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Research Paper

Effects of soil conditioners on physical quality and bromidetransport properties in a sandy loam soil

Shokrollah Asghari a, Fariborz Abbasi b,*, Mohammad Reza Neyshabouri c

aDepartment of Soil Science, Faculty of Agriculture, University of Mohaghegh Ardabili, Ardabil, IranbAgricultural Engineering Research Institute (AERI), P.O. Box 31585-845, Karaj, IrancDepartment of Soil Science, Faculty of Agriculture, Tabriz University, Tabriz, Iran

a r t i c l e i n f o

Article history:

Received 14 May 2010

Received in revised form

27 October 2010

Accepted 16 February 2011

* Corresponding author.E-mail address: abbasi_fariborz@yahoo.co

1537-5110/$ e see front matter ª 2011 IAgrEdoi:10.1016/j.biosystemseng.2011.02.005

In coarse-textured soils, water and nutrients are lost from the root zone through deep

percolation and preferential flow, resulting in poor soil quality. The objective of this study

was to investigate the influences of polyacrylamide, cattle manure, vermicompost and

biological sludge as soil conditioners on moisture retention and bromide transport param-

eters in a sandy loam soil. Polyacrylamide (0.25 and 0.5 g kg�1 of air-dried soil), cattle manure

(12.5 and 25 g kg�1 of air-dried soil), vermicompost (2.5 and 5 g kg�1 of air-dried soil) and

biological sludge (1.7 and 3.4 g kg�1 of air-dried soil) were mixed with the soil and uniformly

packed into plastic pans and PVC columns, and incubated in a greenhouse at 0.7 to 0.8 field

capacity moisture content (0.143e0.163 g g�1) and at 22 � 4 �C for 6 months. Pans were used

to take core samples to determine soil moisture curve parameters at 7, 30, 60, 120, and 180

days. Bromide breakthrough curves were measured at the same time in the PVC columns.

Polyacrylamide significantly increased slope of soil moisture curve at its inflection point as

compared to the control and other soil conditioners. Polyacrylamide also prevented early

breakthrough of bromide at 7 days by decreasing saturated hydraulic conductivity,

compared to the control and biological sludge. All soil conditioners reduced dispersivity

parameter in convectionedispersion model. Significant (P � 0.01) positive correlation

(r ¼ 0.81) was found between dispersivity parameter in convectionedispersion and mobile-

eimmobile models at the five incubation times. The results showed that polyacrylamide was

more effective than other soil conditioners in improving physical quality of sandy loam soils.

ª 2011 IAgrE. Published by Elsevier Ltd. All rights reserved.

1. Introduction Green, Mills, and Clothier (2006) reported that 60% of nitrate

Soil quality is receiving increasing attention in sustainable

agriculture (Haynes, 2005) and can be investigated from

physical, chemical and biological aspects of soils. Physical

quality of coarse-textured soils (sandy, loamy sand and sandy

loam) is often poor due to high percentage of macropores

which results in losses of water and nutrients from the root

zone by deep percolation and preferential flow. Vogeler,

m (F. Abbasi).. Published by Elsevier Lt

in sewage sludge applied in a sandy loam soil was lost by

leaching in a lysimeter experiment.

One of themost important indices of soil physical quality is

the slope (Sp) of the soil moisture curve (SMC) at its inflection

point (Dexter, 2004). At this SMC point, the curvature is zero

and corresponds to the water content (qi) and the matric

suction (hi) at which the air content of the soil increases with

increasing log(hi) (Dexter & Bird, 2001). The SMC inflection

d. All rights reserved.

Nomenclature

Variable

a, m and n van Genuchten’s parameters

C/C0 relative concentration

Dh hydrodynamic dispersion coefficient, cm2 min�1

hi matric suction at inflection point of SMC, kPa

Ks saturated hydraulic conductivity, cm min�1

l dispersivity parameter, cm

Pv pore volume

qs saturated flux density, cm min�1

Sp slope of SMC at its inflection point

qi water content at inflection point of SMC, cm3 cm�3

qr residual water content, g g�1

qs saturation water content, g g�1

t time, min

V0 measured outflow volume, cm3

Vs bulk soil volume, cm3

Abbreviations

BS biological sludge

BTC breakthrough curve

CDE convectionedispersion equation

CM cattle manure

FC field capacity

MIM mobileeimmobile

PAM polyacrylamide

SC soil conditioner

SMC soil moisture curve

VC vermicompost

b i o s y s t em s e ng i n e e r i n g 1 0 9 ( 2 0 1 1 ) 9 0e9 7 91

point is important from two aspects: its position (qi, lnhi), and

its slope, Sp ¼ dqi/d(lnhi) (Dexter, 2004) which are related to or

reflect soil physical quality. Therefore, Dexter and Bird (2001)

