effects of pre-harvest cultural practices on the …

The Pennsylvania State University

The Graduate School

College of Agricultural Sciences

EFFECTS OF PRE-HARVEST CULTURAL PRACTICES ON THE DIVOT

RESISTANCE OF THICK-CUT KENTUCKY BLUEGRASS SOD

A Thesis in

Agronomy

by

Evan C. Mascitti

2015 Evan C. Mascitti

Submitted in Partial Fulfillment

of the Requirements

for the Degree of

Master of Science

May 2015

ii

The thesis of Evan C. Mascitti was reviewed and approved* by the following:

Andrew S. McNitt

Professor of Soil Science

Thesis Advisor

Maxim J. Schlossberg

Associate Professor of Turfgrass Nutrition

Jack Watson

Professor of Soil Science

Peter Landschoot

Professor of Turfgrass Science

Agronomy Graduate Program Coordinator

*Signatures are on file in the Graduate School

iii

ABSTRACT

Athletic fields must provide stable and consistent footing to minimize injuries and

maximize player performance. Professional athletes in the National Football League

(NFL) impart extreme shearing forces to the surface during competition, producing

divots. Divots are defined as portions of the turf gouged from the surrounding area by

athletes’ cleated footwear. Divoting is the primary mechanism of damage on NFL fields,

as opposed to the abrasive wear and soil compaction common on more-frequently but

less-intensively trafficked surfaces.

During the latter stages of the NFL season, the cumulative removal of above- and below-

ground vegetation through divoting can destabilize the playing surface. At this time of

year the prevailing atmospheric and edaphic conditions in the northeastern United States

are unconducive to turfgrass growth and effectively eliminate turf recovery. To restore

stable footing the surface must be replaced with new sod.

Aside from ambient environmental conditions at sod farms, the quality of the sod

installed at NFL stadia is a direct consequence of management decisions by sod growers

prior to the sod harvest and installation. Since the surface will be used for competition

immediately after installation, there is little time for athletic field managers to alter the

surface characteristics through management practices. While some divoting is inevitable,

surface stability will be prolonged if divot sizes and numbers are minimized. It is thus

imperative that divot resistance is previously optimized through cultural practices at the

sod farm prior to harvest, transport, and installation.

iv

The objectives of this research were (1) Maximize divot resistance while maintaining

tensile strength of thick-cut Kentucky bluegrass sod through manipulation of pre-harvest

cultural practices, and (2) Determine the effects of mowing height, sand topdressing, and

nitrogen fertilization on shoot density, thatch accumulation, and below ground biomass

and their relationships to divot resistance.

Two field experiments were conducted to evaluate the effects of cutting height, sand

topdressing, and nitrogen fertilization on the divot resistance of thick-cut sod

immediately after harvest. Experiment 1 was spatially replicated at the Joseph Valentine

Turfgrass Research Center (University Park, PA) and Tuckahoe Turf Farms

(Hammonton, NJ). A four-way blend of Kentucky bluegrass (KBG) (Poa pratensis L.)

cultivars was seeded during early fall of 2012. Treatments were initiated in spring of

2013.

Cutting height treatments were established as discrete “experiments” maintained at 3.18

and 3.81 cm. Within each cutting height experiment a 2x6 topdressing x nitrogen

factorial experiment was conducted. The topdressing treatments were a control receiving

no sand and a treatment including three sand applications to total 8.5 kg sand m-2. The six

nitrogen treatments ranged from 96-244 kg total N ha-1 yr-1 and were further

differentiated by the application timing. Applications supplied 49 kg N ha-1 via granular

ammonium sulfate. Plots received either 2, 3, or 4 N applications from March-June and

either no additional N or a final N application in September of 2013.

v

Sod was harvested and tested in November 2013 at a standard “thick-cut” profile

thickness of 4.45 cm. Divots were produced with Pennswing, a weighted pendulum

device. The size of each divot was measured with smaller divots indicating high divot

resistance. Other parameters measured in the field included turfgrass color, surface shear

strength, and sod strength. To determine the associations among these parameters and

potentially related turfgrass morphological characteristics, core samples were collected

from each plot and evaluated for shoot density, thatch accumulation, and below-ground

biomass.

Experiment 2 evaluated the effects of four cutting heights (2.54, 3.18, 3.81, or 4.45 cm)

on divot resistance, shear strength, and sod strength. Plots were maintained under

identical fertilization and topdressing regimes. Treatment evaluation occurred in

November 2013 using the same methods as Experiment 1.

All plots in Experiments 1 and 2 were treated with trinexapac-ethyl (TE), a plant-growth

regulator which has been shown to increase divot resistance. The use of TE is common

among NFL field managers and by sod growers producing turf for the NFL, so TE

applications were included as part of the plot maintenance to better simulate a real-world

scenario.

Cutting height did not significantly affect divot resistance in Experiment 1 or 2. While it

is possible that cutting height in fact has no influence on divot resistance, the lack of a

cutting height effect in this project may be attributable to other factors in the experiments

masking such an effect. The blend of cultivars was uniform across all experimental units.

vi

KBG cultivars are known to respond differently to various cutting heights. The individual

cultivars therefore may have responded in opposing manners, masking the cutting height

effect. In addition, the use of TE regulates plant morphology in a fashion similar to close

defoliation (producing compact shoots and increased plant density). TE was regularly

applied to all plots in Experiments 1 and 2, and may have helped mask any cutting height

effect which would otherwise have occurred.

Lower cutting heights tended to produce higher shear strength at VRC (both Experiments

1` and 2), although TTF showed a weak trend in the opposite direction. Increased shear

strength under closer cutting may be partially attributed to higher shoot density. Shear

strength and density were positively, correlated, though the relationship was relatively

weak (r=0.26). The low correlation coefficient indicates other turfgrass properties also

influence shear strength.

Cutting height had no effect on sod strength in Experiment 1, but greater sod strength was

obtained in Experiment 2 with higher cutting heights. However the benefit was minor and

not realized until cutting height reached 4.45 cm, which is likely too high for sod

intended for the NFL. As acceptable sod strength was obtained under all cutting heights,

it is recommended that sod growers producing thick-cut sod for in-season replacements

maintain the production field close to 3.18 cm. This cutting height is comparable to those

used at NFL stadia and would not require the stadium manager to severely reduce the

cutting height prior to play.

vii

Divot resistance was negatively impacted by high N rates. Small divots indicated higher

divot resistance. At the VRC location divot lengths were 37% larger under the 4-1 N

treatment than the 3-0 treatment, which was most effective. Smaller yet analogous

increases in divot width and depth were also noted at each location under the 4-1 N

treatment.

The 4-1 N treatment (244 kg ha-1 total N) was the treatment most similar to the actual

fertilization schedule used by TTF in 2013 during production of thick-cut sod for NFL

stadia. This research project suggests N rates below the current standard may be

advantageous with regard to divot resistance. High shoot density and darker green color

were associated with greater N rates, but on NFL surfaces these traits are of minimal

importance compared to divot resistance.

Anecdotal concerns that close mowing and/or topdressing would render the turf

unharvestable at 4.45 cm sod thickness were not substantiated in this project. All

treatment combinations produced sod strength greater than 100 kg, which in these

experiments was estimated as the minimum acceptable strength for thick-cut, big-roll

sod.

Significant correlations among response variables occurred, but the correlation

coefficients were relatively weak. These relationships indicate divot resistance is affected

by multiple properties rather than a single turfgrass characteristic. Divot length was the

strongest measure of divot resistance and was negatively related to shear strength

viii

(r= -0.47) and sod strength (r= -0.38). Surprisingly, divot length was not significantly

correlated to below-ground biomass. Thatch thickness, however was significantly related

to divot length (r= -0.26). The relationship was negative, indicating plots with thicker

thatch layers also had shorter divots. Such a relationship is contrary to reports from

practitioners, most of whom opine divot resistance to be compromised by thatch buildup.

The relationship between thatch and divot resistance is complex and may depend on

factors not accounted for in this study such as depth of cleat penetration, impact angle,

and the physiochemical properties of the thatch layer (e.g. water status, lignin content,

state of decomposition). In the future, a research tool should be developed which more

accurately simulates the divot-producing mechanisms of NFL athletes.

Little research has investigated production of thick-cut sod with regard to in-season

replacement of American football fields. The goal of this project was to optimize the

cultural practices used by sod growers when producing thick-cut Kentucky bluegrass sod

for NFL football stadia. All treatments produced harvestable sod at 4.45 cm thickness

despite prior industry concern toward the imposition of close clipping as well as

applications of TE and sand topdressing. Under the conditions of this study, divot

resistance was improved by reducing nitrogen inputs from the current standard. Further

research is needed to understand the effects of more-refined nitrogen regimes as well as

the influence of thatch on divot resistance. The results of this project will aid sod growers

and turfgrass managers in producing divot-resistant natural grass playing fields.

ix

TABLE OF CONTENTS

LIST OF FIGURES ..................................................................................................... xi

LIST OF TABLES ....................................................................................................... xiv

DEFINITION OF TERMS ......................................................................................... xxi

ACKNOWLEDGEMENTS ......................................................................................... xxii

INTRODUCTION ................................................................................................................... 1

LITERATURE REVIEW ........................................................................................................ 4

Overview of turfgrass sod production .............................................................................. 4 Influence of clipping and nitrogen fertilization on turfgrass sod ..................................... 7

Clipping .................................................................................................................... 7 Nitrogen fertilization ................................................................................................ 10

Turfgrass thatch ................................................................................................................ 13 Consequences of thatch on athletic playing surface ................................................. 13 Effects of clipping on thatch development ............................................................... 15 Effects of nitrogen thatch development.................................................................... 15 Supplementary cultural practices to manage thatch ................................................. 17

Research methods used to evaluate surface stability and sod strength ............................ 19 Surface stability on athletic fields ............................................................................ 19 Sod strength .............................................................................................................. 24

OBJECTIVES .......................................................................................................................... 26

MATERIALS AND METHODS ............................................................................................. 27

Experiment 1: The effects of cutting height, topdressing, and nitrogen fertilization

on the divot resistance of thick-cut Kentucky bluegrass sod ................................... 28 Overview of Experiment .......................................................................................... 28 Plot Establishment .................................................................................................... 28 Treatment Application .............................................................................................. 32 Experimental Design ................................................................................................ 36 Additional Plot Maintenance .................................................................................... 36 Treatment evaluation ................................................................................................ 38 Statistical Analysis ................................................................................................... 51

Experiment 2: The effects of varying cutting height on the divot resistance of thick-

cut Kentucky bluegrass sod ...................................................................................... 54 Overview of Experiment .......................................................................................... 54 Plot Establishment .................................................................................................... 54 Treatment Application .............................................................................................. 54

x

Experimental Design ................................................................................................ 55 Additional Plot Maintenance .................................................................................... 55 Treatment evaluation ................................................................................................ 55 Statistical Analysis ................................................................................................... 55

RESULTS ................................................................................................................................ 56


on the divot resistance of thick-cut Kentucky bluegrass sod ................................... 57 Joseph Valentine Research Center (VRC) Location ................................................ 57 Tuckahoe Turf Farms (TTF) Location ..................................................................... 101 Variability across locations ...................................................................................... 146 Weather conditions ................................................................................................... 147 Correlations .............................................................................................................. 150


cut Kentucky bluegrass sod ...................................................................................... 153 Divot length, width, and depth ................................................................................. 153 Sod strength .............................................................................................................. 155 Shear strength ........................................................................................................... 155 Shoot density ............................................................................................................ 158 Thatch accumulation ................................................................................................ 158 Below-ground biomass ............................................................................................. 158

DISCUSSION .......................................................................................................................... 161

Field Evaluations .............................................................................................................. 162 Divot Resistance ....................................................................................................... 162 Sod Strength ............................................................................................................. 169 Shear Strength .......................................................................................................... 175

Turfgrass morphological characteristics .......................................................................... 177 Shoot density ............................................................................................................ 177 Thatch ....................................................................................................................... 179 Below-ground biomass ............................................................................................. 181 Correlations among measured parameters ............................................................... 182 Potential for related future research ......................................................................... 185

SUMMARY AND CONCLUSIONS ...................................................................................... 190

REFERENCES ........................................................................................................................ 193

APPENDIX .............................................................................................................................. 202

Additional Materials ........................................................................................................ 202

xi

LIST OF FIGURES

Figure 1. Generalized Mohr-Coulomb failure envelope; soil fails when the shear

stress exceeds the normal stress (confining pressure) as indicated by red line.

