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Research Paper

Effects of water quality and PAM application rate on thecontrol of soil erosion, water infiltration and runoff fordifferent soil textures measured in a rainfall simulator

A.R. Sepaskhah*, V. Shahabizad

Irrigation Department, Shiraz University, Shiraz, Islamic Republic of Iran

a r t i c l e i n f o

Article history:

Received 5 January 2010

Received in revised form

22 May 2010

Accepted 28 May 2010

Published online 13 July 2010

* Corresponding author.E-mail address: sepas@shirazu.ac.ir (A.R.

1537-5110/$ e see front matter ª 2010 IAgrEdoi:10.1016/j.biosystemseng.2010.05.019

The effects of different rates of polyacrylamide e PAM (0, 2.0, and 6.0 kg ha�1) applied with

a sprinkler using wastewater (electrical conductivity e EC of 1.9 dSm�1) and freshwater (EC

of 0.5 dSm�1) on runoff, soil erosion and infiltration were studied in laboratory using

a rainfall simulator. Three different soil textures (sandy loam, loam, and silty clay loam)

and three irrigations were used but only the first contained PAM. At heavier soil textures,

higher PAM application rates (�6.0 kg ha�1) were effective at enhancing the final infiltration

rate and reducing the runoff and soil erosion. For loam the PAM application rate of 2.0 kg ha�1 reduced runoff 28 and 25% with application of freshwater and wastewater, respectively,

but was not effective at reducing runoff in the second irrigation when using wastewater.

For silty clay loam, using freshwater, 6.0 kg ha�1 PAMwas required to reduce runoff and soil

erosion in the first and second irrigation events, while using wastewater, 2.0 kg ha�1 PAM

reduced the runoff and soil erosion 32 and 46%, respectively, in the first irrigation event,

however, reduction did not occur in the following irrigation events. For the different soil

textures, the threshold value where runoff initiated of soil erosion and the slope was higher

for wastewater compared to freshwater. This was probably because the PAM became bound

to the solids in the wastewater and was not available to stabilise the soil surface.

ª 2010 IAgrE. Published by Elsevier Ltd. All rights reserved.

1. Introduction reduces runoff (Santos & Serralheiro, 2000; Santos, Reis,

Residue management as conservation practise to control soil

erosion has not been readily adopted due to usage of crop

residues for other purposes. In some countries, e.g., the I.R. of

Iran, residues from crops such aswheat and barley are utilised

by animal feed. Therefore, residue management is not avail-

able to protect soil surface from erosion (Sepaskhah &

Bazrafshan-Jahromi, 2006).

Application of polyacrylamide (PAM) to soil stabilises its

structure and increases its resistance to erosion, it decreases

soil erodibility factor, increases water infiltration and it

Sepaskhah).. Published by Elsevier Lt

Martins, Castanheira, & Serralheiro, 2003; Sepaskhah &

Bazrafshan-Jahromi, 2006). The effects of PAM on soil

erosion and runoff reduction and infiltration enhancement

have been studied in furrow and sprinkler irrigationwith non-

saline water (Abu-Zreig, Al-Sharif, & Amayreh, 2007; Lentz &

Sojka, 2009; Sepaskhah & Bazrafshan-Jahromi, 2006;

Sepaskhah & Mahdi-Hosseinabadi, 2008).

Water quality may interact with the chemical structure of

PAM (Shainberg, Warrington, & Rengasamy, 1990; Wallace &

Wallace, 1996) and it can change its behaviour in soil.

Shainberg et al. (1990) found that salts in soil solution that

d. All rights reserved.

