Journal of Hydrology 373 (2009) 177–183

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Journal of Hydrology

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Water retention, hydraulic conductivity of hydrophilic polymers in sandy soilas affected by temperature and water quality

H. Andry a,*, T. Yamamoto a, T. Irie a, S. Moritani a, M. Inoue a, H. Fujiyama b

a Arid Land Research Center, Tottori University, 1390 Hamasaka, Tottori 680-0001, Japanb Faculty of Agriculture, Tottori University, Minami 4-101 Koyama, Tottori 680-8553, Japan

a r t i c l e i n f o

Article history:Received 10 February 2009Received in revised form 16 April 2009Accepted 21 April 2009

This manuscript was handled by G. Syme,Editor-in-Chief

Keywords:Sandy soilCarboxymethylcelluloseIsopropyl acrylamideTemperatureSoil hydraulic properties

0022-1694/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.jhydrol.2009.04.020

* Corresponding author. Tel.: +81 857 23 3411; faxE-mail address: andry_78486@yahoo.com (H. And

s u m m a r y

Hydrophilic polymers can swell by absorbing huge volumes of water or aqueous solutions. This propertyhas led to many practical applications of these new materials, particularly in arid regions for improvingwater retention in sandy soils and the water supply to plants grown on them. The effects of two hydro-philic polymers, carboxymethylcellulose (RF) and isopropyl acrylamide (BF) on the water holding capac-ity and saturated hydraulic conductivity (KS) of a sandy soil at varying soil temperature and water qualitywere evaluated. The RF was less efficient in absorbing water than BF, but the efficiency of BF in retainingwater was negatively affected by its thermo-sensitivity and the quality of water. The temperature depen-dence of the water absorption was not clear for the soils treated with RF, whereas, the efficiency of BFtreatment in absorbing water decreased significantly (P < 0.05) with increasing soil temperature. Thedependence of the KS on soil temperature differed with the type of hydrophilic polymer used. The KS

of the control soil remained nearly constant as the soil temperature increased. The KS of the BF treatedsoil increased significantly (P < 0.05) and linearly with increasing soil temperature, while that of soil trea-ted with RF showed a quadratic response. The soil–absorbent mixtures exhibited different water reten-tion characteristics under different soil temperature conditions. The increase in soil temperature did notaffect the water retention characteristics curve of the control. The effect of soil temperature on the waterpotential curve of the soil treated with RF was not clear particularly when the temperature increasedfrom 25 to 35 �C. The water potential curve for soil–BF mixtures showed that the water content valueat field capacity shifted from 0.21 to 0.10 cm3 cm�3 for 0.1% and from 0.27 to 0.12 cm3 cm�3 for 0.2%,as the soil temperature increased from 15 to 35 �C. This implies that the soil–BF absorbent mixtureswould release some moisture as the soil temperature would increase from 15 to 35 �C, and this watercould be lost by percolation or taken up by plant. It was found that available water content increasedup to four times with RF as compared to control soil whereas it increased up to five times with BF treat-ment. At high temperature, the difference was much reduced except for RF at 0.2%. This understanding ofthe characteristics of the absorbents and the interactions among absorbents, soil, and temperature wouldbe of help in water management in sandy soil.

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Introduction

Sandy soils are characterized by low water-holding capacityand excessive drainage of rain and irrigation water below the rootzone, leading to poor water and fertilizer use efficiency by plantsgrown on them. Seed germination and plant development are crit-ically restricted because of low soil moisture content. Furthermore,the problem becomes accentuated when plants with shallow root-ing are grown. The efficiency of the use of rain and irrigation waterby plants is of great importance in semiarid and arid regions,where shortage of water is frequently experienced and water is of-ten the limiting factor determining the size of the cultivated area.

ll rights reserved.

: +81 857 29 6199.ry).