Vegetative stabilization is responsible for most of the cohesion intercept in

sand-based turfgrass systems. ............................................................................... 23

Figure 2. Sod strips being removed for sod strength testing at TTF............................ 40

Figure 3. The Pennswing device about to be released. ................................................ 42

Figure 4. Examples of divots produced by Pennswing. Photo at left shows a plot

with low divot resistance while the photo at right shows a plot with high

divot resistance. 30 cm ruler included for scale. .................................................. 42

Figure 5. Point gauge used to measure divot depth. Device is placed across the

divot and the metal rod is lowered to the bottom of the depression. Height is

read and the reference height is subtracted to obtain the divot depth in cm. ........ 43

Figure 6. Operation of the shear strength measurement device; handle was turned

clockwise in the horizontal plane until the turf failed. ......................................... 45

Figure 7. Fins on the Turf Shear Tester. ...................................................................... 45

Figure 8. Operation of the sod strength device. ........................................................... 46

Figure 9. Sod strip following tensile strength test. ..................................................... 46

Figure 10. Measurement of thatch layer thickness. ..................................................... 49

Figure 11. Sample plug following removal of verdure for tiller count ........................ 49

Figure 12. Plug being sectioned into thatch portion (lower left) and soil/below-

ground biomass (upper right). ............................................................................... 50

Figure 13. Examples of thatch (left) and washed below-ground biomass samples

(right); top image shows samples before ashing and bottom image shows the

same samples following exposure to 440 °C for 16 hours. .................................. 50

Figure 14. Mean divot lengths for the nitrogen treatment main effect at VRC.

Treatments with overlapping error bars are not statistically different using

Fisher’s Protected LSD. ........................................................................................ 63

xii

Figure 15. Mean divot depths for the nitrogen treatment main effect at VRC.



Figure 16. Conceptual model depicting a possible explanation for the cutting

height by topdressing interaction in Experiment 1. Plugs on left have varying

BGB density with depth but contain essentially the same total amount of

BGB. Plugs on right have been topdressed, reducing the fraction of the plug

sampled from original soil. Less native soil is incorporated, resulting in the

lower CH plots having greater BGB per plug. Cartoon is for conceptual

purposes only and is not drawn to scale. .............................................................. 97

Figure 17. Scatter plot of divot lengths plotted against volumetric water content in

Experiment 1 at TTF. ............................................................................................ 106

Figure 18. Mean divot widths for the nitrogen treatment main effect at TTF.



Figure 19. Scatter plot of divot widths plotted against volumetric water content in

Experiment 1 at TTF. ............................................................................................ 112

Figure 20. Mean divot depths for the nitrogen treatment main effect at TTF.



Figure 21. Comparison of the 3.81 cm area (top) and 3.18 cm area (bottom) at

TTF. ...................................................................................................................... 124

Figure 22. Scatter plot of shear strength plotted against volumetric water content

in Experiment 1 at TTF. ........................................................................................ 129

Figure 23. Scatter plot of thatch thickness plotted against volumetric water

content in Experiment 1 at TTF. ........................................................................... 130

Figure 24. Mean air temperatures at both locations over the duration of

Experiment 1. Lines represent a 5-day moving average of the mean between

daily high and low temperatures. Black bold line at 20 °C represents the

temperature considered optimal for cool-season turfgrasses (Turgeon, 2012).

Green arrows represent treatment application dates. ............................................ 149

Figure 25. Mean sod strength values for the four cutting heights evaluated in

Experiment 2. Treatments with overlapping error bars are not significantly

different using Fisher’s Protected LSD. ............................................................... 156

xiii

Figure 26. Mean shoot density values for the four cutting heights evaluated in


using Fisher’s Protected LSD. .............................................................................. 159

Figure 27. Divot lengths as affected by a cultivar by cutting height interaction; the

unpublished data were provided by McNitt (2014, personal communication). ... 164

xiv

LIST OF TABLES

Table 1. Particle size distribution for Ap horizon at the TTF location†. ..................... 31

Table 2. Particle size distribution of the top 15 cm of rootzone material at VRC†. .... 31

Table 3. Particle size analysis for the topdressing sand used at TTF. ......................... 34

Table 4. Particle size analysis for the topdressing sand used at VRC. ........................ 34

Table 5. Monthly schedule of topdressing and nitrogen treatments for Experiment

1. ........................................................................................................................... 35

Table 6. Notation for the linear contrasts performed to compare specific N

treatments and treatment combinations. ............................................................... 53

Table 7. Summary of treatment effects on field parameters in Experiment 1 at

VRC ...................................................................................................................... 58

Table 8. Summary of treatment effects on laboratory parameters in Experiment 1

at VRC. ................................................................................................................. 59

Table 9. Mean divot lengths for the cutting height main effect at VRC. ..................... 62

Table 10. Mean divot lengths for the topdressing main effect at VRC. ...................... 62

Table 11. Mean divot lengths for the nitrogen treatment main effect at VRC. ........... 62

Table 12. Selected contrasts comparing divot lengths at VRC as related to total

both total nitrogen applied and individual nitrogen treatments. ........................... 64

Table 13. Mean divot widths for the cutting height main effect at VRC. .................... 66

Table 14. Mean divot widths for the topdressing main effect at VRC. ....................... 66

Table 15. Mean divot widths for the nitrogen treatment main effect at VRC. ............ 66

Table 16. Mean divot depths for the cutting height main effect at VRC. .................... 68

Table 17. Mean divot depths for the topdressing main effect at VRC. ....................... 68

Table 18. Mean divot depths for the nitrogen treatment main effect at VRC. ............ 68

xv

Table 19. Selected contrasts comparing divot depths at VRC as related to total


Table 20. Mean sod strength values for the cutting height main effect at VRC. ......... 73

Table 21. Mean sod strength values for the topdressing main effect at VRC. ............ 73

Table 22. Mean sod strength values for the nitrogen treatment main effect at

VRC. ..................................................................................................................... 73

Table 23. Selected contrasts comparing sod strength at VRC as related to total


Table 24. Mean sod strength values for the cutting height by topdressing by

nitrogen treatment interaction at VRC. ................................................................. 75

Table 25. Mean shear strength values for the cutting height main effect at VRC. ...... 78

Table 26. Mean shear strength values for the topdressing main effect at VRC. .......... 78

Table 27. Mean shear strength values for the nitrogen treatment main effect at

VRC. ..................................................................................................................... 78

Table 28. Mean shoot density values for the cutting height main effect at VRC. ....... 81

Table 29. Mean shoot density values for the topdressing main effect at VRC. ........... 81

Table 30. Mean shoot density values for the nitrogen treatment main effect at

VRC. ..................................................................................................................... 81

Table 31. Selected contrasts comparing shoot density at VRC as related to total


Table 32. Mean shoot density values for the topdressing by nitrogen treatment

interaction at VRC. ............................................................................................... 83

Table 33. Mean thatch mass values for the cutting height main effect at VRC. ......... 87

Table 34. Mean thatch mass values for the topdressing main effect at VRC. ............. 87

Table 35. Mean thatch mass values for the nitrogen treatment main effect at VRC. .. 87

Table 36. Selected contrasts comparing thatch mass at VRC as related to total


Table 37. Mean thatch mass values for the cutting height by topdressing


xvi

Table 38. Mean thatch mass values for the cutting height by nitrogen treatment


Table 39. Mean below-ground biomass values for the cutting height main effect at

VRC. ..................................................................................................................... 93

Table 40. Mean below-ground biomass values for the topdressing main effect at

VRC. ..................................................................................................................... 93

Table 41. Mean below-ground biomass values for the nitrogen treatment main

effect at VRC. ....................................................................................................... 93

Table 42. Selected contrasts comparing below-ground biomass at VRC as related

to total both total nitrogen applied and individual nitrogen treatments. ............... 94

Table 43. Mean below-ground biomass values for the cutting height by

topdressing interaction at VRC. ............................................................................ 96

Table 44. Mean below-ground biomass values for the cutting height by nitrogen

treatment at VRC. ................................................................................................. 99

Table 45. Summary of treatment effects on field parameters in Experiment 1 at

TTF. ...................................................................................................................... 102

Table 46. Summary of treatment effects on laboratory parameters in Experiment 1

at TTF. .................................................................................................................. 103

Table 47. Mean divot lengths for the cutting height main effect at TTF. .................... 104

Table 48. Mean divot lengths for the topdressing main effect at TTF. ....................... 104

Table 49. Mean divot lengths for the nitrogen treatment main effect at TTF. ............ 104

Table 50. Mean divot widths for the cutting height main effect at TTF. ..................... 108

Table 51. Mean divot widths for the topdressing main effect at TTF. ........................ 108

Table 52. Mean divot widths for the nitrogen treatment main effect at TTF. ............. 109

Table 53. Selected contrasts comparing divot widths at TTF as related to total


Table 54. Mean divot depths for the cutting height main effect at TTF. ..................... 114

Table 55. Mean divot depths for the topdressing main effect at TTF.......................... 114

Table 56. Mean divot depths for the nitrogen treatment main effect at TTF. .............. 116

xvii

Table 57. Selected contrasts comparing divot depths at TTF as related to total


Table 58. Mean sod strength values for the cutting height main effect at TTF. .......... 120

Table 59. Mean sod strength values for the topdressing main effect at TTF. .............. 120

Table 60. Mean sod strength values for the nitrogen treatment main effect at TTF.... 120

Table 61. Selected contrasts comparing sod strength at TTF as related to total both

total nitrogen applied and individual nitrogen treatments. ................................... 121

Table 62. Mean sod strength values for the cutting height by nitrogen treatment

interaction at TTF. ................................................................................................ 123

Table 63. Mean shear strength values for the cutting height main effect at TTF. ....... 127

Table 64. Mean shear strength values for the topdressing main effect at TTF. ........... 127

Table 65. Mean shear strength values for the nitrogen treatment main effect at

TTF. ...................................................................................................................... 127

Table 66. Mean shoot density values for the cutting height main effect at TTF. ........ 132

Table 67. Mean shoot density values for the topdressing main effect at TTF. ............ 132

Table 68. Mean shoot density values for the nitrogen treatment main effect at

TTF. ...................................................................................................................... 132

Table 69. Mean thatch mass values for the cutting height main effect at TTF............ 136

Table 70. Mean thatch mass values for the topdressing main effect at TTF. .............. 136

Table 71. Mean thatch mass values for the topdressing main effect at TTF. .............. 136

Table 72. Selected contrasts comparing thatch mass at TTF as related to total both

total nitrogen applied and individual nitrogen treatments. ................................... 137

Table 73. Mean thatch mass values for the cutting height by topdressing


Table 74. Mean thatch mass values for the cutting height by nitrogen treatment


Table 75. Mean thatch mass values for the topdressing by nitrogen treatment


xviii

Table 76. Mean thatch mass values for the cutting height by topdressing by

nitrogen treatment interaction at TTF. .................................................................. 140

Table 77. Mean below-ground biomass values for the cutting height main effect at

TTF. ...................................................................................................................... 144

Table 78. Mean below-ground biomass values for the topdressing main effect at

TTF. ...................................................................................................................... 144

Table 79. Mean below-ground biomass values for the nitrogen treatment main

effect at TTF. ........................................................................................................ 144

Table 80. Mean below-ground biomass values for the cutting height by

topdressing by nitrogen treatment interaction at TTF. ......................................... 145

Table 81. Mean values for field-measured parameters at each location when

averaged across all treatment levels. .................................................................... 148

Table 82. Mean values for laboratory-measured parameters at each location when

averaged across all treatment levels. .................................................................... 148

Table 83. Spearman correlation coefficients among parameters measured in

Experiment1 .......................................................................................................... 151

Table 84. Mean divot dimensions for the four cutting heights evaluated in

Experiment 2. ........................................................................................................ 154

Table 85. Mean sod strength values for the four cutting heights evaluated in

Experiment 2. ........................................................................................................ 156

Table 86. Mean shear strength values for the four cutting heights evaluated in

Experiment 2. ........................................................................................................ 157

Table 87. Mean shoot density values for the four cutting heights evaluated in

Experiment 2. ........................................................................................................ 159

Table 88. Mean thatch mass values for the four cutting heights evaluated in

Experiment 2. ........................................................................................................ 160

Table 89. Mean below-ground biomass values for the four cutting heights

evaluated in Experiment 2. ................................................................................... 160

Table 90. Comparison of data collected in Experiment 1 with selected published

values for KBG sod strength on a per-unit-area basis. ......................................... 172

xix

Table 91. Properties of sod from this research project compared with actual sod

produced by TTF and installed at NFL stadia in November 2013. All sod

tested was harvested at 4.45 cm profile thickness. ............................................... 202