Nomenclature

BOD biological oxygen demand

C PAM application rate, kg ha�1

COD chemical oxygen demand

clay soil-clay content, %

Ero soil erosion, g

EC electrical conductivity, dSm�1

FIR final infiltration rate

Ks saturated hydraulic conductivity

N number of irrigation event

PAM polyacrylamide

Ro runoff, mm

R2 coefficient of determination

SE standard error

SAR sodium adsorption ratio

sand soil sand content, %

TSS total suspended solids

b i o s y s t em s e n g i n e e r i n g 1 0 6 ( 2 0 1 0 ) 5 1 3e5 2 0514

flocculate clay minerals enhanced the beneficial effect of

polymers on the aggregate stability. El-Morsy, Malik, and Letey

(1991a, 1991b) investigated the combined effects of polymers

and salts in water (electrical conductivity {EC} values of 0.5,

2.0, and 5.0 dSm�1 and sodium adsorption ratio {SAR} values

of 5, 15, and 25) on soil saturated hydraulic conductivity (Ks)

and found that beneficial effects of polymers were greater in

soils treated with water that has high EC values. In addition to

salts in irrigation water, high PAM concentration and surfac-

tants may affect infiltration. Recently, Lentz (2003) found that

applying 10 mg [PAM] l�1 plus anionic surfactant to silty loam

and sandy loam soils reduced Ks by up to 70% relative to the

same PAM concentration without surfactant. Ajwa and Trout

(2006) indicated that PAM applied in irrigation water will

reduce infiltration unless the materials improve surface soil

aggregate structure and sustain pores sufficient to mask the

effect of solution viscosity.

As metropolitan areas extended, the use of freshwater for

municipal and industrial use increases. Therefore, water

resources for irrigation become limited. Under conditions of

freshwater shortage, wastewater reuse for irrigation is

a remedial measure. Hence, the effects of suspended solids in

wastewater on the soil physical and chemical properties are

considered. One of themost important soil physical properties

that are affected by wastewater use is soil saturated hydraulic

conductivity, Ks.

Viviani and Lovino (2004) reported a 20% reduction in Ks by

applying 175 mm of wastewater with total suspended solids

(TSS) of 57e60 mg l�1 in a loam soil. They showed a higher

reduction in Ks in a clay soil. Blocking the soil pores of the top

soil layer by the TSS of wastewater was the main reason for

the Ks reduction (Viviani & Lovino, 2004). Vinten, Mingelgrin,

and Yaron (1983a, 1983b) studied the effect of TSS on Ks in

sandy, loam, and silty loam soils. They reported the

maximum Ks reduction in silty loam soil, and concluded that

continuous use of wastewater resulted in flooding, surface

runoff and erosion. Sepaskhah and Sokoot (in press) studied

the effects of wastewater with different TSS on Ks reduction of

different soil textures. They found the Ks reduction of 80% for

the surface layer of sandy loam, loam, and clay loam soils.

However, this reductionwas very low for the subsurface layer.

Baveye, Vandevivere, Hoyle, Deleo, and Delozada (1998)

indicated that organic carbon in wastewater increased the

microorganism activity in soil and the higher microorganism

population which resulted in blockage of the soil pores.

Ragusa, de Zoysa, and Rengasamy (1994) showed that high

concentration of polysaccharide in wastewater resulted in Ks

reduction in soils. With respect to the possible effects of dis-

solved organic matter on the soil, a number of studies have

shown that its presence in wastewater enhanced soil-clay

dispersivity and increased the clay flocculation value

(Tarchitzky, Golobati, Keren, & Chen, 1999).

Bhardwaj, Goldstein, Azenkot, and Levy (2007) studied the

effects of wastewater application by drip and sprinkler irri-

gations on Ks of disturbed and undisturbed soils. They indi-

cated that the effect of wastewater on Ks reduction was more

pronounce in undisturbed soils and the Ks reduction affected

more by irrigation methods. Reduction in Ks usually results in

higher runoff and soil erosion. Application of different soil

conditioners may overcome the Ks reduction. Application of

natural zeolite increased the Ks as reported by Sepaskhah and

Yousefi (2007).

McElhiney and Osterli (1996) showed that PAM, applied to

a fine-textured soil in the San Joaquin Valley, California, USA

resulted in a 10e40% increase in infiltration rate. Most of the

PAM studies have been performed on clay loam or silt loam

soils with low aggregate stability where soil erosion is evident.

Trout and Ajwa (2001) performed a series of field test on

a sandy loam soil to determine whether emulsion PAM addi-

tion to furrow irrigation resulted in increased infiltration

rates. Their trials using water of three ion concentrations

(EC¼ 0.03, 0.3, and 1.2 dSm�1) failed to show any increase in

infiltration with PAM. Although the chemical composition of

water can affect infiltration rates and Ks of soils, limited

information is available on the interaction between PAM and

salt and TSS in wastewater as irrigation water on the infil-

tration rate.