In modern agriculture many hydrophilic polymers are used toenhance both the nutritional and water status of plants. It has beenreported that these hydrophilic polymers are capable of retainingwater up to 500 times of their weight (Buchholz, 1998), can buildan additional water reservoir for the plant–soil–system (e.g. Bour-anis et al., 1995), and can, therefore, reduce water stress in plants.Flannery and Busscher (1982) and Johnson (1984) have reportedthat the use of hydrophilic polymers increases the amount of avail-able moisture in the root zone, thus permitting longer intervals be-tween irrigations. Hydrophilic polymers are effective in increasingthe water holding capacity, decreasing deep percolation, andreducing evaporation losses in sandy soils (El-Shafei et al., 1992).Moreover, the use of hydrophilic polymers leads to increased wateruse efficiency since the water that would have otherwise leachedbeyond the root zone is captured. During hot days, the root hair

178 H. Andry et al. / Journal of Hydrology 373 (2009) 177–183

system of a plant pulls out and depletes most of the water from thearea close to the root system, thus causing the plant to go intostress. While increasing the amount of available moisture, hydro-philic polymers help reduce water stress of plants resulting in in-creased growth and plant performance (Baker, 1991). It has alsobeen reported that hydrophilic polymers have the potential for aid-ing seed germination and emergence and increasing the seedlingsurvival (Gray, 1981; Azzam, 1983), and increasing the nutrientrecovery from applied fertilizers. Soil water diffusivity as a func-tion of soil water content was also found to decrease substantiallywith an increase in the hydrophilic polymer soil conditioner (El-Shafei et al., 1994). The saturated hydraulic conductivity decreasedconsiderably with an increase in the concentration of hydrophilicpolymer soil conditioner in the soil (El-Shafei et al., 1992, 1994).

Although the improvement of sandy soil hydraulic propertiestreated with the hydrophilic polymer has been widely reported;the knowledge of the polymer absorption and desorption charac-teristics under different soil temperature conditions could help inproper design of irrigation management. It is well-known thatpolymers with suitable hydrophilic–hydrophobic balance may ex-hibit thermo-sensitivity. Zhao et al. (2005) reported that hydro-philic polymer absorption decreased with increasing temperaturefrom 30 to 60 �C; however, there is a lack of information on thedependence of hydrophilic polymers characteristics on soiltemperature.

Fluctuations in soil temperature and soil moisture are closelylinked, but rarely studied together (Bryla et al., 2001). Soil moisturenot only affects root physiology directly, but also affects soil ther-mal properties. Thus, dry soils typically fluctuate much morewidely in daily temperature than wet soils. Soil temperature isan important physical factor because of the role it plays in plantgrowth and yield. It determines the type and rate of different phys-ical and chemical reactions in the soil. The functional activities ofplant roots such as absorption and translocation of water are alsorelated to the soil temperature (Monteith, 1977). The soil proper-ties that determine the behavior of soil water flow are mainlythe hydraulic conductivity and water retention characteristics.The hydraulic conductivity of a soil is a measure of its ability totransmit water and it is the fundamental process upon whichplants water uptake depends. Thus, knowledge of the unsaturatedhydraulic conductivity of soils as a function of soil water contentand as affected by hydrophilic polymer under different tempera-ture conditions is essential. A detailed understanding of the hydro-philic polymer absorption and desorption characteristics underdifferent soil temperature conditions will be essential for designingirrigation scheduling system that may lead to the improvement ofthe water use efficiency in arid regions.

Hydrophilic polymers are derived from many sources with wideranging properties, and many of them have considerable economicand technical importance (Azzam, 1980). Simultaneous manage-ment of the environment with rehabilitation of agriculture condi-tion is among the processes that promote sustainabledevelopments in arid regions. For instance, incorporating hydro-philic polymer in the sandy soil could save much water by decreas-ing the water loss from percolation and releasing the water at thetime when plants need it. It has been found that plants grown insoil amended with hydrophilic polymers were slower to wilt thanthose in unamended medium (Woodhouse and Johnson, 1991). Inorder to achieve this aim, the use of hydrophilic polymers derivedfrom industrial waste material is among the most suitable soilwater conditioning practices. This will improve not only the wateruse efficiency in sandy soil but can also alleviate the industrialwaste material disposal issues in the region. However, informationregarding the effects of a given hydrophilic polymer type on someof the physical properties of the soil under sandy soil conditions isnecessary before its field application. The objective of this study

was to examine the effect of two hydrophilic polymers derivedfrom industrial waste on the water holding capacity and hydraulicconductivity of sandy soil, as affected by soil temperature andwater quality.