Table 92. Mean visual color ratings for the cutting height main effect at VRC. ......... 203

Table 93. Mean visual color ratings for the topdressing main effect at VRC. ............ 203

Table 94. Mean visual color ratings for the nitrogen treatment main effect at

VRC. ..................................................................................................................... 203

Table 95. Selected contrasts comparing visual color at VRC as related to total


Table 96. Mean visual color ratings for the cutting height main effect at TTF. .......... 205

Table 97. Mean visual color ratings for the topdressing main effect at TTF. .............. 205

Table 98. Mean visual color ratings for the nitrogen treatment main effect at TTF.... 205

Table 99. Mean visual color ratings for the cutting height by nitrogen treatment


Table 100. Selected contrasts comparing visual color at TTF as related to total


Table 101. Mean thatch thickness values for the cutting height main effect at

VRC. ..................................................................................................................... 208

Table 102. Mean thatch thickness values for the topdressing main effect at VRC. .... 208

Table 103. Mean thatch thickness values for the nitrogen treatment main effect at

VRC. ..................................................................................................................... 208

Table 104. Selected contrasts comparing thatch thickness at VRC as related to

total both total nitrogen applied and individual nitrogen treatments. ................... 209

Table 105. Mean thatch thicknesses for the cutting height by nitrogen interaction

at VRC. ................................................................................................................. 210

Table 106. Mean thatch thickness values for the cutting height main effect at TTF. .. 211

Table 107. Mean thatch thickness values for the topdressing main effect at TTF. ..... 211

Table 108. Mean thatch thickness values for the nitrogen treatment main effect at

TTF. ...................................................................................................................... 211

xx

Table 109. Selected contrasts comparing thatch thickness at TTF as related to

total both total nitrogen applied and individual nitrogen treatments. ................... 212

xxi

DEFINITION OF TERMS

Below-ground biomass- the structural components of turfgrass plants which reside

beneath the soil surface; namely roots and rhizomes, with a minor component of crowns

and leaf sheathes.

Divot- a portion of turf partially or completely gouged out of surrounding turf by a golf

club head, horse shoe, or studded footwear.

Newton-meter (Nm)- the SI unit for torque, calculated as the product of an applied

rotational force and the length of the lever arm.

Scuff- a portion of turfgrass shoots and thatch gouged from surrounding turf; less severe

than a divot in that most crowns, roots, and rhizomes remain intact.

Shear strength- the tendency of a material to resist strain in a direction coplanar with an

applied force. Generated in turfgrass systems mostly by vegetative stabilization but also

by friction, cementation, and molecular attraction among soil particles.

Shoot- the above-ground portion of an individual turfgrass plant; may be initially derived

from a seed, tiller, stolon, or rhizome.

Sod- a surface layer of turf harvested for transplanting.

Sod strength- the uniaxial tension force required to separate a strip of turfgrass sod into

multiple pieces.

Studded footwear- a type of shoe containing posts on the sole of the shoe that penetrate

into the turf at footstrike; commonly worn by athletes in order to improve traction during

athletic maneuvers.

Thatch- an accumulation of living and dead crown, root, rhizome, and leaf tissues

between the green verdure and the soil surface.

Turf- a community of plants, usually turfgrasses, in consort with the portion of soil in

which the plants grow.

Turfgrass- a plant species which forms a contiguous ground cover and persists under

regular defoliation and traffic.

Verdure- the layer of above-ground green living plant tissue remaining after mowing.

xxii

ACKNOWLEDGEMENTS

I am tremendously grateful to my major professor, Dr. Andrew McNitt. Thank you Andy, for

taking a chance on me as a new graduate student with no prior turf education. You always made

feel like I belonged here, and I feel privileged to have been trained by you.

Thanks are extended to the additional members of my graduate committee, Drs. Jack Watson and

Max Schlossberg. Jack, I admire your enthusiasm for soil science and your ability to engage

students in learning. Max, you’ve taught me more than you can realize; your unique blend of

cerebral thought and informal discourse have greatly heightened my appreciation for both

statistical analysis and turfgrass nutrition.

With regard to my mentors at Penn State, Tom Serensits was also among the most important.

Tom, thanks for answering all my questions, both astute and silly. I am also indebted for your

extensive aid with logistics and data collection. Thanks also to Dianne Petrunak for your practical

advice and camaraderie at various turf conferences and events.

Thanks to Tuckahoe Turf Farms for providing space, materials, and the impetus for this project,

as well as an enlightening glimpse into the practical side of sod production.

I would also like to acknowledge Tom Bettle and the Valentine Research Center staff. Your can-

do attitude and assistance with equipment and other tasks are greatly appreciated.

I am thankful to the numerous Penn State faculty, staff, and students who helped make my time

here both educational and enjoyable. In particular I’d like to recognize my office-mates, Nur

Suhada Abu Bakar and James Banfill. The countless Creamery breaks, late nights at the office,

and sessions of “unstructured learning” I shared with you were critical in my success during these

two years.

Finally, but most importantly, I am grateful to my parents Julie and Jason, and my brother Marco.

I attribute most of my success to the positive attitude and work ethic you have instilled in me, and

to your unwavering encouragement and love.

1

INTRODUCTION

An athletic field should provide a consistent and predictable level of footing for athletes

making maneuvers during competition. The surface should be stable and should not

excessively displace or move when contacted by the athlete. Expectations for quality

natural grass playing surfaces are at an all-time high. These demands are driven by the

availability of sophisticated equipment and scientific knowledge, increased scrutiny on

player safety and performance, and competition with infilled synthetic turf systems.

In an attempt to provide a consistent and predictable surface in all weather conditions,

professional sports stadia have installed very high-sand rootzones to provide excellent

drainage and good air exchange to the turfgrass root system (Canaway, 1983). Without

vegetative or synthetic reinforcement, sand is essentially a non-cohesive soil when

compared with a finer-textured soil containing moderate to low soil moisture (Brady and

Weil, 2007). Thus surface stability on high-sand athletic field rootzones is provided

primarily by the interaction of roots and rhizomes with the sand. When the roots and

rhizomes fail to stabilize the surface, a divot can form. On a natural turfgrass playing

surface, a divot is defined as the complete shearing of turfgrass shoots, crowns, and soil

adhering to roots and/or rhizomes from the soil below (McNitt, 2000). Divoting is of

particular concern on professional American football fields. The athletes possess

exceptional size and speed, and impart accordingly large forces to the surface. The

2

potentially low surface stability of high-sand rootzones can increase certain types of

athlete injuries if adequate turf cover is not maintained (McNitt, 2000); thus, turf

managers aim to maximize the turf’s above-ground cover as well as root and rhizome

production.

Athletes wearing studded footwear cause abrasive, compressive and shearing forces to

the surface during competition. These forces injure the turfgrass plants and reduce the

vegetative cover (Canaway, 1975). Heavy wear from field usage may damage the surface

at a rate faster than the plant community can recuperate. Such damage is commonplace in

American football as approximately 80% of the wear is concentrated over less than 10%

of the field (Cockerham and Brinkman, 1989). This thinning of the turfgrass stand

through either divoting or abrasion results in a decrease of surface stability. When

vegetative cover is reduced the field manager should attempt to remediate the damage by

limiting play, overseeding and allowing the field to recuperate. If the schedule of events

does not permit this remediation the damaged areas must be replaced with sod. Sod is a

layer of turfgrass plants and the adhering soil harvested for transport (Turgeon, 2012). On

high-profile fields the sod is expected to provide a safe and stable surface immediately

after planting. Most National Football League (NFL) stadia install new sod quite

frequently, as often as 2-3 times each year. Consequently, the playing surface stability of

the sod after it is installed at a stadium is largely dependent on the cultural practices

employed at the sod farm prior to harvest.

3

Newly installed sod is inherently less stable than a mature, healthy stand of turf. The

harvesting process is highly stressful to the turfgrass plants as it removes a significant

portion of their root system, hindering the plants’ ability to acquire water and nutrients.

Until the sod is sufficiently re-rooted, the interface between the sod layer and underlying

soil provides a plane of weakness along which portions of the turf can be sheared away

(Turgeon, 2012). In response to these challenges, most sports field managers use sod with

a relatively thick soil layer (up to ~5 cm) for in-season re-sodding. Thick-cut sod is a

relatively specialized product that is used only when there is not enough time for the sod

to root prior to play. It is also expensive as the added weight of soil necessitates

specialized machines to harvest and install the sod and may increase shipping costs up to

4 times that of conventional sod (Trulio, 1994). A thicker cut provides additional weight

to the sod strip to reduce the chance of the strip moving during play. Despite the popular

use of thick-cut sod for in-season repairs of athletic fields, little research-based literature

exists on production methods for thick-cut sod. Research is needed to improve these

methods in order to help growers produce sod with maximum surface stability.

4

LITERATURE REVIEW

The following literature review summarizes prior work concerning this research project’s

objectives. It is divided into four sections: (1) a synopsis of turfgrass sod production (2) a

summary of the influence of primary cultural practices on sod properties, (3) an overview

of thatch management in turfgrass systems, and (4) a review of research methods used to

evaluate the quality of sod and athletic fields.

Overview of turfgrass sod production

Before considering specific research goals pertaining to thick-cut sod, it is instructive to

briefly examine the overall practice of sod production. Production of sod as an

agricultural commodity in the United States began around the 1920s, when strips of

pasture grass were harvested and transplanted to provide rapid ground cover. Since then

the industry has advanced considerably through development of improved cultivars,

mechanized harvesting equipment, and heightened demand for “instant” turf (Beard et al.,

1969). Quality sod is defined by uniform appearance, high shoot density, acceptable

color, adequate carbohydrate reserves for rooting, adequate sod strength for handling, a

minimal thatch layer, and freedom from disease, weed, and insect pests (Beard, 1973).

Sod is produced on a variety of soil types including mineral soils, organic/muck soils, and

various types of organic waste (e.g. dairy manure, composted sewage sludge) (Beard et

al., 1969; Vietor et al., 2002; Tesfamariam et al., 2009). Mineral soils are the preferred

5

substrate for sod that will be planted on athletic fields, due to its greater weight and

stability in comparison to muck soils and organic by-products (Rieke and Beard, 1969).

Production time for cool-season turfgrass sod ranges from 6 to 24 months, depending on

edaphic, climatic, and management factors. In general, sod can be produced more rapidly

on organic soils than on mineral soils (Rieke and Beard, 1969). When possible, a very

sandy soil is chosen in order to match the high-sand rootzone over which the sod will be

installed. This reduces the chance of forming a perched water table at the textural

discontinuity between the sod layer and the rootzone. Such an interface could restrict

drainage and rooting, potentially creating a shear plane along the boundary.

Sod may be harvested as soon as roots and rhizomes have knitted together enough to

allow the sod to be handled without tearing (Beard et al., 1969). Once sufficiently knitted,

the sod is harvested using a machine with a horizontal blade 1-6 cm beneath the soil

surface. The blade severs roots and produces a layer containing soil and the turfgrass

plants. This layer can then be rolled up or stacked, transported, and re-laid on a prepared

site.

In northern U.S. climates, Kentucky bluegrass (Poa pratensis L.) is the predominant

species used for commercial sod production (Watson et al., 1992). Kentucky bluegrass

(KBG) is the only cool-season turfgrass species with a strong rhizomatous growth habit,

which permits the sod to knit together. Tall fescue (Festuca arundinacea) and fine

fescues (Festuca rubra spp. and Festuca ovina spp.) have also been used to produce sod.

Tall fescue provides improved heat and drought tolerance over Kentucky bluegrass, as

6

well as lower nitrogen requirements. However, because Festuca spp. have a

predominantly bunch-type or very weakly rhizomatous growth habits, sod produced

using these species has a low tensile strength and tends to tear apart during harvesting,

transport, and installation. Sod tensile strength is often referred to simply as sod strength.

To mitigate this lack of sod strength, some producers substitute a small percentage (10-

20%) of KBG seed for tall fescue. The KBG rhizomes provide sufficient sod strength for

harvesting, while tall fescue remains the dominant species in the sod. Alternatively,

reinforcing material such as plastic netting can be used to provide sufficient sod strength

for harvesting. The net method can produce harvestable tall fescue sod in as little as 7

weeks (Burns, 1980). The netting adds to production costs and is not preferred for use on

athletic fields as it poses a potential safety hazard if athletes’ studded footwear become

entangled in it. Tall fescue also has a coarse leaf texture, intolerance to close cutting,

slower recuperative capacity, and overall inferior turf quality when compared to KBG.

