Modelling the change in conductivity of soil associated with the application of saline-sodic water

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Faculty of Engineering and Surveying

Modelling the Change in Conductivity of Soil Associated

with the Application of Saline –Sodic Water

A dissertation submitted by

YOUNES DAW EZLIT

BSc. (Hons) M.Sc. (Hons)

FOR THE AWARD OF

DOCTOR OF PHILOSOPHY

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PhD Dissertation

I dedicate this work to my mother Fatima, my brothers Ali,

Abdol-Fattah, Nor-Addhin, sisters Salmeen, Mabroka, Amal,

my wife Safia, my children Hibba, Joud-Addhin, Juriya, and to

the spirits of my father Daw and my best friend Abdu-Razaq.

YOUNES DAW ZIDE EMBARAK EZLIT

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PhD Dissertation I

Abstract

Scarcity of fresh water has led to use of low quality waters (high sodicity and salinity)

that were considered unsuitable for irrigation in the past. Mismanagement of irrigation

using this water can increase the potential for soil degradation and limit crop production

in the long term. Irrigation using highly saline-sodic water requires appropriate

management to avoid long term development of sodicity and salinity problems. The

main factors that control the sodicity and salinity problems are maintenance of sufficient

leaching and avoidance of soil structure degradation due to sodicity. The management

options are determined by complex factors such as soil type and condition, water quality,

irrigation practice and crop type.

Investigating the management options for using highly saline-sodic water in irrigation

experimentally is costly and time consuming. However, it could be done using an

appropriate modelling tool that can handle the degradation of soil structure due to

sodicity along with the chemical reaction system within the soil profile.

UNSATCHEM has been widely used to model sodicity and salinity effects under

irrigation. It has a feature to deal with soil structure degradation along with water and

solute movement, major ion chemistry, CO2 production and movement and heat

transfer under sodic conditions. It uses a hydraulic conductivity reduction function to

relate the change of chemical properties to the change in hydraulic properties of the

soil. However, the evaluation of the hydraulic conductivity reduction function under

high sodicity during simulation has not been done. Hence, the core of this research

project has been to improve quantification of soil structure degradation under sodic

conditions and enhance the modelling of water and solute movement under sodic

conditions. The hydraulic conductivity reduction function incorporated in

UNSATCHEM was evaluated using data obtained from soil column experiments.

Columns of two local soils were used in an experiment to investigate the effect on soil

structural stability of different amendments to highly saline-sodic water rich with

bicarbonates (EC = 4.6 dS/m and SAR = 117). The column experiments were used to

examine the effect of reducing water pH to different levels using sulphuric acid and

combined gypsum and dilution treatments. It was found that reducing the pH of highly

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PhD Dissertation

II

naturally high relative sodium concentrations. However, the application of diluted highly

saline-sodic water amended with gypsum showed no significant effect on soil structure

and permeability. It is concluded that different amendments associated with appropriate

irrigation management can be applied to sustain irrigation and prevent long term salinity

and sodicity problems.

The data from the column experiments was used to evaluate the quantification of the

soil structure degradation in UNSATCHEM. The resultant simulations for the soil

columns showed that the estimated outflow and hydraulic conductivity were less than

the experimental measurements, which suggested that the soil structure degradation

was not accounted for properly. The sodicity effect was accounted for in

UNSATCHEM by a reduction function, which is a combined function of the McNeal

(1968) clay swelling model and the Simunek et al. (1996) pH effect equations. The

empirical pH effect equation accounts for the reduction of the conductivity due to

increasing pH and clay swelling. The evaluation of UNSATCHEM under highly sodic

conditions suggests that the hydraulic conductivity reduction function is limiting the

UNSATCHEM performance.

Consideration of the first term of the hydraulic conductivity reduction function (i.e. the

McNeal (1968) clay swelling model) has highlighted the weaknesses of the McNeal

model and led to develop a generic clay swelling model (GCSM). Calibration of the

GCSM using the data of McNeal showed good agreement between the estimated and

measured relative conductivity data. Further calibration of the GCSM using relative

conductivity data obtained for five local soils also showed good agreement between the

model estimation and the measured data.

