the effect of superabsorbent polymers on the water holding capacity and water potential of karkhe...

International Journal of Scientific Research in Knowledge (IJSRK), 1(9), pp. 317-324, 2013 Available online at http://www.ijsrpub.com/ijsrk

ISSN: 2322-4541; ©2013 IJSRPUB

http://dx.doi.org/10.12983/ijsrk-2013-p317-324

317

Full Length Research Paper

The Effect of Superabsorbent Polymers on the Water Holding Capacity and Water

Potential of Karkhe Noor Sandy Soils

Heydar Ali Kashkuli1*

, Narges Zohrabi2

1Department of Irrigation and Drainage, Sciences and Research Branch, Islamic Azad University, Khouzestan, Iran

2Young Researchers Club, Khouzestan Sciences and Research Branch, Islamic Azad University, Ahvaz, Iran

*Corresponding Author: Email: [email protected]

Received 30 June 2013; Accepted 22 July 2013

Abstract. Superabsorbent polymers are used in agriculture for the purpose of increasing water use efficiency in arid and semi-

arid regions. In this research two kinds of superabsorbent polymers, Super AB A200 and Herbosorb were used on sandy soils

of Karkhe Noor river bank near Hamidieh. The effect of 5 concentration levels of 0.3, 0.6, 0.8, 2 and 4 grams per kilogram of

soil in 3 replications was studied on the parameters of soil moisture characteristic curve using RETC program and Rosetta

database. It was observed that fitting of the data to the RETC model was better compared to Rosetta. Statistical analysis of the

research results show that for sandy soils in these experiments there was a significant difference at one percent level for all the

polymers used and the control treatment at suctions of 0.3, 1, 3, 5 and 15 bars. On the other hand for the different concentration

levels of 4, 2, 0.8, 0.6 and 0.3 g/kg soil, volumetric soil moisture content showed a significant difference at one percent level.

Among the superabsorbents used A200 with application rate of 4 g/kg soil resulted in the highest effect. Soil available water

for plant use showed an increase compared to the control treatment. It was finally concluded that the application of 4 gram

Super AB A200 and Herbosorb per kilogram soil increased soil available water about 350 and 320 percent respectively.

Key words: Model of characteristic moisture curve, sandy soil, superabsorbent polymers, water holding capacity in soil.

1. INTRODUCTION

Water use efficiency is one of the main concerns in

sustainable agriculture development in arid and semi-

arid regions. Water holding capacity of sandy soils is

very low and thus requires very frequent irrigation

applications in arid regions leading to greater losses

and lower irrigation efficiencies. Leaching of salts and

chemical fertilizers is also considerable under these

conditions. One of the recent methods for more

optimum utilization of water resources under these

conditions is the use of superabsorbent polymers.

Superabsorbent polymers are hydrophobic gels called

hydrogels that absorb a lot of water, salts and

physiologic solutions. These polymers not only absorb

and hold a lot of water but can also act as miniature

water holding reservoirs that supply water for plant

use in the time of need. Agricultural superabsorbent

chemicals were introduced in 1970 by American

researchers. Several American, European and Asian

companies are at present producing these polymers.

Yearly production of these polymers reached 1290

m tons in 2005. Sohrab (2003) investigated the effect

of adding six different types of water absorbents, two

types of superabsorbents and four natural water

absorbents at 4 levels, to 3 different soils i.e. sandy,

loam and clay textures. They also indicated that

increasing the level of superabsorbent addition for all

soil types caused an increase in the water holding

capacity at saturation (θs) and residual volumetric

water content (θr). Superabsorbent polymers showed a

greater effect on increasing soil water holding

capacity. With the addition of superabsorbent

polymers, capillary pressure soil moisture models of

Brooks – Corey and Van- Genuchten showed a better

fitting of data compared to the program using Rosetta

database.