For these reasons use of tall fescue on sports fields is limited to lower-maintenance

scenarios such as those at community fields and parks, while KBG is preferred for

higher-profile athletic surfaces (Puhalla et al., 2010).

Among KBG cultivars, significant morphological differences exist including leaf texture,

optimum cutting height, shoot density, and lateral spread rate/aggressiveness (Murphy et

al., 2004). Specific attributes of interest in sod production include sod strength and lateral

spread rate. In an evaluation of 103 KBG varieties, Shearman et al. (2001) found that the

strongest cultivars had sod strength 3-5 times that of the weakest cultivars. In addition,

significant differences in lateral spread rate existed among cultivars. Interestingly, sod

7

strength was not correlated with lateral spread rate. This is contrary to the widely-held

assumption that rhizome growth is the main factor associated with both lateral spread rate

and sod strength. Other factors may also be important in these measured characteristics,

such as tiller production and root mass.

Influence of clipping and nitrogen fertilization on turfgrass sod

Factors of interest in this research project include two basic cultural practices- cutting and

fertilization. The following two sections summarize prior research on these practices as

they pertain to sod production and playing surface quality.

Clipping

The relationship between regular defoliation (i.e. clipping) and turfgrass plant

morphology is well documented in literature. A higher cutting height (CH) leads to

increased rooting depth, longer rhizomes, and decreased tiller/shoot density. Conversely,

lower cutting heights produce a greater number of aerial shoots with a shallower root

system and decreased rhizome production (Goss and Law, 1967; Adams et al., 1974;

Nyahoza et al., 1974). The turf compensates for removal of leaf tissue by producing

additional tillers (intravaginal branches) and a more compact growth habit with more

leaves per shoot (Eggens, 1981). This morphological change is attributed to hormonal

effects, primarily triggered by additional light penetration through the canopy. These

signals release axillary buds from apical dominance and permits them to differentiate as

tillers (Simon and Lemaire, 1987). On closely mown turf the leaf angles are more

8

prostrate, as opposed to the upright angles found on higher-cut turf. These adaptations

minimize the loss of photosynthetic area, although close cutting still results in a net

decrease of carbohydrate product (Eggens, 1981, 1982). The net energy loss is probably

the main reason for the decreases in root and rhizome growth associated with low cutting

heights (Juska and Hanson, 1961).

Cutting height may affect divot resistance and therefore is of interest to sports turf

managers and sod producers. Unpublished data from research at The Pennsylvania State

University suggest for certain cultivars, divot resistance is actually increased by closer

cutting (McNitt, 2014, personal communication). This phenomenon may be a function of

greater root density in the uppermost profile, higher shoot density, and/or other factors.

Divot length was negatively correlated to tiller density and below-ground biomass in a

further study of KBG cultivars (Serensits, 2008).

During sod production, height of cut should be within the optimal range for the turfgrass

species being grown. As root and rhizome growth are favored by higher cutting heights, it

might be expected that sod strength would also improve. Satari (1967) reported higher

sod strength under cutting heights of 5.72 cm and 3.81 compared to lower heights.

Other research suggests that within this optimal range, it makes little difference whether

the turf is maintained at the higher or lower ends of the range. In a 3-year study, Mitchell

& Dickens (1979) found varying results with respect to cutting height. In 1973, sod

strength of ‘Tifway’ bermudagrass (Cynodon dactylon x C. transvaalensis) was improved

with higher cutting heights (2.50 cm or 2.00 cm) compared to a lower height of 1.25 cm,

9

while in 1974, the opposite response occurred. In 1975, no significant difference was

observed. The authors suggested the differences may have occurred due to chance rather

than to a repeatable physiological response. Similarly, Li et al. (2011) reported no

difference in sod strength of KBG sod grown on clayey soil when cutting height was

raised from 4.5 cm to 7.5 cm.

Research by Li et al. (2011) and Mitchell and Dickens (1979) tested sod harvested at

standard thicknesses of 1.25 cm and 2 cm, respectively. When sod is harvested at greater

soil thickness, greater sod strength is needed to support the increased mass of adhering

soil. Cutting height therefore may be an important variable when sod is cut at greater

depths.

Given no difference in sod tensile strength due to cutting height, Li et al. (2011)

suggested sod producers maintain their turfgrasses near the high end of the range for

economic reasons; in other words, less-frequent cutting is required for grass maintained

higher heights of cut. It should be noted that this suggestion was geared towards growers

of standard sod, rather than thick-cut sod produced specifically for high-end sports fields.

Even the lower height tested by Li et al. (2011) (4.5 cm) would be considered too tall for

a professional football surface. If the sod were maintained at this height, lowering the

canopy to a more acceptable height would be required immediately before or after sod

installation. This practice would be discouraged due to its imposition of two simultaneous

stresses and aesthetics- a severe reduction in canopy height followed by root pruning (i.e.,

sod harvesting). The likelihood of damage from a MH reduction is compounded when

other stresses are present (Turgeon, 2012). Therefore it is preferable to maintain the sod

10

close to its eventually desired height of cut (~2.5 to 3 cm) during establishment. No

published data exist on the effect of these low cutting heights on KBG during sod

production.

Nitrogen fertilization

Nitrogen is the mineral nutrient required in greatest quantity by higher plants, and in

nearly all cases is the growth-limiting nutrient of a turfgrass system (Kussow et al., 2012;

Marschner, 2012). Maximum biomass production occurs in KBG under extraordinary N

rates of 600-800 kg N ha-1 yr-1 (Kussow et al., 2012). However maximum biomass

production is seldom the goal of turf management. N is instead applied to produce the

desired surface characteristics, which may be of a functional, recreational, and/or

aesthetic nature (Beard, 1973; Bowman, 2003). In addition to management goals,

recommended N rates on athletic fields and sod farms vary substantially according to soil

conditions, turfgrass genotype, and weather patterns.

Turfgrasses typically exhibit shoot priority, meaning that in general shoots are a preferred

sink for photosynthate compared to roots or stems (Bell, 2011). When carbohydrate

supply is limited, the available carbohydrates will be preferentially allocated to

production of leaf tissue rather than roots, crowns or rhizomes (Satari, 1967; Carrow et

al., 2001; Bell, 2011). Shoot priority is exacerbated by abundant N supply because the as

N becomes less limiting, the plants mobilize stored carbohydrates to produce leaf

biomass. Restricting N is hypothesized to favor root growth because of roots’ lower basal

11

N requirement relative to shoots. Under low N availability, the leaves are relatively N

deficient and thus are unable to utilize stored carbohydrates for growth. Roots, however,

are not as sensitive to low N supply and are able to mobilize photoassimilates for

structural growth (Adams et al., 1974).

When shoot growth is too rapid the plants consume carbohydrates at a greater rate than

they can be produced (Juska and Hanson, 1961). Numerous studies have examined the

effects of nitrogen fertilization on sod strength. Data from sod production research

generally support this phenomenon, showing weaker sod under high N, although data

documenting the opposite response have also been published (Kurtz, 1967).

An early study of Merion KBG concluded monthly applications of 17 kg N ha-1 improved

sod strength when compared with higher monthly rates of 34 or 68 kg N ha-1 (Satari,

1967). The sod was harvested 17 months after seeding. However this study was

conducted on an organic muck soil which likely contributed additional N through

microbial mineralization.

Similarly, bermudagrass sod strength was consistently higher when N was applied every

4 weeks at 25 or 50 kg ha-1, compared to 100 or 200 kg ha-1 (Mitchell and Dickens,

1979). Sod was harvested 4 months following a June sprigging. The authors attributed the

lower sod strength under high N to excessive aerial shoot growth, which depleted the

plant’s carbohydrate reserves, suppressing root and rhizome growth, although no data

were presented to support this hypothesis.

12

Li et al. (2011) tested sod strength of 14-month old KBG sod harvested in October. Sod

strength was higher under annual nitrogen applications of 120 kg ha-1 than under N rates

of 240 kg ha-1. N timing was also investigated by Li et al. (2011). Sod strength was

higher when N applications were restricted during the summer months, and the strongest

sod resulted from applying much of the N during fall. Direct measurements of roots and

rhizomes were not performed.

In contrast, Kurtz (1967) found KBG sod strength to increase with higher N rates, up to

175 kg N ha-1 yr-1 . These results were derived from a turf establishment study during

which the turf was seeded in spring and fertilized beginning in July before being

harvested in October. Highest sod strength was obtained with light applications in the

summer and a heavier dose of N at the final fertilizer application in September.

Although N fertilization is a practice fundamental to turfgrass culture, little published

research exists about the effects of N levels on divot resistance. Most research pertaining

to N and athletic playing surface quality has focused on tolerance to abrasive wear and

subsequent recovery. It is sometimes suggested that athletic fields receive higher than

normal fertilization to promote recovery from damage (Puhalla et al., 2010), although

excessive N levels will decrease wear tolerance via greater leaf moisture content and

decreased rooting (Hoffman et al., 2010). It is likely that wear tolerance shows a

quadratic response as N levels increase from zero, showing an initial improvement before

plateauing and eventually declining (Canaway, 1984). Sod transplanted to athletic

playing surfaces is not exposed to wear during production; consequently, a different

approach to N fertilization may be necessary.

13

Turfgrass thatch

Thatch is an intermingled accumulation of living and dead plant tissue which lies

between the green verdure and the soil surface in a turfgrass system. Any factor

increasing the rate of biomass production or decreasing the rate of biomass

decomposition will hasten the development of thatch, although interactions between

buildup and breakdown mechanisms are not fully understood (Beard, 1973; Waddington,

1992). The following subsections review the influence of thatch on athletic playing

surfaces.

Consequences of thatch on athletic playing surface

A small amount of biomass accumulation decreases surface hardness and increases wear

tolerance on athletic fields (Duncan and Beard, 1975; Puhalla et al., 2010). The increase

in wear tolerance is attributed to the thatch layer’s cushioning effect, which shields the

turfgrass crowns from physical injury. The cushioning effect is most beneficial on

frequently trafficked athletic field (e.g., multipurpose high school fields) because wear

injury on these fields is associated with soil compaction and repetitive abrasion of the

turfgrass plants (Canaway, 1975).

Conversely, a thatch cushion provides little benefit on sand-based American professional

football fields. On these fields, soil compaction is minimal due to the single-grained

structure of sand, and most wear injury is associated with formation of large divots rather

than repeated abrasion. Excessive accumulation of organic matter at the surface may

14

reduce surface stability (i.e. divot resistance) and playing quality (Sherratt et al., 2005;

Serensits, 2008).

Other detrimental effects of excessive thatch include slowed infiltration, reduced

fertilizer and pesticide efficacy, increased disease pressure, and proneness to scalping

(McCarty et al., 2007). These effects are detrimental to both playing quality and turfgrass

health.

For the reasons outlined above, NFL sports turf managers generally desire sod with

minimal thatch when resurfacing their fields. Sod would ideally be harvested and

installed before any thatch develops, but in reality this goal is difficult to achieve. The

sod may not be mature enough for use on high-end athletic fields before thatch begins to

form. Additionally, the aggressive cultivars used in athletic field sod production tend to

produce thatch quickly (Shearman, 1980).

Sod growers must take measures to minimize thatch development when producing turf

for NFL stadia. Turfgrass thatch involves interactions among many factors – thatch

reduction practices are widely conducted in the turfgrass industry, yet their effects in

controlled, replicated research trials are often murky. Waddington (1992) noted that

depending on the study, one could reasonably conclude cutting height, N fertilization,

clipping removal, core cultivation, verticutting, and topdressing all either do or do not

affect thatch levels.

15

Effects of clipping on thatch development

Cutting practices have been shown to influence thatch accumulation. Changes in cutting

height alter the plants’ morphology and partitioning of biomass (Shearman, 1989).

Shearman (1980) found that increasing cutting height of Kentucky bluegrass from 2.5 cm

to 5 cm resulted in greater thatch accumulation. A similar effect was observed by Dunn et

al. (1981), who found thatch was thicker in zoysiagrass (Zoysia japonica Steud.) at a

cutting height of 3.8 cm compared to 1.9 cm. The authors suggested the increased thatch

at higher cutting heights is a function of more stem tissue being produced by the plant.

This conclusion was based on stem tissue having higher sclerenchyma content and a

slower degradation rate.

Increased stem tissue production at higher cutting heights was also reported by (Juska

and Hanson, 1961). Their study showed greater rhizome weight for Kentucky bluegrass

mowed at 5.08 cm as opposed to 2.54 cm. Additional rhizome production can lead to

greater thatch accumulation since rhizome tissue degrades slowly (Dunn et al., 1981)

Effects of nitrogen thatch development

High N rates are often blamed for thatch buildup because nitrogen stimulates excessive

biomass production. However, research data indicate N rate plays a lesser role in thatch

buildup than is commonly assumed in the turf industry (Waddington, 1992). For

example, Carrow et al., (1987) determined that bermudagrass thatch accumulation was

not different among a wide range of N rates (96 to 296 kg ha-1 year1).

