TESTING NITROGEN AND IRON BASED COMPOUNDS AS
ENVIRONMENTALLY SAFER ALTERNATIVE TO CONTROL BROADLEAF
WEEDS IN TURFGRASS
by

Simran Gill
B.Sc. Agriculture, Punjab Agricultural University, Punjab

THESIS SUBMITTED IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
IN
NATURAL RESOURCES AND ENVIRONMENTAL STUDIES
(ENVIRONMENTAL SCIENCE)

UNIVERSITY OF NORTHERN BRITISH COLUMBIA
April 2024

© Simran Gill, 2024

Abstract
Turfgrass is an important component of urban and rural lawns and landscapes. However,
broadleaf weeds such as dandelions (Taraxacum officinale Weber ex. F.H. Wigg) and white
clovers (Trifolium repens L.) pose major challenges to the health and aesthetics of turfgrass
fields. Traditional chemical weed control methods, such as 2,4-dichlorophenoxyacetic acid
(2,4-D) herbicides, are commonly used, but their safety and environmental impacts are
contentious. Seeking environmentally friendly alternatives, this research investigated the
effectiveness of nitrogen and iron compounds as nutrient management methods for weed
control. In a two-phase experiment; the first was conducted on a mix of cool season
turfgrasses (included perennial ryegrass (Lolium perenne L.), Kentucky bluegrass (Poa
pratensis L.) and creeping red fescue (Festuca rubra L.)) grown in plastic containers under
controlled conditions in the greenhouse. The treatment application included individual
nitrogen (1 = urea and 2 = ammonium sulphate) and iron (3 = chelated iron and 4 = iron
sulphate) compounds and their combinations (5 = urea × chelated iron, 6 = urea × iron
sulphate, 7 = ammonium sulphate × chelated iron, 8 = ammonium sulphate × iron sulphate)
contrasted with 9 = a conventional synthetic herbicide (Killex) and a 10 = control (no
application) treatment. Weekly assessments over a 12-week period revealed that the
combination of ammonium sulphate × iron sulphate had overall best results for weed control
and turfgrass quality indicators, and thus was the most effective in inhibiting the growth of
dandelions and white clovers while improving the health of turfgrass. The second part,
following the greenhouse studies, tested the efficacy of the ammonium sulphate × iron
sulphate treatment versus Killex and a control (no application) treatment under natural open
environmental conditions at two sites (site 1: no shade vs. site 2: partial shade) with existing
broadleaf weeds. The ammonium sulphate × iron sulphate treatment combination resulted in
ii

significant reduction in weed cover (66% and 33% in sites 1 and 2, respectively) as well as
yielded superior turfgrass quality (based on visual quality ratings and photosynthetic capacity
recorded) as compared to both Killex and the control treatments. Overall, the results of this
research demonstrate that the combination of ammonium sulphate × iron sulphate is a
promising nutrient management solution capable of achieving both aesthetic goals of weed
control and turfgrass quality.

iii

Preface
This MSc. thesis consists of two data chapters, both are being prepared for submission. These
papers were all primarily the work of me, Simran Gill, who designed and carried out the
research, collected data, analyzed and interpreted the research results under the direction of
Samuel Bartels.
Chapter 2: Under preparation
Gill, S. and Bartels, S. F. (in prep) Performance of nitrogen and iron-based compounds on
broadleaf weeds growth and turfgrass quality under controlled environmental conditions in
the greenhouse.

Chapter 3: Under preparation
Gill, S. and Bartels, S. F. (in prep) Performance of ammonium sulphate × iron sulphate on
health of broadleaf weeds and turfgrass quality on already established turfgrass fields under
natural environmental conditions.

iv

Acknowledgments
This thesis would not have been possible without the guidance and unwavering support of
several individuals who in one way or another contributed and extended their valuable
assistance in the completion of this study, and it is a pleasure to thank each and everyone of
those who made it a possibility.
I am indebted to my supervisor Dr. Samuel Bartels whose encouragement bolstered my
confidence, particularly during the most challenging phases of my academic journey. Dr.
Bartels’s guidance and expertise were instrumental in enabling me to successfully complete
my Master’s within the timeframe. I would like to extend a heartfelt thanks to my
supervisory committee members Dr. Lisa Wood and Dr. Balbinder Deo for their excellent
guidance, encouragement and constructive feedback contributing significantly to my growth
as a researcher.
I express sincere appreciation to the curators at the I.K. Barber Enhanced Forestry
Laboratory, Doug Thompson and Dr. Kennedy Boateng, whose valuable guidance was
crucial for the successful completion of my greenhouse experiments. Special gratitude goes
to Sunny Tseng for her assistance with data analysis. I would like to acknowledge the
funding support from the University of Northern British Columbia through Research Project
Award, which provided the necessary funds to conduct my research.
I extend my deepest gratitude to the Almighty Waheguru, as well as and my family and
friends for their unwavering support. Special thanks to my parents, parents-in-law, and my
sister for their endless encouragement throughout this journey. A heartfelt appreciation is
reserved for my husband, who stood by me through every high and low without a complaint.
Together, we have finally made it to the end of this academic endeavour.
v

Table of contents
Contents
Abstract .................................................................................................................................................. ii
Preface ................................................................................................................................................... iv
Acknowledgments .................................................................................................................................. v
Table of contents ................................................................................................................................... vi
List of figures ........................................................................................................................................ ix
1. Chapter 1-Introduction ....................................................................................................................... 1
1.1. Turfgrass...................................................................................................................................... 2
1.2. Weeds .......................................................................................................................................... 4
Dandelion (Taraxacum officinale Weber ex. F.H. Wigg) ......................................................... 4
White clover (Trifolium repens L.) ........................................................................................... 7
1.3. Weed Control Measures .............................................................................................................. 8
Cultural control methods ........................................................................................................... 8
Mechanical control methods ..................................................................................................... 9
Biological control methods ..................................................................................................... 10
Naturally occurring products used as herbicides ..................................................................... 11
Chemical control methods ....................................................................................................... 12
Fate of 2,4-dichlorophenoxyacetic acid .................................................................................. 12
1.4. Low-risk chemical management of broadleaf weeds in turfgrass ............................................. 14
Effects of nitrogen (N) on broadleaf weeds ............................................................................ 14
Effect of iron (Fe) on broadleaf weeds .................................................................................... 15
1.5. Soil Properties ........................................................................................................................... 16
Soil chemical properties .......................................................................................................... 17
Soil biology ............................................................................................................................. 18
1.6. Environmental Impact of Nutrient Fertilizers ........................................................................... 19
1.7. Research gaps and opportunities ............................................................................................... 20
1.8. Thesis structure.......................................................................................................................... 20
1.9. Research Questions ................................................................................................................... 21
2. Chapter 2- Performance of nitrogen and iron-based compounds on broadleaf weed growth and
turfgrass quality under controlled environmental conditions in a greenhouse ..................................... 23
2.1. Introduction ............................................................................................................................... 23
vi

2.2. Materials and Methods .............................................................................................................. 26
2.2.1. Seeds and Planting Materials......................................................................................... 26
2.2.2. Experimental Setup ....................................................................................................... 29
2.2.3. Data Collection .............................................................................................................. 32
2.2.4. Statistical Analysis ........................................................................................................ 34
2.3. Results ....................................................................................................................................... 35
2.3.1. Broadleaf weed’s response to treatment ........................................................................ 36
2.3.2. Turfgrass’s response to treatments ................................................................................ 42
2.3.3. Effect of treatments on growth medium (peat) .............................................................. 45
2.4. Discussion ................................................................................................................................. 47
3. Chapter 3- Performance of treatment combination of nitrogen and iron on broadleaf weeds and
turfgrass on already established turfgrass fields under natural environmental conditions. .................. 51
3.1. Introduction ............................................................................................................................... 51
3.2. Methods ..................................................................................................................................... 53
3.2.1. Study Area ..................................................................................................................... 53
3.2.2. Experimental Setup ....................................................................................................... 54
3.2.3. Treatment applications .................................................................................................. 56
3.2.4. Data Collection .............................................................................................................. 58
3.2.5. Statistical analysis ......................................................................................................... 60
3.3. Results ....................................................................................................................................... 61
3.3.1. Broadleaf weed response to treatments ......................................................................... 62
3.3.2. Turfgrass response to treatments ................................................................................... 71
3.3.3. Soil sample analysis ...................................................................................................... 76
3.3.4. Pre- and post-treatment conditions of weed and turfgrass............................................. 80
3.4. Discussion ................................................................................................................................. 86
4. Conclusion and recommendations .................................................................................................... 90
References ............................................................................................................................................ 93

vii

List of tables
Table 2.1. Chemical composition of the treatments and the proportion of nitrogen, iron, and
sulphur contained in them. ...................................................................................................... 30
Table 2.2. Effects of the experimental treatments, time since application, and their interaction
on the quality and properties of white clover, and dandelion weeds and turfgrass, under
controlled environmental conditions in a greenhouse. Values are p-values from a liner mixed
effect model analysis............................................................................................................... 35
Table 2.3. Before and after comparison of the physical and chemical properties of the growth
medium (peat) for the different treatments ............................................................................. 46
Table 2.4. Before and after comparison of the nutrient (nitrogen, phosphorous, potassium,
and iron) contents of the growth medium (peat) for the different treatments. ........................ 47
Table 3.1. Effects of the experimental treatments, time since application, and their interaction
on the properties of white clover and dandelion weeds, and turfgrass growing under natural
environmental conditions at both the sites. Values are p-values from a linear mixed effect
model analysis. ........................................................................................................................ 62
Table 3.2. Before and after comparison of the physical and chemical properties of the soil
samples from Site 1 and Site 2 under different treatment applications. ................................. 78
Table 3.3. Before and after comparison of the nutrient (nitrogen, phosphorous, potassium,
and iron) contents of the soil samples from Site and Site 2 under different treatment
applications. ............................................................................................................................ 79

viii

List of figures
Figure 1.1. Fate of 2,4-D in the environment after agricultural and domestic application
(Islam et al. 2018). .................................................................................................................. 13
Figure 2.1. Arrangement of sowing spots for dandelion and white clover seeds in columns
marked with different colours (A) and removal of grass from the spots to create space for
sowing the weeds (B). ............................................................................................................. 28
Figure 2.2. Transplanting the dandelion seedlings from plug tray to the desired experimental
bins to fulfil the minimum number of dandelion plants per bin. ............................................ 29
Figure 2.3. Tabular representation of the experimental layout of the treatments on different
shelves in the Enhanced Forestry Laboratory, at University of Northern British Columbia. . 31
Figure 2.4. Grouped bar graph representing the change in quality of white clover plants under
different treatments over the period of 12 weeks while growing under controlled conditions.
................................................................................................................................................. 37
Figure 2.5. Grouped bar graph representing the change in total number of white clover plants
under different treatments over the period of 12 weeks while growing under controlled
conditions.. .............................................................................................................................. 38
Figure 2.6. Grouped bar graph representing the change in quality of dandelion plants under
different treatments over the period of 12 weeks while growing under controlled conditions..
................................................................................................................................................. 39
Figure 2.7. Grouped bar graph representing the change in number of leaves per dandelion
plant under different treatments over the period of 12 weeks while growing under controlled
conditions. ............................................................................................................................... 40
Figure 2.8. Grouped bar graph representing the average length of the longest leaf of
dandelion under different treatments over the period of 12 weeks while growing under
controlled conditions... ............................................................................................................ 41
Figure 2.9. Grouped bar graph representing the change in quality of turfgrass under different
treatments over the period of 12 weeks while growing under controlled conditions.. ........... 42
Figure 2.10. Grouped bar graph representing average photosynthetic capacity (Pc) of
turfgrass under different treatments over the period of 12 weeks while growing under
controlled conditions.. ............................................................................................................. 44
Figure 2.11. Grouped bar graph representing the change in dry weight of turfgrass under
different treatments over the period of 12 weeks while growing under controlled conditions.
................................................................................................................................................. 45
Figure 3.1. Experimental plots at (A) field Site 1 with partial shade, and (B) field Site 2 with
no shade conditions. ................................................................................................................ 55
Figure 3.2. Layout of different treatment applications on field Sites 1 and 2 ........................ 56
Figure 3.3. Grouped bar graph representing the change in Photosynthetic capacity (Pc) of
white clover plants subjected to different treatments over the period of 12 weeks growing
under natural field conditions (A) at Site 1 and (B) at Site 2. ................................................ 64
ix

Figure 3.4. Grouped bar graph representing the change in Photosynthetic capacity (Pc) of
dandelion plants subjected to different treatments over the period of 12 weeks growing under
natural field conditions (A) at Site 1 and (B) at Site 2. ........................................................... 65
Figure 3.5. Grouped bar graph representing the change in quality rating of dandelion plants
subjected to different treatments over the period of 12 weeks growing under natural field
conditions (A) at Site 1 and (B) at Site 2. ............................................................................... 67
Figure 3.6. Grouped bar graph representing the change in number of leaves per dandelion
plant subjected to different treatments over the period of 12 weeks growing under natural
field conditions (A) at Site 1 and (B) at Site 2. ....................................................................... 69
Figure 3.7. Grouped bar graph representing the change in the length of the longest leaf of
dandelion plant subjected to different treatments over the period of 12 weeks growing under
natural field conditions (A) at Site 1 and (B) at Site 2. ........................................................... 71
Figure 3.8. Grouped bar graph representing the change in quality rating of turfgrass subjected
to different treatments over the period of 12 weeks growing under natural field conditions
(A) at Site 1 and (B) at Site 2. ................................................................................................. 72
Figure 3.9. Grouped bar graph representing the change in Photosynthetic capacity (Pc) of
turfgrass subjected to different treatments over the period of 12 weeks growing under natural
field conditions (A) at Site 1 and (B) at Site 2. ....................................................................... 73
Figure 3.10. Grouped bar graph representing the change in weed coverage of each plot
subjected to different treatments over the period of 12 weeks growing under natural field
conditions (A) at Site 1 and (B) at Site 2. ............................................................................... 75
Figure 3.11. Visual comparison of weed coverage in three experimental plots before (A1, C1,
and E1) and after 12 weeks of (NH4)2SO4 × FeSO4 application (B1, D1, and F1) at Site 1 .. 80
Figure 3.12. Visual comparison of weed coverage in three experimental plots before (G1, I1,
and K1) and after 12 weeks in control (no application) plots (H1, J1, and L1) at Site 1 ....... 81
Figure 3.13. Visual comparison of weed coverage in three experimental plots before (M1,
O1, and Q1) and after 12 weeks of Killex application (N1, P1, and R1) at Site 1 ................. 82
Figure 3.14. Visual comparison of weed coverage in three experimental plots before (A2, C2,
and E2) and after 12 weeks of (NH4)2SO4 × FeSO4 application (B2, D2, and F2) at Site 2 .. 83
Figure 3.15. Visual comparison of weed coverage c in three experimental plots before (G2,
I2, and K2) and after 12 weeks in control (no application) plots (H2, J2, and L2) at Site 2 .. 84
Figure 3.16. Visual comparison of weed coverage in three experimental plots before (M2,
O2, and Q2) and after 12 weeks of Killex application (N2, P2, and R2) at Site 2 ................. 85

x

Chapter 1-Introduction

1. Chapter 1-Introduction
Turfgrass systems play a prominent aesthetic role in contemporary society, seamlessly
integrating into urban and suburban landscapes, outdoor sports, private lawns, land
management, and beautification initiatives. Beyond the intrinsic benefits of turfgrass, the
turfgrass industry contributes greatly to the economy and serves as a vital source of
employment (Haydu et al. 2006; Cohen 2021; Iranca 2022). However, weeds pose the
greatest problem to the maintenance of turfgrass lawns. Presence of weeds generally
indicates a weakened and stressed turfgrass, which may have been a result of poor soil
physical properties, adverse soil chemical properties, unfavourable environmental conditions,
or improper turfgrass maintenance (Hatterman-Valenti 2007).
The synthetic herbicide, 2,4-D is most commonly used for domestic (non-agricultural)
purposes in Canada and USA, due to its relatively easy application methods, and proven
effectiveness. However, herbicide use in both residential and commercial landscapes is
becoming heavily regulated as concerns about safety and environmental impacts grow
(Quarles 2010). Although herbicides were developed to prevent, eliminate, or control
unwanted plants, numerous investigations have raised concerns about the potential hazards of
herbicides to both the environment and human health. For instance, surveys conducted
concerning the effect of toxic chemicals have revealed elevated risks of childhood leukemia
in households where pregnant mothers are exposed to pesticides (Lowengart et al. 1987). The
toxicity of 2,4-D ranks from slight to high for birds, fishes, and insects (USEPA 2001) and is
known to be carcinogenic, causing mutations, birth defects, liver, and kidney damage (Hoar
et al. 1986; Blair & Thomas 1979). Moreover, under frequent lawn irrigation, herbicides can
leach through soil profiles causing water contamination (Starrett et al. 2000).
1

Chapter 1-Introduction
In Canada, the regulation of 2,4-D has been closely monitored under the Pest Control
Products Act (PCPA) which governs the registration and usage of pesticides. The Pest
Management Regulatory Agency (PMRA) of Health Canada has consistently conducted
periodic reviews and reassessments to gauge the safety and efficacy of 2,4-D products.
Furthermore, recognizing the associated health and environmental risks, jurisdictions such as
Ontario took a proactive step in 2009 by implementing a ban on the use of synthetic
herbicides for residential lawns and gardens (Health Canada 2021). Addressing the
challenges of maintaining a healthy and aesthetically pleasing turfgrass fields necessitates a
shift towards environmentally sustainable alternative to synthetic herbicide, with particular
emphasis on finding viable substitutes for 2,4-D.