Although several studies evaluated optimum PAM appli-

cation for medium-to- heavy texture soils (Bjorneberg et al.,

2003; Lentz, Sojka, & Mackey, 2002), limited information is

available on application practises for use of PAM with various

quality of wastewater in sprinkler water application in

different soil textures.

Literature on PAM use in agriculture has recently been

reviewed (Sojka, Bjorneberger, Entry, Lentz, & Orts, 2007).

A 1e2 kg [PAM] ha�1 application was shown to be effective for

erosion and infiltration management in furrow irrigation.

Furthermore, other researchers discovered that this approach

decreased runoff losses of nutrients, sediment-associated

pesticides, and microorganisms (Oliver & Kookana, 2006a,

2006b; Sojka et al., 2007). However, the optimum application

rate for PAM is influenced by soil slope (Sepaskhah &

Bazrafshan-Jahromi, 2006) and may also be affected by the

quality of the wastewater.

b i o s y s t em s e ng i n e e r i n g 1 0 6 ( 2 0 1 0 ) 5 1 3e5 2 0 515

The objectives of this study were to determine the effects of

different ratesof PAM(0, 2.0, and6.0 kg [PAM] ha�1) appliedwith

sprinkler irrigation with wastewater (EC of 1.9 dSm�1) and

freshwater (EC of 0.5 dSm�1) on runoff, soil erosion and

improving infiltration rates under a rainfall simulator in labo-

ratory. There were three different soil textures (sandy loam,

loam, silty clay loam) and three irrigations that only the first

contained PAM.

2. Methods and materials

The study was conducted in the Sediment Hydraulic Labora-

tory of the Irrigation Department, Shiraz University at Shiraz,

I.R. of Iran. Surface layer soil (0e0.2 m depth), of three soils

with different textures was obtained for the study and placed

in large bags. The three soil textures are sandy loam, loam and

silty clay loam. Some physical and chemical properties of

these soils are shown in Table 1.

Seven steel boxes were used for the study (Fig. 1). Each box

was 1.4 m long, 1.4 m wide and 0.09 m deep. The down-slope

edge of the box kept level to provide uniform runoff through to

funnel water and sediment into catch containers (Fig. 1). The

boxes were hinged so surface slope could vary. The experi-

ment was conducted at a slope of 2.5%.

Large clods were removed or broken prior to filling the

boxes by passing the soil through a 5e8 mm screen. The soil

surface was stirred, mixed and slightly packed prior to level-

ling. The resulted bulk density varied between about

1.0 Mgm�3 for silty clay loam and 1.4 Mgm�3 for sandy loam.

The soil surface and soil depth mimicked a dry freshly tilled,

field seedbed. Soil water contents were between 8.4% and

12.6% (mass basis) for sandy loam (about 56% of total available

water), 13.7% and 14.8% (mass basis) for loam (about 57% of

total available water), and 16.9% and 17.6% (mass basis) for

silty clay loam (about 20% of total available water) before

different irrigation treatments at the start of each test.

Irrigation water was applied through a rainfall simulator,

similar to that originally designed by Morin, Goldberg, and

Seginer (1967). Details of this apparatus are given in the user

manual of the manufacturer (Anonymous, 1998). The appli-

cation rate through the nozzle was 64.3 mmh�1 under a pres-

sure of 100 kPa mounted at a height of 2.65 m. Well water, as

freshwater, andwastewater were used in this study. Chemical

properties of thewaters are shown inTable 2. Each soil boxwas

irrigated for 25 min to apply 26.8 mm of water. Based on the

equation presented by Wischmeier and Smith (1978), the

rainfall energy striking the soil surface was about 741 Jm�2.

Table 1 e Some physical and chemical properties of soils.

