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SOLUTE MOVEMENT ASSOCIATED WITH 
INTERMITTENT SOIL WATER FLOW 
A thesis presented in partial fulfilment of the requirements for the degree of Doctor 
of Philosophy in Soil Science at Massey University 
RUSSELL WOODFORD TILLMAN 
1991 
Massey University Library 
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NAME AND ADDRESS DATE 
15 
TO WHOM IT MAY CONCERN 
This is to state that the research carried out for my Ph.D thesis 
entitled "Solute Movement Associated with Intermittent Soil Water 
Flow" in the Soil Science Department at Massey University, 
Palmerston North, New Zealand is all my own work. 
This is also to certify that the thesis material has not been used for 
any other degree. 
Date 
Russell WJodford TILLMAN 
11/t?/1; 
MASSEV 
UNIVERSITY 
Palmerston North 
New Zealand 
Telephone (0631 69-099 
ii 
ABSTRACT 
The movement of nutrients within the root zone of orchard crops is important in 
determining both fruit yield and quality. Currently much of the research on solute 
movement in field soils concerns movement of chemicals to ground water. Little 
attention has been paid to smaller scale movement. In this study the movement of 
solutes in response to intermittent soil water flow was investigated in columns of 
repacked silt loam in the laboratory and in a similar soil in the field. 
In the laboratory study a 5mm pulse of a solution of potassium bromide and urea in 
tritiated water was applied to columns of repacked soil, left for three or ten days, and 
then leached with 30 mm of distilled water. Twelve days after the solute pulse was 
applied, the distributions of water, tritiated water, applied and resident nutrients and pH 
were measured. 
The bulk of the bromide and tritiated water was moved to between 50 and 150 mm 
depth in both water treatments. As the nitrogen applied in urea was mainly in the form 
of ammonium after three days, the water applied then caused little movement of 
nitrogen. But the water applied after 10 days caused the nitrogen, now in the form of 
nitrate, to move in a similar fashion to the bromide. 
The soil solution anion concentration determined the amount of cations leached. 
Calcium and magnesium were the dominant cations accompanying the nitrate and 
bromide downwards. The added potassium remained near the soil surface. 
Given the soil hydraulic properties, the behaviour of water and solutes could be 
simulated by coupling the water flow equations with the convection-dispersion equation, 
and by using solute dispersion , diffusion and adsorption parameters derived from the 
literature. The model assumed the Gapon relationship for cation exchange, and that 
hydrogen ion production during nitrification reduced the effective cation exchange 
capacity. It was able to simulate closely the experimental data. 
iii 
Two field experiments were conducted. The first involved application of a 5 mm pulse 
of potassium bromide solution followed by 50 mm of water to pasture plots of 
contrasting initial water content. Twenty-four hours later core samples of soil were 
collected and the distribution of water and bromide measured. Bromide applied to 
initially dry soil was much more resistant to leaching than bromide applied to moist 
soil. 
The second experiment lasted 12 days and was essentially an analogue of the laboratory 
experiment. The final nutrient distributions however differed considerably from those 
obtained in the laboratory, due to non-uniform flow in the structured field soil. 
Coupling a mobile-immobile variant of the convection-dispersion model with a 
description of the water flow provided a mechanistic model. When combined with the 
submodels developed in the laboratory study describing nutrient interactions and 
transformations, this model successfully described the solute movement under the four 
different field regimes of water and solute application. Evaporation and plant uptake, 
and diffusion between mobile and immobile phases emerged as key processes affecting 
nutrient movement. It is suggested some control over nutrient movement is possible 
by varying the relative timing of water and fertiliser applications. 
iv 
ACKNOWLEDGEMENTS 
I would like to express my gratitude to the following people: 
Dr D.R. Scotter for his enthusiasm, encouragement and assistance above and beyond 
the call of duty. Thanks Dave! 
Dr B.E. Clothier for his great enthusiasm, helpful comments and for the seminar on 
solute movement many years ago which inspired this study. 
Prof. R.E. White for his helpful comments and also for his assistance and 
encouragement as my Head of Department, in enabling me to complete this thesis. 
My colleagues in the Department, particularly Dr M.J. Hedley and Dr P.E.H. Gregg, 
for the increased workload they have carried during this protracted study. 
Ian Furkert, Bronwyn White, Alistair Picken, Malcolm Boag and Lance Currie for 
valued technical assistance. 