1.1.

Turfgrass

Turfgrass offers functional advantages by mitigating soil erosion, dust, air pollution and
excessive temperatures. Additionally, turfgrass surfaces also contribute to improved
recreational experiences and reduced sports injuries, while the aesthetic values of turfgrass
further enhances beauty, mental health, and overall quality of life (Beard & Green 1994).
Since turfgrass reigns as the preferred ground cover for diverse spaces, including home
lawns, commercial sites, parks, playgrounds, athletic fields, golf courses, and roadsides, its
management fosters employment across various sectors (Schleicher 2002). An early report
from 2006 mentions that the turfgrass industry in British Columbia managed approximately
180 thousand acres throughout the province. Additionally, the industry’s budget was
estimated to fall within the range of $1.02 billion, supporting employment for approximately
16.7 thousand individuals during the same year (Tsiplova et al. 2008).

2

Chapter 1-Introduction
The utilization of turfgrass grounds significantly shapes the selection of turfgrass varieties
and plays a pivotal role in influencing their development, particularly in response to
temperature and moisture stress. For instance, grass designated for golf greens must exhibit
resilience to close clipping, endure heavy traffic, and demonstrate swift damage recovery,
aligning morphologically and physiologically with the specific growth and usage conditions.
Similarly, for the sequence of sporting activities, traffic tolerance and the time of the use of
the field also determine the type of turfgrass being grown. Characteristics such as resistance
to abrasion and high sheer strength are some desirable qualities of grasses for football fields.
Broadly, turfgrass have been classified based on the general climatic regions, which are coolseason turfgrass and warm-season turfgrass. However, due to differences in elevation within
climatic zones and changing weather conditions, these classifications are not absolute (Stier
et al. 2020). Forest margins at higher altitudes in Africa are believed to be the primitive
centre of origin of cool season turfgrass, later on evolving and adapting to colder regions of
Eurasia (Clayton 1981). The cool season turfgrasses occur in the temperate climates of both
the northern and southern hemisphere now, where the optimum temperature range lies
between 16-24° C and have C3 physiology (Beard 2012; Stier 2020). Some examples of cool
season turfgrasses are fine-leaf fescue (Festuca spp.), bluegrass (Poa spp.), ryegrass (Lolium
spp.), bentgrass (Agrostis spp.), and tall fescue (Festuca arundinacea).
Warm season turfgrasses are believed to have originated in Gondwanan, Africa, as its
primitive ancestral centre (Clayton 1981). The C4 photosynthetic pathway characteristic of
warm season turfgrasses evolved in Africa from C 3 ancestral grasses (Stier et al. 2020).
Warm season turfgrasses are generally found in warmer areas of tropical or sub tropical
climates where the temperatures range from 25-75° C and may undergo discoloration or
3

Chapter 1-Introduction
winter dormancy where the temperatures drop below 10° C (Beard 2012). Some common
warm season turfgrasses are Bermudagrass (Cynodon spp.), Zoysiagrass (Zoysia spp.),
Carpetgrass (Axonopus spp.), Bahiagrass (Paspalum spp.), and St. Augustinegrass
(Stenotaphrum spp.).

1.2.

Weeds

A weed can be defined as a plant growing out of place. It competes with the host plant for
space, light, and nutrition thus affecting the performance of the host plant (Christians et al.
2016). Weeds are generally classified as grassy or broadleaved. Broadleaf weeds are also
called dicot weeds, they have wide leaves containing a main vein in the center giving rise to
smaller veins arranged in a netlike pattern, vascular bundles arranged in a ring, bearing a
strong tap root system and can be either annual or perennial. While the grassy weeds, also
known as monocot weeds, have parallel venation, with complex arrangement of vascular
bundles and they have a fibrous root system, grassy weeds can also be annual or perennial
(Polomski & McCarty 2022). In lawns and landscapes, broadleaf weeds such as Taraxacum
officinale (dandelion) and Trifolium repens (white clover) can be easily distinguished from
turfgrass and interrupt uniformity, reduce grass density, and cause aesthetic problems during
the flowering and seed production period, and therefore considered undesirable (Holm et al.
1997; Hahn et al. 2020). This study focuses on testing efficiency of combination of nitrogen
and iron compounds for controlling the menace caused by two major broadleaf weeds
mentioned below.

Dandelion (Taraxacum officinale Weber ex. F.H. Wigg)
Dandelion is a lactiferous perennial herb. The first true leaves of the seedling are alternate,
hairless, spatula to upside down teardrop shaped, and greyish green on the lower surfaces
4

Chapter 1-Introduction
with wavy edges and irregularly toothed and lobed at the third leaf stage. Later emerging
leaves are widely toothed and deeply lobed, with lobe tips pointed towards the center of the
rosette. Leaves are stalkless, narrow, and deeply divided towards the base, with the sparsely
pubescent midrib and lower leaf surface, and generally range from 5-4 cm in length to 0.7-15
cm in width. The thick branched taproot can be up to 2-3 cm in diameter and can grow up to
1-2 m in length with the later roots spiraling around the taproot (Stewart-Wade et al. 2002).
Single flowers are borne on glabrous, hollow, cylindrical, sparsely hairy leafless stalks which
can be 5-50 cm tall. The bright yellow flower head is 2-5 cm in diameter and set on top of 2
rows of long, green, narrow bracts. The outer bract is curled back to touch the stem and the
inner row encases the immature flower head which consists of up to 250 ligulate, perfect,
yellow florets. Seeds have a rough surface and are usually grey-yellow to grey-brown in
color, obovoid-oblong, 3-4 mm in length, and 1 mm in width. Each seed is consisting of a
white pappus composed of numerous hairs, 3-4 mm in length, fused at the base (Holm et al.
1997).
Dandelion is regarded as one of the most competitive plant species owing to its ability to
survive in widely variable environments with a wide range of soil types, a wide range of soil
pH, resistance to drought and adaptability to a wide range of light and shade intensity, Frick
& Thomas (1992) explain that dandelions are considered the toughest weeds to control in
reduced or no tillage fields, due to the possibility of being trapped by the high amount of crop
residues present in these types of fields. The tap root extends below the level of grassroots,
making it difficult to remove manually and even a tiny bit of the plant left in the soil can
regenerate a whole plant (Solbrig 1971).

5

Chapter 1-Introduction
The ability of the dandelion crown to contract by the end of the growing season helps the
plant to thrive over the harsh winter. Another excellent trait of dandelion is attributed to its
seed production and dispersal mechanism, dandelion plants can produce light seeds with
feathery pappi which can sum up to 2,170-23,000 seeds per plant, which can be easily
transported to long distances (more than 100 m) via wind (Tackenberg et al. 2003). Lastly,
the dandelion’s capability to manipulate carbohydrate reserve according to seasonal
fluctuation helps the plant to adapt to temporal environmental stresses over other plants in the
community (Wilson et al. 2001). As a result of the excellent survival mechanism of
dandelions, their effective and complete control is difficult.
Dandelion is an invasive alien plant that was introduced to North America from Europe, in
the mid-1600s to cultivate for food and medicine, and since then it has spread across the
continent as a weed (Roncoroni 2018). The earliest recorded observation of dandelion in
North America was in the New England area in 1672 and the first Canadian collection of
dandelions was made in Montreal, QC, in 1821, where it was observed as common species
(Rousseau 1968). Dandelion has been reported from all provinces and territories of Canada,
including the Northwest, Yukon, and Nunavut territories. This species is widely distributed
within Canada and records were also found from almost all isolated regions (Stewart-Wade
et al. 2002). Dandelion is also found in over 60 countries worldwide (Holm et al. 1997).
Dandelions possess the capability to establish a thick mat of leaves, which can potentially
outcompete desirable plant species, diminishing the vitality of those that manage to survive.
In turfgrass, dandelions tend to form clumps, negatively impacting the footing of athletic
fields and golf courses (Roncoroni 2018). Furthermore, their distinct texture and colour
interrupts uniformity, and grass density, and is considered an undesirable weed causing
6

Chapter 1-Introduction
aesthetic problems during the flowering and seed production period which gives the field a
weedier appearance than is really the case (Holm et al., 1997). Dandelion is also found to be
causing allergic contact and photoallergic contact dermatitis (Mark et al. 1999). It is also
important to note that dandelion flowers may attract bees, posing a concern in areas
frequented by children or individuals with bee allergies (Roncoroni 2018).

White clover (Trifolium repens L.)
White clover is a leguminous plant belonging to the family Fabaceae and is native to Eurasia,
indigenous to all of Europe, southwestern Asia, and northern Africa (Turkington & Burdon
1983). It is perennial, creeping, multi-branched, and essentially a shallow-rooted plant with a
greater portion of the root mass down to 10 cm but with a rooting depth of up to 60 cm
(Turkington & Burdon 1983). Its roots are adventitious from stolon nodes, and a taproot is
developed from the seedling's primary root. Stolons are 1.9-4.0 mm in diameter and
internodes are up to 6 cm long. Leaves are glabrous, palmately trifoliate; leaflets 10-35 mm,
conspicuously toothed, usually with a whitish angled band towards the base (LeStrange &
Reynolds 2004). The inflorescence is an axillary racemose head, 15-20 mm in diameter,
globular, usually bearing 20-40 flowers. Flowers are white to pale-pinkish in color and
scented. The seeds are irregularly round and somewhat flattened, with sizes varying from
0.9-1.8 mm by 1.0 mm, yellow to brown in color (Elmore et al. 2000).
As a leguminous species, white clover’s symbiotic relationship with nitrogen-fixing bacteria
contributes towards its broad edaphic tolerances thus making its survival easy on soils
ranging from markedly acidic to highly calcareous. White clover occurs in virtually all soil
types, especially clays, but it is scarce on soils with pH values less than 4.0 but thrives well
under conditions of moderate acidity (pH 5.6-7.0) (Turkington & Burdon 1983). Secondly,
7

Chapter 1-Introduction
the white clovers can quickly infest an area owing to the vegetative propagation with the help
of stolons and spread through the entire field and soon may become hard to control (Burdon
1983). Lastly, the white clover seed coat is very hard and tolerant to heat, composting, and
soil solarization, and therefore these practices are not effective in reducing white clover’s
seed viability as they are with other weed species. This hard seed coat also allows the seed to
survive longer in soil, thus white clover seeds can germinate over many years making the
control of these plants an ongoing effort (Smith et al. 2007).
The earliest collection in Manitoba was in 1896 by Macoun who found it along a railroad
ditch near Brandon (Scoggan 1957). It has been often found to be widespread along
roadsides, and waste places, but it is not regarded as pioneer legume species (Sears 1962).
White clover is an agricultural escapee and is often continuous over large areas of roadsides
and waste places (Turkington & Burdon 1983). White clover can be a concern in turfgrass or
landscape areas since they reduce the uniformity of the turfgrass because its texture, color,
and growth rate are different from that of turfgrass. Additionally, during the flowering phase,
bees are drawn to the blooms or white clover. This can pose a risk to individuals with bee
allergies and may result in stings, especially in areas where people are actively playing or
utilizing the turfgrass (Smith et al. 2007).

1.3.

Weed Control Measures

Cultural control methods
Most cultural approaches for controlling broadleaf weeds usually entail boosting competition
from turfgrass to make it difficult for them to survive. Common cultural practices to control
weeds in turfgrass include soil solarisation, cultivation practices, selection of proper turfgrass
species, and fertilization(Busey 2003). Soil solarisation is a technique that uses clear
8

Chapter 1-Introduction
polyethylene film to cover moistened soil and trap lethal amounts of heat from solar radiation
to reduce soil-borne pests and kills seeds of weed thriving in the soil. The temperatures
obtained in the moistened soil covered by the transparent sheeting and the exposure time of
the weed seeds to these elevated temperatures are both important characteristics of this preplant soil treatment (Reddy 2012).
The selection of proper turfgrass species is also essential for weed control since some
varieties are reported to be more resistant to weed infestation as compared to others.
Additionally, deciding a proper seeding rate as well as the use of over-seeding to increase
turfgrass densities can provide a competitive edge over the weeds, however, over-seeding
accompanied by following a proper fertilizer regime can help in better control of weeds
(Vargas & Turgeon 2004). A high rate of N (nitrogen) fertilization (600 kg ha-1 yr-1) reduces
the population of dandelion and other broadleaf weeds in cool season turfgrass (Johnson &
Bowyer 1982). On the other hand, the density and abundance of dandelions and white clovers
was positively correlated with potassium level in their tissues, and the use of potassium-free
lawn fertilizers decreased their populations because of increased competition from grasses
(Tilman et al. 1999). Mulching with maple and oak leaves is another control practice reported
to reduce broadleaf weed infestation in turfgrasses by 80% and 53% after 1 and 2 mulch
applications respectively, without hampering the quality of the original turfgrass
(Kowalewski et al. 2009).

Mechanical control methods
Mechanical methods of weed control in turfgrass fields consist of physical uprooting or
cutting or any mechanical removal of weeds from the fields, and is often performed by
tillage, manual uprooting, and mowing (McCarty & Murphy 1994). Tillage is usually
9

Chapter 1-Introduction
practiced before turfgrass establishment, and weeds are destroyed by breaking them apart,
removing them from the soil, and disturbing their root systems. However, if weeds are
mature when tilled, their seeds can be buried and become a future source of weeds (McCarty
& Murphy 1994). Manual weed control often performed by hand pulling, hoeing or rouging
is not widely practiced and is generally impractical in a large turfgrass areas (Uddin et al.
2012). Mowing is a valuable weed control practice, which if frequently repeated at
appropriate height can favour the growth of turfgrass species, while depleting the
underground weed food reserves (Sheley et al. 2003). The height of mowing also affects the
quality of turfgrass, and the appropriate height of mowing for maintaining good quality of
cool season turfgrass was found to be > 4 cm (DeBels et al. 2012; Voigt 2001). The
frequency of mowing and mowing height also influences the weed growth slightly. Cutting
the grass at greater height tends to shade the ground and retard the development of weeds.
Studies suggest that mowing and fertilization are able to reduce the densities of weeds but are
not successful in providing complete control (Busey 2003). Many broadleaf weeds have
evolved and adapted to mechanical weed management practices. For example, turfgrass
weeds commonly adapt to continuous defoliation through a routine mowing, a trait notably
observed in the case of common dandelion (Taraxacum officinale). The rosette growth
pattern of dandelion ensures that its growing point remains below the mowing height,
allowing it to withstand and thrive despite regular mowing practices (Hatterman-Valenti
2007).

Biological control methods
Biological control, or biocontrol, involves the deliberate use of one organism to reduce the
population of or mitigate a target pest below a desired threshold (Schnick et al. 2002).

10

Chapter 1-Introduction
Phoma herbarum and Phoma macrostoma have been reported as potential bioherbicides for
the control of broadleaf weeds and Canada thistle in turfgrass (Neumann & Boland 1999).
Another fungal pathogen with proven herbicidal effects is Sclerotinia minor which causes
white mold disease in susceptible plants (Abu-Dieyeh & Watson 2007). S. minor is the active
component of SarritorTM Granular Biological Herbicide manufactured in Quebec, Canada.
The disease develops rapidly upon application and the complete death of broadleaf weeds
may be achieved in as less as seven days without harming the majority of the turfgrass
species (Abu-Dieyeh & Watson 2007).

Naturally occurring products used as herbicides
Among the alternative herbicides that are available for use and derived from natural products
are vinegar, essential oils (clove and cinnamon oil), citric acid, fatty acid (pelargonic acid),
and combinations of these different products. However, the effectiveness of these products is
dependent on the product concentrations and using higher product rates may result in greater
potential for non-target crop injury (Smith et al. 2015).
Corn gluten meal is a popular naturally occurring pre-emergent herbicide and a nitrogen
source (Abu-Dieyeh & Watson 2007). The active ingredient in corn gluten maize is
dipeptides glycinyl-glycine and alaninyl-alanine which are found to inhibit root formation of
susceptible species and are reported to reduce the survival of broadleaf weed emergence by
75% (Bingaman & Christians 1995; Liu & Christians 1996). However, it does not affect the
matured well-established plants and the feasibility of the use of corn gluten is questioned due
to the cost constraints (Nonneke & Christians 1992; Wilen & Shaw 2002).