Soil texture Clay%

Silt%

Sand%

Field capacitym3m�3

Silty clay loam 35 48 17 0.34

Loam 13 46 41 0.24

Sandy loam 10 19 71 0.23

Dry granular anionic PAM copolymer with a molecular

weight of over 5 MgM�1 was used. The required irrigation

water was stored in a tank with dimensions of

0.65 m� 1.22 m� 0.62 m. The required active ingredient of

PAM was added to the tank to prepare solutions of 0, 8.5 and

25.5 mg g�1 for application rates of 0, 2, and 6 kg ha�1. The

prepared solution was pumped to the irrigation nozzle and

applied to the soil surface with the specified initial water

content.

PAMwas added in the first irrigation in every test, followed

by two water-only irrigations. Between each irrigation appli-

cation, the soil was allowed to dry for 2e8 d until water

contents of the soil reached to 8.4e12.6% (mass basis) for

sandy loam, 13.7e14.8% (mass basis) for loam, and 16.9e17.6%

(mass basis) for silty clay loam before different irrigation

treatments at the start of each test. Each test for PAM appli-

cation rate and soil texture was repeated three times.

Prior to each test, four soil samples were taken from each

box with a 50 mm core sampler to determine antecedent soil

water content by gravimetric method. The holes left by the

core samples were filled with soil and gently packed to

prevent preferential flow.

The runoff volume in the catch container was measured at

different times, and by dividing it by the soil surface area, the

runoff per unit area was determined. Therefore, the runoff rate

per unit area was measured at different times. The, infiltration

ratewasdetermined by subtracting the runoff rate per unit area

from the water application intensity. A 1.5-m high curtain was

placed around the soil tray as close as possible to protect the

water splash and loss. In this determination, the soil surface

water detention in small depressions was assumed negligible.

Data from three replications was used in fitting infiltration rate

equation for each treatment. The infiltration rate at the end of

the irrigationwaterapplicationwasconsideredasthemeasured

final infiltration rate in this experiment. At the end of each

experiment, total runoff volume was collected in a bucket and

measured by a volumetric cylinder. The sediment in the runoff

was settled for 24 h and separated from the runoff by filter

paper. The settled sediment oven dried for 2 days andweighed.

Experiments for each soil texture were conducted in a 3� 2

factorial arrangement with three replications.

3. Results and discussion

3.1. Runoff

Runoff was not statistically significantly influenced by PAM

application with the consecutive application of freshwater

Permanentwilting point

m3m�3

Organicmatter %

pH Saturationextract salinity

dSm�1

0.13 2.4 7.9 1.70

0.08 1.1 7.8 0.42

0.04 0.8 7.8 0.37

Fig. 1 e Schematic diagram of the soil tray and runoff and

soil erosion collection accessories.

b i o s y s t em s e n g i n e e r i n g 1 0 6 ( 2 0 1 0 ) 5 1 3e5 2 0516

and wastewater (Table 3) in sandy loam. Therefore, up to

a PAM application of 6.0 kg ha�1 it was not effective at

reducing runoff for applications of the wastewater and

freshwater. Application rates higher than 6.0 kg ha�1 were

effective for sandy loam. This finding is in accordance to the

findings of Letey (2000) that indicated the PAM application is

not effective for controlling runoff for sand and sandy loam.

One possible reason is that these soils do not tend to have

surface sealing that reduces infiltration. In other words, the

PAM cannot reduce surface sealing if it does not form a seal.

Runoff was statistically significantly increased by consec-

utive applications of the wastewater compared with applica-

tion of the freshwater (Table 3) in sandy loam. This occurred

due to the differences in quality of wastewater and freshwater

(Table 2). It is anticipated that application of the wastewater

with higher values of EC and SAR dispersed the soil particles

and resulted in crust formation on the soil surface (Kazman,

Shainberg, & Gal, 1983; Mamedov, Shainberg, & Levy, 2000).

The effect of EC and SAR of irrigation water on runoff

enhancement was increased at PAM application of 6.0 kg ha�1

in the first irrigation event (Table 3). In other words, the

difference between runoff from freshwater and wastewater is

greater for 6 kg [PAM] ha�1 compared to 0 and 2 kg [PAM] ha�1.