identified qi as the optimum soil water content for tillage.

There are several soil physical quality indicators other than

Sp such as water aggregate stability, mean weight diameter of

aggregates, macroporosity, mesoporosity, microporosity, bulk

density, air porosity, field capacity (FC) and permanent wilting

point.

Application of various soil conditioners (SCs) is widely prac-

tised to improve physical quality indicators of coarse-textured

soils. Effects of some SCs on aggregate stability and pore size

distribution have been discussed by Asghari, Neyshabouri,

Abbasi, Aliasgharzad, and Oustan (2009). Several studies on

application of natural organic SCs (Felton & Ali, 1992; Gupta,

Dowdy, & Larson, 1977; Lindsay & Logan, 1998; Nyamangara,

Gotosa, & Mpofu, 2001; Schjonning, Christensen, & Carstensen,

1994) and synthetic organic SCs (Al-Darby, 1996; Sadegian,

Neyshabouri, Jafarzadeh, & Tourchi, 2006) to sandy and sandy

loamsoilshave indicatedthedisplacingofSMCshapetoahigher

position, improving water content compared to the control

treatment. However, information on the quantitative effects of

SCs on the shape of SMC, especially on its Sp, is still inadequate.

Valuable information on solute and pollutant transport and

preferential flow phenomena in soils can be deduced from

breakthrough curves (BTCs) (Hillel, 1998). Wang, Horton, and

Jaehoon (2002) and Mohammadi, Neishabouri, and Rafahi (2007)

found that there is a strong correlation between SMC and BTC.

Other researchers have reported relationships between the

parameters of the van Genuchten (1980) equation and solute

transport parameters in the soil. For example, the study of

Vervoort, Radcliffe, and West (1999) showed that soil saturated

hydraulic conductivity (Ks) decreases with reducing van Gen-

uchten-aparameterduetodecrease indiameterof the largestsoil

pore. However, it has not been adequately considered whether

the addition of SCsmay affect BTC similar to SMC or not?

Two models have been used to study BTC of solutes in

different soil textural classes: convectionedispersion equation

(CDE) and mobileeimmobile water content (MIM). Ventrella,

Mohanty, Simunek, Losavio, and van Genuchten (2000) repor-

ted that MIM predicted chloride transport parameters some-

what better than CDE in a heterogeneous fine-textured soil.

Abbasi, Simunek, Feyen, van Genuchten, and Shouse (2003)

showed that CDE can predict solute transport parameters in

homogeneous soils more accurately than MIM.

The objectives of this study were to investigate the effects

of various soil conditioners on Sp, shape and position of

bromide BTC, and dispersivity parameter (l) in the CDE and

MIM models in a sandy loam soil, as well as to assess the

temporal variability of their effects.