11

Chapter 1-Introduction

Chemical control methods
Chemical herbicides are the most convenient option for weed control due to their easy
availability, low cost, and effective control (Carroll et al. 2022). Phenoxyacetic acid
herbicides, such as 2,4-D and mecoprop; or the benzoic acid dicamba, or a combination
product of all three such as ‘Killex’ are used for chemical control of broadleaf weeds
(Stewart-Wade et al. 2002). Experiments have shown that 2,4-D killed broadleaf weeds
within three weeks of application leaving the turfgrass unharmed; and dandelions have been
classified to have intermediate susceptibility to 2,4-D because of its severe impact on the
young seedlings and tolerance on older established plants (Peterson et al. 2016).

Fate of 2,4-dichlorophenoxyacetic acid
2,4 dichlorophenoxyacetic acid (2,4-D) was the first commercial herbicide to be introduced
in 1940’s for broadleaf weed control (Islam et al. 2018). The primary introduction of 2,4-D
into the environment occurs through effluents and spills associated with its manufacturing,
and transportation processes, as well as directly through its application as a herbicide agent
through leaching, spray drift and surface run-off (Fig. 1.1).

12

Chapter 1-Introduction
Figure 1.1. Fate of 2,4-D in the environment after agricultural and domestic application
(Islam et al. 2018).

Unfortunately, 2,4-D lacks specificity in targeting weeds, affecting non-target species such as
desirable plants, animals, and microorganism. Its impact includes reduced growth rates,
reproductive issues, alterations in appearance or behaviour, and even potential mortality
among non-target organisms (Zabaloy & Gómez 2014). Furthermore, 2,4-D is recognized as
an endocrine disruptor, capable of influencing developmental processes even at low
concentrations (Pattanasupong et al. 2004). The highest 2,4-D contamination of the fields and
water bodies is estimated to occur during the planting period of each season, when farmers
intensively apply herbicides to prevent weeds in their fields (Ding et al. 2000). Following
herbicide application, the concentration of 2,4-D tends to be higher than anticipated,
particularly during or immediately after the process. Numerous studies have demonstrated
the rapid bioaccumulation of 2,4-D by organisms, reaching concentrations well above lethal
levels for various aquatic species. This phenomenon is especially pronounced in instances of
direct agricultural and aquatic applications of the herbicide (Islam et al. 2018).
An epidemiological study conducted on corn farmers exposed to 2,4-D revealed a significant
presence of 2,4-D in their urine compared to control group. The study demonstrated that five
times increase in urinary 2,4-D was associated with an 11% rise in 8-OHdG, a promutagenic
DNA lesion generated in response to reactive oxygen species (ROS), and a 14% increase in
8-isoPGF, a prostaglandin-like compound produced through non-enzymatic lipoprotein
peroxidation. The findings of Lerro et al. (2017), supported evidence from laboratory
animals, suggest that 2,4-D induced oxidative stress may play a crucial role in the
pathogenesis in cancer and other chronic diseases. Previously, in USA and Canada, farmers
13

Chapter 1-Introduction
with frequent use of phenoxy herbicides like 2,4-D reported a substantial increase (2 to 8fold) in the incidence of non-Hodgkins’s lymphoma (NHL) (Zahm & Blair 1992; Wigle et al.
1990). However, recent occupational and meta-data analysis studies indicate a broader
spectrum of health risk associated with 2,4-D exposure. These risks extend beyond NHL to
include the development of Parkinson’s disease and various types of cancers, such as
respiratory cancers, soft-tissue sarcoma, and bladder cancer. This heightened risk is observed
among both farmers and factory workers exposed to 2,4-D during the manufacturing and
application processes (Islam et al. 2018).

1.4.

Low-risk chemical management of broadleaf weeds in turfgrass

With the rising environmental and human safety concerns related to synthetic herbicidal
application, there is a dire need to switch to an integrated strategy of weed management.
Nitrogen and iron compounds have been individually studied to suppress growth of broadleaf
weeds and improve the health and quality of turfgrass (Busey 2003; Yust et al. 1984).

Effects of nitrogen (N) on broadleaf weeds
Nitrogen helps in the growth of above-ground biomass, thereby shading the low-lying weeds
and ultimately suppressing their growth. A study has reported that fertilization with 165 kg N
ha -1 yr -1 consistently reduces white clover and the effect is more marked when N is applied
in early spring than later (Busey 2003). The population of dandelions also reduces from 25%
to 4% when 190 kg N ha -1 yr -1 is applied instead of 90 kg N ha -1 yr -1 as reported by
Callahan & Overton (1978). The usual rate of application of nitrogen for obtaining optimal
turfgrass quality is 123 to 196 kg N ha-1 yr-1 (Walker et al. 2007; DeBels et al. 2012).
However, higher nitrogen levels have been found to restrict the growth of broadleaf weeds

14

Chapter 1-Introduction
due to stimulation of the turfgrass to grow more rapidly and be more competitive thus
providing an effective management strategy (Voigt et al. 2001).
Fertilizers are most commonly applied as combination of N, P, and K. However, white clover
and dandelion respond positively to K application and P also may occasionally increase the
composition of white clovers (Busey 2003; Hahn et al. 2019). Therefore, only N application
is effective in reducing the broadleaf weed cover in the turfgrass systems. Broadleaf weeds
become somewhat less competitive when the soil pH is lowered which could potentially be
achieved with long-term applications of ammonium sulphate and it has been found to reduce
the broadleaf weed cover and even weed-free turfgrass in some cases as reported by Hahn et
al. (2019). Thus, nitrogen can be applied as urea, ammonium sulphate ((NH4)2SO4), and
ammonium nitrate (NH4NO3) in the fields for effective broadleaf weed control.

Effect of iron (Fe) on broadleaf weeds
Recently iron-based bioherbicides are being widely used for controlling broadleaf weeds in
turfgrass fields and garden spaces as an alternative to chemical herbicides. Iron
hydroxyethylenediaminetetra-acetic acid (Fe-HEDTA), a chelated iron formulation was
registered by U.S. Environmental Protection Agency as a bioherbicide (Wolfe et al. 2016). It
is used as a post-emergence herbicide and has shown excellent control over a wide range of
broadleaf weeds such as dandelion, white clovers, and ground-ivy and moderate control over
broadleaf plantains (Smith-Fiola & Gill 2014). Besides chelated iron, ferrous sulphate
(FeSO4) has also shown herbicidal effects on broadleaf weeds in turfgrass.
Since the broadleaf weeds absorb iron more easily and in higher quantities than turf, weeds
are impacted almost instantly and severely, while the turfgrass remains unharmed. Iron
oxidation causes plant necrosis causing the weed to quickly dry up, turn black, shrivel, and
15

Chapter 1-Introduction
die within hours of application (Smith-Fiola & Gill 2019). A study conducted by Yust et al.
(1984) has also shown that iron sulphate and chelated iron help in enhancing the turfgrass
color and quality and thus helps in maintaining a healthy turfgrass system.
The response of weeds and turfgrass to nitrogen and iron can vary across species of
turfgrasses, not all the species show similar results, for example a study conducted to
evaluate the turfgrass performance and weed abundance at different levels of nitrogen
application revealed that tall and fine fescues respond well under low and high fertilizer
inputs and have lower weed coverage. However, Kentucky bluegrass and its improved
varieties, show dramatic improvement in quality and weed control only under high inputs of
fertilizers (DeBels et al. 2012). Other environmental factors such as soil properties can also
affect the uptake of nutrients and eventually influence the growth of turfgrass and broadleaf
weeds.

1.5.

Soil Properties

Soil is the reservoir for water and the source of most of the essential nutrients for turfgrass
plants, and a house of constant complex and dynamic activities (Carrow et al. 2002).
Components that make up soil namely, mineral constituents, organic matter, and biological
entities, are very different in physical, chemical and biological properties and thus contribute
to great diversity among soils (Carrow et al. 2002). Some of the essential soil properties are
discussed below.

Physical soil properties
The composition and proportion of mineral, soil organic matter, water and air greatly
influence the physical soil properties including texture, structure, and porosity. Soil texture is
the most important physical property which determines the proportion of three mineral
16

Chapter 1-Introduction
particles; sand, silt and clay, which are distinguished by size and make up the fine mineral
fraction. The relative amount of various particles sizes in soil defines its texture i.e. whether
it is clay loam, sandy loam or another textural category (McCauley et. al. 2005).

Soil chemical properties
Plant nutrient availability is highly influenced by soil pH, generally the macronutrients (N, K,
Ca, Mg, and S) are readily available when soil pH lies in the range of 6.5-8, with the
exception of P, which is most available in the pH range of 5-7. These alterations in pH also
alters the availability of the nutrients to plants. Ideally near neutral soil pH is most suitable
for growth of plants (Fernández & Hoeft 2009).
Soil pH is a measure of hydrogen ions (H+) in the soil which determines the acidity or
alkalinity of soil. The amount of H+ ions is responsible for the variation in pH, the higher the
number of H+ ions, the higher the acidity, while lower number of H+ ions accounts for more
alkalinity. The pH scale ranges from 0-14, with 7 corresponding to neutral pH, below 7 is
acidic and above 7 is alkaline (basic). Soil pH can affect cation exchange capacity (CEC)
and anion exchange capacity (AEC) by altering the surface charge on the colloids, a higher
concentration of H+ (lower pH) will neutralize the negative charge, thereby decreasing CEC
and increasing AEC, and the vice versa when pH increases (McCauley et. al. 2009).
Most chemical interactions in soil occur on colloidal surfaces because of their charged
surfaces. These charged surfaces can attract and hold ions present in the soil solution. This
ability of soil particles to attract and exchange ions is called the ‘Exchange Capacity or EC’
(McCauley et. al. 2005). In soils there are more negative charges than positive ones,
therefore resulting in net negative charge, thus attracting more cations and giving soils a
higher Cation Exchange Capacity (CEC) as compared to the Anion Exchange Capacity
17

Chapter 1-Introduction
(AEC). Soils with low CEC often results in several problems such as deficiency of certain
nutrients, such as N as NH+4, K+, Fe+2/Fe+3 and Ca+2 in plants. Besides this low CEC could
also increase leaching potential of environmentally sensitive compounds such as pesticides.
Because of low CEC, chemical buffering is limited and thus it could easily change the
nutrient balance in soil (Carrow et. al. 2002). Another early study stated that mobility of
pesticides is directly associated with water flux and shows and inverse relationship with CEC
and organic matter (Helling 1971).

Soil biology
Plants act on the soil environment by aiding in structure and porosity and supplying soil
organic matter in the form of shoot and root residue. Likewise, soil fauna act like soil
engineers by initiating the breakdown of dead plant and animal material, ingesting and
processing large amounts of soil, burrowing and making channels for water and air
movement, mixing soil layers and increasing soil aggregates (Tugel & Lewandowski 1999).
Soil is also the domain of myriads of microorganism which are intimately associated with
soil organic fraction. The number, kind and activities of these microorganism will depend on
organic matter content of the soil, plant species, soil texture, pH and other soil parameters
(Martin & Focht 1977). Soil biological activity is controlled by various factors in soil such as
plant residue, soil organic matter quantity and quality, primarily nitrogen (N) content are the
major limiting factors for soil organism activity. If the N content is below 1.5% the
decomposition activity is delayed (Martin & Focht 1977). Fertilizer applications can also
influence soil organism population and activity. In soils characterized by low fertility or
organic matter content, the introduction of fertilizers especially those rich in nitrogen (N)
tends to stimulate biotic activity, resulting in populations undergoing an initial surge,

18

Chapter 1-Introduction
ultimately reaching a state of equilibrium as the available nitrogen is progressively utilized
(Tugel & Lewandowski 1999).

1.6.

Environmental Impact of Nutrient Fertilizers

Nitrogen fertilization is essential for the upkeep of a dense, resilient, and visually appealing
turfgrass field, capable of withstanding various pests and environmental challenges.
However, the widespread application of nitrogen to turfgrass has raised environmental
concerns, particularly regarding the fate of nitrogen, with nitrate leaching being a significant
issue. Nitrate leaching has received a lot of attention because of the concerns related to
pollution in water bodies and a major cause of eutrophication.
Studies indicate that significant nitrate leaching occurs primarily under specific conditions,
such as applying excessive nitrogen rates (~ 6 × the recommended rate) to mature turfgrass
stands; however, when nitrogen is applied at agronomically correct rates, the likelihood of
significant nitrate leaching diminishes (Frank & Guertal 2013). Neglecting to adjust nitrogen
rates to account for contributions from irrigation with reused wastewater is identified as
another significant factor contributing to nitrate leaching (Devitt et al. 2008).
Soil composition, particularly sand content and irrigation rates are critical factors influencing
nitrate leaching. Soils with lower sand content are less prone to nitrogen leaching.
Furthermore, adopting irrigation schedules that prevent water movement beyond the rooting
zone has proven effective in reducing nitrate and ammonium leaching without compromising
turfgrass growth or quality (Barton & Colmer 2006). There have been limited studies
addressing the environmental impact of applying iron compounds to turfgrass. Iron, being a
micronutrient, is typically applied at recommended rates. Turfgrass often exhibits iron

19

Chapter 1-Introduction
deficiency, and the judicious application of recommended doses can effectively enhance the
colour and aesthetic appeal of the turfgrass fields (DeVetter 2007).

1.7.

Research gaps and opportunities

Despite the studies supporting the negative impact of chemical herbicides such as 2,4-D on
both human health and the environment, a viable alternative that can yield comparable results
to conventional herbicide remains elusive. While nitrogen and iron fertilizers have been
researched in nutrient management studies for their capacity to enhance the colour and
quality of turfgrass fields, limited attention has been given to their potential impact on the
health of broadleaf weeds in turfgrasses. If true, then nutrient management can be an
alternative to chemical herbicides. This study endeavours to address this knowledge gap, by
identifying an efficient weed control method that minimizes the negative impact on both
turfgrass health and the environment.

1.8.

Thesis structure

This thesis used a combination of approaches, including greenhouse and field trials to
investigate the effectiveness of nitrogen and iron-based compounds in controlling broadleaf
weeds as well as improving the quality of turfgrass. Chapter 2 of this thesis explored how
various combinations of nitrogen and iron compounds compared with a 2,4dichlorophenoxyacetic acid herbicide (Killex) as conventional method of weed control,
influenced the growth and quality indicators of broadleaf weeds and cool season turfgrass
under controlled settings in greenhouse. The aim was to determine the best treatment
combinations for further testing in open field trials.
In Chapter 3, field trials were conducted for the most promising treatment combinations from
the greenhouse experiments, based on the assessed weed and turfgrass quality indicators. The
20

Chapter 1-Introduction
selected nitrogen and iron treatment combination was compared with the chemical herbicide
treatment and a reference control (no treatment) on established turfgrass with perennial
broadleaf weeds under natural open environmental conditions. The test sites for this trial
included an open field with no shade and an open field with a partial shade environment.

1.9.

Research Questions

Chapter 2: Performance of nitrogen and iron-based compounds on growth of broadleaf weeds
and turfgrass quality under controlled environmental conditions in a greenhouse.
Research questions:
•

How do different formulations of nitrogen (urea, ammonium sulphate) and iron (iron
sulphate, chelated iron) compounds and their combinations influences the quality and
growth parameters of broadleaf weeds compared with the conventional herbicide
method of weed control, applied under controlled environmental conditions?

•

How do the various treatment combinations of nitrogen and iron compounds effect
the quality and growth parameters of turfgrass compared with conventional herbicide
method of weed control, applied under controlled environmental conditions?

•

How do the various treatment combinations influence the soil properties and nutrient
composition?

Chapter 3: Field trial of the efficacy of ammonium sulphate × iron sulphate treatment
combination versus conventional herbicide method of weed control on broadleaf weeds in
open grown turfgrass.
Research questions:

21

Chapter 1-Introduction
•

What is the efficacy of the treatment combination of ammonium sulphate × iron
sulphate compared with conventional herbicide method of weed control in controlling
the growth and establishment of broadleaf weeds?

•

Which of these two treatments yield the best outcome on turfgrass quality?

•

How do these two treatments influence soil properties and nutrient composition?