These results are in contradiction to those reported by

El-Morsy et al. (1991a, 1991b) that found the beneficial effects

of the polymers were greater in soils treated with water that

had high EC values. This might have occurred due to the

texture of soil (sandy loam) used in this study. Ajwa and Trout

(2006) indicated that PAM applied by irrigation water in sandy

loam reduced infiltration rates. Therefore, the application of

6.0 kg [PAM] ha�1 was less effective on runoff reduction when

applied by the wastewater compared with that of freshwater.

This might have occurred because the value of SAR (sodium

Table 2 e Chemical and biological properties of freshwater an

Water type pH EC dSm�1 SAR TSS mg l�1

Wastewater 7.8 1.9 5.6 95

Freshwater 7.4 0.5 0.48

a Chemical oxygen demand.

b Biological oxygen demand.

c Escherichia coli.

content) for wastewater is higher than that for freshwater

(Table 2).

Application rates of 2.0 and 6.0 kg [PAM] ha�1 with the

freshwater andwastewater significantly reduced the runoff in

the loam in the first irrigation event. However, there was no

statistical difference between 2.0 and 6.0 kg [PAM] ha�1 appli-

cation rates with the freshwater and wastewater (Table 3).

Furthermore, the freshwater application with 2.0 and 6.0 kg

[PAM] ha�1 significantly reduced the runoff in the first and

second irrigation events, while, these rates of PAM application

with the wastewater resulted in significant runoff reduction

only in the first irrigation event. The effects of PAM applica-

tion with the wastewater were not shown in the second and

third irrigation events.

An application rate of 6.0 kg [PAM] ha�1 with the fresh-

water significantly reduced the runoff in the silty clay loam in

the first and second irrigation events, but it was not effective

in the third irrigation event (Table 3). Application rates of 2.0

and 6.0 kg [PAM] ha�1 with the wastewater significantly

reduced the runoff only in the first irrigation event and their

effects were not appeared in the second and third irrigation

events. Furthermore, no statistical difference occurred

between 2.0 and 6.0 [PAM] kg ha�1 applications in the waste-

water application in the first irrigation event.

The effects of PAM application on the silty clay loam was

quite different from the other soils. This was due to the higher

clay, silt and organic matter contents in the silty clay loam

compared with the loam and sandy loam. In the silty clay

loam application rate of 2.0 kg [PAM] ha�1 with the freshwater

PAM was not effective for runoff reduction although this

amount of PAM application with the wastewater was effective

for runoff reduction in the first irrigation event. This occurred

because soils with higher clay content show lower infiltration

rates and are more susceptible to particle dispersion by using

wastewater with higher values of EC and SAR and this results

in higher runoff. Therefore, applications of lower amounts of

PAM become effective for runoff reduction (Lentz, Steiber, &

Sojka, 1995).

3.2. Final infiltration rate

For sandy loam, application rate of 6.0 kg [PAM] ha�1 signifi-

cantly increased the final infiltration rate (FIR) in the first

irrigation event with both freshwater and wastewater (Table

4). PAM application was not effective at enhancing FIR in the

second and third irrigation events with the wastewater and

freshwater applications. Because there may be some water

loss due to splash (less than 5%, Sepaskhah, unpublished

d wastewater.

CODa mg l�1 BODb mg l�1 E. colic per 100 ml

50.6 15.6 1600

Table 3 e Measured values of runoff (mm) for differentrates of PAM, water types, irrigation events, and soiltextures.

Irrigation event Freshwater Wastewater

Application rate,kg [PAM] ha�1

Application rate, kg[PAM] ha�1

0 2 6 0 2 6

Sandy loam

1 4.3efg 4.2fg 3.3ga 7.0def 7.1de 6.4def

2 7.0def 5.9defg 5.9defg 11.4ab 10.5bc 11.8ab

3 8.1cd 7.1de 7.2d 14.0a 13.7a 12.6ab

Loam

1 9.7e 7.0f 5.0f 13.4d 10.7e 9.6e

2 14.0cd 10.7e 10.2e 18.0a 16.5ab 16.2abc

3 15.4bcd 13.9d 13.3d 17.9a 18.0a 17.9a

Silty clay loam

1 8.6e 7.6e 3.3f 15.1d 10.3e 9.9e

2 13.5d 13.9d 8.2e 18.8abc 15.6cd 16.3bcd

3 14.6d 13.8d 13.6d 20.4a 19.1ab 19.0abc

a Means followed by the same letters for each soil texture are not

significantly different at 5% of probability by Duncan’s multiple

range test.

b i o s y s t em s e ng i n e e r i n g 1 0 6 ( 2 0 1 0 ) 5 1 3e5 2 0 517

data), the trend of FIR enhancement followed closely the trend

of the runoff reduction (Table 3).