The slope of the moisture characteristic curve (n)

decreased for all the textures examined. This decrease

was more in sandy soils, indicating a lower rate of

water loss. In these soils air entry pressure (hb = 1/α)

increased in sandy soils, but in loamy and clayey

soils, with the addition of superabsorbent polymers it

decreased. Plant available water was higher for all

textures compared to control. The effect of using

polymers for increasing soil porosity was more

pronounced in sandy soils due to higher expansion of

polymers in such soils which caused 4 times in

microporosity compared the control. In loamy soils

the increase in capillarity and air filled porosity was to

the same extent. In clayey soils air filled porosity did

not show major changes except for higher polymer

concentrations. Montazar (2008) examined the effect

of Stakosorb superabsorbent on the advance phase and

infiltration parameters of soils in furrow irrigation and

showed that by increasing the amount of

superabsorbent polymers soil infiltration and advance

time in furrow irrigation increased. Doraji et al.

mailto:[email protected]

Kashkuli and

Zohrabi

The Effect of Superabsorbent Polymers on the Water Holding Capacity and Water Potential of Karkhe Noor Sandy

Soils

318

(2009) studied the effect of different level of

superabsorbent polymers of Super AB and soil

salinity on the water holding capacity of sandy, loamy

and clay soils and reported that polymers used in soils

specially in sandy soils can be helpful for crop

production in arid and semi-arid climates by

increasing the water holding capacity and decreasing

soil solution salinity. Kabiri (2002) reported that these

materials besides increasing the water holding

capacity of light soils can also improve the infiltration

problems of heavy soils also. Besides water holding

capacity in soils, superabsorbent polymers increase

soil air content due to continual volume change as a

result of expansion and contraction. Karimi et al.

(2007) reported that addition of Igita as the soil

conditioner improves soil physical characteristics

indirectly affecting plant growth, delaying plant

wilting, increasing irrigation interval and hence

resulting in efficient use of irrigation water. Rajaee

and Raeisi (2010) showed that A200 polymer use

under dry conditions results in the improvement of

microbiological and biochemical properties.

Lesijevsky (2009) investigated the use of hydrogel

chemical effect on water holding capacity of sandy

soils of forest nursery soils and found that water

holding capacity especially at pF less than 2 increases.

This is due to the fact that hydrogel polymer prevents

gravitation water from downward movement. Agaba

et al. (2010) studied that effect of hydrogel application

on different soils for water holding capacity

evaluation and plant survival under drought

conditions. They found that for 8 plant species out of

9 planted, evapotranspiration decreases for application

of 0.4 percent by weight hydrogel for all the soil types

due to a decrease in hydraulic conductivity by

hydrogel application. In this research the effect of 2

types of superabsorbent SuperAB A200 and

Herbosorb on the parameters of soil moisture

characteristic curve are studied by matching collected

moisture-suction data to two well known soil moisture

modes. Furthermore volumetric water content at each

suction and the amount of plant available water for the

sandy soils of Karkhe Noor river banks in Khouzestan

province are also evaluated.

2. MATERIALS AND METHODS

Sandy soil material was collected from a field near

Karkhe Noor River close to Hamidieh town. Physical

and chemical soil properties are shown in table 1.

Table 1: Physical and chemical soil properties

90 Sand (percent)

2 Silt (percent)

8 Clay (percent)

sandy texture

1.7 gr/cm³ Bulk density

2.61 gr/cm³ Real specific gravity

0.7 Volumetric water content (percent)

30.1 Saturation moisture content (percent)

7.8 pH

3.5 ECe of saturation extract (ds/m)

In order to compare water absorption capacity of

polymers in distilled water, tap water and soil

saturation extract, 0.1, 0.2 and 0.3 grams of each

polymer was put in the above solutions for 24 hours

and the swollen gels were weighed. The ratio between

the original gel weigh before swelling to the weight

after swelling was evaluated on the degree of

swelling. Super AB A200 was the product of Rahab

Rezin Company under the license of Iranian

Petrochemical Company and Herbosorb made by

Herbosorb Company of England was used. They were

mixed with soil at 5 concentrations of 0.3, 0.6, 0.8, 2

and 4 gram per kilogram of soil in 3 replications. Soils

moisture content was measured at 7 suctions (0, 0.1,

0.3, 1, 3, 5 and 15 atmosphere) using pressure plate

apparatus.

Metal cylinders of 4 cm diameter and 2.2 cm

height were used. A filter paper and rubber band were

used to seal the bottom of cylinders that were filled

with the mixture of 30 grams of soil with

superabsorbent at 5 levels described above. Prepared

samples were put on a saturated sand box for 24 hours

for the samples to reach saturation. The saturated

samples were than weighed and put in the pressure

plate apparatus with pressures regulated at 0.1, 0.3, 1,

3, 5 and 15 atmosphere for 24 hours. After reaching

equilibrium indicated by outflow stoppage at each

applied suction, the samples were taken out and

weighed before and after drying for 24 hours at 105°C

for the calculation of the water content at an specified

suction.