22

Chapter 2-Greenhouse trials

2. Chapter 2- Performance of nitrogen and iron-based compounds on
broadleaf weed growth and turfgrass quality under controlled
environmental conditions in a greenhouse

2.1. Introduction
Turfgrass serves as a critical component of landscapes and recreational spaces, and
immensely contributes towards enhancement of aesthetic appeal and functionality of outdoor
environments. However, presence of weeds in turfgrass takes away much of the functionality
and the environmental benefit received from a healthy stand of dense turf and there have
been constant efforts in eliminating their presence from the desired field sites. Traditional
weed management practices often rely on chemical herbicides, and they have been long used
in the history of turfgrass management, owing to their ease of application and effective
results. Herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D) have been popularly used
to target and kill broadleaf weeds, such as common dandelion, white clover, and broad
plantain in turfgrass fields. 2,4-D is a selective herbicide that affects dicots without harming
the monocot and mimics natural auxins at the molecular level. Physiological responses of
dicots sensitive to auxinic herbicides include cell elongation, epinasty, hypertrophy,
senescence and plant death (Song 2013).
Although chemical herbicides have proved to be effective and reliable for broadleaf weeds,
they have been shown to have negative impacts on the environment and human health. For
example, close proximity of the site of application to the site of human occupation can lead
to chronic exposure and persistence indoor contamination (Robbins & Birkenholtz

23

Chapter 2-Greenhouse trials
2003)Therefore, society increasingly seeks more environmentally responsible solutions and
thus the need for safer alternatives and innovative strategies for weed control in turfgrass
have become paramount.
Previous studies have found that the population of broadleaf weeds is lower in turfgrass
fields with higher nitrogen than fields with lower nitrogen applications due to increased
competition from healthy turfgrass in response to nitrogen availability, thus leading to
restricted availability of nutrients, light, space, and water to the weeds (Busey 2003).
Conversely, excessive application of nitrogen can lead to nitrate leaching in the soil, which
can ultimately affect the properties of drinking water, and can cause detrimental health
effects including blue baby syndrome or methemoglobinemia (Majumdar 2003). Nitrogen
and phosphorous runoff can also become a considerable source of water pollution and
eutrophication (Easton & Petrovic 2004). Other studies also suggest that iron, a micronutrient
essential for chlorophyll synthesis and nitrogen metabolism in plants, can be toxic to
broadleaf weeds while being beneficial to some varieties of turfgrass (Charbonneau 2010).
Excessive iron application can also adversely impact germination, enzymatic activities, and
chloroplast structure, leading to cell toxicity and hindered carbon metabolism (Zahra et al.
2021). It’s also crucial to note that the application of iron can potentially lead to toxicity and
eventually death of certain sensitive turfgrass species, like bentgrass (Smith-Fiola & Gill
2014). Therefore, before applying iron compounds, careful consideration and identification
of the specific turfgrass species are imperative to prevent adverse effects and ensure optimal
results.
Common sources of nitrogen in plant fertilizers include urea and ammonium sulphate. Iron
supplements for plants also come in common formulations, such as chelated iron and iron
24

Chapter 2-Greenhouse trials
sulphate. While these nitrogen and iron compounds have their individual benefits to plants,
rarely do they come combined in currently available plant nutrient formulations. As such,
very little is known about the potential of the combination of nitrogen and iron-based
compounds on broadleaf weeds and their benefit to turfgrass. One of the few studies
combined urea and iron sulphate to test as an alternative to chemical herbicides but further
combinations need to be explored (Carroll et al. 2022).
The objectives of this experiment were to (1) investigate the effects of various combinations
of nitrogen and iron compound on the growth and quality indicators of broadleaf weeds and
turfgrass, (2) compare the performance of these nutrient compounds with a selective
herbicide (Killex) as the conventional method of weed control under controlled
environmental conditions in a greenhouse, (3) observe the changes induced in the growth
medium (in this case peat) by the application of various treatment methods.
This research specifically concentrated on investigating the effects of various nitrogen and
iron compounds on the growth parameters of dandelion and white clover separately. The
primary objective was to understand how different treatments influenced the individual
growth parameters of these two plant species. Importantly, the study did not delve into
impact of dandelion and white clover on each other’s growth.
Given the individual benefits of these plant nutrients and their effective control on the
broadleaf weeds discussed earlier, it was hypothesized that the treatment combination of
nitrogen and iron will perform better than individual treatments of nitrogen and iron alone.
Compared to the chemical herbicide treatment, it was hypothesized that both nitrogen and
iron-based treatments and their combinations would result in superior growth of turfgrass and
a consequent reduction in weed growth.
25

Chapter 2-Greenhouse trials

2.2.

Materials and Methods

The experiment was conducted at the greenhouse of the Enhanced Forestry Laboratory at the
University of Northern British Columbia (UNBC), Prince George campus (53.89325° N,
122.81571° W).

2.2.1. Seeds and Planting Materials
Seeds of common dandelion (Taraxacum officinale) were collected from random spots at the
UNBC campus. The seeds were collected and stored in a dry place to prevent contamination
by fungi and bacteria. Seeds of white clover and a mix of cool season turfgrass seeds
containing 10% SR 4550 perennial ryegrass, 60% Kentucky bluegrass, and 30 % creeping
red fescue were purchased from the local retail garden centre, Art Knapp, in Prince George,
British Columbia.
The planting materials included 30 rectangular bins with dimension of 58.8 cm × 38.6 cm ×
15.4 cm each with a capacity of 25 liters. Approximately 8 holes were drilled to the bottom
and lower walls of these bins for proper aeration of the soil and drainage of excess water. The
bins were thoroughly washed and disinfected with ‘Virkon’, and later air dried for 12 hours.
The potting mix, PRO-MIX® HP growth media enriched with mycorrhizae, was used for
growing turfgrass and broadleaf weeds in the bins. The growth media was emptied into a peat
mixer and light water was added until the medium was moist and was allowed to mix so that
a uniform batch was obtained for filling the bins. The growth media was added to the bins to
fill up to 10 cm of the bin or 2/3 the capacity of the bin. All the bins were weighed for
uniformity to 1.5 kg and were later transferred to the greenhouse. The temperature inside the
greenhouse was maintained at 24 ± 2°C during daytime and 16 ± 2°C during nighttime. The
bins were lightly watered for moisture retention for the sowing of grass seeds.
26

Chapter 2-Greenhouse trials
A sample of the growth medium was tested for several properties including pH, EC, initial
nutrient composition, organic matter and micronutrient content. The samples were sent to the
Northern Analytical Laboratory Services (NALS), Prince Geroge, BC for processing. The pH
and electrical conductivity were measured using the sifted (<2mm) and air-dried samples on
a 10:1 (Liquid: Solid) extract. Organic matter contents were determined gravimetrically from
the bulk material. Total nitrogen was assessed on a Costech 4010 elemental combustion
system. Metals (Fe, K, and P) determination was performed using strong mineral acid block
digestion followed by ICP-OES (Agilent Technologies 5100 ICPOES). All the tests were
conducted at NALS at UNBC.
After preparing the bins, 8.5 g of a mix of cool season turfgrass seeds along with 7 g of lawn
starter fertilizer (Home and Garden Excellence Slow Release Lawn starter fertilizer)
containing N:P:K (14-28-8) were uniformly broadcasted over the growth medium in each
bin. The bins were continuously lightly watered twice a day for 2 weeks. After about a month
of healthy turfgrass growth the irrigation schedule was changed to once a day during the cool
evening hours of the day. In total, the container grown turfgrass was allowed to grow for 2
months after sowing before weeds were introduced.
In each bin containing fully established turfgrass, 15 sowing spots were created by cutting
and pulling out the grass from these spots. There were 5 columns with 3 spots each for
sowing (Fig 2.1). The columns were alternately named as A and B, where A was sown with
dandelion seeds and B was sown with white clover seeds. In total, the dandelion seeds were
sown in 3 columns with total of 9 spots, and 3-4 seeds per spot were sown to ensure
germination. White clovers were sown in 2 columns with a total of 6 spots, and 5-8 seeds per
spot were sown to guarantee germination.
27

Chapter 2-Greenhouse trials

Figure 2.1. Arrangement of sowing spots for dandelion and white clover seeds in columns
marked with different colours (A) and removal of grass from the spots to create space for
sowing the weeds (B).

To ensure uniformity in evaluating treatments on broadleaf weeds and turfgrass growth, 5
dandelion plants and 6 white clover plants were desired in each bin. However, as an
insurance, 128 extra dandelion seeds were sown in plug trays separately, which could be used
as transplants in case the dandelion plants did not germinate in the bins. After sowing, the
seeds were allowed to germinate and grow along with the turfgrass for another 3 weeks.
After the 3-week period, the bins were inspected for the germination of weeds, and it was
found that white clovers had fully germinated in all the 30 bins. However, the dandelions had
germinated only in 21 bins and in the remaining 9 bins there was incomplete or no
germination at all. The transplants from the plug trays were used to fill in the empty spots in
the remaining bins to fulfil the minimum number of 5 dandelion plants in each bin (Fig. 2.2).

28

Chapter 2-Greenhouse trials

Figure 2.2. Transplanting the dandelion seedlings from plug tray to the desired experimental
bins to fulfil the minimum number of dandelion plants per bin.
The white clovers had germinated in all 6 spots and there were more than 5 plants in each
spot; however, since the white clover plants were too sensitive to be disturbed, they were not
thinned out but allowed to grow as such. The transplanted seedlings were allowed to grow
and establish for another 2 weeks. The bins were monitored regularly to observe the growth
and establishment of weeds and turfgrass and that the transplanted seedlings were healthy
and well established.

2.2.2. Experimental Setup
The experimental design consisted of 10 treatments with 3 replicates of each treatment. Each
bin represented one replicate and treatment unit, thus adding up to 30 bins in total. Dandelion
and other broadleaf weed populations are reduced by N fertilization with at least 100 to 300
kg N ha-1 yr-1 (Busey 2003). Also for iron, foliar application o 2.2 kg Fe ha-1 have been
shown to be optimum for enhancing the colour of turfgrass (Yust et al. 1984). Therefore, this
experiment used the high rate of 300 kg N ha-1 yr-1 and the optimum rate 2.2 kg Fe ha-1 for
29

Chapter 2-Greenhouse trials
the treatment applications. For the size of the bins used for this experiment, this translated to
7.5 g of N per bin and 0.049 g of Fe per bin. This amount was applied in three split monthly
(4-week interval) doses to prevent toxicity and burning of plants.
The experimental bins were spread out on three different shelves in the greenhouse. Each
shelf had 10 bins of different treatments, including the control (no application) (Fig. 2.3).
The treatment formulations along with their active ingredients are listed in the Table 2.1
below:

Table 2.1. Chemical composition of the treatments and the proportion of nitrogen, iron, and
sulphur contained in them.
Treatment

Chemical component composition
(nitrogen-N, sulphur-S, iron-Fe)

Urea

46% N

Ammonium sulphate ((NH4)2SO4)

21% N, 24% S

Chelated iron (Fe-HEDTA)

13% Fe

Iron sulphate (FeSO4)

20% Fe, 12% S

Urea × chelated iron

46% N, 13% Fe

Urea × iron sulphate

46% N, 20% Fe, 12% S

Ammonium sulphate × chelated iron

21% N, 24% S, 13% Fe

Ammonium sulphate × iron sulphate

21% N, 24% S, 20% Fe, 12% S

Killex

95 g/L 2,4-D, Mecoprop-P, Dicamba

Control

-

30

Chapter 2-Greenhouse trials

- Fe-

Urea

FeSO,

FeSO,

• FeSO,

HFDTA

so.

Fe-

PT

HEDTA

FeSO,

Fe

♦Fe-

Urea •

HEDTA

Figure 2.3. Tabular representation of the experimental layout of the treatments on different
shelves in the Enhanced Forestry Laboratory, at University of Northern British Columbia.

For the treatments receiving urea, 4.9 g of urea dissolved in 250 ml of water was applied to
each bin, while for the treatments receiving ammonium sulphate, 10.79 g of ammonium
sulphate dissolved in 250 ml of water was applied to each bin. For the treatments receiving
iron (ferrous) sulphate, 0.081 g of FeSO4 dissolved in 250 ml of water was applied to each
bin, while for the treatments receiving chelated iron, 0.125 g of Fe-HEDTA dissolved in 250
ml water was applied to each bin. For the selective herbicide Killex, a broadcast foliar
application of 105 ml of diluted ready to use formulation (containing 2,4-D, Mecoprop-P,
and Dicamba as active ingredients) was applied to each bin. The desired concentrations of
the solutions were evenly sprayed meticulously onto the treatment bins using handheld
sprayers of 2 L capacity.

31

Chapter 2-Greenhouse trials

2.2.3. Data Collection
Initial measurements for both weed and turfgrass growth and quality were recorded prior to
the application of the treatments. The growth parameter assessed for white clovers was the
number of plants per spot, while those for dandelion plants were the number of leaves per
dandelion plant, and the length of the longest leaf of the dandelion plant which are important
indicators of plant growth. For recording the leaf length, the dandelion leaf was demarcated
using a thin thread. While the growth parameter assessed for turfgrass was the weight (yield)
of dried clippings collected from trimming the turfgrass at constant length after every two
weeks.
The quality ratings of dandelion, white clovers and turfgrass were recorded every week for 3
months, as was the intended duration of the trial. Quality indicators of dandelion and white
clover plants were based on the overall condition of the plants, which included colour,
growth and vigour, and any visible signs of damage etc. This rating was scored on a nominal
scale of 0 - 9, where 0 = completely dead plant, 1 - 3 = poor quality of plant with no apparent
growth and black brown discolouration, 4 = minimal growth of the plant with brown or
yellow patches on the leaves, 5 = moderate growth of plants with light green coloured leaves
and slight discoloration, 6 - 8 = uniform growth of plants with medium coloured green
leaves, and 9 = uniform and healthy growing plants with dark green coloured leaves. Other
metrices, such as the number of leaves and length of leaf of dandelion plants were recorded
and measured with a tape measure by stretching the leaves flat and horizontal to the surface
of the scale.
Quality ratings of turfgrass were based on visual assessment (such as color of turfgrass,
presence of brown patches, uneven growth of turfgrass, and appearance of any
32

Chapter 2-Greenhouse trials
discolouration) and rated according to the National Turfgrass Evaluation Program (NTEP) on
a scale of 0 - 9, where 0 = completely dead grass, 1 - 3: Very poor or completely brown=
turfgrass is in poor condition, with severe imperfections, low density, and completely brown;
4: Poor = turfgrass has significant imperfections, reduced density, and may show signs of
stress, or disease, colour and texture are noticeably compromised; 5: Fair = turfgrass is
somewhat uniform but may have noticeable imperfections, and may show signs of stress or
disease, and the colour and texture might be less desirable light green colour turfgrass with
some yellow patches; 6 - 8: Good = turfgrass is generally uniform with good density, may
have minor imperfections but is visually appealing and the colour and texture are
satisfactory; 9: Excellent = turfgrass is uniform, dense, free of diseases and exhibits
exceptional colour, texture and overall aesthetic appeal.
The growth medium only filled the bins up to a depth of 10 cm, with the bins themselves
being 15 cm deep, the turfgrass was trimmed at each 2-week period, to the uniform length of
5 cm.to align with the bin height using a pair of scissors. Clippings were then collected with
the help of ‘SHARK® Euro Pro’ handheld vacuum cleaner. The clippings were air-dried in a
YAMATO® DX 600 Drying oven at 65° C for 72 hours and then weighed using a
SARTORIUS® scale.
The FM 2 Pulse-Modulated Chlorophyll Fluorescence Monitoring System (OPTISCIENCES®) was used to capture the photosynthetic capacity (PSII) of the already marked
spots on turfgrass on a weekly basis. It involved tracking minimum (F0) and maximum
fluorescence (Fm) along with their difference, known as variable fluorescence (Fv). The Fv/Fm
ratio, ideally around 0.8 for healthy plants, reflects the photochemical efficiency of
photosynthesis and serves as an indicator of plant stress due to factors like drought, nitrogen
33

Chapter 2-Greenhouse trials
deficiency, and herbicide exposure (Pavlovic et al. 2015). The measurements were done on 3
randomly chosen spots in each bin, which were then marked using plant markers for uniform
measurement throughout the duration of the experiment.
Upon the complete and final data collection in the twelfth week, samples of growth medium
for each treatment were sent to NALS, for analysis of several properties, including pH,
electrical conductivity (EC), organic matter, and macro- and micronutrients.

2.2.4. Statistical Analysis
Data for weed and turfgrass growth and quality indicators were analyzed using linear mixedeffects models that included treatments, time since application (i.e. weeks), and their
interaction as fixed effects and the randomly assigned bins on each shelf as the random
effect. Dependent variables included the number of white clover plants, quality ratings of
weeds and turfgrass, leaf readings of dandelion plants, weight of turfgrass clippings, and the
photosynthetic capacity of turfgrass. The data were checked to ensure that all the parametric
assumptions were met, and applied data transformation when necessary. To address the zero
entries (indicating dead plants) and achieve a normal distribution, log transformation was
applied specifically to the quality of dandelion, quality of white clover, length of the longest
leaf of dandelion, and number of leaves per dandelion.
When the main effects or their interaction was significant (at α = 0.05), post hoc tests were
used to evaluate significant differences between the treatment levels or time since
application. All statistical analyses were performed using the R statistical program (R Core
Team 2021). Specifically, linear mixed-effect models were performed using the lme function
in the NLME package (Pinheiro & Bates 2000) and by specifying the first-order
autocorrelation corAR1 function as the correlation structure to account for the repeated
34

Chapter 2-Greenhouse trials
measurements over time. Post hoc tests were performed using the emmeans function in the
LSMEANS package (Lenth et al. 2018) and by specifying the “Bonferroni” adjustment.

2.3.

Results

There were significant interaction effects between the treatments and time on the number of
white clovers, dandelion quality, and dry weight of turfgrass clippings, whereas their
interaction (i.e. treatment × time) effect on quality of white clover and turfgrass was
marginal. Length of the longest leaf of dandelion, dandelion leaf count, and photosynthetic
capacity (Pc) of turfgrass were significantly influenced by the treatments and time but not
their interactions (Table 2.2).