Materials and methods

Soil, hydrophilic polymer material, and experimental set up

The experiments were conducted using samples of a sandy soilfrom Tottori University, Arid Land Research Center, Japan. The soilcontained 40 ± 2, 55 ± 3, and 905 ± 15 g kg�1 of clay, silt, and sand,respectively. The electrical conductivity of the soil in water (1:5)was 0.078 ± 0.002 dS m�1, the cation exchange capacity of the soilat pH 7 was 3.5 ± 0.2 cmolc kg�1, and soil organic carbon contentwas 6 g kg�1.

Two hydrophilic polymers developed by the Miyamazaki Kaga-ku Corporation Company based on Bemberg fiber derived fromindustrial waste material were used in this study: carboxymethyl-cellulose (RF) and isopropyl acrylamide (BF). The median grain sizeof RF and BF was 0.45 and 0.3 mm, respectively. Each of the twohydrophilic polymers was mixed with dry sandy soil to give mix-tures of 0 (control), 0.1%, and 0.2% which corresponded to 0, 1,and 2 g absorbent kg�1 of soil, respectively. These mixing ratioswere selected to ensure that the growth of plant roots would notbe adversely affected. Bradford and Yang (1981) affirmed thatone consideration in deciding the amounts of hydrophilic polymeris that they can cause water-logging side effects, thereby creatingan anaerobic system. Water-logging causes toxin to build up by se-verely limiting oxygen to the roots. Water-logging effects are visi-ble when the plant wilts because water is no longer movingupward from the roots (Bradford and Yang, 1981).

Three sets of air temperature based on the fluctuation of dailyair temperature in arid region i.e., 15, 25, and 35 �C were testedin this study in a controlled environment room. The soil sampleswere prepared and kept in the controlled environment room for3 days at a particular temperature before the studies were startedto establish a soil temperature similar to the air temperature. Allexperiments were conducted at a constant ambient air relativehumidity of 97 ± 3%.

Moisture retention and soil–absorbent mixtures’ hydraulic properties

The water absorption capacities of the hydrophilic polymersalone were determined with the teabag method as described inthe study of Buchholz (1998). Commercial teabag of 9.5 cm lengthand 7 cm height was used in this study. One gram of hydrophilicpolymer was packed in a teabag and submerged into a preparedsolution for 3 days (Buchholz, 1998). Solutions of liquid SumitomoFertilizer (13.42 g nitrogen L�1, 97.6 g phosphorus L�1, and 61 gpotassium L�1) with distilled water dilution ratios of 0, 1:2000,1:1000, 1:500, and 1:100, based on the rate of liquid fertilizer gen-erally applied in arid regions, were prepared and used in this study.Similarly, solutions of saline water were prepared with NaCl at asalt concentration of 1000, 4000, and 15,000 ppm to simulate thequality of irrigation water available in the arid regions. The pH va-lue of all prepared solutions was adjusted to seven with 1 M HCl or1 M NaOH. The weight of the swollen absorbent was measuredafter the excess surface solution was removed by filter paper.The water absorption capacity was computed from the ratio ofthe weight of swelled absorbent and the weight after oven dryingat 105 �C for 48 h.

One hundred and fifty grams of dry soil–absorbent mixtureswere packed in 100 cm3 soil columns (5 cm diameter and 5.1 cmheight) to get a bulk density of 1.55 Mg m�3. The saturation was

H. Andry et al. / Journal of Hydrology 373 (2009) 177–183 179

undertaken from the bottom of the soil columns with deionisedwater (pH = 7) for 24 h under controlled room temperatures.Soil–absorbent swelling over the top edge of the soil column wascut and smoothly removed before performing the studies of soilhydraulic properties.

The water absorption capacity of the soil–absorbent mixtureswas characterized by the swelling ratio. This ratio was calculatedas the difference between the soil bulk densities before and aftersaturation and divided by the former one.

