil ESP levels

tive for certain soils than gypsum application
alone. On the other hand, the application of
PAM with gypsum greatly reduced the soil
loss compared to gypsum alone (Fig. , and Fig.
0). The maximum load of soil loss from soil
treated with PAM mixed with gypsum was 1
Mg haῌ+ whereas the minimum load of soil loss
from that treated with gypsum alone was 2 Mg
haῌ+. In detail, an increase in trend of cumulative soil loss with increasing gypsum application was found particularly on the soil treatedwith PAM at the rate of ,* kg haῌ+. This was
similar to the results of Yu et al. (,**-). He
reported that PAM along with gypsum treatments was found less e#ective than the application of PAM alone for reducing soil loss ofsilty loam. Shrink of the PAM structure ac-companied by a decrease in viscosity in thepresence of electrolyte, especially gypsum,
could be a reason of less e#ectiveness of PAM
with gypsum treatment. Although, surface application of dissolved PAM mixed with asource of electrolytes such as phosphogypsum
has been reported to be more e#ective indecreasing seal formation, surface runo#, andsoil erosion (Shainberg and levy, +33.). The useof dry PAM mixed with gypsum also could
result in lower runo# and wash erosion levels
than gypsum alone in loamy sand and clay
soils (Tang et al., ,**0), which is in agreementwith our result for intake rate observed onhigh ESP soils (Table -).
Basic intake rate of high ESP soil under nonsaline water di#ered among treatments as



62

Fig. 0++*,**2

Characteristics of soil erosion at di#erent ESP and treated with PAM mixed with gypsum
subjected to non-saline water

follows : PAM 2* kg ha+ PAM ,* kg ha+PAM ,*gypsum , Mg ha+ῌPAM 2*gypsum , Mg ha+ PAM ,*gypsum / Mg ha+
(Table -). It seems that improving the soil
inﬁltration is the beneﬁt from the applicationof PAM with a source of electrolytes such as
gypsum on sodic soil conservation, since thePAM e$cacy for preventing seal formation
was enhanced by the presence of electrolytes(Shainberg et al., +33*).
-. . E#ect of PAM on soil loss under various saline rain waters
PAM treated soil showed greater soil loss
under saline water rainfall than non-saline
water rainfall (Fig. . and Fig. 1). The increasein soil loss could be associated to the shrinking
of PAM chain structure as reported by Yu et al.

(,**-). Soil loss decreased with increasing PAM
application rate except with the soil having
medium ESP and also with the low ESP one
when this soil was subjected to 2 dS m+ salinerain water (Fig. 1). A signiﬁcant decrease insoil loss with increasing PAM application rate
was found on the soil having the highest
ESP, ,/../, in which whose ECe was the lowest
among treatments. In the low and high ESP
soils treated with PAM, it seems that increasing EC of the saline rain water enhanced cumulative soil loss but decreased surface runo#(Fig. 1). Decrease in surface runo# with increasing EC in saline rain water shows that thesoil inﬁltration was substantially improved. It
seems that the e#ects of saline water on thesoil treated with PAM were fairly similar to῎῍ : Evaluation of Powdered Polyacrylamide Application along with Source of Electrolytes
in Controlling Sodic Soil Erosion

63

Fig. 1 E#ect of PAM on soil erosion at di#erent ESP subjected to saline rain water

those soils treated with gypsum mixed with
PAM (Fig. 0). Based on the results in Fig. 0 and
Fig. 1, it shows a distinct reduction of soil loss
from soil treated either PAM with gypsum or
PAM with saline water compared to that fromthe soil treated with either gypsum or saline
water alone (Fig. , and Fig. -). The aim of gypsum application was to increase the electrolyte
concentration on soil surface prior to rainfall to
restrict the dispersion of clay particles. In thisexperiment, higher initial electrolyte concentration of the soil could shrink the PAM structure and decrease its e$ciency in binding soil
particles. This could be the reason that PAM
together with saline water induced higher detachments of soil particles and less surface
runo#, which could be veriﬁed by analyzing
the changing pattern of both surface runo#