Coding of the generic clay swelling model into UNSATCHEM and re-simulating the

column experiments showed that the modelling process is improved compared with the

UNSATCHEM version containing the McNeal (1968) clay swelling model. However, the

outflow and conductivity values produced were still less than measured values. This result

suggested that further investigations are required to identify the effect of pH on the change

of hydraulic conductivity, cation exchange capacity, and the exchangeable sodium

percentage. Further research is also required regarding bicarbonate chemistry during

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PhD Dissertation III

Certification of Dissertation

I certify that the ideas, experimental work, analyses, results, and conclusions

reported in this dissertation are my own work, except where otherwise specified. I

further certify that this work is original and has not been previously submitted for

any another award, except where otherwise acknowledged.

Endorsement:

_____________________________

___________

_____________________________

___________

_____________________________

___________

Younes Daw Ezlit, candidate

Date Professor Steven Raine, Co- Supervisor

Date

Professor Rod Smith, Principal supervisor

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PhD Dissertation IV

Acknowledgment

This research has been completed with the support and assistance of a large number

of people. I wish to express my gratitude to some of those who have helped and

inspired me during my candidature.

Firstly, my sincere thanks to my supervisors and mentors Prof. Rod Smith and Prof.

Steven Raine for their guidance and patience during my study. I sincerely thank them

for their encouragement, expert advice, technical assistance and patience. Their

effort in creating an active and inclusive research environment is appreciated.

I wish to greatly acknowledge the support of Al-Fateh University and Libyan Arab

Jamahiriya government, for the full scholarship funding and the CRC for Irrigation

Futures for providing additional funding to support operation costs associated with

the research.

A special thanks to the CRCIF staff for their support during my study, I am grateful

to Dr. Richard Stirzaker and Dr. Tapas Biswas for their valuable discussions and

advice and to Dr. Malcolm Gillies for his help in the MATLAB programming. I also

appreciate the support provided by Prof. Jirka Simunek at the University of

California, Riverside for his valuable advice and support with the modelling aspects

of this research. I also thank the staff at the NCEA at USQ for their support during

the experimental work of this study.

I am grateful also to the lovely staff in the Faculty of Engineering and Surveying,

USQ. I consider them my wonderful family in Australia. Also, a special thanks to

my friends and colleagues at USQ especially Dev Raj Paudyal for their support and

encouragement.

Finally I would like to thank my family and friends in Libya for their continued

support and encouragement throughout my studies. To my family, my mother

Fatima, my brothers and sisters, my wife, my friends, and my little Hibba I say “my

name is written on the first page but your names are written on every page because

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PhD Dissertation

V

List of Figures

Figure 1.1 Development of soil problems under saline-sodic conditions ... 4

Figure 2.1 Comparison of different SAR- ESP relationships published in literature as presented in Qadir and Schubert (2002) at wide range of SAR (0-169) for different type of soils ... 19

Figure 2.2 Root zone salt distribution under different irrigation systems... 20

Figure 2.3 Effects of salinity and sodicity on plants ... 22

Figure 2.4 Basic molecular and structural components of silicate clays ... 29

Figure 2.5 A simple 3-plane model to describe the arrangement of clay crystals in a clay domain ... 31

Figure 2.6 Change of suction head produced by leaching a column of soil dominated by Montmorillonite (15% clay, ESP =30) with 0.01N, SAR 30 solution and pure water added ... 34

Figure 2.7 Variation in charge with pH and electrolyte concentration of the ambient solution for permanent, variable and mixed charge systems ... 38

Figure 2.8 Relationship between soil pH at saturated paste and ESP of Alluvial alkali soil... 39

Figure 2.9 The general guideline adopted for relative infiltration as affected by salinity and sodium adsorption ratio ... 41

Figure 2.10 Concentration of electrolyte required to maintain permeability (10-15% reduction) in Sawyers I soil for varying degrees of sodium saturation ... 43