The saturated hydraulic conductivity (KS) was measured follow-ing the falling-head method as described by Klute and Dirksen(1986). The moisture retention, for the drying cycle, was measuredsuccessively by applying suction equivalent to matrix potentialsranging from pF�0 to pF�2 and the centrifuge method was followedfor the subsequent pF values. The suction was created with a vac-uum pump having a maximum suction of 1000 cm head pressure.The pF�3 and pF�4 were successively measured by centrifuging thesuctioned soil columns for 1 h at turning velocity of 3000 and9500 rpm, respectively. The residual moisture content was deter-mined by oven drying the soil sample at 105 �C for 48 h. The avail-able water content (AWC) for plants was estimated from thedifference between water contents at matrix potentials of pF�1.6

and pF�3, representing, respectively, the field capacity and wiltingpoint of sandy soil in arid regions.

Four replications were used for each treatment. The four repli-cate data of swelling, KS, and AWC were subjected to a mean sep-aration analysis using one-way ANOVA test at significance ofP < 0.05.

Results and discussion

Water absorption capacity of the pure hydrophilic polymer

The amount of distilled water absorbed by the two hydrophilicpolymers during 3 days as a function of temperature is presentedin Fig. 1. The water absorption characteristics of carboxymethylcel-lulose (RF) and isopropyl acrylamide (BF) differed significantly(P < 0.05) as a function of temperature. The water absorption ofRF showed only a slight increase with increasing temperature,the amount of water absorbed being 77, 92, and 95 g g�1 of absor-

0

50

100

150

200

250

300

15 ºC 25 ºC 35 ºC

Temperature

Wat

er u

ptak

e (g

/g)

RF

BF

Fig. 1. Water absorption capacity of the absorbent alone under different temper-ature conditions. Bars indicate ±1 standard deviation.

bent at 15, 25, and 35 �C, respectively. Suo et al. (2007) reported anincrease in water absorbency of carboxymethylcellulose until abath temperature of 50 �C as a result of a higher polymerizationrate, which leads to the decline of the absorbing efficiency accord-ing to Flory’s network theory. Our result implies that RF can beused in a wide range of soil temperature. Fig. 1 further shows thatthe RF was less efficient in absorbing water than BF highlightingthat water-absorbing capacity was inversely related to the mediangrain size of the hydrophilic polymers as reported in the study ofBhardwaj et al. (2007). However, the efficiency of BF decreased sig-nificantly (P < 0.05) up to 60% when the temperature increasedfrom 15 to 35 �C. The amount of water absorbed was 249, 219,and 145 g g�1 of absorbent at temperatures of 15, 25, and 35 �C,respectively. The decrease in water absorption by isopropyl acryl-amide could be the result of the dependence effect of temperature.As the temperature was increased, the water absorbency de-creased, with the most drastic decrease being around the lowercritical solution temperature (LCST), about 25–32 �C. The main rea-son for this characteristic of the hydrophilic polymers is the uniqueand rapid alternation of the hydrophilic and hydrophobic states(Okano et al., 1990; Xu et al., 2006). At temperatures below theLCST, the hydrophilic groups of the hydrophilic polymers formhydrogen bonds with water molecules. These bonds act to form astable shell of hydration around the hydrophobic groups, resultingin greater water uptake and producing larger water absorption. Asthe external temperature increases, the associative interactionsamong the hydrophobic groups release the entrapped water mole-cules from the hydrophilic polymer networks.

The amount of water absorbed by the two hydrophilic polymersduring three days of submersion under different water qualities(pH = 7) at 25 �C is shown in Fig. 2. The water absorption efficiencyof both hydrophilic polymers decreased significantly with increas-ing electrical conductivity (EC) of the solution. This was in agree-ment with the findings reported by Green et al. (2004) withcross-linked polyacrylamides, and Zhao et al. (2005) with poly(aspartic acid). Green et al. (2004) reported that the drastic reduc-tion in water absorption of cross-linked polyacrylamides could beexplained by the collapse of the structure of the hydrophilic poly-mer by the salt effect. On the other hand, Zhao et al. (2005) indi-cated that the commonly observed swelling of ionic hydrophilicpolymers often resulted from a charge screening effect of addi-tional cations causing a non-perfect anion-anion electrostaticrepulsion that led to a decreased osmotic ionic pressure differencebetween the polymer network and the external solution. In ourstudy, the effects indicated by Zhao et al. (2005) might have oc-curred on the hydrophilic polymers when they were submergedinto a solution, since the collapsing of their structure was notclearly noticed. It was also observed in our study that the efficiencyof isopropyl acrylamide (BF) in retaining water was significantly(P < 0.05) affected by the quality of water compared to carboxy-methylcellulose (RF). A slight increase in the EC of the solutioncaused a significant (P < 0.05) decrease in water absorption of BFas compared to that of RF. This result could be useful for selectinga type of hydrophilic polymer suitable based on the water qualityfor the designed irrigation system.