2. Materials and methods

Soil samples with sandy loam texture were collected from the

0e30 cm layer of a fallow farm located at Karkaj Research

Station of Tabriz University, Iran. Four soil conditioners,

anionicpolyacrylamide (PAM) at the ratesof 0.25and0.5 gkg�1,

cattle manure (CM) at the rates of 12.5 and 25 g kg�1, vermi-

compost (VC) at the rates of 2.5 and 5 g kg�1, and biological

sludge (BS) at the ratesof 1.7 and3.4 g kg�1 of air-dried soilwere

added to the preweighed soil masses at 0.75 FC moisture

content. FC was determined as the gravimetric water content

at h¼ 10 kPa obtained by draining the soil from saturation. The

treated moist soils were uniformly packed into plastic pans

(50 cm diameter, 25 cm height) and PVC columns (15 cm

diameter, 25 cm height) with bulk density of 1.48 g cm�3

(according to the initial soil bulk density of field where soil

samples were taken). In order to create suitable conditions for

aggregation, both pans and columns were incubated in

a greenhouse at moisture and temperature conditions of

0.7e0.8 FC and 22� 4 �C, respectively (Paul & Clark, 1996), for 6

months. Criteria to determine the applied rates of SCs and also

details about the soil pan and column preparation and incu-

bation can be found in Asghari et al. (2009). Undisturbed core

samples were taken from 10 to 15 cm depth of the pans for

determining SMC and Sp. BTCs were obtained from the soil

columns. Sampling andmeasurement timeswere 7, 30, 60, 120

and 180 days after the onset of incubation.

The van Genuchten (1980) model parameters (qs, qr, m and

n) were obtained by fitting SMC data (q, h) using RETC (van

Genuchten, Leij, & Yates, 1991) software. Suctions (h) were 1,

2, 3, 4, 6, 8, 10, 20, 30, 60 and 1500 kPa. The van Genuchten m

parameter was assumed to be m ¼ 1 � 1/n. Sp was determined

Table 1 e Some physical and chemical properties of thesoil and soil conditioners (SCs) studied.

Property Soil CattleManure

Vermicompost Biologicalsludge

pHe 8.1 7.7 8 8.1

ECe (dS m�1) 1.87 15 14.65 11.41

OC (g kg�1) 6.2 348 165 266

Total N (g kg�1) e 4 20 74

CCE (g kg�1) 210 e e e

10 kPa

WC (% w/w)

17.41 e 106.7 109.2

1500 kPa

WC (% w/w)

9.72 e e e

AWC (% w/w) 7.69

WAS (%) 7.81

MWD (mm) 0.15

Sand (%) 69.5

Silt (%) 20.9

Clay (%) 9.6

CCE: carbonate calcium equivalent; WC: water content; AWC:

available water capacity; WAS: water aggregate stability; MWD:

mean weight diameter of aggregates.

b i o s y s t em s e n g i n e e r i n g 1 0 9 ( 2 0 1 1 ) 9 0e9 792

by the equation of Dexter (2004) using van Genuchten’s

parameters as follows:

Sp ¼ � nðqs � qrÞ�2n� 1n� 1

���1n� 2

� (1)

where qs and qr are saturation and residual water content

(g g�1), respectively, and n is a dimensionless parameter. The

method of calculating mesopore percentage (30e75 mm) has

been given by Asghari et al. (2009).

For determining BTC, after each incubation time (7, 30, 60,

120 and180days), soil columnswere saturated fromthebottom

with CaCl2 solution (0.01 M), and then leached with the same

solution until steady flow was attained with nearly 1 cm

constant head on the top of the columns. A pulse of CaBr2(0.01M) solution (C0)was then applied for 10min (theminimum

time required to construct complete BTC in the soil columns

used in thepresent study). Subsequently,CaBr2wassubstituted

by CaCl2 and continued until bromide in the outflow reached

a negligible concentration (Skaggs, Wilson, Shouse, & Leij,

2002). Bromide concentration (C ) from bottom of the experi-

mental columns was measured using a bromide specific elec-

trode.Kswasalsomeasured in the soil columnsduringmiscible

displacement experiments by the constant headmethod (Klute

& Dirksen, 1986). To avoid the probably harmful effects of

leaching at each incubation time on soil biological activity

during the rest of incubation, separate soil columns were

employed for each leaching time; in other words, a miscible

displacement experiment was carried out only once on each

soil column, after which the columnwas not used again.

In order to construct BTC, the number of pore volumes (Pv)

in each soil column was computed using the following equa-

tion (Sonon & Schwab, 2004):

Pv ¼ V0

Vsqs(2)

whereV0 (cm3) is themeasured outflow volume,Vs (cm

3) is the

bulk soil volume and qs (cm3 cm�3) is the saturated volumetric

water content.