Table 2.2. Effects of the experimental treatments, time since application, and their
interaction on the quality and properties of white clover, and dandelion weeds and turfgrass,
under controlled environmental conditions in a greenhouse. Values are p-values from a liner
mixed effect model analysis.
Dependent variables

Treatment

Time

Treatment × Time

Quality of white clover†

<0.001

<0.001

0.076

No. of white clover weeds

<0.001

<0.001

0.001

<0.001

<0.001

<0.001

Number of leaves per dandelion

0.001

<0.001

0.208

Length of the longest leaf of dandelion†

<0.001

<0.001

0.810

Quality of turfgrass

<0.001

0.004

0.073

Photosynthetic capacity of turfgrass

<0.001

<0.001

0.175

Weight of dried clippings of turfgrass

<0.001

<0.001

<0.001

Quality of dandelion

†

Notes: † denotes variables that were log-transformed to meet the parametric assumptions.

35

Chapter 2-Greenhouse trials

2.3.1. Broadleaf weed’s response to treatment
Effect of treatments on quality of white clover plants
The quality of white clover weeds decreased across most treatments over time. The quality
ratings for all treatments over time consistently fell below the average quality rating observed
prior to the treatment application. Interestingly, FeSO4 alone did not exhibit a negative
impact on the quality of white clover plants over time. Notably, the treatments most
comparable to Killex in terms of efficacy were (NH4)2SO4, (NH4)2SO4 × FeSO4, and
(NH4)2SO4 × Fe-HEDTA. These treatments resulted in a considerable decline in the quality
of white clovers consistently from week 6 until the conclusion of the experiment. Other
treatments including Fe-HEDTA, urea, urea × Fe-HEDTA, and urea × FeSO4 also
contributed to deterioration in the quality of white clovers, comparable to the impact
observed with Killex, particularly in the later phases of the experiment. A complete
eradication of white clovers was observed in bins treated with Killex, (NH4)2SO4, and
(NH4)2SO4 × Fe-HEDTA (Fig. 2.4).

(0-9)

Control

plants

clover

I

|
Fe-HEDTA

Urea

Fe-HEDTA

Fe-HEDTA

FeSO4

8

quality

Visual

2

4

8

10

12

36

Chapter 2-Greenhouse trials
Figure 2.4. Group bar graph (sample size, n = 3) representing the change in quality of white
clover plants on the scale of 0-9 under different treatments over the period of 12 weeks while
growing under controlled conditions. The legends marked in different colours represent the
different treatment applications. Pre-treatment (measurements taken before treatment
application) results (mean) are marked with solid red line running parallel to x-axis with
standard deviations marked with dotted red lines respectively. Second treatment application
was made after week 4, and third application treatment was made after week 8. See methods
for more details. The x-axis represents the weeks (time), and y-axis represents the quality of
white clover plants. The display letters marked on the top of the bars represent the significant
differences between the treatments as revealed by post hoc tests using emmeans. Same letters
represent no significant differences, while different letters represent significant differences in
the measurements (α = 0.05).

Effect of treatments on number of white clover plants
In week 2, a significant decrease in average number of white clover plants was observed
particularly in bins treated with Killex, (NH4)2SO4, and (NH4)2SO4 × Fe-HEDTA. The
number of white clover plants in bins treated with (NH4)2SO4 × FeSO4 also experienced a
decline. Other treatments either exceeded or equaled control plot plant numbers initially.
Over subsequent weeks there was a gradual reduction in the overall number of white clover
plants. Killex, (NH4)2SO4, (NH4)2SO4 × Fe-HEDTA, and (NH4)2SO4 × FeSO4 were the most
effective treatments until week 6. However, by the conclusion of the experiment, all the
treatments showed comparable effectiveness in controlling the number of white clover plants
in the bins. Notably, bins treated with Killex, (NH4)2SO4, and (NH4)2SO4 × Fe-HEDTA
achieved complete eradication of white clovers (Fig. 2.5).

37

Chapter 2-Greenhouse trials

I
Control

FeSO4
Fe-HEDTA

|
Urea

Urea

Fe-HEDTA

Fe-HEDTA

FeSO4

(A

6

2

8

10

12

(weeks)

Figure 2.5. Group bar graph (sample size, n = 3) representing the change in total number of
white clover plants under different treatments over the period of 12 weeks while growing
under controlled conditions. The legends marked in different colours represent the different
treatment applications. Pre-treatment (measurements taken before treatment application)
results (mean) are marked with solid red line running parallel to x-axis with standard
deviations marked with dotted red lines respectively. Second treatment application was made
after week 4, and third application treatment was made after week 8. See methods for more
details. The x-axis represents the weeks (time), and y-axis represents the number of white
clover plants. The display letters marked on the top of the bars represent the significant
differences between the treatments as revealed by post hoc tests using emmeans. Same letters
represent no significant differences, while different letters represent significant differences in
the measurements (α = 0.05).

Effect of treatments on the quality of dandelion plants
The average quality of dandelion plants consistently declined under all the treatments starting
from week 2. Killex-treated dandelion plants showed no regeneration throughout the
experiment, indicating an inability to recover. In the initial weeks, the quality of dandelion
plants treated with Fe-HEDTA was slightly lower yet comparable to control plants, a trend
persisting in week 4. Similarly, dandelion plants treated with FeSO4 also displayed reduced

38

Chapter 2-Greenhouse trials
quality in these weeks. By week 6, the quality of dandelion plants became comparable among
the bins treated with (NH4)2SO4, (NH4)2SO4 × Fe-HEDTA, (NH4)2SO4 × FeSO4, Fe-HEDTA,
FeSO4 and control group. From week 8 until the conclusion of the experiment, quality of
dandelion plants remained comparable across all treatments. Notably, plots treated with
Killex and (NH4)2SO4 × FeSO4 had no dandelion plants by the end of the experiment (Fig.
2.6).

I
Control
G

|
Fe-HEDTA

Fe-HEDTA

Fe-HEDTA

9

G

c

7

5
4

3

2
1

0

10
(weeks)

Figure 2.6. Group bar graph (sample size, n = 3) representing the change in quality of
dandelion plants on a scale of 0-9, under different treatments over the period of 12 weeks
while growing under controlled conditions. The legends marked in different colours represent
the different treatment applications. Pre-treatment (measurements taken before treatment
application) results (mean) are marked with solid red line running parallel to x-axis with
standard deviations marked with dotted red lines respectively. Second treatment application
was made after week 4, and third application treatment was made after week 8. See methods
for more details. The x-axis represents the weeks (time), and y-axis represents the quality of
dandelion plants. The display letters marked on the top of the bars represent the significant
differences between the treatments as revealed by post hoc tests using emmeans. Same letters
represent no significant differences, while different letters represent significant differences in
the measurements (α = 0.05).

39

Chapter 2-Greenhouse trials
Effect of treatments on leaf number of dandelion plants
The treatment and time interactions were not significant for the number of leaves per
dandelion plant. However, the leaf count across different treatments has shown significant
results. Plants treated with urea and urea × Fe-HEDTA represented an overall increase in leaf
count. Whereas plants treated with Killex, displayed significantly lower values in
measurements. While the plants treated with (NH4)2SO4, (NH4)2SO4 × Fe-HEDTA,
(NH4)2SO4 × FeSO4, Fe-HEDTA, FeSO4, and urea × FeSO4, along with the plants in control
bins demonstrated measurements comparable to each other (Fig. 2.7).

Control

Killex

Control

I

(NH4)2SO4

|Urea Fe-HEDTA
Urea

Fe-HEDTA

FeSO4

Urea

AS

Urea*IS

Treatments

Figure 2.7. Group bar graph (sample size, n = 3) representing the average number of leaves
per dandelion plant under different treatments over the period of 12 weeks while growing
under controlled conditions. The legends marked in different colours represent the different
treatment applications. The x-axis represents the treatments, and y-axis represents the
number of leaves per dandelion plant. The display letters marked on the top of the bars
represent the significant differences between the treatments as revealed by post hoc tests
using emmeans. Same letters represent no significant differences, while different letters
represent significant differences in the measurements (α = 0.05).

40

Chapter 2-Greenhouse trials
Effect of treatments on length of the longest leaf of dandelion plants
The treatment and time interactions were not significant for the length of the longest leaf of
dandelion. However, the leaf length across different treatments has shown significant results.
Plants treated with urea represented an overall increase in leaf length. Whereas plants treated
with Killex, Fe-HEDTA, along with those in control bins displayed significantly lower
values in measurements. While the plants treated with (NH4)2SO4, (NH4)2SO4 × Fe-HEDTA,
(NH4)2SO4 × FeSO4, FeSO4, urea × Fe-HEDTA, and urea × FeSO4, demonstrated
comparable measurements (Fig. 2.8).

Treatments

Figure 2.8. Group bar graph (sample size, n = 3) representing the average length of the
longest leaf of dandelion under different treatments over the period of 12 weeks while
growing under controlled conditions. The legends marked in different colours represent the
different treatment applications. The x-axis represents the treatments, and y-axis represents
the length of the longest leaf of dandelion. The display letters marked on the top of the bars
represent the significant differences between the treatments as revealed by post hoc tests
using emmeans. Same letters represent no significant differences, while different letters
represent significant differences in the measurements (α = 0.05).

41

Chapter 2-Greenhouse trials

2.3.2. Turfgrass’s response to treatments
Effect of treatments on quality of turfgrass
Turfgrass mostly responded positively to the treatments, in terms of visual quality. Notably,
treatments containing nitrogen demonstrated a significant enhancement in average turfgrass
quality, but that of iron appeared comparatively limited. The average quality rating of
turfgrass in bins treated with (NH4)2SO4, (NH4)2SO4 × Fe-HEDTA, (NH4)2SO4 × FeSO4,
urea × FeSO4 and urea × Fe-HEDTA exhibited similar results in week 4. The turfgrasses
treated with (NH4)2SO4 × FeSO4, urea × Fe-HEDTA and urea × FeSO4 exhibited an
exceptional improvement in quality in week 6, with some fluctuations in the following
weeks. Overall, turfgrass treated with (NH4)2SO4 × FeSO4 consistently experienced an
upward trajectory in average quality ratings, reaching peak levels by the conclusion of the
observation period (Fig. 2.9).

I
Control

2

|
Fe-HEDTA

FeSO4

Fe-HEDTA

10

12

Figure 2.9. Group bar graph (sample size, n = 3) representing the change in quality of
turfgrass on a scale of 0-9 under different treatments over the period of 12 weeks while
42

Chapter 2-Greenhouse trials
growing under controlled conditions. The legends marked in different colours represent the
different treatment applications. Pre-treatment (measurements taken before treatment
application) results (mean) are marked with solid red line running parallel to x-axis with
standard deviations marked with dotted red lines respectively. Second treatment application
was made after week 4, and third application treatment was made after week 8. See methods
for more details. The x-axis represents the weeks (time), and y-axis represents the quality of
turfgrass. The display letters marked on the top of the bars represent the significant
differences between the treatments as revealed by post hoc tests using emmeans. Same letters
represent no significant differences, while different letters represent significant differences in
the measurements (α = 0.05).

Effect of treatments on photosynthetic capacity of turfgrass
The treatment and time interaction were not significant for the photosynthetic capacity of
turfgrass. However, the Pc across different treatments showed significant results. Overall,
significantly highest Pc values were recorded in turfgrass treated with (NH4)2SO4 × FeSO4
among all the treatments and turfgrass treated with Killex exhibited the lowest Pc values.
While the rest of the treatments demonstrated comparable measurements to each other (Fig.
2.10).
x FeSO4

Fe-HEDTA

Fe-HEDTA

Fe-HEDTA

FeSO4
Urea

08

of

cap city

Photsyneic

0.1

Killex

Control

AS

AS*IS

Urea+CI

43

Chapter 2-Greenhouse trials
Figure 2.10. Group bar graph (sample size, n = 3) representing average photosynthetic
capacity (Pc) of turfgrass under different treatments over the period of 12 weeks while
growing under controlled conditions. The legends marked in different colours represent the
different treatment applications. The x-axis represents the treatments, and y-axis represents
the photosynthetic capacity of turfgrass. The display letters marked on the top of the bars
represent the significant differences between the treatments as revealed by post hoc tests
using emmeans. Same letters represent no significant differences, while different letters
represent significant differences in the measurements (α = 0.05).

Effect of treatments on weight of dried clippings of turfgrass
All the treatments receiving nitrogen application showed a boost in the turfgrass clipping
yield. Initially, all the nitrogen -receiving treatments demonstrated comparable turfgrass
clipping yield. In week 4, the highest turfgrass clipping yield was observed in plants treated
with (NH4)2SO4, while the lowest yields obtained from plants treated with Killex, FeHEDTA, FeSO4, and the ones present in control bins. However, as the experiment
progressed, an intriguing trend emerged. In week 6, turfgrass clipping yields exhibited an
increasing trend with (NH4)2SO4 × FeSO4 and urea × Fe-HEDTA. However, by the
experiment conclusion, (NH4)2SO4 × FeSO4 showcases the utmost turfgrass clipping yield
among all the treatments (Fig. 2.11).

44

Chapter 2-Greenhouse trials

Time (weeks)

Figure 2.11. Group bar graph (sample size, n = 3) representing the change in dry weight of
turfgrass under different treatments over the period of 12 weeks while growing under
controlled conditions. The legends marked in different colours represent the different
treatment applications. Pre-treatment (measurements taken before treatment application)
results are marked with solid red line running parallel to x-axis with standard deviations
marked with dotted red lines respectively. Second treatment application was made after week
4, and third application treatment was made after week 8. See methods for more details. The
x-axis represents the weeks (time), and y-axis represents the dry weight of turfgrass
clippings. The display letters marked on the top of the bars represent the significant
differences between the treatments as revealed by post hoc tests using emmeans. Same letters
represent no significant differences, while different letters represent significant differences in
the measurements (α = 0.05).

2.3.3. Effect of treatments on growth medium (peat)
By the end of the experiment period, pH of the growth medium (i.e. peat) had increased for
all the treatments, ranging from 6.0 (Fe-HEDTA) to 6.98 (Urea × FeSO4), representing 6.4%
to 23.8% increase as compared to the pre-treatment pH of 5.64. Electrical conductivity
increased for only (NH4)2SO4 × FeSO4 and (NH4)2SO4 × Fe-HEDTA (26.8% and 4.8%
increase respectively) whereas it decreased for all other treatments. Similarly, organic matter

45

Chapter 2-Greenhouse trials
increased only slightly for Urea × FeSO4 (1.6%) and (NH4)2SO4 × FeSO4 (0.6%) whereas it
declined for all other treatments (Table 2.3).

Table 2.3. Before and after comparison of the physical (organic matter – OM) and chemical
(soil pH, electrical conductivity – EC) properties of the growth medium (peat) for the
different treatments.
pH

pH

EC (µS/cm)

EC (µS/cm)

OM (%)

OM (%)

Before
5.64

After
6.8

Before
1395

After
1463

Before
61.03

After
56.2

5.64
5.64
5.64
5.64
5.64
5.64
5.64
5.64
5.64

6.05
6.81
6.98
6.04
6
6.64
6.71
6.57
6.34

1395
1395
1395
1395
1395
1395
1395
1395
1395

1769
238
266
279
300
1237
241
299
339

61.03
61.03
61.03
61.03
61.03
61.03
61.03
61.03
61.03

61.4
59.2
62
60.6
59.6
58.5
58
56.6
57.4

Treatments
(NH4)2SO4 × FeHEDTA
(NH4)2SO4 × FeSO4
Urea × Fe-HEDTA
Urea × FeSO4
FeSO4
Fe-HEDTA
(NH4)2SO4
Urea
Killex
Control

Furthermore, nitrogen content decreased for all treatments by the end of the experiment, but
only slightly for the treatments that contained nitrogen compounds. Also, phosphorous and
potassium decreased considerably for all the treatments, ranging from 46.7% in (NH4)2SO4 ×
Fe-HEDTA to 58.3% in (NH4)2SO4 decrease in phosphorous and from 54.1% in Killex to
79.7% (NH4)2SO4 × FeSO4 decrease in potassium as compared to the pre-treatment levels.
By contrast, iron content was appreciably higher in all the treatments, ranging from 3.7%
(NH4)2SO4 × FeSO4 to 28.9% Urea × FeSO4 increase as compared to the pre-treatment iron
levels (Table 2.4).

46

Chapter 2-Greenhouse trials
Table 2.4. Before and after comparison of the nutrient (nitrogen, phosphorous, potassium,
and iron) contents of the growth medium (peat) for the different treatments. Nitrogen – N,
Phosphorus – P, Potassium – K, Iron – Fe.

(NH4)2SO4 × Fe-HEDTA

N
(%)
Before
0.85

N
(%)
After
0.79

P
(mg/kg)
Before
801

P
(mg/kg)
After
427

K
(mg/kg)
Before
1518

K
(mg/kg)
After
449

Fe
(mg/kg)
Before
1861

Fe
(mg/kg)
After
2352

(NH4)2SO4 × FeSO4

0.85

0.82

801

390

1518

358

1861

1929

Urea × Fe-HEDTA

0.85

0.78

801

363

1518

420

1861

2164

Urea × FeSO4

0.85

0.80

801

390

1518

381

1861

2399

FeSO4

0.85

0.74

801

357

1518

508

1861

2148

Fe-HEDTA

0.85

0.82

801

373

1518

571

1861

2002

(NH4)2SO4

0.85

0.76

801

334

1518

371

1861

2045

Urea

0.85

0.74

801

338

1518

362

1861

2102

Killex

0.85

0.72

801

415

1518

697

1861

1952

Control

0.85

0.77

801

385

1518

635

1861

2270

Treatments

2.4.