Ann Rouse for typing the original papers and for her patient assistance with the thesis. 
Anne West for assistance with the diagrams. 
Robyn, Duncan, Christopher and Cresina for their love, support and understanding, 
despite the holidays that were foregone, the jobs that remained undone and the bed-time 
stories that were never read. 
V 
CONTENTS 
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  ii 
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . w 
CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  v
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii 
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix 
LIST OF SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  xv 
CHAPTER 1 :  Introduction and Literature Review 
The Purpose of the Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 
Review of Solute Movement in Soil . . . . . . . . . . . . . . . . . . . . . . . . 3 
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 
The Convection-Dispersion Equation . . . . . . . . . . . . . . . . . . .  5 
Adsorption and Solute Movement . . . . . . . . . . . . . . . . . . . . . 9 
Other Solute Movement Models . . . . . . . . . . . . . . . . . . . . . 12 
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1 8  
The Structure of the Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  19 
CHAPTER 2: Movement of Non-reactive Solutes 
Associated with Intermittent Water Flow 
in Repacked Soil 
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2 1  
Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  22 
Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 
Experimental Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 25 
Simulation Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 3 1  
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 
CHAPTER 3 :  Movement of  Reactive Solutes Associated 
with Intermittent Water Flow in 
Repacked Soil 
vi 
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 
Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 
Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 
Experimental Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 40 
Simulation Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 45 
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 
CHAPTER 4 :  Movement of a Non-reactive Solute 
During Intermittent Water Flow in a 
Field Soil 
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 
Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  55 
Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61  
Experimental Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 62 
Simulation Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . .  71  
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 
CHAPTER 5:  The Movement of Potassium and Nitrate 
During Intermittent Water Flow in a 
Field Soil 
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  76 
Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  77 
Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 
Experimental Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 86 
Simulation Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 9 1  
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  107 
CHAPTER 6: Conclusions and Directions for Future 
Work 
vii 
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 
Laboratory Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 10 
Field Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 12 
Conclusions and Future Work . . . . . . . . . . . . . . . . . . . . . . . . . .  1 17 
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1 19 
APPENDIX 1 :  Water Repellency and its Measurement 
using Intrinsic Sorptivity . . . . . . . . . . . . . . . . . . . . 129 
Table 
Table 4.1. 
LIST OF TABLES 
Daily rainfall, irrigation, and estimated 
evapotranspiration during the second experiment. 
EW and LW denote early and late water 
treatments respectively, I denotes irrigation, and R 
viii 
Page 
rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  68 
Figure 
Fig. 1.1.  
Fig. 2.1.  
Fig. 2.2. 
Fig. 2.3. 
Fig. 2.4. 
LIST OF FIGURES 
Comparison of molecular diffusion and hydrodynamic 
dispersion as a function of flow velocity (from Campbell, 
ix 
Page 
1985; after Olsen and Kemper, 1968) . . . . . . . . . . . . . . . . . . .  7 
Measured draining retentivity data ( o) , and assumed 
retentivity (_ _ _) and hydraulic conductivity ( ) 
relationships for the soil . . . . . . . . . . . . . . . . . . . . . . . . . . 26 
Measured average soil water contents for early-water (?) 
and late-water (O) treatments and their standard 
deviations. Also shown are the simulated profiles for the 
early-water ( ) and late-water (_ _ _ _  _) 
treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 
Measured ( ?) and simulated ( ) tritiated water 
content profiles for (a) the early-water treatment, and (b) 
the late-water treatment. Means and standard deviations 
are shown for the measured values . . . . . . . . . . . . . . . . . . . . 29 
Measured ( ?) and simulated and . . . . . . .  ) 
bromide content profiles for (a) the early-water treatment, 
and (b) the late-water treatment. Means and standard 
deviations are shown for the measured values. The 
difference between the two simulations is explained in the 
text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30 
Fig. 3.1.  
Fig. 3.2. 
Fig. 3.3.  
Fig. 3.4. 
Fig. 3.5. 
Fig. 3.6. 
Measured pH profiles in water ( ? , o) and calcium 
chloride (Ill, D) for early- ( ) and late- (_ _ _ _  _) 
X 
water treatments and their standard deviations . . . . . . . . . . . . . 4 1  
Measured ammonium concentration profiles for early- (?) 
and late- (O) water treatments and their standard 
deviations. Also shown are the simulated profiles for 
early- ( ) and late- (_ _ _  _) water treatments . . . . . . . . 43 
Measured nitrate concentration profiles for early- (?) and 
late- (O) water treatments and their standard deviations. 