Figure 2.11 Combinations of salt concentration and SAR at which a 25% reduction in hydraulic conductivity occurred ... 45

Figure 2.12 Combinations of salt concentration and ESP at which a 25% reduction in hydraulic conductivity occurred ... 45

Figure 2.13 Relative hydraulic conductivity of the soil as a function of solution concentration and composition (solution concentration > 0.01N) ... 48

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PhD Dissertation

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Figure 2.16 Solubility of gypsum in aqueous solutions of different NaCl

concentrations at 25o C, and 1 atmospheric pressure ... 55 Figure 3.1 Diagram of system used to apply the water treatments and measure the

saturated hydraulic conductivity (constant head method) ... 62

Figure 3.2 Change in pH for a saline-sodic water containing carbonates where the pH

has previously been adjusted to either 5 or 7 using H2SO4 acid ... 64

Figure 3.3 The positions of soil samples taken from the soil columns to determine

the SWCC and bulk density after applying the water quality treatments ... 66

Figure 3.4 The change in K_sat with water applications for the Sodosol... 68

Figure 3.5 The change in K_sat with water applications for the Vertosol ... 69 Figure 3.6 Changes in saturated hydraulic conductivity for the Sodosol when 0.4

dS/m water is applied following the application of 700 mm of the HSS water 70

Figure 3.7 Changes in saturated hydraulic conductivity for the Vertosol when 0.4

dS/m water is applied following the application of 700 mm of the HSS water 71

Figure 3.8 Average relationship between gravimetric water content and suction

applied for the Sodosol samples treated with HSS water and normal tap water

amended with gypsum ... 73

Figure 3.9 Average relationship between gravimetric water content and suction

applied for the Vertosol samples treated with HSS water and normal tap water

amended with gypsum ... 74

Figure 4.1 Sodicity-salinity effects in water and solute movement model

(UNSATCHEM) under isothermic conditions ... 77

Figure 4.2 Comparison of measured and simulated outflow when HSS water applied

for the Sodosol, (a) replicate 1, (b) replicate 2, and (c) replicate 3 ... 83

Figure 4.3 Comparison of measured and simulated outflow for the Sodosol soil

column when diluted HSS water amended with gypsum was applied ... 84

Figure 4.4 Simulated hydraulic conductivity with depth at different simulation time,

for the Sodosol (a) replicate 1, (b) replicate 2, and (c) replicate 3 ... 85

Figure 4.5 Example of the estimated change in SAR of the soil solution with depth at

final time for the Sodosol soil (replicate 1) ... 86

Figure 4.6 Example of the estimated change in pH of the soil solution with depth at

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List of Figures

PhD Dissertation

XII

Figure 4.7 Comparison of measured and simulated outflow for the Vertosol when

HSS water applied (a) replicate 1, (b) replicate 2, and (c) replicate 3 ... 87

Figure 4.8 Comparison of measured and simulated outflow for the Vertosol soil

column when diluted HSS water amended with gypsum was applied ... 88

Figure 4.9 Simulated hydraulic conductivity with depth at different simulation time

for the Vertosol (a) replicate 1, (b) replicate 2, and (c) replicate 3 ... 89

Figure 4.10 Example of the estimated change in SAR of the soil solution with depth

at final time for the Vertosol soil (replicate 1) ... 90

Figure 4.11 Example of the estimated change in pH of the soil solution with depth at

final time for the Vertosol soil (replicate 1) ... 90

Figure 4.12 Comparison of measured and estimated saturated hydraulic conductivity

for HSS water in the Sodosol (a) replicate 1, (b) replicate 2, and (c) replicate 3

... 92

for the Sodosol (when diluted HSS water amended with gypsum was applied)

... 93

for HSS water in the Vertosol (a) replicate 1, (b) replicate 2, and (c) replicate 3