Water absorption capacity of the soil–absorbent mixtures

The water absorption characteristics were determined from theswelling property of the soil–absorbent mixtures after saturation.The saturation resulted in the expansion of the soil–absorbent mix-tures above the upper edge of the soil column, which was removedbefore testing hydraulic properties. Based on the methodologyused in this study, it is noted that the lower value was the dry bulkdensity after the experiment, greater was the swelling of the treat-ment. The expending of the soil–absorbent mixtures occurred

0

50

100

150

200

250

300

350

Distilled water 0.0005 0.001 0.002 0.01 1000 4000 15000

Rate of fertilizer application (v/v) Saline water concentration (ppm)

Treatment

Wat

er u

ptak

e (g

/g)

0

5

10

15

20

25

30

Ele

ctri

cal c

ondu

ctiv

ity

EC

(dS

/m)

RF BF

EC

Fig. 2. Water absorption capacity of the absorbent alone under different water quality treatments at temperature of 25 �C. Bars indicate ±1 standard deviation.

180 H. Andry et al. / Journal of Hydrology 373 (2009) 177–183

mainly as a result of the absorbent swelling which increased withincreasing concentration of the absorbent in the soil as has alsobeen reported by Buchholz (1998). The swelling depended on theamount and type of the absorbent used in the mixture. Fig. 3 showsthat the water absorption increased with increasing mixing ratio ofthe soil–absorbent, and isopropyl acrylamide (BF) was more effi-cient than carboxymethylcellulose (RF).

The effect of temperature on the soil mixtures of the two hydro-philic polymers (Fig. 3) differed as they followed the trend of theirrespective water absorption characteristics without soil in thedeionised water as shown in Fig. 1. The swelling ratio of soil trea-ted with RF increased significantly (P < 0.05) at low rate of mixing(0.1%) with increasing temperature while at the higher rate of mix-ing (0.2%) there was a significant (P < 0.05) decrease as the temper-ature increased from 25 to 35 �C. The efficiency of BF treatment inabsorbing water decreased significantly (P < 0.05) with increasingsoil temperature at both levels of mixing. Comparing the resultsin Figs. 1 and 3, it is clear that the decrease in water absorption

Temperature

Swel

ling

rati

o (%

)

0

2

4

6

8

10

12

14

15 ºC 25 ºC 35 ºC

Control RF-0.1 % RF-0.2 % BF-0.1 % BF-0.2 %

Fig. 3. Swelling capacity of soil–absorbent mixtures under different temperatureconditions. Bars indicate ±1 standard deviation.

of the soils treated with BF as affected by the soil temperaturewas much less than that of absorbent alone. In the treatments, eachabsorbent granule is surrounded by soil particles and subjected toa confining pressure by these particles (Buchholz, 1998). As a re-sult, being confined by the soil matrix, the absorbent granularcan form hydrophilic interactions in the soil block that can stilllead to some water uptake (Xu et al., 2006) though the degree ofswelling of the BF mixture was limited compared to that of the freeabsorbent in a solution.

Saturated hydraulic conductivity of the soil–absorbent mixtures

The saturated hydraulic conductivity (KS) of the soil–absorbentmixtures is shown in Fig. 4. The KS decreased significantly(P < 0.05) with the increase in mixing ratio of hydrophilic polymer.It was inversely correlated with the soil–absorbent swelling prop-erties. The decrease was more under isopropyl acrylamide (BF)treatment than that with carboxymethylcellulose (RF). This could

Satu

rate

d hy

drau

lic c

ondu

ctiv

ity

(cm

/ s

1)

Temperature

0.0001

0.001

0.01

0.1

15 ºC 25 ºC 35 ºC

Control RF-0.1 % RF-0.2 %

BF-0.1 % BF-0.2 %

Fig. 4. Saturated hydraulic conductivity of soil–absorbent mixtures under differenttemperature conditions. Bars indicate ±1 standard deviation.