16

Similarly, Shearman (1980) found no difference in thatch thickness among plots of

Kentucky bluegrass fertilized at either 100 kg N ha-1 or 200 kg N ha-1. Much more

variation existed among cultivars (23 evaluated) and cutting heights (5 cm produced more

thatch than 2.5 cm), suggesting these factors play more important roles in regulating

thatch development compared to N rate.

Weston and Dunn (1985) investigated the effects of N rates on thatch accumulation in

‘Meyer’ zoysiagrass. The authors reported increased thatch development (both thickness

and % organic matter) when 96 kg ha-1 N was applied compared to no N, but no

additional thatch accumulation when the N rate was increased to 196 kg ha-1.

Taken together, these studies suggest when compared to no N fertilization at all, thatch

buildup is initially increased by N applications, but there is a plateau above which

additional N will not affect thatch development. This plateau varies according to species,

soil type, and non-N related management practices.

In addition to N rate, the N source applied to turfgrass can influence thatch accumulation

due to soil acidification. Thatch decomposition is governed by microbial populations and

earthworms which prefer soil with a neutral to slightly acid pH (Murray and Juska, 1970).

Sartain (1985) demonstrated that applying ammonium sulfate (the most acidifying of

common soluble N fertilizers used in turfgrass) significantly increased thatch

development when compared with isobutylidene diurea and a natural organic fertilizer.

The authors concluded that by decreasing the soil pH, ammonium sulfate inhibited

microbial activity and accelerated organic matter accretion. It is also worth noting that the

17

total N recovery from microbially-degraded products can sometimes be less than that of

soluble N salts. Thus the total quantity of plant-available N may have been greater for the

plots receiving ammonium sulfate.

Supplementary cultural practices to manage thatch

Even when correct cutting and fertilization practices are observed, a thatch layer is likely

to form due to the aggressive nature of modern Kentucky bluegrass cultivars. Additional

action must be taken to prevent excessive buildup. Two widely used practices of thatch

removal are core aeration and verticutting. When the cores are harvested following an

aeration event, the thatch within the cores is physically removed from the turfgrass

system. The holes are then filled with fresh sand or soil. Similarly, verticutting physically

removes thatch by invoking a series of vertically aligned blades to tear thatch from

beneath the canopy and deposit it at the surface, where it can be raked or blown into a

pile for removal (Turgeon, 2012). By puncturing the thatch layer, these processes also

expose additional surface area along which aerobic soil microbes can contact the thatch.

Turfgrass managers frequently use these core aeration and verticutting practices to

manage thatch. However, sod producers often wish to avoid core cultivation and

verticutting. These practices sever roots and rhizomes, temporarily reducing sod strength.

Even if the sod remains harvestable, its athletic playing quality may be compromised

once it is transplanted (Kowalewski et al., 2008).

18

A less disruptive means of thatch control known as topdressing involves the application

of a thin layer of soil (usually >90% sand) to the turfgrass surface. Topdressing is often

conducted concurrently with mechanical cultivation (coring and/or vertical cutting) on

established turf. However, some research suggests the mechanical removal can be

omitted so long as sufficient volume of topdressing is applied, and a significant thatch

layer does not already exist (Fermanian et al., 1985; McCarty et al., 2007). Light,

frequent topdressing progressively dilutes the thatch with fresh mineral matter as it

develops, preventing a layer of pure organic material from forming. It also helps keep soil

microorganisms in contact with the organic matter and maintains more constant humidity,

permitting more rapid bio-degradation (Parker, 2011; Beasley et al., 2013).

McCarty et al. (2007) compared various methods of thatch control traditionally used by

turf managers. Topdressing, verticutting (6 or 19 mm depth), grooming (3 mm depth),

and core aerification all maintained baseline organic matter levels in a USGA sand

putting green. The only treatment to actually reduce OM was a combination of coring,

grooming, and verticutting. However, this research suggests that if a turf is topdressed

diligently before a substantial thatch layer develops, topdressing alone may be a viable

option of thatch control.

Similarly, Barton et al. (2009) found topdressing to be equally effective as verticutting at

reducing soil organic matter levels. This effect occurred regardless of whether the soil

had high or low OM at the beginning of the experiment.

19

Among others, these two studies suggest topdressing alone may be used to offset thatch

formation. However sand has little cohesion until roots and rhizomes can stabilize it, and

over-application on sports fields can result in an unstable surface (Kowalewski et al.,

2010). Little controlled research exists on how sand topdressing affects divot resistance.

Additionally, applying sand topdressing to a sod production field is a relatively new

concept and has not been evaluated in research trials.

Research methods used to evaluate surface stability and sod strength

Surface stability on athletic fields

The means by which a divot forms on a sports field is challenging to replicate within a

controlled research setting. Athletes contact the surface at various angles and speeds.

There are considerable differences among players’ body weights and shoe types, not to

mention the many types of motion involved in different sports. All are factors in the type

of force a given athlete applies to the surface. Several mechanisms in turfgrass research

have been used to simulate divot formation and related properties of surface stability.

Divot resistance

The Turf Shear Tester (TST) has been used in divot studies of turfgrass used for both golf

and sports turf (Sherratt et al., 2005; Kowalewski et al., 2011; Trappe et al., 2011;

20

Anderson, 2012). The TST has a 50-mm wide paddle that can be inserted to a depth

specified by the user. The paddle is connected to a lever, which when pulled rotates the

paddle upward until the turf fails. A force gauge measures the amount of rotational torque

necessary to rotate the paddle. A higher torque value is interpreted as more divot resistant

turf. Trappe et al. (2011) evaluated the divot resistance of various zoysiagrass and

bermudagrass cultivars. The researchers found the TST to have less variability in its

measurements as an indicator of divot resistance than divot volume or visual ratings of

divot severity. However, divot volume and visual ratings were measured on divots

produced by golfers actually hitting balls off the research plots. While there was no

statistical difference between the divot sizes produced by each golfer, variation among

golfers may also have contributed to the larger variability in these measurement

techniques.

A device termed Pennswing was used by McNitt and Landschoot (2001) and Serensits

(2008) to evaluate divot resistance of athletic fields. Pennswing creates divots by

impacting the turf surface with the head of a pitching wedge golf club. Shear strength

values from the shear vane described above correlated (r = -0.40) with values obtained by

Pennswing (Serensits, 2008). However, Pennswing was better able to detect differences

among treatments and may be a more precise indicator of divot resistance than the shear

vane.

21

Shear Strength

The Turf-Tec Shear Strength Tester (Turf-Tec International, Tallahassee, FL measures

shear strength in the upper portion of the turf-soil system. Shear strength is defined as the

maximum resistance of a soil or rock to shearing stresses (ASTM D653, 2014). A given

soil’s shear strength is the sum of: (1) electrostatic attraction and cementation between

mineral particles (2) friction between mineral particles during application of the shear

force, and (3) root reinforcement (Yokoi, 1968; Adams and Jones, 1979). In a high-sand

content soil, mineral cohesion and friction are low due to sand particles low surface area;

thus it can be assumed that the majority of shear strength is obtained from vegetative

stabilization (Ross et al., 1991). The Shear Strength Tester device consists of a 7.0 cm

diameter disk mounted to a shaft. The disk has 12 radially-mounted fins of alternating

lengths (2.0 and 1.0 cm) welded to one side. The disk is pressed into the soil surface and

the shaft is rotated until the surface fails under the shearing force. A torque wrench is

attached to the shaft during this process and used to record the maximum force in

Newton-meters (Nm). The Shear Strength Tester is essentially equivalent to the

Eijkelkamp Type 1B shear vane method (Kowalewski et al., 2008; Trappe et al., 2011),

which is no longer in production.

It should be noted that while the term “shear strength” is often used in soil science and

engineering to describe values obtained with the direct shear test (ASTM D 3080, 2011)

or triaxial tests (ASTM D7181, 2011), the Shear Strength Tester is more similar to the in-

situ system is tested in a “drained” condition (i.e. pore water pressure ~0) rather than an

“undrained” or saturated state, for which ASTM D2573 (2008) is intended. The shearing

http://en.wikipedia.org/wiki/ASTM

22

mechanisms exerted by the Shear Strength Tester still follow the generalized Mohr-

Coloumb failure criterion:

Τ = σ' tan(φ') + c'

Where τ is the critical shear strength, σ' is the normal stress (perpendicular to the shear

plane), φ' is the angle of internal friction (a property inherent to a given soil), and c' is

the cohesion (Fig. 1) (Handin, 1969). Cohesion is defined in soil mechanics as a soil’s

shear strength when the compressive stresses are zero (Yokoi, 1968). This definition

differs somewhat from the conventional soil physics definition of cohesion as the

electrostatic forces which attract soil particles toward one another. Due to low inherent

cohesion of the engineered sand media commonly used in turfgrass culture, cohesion is

mostly a function of vegetative stabilization.

The measurement of shear strength with the Shear Strength Tester is simplified in that the

first term of the Mohr-Coloumb equation is essentially zero, since no confining pressure

(i.e. downward force) is used during the test. Thus the shear strength is essentially a

function of root and rhizome stabilization.

23

Figure 1. Generalized Mohr-Coulomb failure envelope; soil fails when the shear stress

exceeds the normal stress (confining pressure) as indicated by red line. Vegetative

stabilization is responsible for most of the cohesion intercept in sand-based turfgrass

systems.

24

Sod strength

Sod strength (SS), sometimes known as sod tensile strength, is defined as the longitudinal

force necessary to separate a piece of sod (Beard et al., 1969). A minimum SS is required

for successful harvest, handling, and installation of turfgrass sod. . Sod strength is

measured by applying a tensile force to a strip of sod until the strip tears. The applied

force at which the sod fails is considered the SS. This measurement is useful in

determining whether a given piece of sod is considered harvestable. Minimum SS values

for commercially harvestable sod range from 20-50 kg depending on the study (Li et al.,

2011). Such values are applicable to standard-size, palletized sod rather than “big rolls”

measuring up to 1.2 m wide and 19.8 m long. Such rolls would require additional sod

strength for harvesting, Researchers have investigated sod grown under climatic and

edaphic environments, as well as several turfgrass species. It is therefore instructive to

consider SS as a function of per unit cross-sectional area to standardize values across

studies. The amount of force per unit cross sectional area can be used to standardize

across sod strip dimensions. The minimum value for thick-cut sod is unknown, but is

likely higher than for standard-depth sod since during handling and installation the sod

must support additional force due to the greater soil weight.

The majority of devices used to test SS are variations of the same basic apparatus. This

type of machine consists of two horizontal platforms. One platform is fixed to the frame

and the other can be slid along a set of tracks. Both platforms have clamps that are

fastened to either end of a sod strip. The original design used by Rieke et al. (1968) used

a bucket hanging from a pulley to apply tensile force to the sod strip. Sand was added to

25

the bucket at a constant rate until the sod failed. The weight of sand in the bucket was a

measure of the sod’s strength. The device described by Jagschitz (1980) invoked an

electric motor to apply the tensile force rather than a sand bucket. A force gauge recorded

the maximum tensile force required to tear the sod strip, which was expressed as a mass

per unit area (i.e., kg dm-1). Other versions of this type of machine incorporated a lever or

wheel and a standard torque wrench. The device built by Parrish (1995) used a lever

mounted on the movable platform, rather than a pulley arrangement. The lever is rotated

up to 20 degrees, which was sufficient displacement to break a sod strip. The maximum

torque required to tear the sod strip was recorded.

A more sophisticated device incorporating an Instron Universal Testing Instrument has

been used in some sod studies (Burns and Futrap, 1979; Ross et al., 1991). The Instron

instrument was a force gauge initially developed for research and quality control of

engineering and textile materials. It can measure the elastic and plastic displacement of

an object as it is broken, with measurements taken at high frequencies throughout the

breaking process. However Burns and Futrap (1979 ) and Ross et al. (1991) adapted the

gauge to test SS. This device has the added advantage of measuring how much total

elongation the sod strip undergoes before tearing. The Instron device also records the

amount of elongation that occurs for each unit of added tensile force (i.e. breakage

pattern).