Discussion

Interaction among plant nutrients can yield antagonistic or synergistic outcomes in regard to
plant yield or pest control. In this experiment, two nutrients, nitrogen and iron were selected
to observe their effects on the growth of two broadleaf weeds, dandelion (Taraxacum
officinale Weber ex. F.H.Wigg) and white clover (Trifolium repens L.), while simultaneously
studying their impact on the health of turfgrass. The experiment was conducted based on
previous research studies, confirming the deleterious impact of nitrogen and iron on
broadleaf weeds when compared to control blocks.
Early research indicates that the suppression of white clover may be a direct effect of applied
nitrogen, as fertilizer N depresses the nodulation of white clover (Heddle 1966). White
clovers are also found to be sensitive to low levels of soil pH and therefore thrive well in
47

Chapter 2-Greenhouse trials
soils with pH higher than 5.5, which explains the study conducted by Low & Armitage
(1970), that the growth of white clovers is considerably reduced with application of
(NH4)2SO4 as compared to application of urea, each applied at the rate of 236 kg N/ha. The
results from the greenhouse experiment are in accordance with this study and confirm that
the number and quality of white clover is highly deteriorated by the application of
ammonium sulphate, alone as well as in combination with iron sulphate and chelated iron.
The pH of growth medium treated with (NH4)2SO4 treatment was noted to be 6.64, while that
of (NH4)2SO4 × Fe-HEDTA treatment was noted to be 6.80, and of (NH4)2SO4 × FeSO4
treatment was noted to be 6.05. On the other hand, FeSO4 treatment and Fe-HEDTA
treatment have lower levels of pH corresponding to 6.04 and 6.00 respectively, but both the
treatments still have a higher number and higher quality of white clovers than control. This
suggests that factors other than pH may be influencing this outcome.
Siva (2014) conducted tests revealing that two applications of Fe-HEDTA at a rate of 1 g ai
m-2, sprayed at a volume of 4000 L/ha, effectively reduced the cover of broadleaf weeds such
as common dandelion, white clover, and black medic to less than 5%. Additionally, Wilen
(2012) reported that post-emergence applications of Fe-HEDTA selectively controlled a wide
range of broadleaf weeds. This treatment included foliar necrosis in the targeted species
within three days of application, without causing harm to the turf. It was observed in the
greenhouse experiments that Fe-HEDTA and FeSO4 negatively impacted the quality of
dandelion plants, however, their impact on white clovers wasn’t very evident. It was rather
observed that the quality of white clover plants treated with Fe-HEDTA and FeSO4 was
higher than or equivalent to the control plants. However, when FeSO4 and Fe-HEDTA are
used in combination with (NH4)2SO4, a considerable control of white clovers is observed.

48

Chapter 2-Greenhouse trials
Thus, indicating that (NH4)2SO4 alone is responsible for controlling the number and quality
of white clover. Such difference in results could be due to the different concentration of iron
compounds used in this research, and higher rates may provide better results.
Studies conducted on dandelion in turfgrass have revealed that it is a poorer competitor for
potassium than turfgrass and therefore flourishes very well on soils which receive potassiumrich fertilizer. Conversely, fields with abundant nitrogen supply have shown a low incidence
of dandelion infestation (Tilman et al. 1999). However, the application of urea alone did not
yield any effective results, as studied by Carroll et al. (2022), where the application of two
rates of urea (24.4 kg N/ha and 43.9 kg N/ha), and one application of urea and iron sulphate
were found to be ineffective as compared to synthetic selective herbicides. The highest rate
of Fiesta (26.52% Fe-HEDTA) was found to be most effective in this study, providing an
effective control over major broadleaf weeds including dandelion and white clover resulting
in <1% dandelion populations within one week upon fall application. Likewise, the results
from greenhouse studies suggest that, although iron compounds including FeHEDTA and
FeSO4 are responsible for the initial decrease in quality of dandelions in turfgrass, however,
they can not completely eradicate the dandelion plants from the entire plot. When used in
combination with (NH4)2SO4, FeSO4 provides desirable results, leading to the complete
eradication of dandelions from the treatment plot.
Turfgrass quality showed positive responses to nutrient treatments, particularly those
containing nitrogen, which demonstrated a significant enhancement in quality. This is quite
evident of the fact that nitrogen is the most important nutrient for maintaining good turfgrass
health (Frank & Guertal 2013); since nitrogen affects numerous turfgrass responses including
colour, shoot density, root, rhizome, and stolon growth, high and low temperature stress,
49

Chapter 2-Greenhouse trials
wear tolerance and recuperative ability (Carrow et al. 2002). It was also noted that turfgrass
receiving nitrogen application showed higher photosynthetic capacity and visual quality
ratings. This suggests a correlation between enhanced visual quality and improved ability of
turfgrass to withstand stressful conditions.
The results of soil properties indicate that treatments containing (NH4)2SO4 led to an increase
in the electrical conductivity comparative to the rest of the treatments. This rise can be
attributed to the easy solubility and dissociation of NH4+ ions in the growth medium
(Machado et al. 2012). Additionally, a noticeable increase in EC was also observed in
treatments containing (NH4)2SO4 × FeSO4. A slight increase in organic matter was also
observed in treatment applications of urea × FeSO4 and (NH4)2SO4 × FeSO4. The results of
nutrient composition from growth medium analysis suggest that the since phosphorous and
potassium were not added to any of the treatment applications, the levels have considerably
depleted thus exhausting the growth medium. The levels of nitrogen declined in all the
treatments, however, there wasn’t a drastic change in the numbers.
This study, conducted under controlled conditions found that effective control of broadleaf
weeds can be achieved through application of different combinations and sources of nitrogen
and iron compounds, including (NH4)2SO4, (NH4)2SO4 × FeSO4, and (NH4)2SO4 × FeHEDTA. Among the various treatments considered, there were evidence that the
combination of (NH4)2SO4 × FeSO4 may yield superior quality, enhanced photosynthetic
capacity and high biomass in turfgrass as well as an increased electronic conductivity of the
soil. These promising results necessitated further testing under natural environmental
conditions to ascertain their efficacy.

50

Chapter 3-Field trials

3.

Chapter 3- Performance of treatment combination of nitrogen and
iron on broadleaf weeds and turfgrass on already established
turfgrass fields under natural environmental conditions.

3.1. Introduction
In natural field conditions, variable environmental factors such as shade, temperature,
aeration of soil, available oxygen and moisture in soil, pH and EC values of soil greatly
influence the fertilizer uptake capacity of turfgrass (Griffin & Waltz 2021). Cool season
turfgrasses can perform well under partial shade, and it has been found that in general, cool
season turfgrass reach light saturation for their photosynthesis apparatus at approximately
50% of full sunlight, and thus any additional light received cannot be effectively used for
photosynthesis and it lost to radiation less transfer and other processes (Gardener & Goss
2013). Cool season turfgrasses exhibit lower light compensation points (the minimum light
needed for sustained growth) and light saturation points, enabling them to thrive more
effectively in shaded environments as compared to warm-season grasses. During the fall,
these turfgrasses tend to enhance both cover percentage and stand density which can be
attributed to increased carbohydrate availability due to reduced respiration rates and lower
temperatures during this season (Gardner & Goss 2013).
Sufficient soil moisture is essential for optimal grass utilization of fertilizer nutrients.
Adequate soil moisture is indispensable for the biological activities that convert nutrients into
a usable form. Furthermore, effective root growth and nutrient uptake also hinge on the
presence of ample soil moisture when utilizing nutrients (Paul & Frey 2023). However, an

51

Chapter 3-Field trials
excess of soil moisture and soil compaction should be avoided since it depletes the available
oxygen in soil and does not allow adequate movement of air and water into the soil, thus
limiting the availability of nutrients (Griffin & Waltz 2021).
Soil pH is another critical factor impacting turfgrass growth. An imbalanced soil pH, whether
too low or too high, can hinder nutrient absorption by plant roots. Additionally, soil pH plays
a role in various soil reactions, including microbial activity. Optimal turfgrass growth
typically occurs in soils with slightly acidic pH. Cation and anion exchange capacities are
influenced by pH as well. Although a high cation exchange capacity (CEC) in soil is
beneficial, it is not a direct determinant of yield. CEC plays a role in retaining positively
charged chemical elements, preventing leaching, and supplying nutrients to plant roots
through an exchange of hydrogen ions (H+). The CEC of soil results from negatively charged
electrostatic charges in minerals and organic matter. Organic residues initially possess low
CEC, but this increases as the residues transform into humus (Fernández & Hoeft 2009).
Ammonium sulphate and iron (ferrous) sulphate were identified as the most effective
combination for minimizing weed coverage while enhancing the quality of turfgrass in the
greenhouse study (Chapter 2). However, since conditions in the greenhouse trial may be
quite different from actual field conditions, it is imperative to determine how this
combination of (NH4)2SO4 × FeSO4 performs on broadleaf weeds and already established
turfgrass in natural field setting.
The objectives of this experiment were to (1) study the effect of (NH4)2SO4 × FeSO4 on the
growth and quality indicators of broadleaf weeds and turfgrass and how this compares to a
conventional selective herbicide (Killex) under natural environmental conditions and (2)

52

Chapter 3-Field trials
examine the impact of this nutrient combination versus 2,4-D on the soil physical and
chemical properties.
Given the promising results of (NH4)2SO4 × FeSO4 in managing broadleaf weeds and
improving turfgrass quality as observed under greenhouse conditions (Chapter 1 of this
thesis), it was expected that this combination would effectively provide similar results under
natural environmental conditions. It was hypothesized that (NH4)2SO4 × FeSO4 would yield
comparable outcomes to Killex in terms of weed control but yield superior turfgrass quality.

3.2.

Methods

3.2.1. Study Area
The field trial was conducted in a private lawn area owned and managed by the University of
Northern British Columbia (UNBC), Prince George, BC. Two field sites that differed in
exposure to sunlight were selected. Site 1 (53.8926o N, -122.8137o W) was characterized as a
partial shade field site as it experienced about 50% shade during both sunrise and sunset
owing to the presence of buildings on both sides. Site 2 (53.8941o N, -122.8122o W) was
fully exposed and therefore had elevated sunlight hours and absence of shade during sunrise,
noon and sunset. The average photosynthetic photon flux density (PPFD) recorded for Site 1
during the daytime was 1009.34 µmol s-1 m-2, and during morning and evening hours was
314.11 µmol s-1 m-2 and 291.42 µmol s-1 m-2 respectively. The average PPFD recorded for
Site 2 during daytime was 1221.54 µmol s-1 m-2, and for morning hours was 620.21 µmol s1

m-2, while for evening hours was 517.84 µmol s-1 m-2. Both the sites had identical turfgrass

varieties growing from the mix of cool season turfgrass “City Lawn Mix” from Spruce
Capital, Prince George. The turfgrass mix included 50% creeping red fescue, 25% perennial
ryegrass and 25% Kentucky bluegrass.
53

Chapter 3-Field trials
Soil samples were collected from the field sites before and after the application of treatments,
from a depth of 15 cm, utilizing a soil auger (bit 7 cm). The samples were dried at 55°C for
72 hours before sending to the Northern Analytical Laboratory Services (NALS) at UNBC
for analysis of soil parameters, including soil composition. The pH and electrical
conductivity were measured using the sifted (<2mm) and air-dried samples on a 5:1 (Liquid:
Solid) extract. Organic matter and moisture contents were determined gravimetrically from
the bulk material. Total nitrogen was assessed on a Costech 4010 elemental combustion
system. Metals (Fe, K, and P) determination was performed using strong mineral acid block
digestion followed by ICP-OES (Agilent Technologies 5100 ICPOES). Particle size analysis
was performed on a Malvern Mastersizer 3000 using the Hydro LV module. All the tests
were conducted at NALS at UNBC.

3.2.2. Experimental Setup
A designated research area measuring a total of 49 m2 was meticulously demarcated using
bamboo sticks and identified with flagging tape to distinguish it from the surrounding area.
Each treatment plot covering an area of 1 × 1 m2, was precisely marked with distinctive
coloured flag stakes. Yellow flags delineated zones subjected to nutrient treatment
application, red flags indicated areas treated with Killex, and pink flags identified control
areas (Fig. 3.1).

54

(A)

Chapter 3-Field trials
(B)

Figure 3.1. Experimental plots at (A) field Site 1 with partial shade, and (B) field Site 2 with
no shade conditions.

For each treatment, 3 replicates were distributed randomly in a 3 × 3 plot distribution on the
designated sites, resulting in a total of nine plots featuring various treatments. On a relatively
flat site, a one-meter buffer space was considered adequate and was intentionally left
between adjacent treatment plots and along the plot boundaries, ensuring a standardized
layout (Fig. 3.2). Consequently, each side of the site measured 7 meters, and with a total of
nine plots, the occupied area summed to 49 m2. The sites were deliberately selected to
contain high levels of weed infestation to check the efficacy of the treatments in comparison
with the control (no treatment application) plots. The sites had different types of broadleaf
weeds, such as broad plantain (Plantago major), white clovers (Trifolium repens), yellow
hawkweed (Hieracium spp.), orange hawkweed (Pilosella aurantiaca), and dandelions
(Taraxacum officinale). The target species, dandelions and white clovers, were the most
frequent and dominant weed species present on both sites.

55

Chapter 3-Field trials

BUFFER
ZONE

B

BUFFER
ZONE

B

BUFFER
ZONE

B
Control

F

U

B
KUlex

F

BUFFER
ZONE

BUFFER

ZONE

ZONE

E

E

E

E

R

R

R

R

Z

ZONE

Z

o

o

N

N

BUFFER
ZONE

Z

BUFFER

o

Z

o
Control

E

N

E

BUFFER

BUFFER

ZONE

ZONE

BUFFER
ZONE

Figure 3.2. Layout of different treatment applications on field Sites 1 and 2

3.2.3. Treatment applications
The field sites were regularly irrigated twice a week on Tuesdays and Thursdays, for 45-60
minutes each, contingent upon prevailing weather conditions. This irrigation strategy
employed sprinklers to mitigate heat stress and maintain the health and quality of turfgrass.
To facilitate the nutrient treatments, a homogenous mixture was prepared for spraying on the
field sites. This involved dissolving 15 g of iron sulphate and 80 g of ammonium sulphate in
7 L of water in separate containers for each treatment application. Additionally, 49 ml of
ORTHO Killex® concentrate (containing 2,4-D, Mecoprop-P, and Dicamba as active
ingredients) was added to 7 L of water in a separate backpack sprayer.

56

Chapter 3-Field trials
The different nutrient treatments were applied using CHAPIN® 27020: 2-gallon SureSpray
Select Poly Tank Sprayer purchased from Canadian Tire, Prince George. In the case of
Killex, a 4 gallon, AP-25 SUN (Piston pump) Backpack Sprayer, SUN SPRAYERS® was
employed for application.
Upon preparation of the solutions, the treatment application involved the spraying of 1 litre
of solution per plot to deliver the equivalents of 300 kg ha-1 of nitrogen and 2.2 kg ha-1 of
iron sulphate on the nutrient treatment plots. The treatments were applied in three split doses
each at an interval of 4 weeks to prevent any damage to turfgrass due to excessive nutrient
application. The treatments were applied during cool evening hours to minimize the risk of
potential burning effects on the turfgrass by the administered nutrients and chemicals. The
nozzle of the sprayer was kept close to the ground and a plastic sheet was used as a shield
while applying treatments to minimize the spray drift from one plot to another.
Preceding the treatment application, the field was deliberately left without irrigation to
ensure optimal nutrient absorption by the plants. Subsequent irrigation was carried out two
days after the treatment application to avoid washing off the nutrients, thereby maximizing
the efficacy of the treatments and their impact on the broadleaf weeds and turfgrass. Run off
and potential contamination of nearby plots and the surrounding land was not anticipated as
the study sites were located on a relatively flat terrain. The turfgrass was also trimmed down
to a height of 5 cm after every 2 weeks using shears to minimize disturbance to the marked
broadleaf weed species.