... 94

for the Vertosol when diluted HSS water amended with gypsum was applied 95

Figure 5.1 Graphical method for estimating the swelling factor as a function of ESP*

and salt concentration in soil-water ... 101

Figure 5.2 The effect of soil solution concentration on montmorillonite swelling

(ESP =100%) as described by Norrish (1954) ... 106

Figure 5.3 Lattice expansion up to 2 nm and more than 40 nm) of montmorillonite

under two Na-solutions (i.e. × NaCl, o Na2SO4, and --- fitted line) with the

square root of different concentrations ... 107

Figure 5.4 Demonstration of d* equation under sodic condition (ESP= 100%) and its

adjustment as described by McNeal (1968)... 108

Figure 5.5 Three dimensional representation of the McNeal function (RK_Sat versus

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PhD Dissertation

XIII

Figure 5.6 Three dimensional plot of the McNeal function with RK_Sat limited to

100% ... 114

Figure 5.7 McNeal (1968) n values with ESP ... 115

Figure 5.8 McNeal (1968) c values with ESP ... 115

Figure 5.9 Change of ESP and electrolyte concentration at threshold level (i.e. RK_Sat =0.9) for soil group (a) having clay content of 5.7%... 118

Figure 5.10 Change of ESP and electrolyte concentration at threshold level (i.e.

Sat

RK =0.9) for soil group (b) having average clay content of 16.2% ... 119

Figure 5.11 Change of ESP and electrolyte concentration at threshold level (i.e.

Sat

RK =0.9) for soil group (c) having average clay content of 48.5 % ... 119

Figure 5.12 Proposed threshold level by McNeal (1968) compared with threshold

levels at 10% RK_Sat reduction for three soils group obtained from McNeal et al. (1968) ... 120

Figure 5.13 Change of n parameter obtained (by best fit) with different levels of

exchangeable sodium percentage (ESP) for soils group (b) of McNeal data

(1968) ... 122

Figure 5.14 Change of n parameter obtained (by best fit) with different levels of

exchangeable sodium percentage (ESP) for soils group (c) of McNeal data

(1968) ... 122

Figure 5.15 Change of c parameter obtained (by best fit) with different levels of ESP

for soils group (b) of McNeal data (1968) ... 123

Figure 5.16 Change of c parameter obtained (by best fit) with different levels of ESP

for soils group (c) of McNeal et al. (1968) data ... 123

Figure 5.17 Three dimensional surface of best fit and the residuals of RK_Sat (i.e.

between predicted and measured) for the for the group (a) soils ... 128

between predicted and measured) for the group (b) soils ... 129

between predicted and measured) for the group (c) soils ... 130

Figure 6.1 Electrolyte concentration and SAR of the water quality treatments applied

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List of Figures

PhD Dissertation

XIV

Figure 6.2 Electrolyte concentration and SAR of the water quality treatments applied

to the Grey Vertosol... 136

between predicted and measured) for the Sodosol soil ... 146

between predicted and measured) for the Brown Vertosol soil ... 147

between predicted and measured) for the Grey Vertosol soil ... 148

between predicted and measured) for the Red brown soil ... 149

between predicted and measured) for the Alluvial soil ... 150

Figure 6.8 Change of RK_Sat with electrolyte concentration and SAR for the Sodosol

as produced using the GCSM ... 152

Figure 6.9 Change of RK_Sat with electrolyte concentration and SAR for the Brown

Vertosol as produced using the GCSM ... 152

Figure 6.10 Change of RK_Sat with electrolyte concentration and SAR for the Grey

Vertosol as produced using the GCSM ... 153

Figure 6.11 Change of RK_Sat with electrolyte concentration and SAR for the Red

brown soil as produced using the GCSM ... 153

Figure 6.12 Change of RK_Sat with electrolyte concentration and SAR for the Alluvial

soil as produced using the GCSM ... 154

Figure 6.13 Change of RK_Sat with electrolyte concentration and SAR as produced

from the McNeal (1968) clay swelling model using the parameters

incorporated in the UNSATCHEM model for any soil ... 154

Figure 7.1 DOS window to enter the GCSM parameters into UNSATCHEM (i.e.