26

OBJECTIVES

Installation of thick-cut sod is an important strategy for managers of high-end athletic

facilities. By resurfacing a playing field with thick-cut sod, the surface can be used

almost immediately. In some cases, a field may be re-sodded so frequently that the turf

management practices at the sod farm have equal or greater influence on playing surface

quality than the management at the field itself. Despite its widespread use in sports such

as American football, little scientific research has investigated the production of thick-cut

sod. The goals of this research project are:

(1) Maximize divot resistance while maintaining tensile strength of thick-cut KBG

sod through manipulation of pre-harvest cultural practices

(2) Determine the effects of mowing height, sand topdressing, and nitrogen

fertilization on shoot density, thatch accumulation, and below ground biomass and

their relationship to divot resistance

27

MATERIALS AND METHODS

Although thick-cut Kentucky bluegrass sod is commonly installed on NFL playing fields,

little research-based knowledge exists about the production of this type of sod. The

Literature Review section of this thesis summarized the need for thick-cut sod and how

cutting, topdressing, and nitrogen fertilization practices influence the properties of

turfgrass plant communities.

Research was conducted to clarify how cutting, topdressing, and nitrogen fertilization

practices translate to thick-cut sod production, and how they ultimately impact surface

stability on athletic playing fields. This project consisted of two experiments: Experiment

1 – The effects of cutting height, topdressing, and nitrogen fertilizer regime on the divot

resistance of thick-cut Kentucky bluegrass sod, and Experiment 2 – The effects of

varying cutting height on the divot resistance and tensile strength of thick-cut Kentucky

bluegrass sod. The following sections detail how the experiments were conducted.

28


on the divot resistance of thick-cut Kentucky bluegrass sod

Overview of Experiment

Experiment 1 evaluated the effects of cutting height, sand topdressing, and nitrogen

fertilization on several response variables. Plots were subjected to one of two cutting

heights, one of two topdressing treatments, and one of six nitrogen regimes. Response

variables measured in the field included divot resistance, surface shear strength, and sod

tensile strength. Plugs were removed from each plot and analyzed in the laboratory for

thatch thickness and mass, tiller density, and below-ground biomass. The experiment was

replicated at two geographic locations.

Plot Establishment

Field plots for Experiment 1 were established at two locations: the Joseph Valentine

Turfgrass Research Center (“VRC location”- University Park, PA), and Tuckahoe Turf

Farms (“TTF location”- Hammonton, NJ). Tuckahoe Turf Farms holds over 1400 acres

within the New Jersey Pine Barrens, with roughly half the land in cool-season turfgrass

sod production at a given time. The native soils at the TTF location are sands and sandy

loams of fluvio-marine origin (National Resource Conservation Service, 2014). The

sandy texture of these soils makes TTF an ideal location for producing athletic field sod.

The native texture closely mimics that of the sand-based rootzones commonplace at

29

professional sporting venues, thus minimizing the textural discontinuity at the sod-soil

interface. A large discontinuity would likely impede drainage and inhibit root growth by

creating a perched water table (Li et al., 2013). A soil sample taken from the

experimental area contained 0.8% gravel, 85.2% sand, 12.3% silt, and 1.6% clay. A

detailed particle size analysis is given in Table 1. The treatments and experimental design

were identical at the two locations.

Plots were established to a Kentucky bluegrass blend containing the following cultivars:

30% ‘Everest,’ 30% ‘Boutique,’ 30% ‘P-105,’ and 10% ‘Bewitched.’ The experimental

area at the TTF location was seeded in October 2012. The turf that was utilized at the

VRC location was seeded with this blend in August 2012 at the TTF location and later

transplanted to University Park as described below. In both cases the turf was mowed as

necessary and fertilized twice in the fall of 2012, to supply a total of 84 kg N ha-1, 37 kg

P ha-1 139 kg K ha-1.

The sod used at VRC was harvested from the TTF location on April 12, 2013 as 1.21 m

wide x 9.14 m long rolls at a 3.8 cm soil depth. The sod was installed over a rootzone

profile conforming to United States Golf Association (USGA) specifications for greens

construction (USGA, 2004). The profile consisted of a 15 cm gravel drainage blanket

overlain by a 2.54 cm intermediate layer of fine gravel and coarse sand and 25 cm of an

80-20 sand-peat blend. The profile was originally constructed in 2001, and through years

of sand topdressing the rootzone thickness had increased to 35 cm by the time of this

project. The existing sod and top 3.8 cm of the profile were removed to allow the

30

experimental sod to be installed to a flat grade with the surrounding areas. Thus the

rootzone depth prior to sodding was approximately 30 cm. A particle size distribution of

the top 15 cm of rootzone material is shown in Table 2. Plot size at VRC was 1.2 m by

2.4 m. Plots at TTF measured 1.8 m by 1.8 m.

31

Table 1. Particle size distribution for Ap horizon at the TTF location†.

Size fraction Percent of sample

----- mm -----

--- % by mass ---

>2.0

0.8%

2.0-1.0

5.4%

1.0-0.5

23.1%

0.5-0.25

35.2%

0.25-0.15

14.8%

0.15-0.05

6.7%

0.05-0.002 12.3%

<0.002

1.6%

Total 100.0%

† As determined using ASTM F-1632-10 (2010)

Table 2. Particle size distribution of the top 15 cm of rootzone material at VRC†.

Size fraction Percent of sample

----- mm -----

--- % by mass ---

>2.0

0.4%

2.0-1.0

3.9%

1.0-0.5

19.6%

0.5-0.25

46.2%

0.25-0.15

17.6%

0.15-0.05

5.1%

0.05-0.002

4.8%

<0.002

2.4%

Total 100.0%


32

Treatment Application

Plots were subjected to one of two cutting heights (3.18 cm and 3.81 cm). At TTF the

plots were mowed with a 5-reel Jacobsen® fairway mower. At the VRC location plots

were mowed with a walk-behind rotary mower. Plots at both locations were mown twice

weekly. Clippings were returned at both locations.

Sand topdressing treatments were applied to the plots using a drop spreader. The

appropriate mass of dry sand was weighed with a scale and applied evenly in two

directions. Rates were chosen on the basis of the observed thatch development rate. The

first two applications (May and June) were made at 3.4 kg sand m-2 and the September

application was made at 1.7 kg sand m-2 to total 8.5 kg sand m-2 for plots receiving

topdressing. Particle size analyses for the topdressing materials used at both locations

appear in Tables 3 and 4.

Two applications of soluble nitrogen were made to the entire experimental area in early

spring of 2013 (March 15 and April 1) prior to the start of experimental treatments. Each

application equated to approximately 49 kg N ha-1. N treatments included 0, 1, or 2

additional N applications (49 kg N ha-1) during the spring plus either 0 or 1 application

(also 49 kg N ha-1) in the fall. Thus the “negative control” plots received a total of 98 kg

N ha-1 during the entire experiment, while the most heavily fertilized plots received a

total of 244 kg N ha-1. The 244 kg N ha rate was similar to the actual N rate used by TTF

in thick-cut sod production, and thus served as a "positive control." The N source was

33

granular ammonium sulfate (21-0-0). Fertilizer was applied in two perpendicular

directions by hand using a shaker jar. The 12 combinations of topdressing treatment x

nitrogen regime are presented in Table 5.

Due to travel time between the sites, treatments were not applied on the same days at

both locations. However, the treatments were applied on as similar a schedule as possible

to maintain consistency between the sites. Fertilizer and topdressing were applied on the

following dates: 10 May, 6 June, and 6 September (TTF location); 13 May, 9 June, and

12 September (VRC location).

34

Table 3. Particle size analysis for the topdressing sand used at TTF.

Size fraction Percent of sample†

----- mm -----

--- % by mass ---

>2.0

0.0%

2.0-1.0

1.1%

1.0-0.5

15.9%

0.5-0.25

55.3%

0.25-0.15

23.8%

0.15-0.05

2.8%

0.05-0.002 0.8%

<0.002

0.4%

Total 100.0%


Table 4. Particle size analysis for the topdressing sand used at VRC.

Size fraction Percent of sample†

----- mm -----

--- % by mass ---

>2.0

0.0%

2.0-1.0

0.3%

1.0-0.5

36.7%

0.5-0.25

52.5%

0.25-0.15

7.2%

0.15-0.05

0.9%

0.05-0.002 0.8%

<0.002

0.2%

Total 100.0%


35

Table 5. Monthly schedule of topdressing and nitrogen treatments for Experiment 1.

Topdressing

rate

Number of N

applications Mar.† Apr.† May† June† July† Aug.† Sept.† Oct.† Nov.†

-- kg sand m-2 -- -- no. in spring-fall,

respectively --

0 2-0 N N

0 3-0 N N N

0 4-0 N N N N

0 2-1 N N

N

0 3-1 N N N

N

0 4-1 N N N N

N

8.5 2-0 N N T T

T

8.5 3-0 N N TN T

T

8.5 4-0 N N TN TN

T

8.5 2-1 N N T T

TN

8.5 3-1 N N TN T

TN

8.5 4-1 N N TN TN TN

† N indicates an application of 49 kg N ha-1.

T indicates an application of sand topdressing. May and June applications were made at 3.4 kg sand m-2 and September applications were made at 1.7 kg sand m-2.

36

Experimental Design

TTF had previously decided to maintain half of the sod production field utilized in this

experiment at 3.18 cm and the other half at 3.81 cm. While the effect of mowing height

was of interest in this research project (i.e. fixed effect), it was impractical to make

mowing a completely random factor, or even a split-plot or strip-split plot factor. The

time and effort required to mow individual, randomly located plots with the wide gang-

style reel mowers used at TTF would be prohibitive to such a design. Therefore a design

was chosen in which plot areas were established on both ends of the sod field, one under

each MH. The two areas were considered separate experiments and the main effect and

interactions associated with mowing height were tested using a combined analysis and

the error terms specified by (McIntosh, 1983). Within each mowing height “experiment,”

the two topdressing treatments and six nitrogen treatments comprised a 2x6 factorial

experiment arranged in randomized complete blocks with three replications.

Additional Plot Maintenance

Irrigation

At TTF, irrigation water was applied every 3-4 days with a pivot-type irrigation system.

At VRC, overhead irrigation was applied to prevent drought stress. Rainfall data for each

location are presented in the Results section of this thesis.

37

Fertilization

Soil tests revealed low levels of potassium at both locations. Potassium was supplied to

each location via three applications over the course of the season. Each application

consisted of 41 kg K ha-1 from potassium sulfate (0-0-50). No other pH or nutrient

deficiencies were detected.

Plant growth regulators

Beginning in May, all plots were treated with the gibberellin inhibitor trinexapac-ethyl.

At TTF, the TE was applied on 3-week intervals. At VRC, the TE was applied at the label

rate of 0.20 kg a.i. ha-1 every 28 days using a spray volume of 815 L ha-1.

Fungicides

At TTF, one application of propiconazole fungicide was made on 4 June to control rust

disease (Puccinia spp). At VRC, fungicide applications were made on 16 July, 24 July,

and 4 September to control dollar spot (Sclerotinia homoeocarpa) and other pathogenic

fungi. The three applications consisted (respectively) of chlorothalonil, a

vinclozolin/triticonazole tank mix, and a propiconazole/chlorothalonil tank mix.

Herbicides

One application of the pre-emergent herbicide prodiamine was made to the TTF plots on

6 May 2013 as a preventative control of crabgrass. No herbicides were applied at VRC.

38

Insecticides

No insecticides were applied at TTF. At VRC, one application of imidacloprid insecticide

was made on 1 July 2013 to preventatively control white grubs.

Treatment evaluation

Sod was cut and tested November 8-16 at VRC and November 18-22 at TTF. Late

November was chosen because American professional football fields are typically re-

sodded at that time of year. Sod was cut using a Ryan HD walk-behind sod cutter with a

46 cm cutting width. The sod profile was 4.45 cm thick, a standard thickness for sod

installed mid-season on football fields.

Half of each treatment plot was used to evaluate divot resistance and surface shear

strength. This portion of sod was severed from the underlying soil with the sod cutter, but

not removed from the surface. This produced a turfgrass surface that simulated a newly

sodded football field. The other half of each treatment plot was cut and removed to

evaluate sod tensile strength (Fig. 2).

After field measurements were complete, two 5.08-cm diameter cores were removed

from undamaged areas of each treatment plot with a tubular turf plugger (Turf-Tec

International, Tallahassee, Florida). Since the sod in each plot had already been severed

from the underlying soil, each plug measured 4.45 cm high. The cores were refrigerated

39

at 5 °C until they were analyzed. Measurements of thatch thickness, tiller density, thatch

mass, and below-ground biomass were collected from each plug. Both plugs from each

plot were analyzed and the average of the two values was used to represent that

experimental unit.