and soil loss on the medium ESP soil in Fig. 1.
Laboratory and ﬁeld studies with anionic
PAM (e.g., Gardiner and Sun, ,**, ; Bjorneberg
et al., ,**- ; Vacher et al., ,**-) have demonstrated that addition of small amounts of PAM(+*ῌ,* kg haῌ+) on the soil surface were e#ective to maintain high permeability and decrease runo# and soil loss from soils exposed to
impact of rain drops, especially when the PAM
was applied together with a source of electrolytes (Tang et al., ,**0). In our study, where thee#ect of PAM on soil erosion of sodic soils wastested with solutions of di#erent electrolyte
concentrations ; the results obtained were inconsistent and could not relate to the salt concentration of rain water used particularly on
the medium ESP soil (Fig. 1). Ben-Hur et al.
(+33,b) and Levy et al. (+33/) have noted that



64

even at ESP 3, the impact of PAM tested withsolutions of di#erent electrolyte concentrations was found ine#ective or less e#ective on
soil erosion from sodic soil as compared tonon-sodic conditions. Conversely, these sameauthors found that PAM mixed with source ofelectrolytes was very e#ective in reducing soil
erosion even at ESP,/ (Levy et al., +33/). In
our study, it seems that the impact of PAM
tested with solutions of di#erent electrolyte
concentrations was found e#ective in reducing
surface runo# only on the soil having high ESP
and low ECe, precisely under the soil treatedwith 2* kg ha+ PAM (Fig. 1).
The increased PAM application exhibited
lower inﬁltration rate in the high ESP soil of
intake rate experiment (Table -). The ﬁnal rateof water intake di#ered among the treatments
as follows : PAM 2* kg ha+ with non-saline
waterPAM ,* kg ha+ with non-saline waterPAM 2* with saline water of , dS m+PAM,* with saline water of , dS m+ῌPAM ,* withsaline water of / dS m+PAM 2* with saline
water of , dS m+. When PAM was mixed withsaline water, the accumulated electrolytes on
soil surface improved hydraulic conductivity
even under high sodic conditions. However,adding PAM with high concentration (2* kgha+) might induce soil surface sealing and consequently inhibit inﬁltration rate. In the study
conducted by Tang et al. (,**0), he found increasing ESP from / to ,* in the loamy sanddecreased ﬁnal inﬁltration rate from +. to , mmh+ and increased runo# and wash erosion in
the control ; similar trends but of di#erent
magnitude were noted in the other soil types.
He concluded that spreading PAM mixed with
gypsum or gypsum alone was e#ective inmaintaining ﬁnal inﬁltration rate, low runo#,and low wash erosion levels as compared with
control.
..

Conclusion

The e#ects of anionic PAM mixed with
gypsum and subjected to saline rain water on
artiﬁcial sodic soil erosion under simulated++*

,**2

rainfall condition were studied. The e#ects ofgypsum and saline water treatments on surface runo# and soil loss on di#erent soil
sodicity level were a#ected initial soil ESP,
ECe, and SAR and EC of rain water. Soil loss
seems to be controlled by soil surface conditions such as ECe, and ESP of the soil and EC
and rain drop impact of simulated saline water
rainfall while inﬁltration and runo# may bea#ected whole soil chemical conditions.
The anionic PAM was very e#ective thanapplying electrolyte source alone in controlling soil loss. Beside, PAM could not reduceruno# or in some case reduced water intake ofsoil since PAM clogged pores of the surface
soil. This side e#ect was improved by supplying electrolytes by either applying gypsum orsaline water rainfall. Those electrolytes may
shrink PAM structure and prevent clogging
pores by PAM. PAM application is e#ective to
reduce soil loss, however sensitivity of PAM
structure and physical properties on electrolyte concentration must be considerd. This isimportant especially planning PAM application onto saline and sodic soil that inherently
contains some sort of electrolytes.
Acknowledgement
The authors gratefully acknowledge the assistance support provided by Mr. T. Shimizu
during the rainfall simulation experiments.
Acknowledgement is also extended to Dr. M.
Irshad, visiting professor of Arid Land Research Center (ARLC), Tottori University, for
his editorial comments. This research was
carried out under the Cooperative Research
Program of ARLC.
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