HYDRUS 1D) ... 157

Figure 7.2 The estimated outflow by the UNSATCHEM when the GCSM was used

compared with the estimated outflow using the UNSATCHEM that

incorporated the McNeal model for the Sodosol soil column during application

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PhD Dissertation

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Figure 7.3 The estimated K_Sat by the UNSATCHEM when the GCSM was used

compared with the estimated K_Sat produced using the UNSATCHEM that incorporated the McNeal model for the Sodosol soil column during application

of the HSS water (a) replicate 1, (b) replicate (2), and (c) replicate 3... 160

incorporated the McNeal model for the Sodosol soil column during application

of diluted HSS water ... 161

Figure 7.5 The estimated K_Sat by the UNSATCHEM when the GCSM was used compared with the estimated K_Sat produced using the UNSATCHEM that incorporated the McNeal model for the Sodosol soil column during the

applications of diluted HSS water ... 161

compared with the estimated outflow using the UNSATCHEM that incorporated

the McNeal model for the Vertosol soil columns during application of the HSS

water (a) replicate 1, (b) replicate (2), and (c) replicate 3 ... 163

compared with the estimated K_Sat produced using the UNSATCHEM that

incorporated the McNeal model for the Vertosol soil columns during application

of the HSS water (a) replicate 1, (b) replicate (2), and (c) replicate 3 ... 164

incorporated the McNeal model for the Vertosol soil column during

application of diluted HSS water ... 165

compared with the estimated K_Sat produced using the UNSATCHEM that

incorporated the McNeal model for the Vertosol soil column during the

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List of Tables

PhD Dissertation

XVI

List of Tables

Table 3.1 Field description of the Vertosol soil profile ... 60

Table 3.2 Field description of the Sodosol soil profile ... 60

Table 3.3 Selected chemical properties for the soils used in the experiment ... 61

Table 3.4 Selected chemical properties of the highly saline-sodic (HSS) water ... 63

Table 3.5 The mean KSat of the Sodosol and Vertosol soils after infiltrating 700 mm of the various water quality treatments ... 67

Table 3.6 TheK_Sat of the Sodosol and Vertosol when 0.4 and 0.1 dS/m water was applied after various HSS water pre-treatments ... 70

Table 3.7 Bulk density of the soil (5-10cm below surface) after application of either tap water amended with gypsum or HSS water ... 72

Table 4.1 van Genuchten (1980) hydraulic function parameters obtained for the Sodosol and Vertosol soils ... 79

Table 4.2 The UNSATCHEM input parameters for simulation of the HSS water and diluted HSS water amended with gypsum application for both the Sodosol and Vertosol soils ... 80

Table 5.1 Relative saturated hydraulic conductivity of Imperial Valley soils in the presence of mixed NaCl-CaCl2 solutions ... 117

Table 5.2 The n and c parameters obtained from non-linear regression analysis for soil groups (b) and (c) at different levels of ESP... 121

Table 5.3. Summary of the surface fit output for three group of soils from McNeal (1968) ... 127

Table 6.1 Selected chemical properties for the Grey Vertosol soil... 133

Table 6.2 Saturated hydraulic conductivity RK_Sat measurements for the Sodosol soil columns at different mixed NaCl-CaCl2 solutions with different electrolyte concentration... 137

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PhD Dissertation

XVII

Table 6.4 Saturated hydraulic conductivity RK_Sat measurements for the Grey

Vertosol soil columns at different mixed NaCl-CaCl2 solutions with different

electrolyte concentration ... 139

Table 6.5 Selected physical and chemical properties of the Alluvial and Red brown

soils ... 140

Table 6.6 Relative saturated hydraulic conductivity of the Red brown soil for water

quality treatments. Bulk density 1.22 g/cm3 ... 141 Table 6.7 Relative saturated hydraulic conductivity of the Alluvial soil for different