40

Figure 2. Sod strips being removed for sod strength testing at TTF.

41

Divot resistance

Divot resistance was evaluated with the “Pennswing” apparatus described by McNitt &

Landschoot (2001) and Serensits (2008). Pennswing consists of a pitching wedge golf

club head mounted on a pendulum. A 70 kg lead cylinder is fixed to the shaft to provide

additional force upon impact with the turf (Fig. 3-4). The device is mounted to the three-

point hitch of a tractor. Two adjustable metal pads support the device as it is lowered to

the turf surface. Six 11.3 kg cylindrical weights were secured to the device, to stabilize it

upon club head impact. Two fabric ratchet straps were fastened between the tractor axles

and Pennswing to further secure the device. The pendulum was released from a

horizontal position to ensure a consistent striking force for each divot. The club head

caused partial or complete shearing of the turf as it impacted the surface.

Divot length and width were measured with a standard ruler. Divot depth was measured

using a point gauge (Fig. 5). A “T” shaped rod was fitted into the gauge’s groove, and the

gauge was placed across the divot with its base resting evenly on the divot’s edges. The

rod was lowered to the deepest portion of the divot, the depth recorded and the “blank”

reading subtracted to yield the actual vertical displacement in centimeters.

Plots with small divots were considered to have high divot resistance. The dimensions of

three divots per plot were averaged to produce a representative divot length, width, and

depth for each experimental unit.

42

Figure 3. The Pennswing device about to be released.

Figure 4. Examples of divots produced by Pennswing. Photo at left shows a plot with

low divot resistance while the photo at right shows a plot with high divot resistance. 30

cm ruler included for scale.

43

Figure 5. Point gauge used to measure divot depth. Device is placed across the

divot and the metal rod is lowered to the bottom of the depression. Height is read

and the reference height is subtracted to obtain the divot depth in cm.

Actual divot depth

Reference height

Measured height

44

Shear strength

Shear strength was measured using the Shear Strength Tester (Turf-Tec International,

Tallahassee, Florida). The device was built to replicate the Eijkelkamp device described

in the literature review of this thesis. The vertical fins were inserted into the turf and the

device was rotated slowly with no down pressure until the turf gave way (Fig. 6-7). A

follower needle registered the maximum torque applied to the device in Newton-meters

(Nm). Three shear measurements were taken per plot with the average of the three used

to represent the shear strength of that experimental unit.

Sod strength

Sod strength (SS) was evaluated from the half of each plot not used to measure divot

resistance or shear strength. The apparatus used to measure sod strength was constructed

at Penn State, on the basis of previous published designs (Rieke et al., 1968; McCalla et

al., 2008). The device consisted of two platforms, one fixed to a large metal frame and

the other movable along a set of wheeled tracks (Fig. 8). A sod strip was secured to the

device via two hand-tightened clamps on each platform. Each clamp assembly had

several brass golf spikes on the inward-facing sides, preventing the sod from slipping as

the device was operated. One end of a braided steel cable was attached to the movable

platform, with the other end secured to a force gauge (Chatillon DFS II-1000, AMETEK

Test & Calibration Instruments, Largo, Florida) mounted on the fixed platform.

45

Figure 6. Operation of the shear strength measurement device; handle was

turned clockwise in the horizontal plane until the turf failed.

Figure 7. Fins on the Turf Shear Tester.

46

Figure 8. Operation of the sod strength device.

Figure 9. Sod strip following tensile strength test.

47

To test a piece of sod, a winch connected to the steel cable was activated by a 12-volt

marine battery until the sod ruptured (Fig. 9). The force gauge recorded the maximum

tensile force experienced during the test. STS was recorded for three sub-samples per

plot, which were averaged to produce a representative value for that experimental unit.

Soil volumetric water content

Soil volumetric water content in the top 3.8 cm was recorded for each plot using a Field

Scout TDR 300 probe (Spectrum Technologies, Inc., Aurora, Illinois).The average of

three measurements was used to represent the value for that plot.

Visual turfgrass quality (1-9 scale)

Visual ratings of turfgrass color were recorded in November using a protocol established

by the National Turfgrass Evaluation Program (NTEP) (Morris and Shearman, 1999).

Color was evaluated on a 1-9 scale, with 1 being poorest and 9 being best. A rating of 6 is

generally considered acceptable, though “acceptable” thresholds for turfgrass color vary

according to the turf’s function.

Thatch thickness

Thatch thickness was measured with a standard ruler under the compression of a 450 g

weight. The plug was first placed in a vertically-slit PVC cylinder to enable the plug to be

48

viewed (Fig. 10). The cylinder helped stabilize the weight atop the plug and provided a

straight edge along which to measure the thatch layer.

Shoot density

After thatch thickness was measured, verdure was removed using scissors. Two rubber

bands were placed around the vertical axis of the plug to divide the surface into four

quadrants and simplify the counting process (Fig. 11). The aerial shoots (tillers) on the

plug were counted. This value was divided by the plug’s cross-sectional area to produce a

density value (i.e. number of shoots per unit area).

Thatch mass and below-ground biomass

The remaining portion of the plug was sectioned to separate the thatch layer from the

portion of the plug containing soil (Fig. 12). The soil portion was enclosed between two

60-mesh sieves and immersed in a tub of water. The sieves were agitated by hand to

remove most of the soil from the roots and rhizomes. The total amount of roots and

rhizomes in this portion of the plug was considered below-ground biomass (BGB).

Thatch and BGB were dried in separate crucibles at 60° C. The crucibles were then

weighed, heated to 440°C for 16 hours, and re-weighed. The loss on ignition was used to

represent the mass of the thatch or BGB contained in the plug (Fig. 13).

49

Figure 10. Measurement of thatch layer thickness.

Figure 11. Sample plug following removal of verdure for tiller count

50

Figure 12. Plug being sectioned into thatch portion (lower left) and

soil/below-ground biomass (upper right).

Figure 13. Examples of thatch (left) and washed below-ground biomass

samples (right); top image shows samples before ashing and bottom image

shows the same samples following exposure to 440 °C for 16 hours.

51

Statistical Analysis

Data were subjected to analysis of variance using mixed models in the SAS system (SAS

Institute Inc., Cary, North Carolina). An initial analysis identified large statistical

differences among the two locations, so it was deemed more appropriate to analyze each

location separately, as opposed to pooling data from both locations for a combined

analysis. Within each location, data from both cutting heights were pooled after testing

for homogeneity of variance and the main effect of cutting height was tested as a fixed

effect. This analysis utilized the appropriate error term for combined experiments

(McIntosh, 1983). Topdressing and nitrogen fertilizer regime, as well as the associated

interactions among these factors and cutting height were treated as fixed effects. Block

was nested under cutting height and considered a random effect. Volumetric water

content was used as a covariate in the analyses of field data.

Main effects and interactions were considered statistically significant if an F-test yielded

a p-value less than 0.05. A sole exception was for below-ground biomass data; due to the

high degree of variability normally associated with root quantification, an alpha value of

0.1 was chosen prior to data analysis for below-ground biomass only.

When the p-value was smaller than the critical alpha value, means were separated with

Fisher’s least significant difference (LSD) test. The LSD value expressed the minimum

difference between two treatments necessary for them to be considered statistically

different. Per the stipulations of Fisher’s Protected LSD test, LSD values were not

calculated for analyses yielding non-significant p-values.

52

Selected linear contrasts were computed for the six nitrogen regimes, in order to compare

specific regimes and the individual influences of N rate and N timing. Null hypotheses

for these contrasts appear in Table 6.

Spearman correlation coefficients were calculated to determine whether measured

parameters were linearly related to one another. The measured parameters included divot

length, width, and depth, sod tensile strength, shear strength, thatch mass and thickness,

shoot density, and below-ground biomass.

53

Table 6. Notation for the linear contrasts performed to compare specific N treatments and

treatment combinations.

Contrast label Nitrogen applications†

A 0 fall vs. 1 fall

B 3 total vs. 4 total

C 4 total vs. 5 total

D 3 total vs. all other rates

E 5 total vs. all other rates

†

Each application supplied 49 kg N ha-1. Labels indicate which N treatment

combinations were pooled for the contrast. Nomenclature for each contrast's

null hypothesis is as follows:

A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

54


cut Kentucky bluegrass sod

Overview of Experiment

Space and labor limitations prevented experiment 1 from being conducted at more than

two cutting heights. Experiment 2 was designed to investigate the effects of additional

mowing heights and was conducted only at VRC.

Plot Establishment

Plot establishment for Experiment 2 was identical to that of Experiment 1 at the VRC

location.

Treatment Application

Plots were mown twice weekly at one of four cutting heights (2.54, 3.18, 3.81, or 4.45

cm). All plots were maintained at 3.18 cm for four weeks after sod installation.

Treatments were then "applied” at each mowing event throughout the growing season, up

until the simulated sod harvest.

55

Experimental Design

The experimental design was a randomized complete block. Each treatment was

replicated three times.

Additional Plot Maintenance

Fertilizer and sand applications followed the schedule of treatment 8 in Experiment 1 —

two N applications in the spring, no N applied in the fall, and topdressed three times to

total 8.5 kg sand m-2 (Table 1). Other plot maintenance (irrigation, K fertilization, and

applications of growth regulators/pesticides) was identical to that of Experiment 1.

Treatment evaluation

Data collection for Experiment 2 was identical to Experiment 1. Measurements of divot

resistance, shear strength, sod tensile strength, and turfgrass color were collected in the

field from 8 Nov-16 Nov, 2013. Following field evaluation, plugs were collected from

each plot and analyzed for thatch thickness, tiller density, thatch mass, and below-ground

biomass as in Experiment 1.

Statistical Analysis

Data were analyzed in the SAS system using the GLM procedure. Where statistically

significant differences occurred (p<0.05), means were separated with Fisher’s LSD.

56

RESULTS

The goal of this research project was to optimize cultural practices for thick-cut KBG sod

production, in the context of athlete safety and playability. Several dependent variables

were measured to evaluate the experimental treatments. Divot resistance, sod strength

and shear strength comprised the data collected from the experimental units in the field,

while shoot density, thatch accumulation, and below-ground biomass were evaluated in

the lab from samples extracted from the field plots. Values obtained from these

measurements are presented and compared in this section. Visual assessments of turfgrass

color were also made in November 2013. The visual quality of sod was not a focus of this

project, but these values are included for reference in the Appendix.

This section is divided into three main subsections: one for each experiment described in

the Methods section of this thesis, and a third to present correlations among the measured

parameters. In Experiment 1 notable disparities occurred between the VRC and TTF

locations; thus data are presented separately for the two. The trends across locations are

then compared. Within each location, the results are is further subdivided by response

variable. For consistency, all main effects are presented regardless of statistical

significance.

57


on the divot resistance of thick-cut Kentucky bluegrass sod

Joseph Valentine Research Center (VRC) Location

At the VRC location all dependent variables were significantly affected by at least one

treatment with the exception of divot width (Tables 7-8). Prior research with the

Pennswing apparatus has suggested divot length is the best indicator of divot resistance

while width and depth are mostly controlled by the swing plane and path of the device

(McNitt, 2000; Serensits, 2008). Divot lengths likely have the greatest practical value;

however, divot depths were affected in a similar fashion to lengths. For the sake of

consistency, data treating all three dimensions are reported below regardless of statistical

significance.

58

Table 7. Summary of treatment effects on field parameters in Experiment 1 at VRC

NS = not significant, * = significant at 0.05 level, ** = significant at 0.01 level

Source Degrees of freedom

Divot

Length

Divot

Width

Divot

Depth

Sod

Strength

Shear

strength

Cutting height ( C ) 1 NS NS NS NS *

Block (B) 2 N/A N/A N/A N/A N/A

CB (Error 1) 2 N/A N/A N/A N/A N/A

Topdressing (T) 1 NS NS NS ** **

Nitrogen treatment (N) 5 * NS * ** NS

CT 1 NS NS NS NS NS

CN 5 NS NS NS NS NS

TN 5 NS NS NS NS NS

CTN 5 NS NS NS * NS

Volumetric water content 1 NS NS NS NS NS

Residual error 43

Total 71

59

Table 8. Summary of treatment effects on laboratory parameters in Experiment 1 at VRC.