The effect of PAM application with the freshwater on the

enhancement of FIR in the loam was similar to that obtained

in the sandy loam. However, its application with the waste-

water was not effective on FIR. Therefore, application rate of

2.0 and 6.0 kg [PAM] ha�1 with the freshwater in the first irri-

gation event enhanced FIR. FIR enhancement in the silty clay

Table 4 e Measured values of soil final infiltration tare(mmhL1) for different rates of PAM, water types,irrigation events, and soil textures.

Irrigationevent

Freshwater Wastewater

Application rate, kg[PAM] ha�1

Application rate,kg [PAM] ha�1

0 2 6 0 2 6

Sandy loam

1 25.6bc 26.3b 31.4aa 13.8fgh 12.5ghi 19.9de

2 18.3def 22.1bcd 21.2cd 6.6jk 9.9hij 8.0ijk

3 16.2efg 20.4de 18.3def 3.7k 6.3jk 8.0ijk

Loam

1 14.1c 18.2b 24.6a 7.5efg 7.7efg 9.4def

2 9.7def 12.9cd 12.1cd 6.2fg 6.2fg 6.9efg

3 6.4fg 7.6efg 10.cde 6.0fg 5.3g 4.7g

Silty clay loam

1 19.3a 18.9a 24.3a 6.8bcde 10.8bcd 11.3bc

2 8.6bcde 12.2b 10.8bcd 4.7de 5.6cde 7.5cde

3 3.7e 8.5bcde 6.8bcde 3.9e 5.0cde 6.3bcde

a Means followed by the same letters for each soil texture are not

significantly different at 5% of probability by Duncan’s multiple

range test.

loam was not statistically significantly improved by PAM

application with different rate and irrigation events.

3.3. Soil erosion

PAMapplicationwith thewastewater and freshwater in thefirst

and other irrigation events was not effective at reducing soil

erosion (Table 5) in the sandy loam. Soil erosion is related to the

runoff. Therefore, these results for the soil erosionare similar to

those obtained for runoff reduction (Table 3). Similar to the

runoff, application rates higher than 6.0 kg [PAM] ha�1 may be

effective on the soil erosion reduction. Soil erosion with the

wastewater applicationwas higher than that obtainedwith the

freshwater application (Table 5) due to the effect of higher salt

and SAR that result in soil dispersion and crust formation. The

least soil erosion occurred in the first irrigation event and itwas

significantly lower than those in the second and third irrigation

events. This might be because of the possible formation of

a crust in the subsequent irrigation events as the effect of rain

drop impact energy on the soil surface is increased.

For the loam, different PAM application rates with the

freshwater were affected differently on the soil erosion and

the lowest soil erosion occurred at 6.0 kg [PAM] ha�1 applica-

tion rate in the first irrigation event (Table 5). However, in the

second irrigation event, PAM application was effective in the

soil erosion reduction but 2.0 and 6.0 kg [PAM] ha�1 applica-

tion rates were equally effective. There was no difference in

the soil erosion with different PAM application rates during

the third irrigation event. Application of the wastewater

reduced the effect of PAM application rates on the soil erosion

and there was no difference between the 2.0 and 6.0 kg [PAM]

ha�1 rates of application in the first irrigation event. However,

both 2.0 and 6.0 kg [PAM] ha�1 rates had less erosion than no

PAM. Furthermore, PAM application with the wastewater in

the second and third irrigation events was not effective at

reducing soil erosion.

In general, the soil erosion in the loam was higher than

obtained in the sandy loam for the corresponding rates of PAM

and irrigation events. This occurred due to the higher silt

content in the loam that makes soils more susceptible to soil

erosion.

For the silty clay loam, in the first and second irrigation

events, the freshwater with 6.0 kg [PAM] ha�1 application rate

significantly reduced the soil erosion (Table 5). However, the

PAMapplication effect diminished in the third irrigation event.