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List of Symbols

PhD Dissertation

XVIII

List of Symbols

a empirical parameter in generic clay swelling model

à empirical parameter which is varying with different mixed solutions

i

a fitted parameters

A0 parameters a in n function as defined in the user function in TableCurve program

A1 parameter b in n function as defined in the user function in TableCurve program

A2 parameter g in c function as defined in the user function in TableCurve program

A3 parameter m in c function as defined in the user function in TableCurve program

A4 parameter s for ESPT function as defined in the user function in TableCurve program

A5 parameter l for ESPT function as defined in the user function in TableCurve program

A6 parameter f

b empirical parameter in generic clay swelling model

B water flow geometry term

i

b fitted parameters

z

b proportion of applied water moving as bypass flow past z

c empirical parameter in clay swelling model

C an ion concentration in soil solution

'

c adjusted c parameter for different montmorillonite contents

C linearly averaged salt concentration of the root zone

Ο

C salt or electrolyte concentration

Cl

C depth weighted mean soil-water chloride concentration at saturation above z

2

CO

Ca volumetric concentration of CO2 in the soil air

Cd concentration in the drainage water

CEC cation exchangeable capacity

Cir salt concentration in the irrigation water

IW

C chloride concentration of soil-water at z

Ck total dissolved concentration of the soil solution species k

k

Cˆ total solid phase concentration of aqueous component

k

C total surface species concentration of the aqueous component k

Cp(θ) volumetric heat capacities of the soil system

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PhD Dissertation XIX

2

CO

Cw CO2 concentration in soil solution

ws

C an average salt concentration in the soil solution,

z

C chloride concentration of soil-water at z at field saturation water content,

dˆ interlayer distance of the montmorillonite due to increasing of relative sodium

concentration

D dispersion coefficient

ij

D generic component of the dispersion coefficient

d* adjusted interlayer spacing

D* distance between the montmorillonite platelets

a

D diffusivity of the CO2 in soil air

d

D depth of drained water

DL longitudinal dispersivity

irr

D depth of irrigated water

dL leaching rate

dV increase of volume (expansion) within Smectite soils

2

wCO

D CO2 diffusivity in soil solution

Dw molecular diffusion coefficient in free water

d

EC electrical conductivity of the drainage water

irr

EC electrical conductivity of the irrigation water

ESP* adjusted ESP in McNeal clay swelling model

T

ESP critical average ESP at whichK_satbegan to decline for given salinity ESPT Mont. montmorillonite threshold of sodicity

EXN adsorbed concentration of any cation

EXCa2+ amounts of calcium involved in balancing the charge of the soil’s exchange complex

EXNa+ amounts of sodium involved in balancing the charge of the soil’s exchange complex in units

f empirical parameter related to weighted fraction of montmorillonite

amount

f weight fraction of montmorillonite in the soil

) (CO2

f reduction coefficient of oxygen (O2) gas concentration

) (h

f reduction coefficient of pressure head (soil-water content)

) (h_φ

f reduction coefficient of osmotic effect

) (T

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List of Symbols

PhD Dissertation XX

Fw weighting function

z

f proportion of flow at the concentration of the soil matrix

) (z

f reduction coefficient of the soil depth

G water potential gradient from the soil to the root

g empirical parameter in generic clay swelling model

H soil-water potential

h soil-water pressure head

0

h osmotic potential

m

h matric potential

hr root water potential

hrs water potential at the root- bulk soil solution interface

i

i rate of irrigation water application

ir

I depth of irrigation water

K hydraulic conductivity

k′′ linear adsorption coefficient

!