Also shown are the simulated profiles for early-
( ) and late- (_ _ _  _) water treatments . . . . . . . . . . . . 44 
Measured potassium concentration profiles for early- ( ?) 
and late- (O) water treatments and their standard 
deviations. Also shown are the simulated profiles for 
early- ( ) and late- (_ _ _  _) water treatments ..... ... 46 
Measured calcium concentration profiles for early- ( ?) 
and late- ( o) water treatments and their standard 
deviations. Also shown are the simulated profiles for 
early- ( ) and late- (_ _ _  _) water treatments . ... ... .  47 
Measured magnesium concentration profiles for early- ( ?) 
and late- (O) water treatments and their standard 
deviations. Also shown are the simulated profiles for 
early- ( ) and late- (_ _ _  _) water treatments . . . . . . . 48 
Fig. 4.1. 
Fig. 4.2. 
Fig. 4.3. 
Fig. 4.4. 
Fig.4.5. 
Measured (symbols) and simulated (lines) water content 
profiles for the first experiment. The control is ? and the 
solid line, the first treatment is e and the dashed line, 
xi 
and the second treatment is 0 and the dotted line . . . . . . . . . . 63 
Bromide concentration profiles for the nine individual 
cores from a replicate plot for the first experiment. (a) 
First treatment: 5 mm KBr solution then 50 mm water. 
(b) Second treatment: 20 mm water, then 5 mm KBr 
solution, then 50 mm water . . . . . . . . . . . . . . . . . . . . . . . . 65 
Measured (symbols) and simulated (lines) bromide 
concentration profiles for the first experiment. The first 
treatment is e and the solid line, and the second 
treatment is 0 and the dashed line . . . . . . . . . . . . . . . . . . . . 66 
Measured (symbols) and simulated (lines) water content 
profiles for the second experiment. The profile at the 
start of the experiment is ? and the dotted line. Profiles 
at the end of the experiment are e and the solid line for 
the early-water treatment, and 0 and the dashed line for 
the late-water treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 
Measured (symbols) and simulated (lines) bromide 
concentration profiles for the second experiment. The 
early-water treatment is e and the solid line, and the 
late-water treatment is 0 and the dashed line . . . . . . . . . . . . . 70 
Fig. 4.6. 
Fig. 5.1 .  
Fig. 5.2. 
Fig. 5.3. 
Fig. 5.4. 
Simulated bromide concentration profiles for the second 
experiment with early water. The solid line is redrawn 
from Fig. 4.5. The dashed line is as for the solid line, 
but with uniform water extraction with depth. The dotted 
line is as for the solid line, but with no immobile water. 
The dotted and dashed line is as for the solid line, but 
with all the water loss from the soil surface and no 
xii 
immobile water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 
Potassium distribution at the completion of the first 
experiment. Bars indicate standard errors of the mean . . . . . . . 87 
Potassium distribution at the completion of the second 
experiment. Bars indicate the standard errors of the 
means . .. . . . . .. . .. . . . . . . . . . . ... . . . . . . . . . . . . 90 
Nitrate-nitrogen distribution at the completion of the 
second experiment. Bars indicate the standard errors of 
the means . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 
Measured (symbols) and simulated (lines) potassium 
distributions for treatment 1 in the first experiment. The 
solid line is when cation exchange capacity is assumed to 
be distributed between immobile and mobile phases. The 
dotted line is when all cation exchange capacity is 
assumed to be solely in the immobile phase . . . . . . . . . . . . . .  95 
Fig. 5.5. 
Fig. 5.6. 
Fig. 5.7. 
Fig. 5.8. 
Fig. 5.9. 
Fig. 5.10. 
Fig. 5.11. 