Soil moisture characteristic curve parameters of

Brooks – Corey and Van Genuchten equations, were

derived using RETC curve fitting programs. The

equations are:

International Journal of Scientific Research in Knowledge (IJSRK), 1(9), pp. 317-324, 2013

319

= r + (s - r) (h)-

(1)

mnrsr ]h)()[1θ(θθθ

(2)

In which θs, θr, α, n and λ are volumetric saturated

moisture content, volumetric residual moisture

content, reciprocal of air entry suction, slope of the

moisture characteristic curve between field capacity

and wilting point and grain size distribution index

(Van Genochten, 1991). Rosetta program uses the

neural network logic for the estimation of three

parameters using soil texture data an input (Schaap

and Bouten, 1996).

Soil pedotransfer functions relate easily obtainable

soil parameters like bulk density, soil texture, organic

matter and suctions at 33 and 1500 Kilo Pascal to

costly measured properties like soil moisture

characteristic curve h (θ) and unsaturated hydraulic

conductivity function.

3. RESULTS AND DISCUSSION

Water absorption rate of A200 and Herbosorb

polymers in water of different electrical conductivities

is shown in figure (1).

Fig. 1: Polymers water absorption rate of different electrical conductivities.

3.1. The effect of superabsorbent polymers on the

parameters of soil moisture characteristics curve

3.1.1. Saturation moisture content (θs)

Generally saturation moisture content (θs) increases

with increasing added superabsorbent rate. The

increase in θs estimated by the 2 models of RETC

were the same and showed a better fitting compared to

θs of Rosetta. For sandy soils the highest θs value was

for A200 polymer used. As to the superabsorbent

used, the rates 4, 2, 0.8, 0.6 and 0.3 gave higher values

of (θs), respectively as shown in figure (2).

3.1.2. Residual moisture content (θr)

According figure (3) results of the effect of both

polymers used shows that θr values increase by

increasing the rate of polymer application. In both

cases θr values derived by using Van- Genuchten and

Brooks – Corey’s model were equal and showed a

better fitting compared to Rosetta. The highest amount

of θr was for A200 superabsorbent at a rate of 4 grams

per kilogram that was 230 percent higher than the

control sample.

Electrical conductivity (ds)

Wat

er a

bso

rpti

on

rat

e (p

erce

nt)

Kashkuli and

Zohrabi


Soils

320

Fig. 2: Variation of soil saturation moisture content (θs) with polymers A200 and Herbosorb

Fig. 3: Variation of residual volumetric moisture content with different levels of A200 and Herbosorb polymers

3.1.3. Slope of soil moisture characteristic curve (n)

By adding superabsorbents to the soil, the slope of

the soil moisture characteristic curve decreases due to

an increase in water holding capacity. The lowest

value of n was obtained from Brooks – Corey and Van

Genuchten matching of measured values. Van

Genuchten model gave a higher value of n with

increasing amount of polymer used whilst as was

shown previously n value decreases with increasing

polymer rate for both models of Brooks – Corey and

Van Genuchten. Therefore it can be concluded that

Van Genuchten model for estimation of n in sandy

soils is reliable. Table (2) shows n values of Brooks –

Corey for all the treatments including the control

treatment.

Different levels of polymer (gr / kg of soil)

Sat

ura

tio

n m

ois

ture

con

ten

t of

soil

(p

erce

nt)

R

esid

ual

vo

lum

etri

c m

ois

ture

co

nte

nt

of

soil

(per

cen

t)

Different levels of polymer (g/kg of soil)


321

Table 2: n values of Brooks – Corey and control treatment for different levels of superabsorbent polymer

Control

Levels different of polymer (gr/kg) Superabsorbent

0.3 0.6 0.8 2 4

0.74 0.71

0.71

0.67

0.67

0.64

0.66

0.62

0.63

0.59

0.60

A200

Herbosorb

3.1.4. Air entry pressure (hb = 1/α)

In sandy soils due to larger pore sizes, water drains

out at lower suctions. In other words α is large in such

soils. Adding superabsorbent polymers to such soils at

higher dosage causes their expansion and extension of

sandy pores, thus increasing the contact between soil

and water requiring higher suctions for water release

(Bybordi (1993), Alizade (2009).

Results obtained from all the 3 models indicate a

decrease in α and an increase in air entry pressure.

A200 and Herbosorb used at 4 grams per kilogram of

soil gives the least value for α. Values of α of Brooks

– Corey equation in comparison with the control is

shown in table (3).