The value of l in the CDE and MIMmodels was determined

by fitting the measured BTC data (C/C0, t) to those models

using HYDRUS-1D (Simunek, Sejna, & van Genuchten, 1998)

software. As estimate, l is equal to 10 percent of the soil

column length and it can be calculated from the following

equation (Jury & Horton, 2004).

l ¼ Dhqs

qs(3)

where Dh (cm2 min�1) is hydrodynamic dispersion coefficient,

qs (cm3 cm�3) is saturation water content and qs (cm min�1) is

saturated flux density (qs ¼ 1.05Ks in this study).

The experimental design was a factorial with randomized

complete block design, in 3 replicates either for the pans or for

the columns. The three factors of the experiments were: four

typesofSCs, three ratesof application (thecontrol, and two rates

ofapplicationsforeachsoil conditionerasexplainedbefore),and

five incubation times. In order to obtain normal distributions, Ks

data were log-transformed prior to ANOVA. Statistical analysis

of the data and comparison of the means by Duncan’s multiple

range test was carried out using MSTAT (1988).

3. Results

Some physical and chemical properties of the examined soil

and applied SCs measured by standard methods (Klute, 1986;

Page, 1985) are shown in Table 1. Due to the low organic

carbon and clay content, the soil had low water aggregate

stability and mean weight diameter of aggregates. Also, the

available water capacity of this soil was very low due to high

percentage of sand (69.5%).

The results of ANOVA are presented in Table 2. Means

comparison for the treatment interaction effects on the Sp,

mesopores, Ks, and lCDE using Duncan’s multiple range test

are shown in Figs. 1, 3, 5, and 7 (Table 3).

Effects of SCs at the high applied rate on the shape and

position of bromide BTC peak are shown as the mean of 3

replicates at 7, 30, 60, 120, and 180 days after the start of incu-

bation in Fig. 6 (A, B, C, D, and E). BTCs were constructed by

plotting relative concentration (C/C0) against the number of pore

volumes (Pv). Relative concentration is the bromide concentra-

tion (C ) in the effluent divided by the input concentration (C0).

Saturation flux density (qs) was kept nearly constant during the

miscibledisplacement experiments ineachcolumn (qs¼ 1.05Ks).

Ks was affected by SCs types, rates, and incubation times (Fig. 5)

and, therefore, qs differed among various treatments.

4. Discussion

4.1. Effect of SC on Sp

According to equation (1), Sp is negative, but it is often

convenient to use the modulus of Sp in discussions (Dexter,

2004). We also used that convention in calculations. The low

rate of PAM significantly (P� 0.05) increased Sp as compared to

the control due to increasing aggregation and mesopore

0

0.01

0.02

0.03

0.04

0.05

0.06

1.2 1.25 1.3 1.35 1.4 1.45

S p

n

Fig. 2 e Correlation between means of van Genuchten-n

parameter and slope of soil moisture curve at its inflection

point (Sp) at 5 incubation times (N [ 5).

(Sp [ 0.044n L 0.014, r [ 0.51).

Table 2 e Analysis of variance (F value) for measuredparameters.

Source Df Sp Mesopores(30e75 mm)

Ks lCDE lMIM

SCT 3 6** 16.8** 2.7* 0.4n.s 0.16n.s

SCR 2 0.2n.s 9.2** 3.5* 3.2* 4.6*

IT 4 60** 109.9** 32.46** 6.6** 12.6**

SCT � SCR 6 2.2* 7.22** 7.3** 0.56n.s 1n.s

SCT � IT 12 0.8n.s 1.04n.s 2.35** 1.06n.s 0.66n.s

SCR � IT 8 0.26n.s 1.15n.s 2.7** 3.2** 3.7**

SCT �SCR � IT

24 0.8n.s 0.57n.s 3.4** 11n.s 0.66n.s

Error 118 e e e e e

CV (%) e 10.45 12 35.78 37.81 33.82

SCT: soil conditioner type; SCR: soil conditioner rate; IT: incubation

time; n.snot significant; *P � 0.05; **P � 0.01. Df: degree of freedom;

Sp: slope of soil moisture curve at its inflection point; Ks: saturated

hydraulic conductivity; CDE: convectionedispersion equation;

MIM: mobileeimmobile; l: dispersivity parameter; CV: coefficient

of variation. Descriptive statistics for some measured parameters

are represented in Table 3.

b i o s y s t em s e ng i n e e r i n g 1 0 9 ( 2 0 1 1 ) 9 0e9 7 93

percentage (Figs. 1 and 3). From Fig. 4, it is found that all SCs,

and especially PAM, decreased macropores (inter-aggregate

pores) in the sandy loam soil by aggregation and consequently

increased mesopores and micropores (intra-aggregate pores).