H. Andry et al. / Journal of Hydrology 373 (2009) 177–183 181

be attributed to the difference in their water absorption character-istics. The increase in soil–absorbent swelling and the clay disper-sion affected by the use of deionized water during saturation mighthave caused soil structure degradation leading to decrease in porespace between soil aggregates and, ultimately decreased KS value(Levy et al., 2004). A similar decrease in KS with application ofhydrophilic polymer was reported by El-Shafei et al. (1992).

The dependence of the saturated hydraulic conductivity on soiltemperature differed with the type of hydrophilic polymer used.The KS of the untreated soil (control) remained nearly constant asthe soil temperature increased. The KS of the soil treated with BFincreased significantly (P < 0.05) and linearly with increasing soiltemperature, while a quadratic response was found with RF treat-ment. However, as shown in Fig. 4, all the treatments induced anincrease in KS at 35 �C. Based on this result, applying the irrigationwater in the early morning when the temperature is generally low-er than 25 �C could result in more water saving from deep percola-tion loss.

Water retention of the soil–absorbent mixtures

The amount of water retained by the soil alone and the soil–absorbent mixtures as a function of matrix potential is shown inFig. 5. The soil–absorbent mixtures retained significantly(P < 0.05) more water than the control soil, and the water contentincreased with increasing amount of hydrophilic polymer in thesoil. Isopropyl acrylamide (BF) was more efficient than carboxy-

5.0

4.0

3.0

2.0

1.0

0.0

5.0

4.0

3.0

2.0

1.0

0.0

25 ºC

35 ºC

15 ºC

0.0 0.2 0.4

Volumetric w

pF

pF

5.0

4.0

3.0

2.0

1.0

0.0

5.0

4.0

3.0

2.0

1.0

0.0

25 ºC

35 ºC

15 ºC

0.0 0.2 0.4

Volumetric w

pF

pF

Control BF-0.1 %

RF-0.1 %

Fig. 5. Water retention characteristics of soil–absorbent mixtures under different tempeand wilting point (pF�3) of the sandy soil on its own.

methylcellulose (RF), which is consistent with the soil–absorbentswelling characteristics, and the water retention has positive cor-relation with soil saturated hydraulic conductivity. The controland soil–absorbent mixtures exhibited different water retentioncharacteristics under different soil temperature conditions. The in-crease in soil temperature did not affect the water retention char-acteristics curve of the control. The water potential curve showedthat the water content value at field capacity shifted from 0.21 to0.10 cm3 cm�3 for the soil treated with 0.1% BF and from 0.27 to0.12 cm3 cm�3 for the soil treated with 0.2% BF as the soil temper-ature increased from 15 to 35 �C. This would imply that the soil–absorbent mixtures would be releasing moisture as the tempera-ture would increase from 15 to 35 �C, and this water could be lostby percolation or taken up by plant. The effect of soil temperatureon the water potential curve of the soil treated with RF was notclear particularly when the temperature increased from 25 to35 �C.

The available water content (AWC) retained by the soil–absor-bent mixtures is shown in Fig. 6. It was found that AWC increasedup to four times with RF as compared to control whereas it in-creased up to five times with BF treatment. The control soil showeda slight increase in AWC with increase in soil temperature, whereasin case of soil–absorbent mixtures a decrease in AWC was ob-served. A significant decrease (P < 0.05) was found in the soil trea-ted with BF. The isopropyl acrylamide (BF) treatment showed anegative linear dependence of water retention on soil temperature,whereas a quadratic relationship was observed with the carboxy-

0.6 0.0 0.2 0.4 0.6

ater content (cm3/cm3)

0.6 0.0 0.2 0.4 0.6

ater content (cm3/cm3)

BF-0.2 %

RF-0.2 %

rature conditions. The horizontal lines represent the assumed field capacity (pF�1.6)

0

0.05

0.1

0.15

0.2

0.25

15 ºC 25 ºC 35 ºC

Temperature

Ava

ilabl

e w

ater

con

tent

(cm

3 / cm

3)

Control RF-0.1 % RF-0.2 % BF-0.1 % BF-0.2 %

Fig. 6. Available water content in soil–absorbent mixtures at different temperature conditions. Bars indicate ±1 standard deviation.