Table 3: Values of α of Brooks and Corey in comparison with the control due to the use of different levels of superabsorbent

polymer

Superabsorbent Polymer dosage rate (g/kg)

Control 0.3 0.6 0.8 2 4

A200

Herbosorb

0.054

0.054

0.049

0.049

0.047

0.047

0.044

0.045

0.043

0.043

0.024

0.025

3.2. Soil moisture characteristic curve

Soil moisture characteristics curve for each polymer

based on the comparison between different levels of

superabsorbent polymers used and control treatment is

given in Figs (4) and (5). Study of soil moisture

curves in the low moisture suction range of 0-3 bar to

higher range of 3-15 bar reveals that:

(a) At low suction most of the water absorbed by

the polymer is released. For example by application of

4 gram A200 polymer per kilogram soil (Fig 4), soil

moisture drops from 49.64 to 14.25 percent. Moisture

release at low suction is therefore considered to be an

advantage of superabsorbents because plants can

absorb most of the water stored at low suction.

(b) Comparison of residual moisture content at

high suctions (3-15 bar) and the moisture content at

low suctions (0-3 bar) with control treatment show

that the difference between the residual moisture

content of all treatments compared to the control

treatment increases with increasing polymer

application rate. For example at the application rate of

4 gram A200 polymer per kilogram soil, soil moisture

increases by 250 percent compared to the control in

the moisture suction ranges.

3.3. Analysis of moisture characteristic curve at

different suctions

0.1, 0.3, 1, 3, 5 and 15 bar suction

Generally at 5 measured suctions significant

difference at 1% level was observed between 2

polymers A200 and Herbosorb used and the control

treatment. On the other hand between application rates

of 4, 2, 0.8, 0.6 and 0.3 gram per kilogram, significant

differences at 1% level of soil moisture content at

seven suctions was observed. For sandy soils the

effect of both polymers for increasing soil moisture at

each suction was considerable and close to each other.

Statistical analysis shows that A200 polymer

application at 4g/kg gives the largest increase in

moisture content at any suction.

Volumetric moisture percent increases by 105 to

about 300 percent compared to the control depending

on the application rate.

Kashkuli and

Zohrabi


Soils

322

Fig. 4: The effect of superabsorbent A200 application rate in g/kg soil on the soil moisture characteristic curve of sandy soils

Fig. 5: The effect of superabsorbent Herbosorb application rate in g/kg soil on the soil moisture characteristic curve of sandy

soils.

3.4. Plant available moisture (0.3 to 15 bars)

For sandy soils used in this research, available soil

moisture increase compared to the control treatment

was significant at 1% level for the polymers used.

Table (4) shows soil moisture percent at field

capacity (FC), wilting point (PWP) and available soil

moisture for the control and polymer application

treatments. According to table (4) soil moisture at FC

and PWP increase 110 to about 280 percent. The

largest increase of available moisture was due to A200

polymer use at a rate of 4 g/kg application which is

344 percent greater than the control. Herbosorb

however showed an increase of 317 percent compared

to the control.


323

Table 4: Volumetric water content at FC, PWP and available water for different superabsorbent polymers of sandy soils

Moisture Condition Polymer type Control Polymer dosage rate (g/kg)

0.3 0.6 0.8 2 4

Field Capacity Super AB A200

Herbosorb

7.32 8.77

8.39

11.03

9.76

12.72

10.68

15.34

13.43

21.08

18.61

Wilting Point Super AB A200

Herbosorb

4.28 5.21

4.99

6.62

5.82

7.79

6.29

9.32

7.46

10.62

8.96

Plant Available Moisture Super AB A200

Herbosorb

3.04 3.56

3.4

4.41

3.94

4.93

4.39

6.02

5.97

10.46

9.65

4. CONCLUSION

The following conclusions can be drawn from this

research:

(a) By increasing salinity polymer swelling

decreases. A200 swelling rate is greater than

Herbosorb; (b) Improvement of soil structure is

obtained by using superabsorbent polymers; (c)

Percent soil moisture at saturation and residual

moisture content as well as soil moisture content at

any suction increase considerably by polymer

application and is higher for A200 compared to

Herbosorb; (d) Soil moisture is released of low

suctions; (e) Increase in available moisture occurs at

high suctions; (f) At high polymer application rates,

available moisture increases by more than 300

percent; (g) At present, application of polymers may

not be economically recommendable due to the price

of these chemicals in Iran, but considering that their

application can increase the available soil moisture

several fold, this will reduce the number of irrigations

and therefore reduce the cost of irrigation applications

which make their use economical if water pricing

policies are implemented.