By using the wastewater in the silty clay loam, 2.0 and 6.0 kg

[PAM] ha�1 application rates only reduced the soil erosion in

the first irrigation event. Furthermore, it was shown that the

wastewater application resulted in higher soil erosion in

different irrigationeventsandPAMapplicationratescompared

with those obtainedwith the freshwater application. This was

because PAM attached to the solids in the wastewater and

therefore was not available to stabilise the soil surface.

The soil erosion in the silty clay loamwashigher than those

obtained in the loamdue to thehigher clay, organicmatter and

silt contents. Similar to the loam, the PAMapplication effect in

the silty clay loam remained in the second irrigation of the

freshwater with a rate of 6.0 kg [PAM] ha�1. However, for loam,

2.0 kg [PAM] ha�1 was also effective. Furthermore, the effects

of PAM application rates with the wastewater and irrigation

Table 5 e Measured values of soil erosion (g) for different rates of PAM, water types, irrigation events, and soil textures.

Irrigation event Freshwater Wastewater

Application rate, kg [PAM] ha�1 Application rate, kg [PAM] ha�1

0 2 6 0 2 6

Sandy loam

1 88.7f 83.0f 71.7fa 148.7de 144.7e 135.7e

2 143.0e 144.7e 139.0e 293.3bc 286.3c 283.0c

3 167.7d 171.0d 172.0d 317.0a 314.3ab 315.0ab

Loam

1 235.9f 155.3g 102.3h 329.2e 239.7f 202.3fg

2 467.8c 380.5d 379.0d 567.2b 583.4ab 570.1b

3 504.9c 471.5c 484.3c 624.0a 614.4ab 628.2a

Silty clay loam

1 491.3efg 366.8gh 151.4h 930.4cd 563.2efg 504.2efg

2 689.0def 699.7de 416.3g 1308.9b 1073.5bc 1052.4bc

3 1014.6c 1001.7c 887.4cd 1705.3a 1610.9a 1597.6a

a Means followed by the same letters for each soil texture are not significantly different at 5% of probability by Duncan’s multiple range test.

b i o s y s t em s e n g i n e e r i n g 1 0 6 ( 2 0 1 0 ) 5 1 3e5 2 0518

eventsweresimilar insilty clay loamand loamand theydidnot

remain in the second and third irrigation events.

3.4. Relationships between runoff and soil erosion

Relationships between the runoff and soil erosion for different

soil textures were determined. The data from different PAM

treatments and irrigation events were used to obtain these

relationships. The equations for these relationships are pre-

sented in Table 6. For the sandy loam, non-linear equation is

obtained that is in correspondence to that reported by Aase,

Bjornbeg, and Sojka (1998) for a silty loam. However, for the

loam and silty clay loam, these relationships are described by

linear equations that are in correspondence to those reported

by Sepaskhah and Bazrafshan-Jahromi (2006) for similar soil

texture. The intercepts of the equations in Table 6 indicate

threshold values of the runoff to initiate the soil erosion. Their

values are different for different water types and soil textures.

The runoff threshold values for the freshwater for different

textures were not significantly different. However, their

values for the wastewater were different for the sandy loam,

loam and silty clay loam. That might be due to higher aggre-

gation of loam and silty clay loam than sandy loam.

The slopes of the equations in Table 6 indicate the soil

erosion for a unit increase in runoff. These values are gener-

ally higher for the wastewater application compared with the

Table 6 e Relationships between the runoff and soil erosion fo

Water type Equa

Sandy loam Freshwater Er0¼ 115.9L

Wastewater Er0¼199.8Ln

Loam Freshwater Eor¼ 40.0(R

Wastewater Eor¼ 46.5(R

Silty clay loam Freshwater Eor¼ 67.8(R

Wastewater Eor¼ 108.4(

freshwater thatmight be due to the higher salt and SAR values

in the wastewater. Furthermore, these values in general are

higher for the silty clay loam than those of loam that is more

susceptible to erosion.