K conductivity term (including the root and soil conductivities)

2

CO

K Henty law constant

KG Gapon selectivity coefficient

KGij Gapon selectivity coefficient for species i and j

) (h

K unsaturated hydraulic conductivity function

A ij

K generic component of the dimensionless anisotropy tensor for the unsaturated

conductivity

Kr root hydraulic conductivity

s

κ empirical constant

Sat

K saturated hydraulic conductivity

Max Sat

K maximum saturated hydraulic conductivity achieved when the soil is stable

Unsat

K unsaturated hydraulic conductivity

l empirical parameter, which depend on soil type and soil condition

f

L leaching fraction

m empirical parameter in generic clay swelling model

i

m empirical parameter dependent on the soil type

i

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PhD Dissertation XXI

n empirical parameter

c

N number of primary aqueous species

r

q rate of root water uptake

wj

q Darcy water flux density component in the i direction

w

q absolute value of the Darcian water flux density

w

q Darcy water flux density

r hydraulic conductivity reduction function

Rf retardation factor

R universal gas constant which is 8.314 (kg×m2 / s. × K× mol)

r1 reduction of KSat due to the clay swelling

r2 reduction of KSat due to an increase in the net negative charges on the clay

colloids associated with the increase in soil solution pH

Sat

RK relative saturated hydraulic conductivity

p

r root activity function

S water sink term (root water uptake)

s empirical parameter, which depend on soil type and soil condition

start

Sa initial amount of the salt in the root zone

SCw dissolved CO2 removed from soil by root water uptake

S′ plant salt uptake

t time

T absolute temperature

Tr transpiration rate per unit soil surface area

v average soil pore velocity

x valence of species i and j, respectively

x swelling factor (i.e. the calculated interlayer swelling of soil Montmorillonite)

X electrolyte concentration (mmolc/litre) in TableCurve program

ο

x adjusted effective swelling factor

x+ valence of a cation i

i

x spatial coordinate and i,j = 1,2,3

y+ valence of species a cation j

Y exchangeable sodium percentage (ESP) in user function in TableCurve program

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List of Symbols

PhD Dissertation XXII

z soil depth

zr depth of the root zone

z relative soil depth according to the entire soil column length

λ₍θ₎ _{coefficient of the apparent thermal conductivity of the soil}

Sa

∆ change of salt storage within the root zone

∆_z _{thickness of the layer of soil}

s

γ sum of the production of CO2 by the soil micro-organisms

r

γ sum of the production of CO2 by plant roots

0

r

γ optimum CO2 production from plant roots

0

s

γ optimum CO2 production from micro-organisms

β empirical parameter depends on soil type and clay mineralogy

α depth weighted mean anion exclusion volume as a proportion of the volumetric water content above z

δ empirical constant set to 0.2z

µ production coefficient

ρ soil bulk density

ζ equivalent Pore Neck Radius

a

θ soil air content

fc

θ volumetric soil-water content at field capacity

s

θ depth weighted mean volumetric soil-water content at field above z

w

θ volumetric soil-water content

w

τ tortuosity factor in the liquid phase

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PhD Dissertation XXIII

List of Abbreviations

BC Boundary Conditions

CDE Convection Dispersion Equation

CEC Cation Exchange Capacity

DDL Diffuse Double Layer theory EC Electrical Conductivity

ECe Electrical conductivity of saturated extract

ESC Exchangeable Sodium Content ESP Exchangeable Sodium Percentage

ESPT Exchangeable Sodium Percentage Threshold

ESR Exchangeable Sodium Ratio FC Flocculation Concentration

Fit Std Error Standard Error Coefficient

GCSM Generic Clay Swelling Model HSS water Highly Saline-Sodic water

k Soil Permeability

LR Leaching Requirements M Solute Molarities

PA Attractive Pressure

PSI Pore Size Index

PR Repulsive Pressure

PZNC Point of Zero Net Charge

R2 Coefficient of Determination

RCBD Randomized Complete Block Designs

RSC Residual Sodium Concentration

SAG Sulphuric Acid Generator

SAR Sodium Adsorption Ratio

SAR1:5 Sodium Adsorption Ratio in soil-water extract 1: 5

SE. Coeff. Standard Error Coefficient

SWCC Soil-Water Characteristic Curve

TDR Time Domain Reflectometry TDS Total Dissolved Solids

TEC Threshold Electrolyte Concentration

Modelling the change in conductivity of soil associated with the application of saline-sodic water

Faculty of Engineering and Surveying