ACKNOWLEDGMENTS

The paper presents part of a research project by the

title of "Investigation of hydraulic characteristics

of sandy soils under the application of

Superabsorbents” in the department of irrigation,

Science and Research Branch, Islamic Azad

university, Khouzestan –Iran. The authors thank

Science and Research Branch, Islamic Azad

University, Khouzestan –Iran for their valuable

support during the study.

REFERENCES

Agaba H, Orikiriza, LJB, Esegu JFO, Obua J, Kabasa

JD (2010). Effects of Hydrogel Amendment to

Different Soils on Plant Available Water and

Survival of Trees under Drought Conditions.

Clean – Soil, Air, Water, 38 (4): 328 – 335.

Brooks R H, Corey A T (1964). Hydraulic Properties

of Porous Media. Hydrology Paper, Colorado

State Univ. Fort Collins, Colorado, No3.

Kabiri K (2002). An Introduction to the uses of

Superabsorbent Hydrogel Polymers in Different

Industries. Proceeding of the Second Workshop

on the use of Superabsorbent Hydogels, Tehran,

Iran, p 1-32.

Karimi A, Noshadi M, Ahmadzade M (2007). The

Effect of Superabsorbent Polymer Application

on Soil, Water, Plant Growth and Irrigation

Period. Journal of Water and Soil Science

(Science and Technology), 46(13): 403-414.

Leciejewski P (2009). The Effect of Hydrogel

Additives on the Water Retention Curve on

Sandy Soil from Forest Nursery in Julinek.

Journal of Water and Land Development, 13a:

239-247.

Montazar A (2008). Study of the Effect of Stockosorb

Superabsorbent Polymer on the Flow Advance

and Infiltration Parameters of Furrow Irrigation.

Journal of water and soil, 22(2): 341-357.

Rajaee F, Raeesi F (2010). The Role of Superab A200

on Soil Moisture Stress and its Effect on

Nitrogen Availability and Enzymatic Activity

of Urea in Soils. Iranian Journal of Water

Research, 14(7): 13-24.

Schaap MG, Bouten W (1996). Modeling Water

Retention Curves of Sandy Soils using Neural

Networks. Water Resource, 32:3033-3040.

Seyed Doraji S, Golchin A, Ahmady SH (2009).

Effect of Different Application Rates of

Superab A200 and Soil Salinity on the Water

Holding Capacity of 3 Sand, Loam and Clay

Soil Textures. Journal of Soil and Water, 24(2):

306-316.

Sohrab F (2003). Evaluation of the Effect of

Superabsorbent Polymers on the Water Holding

Capacity of Ardestan Soils. MS thesis,

Irrigation and Drainage Department, Esfahan

Sanaati University. 132 pages.

Van Genuchten MTh, Leij FJ, Yates SR (1991). The

RETC Code for Quantifying the Hydraulic

Functions of Unsaturated Soils. Res. Rep. 6002-

91 065. USEPA, Ada, Ok.

Van Gneuchten, MTh (1980). A Closed-Form

Equation for Predicting the Hydraulic

Conductivity of Unsaturated Soils. Soil Sci.

Soc. Am. J., 44: 892-898.

Kashkuli and

Zohrabi


Soils

324

Dr Heidar. A. Kashkuli is professor of irrigation & drainage at science of research branch of Islamic

Azad University. He studied for his Ph.D. at Colorado state university, M.Sc. at the university of

Wageningen The Netherlands and B.Sc. at the American university of Beirat. His teaching and

research interests is in the field of drainage, groundwater, flow through porous media and water

quality. He has many years of experience as consultant engineer and supervisor. He was appointed as

distinguished irrigation & drainage scholar in 2009.

Dr. Narges Zohrabi holds a Ph.D. in hydrology and water resources from the Science and Research

Branch, Islamic Azad University of Tehran, and M.Sc. in irrigation and drainage from the Shahid

Chamran University of Ahvaz, Iran. Her core research interests include hydroclimate parameter

variability and climate changes, flood frequency analysis, hydrological time series, water quality.

Currently, she is an Assistant professor of irrigation department, science and research branch, Islamic

Azad University, Khouzestan, Iran.

the effect of superabsorbent polymers on the water holding capacity and water potential of karkhe...

Documents