In contrast to PAM, the high rate of BS significantly (P � 0.05)

decreased Sp due to reducing mesopore percentage (Fig. 3) as

compared to the control and other SCs rates. VC and CM could

not influence Sp (Fig. 1) because of the coarse-textured nature

of the soil or their insignificant effects on aggregation (Asghari

et al., 2009). These findings agreewith the results of the effects

of applied rates of SCs on van Genuchten’s n parameter

(Asghari, 2009). The value of n significantly (P� 0.05) decreased

by applying BS and this reduced Sp as compared to the control.

bc bc bc bc

a

cd cdabc

a

d

abcabc

0

0.01

0.02

0.03

0.04

0.05

0.06

PAM BS VC CM

S p

Soil conditioner

Control

Low rate

High rate

Fig. 1 e Interaction effects of the soil conditioners (SCs)

type and rate on mean slope of soil moisture curve at its

inflection point (Sp). PAM1, PAM2: 0.25, 0.5 g

polyacrylamide; BS1, BS2: 1.7, 3.4 g biological sludge; VC1,

VC2: 2.5, 5 g vermicompost; CM1, CM2: 12.5, 25 g cattle

manure (all rates are kgL1 of air-dried soil). Values with

common letters are not significantly different at P £ 0.05

(Duncan’s multiple range test).

Fig. 2 shows that there was no significant correlation between

n and Sp at all incubation periods. However, findings reported

by Dexter (2004) on the values of n and Sp for the 12 FAO/USDA

soil texture classes indicated that, with decreasing n, Sp would

also decrease. Change of pore size distribution affects the

middle part of the SMC and consequently alters the value of

the n parameter in the van Genuchten equation (van

Genuchten et al., 1991). Dexter (2004) also reported a signifi-

cant (P � 0.01) positive correlation (r ¼ 0.95) between organic

matter and Sp in a loamy sand soil. Findings of Dexter and

Richard (2008) showed that soil physical quality increased

with increasing Sp. They determined the value of Sp ¼ 0.035 as

the boundary between “good” and “poor” soil physical quality.

b b b b

a

b b b

a

c

ba

0

2

4

6

8

10

12

PAM BS VC CM

)%(seropose

M

Soil conditioner

Control

Low rate

High rate

Fig. 3 e Interaction effects of the soil conditioners (SCs)

type and rate on meanmesopores. PAM1, PAM2: 0.25, 0.5 g

polyacrylamide; BS1, BS2: 1.7, 3.4 g biological sludge; VC1,

VC2: 2.5, 5 g vermicompost; CM1, CM2: 12.5, 25 g cattle

manure (all rates are kgL1 of air-dried soil). Values with

common letters are not significantly different at P £ 0.01

(Duncan’s multiple range test).

ab b

b a a

b a a

0

10

20

30

40

50

60

70

Control (zero) Low rate High rate

)%(

seroP

Soil conditioner rate

Macro

Meso

Micro

Fig. 4 e Effect of the soil conditioners (SCs) rates on means

of macropores (>75 mm), mesopores (30e75 mm), and

micropores (<30 mm). Common letters indicate no

significant difference at P £ 0.01 (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 9 ( 2 0 1 1 ) 9 0e9 794

4.2. Effect of SC on bromide BTC

Fig. 6(A) shows that, 7 days after the start of incubation, PAM

caused late appearance (greater number of Pv) of bromide in

the outflow by decreasing Ks (Fig. 5), as compared to the

control and other SCs. In the PAM treatment, at about 1.04 Pv,

C/C0 approached 0.5, whereas in the control, C/C0 reached 0.5

at about 0.83 Pv, indicating early breakthrough of bromide in

the control treatment due to its high Ks at 7 days (Fig. 5).