57

Chapter 3-Field trials

3.2.4. Data Collection
Initial measurements from both sites were recorded before the beginning of the treatment
applications. In order to capture a comprehensive visual record, photographs of the treatment
plots were taken using a camera that was strategically positioned on a custom cardboard box
of length 61 cm, breadth 45.7 cm and height 45.7 cm. The cardboard box was cut from one
side to maximize the surface exposure, placing two LED bulbs inside the roof of the
cardboard box to ensure uniform lighting, and incorporating a precisely cut square-shaped
hole on the roof of the box to accommodate the camera. The LED bulbs were switched on
and the box was centrally positioned within each plot, ensuring even pressure to prevent
external light interference, and photographs were clicked. The photographs were taken both
before and after the completion of the experiment to aid estimation of weed coverage and
turfgrass quality.
Other initial readings included the quality of turfgrass, quality of dandelion plants, length of
dandelion leaf, number of leaves per dandelion plant, photosynthetic capacity of turfgrass,
photosynthetic capacity of dandelion, photosynthetic capacity of white clovers, and total
weed coverage of the plots. Assessment of weed coverage were limited to only dandelion and
white clover as the target species. Moreover, these two weeds were the dominant broadleaf
weed species in each plot area. Thus, the weed quality indicators do not account for the
possible interactions, if any, among all the different kinds of weeds. To capture detailed
information about dandelion and white clover plants, three robust and healthy plants were
carefully selected from the field sites, individually marked, and assigned unique identifiers
using plant tags for data collection. Similarly, for assessing turfgrass observations, three

58

Chapter 3-Field trials
random spots within each plot were chosen prior to the experiment, labelled with vertical
plant markers, and carefully excavated for a thorough examination.
Quality indicators of dandelion and white clover plants were based on the overall condition
of the plants, which included colour, growth and vigour, and any visible signs of damage.
This rating was scored on a scale of 0 - 9, where 0 = completely dead plant, 1-3 = poor
quality of plant with no apparent growth and black brown discolouration, 4 = minimal
growth of the plant with brown or yellow patches on the leaves, 5 = moderate growth of
plants with light green coloured leaves and slight discoloration, 6-8 = uniform growth of
plants with medium coloured green leaves, and 9 = uniform and healthy growing plants with
dark green coloured leaves. Other metrices, such as the number of leaves and length of leaf
of dandelion plants were recorded and measured with a tape measure by stretching the leaves
flat and horizontal to the surface of the scale.
Quality ratings of turfgrass was based on visual assessment (such as color of turfgrass,
presence of brown patches, uneven growth of turfgrass, and appearance of any
discolouration) and rated according to the National Turfgrass Evaluation Program (NTEP) on
a scale of 0 - 9, where 0 = completely dead grass, 1 - 3: very poor or completely brown=
turfgrass is in poor condition, with severe imperfections, low density, and completely brown;
4: Poor = turfgrass has significant imperfections, reduced density, and may show signs of
stress, or disease, colour and texture are noticeably compromised; 5: Fair = turfgrass is
somewhat uniform but may have noticeable imperfections, and may show signs of stress or
disease, and the colour and texture might be less desirable light green colour turfgrass with
some yellow patches; 6 -8: Good = turfgrass is generally uniform with good density, may
have minor imperfections but is visually appealing and the colour and texture are
59

Chapter 3-Field trials
satisfactory; 9: Excellent = turfgrass is uniform, dense, free of diseases and exhibits
exceptional colour, texture and overall aesthetic appeal.
The FM 2 Pulse-Modulated Chlorophyll Fluorescence Monitoring System (OPTISCIENCES®) was used to capture the photosynthetic capacity (PSII) of already marked spots
of turfgrass, dandelions and white clovers on a weekly basis. To assess weed coverage, a
visual examination of the plots was conducted, involving the partitioning of each plot into 4
quadrants and subsequently estimating the overall percentage of the area covered by
broadleaf weeds.
Upon the complete and final data collection in the twelfth week, soil samples from each site
were sent to NALS, for analysis of several properties, including pH, electrical conductivity
(EC), organic matter, and macro- and micronutrients.

3.2.5. Statistical analysis
Data for weed and turfgrass growth and quality indicators were analyzed using linear mixedeffects models that included treatments, time since application (i.e. weeks), and their
interaction as fixed effects and the plot number as the random effect. Dependent variables
included the quality rating of dandelion and turfgrass, leaf ratings of dandelion plants, the
photosynthetic capacity of white clover, dandelion, and turfgrass. The data were checked to
ensure that all the parametric assumptions were met, and no data transformation was
necessary.
When the main effects or their interaction was significant (at α= 0.05), post hoc tests were
used to evaluate significant differences between the treatment levels or time since
application. All statistical analyses were performed using the R statistical program (R Core

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Chapter 3-Field trials
Team 2021). Specifically, linear mixed-effect models were performed using the lme function
in the NLME package (Pinheiro & Bates 2000) and by specifying the first-order
autocorrelation corAR1 function as the correlation structure to account for the repeated
measurements over time. Post hoc tests were performed using the emmeans function in the
LSMEANS package (Lenth et al. 2018) and by specifying the “Bonferroni” adjustment.
Changes in soil physical and chemical properties before and after the treatments were
examined using t-test (α = 0.05).

3.3.

Results

There were significant effects of the treatments, time, and their interaction on almost all the
parameters recorded for the growth and quality indicators of broadleaf weeds and turfgrass
tested under natural environmental conditions at both sites, with exception of the
photosynthetic capacity of turfgrass (Pc) which was significantly influenced by the
treatments and time but not their interaction (Table 3.1).

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Chapter 3-Field trials
Table 3. 1. Effects of the experimental treatments, time since application, and their
interaction on the properties of white clover and dandelion weeds, and turfgrass growing
under natural environmental conditions at both the sites. Values are p-values from a linear
mixed effect model analysis. Abbreviation Pc – photosynthetic capacity.
Dependent variables

Site 1
Treatment

Time

Pc white clover

0.007

<0.001

Pc dandelion

0.048

Quality of dandelion
No. of dandelion leaves

Site 2
Treatment ×

Treatment

Treatment

Time

<0.001

0.009

<0.001

<0.001

0.036

0.050

0.047

<0.001

<0.001

0.006

<0.001

0.006

0.001

<0.001

<0.001

<0.001

<0.001

<0.001

<0.001

<0.001

<0.001

0.102

<0.001

0.063

0.010

0.003

<0.001

Quality of turfgrass

<0.001

<0.001

<0.001

0.002

0.059

0.001

Pc Turfgrass

<0.001

<0.001

0.129

0.001

<0.001

0.306

Weed coverage

0.007

0.002

<0.001

<0.001

<0.001

0.033

Length of the longest leaf
of dandelion

Time

× Time

3.3.1. Broadleaf weed response to treatments
Effect of treatments on photosynthetic capacity of white clover plants
At Site 1, white clover plants in plots treated with and without (NH4)2SO4 × FeSO4 and
Killex initially exhibited comparable photosynthetic capacity. However, the Pc of white
clover was consistently higher in the control plots whereas it decreased significantly in plots
treated with Killex notably from week 4 to week 10, until eventually resulting in the absence
of any white clover plants in the plots treated with Killex by the conclusion of the experiment
in week 12. Similarly, the Pc of white clover plants in plots treated with (NH4)2SO4 × FeSO4
decreased significantly compared to the control plots over time (Fig. 3.3A).
At Site 2, the photosynthetic capacity of white clover initially did not differ among the
treatments until after week 4 where it was significantly lower in plots treated with Killex than
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Chapter 3-Field trials
in the (NH4)2SO4 × FeSO4 and control plots. However, the photosynthetic capacity of white
clover plants did not vary significantly between the (NH4)2SO4 × FeSO4 and control plots
(Fig. 3.3B).

(NH4)2SO4 × FeSO4

Control

Killex

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Chapter 3-Field trials
Figure 3.3. Grouped bar graph (sample size, n = 3) representing the change in photosynthetic
capacity (Pc) of white clover plants subjected to different treatments over the period of 12
weeks growing under natural field conditions (A) at Site 1 and (B) at Site 2. The legends
marked in different colours represent the different treatment applications. Pre-treatment
(measurements taken before treatment application) results (mean) are marked with solid red
line running parallel to x-axis with standard deviations marked with dotted red lines
respectively. Second treatment application was made after week 4, and third application
treatment was made after week 8. See methods for more details. The x-axis represents the
weeks (time), and y-axis represents the photosynthetic capacity of white clover. The display
letters marked on the top of the bars represent the significant differences between the
treatments as revealed by post hoc tests using emmeans. Same letters represent no significant
differences, while different letters represent significant differences in the measurements (α =
0.05).

Effect of treatments on photosynthetic capacity of dandelion plants
At Site 1, the photosynthetic capacity of dandelion plants did not vary significantly among
the control, (NH4)2SO4 × FeSO4, and Killex treatments until week 12 where it was
significantly lower in plots treated with (NH4)2SO4 × FeSO4 and Killex as compared to the
control treatments. But it still it did not differ significantly between plots treated with
(NH4)2SO4 × FeSO4 and Killex (Fig. 3.4A)
Similarly, at Site 2, the photosynthetic capacity of dandelion plants did not differ among the
treatments until after the third treatment in week 10 where it was significantly lower in plots
treated with Killex than in the control plots. (Fig. 3.4B).

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Chapter 3-Field trials
(NH4)2SO4 × FeSO4

Control

Killex

Figure 3.4. Grouped bar graph (sample size, n = 3) representing the change in photosynthetic
capacity (Pc) of dandelion plants subjected to different treatments over the period of 12
weeks growing under natural field conditions (A) at Site 1 and (B) at Site 2. The legends
marked in different colours represent the different treatment applications. Pre-treatment
(measurements taken before treatment application) results (mean) are marked with solid red
65

Chapter 3-Field trials
line running parallel to x-axis with standard deviations marked with dotted red lines
respectively. Second treatment application was made after week 4, and third application
treatment was made after week 8. See methods for more details. The x-axis represents the
weeks (time), and y-axis represents the photosynthetic capacity of dandelion. The display
letters marked on the top of the bars represent the significant differences between the
treatments as revealed by post hoc tests using emmeans. Same letters represent no significant
differences, while different letters represent significant differences in the measurements (α =
0.05).

Effect of treatments on quality of dandelion plants
At Site 1, the visual quality rating of dandelion plants did not differ among the treatments
until after the second treatment application in week 8where it was consistently lower in plots
treated with Killex and (NH4)2SO4 × FeSO4 up till week 12 than in the control plots, but it
did not differ between Killex and (NH4)2SO4 × FeSO4 treatment plots (Fig. 3.5A).
At Site 2, visual quality of dandelion plants initially did not differ among treatments;
however, after the second application in week 4 up to week 12, it was consistently lower in
plots treated with Killex than in the (NH4)2SO4 × FeSO4 and control plots. But visual quality
of dandelions after the second and third treatment application did not differ between the
(NH4)2SO4 × FeSO4 and the control plots (Fig. 3.5B).

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Chapter 3-Field trials
(NH4)2SO4 × FeSO4

Control

Killex

Figure 3.5. Grouped bar graph (sample size, n = 3) representing the change in quality rating
of dandelion plants on a scale of 0-9 subjected to different treatments over the period of 12
weeks growing under natural field conditions (A) at Site 1 and (B) at Site 2. The legends
marked in different colours represent the different treatment applications. Pre-treatment
(measurements taken before treatment application) results (mean) are marked with solid red
line running parallel to x-axis with standard deviations marked with dotted red lines
67

Chapter 3-Field trials
respectively. Second treatment application was made after week 4, and third application
treatment was made after week 8. See methods for more details. The x-axis represents the
weeks (time), and y-axis represents the quality of dandelion plants. The display letters
marked on the top of the bars represent the significant differences between the treatments as
revealed by post hoc tests using emmeans. Same letters represent no significant differences,
while different letters represent significant differences in the measurements (α = 0.05).

Effect of treatments on number of leaves of dandelion plants
At Site 1, the number of leaves per dandelion plant was similar among the treatments (week
4) or lower in plots treated with Killex than the control plots. However, the number of leaves
of per dandelion plant by weeks 10 – 12 was significantly lower in the plots treated with
Killex and (NH4)2SO4 × FeSO4 as compared to the control, whereas it did not differ between
Killex and (NH4)2SO4 × FeSO4-treated plots (Fig. 3.6A).
At Site 2, the average number of leaves per dandelion plant did not differ among the
treatments by week 2; but thereafter it was consistently lower in plots treated with Killex
than in either (NH4)2SO4 × FeSO4 or the control pants, whereas it did not differ between
(NH4)2SO4 × FeSO4 and the control treatments (Fig. 3.6B).

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Chapter 3-Field trials
(NH4)2SO4 × FeSO4

Control

Killex

Figure 3.6. Grouped bar graph (sample size, n = 3) representing the change in number of
leaves per dandelion plant subjected to different treatments over the period of 12 weeks
growing under natural field conditions (A) at Site 1 and (B) at Site 2. The legends marked in
different colours represent the different treatment applications. Pre-treatment (measurements
taken before treatment application) results (mean) are marked with solid red line running
parallel to x-axis with standard deviations marked with dotted red lines respectively. Second
treatment application was made after week 4, and third application treatment was made after
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Chapter 3-Field trials
week 8. See methods for more details. The x-axis represents the weeks (time), and y-axis
represents the number of leaves per dandelion plant. The display letters marked on the top of
the bars represent the significant differences between the treatments as revealed by post hoc
tests using emmeans. Same letters represent no significant differences, while different letters
represent significant differences in the measurements (α = 0.05).

Effect of treatments on length of the longest leaf of dandelion plants
At Site 1, the length of the longest leaf of dandelion plants did not vary significantly among
the treatments, while the treatment × time interaction effect was only marginal (Table 3.1).
At Site 2, however, the longest dandelion leaf length did not differ among the treatments up
till the third application in week 8 and thereafter where it was considerably lower in plots
treated with Killex than in the (NH4)2SO4 × FeSO4 and control plots. But the longest
dandelion leaf length did not differ between (NH4)2SO4 × FeSO4 and the control plots in
weeks 10 – 12 (Fig. 3.7).
(NH4)2SO4 × FeSO4

Control

Killex

70

Chapter 3-Field trials
Figure 3.7. Grouped bar graph (sample size, n = 3) representing the change in length of leaf
of dandelion plant subjected to different treatments over the period of 12 weeks growing
under natural field conditions at Site 2. The legends marked in different colours represent the
different treatment applications. The x-axis represents the weeks (time), and y-axis represents
the length of the longest leaf of dandelion (cm). Pre-treatment (measurements taken before
treatment application) results (mean) are marked with solid red line running parallel to xaxis with standard deviations marked with dotted red lines respectively. Second treatment
application was made after week 4, and third application treatment was made after week 8.
See methods for more details. The display letters marked on the top of the bars represent the
significant differences between the treatments as revealed by post hoc tests using emmeans.
Same letters represent no significant differences, while different letters represent significant
differences in the measurements (α = 0.05).

3.3.2. Turfgrass response to treatments
Effect of treatments on quality of Turfgrass
At Site 1, the quality of turfgrass was consistently highest in plots treated with (NH4)2SO4 ×
FeSO4 throughout the duration of the experiment whereas it lower in plots treated with Killex
than even in the control treatments (Fig. 3.8A).
Also in Site 2, the quality of turfgrass was highest in plots treated with (NH4)2SO4 × FeSO4
at all time periods. However, the quality of turfgrass did not differ between the control versus
Killex treatments (Fig. 3.8B).

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Chapter 3-Field trials
(NH4)2SO4 × FeSO4

Control

Killex

Figure 3.8. Grouped bar graph (sample size, n = 3) representing the change in quality rating
of turfgrass on a scale of 0-9 subjected to different treatments over the period of 12 weeks
growing under natural field conditions (A) at Site 1 and (B) at Site 2. The legends marked in
different colours represent the different treatment applications. Pre-treatment (measurements
taken before treatment application) results are marked with solid red line running parallel to
x-axis with standard deviations marked with dotted red lines respectively. Second treatment
application was made after week 4, and third application treatment was made after week 8.
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Chapter 3-Field trials
See methods for more details. The x-axis represents the weeks (time), and y-axis represents
the quality of turfgrass. The display letters marked on the top of the bars represent the
significant differences between the treatments as revealed by post hoc tests using emmeans.
Same letters represent no significant differences, while different letters represent significant
differences in the measurements (α = 0.05).

Effect of treatments on Photosynthetic capacity of Turfgrass
The photosynthetic capacity of turfgrass, at both sites, varied consistently among the
treatments, but not with the treatment x time interaction (Table 3.1). At both the sites, the
photosynthetic capacity of turfgrass was significantly higher in plots treated with (NH4)2SO4
× FeSO4 that the other treatments whereas it did not differ between the Killex and control
treatments (Fig. 3.9A and B).

(NH4)2SO4 × FeSO4

Control

Killex

Figure 3.9. Bar graph (sample size, n = 3) comparing the photosynthetic capacity (Pc) of
turfgrass subjected to different treatments growing under natural field conditions (A) at Site 1
and (B) at Site 2. The legends marked in different colours represent the different treatment
applications. The x-axis represents treatments and y-axis represents the photosynthetic
capacity of turfgrass. The display letters marked on the top of the bars represent the
significant differences between the treatments as revealed by post hoc tests using emmeans.
73

Chapter 3-Field trials
Same letters represent no significant differences, while different letters represent significant
differences in the measurements (α = 0.05).