182 H. Andry et al. / Journal of Hydrology 373 (2009) 177–183

methylcellulose (RF) treatment. The increase in mixing ratio from0.1% to 0.2% did have a significant effect (P < 0.05) on AWC atany soil temperature except in the case of soil treated with RF at15 �C.

This study highlighted that carboxymethylcellulose (RF) andisopropyl acrylamide (BF) hydrophilic polymers can be used aswater absorbents in sandy soils of arid and semi arid regions.The results could help in deciding the right irrigation water timingsuch as in the early morning when the soil temperature is gener-ally below 25 �C. AWC of all treatments was higher at 15 �C anda gradual release in the portion of AWC could be expected withdiurnal changes in soil temperature. This would be of help inincreasing water use efficiency and plant production in thoseregions.

Conclusions

In this study, the effects of two hydrophilic polymers, carboxy-methylcellulose (RF) and isopropyl acrylamide (BF) on the waterholding capacity and saturated hydraulic conductivity (KS) of a san-dy soil as affected by soil temperature and water quality wereevaluated.

The difference in the water absorption characteristics of RF andBF was controlled by temperature of the solution. The RF was lessefficient in absorbing water than BF. However, the efficiency of BFin retaining water was negatively affected by its thermo-sensitivityand the quality of water. A significant decrease in water absorptioncapacity of BF was observed with increasing solution temperatureor a slight increase in electrical conductivity in the solution ascompared to that of RF.

The temperature dependence of the water absorption was notclear for the soils treated with RF, whereas, the efficiency of BFtreated soil in absorbing water decreased significantly (P < 0.05)with increasing soil temperature. The dependence of the saturatedhydraulic conductivity of treatment on soil temperature differedwith the type of hydrophilic polymer used. The KS of the controlshowed little change with increasing soil temperature. The KS ofthe soil treated with BF increased significantly (P < 0.05) and line-arly with increasing soil temperature, while a quadratic responsewas found with the RF treatment. However, it was found that allthe treatments induced an increase in KS at 35 �C. The controland soil–absorbent mixtures exhibited different water retention

characteristics under different soil temperature conditions. The in-crease in soil temperature did not affect the water retention char-acteristics curve of the control. The water potential curve of the soiltreated with RF was not much conspicuously affected particularlywhen the temperature increased from 25 to 35 �C. The water po-tential curve for soil–BF mixtures showed that the water contentvalue at field capacity shifted from 0.21 to 0.10 cm3 cm�3 for0.1% and from 0.27 to 0.12 cm3 cm�3 for 0.2%, as the soil tempera-ture increased from 15 to 35 �C. This would imply that the soil–absorbent mixtures would be releasing moisture as the tempera-ture would increase from 15 to 35 �C, and this water could be lostby percolation or taken up by plant. AWC increased up to fourtimes with RF as compared to control soil whereas it increasedup to five times with BF treatment.

Information on the AWC improvement in sandy soil through thebeneficial effects of adding hydrophilic polymer is significantlyimportant for designing irrigation management systems. Thisstudy highlighted that applying the irrigation in the early morningcould help to save more water on a sandy soil treated with hydro-philic polymer by reducing percolation loss. Also, better under-standing of the characteristics of the two hydrophilic polymerswill be helpful in selecting a type of absorbent suitable for a giventype of irrigation management system, such as the quality of irriga-tion water used.

Acknowledgments

This research was supported by the G-CEO Project in Arid LandResearch Center of Tottori University. The authors thank to theMiyamazaki Kagaku Corporation for providing the two hydrophilicpolymers reported in this study. Acknowledgement is also ex-tended to Dr. Mohan Saxena, visiting professor at ALRC, for his edi-torial comments.

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