The maximum of C/C0 in the control occurred at 2.75 Pv(Fig. 6A). Measurements showed that Ks gradually decreased

during leaching in the control soil column due to aggregate

breakdown, whereas, in SC (especially PAM) treated columns,

Ks remained almost constant due to formation of stable

aggregates (Asghari et al., 2009). In other words, little differ-

ence was observed between initial and final Ks values during

leaching for PAM-treated soil columns.

BTC of other conditioners (except BS and VC for 30 days of

incubation) lay between the BTCs of PAM and the control. In

a

b

def

bb

a

bab

b

bb

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

7 30

Ks

nim

mc(1-)

Incubat

Fig. 5 e Interaction effects of the soil conditioners (SCs) type and

(Ks). PAM: polyacrylamide; BS: biological sludge; VC: vermicomp

significantly different at P £ 0.01 (Duncan’s multiple range test)

general, after 7 days from application, all SCs decreased mac-

ropores (>75 mm) and increased mesopores (30e75 mm), and

micropores (<30 mm) (Fig. 4), and consequently by reducing Ks

(Fig. 5) caused the BTCs to shift to the right of the control after

the peak point (C/C0 maximum). This displacement was more

pronounced for PAM and CM. Similar findings have been

reported by Biggar and Nielsen (1962) and Fahad Ali and Ali

Abdul-Hussein (2002). Wang et al. (2002) and Mohammadi

et al. (2007) showed that there was a strong correlation

between SMC (pore size distribution) and BTC. They concluded

that BTC of each soil could be simulated from its SMC.

Fig. 6 (B) shows that 30 days after the onset of incubation,

the difference between the observed bromide breakthrough

time (the time that bromide first appeared in outflow or C/C0

started to ascend in BTC) for the control and SCs treatments

was negligible because there was no significant difference

among Ks of the control and SCs at that time (Fig. 5).

Fig. 6(C, D and E) shows that at 60, 120, and 180 days after

the start of incubation, BTC of SC treatments shifted to the

right of the control after peak point, probably due to the

greater decrease of Ks (Fig. 5) in the control relative to SC

treatments (especially PAM). Also, the higher position of peak

point in PAM BTC as compared to the control and other SCs

(Fig. 6C, D, E) indicates the complete miscible displacement of

bromide in PAM. Similar results have been reported by Everts,

Kanwar, Alexander, and Alexander (1989).

The shape of BTC for PAM was almost symmetric at all

incubation times (Fig. 6). Small tailing which occurred either

before or after the peak of C/C0, indicated that almost no pref-

erential flow took place in the PAM treatment because of the

decrease in macropores (Fig. 4). In general, macropores (inter-

aggregate pores) lead to early breakthrough by enhancing

preferential flow and consequently producemore asymmetric

BTCs (Ersahin, Papendick, Smith, Keller, & Manoranjan, 2002).

4.3. Effect of SC on dispersivity (l)

l is anexperimental parameterand itsvalue incoarse-textured

and homogeneous soils is often less than in fine-textured and

heterogeneous soils (Perfect, Sukop, & Haszler, 2002).

ghij

c cc

defg

i

defgh

eh

def

h

60 120 180

ion time (days)

Control

PAM

BS

VC

CM

incubation time on mean saturated hydraulic conductivity

ost; CM: cattle manure. Values with common letters are not

.

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

C/C

0

Number of pore volumes

Control

PAM

BS

VC

CM

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

C/C

0

Number of pore volumes

Control

PAM

BS

VC

CM

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

C/C

0

Number of pore volumes

Control

PAM

BS

VC

CM

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

C/C

0

Number of pore volumes

Control

PAM

BS

VC

CM

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

C/C

0

Number of pore volumes

Control

PAM

BS

VC

CM

A

B

C

D

E

Fig. 6 e Effect of soil conditioners (SCs) at the high rate of application (see Fig. 1) on the shape and position of breakthrough

curve (BTC) peak at 7 (A), 30 (B), 60 (C), 120 (D), and 180 (E) days after the onset of incubation. PAM: polyacrylamide; BS:

biological sludge; VC: vermicompost; CM: cattle manure; C/C0: relative concentration.

b i o s y s t em s e ng i n e e r i n g 1 0 9 ( 2 0 1 1 ) 9 0e9 7 95

cd

a a

abc abcbcd

abab

bcd

dee

bcd bcdcd

cde

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

7 30 60 120 180

)mc(rete

marapytivisrepsid

ED

C

Incubation time (days)

Control

Low rate

High rate

Fig. 7 e Interaction effects of the soil conditioners (SCs)

rates and incubation times on mean

convectionedispersion equation (CDE) dispersivity

parameter. Common letters indicate no significant

difference at P £ 0.01 (Duncan’s multiple range test).