Measured (symbols) and simulated (lines) potassium 
distributions for treatment 2 in the first experiment. The 
solid line is when cation exchange capacity is assumed to 
be distributed between immobile and mobile phases. The 
dotted line is when cation exchange capacity is assumed 
xiii 
to be solely in the immobile phase . . . . . . . . . . . . . . . . . . . . 96 
Measured (symbols) and simulated (lines) potassium 
distributions in the second experiment, assuming cation 
exchange capacity is distributed between mobile and 
immobile phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 
Measured (symbols) and simulated (lines) potassium 
distributions in the second experiment, assuming cation 
exchange capacity is solely in the immobile phase . . . . . . . . . . 98 
Measured (symbols) and simulated (line) nitrate-nitrogen 
distributions in the unirrigated control area in the second 
experiment. The initial distribution is 0 and the final 
distribution is ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 
Measured (symbols) and simulated (lines) final nitrate?
nitrogen distributions in the irrigated control plots in 
treatment 2 of the second experiment . . . . . . . . . . . . . . . . . 102 
Measured (symbols) and simulated (line) final nitrate?
nitrogen distributions in the fertilised early-water 
treatment in the second experiment . . . . . . . . . . . . . . . . . . . 103 
Measured (symbols) and simulated (line) final nitrate?
nitrogen distributions in the fertilised late-water treatment 
in the second experiment . . . . . . . . . . . . . . . . . . . . . . . . . 104 
Fig. 5.12. 
Fig. 5.13. 
Fig. 6.1. 
Measured (symbols) and simulated (lines) final nitrate?
nitrogen distributions in the fertilised early-water 
treatment in the second experiment. The solid line is 
when () c is set at 0. 18. The dotted line is when () c is set 
xiv 
at 0. 001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1 0 5 
Measured (symbols) and simulated (lines) final nitrate?
nitrogen distributions in the fertilised late-water treatment 
in the second experiment. The solid line is when ()c is set 
at 0. 18. The dotted line is when ()c is set at 0. 0 0 1 . . . . . . . . . 1 06 
Simulated bromide concentration in the top 2 5mm of soil 
in the second field experiment. The dotted line is the 
early-water treatment and the solid line is the late-water 
treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5  
LIST OF SYMBOLS 
ARABIC 
a empirical coefficient [m] 
b empirical coefficient [dimensionless] 
C soil solution concentration [mol m-3 solution] 
Cenz soil solution concentration at input surface [mol m-3 solution] 
Cex soil solution concentration at exit surface [mol m-3 solution] 
c empirical constant [m s-1] 
d empirical constant [dimensionless] 
D molecular diffusion coefficient (m2 s-1] 
Do molecular diffusion coefficient in pure solution 
E dispersion coefficient (m2 s-1] 
f probability density function (m-1] (Chapter 1) 
f porosity [m3 m-3] (Chapters 2 & 4) 
I cumulative drainage [m] 
j solute flux density [mol m-2 s-1] 
K hydraulic conductivity (m s-1] 
Kd distribution coefficient [m3 kg-1] 
ka rate constant for ammonia nitrification [s-1] 
k0 selectivity coefficient in Gapon equation [(mol m-3)'h] 
ku rate constant for urea hydrolysis [s-1] 
M adsorbed plus solution solute concentration [mol m-3 soil] 
P cation exchange capacity [mol charge m-3 soil] 
p number of compartments in model 
q Darcy flux density of water [m s-1] 
R retardation factor [dimensionless] 
S sink for root water uptake [m3 water m-3 soil s-1] 
t time [s] 
v average velocity in soil (m s-1] 
X amount of cation charge balanced [mol m-3 soil] 
Y adsorbed solute concentration (mol kg-1] 
z depth [m] 
XV 
GREEK SYMBOLS 
e empirical constant [dimensionless] (Chapter 2) 
a Mk + Ma + Ms [mol m-3 soil] (Chapter 3) 
a rate coefficient for mobile-immobile exchange [s-1] (Chapters 1,4 & 5) 
{3 Me + Mg [mol m-3 soil] 
'Y (a + 2{3 - P)/8 [mol m-3 sol] (Chapter 3) 
'Y empirical constant [m-1] (Chapter 4) 
8 0- ox 
0 soil water content [m3 m-3] 
Oc water content dividing mobile and immobile water 
Ok water content used in describing K(O) in Chapter 2 
Ox water content of double-layer 
A. dispersivity [m] 
p, mean 
Pb bulk density [kg m-3] 
ff standard deviation 
if; matric potential [m] 
COMMON SUBSCRIPTS 
a ammonium 
B bivalent cations 
c calcium 
g magnesium 
i chemical species of interest (Chapters 2 and 3) 
i immobile phase (Chapters 1,4 and 5) 
k potassium 
M monovalent cations 
m mobile phase 
n nitrate or compartment number 
s sodium 
u urea 
xvi