3.5. Empirical models for estimation of runoff and soilerosion

Usingmultiple regression analysis between the runoff and soil

erosion, irrigation event numbers, salinity of water and soil

primary particles contents (clay and sand), an empirical

model was developed as follows:

Ro ¼ �0:38� Cþ 3:13�Nþ 3:27� ECþ 0:13� clay

R2 ¼ 0:97; SE ¼ 2:40; n ¼ 54; p < 0:01(1)

Ero ¼ �17:68� Cþ 207:69�Nþ 12:36� clay� 7:4

� sandþ 177:47� EC

R2 ¼ 0:93; SE ¼ 176:7; n ¼ 54; p < 0:01

(2)

where Ro is the runoff inmm, Ero is the soil erosion in g, C is the

PAMapplicationrate in thefirst irrigationevents inkg ha�1,N is

the number of irrigation event, clay and sand are in%, EC is the

salinity of water in dSm�1, R2 is the coefficient of determina-

tion and SE is the standard error. Equation (1) indicates that

increase in the PAMapplication rate in the first irrigation event

reduces the runoff and its effect decreases at the consecutive

r different water types, and soil textures.

tion R2 Runoff threshold,mm

nRo� 69.3 0.81 1.82

Ro� 210.5 0.75 2.87

o� 2.2) 0.90 2.20

o� 4.9) 0.87 4.90

o� 1.4) 0.85 1.40

Ro� 5.5) 0.90 5.50

b i o s y s t em s e ng i n e e r i n g 1 0 6 ( 2 0 1 0 ) 5 1 3e5 2 0 519

irrigation events as the coefficient of N in Eq. (1) is positive.

Furthermore, by increasing the clay content and salinity of the

water the amount of runoff increases.

Equation (2) also shows that by increasing the PAM appli-

cation rates and sand content the soil erosion is decreased and

by increasing the number of irrigation events, clay content

and salinity of water the soil erosion is increased. Equations

(1) and (2) were obtained for irrigation application rate of

64.3 mmh�1 and initial soil water contents of 7.4e14.7% (mass

basis) for the sandy loam, 13.2e15.7% (mass basis) for loam

and 15.9e18.5% (mass basis) for silty clay loam. These soil

water contents correspond to the field soil water content

before farm irrigation.

4. Conclusions

It was found that, at heavier soil texture, higher PAM appli-

cation rates (�6.0 kg [PAM] ha�1) may be effective at

enhancing the FIR to reduce the runoff and soil erosion. For

light textured soil (sandy loam) with the wastewater and

freshwater, PAM application rate of 6.0 kg [PAM] ha�1 was only

effective in the first irrigation event. However, application

rates greater than 6.0 kg [PAM] ha�1 may be effective for

wastewater in the loam.

For runoff and soil erosion reduction, PAMapplication rates

greater than 6.0 kg [PAM] ha�1 may be effective for the sandy

loamwith the freshwater and wastewater. However, the loam

the application rate of 2.0 kg [PAM] ha�1 began to reduce the

runoff with applications of freshwater and wastewater in

thefirst irrigation event, but itwasnot effective at reducing the

runoff in the second irrigation using the wastewater.

For silty clay loam, using freshwater, a 6.0 kg [PAM] ha�1

application rate was effective on runoff and soil erosion

reduction in the first and second irrigation events, while using

the wastewater, 2.0 kg [PAM] ha�1 began to reduce the runoff

and soil erosion in the first irrigation event, but its effect was

not continued in the subsequent irrigation events.

For different soil textures, the threshold value of runoff for

initiation of soil erosion was higher for wastewater compared

with that for the freshwater. In general, runoff and soil

erosion were higher using wastewater compared with fresh-

water. Furthermore, the application of the wastewater

reduced the effect of PAM application on the reduction of

runoff and soil erosion. Therefore, higher amounts of PAM

application rates will be needed to obtain similar amounts of

runoff and soil erosion with wastewater compared to fresh-

water. Empirical equations were developed for estimation of

runoff and soil erosion based on the PAM application rates,

soil primary particle contents (clay and sand), number of

irrigation events, and salinity of the irrigation water.

Acknowledgement

This research was supported in part by Grant no. 88-GR-AGR-

42 of the Shiraz University Research Council and Center of

Excellence for On-Farm Water Management.

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