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6CDE dispersivity parameter (cm)

mc(retemarap

ytivisrepsidMI

M)

Fig. 8 e Correlation between convectionedispersion

equation (CDE) and mobileeimmobile (MIM) dispersivity

parameter (l) at 5 incubation times (N [ 15).

(lMIM [ 0.9128lCDE D 0.1732, r [ 0.81**, P £ 0.01).

b i o s y s t em s e n g i n e e r i n g 1 0 9 ( 2 0 1 1 ) 9 0e9 796

Fig. 7 shows that at all incubation times, application of

SCs decreased lCDE as compared to the control. According to

equation (3), the decrease in qs at 7 days (data not shown) and

increase in Ks at the other times (Fig. 5) due to SCs applica-

tion, and particularly the decrease in Dh at PAM-treated

columns, all may have contributed to the lower lCDE in SC-

applied columns compared to the control. According to Fig. 6

(C, D and E), peak values of the bromide pulse with SCs,

especially with PAM-treated columns, are greater than the

control, indicating lower value of Dh (Jury & Horton, 2004).

Moreover, during 180 days of incubation, approximately 94%

reduction in Ks value in the control treatment caused 16%

increase in lCDE value (Figs. 5 and 7). Fig. 8 shows that there is

a significant (P � 0.01) positive correlation (r ¼ 0.81) between

lCDE and lMIM in all incubation times. Reports about the effect

of SCs on l (either CDE or MIM) were not found in the liter-

ature for comparison.

Table 3 e Descriptive statistics (N [ 15) for somemeasured parameters.

Treatmenta Mesopores van Genuchten-n lCDE

Mean St. db Mean St. d Mean St. d

Control 9.017 2.176 1.341 0.0659 1.089 0.397

PAM1 11.038 1.473 1.406 0.074 0.869 0.385

PAM2 11.146 3.108 1.39 0.066 1.139 0.595

BS1 9.057 2.052 1.34 0.055 0.962 0.498

BS2 8.03 2.074 1.329 0.066 0.833 0.436

VC1 9.133 1.927 1.355 0.076 0.878 0.481

VC2 9.664 2.372 1.363 0.075 0.896 0.354

CM1 9.26 1.811 1.357 0.062 1.032 0.433

CM2 10.678 2.243 1.387 0.089 0.89 0.420

a PAM1, PAM2: 0.25, 0.5 g polyacrylamide; BS1, BS2: 1.7, 3.4 g bio-

logical sludge; VC1, VC2: 2.5, 5 g vermicompost; CM1, CM2: 12.5, 25 g

cattle manure (all rates are kg�1 of air-dried soil). CDE: con-

vectionedispersion equation; l: dispersivity parameter.

b Standard deviation.

5. Conclusion

In this study, the influences of polyacrylamide (PAM), cattle

manure (CM), vermicompost (VC) and biological sludge (BS) as

soil conditioners (SCs) was investigated onmoisture retention

and bromide transport parameters in a sandy loam soil.

Results showed that application of PAM improved the physical

quality of examined soil, i.e. increasing Sp due to aggregation

and modifying pore size distribution. PAM, by decreasing Ks,

prevented early breakthrough of bromide at 7 days and

maintained greater Ks relative to the control and to other SCs,

by formation of water stable aggregates. The high rate of BS

significantly reduced Sp due to decreasing mesopores. Manure

maintained Ks in large values at 120 and 180 days relative to BS

and VC. Ks of the control decreased 16-fold at 180 days relative

to 7 days. l in CDE and MIM models was not affected by soil

conditioner type. The results showed that application of

0.25 g kg�1 PAM. taking into account its low degradation rate

(10% year�1) in soils (Tolstikh, Akimov, Golubeva, & Shvetsov,

1992) and its low cost, would appreciably improve physical

conditions of coarse-textured soils.

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