Effect of treatments on weed coverage per plot
At Site 1, cover of the target weeds were initially similar among the treatments up till week
4. However, weed cover thereafter from weeks 6 -12 was significantly lower in both
(NH4)2SO4 × FeSO4and Killex treatment plots than in the control, whereas it did not differ
between (NH4)2SO4 × FeSO4 and Killex treatment plots (Fig 3.10A).
At Site 2, weed cover did not differ among the treatments until after the third treatment
application from week 8 – 10 where it was significantly lower in the plots treated with Killex
than in the other treatments. However, by week 12, weed cover did not differ between Killex
and (NH4)2SO4 × FeSO4 treatment plots but cover in both of these treatment were
significantly lower than that of the control (Fig. 3.10B).

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Chapter 3-Field trials
(NH4)2SO4 × FeSO4

Control

Killex

Figure 3.10. Grouped bar graph (sample size, n = 3) representing the change in weed
coverage of each plot subjected to different treatments over the period of 12 weeks growing
under natural field conditions (A) at Site 1 and (B) at Site 2. The legends marked in different
colours represent the different treatment applications. Pre-treatment (measurements taken
before treatment application) results are marked with solid red line running parallel to x-axis
with standard deviations marked with dotted red lines respectively. Second treatment
75

Chapter 3-Field trials
application was made after week 4, and third application treatment was made after week 8.
See methods for more details. The x-axis represents the weeks (time), and y-axis represents
the plot weed cover. The display letters marked on the top of the bars represent the
significant differences between the treatments as revealed by post hoc tests using emmeans.
Same letters represent no significant differences, while different letters represent significant
differences in the measurements (α = 0.05).

3.3.3. Soil sample analysis
Soil physical and chemical properties
The treatments including the control resulted in a range of changes in the physical and
chemical properties of the soil (Table 3.2; Table 3.3).
(NH4)2SO4 × FeSO4 At Site 1 there were no significant changes in soil pH and soil moisture
before and after the treatment applications. However, electrical conductivity of the soil and
organic matter were lower after than before the treatment applications (Table 3.2).
At Site 2, there were no changes in soil pH after the experiment in both (NH4)2SO4 × FeSO4
and the control plots, but soil pH increased in the plots treated with Killex. Additionally,
electrical conductivity increased with (NH4)2SO4 × FeSO4 after the experiment whereas that
of the Killex and control plots were reduced after the experiment. Similarly, organic matter in
both Killex and the control plots was reduced after the experiment. There were no significant
changes in soil moisture before or after the experiment (Table 3.2).
Soil nutrient composition
There were no major changes in soil nutrients after the experiment (Table 3.3).
At Site 1, soil nitrogen did not vary significantly following (NH4)2SO4 × FeSO4 application
or in the control plots, but it was lower in the plots treated with Killex after the experiment.

76

Chapter 3-Field trials
There was no difference in the other nutrients including phosphorus, potassium, and iron
(Table 3.3).
At site 2, soil nitrogen was lower in Killex and in the control plots whereas there was no
difference in the plots treated with (NH4)2SO4 × FeSO4. Additionally, potassium was
marginally lower in the Killex and the control plots after the experiment (Table 3.3).

77

7.10a
7.00a

6.75a
6.75a

Killex

Control

7.46b
7.16a

6.79a
6.79a

Killex

Control

196b

196b

196a

257b

257b

257b

EC
(µS/cm)
Before

139a

166a

397b

130a

208a

133a

EC
(µS/cm)
After

7.90b

7.90b

7.90a

8.20b

8.20b

8.20b

OM
(%)
Before

5.63a

6.07a

7.00a

5.73a

4.60a

5.70a

OM
(%)
After

1.00a

1.00a

1.00a

1.00a

1.00a

1.00a

SM
(%)
Before

0.83a

0.93a

0.97a

0.83a

0.70a

0.76a

SM
(%)
After

Notes: superscript letter denote statistical significance based on a t-test. For each parameter, values with same superscript letter
indicate no significant differences before and after the experiment while values with different letters indicate statistically significant
differences.

7.02a

6.79a

(NH4)2SO4 × FeSO4

Site 2

6.80a

After

Before
6.75a

pH

pH

(NH4)2SO4 × FeSO4

Site 1

Treatments

Table 3.2. Before and after comparison of the physical (organic matter – OM, soil moisture – SM) and chemical (soil pH, electrical
conductivity – EC) properties of the soil samples from Site 1 and Site 2 under the different treatment applications.

78

Chapter 3-Field trials

0.11a
0.18a

0.25b
0.25a

Killex

Control

0.15a
0.15a

0.28b
0.28b

Killex

Control

929a

929a

929a

1037a

1037a

1037a

883a

918a

911a

1136a

977a

959a

1717a

1717b

1717a

1227a

1227a

1227a

Phosphorous Phosphorous Potassium
(mg/kg)
(mg/kg)
(mg/kg)
Before
After
Before

1591b

1561a

1739a

1214a

1192a

1144a

Potassium
(mg/kg)
After

24717a

24717a

24717a

23042a

23042a

23042a

Iron
(mg/kg)
Before

79

26044a

26729a

26174a

23275a

23552a

22570a

Iron
(mg/kg)
After

Notes: superscript letter denote statistical significance based on a t-test. For each parameter, values with same superscript letter
indicate no significant differences before and after the experiment while values with different letters indicate statistically significant
differences.

0.21a

0.28a

(NH4)2SO4 × FeSO4

Site 2

0.17a

Nitrogen
(%)
After

0.25a

Nitrogen
(%)
Before

(NH4)2SO4 × FeSO4

Site 1

Treatments

Table 3.3. Before and after comparison of the nutrient (nitrogen, phosphorous, potassium, and iron) contents of the soil samples from
Site and Site 2 under different treatment applications.

Chapter 3-Field trials

Chapter 3-Field trials

3.3.4. Pre- and post-treatment conditions of weed and turfgrass
Before and after visual assessments of the treatments indicate reduced dandelion and white
clover weed coverage and superior turf quality in plots treated with (NH4)2SO4 × FeSO4 as
compared with Killex and the control (no application) at both sites (Figs. 3.11 – 3.16).

Figure 3.11. Visual comparison of weed coverage in three experimental plots before (A1,
C1, and E1) and after 12 weeks of (NH4)2SO4 × FeSO4 application (B1, D1, and F1) at Site 1
80

Chapter 3-Field trials

Figure 3.12. Visual comparison of weed coverage in three experimental plots before (G1, I1,
and K1) and after 12 weeks in control (no application) plots (H1, J1, and L1) at Site 1

81

Chapter 3-Field trials

Figure 3.13. Visual comparison of weed coverage in three experimental plots before (M1,
O1, and Q1) and after 12 weeks of Killex application (N1, P1, and R1) at Site 1

82

Chapter 3-Field trials

Figure 3.14. Visual comparison of weed coverage in three experimental plots before (A2,
C2, and E2) and after 12 weeks of (NH4)2SO4 × FeSO4 application (B2, D2, and F2) at Site 2

83

Chapter 3-Field trials

Figure 3.15. Visual comparison of weed coverage c in three experimental plots before (G2,
I2, and K2) and after 12 weeks in control (no application) plots (H2, J2, and L2) at Site 2

84

Chapter 3-Field trials

Figure 3.16. Visual comparison of weed coverage in three experimental plots before (M2,
O2, and Q2) and after 12 weeks of Killex application (N2, P2, and R2) at Site 2

85

Chapter 3-Field trials

3.4.

Discussion

Influence of nitrogen and iron compounds on broadleaf weeds
As expected, following the promising results from the greenhouse experiment, the treatment
combination of ammonium sulphate × iron sulphate performed similarly, and even superior
to the conventional herbicide Killex, with differences generally varying with time since
application. The observed effectiveness in comparison to Killex, was evidenced by a
reduction in the quality of growth and morphological characteristics of dandelion and white
clover weeds. These results are consistent with previous studies that also report the
effectiveness of cultural weed control methods such as fertilization with nitrogen and iron
compounds (Busey 2003; Voigt et al. 2001; Smith-Fiola & Gill 2014). For example, Voigt et
al. (2001) found that different rates of nitrogen application significantly reduced the
broadleaf weed cover as compared to untreated plots, however only higher rates of nitrogen
application (198-293 kg N ha-1 yr-1) provided acceptable results for turfgrass quality. While
iron sulphate was used as a selective herbicide against broadleaf weeds in turfgrass before
2,4-D was introduced (Timmons 1970), chelated iron is also popularised for its effective
control against broadleaf weeds. Chinery et al. (2012) found that two-three applications of
chelated iron formulation can control major broadleaf weeds such as white clover, broadleaf
plantains, and henbit. While most studies mostly focused on the individual effects of either
nitrogen (Voigt et al. 2001: Miltner et al. 2005; Calhoun et al. 2005) or iron (Chinery et al.
2012; Smith-Fiola & Gill 2014), the promising results of this experiment suggest that the
combination of nitrogen and iron can be most effective in broadleaf weed control.
Additionally, previous studies that have investigated the effects of nitrogen fertilization have
mostly used lower (< 300 kg N ha-1 yr-1) amounts of nitrogen to obtain acceptable turfgrass
86

Chapter 3-Field trials
quality for different species of turfgrass (Teuton et al. 2007; Liu et al. 2008). This experiment
used a relatively higher amount, 300 kg N ha-1 yr-1, which is suggested to be optimal for
broadleaf weed control (Busey 2003), and achieved considerably satisfactory results. The
results of this study thus suggest that higher amount of nitrogen fertilization may be
beneficial in controlling broadleaf weeds, but further testing is needed.
Influence of nitrogen and iron compounds on turfgrass
Addition of nitrogen to turf can make up for any deficiencies in the soil and spur growth of
turfgrass, thus maintaining dense and persistent turfgrass stand capable of withstanding
numerous pests and environmental stresses (Frank & Guertal 2013). However, excessively
high amounts of nitrogen can be toxic to turfgrass or possibly cause injury and burn turfgrass
(Henry et al. 2002) . Furthermore, iron (chelated or sulphate) is known to cause enhanced
quality of turfgrass (Yust et al. 1983). In this study, the combination of nitrogen and iron
resulted in enhanced quality ratings of turfgrass. This suggest that the addition of iron to
nitrogen-based compound fertilizer may confer added benefits of complementary interactions
with nitrogen that is needed in higher amount by turfgrass given their high turnover, as well
as enhance their visual quality and vigour. Further testing is needed to understand the
chemical interactions between these two important nutrients to turfgrass.
Additionally, the photosynthetic capacity of turfgrass, in other words, a measure of the ability
to which the leaves are able to fix carbon during photosynthesis, also improved with the
application of ammonium sulphate × iron sulphate. This suggested an improved ability of
turfgrass to withstand stressful conditions. Thus, unlike conventional herbicide treatments
such as 2,4-D, cultural methods such as nutrient management may provide vitality to
functioning and performance of turfgrass in addition to weed control.
87

Chapter 3-Field trials
Management of turfgrass can be a costly investment (Haydu et al. 2006). The results of this
study suggest that nutrient management using ammonium sulphate x iron sulphate may offer
cheaper, environmentally friendly alternatives to weed management in turf, with the added
benefits of improving growth and enhancing the visual quality of turfgrass.
Influence of nitrogen and iron compounds on soil properties
The ammonium sulphate × iron sulphate treatment application had very little effects on the
soil physical and chemical properties. For example, soil pH remained relatively unchanged
whereas Killex increased soil pH. Thus, the combination of ammonium sulphate × iron
sulphate as nutrient fertilizer may not be detriment or adversely alter the soil chemistry
unlike chemical herbicides. However, it is essential to conduct long-term application studies
to help assess any potential adverse effects of this combination on soil chemistry over time.
Additionally, the ammonium sulphate × iron sulphate combination, although containing
nitrogen, did not significantly alter the nitrogen contents of the soil. In contrast, Killex
reduced nitrogen contents of the soil, likely due to the fact that the plots that received the
herbicide treatment received no nutrient supplements at all and therefore used up all the
nitrogen quickly. The results thus suggest that selective chemical herbicides such as Killex
may still require other nutrients, particularly nitrogen, in order to ensure the sustenance and
persistence of turfgrass.
Influence of site factors
The results were generally not consistent between the two study sites, which had little
variation in site conditions except exposure to shade, and by extension, the photoperiod.
Hatfield’s (2017) study indicates that cool-season turfgrass exhibits distinct responses to
different environmental conditions. Specifically, these turfgrasses tend to thrive under low
88

Chapter 3-Field trials
temperatures, which are often associated with shorter photoperiods. Moreover, in areas with
summer temperatures >26°C, cool season turfgrasses are often stressed, and may result in
reduced growth and poor appearance (Henry et al. 2002). Understanding this correlation is
crucial, as potential physiological stresses on turfgrass due to elevated temperature or
drought conditions create an environment conducive to increased weed pressures. McElroy
and Bhowmik (2013) conducted a comprehensive review on weed management in turfgrass,
emphasizing that weed pressure is not limited to suboptimal growing conditions but are more
likely to manifest when turfgrasses are under stress. It is possible that other site factors not
considered in this study, such as slope and aspect, soil drainage, among others may play a
role in the effectiveness of herbicides or cultural control methods (Freitas et al. 2008; Nolan
et al. 1995). Also, it is not clear the extent to which other established weed species on the
study sites, beyond the target dandelion and white clovers, interacted or interfered with the
treatment applications and the observed results. Other considerations, such as spray drift,
leaching, or nutrient wash have been found to be influential in nutrient management
applications (Kleijn & Snoeijing 1997; Frank & Guertal 2013). Further testing is thus needed
to establish the potential influence of site conditions on the performance of nitrogen and iron
compound fertilizers.

89

Chapter 4-Conclusion and recommendations

4.

Conclusion and recommendations

To maintain a healthy, good-looking weed-free turf, it is usually necessary to apply
herbicides for weed control and fertilizer to boost turfgrass growth. The results of this study
suggest that it may be possible to substitute herbicide with a combination of fertilizer to
achieve effective weed control while maintaining a good quality turf. Among the various
combinations of ammonium and iron compounds tested, the application of ammonium
sulphate × iron sulphate demonstrated promising results of weed control comparable to
conventional herbicides while concurrently enhancing turfgrass health and quality. While the
application of nitrogen and iron compounds is commonly recognized for enhancing the
quality and color of turfgrass fields, its impact on specific weeds has been relatively
understudied. This research sheds light on the efficacy of ammonium sulphate × iron sulphate
in curbing common broadleaf weeds, such as dandelion and white clovers.
The application of ammonium and iron compounds were first tested under controlled
environmental conditions during the initial establishment phases of the broadleaf weeds in
turfgrass. The results suggest that the combination of ammonium sulphate × iron sulphate
may be an effective preventive control measure during the initial stages of laying new
turfgrass sod. The application of ammonium sulphate × iron sulphate could potentially
thwart the establishment of broadleaf weeds by promoting the development of a healthy and
dense turfgrass sod. Future research endeavours should focus on determining the optimal rate
of application for ammonium sulphate × iron sulphate over an extended period of time to
achieve results comparable to conventional herbicide method of weed control. Exploring
different ratios and concentrations of ammonium sulphate and iron sulphate on both newly
90

Chapter 4-Conclusion and recommendations
laid and already established turfgrass fields would contribute valuable insights. Moreover,
extensive trials should encompass a diverse range of broadleaf weeds found in turfgrass
fields, analyzing the variable impact of this combination across different stages of weed
growth to identify the most effective application timing. Studying the impact on weed
species, both above and below ground, will be crucial for gaining a comprehensive
understanding of how these plants compete in both realms over an extended period of time.
Given the variable results observed at the different sites under natural environmental
conditions, future studies should investigate the effects of ammonium sulphate × iron
sulphate on turfgrass fields experiencing diverse micro-climatic conditions, such as
temperature, rainfall, and humidity. Additionally, exploring the influence of slope and other
topographic features and soil properties is essential. Other considerations such as spray drift,
chemical migration, runoff, and nutrient leaching in these scenarios will enhance our
understanding of the broader environmental implications of utilizing ammonium sulphate ×
iron sulphateand the need for a judicious approach in application of these compounds in
turfgrass management practices.
Future experiments should also include a negative control with the rate of nitrogen
application recommended for normal maintenance of turfgrass to serve as a baseline for
comparison against higher nitrogen application rates. Additionally, testing higher rates of
both chelated iron and iron sulphate can help determine if improved weed control can be
achieved without compromising turfgrass quality. The effects of ammonium sulphate, and a
combination of ammonium sulphate × iron sulphate should be tested on broadleaf weeds
grown individually, without competition from turfgrass. This will help determine whether

91

Chapter 4-Conclusion and recommendations
these treatments directly influence weed control or if their effectiveness is solely due to
enhanced competition from turfgrass.
This research adds to the growing evidence that cultural methods of weed control, such as the
application of ammonium and iron compounds are a promising alternative to conventional
herbicides, potentially resulting in substantial cost savings within the turfgrass industry.
Traditionally, significant resources have been allocated to managing broadleaf weeds in the
pursuit of maintaining high-quality, weed-free turfgrass fields. The results of this research
demonstrate that the combination of ammonium sulphate × iron sulphate is a formidable
solution capable of achieving both aesthetic goals and efficient weed control. This low-cost
formulation presents an opportunity to save valuable time and optimize financial resources
that would otherwise be invested in synthetic herbicides.

92

References

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