Source Degrees of freedom Shoot density Thatch Mass Thatch Thickness Below-ground Biomass

Cutting height ( C ) 1 * * * +

Block (B) 2 N/A N/A N/A N/A

CB (Error 1) 2 N/A N/A N/A N/A

Topdressing (T) 1 NS ** ** **

Nitrogen treatment (N) 5 ** ** ** +

CT 1 NS ** NS **

CN 5 NS ** ** **

TN 5 * NS NS NS

CTN 5 NS NS NS NS

Residual error 44

Total 71

NS = not significant, + = significant at 0.1 level * = Significant at 0.05 level,** = significant at 0.01 level

60

Divot length

Cutting height main effect-

Cutting height did not significantly affect divot length at VRC. The mean divot length

values for the two cutting heights were within 1 cm when averaged across all topdressing

and N treatments (Table 9).

Topdressing main effect-

Topdressing did not significantly affect divot length at VRC (Table 10). Topdressed plots

had slightly longer divots when compared to the control receiving no topdressing.

Nitrogen treatment main effect-

Significant differences were observed between nitrogen treatments at the VRC location

(Table 11). The longest divots at VRC were produced on plots receiving the 4-1 N

treatment. Fisher’s Protected LSD test indicated that these divots were larger than divots

from all other nitrogen treatments.

Experimental units treated with the 3-0 N treatment had the shortest mean divot length

(21.0 cm); however, this mean length was not significantly different from any treatment

other than the 4-1 N treatment using the protected LSD separation. (Table 11; Fig. 14).

Selected contrast statements were computed to further compare N treatments (Table 12).

Contrast statements permit comparison of an individual treatment of interest with the

61

mean of several other treatments. For example, the mean divot length of the 4-1 N

treatment was tested against the mean divot length of all other N treatments pooled

together. Additionally the difference between two pre-specified treatment groups can be

tested. For example, Table x also compares the mean divot length of all experimental

units receiving the fall N application (2-1, 3-1, and 4-1 treatments) with the mean divot

length of all those which did not (2-0, 3-0, and 4-0 treatments). In general, plots receiving

three total N applications had shorter divots than those receiving two, four, or five total

applications.

Three contrasts showed statistically significant differences in divot length as a function of

the N treatment. Plots receiving 3 total N applications (mean of 2-1 and 3-0 treatments)

had significantly shorter divots than the four other treatments averaged together. Plots

receiving 4 total applications had shorter divots than those receiving 5 total applications.

Similarly, the 4-1 application schedule had longer divots than the mean of all other N

treatments. The contrast between plots receiving fertilizer in fall and those not receiving a

fall application indicates divot lengths were shorter for the plots not fertilized in fall,

although the difference was small and not statistically significant.

Interactions-

No significant two-way or three-way interactions on divot length occurred at VRC

between cutting height, topdressing, and nitrogen treatment treatments.

62

Table 9. Mean divot lengths for the cutting height main effect at VRC.

Cutting height Divot length Letter grouping

---- cm ---- ---- cm ----

3.18 24.4 -

3.81 23.9 -

LSD (0.05) NS -

Table 10. Mean divot lengths for the topdressing main effect at VRC.

Topdressing applied Divot length Letter grouping

---- kg sand m-2 ---- ---- cm ----

0.0 23.3 -

8.5 25.1 -

LSD (0.05) NS -

Table 11. Mean divot lengths for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Divot length Letter grouping

---- cm ----

2-0 24.7 B

2-1 22.0 B

3-0 21.0 B

3-1 24.3 B

4-0 23.6 B

4-1 29.4 A

LSD (0.05) 4.6 -

† indicates number of N applications (each at 49 kg N ha-1) made in the spring

and fall, respectively

63

Figure 14. Mean divot lengths for the nitrogen treatment main effect at VRC. Treatments

with overlapping error bars are not statistically different using Fisher’s Protected LSD.

10.0

15.0

20.0

25.0

30.0

35.0

2-0 2-1 3-0 3-1 4-0 4-1

Div

ot

len

gth

(cm

)

Nitrogen treatment

(no. of applications of 49 kg N ha-1 in spring-fall, respecitvly)

64

Table 12. Selected contrasts comparing divot lengths at VRC as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Divot length

Difference relative to

second value Pr > F

Statistical

Significance ††

------ cm ------ -------- % --------

A 0 fall vs. 1 fall 23.1 vs. 25.2 -9% 0.115 NS

B 3 total vs. 4 total 21.5 vs. 24.0 -10% 0.131 NS

C 4 total vs. 5 total 24.0 vs. 29.4 -18% 0.009 **

D 3 total vs. all other rates 21.5 vs. 25.5 -16% 0.006 **

E 5 total vs. all other rates 29.4 vs. 23.1 +27% 0.001 **

† Each application supplied 49 kg N ha-1. Labels indicate which N treatment combinations were pooled for the contrast.

Nomenclature for each contrast's null hypothesis is as follows:

A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

††

* = significant at 0.05 level, ** = significant at 0.01 level, *** = significant at 0.001 level

65

Divot width

Cutting height main effect -

Cutting height did not significantly affect divot width at VRC. Divot widths for each

cutting height are presented in Table 13.


Topdressing treatment did not significantly affect divot width at VRC. Mean divot widths

for each topdressing treatment are presented in Table 14.


Nitrogen treatment did not significantly affect divot width at VRC. Mean divot widths for

each topdressing treatment are presented in Table 15.

Interactions-

No significant two-way or three-way interactions on divot width occurred at VRC


66

Table 13. Mean divot widths for the cutting height main effect at VRC.

Cutting height Divot width Letter grouping

---- cm ---- ---- cm ----

3.18 5.3 -

3.81 5.9 -

LSD (0.05) NS -

Table 14. Mean divot widths for the topdressing main effect at VRC.

Topdressing applied Divot width Letter grouping

---- kg sand m-2 ---- ---- cm ----

0.0 5.6 -

8.5 5.7 -

LSD (0.05) NS

Table 15. Mean divot widths for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Divot width Letter grouping

---- cm ----

2-0 5.6 -

2-1 5.3 -

3-0 5.2 -

3-1 6.0 -

4-0 5.6 -

4-1 5.9 -

LSD (0.05) NS -

† indicates number of N applications (each at 49 kg N ha-1) made in the spring and fall,

respectively

67

Divot depth


Cutting height did not significantly affect divot depth at VRC. Divots were slightly

deeper under the 3.81 cm height of cut (Table 16)


Topdressing did not significantly affect divot depth at VRC. The mean divot depth was

equal for experimental units receiving topdressing and those which did not (Table 17).


The effect of nitrogen on divot depths was statistically significant and had a trend similar

to that for divot lengths, though less pronounced (Tables 18-19, Fig. 15). At the VRC

location divot depths ranged from 1.4-1.8 cm for the various N treatments. The highest N

treatments resulted in the deepest divots. The 4-1 N treatment produced divot depths 17%

greater than the mean of all other rates. The fall N application increased divot depth by

14% irrespective of the spring application.

Interactions-

No significant two-way or three-way interactions on divot depth occurred at VRC


68

Table 16. Mean divot depths for the cutting height main effect at VRC.

Cutting height Divot depth Letter

grouping

---- cm ---- ---- cm ----

3.18 1.5 -

3.81 1.8 -

LSD (0.05) NS -

Table 17. Mean divot depths for the topdressing main effect at VRC.

Topdressing

applied Divot depth

Letter

grouping

---- kg sand m-2 ---- ---- cm ----

0.0 1.6 -

8.5 1.6 -

LSD (0.05) NS -

Table 18. Mean divot depths for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Divot depth Letter grouping

---- cm ----

2-0 1.5 C

2-1 1.6 ABC

3-0 1.4 C

3-1 1.8 AB

4-0 1.6 BC

4-1 1.8 A

LSD (0.05) 0.2 -


respectively

69

Figure 15. Mean divot depths for the nitrogen treatment main effect at VRC. Treatments


0.0

0.5

1.0

1.5

2.0

2.5

2-0 2-1 3-0 3-1 4-0 4-1

Div

ot

dep

th (

cm)

Nitrogen treatment

(no. of applications of 49 kg N ha-1 in spring-fall, respectively)

70

Table 19. Selected contrasts comparing divot depths at VRC as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Divot depth


second value Pr > F

Statistical

Significance ††

------ cm ------ -------- % --------

A 0 fall vs. 1 fall 1.5 vs. 1.7 -14% 0.001 ***


C 4 total vs. 5 total 1.7 vs. 1.8 -9% 0.129 NS

D 3 total vs. all other rates 1.5 vs. 1.7 -9% 0.045 *

E 5 total vs. all other rates 1.8 vs. 1.6 +17% 0.008 **

† Each application supplied 49 kg N ha-1. Labels indicate which N treatment combinations were pooled for the contrast. Nomenclature

for each contrast's null hypothesis is as follows:

A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

††


71

Sod strength

Sod strength (SS) was defined as the maximum tensile force recorded during extension of

the sod strip. During harvesting and installation of thick-cut, big-roll sod, the strip may

fall apart into clumps if not sufficiently anchored together by roots and rhizomes. Thus

SS must exceed a minimum threshold to be considered harvestable.


The main effect of cutting height was not significant in Experiment 1 at VRC. SS values

obtained from the two cutting heights were nearly identical (Table 20).


SS was significantly lower for plots receiving sand applications compared to the

untreated control plots at VRC. Mean SS values are presented in Table 21.


Nitrogen treatments significantly affected SS at VRC. Mean sod strength for the six N

treatments ranged from 203.1 kg to 219.3 kg (Table 22).

Lowest SS resulted from the 2-0 and 2-1 N treatments. Sod strength was increased by

additional N applications (i.e. the 3-0, 4-0 or 3-1 treatments), but tended to slightly

72

decline under the 4-1 program (highest N). Using Fisher’s protected LSD, there was no

significant difference among the 3 best-performing treatments.

Selected contrasts were computed to compare the effect of total N rate and make specific

comparisons among N treatments. These contrasts are presented in Table 23. The only

statistically significant contrast was between treatments totaling 3 N applications (2-1 and

3-0) with those including 4 total applications (3-1 and 4-0). While statistically significant,

the difference tested by this contrast was small (3%).

Cutting height x topdressing x N treatment interaction-

The CH x T x N interaction on sod strength at VRC was statistically significant (p=0.03).

Mean values for each three-way treatment combination are presented in Table 24. One

probable reason for the statistical significance of this interaction is that for two N

treatments (3-1 and 4-0) under the 3.18 cm cutting height, topdressed plots actually had

increased sod strength when compared to the non-topdressed control. This reversal of the

overall trend was not observed for any N treatments under the 3.81 cm cutting height.

Given that no significant two-way interactions were present at VRC, the practical value

of this interaction and the exact reasons for its occurrence remain unclear.

Other interactions-

The cutting height by topdressing, cutting height by nitrogen, and topdressing by nitrogen

interactions each were not significant at VRC.

73

Table 20. Mean sod strength values for the cutting height main effect at VRC.

Cutting height Sod strength Letter grouping

---- cm ---- ---- kg ----

3.18 211.7 -

3.81 211.3 -

LSD (0.05) NS -

Table 21. Mean sod strength values for the topdressing main effect at VRC.

Topdressing applied Sod strength Letter grouping

---- kg sand m-2 ---- ---- kg ----

0.0 216.1 A

8.5 206.8 B

LSD (0.05) 4.7 -

Table 22. Mean sod strength values for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Sod strength Letter grouping

---- kg ----

2-0 205.7 BC

2-1 203.1 C

3-0 214.1 A

3-1 212.6 AB

4-0 219.3 A

4-1 214.2 A

LSD (0.05) 8.1 -

74

Table 23. Selected contrasts comparing sod strength at VRC as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Sod strength

Difference relative

to second value Pr > F

Statistical

Significance ††

------ kg ------ -------- % --------

A 0 fall vs. 1 fall 213.0 vs. 210.0 1% 0.186 NS

B 3 total vs. 4 total 208.6 vs. 216.0 -3% 0.014 *

C 4 total vs. 5 total 216.0 vs. 214.2 1% 0.602 NS

D 3 total vs. all other rates 208.6 vs. 213.0 -2% 0.085 NS

E 5 total vs. all other rates 214.2 vs. 210.9 2% 0.327 NS



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

†† * = significant at 0.05 level, ** = significant at 0.01 level, *** = significant at 0.001 level

75

Table 24. Mean sod strength values for the cutting height by topdressing by nitrogen treatment interaction at VRC.

N treatment

Cutting height Topdressing applied 2-0 2-1 3-0 3-1 4-0 4-1 LSD (0.05)

---- cm ---- ---- kg sand m-2 ---- --------------------------------- kg --------------------------------

3.18 0.0 202.3 210.6 226.2 206.3 213.2 228.2 16.2

8.5 201.7 200.5 215.6 217.4 217.2 201.6 16.2

3.81 0.0 219.5 210.3 209.3 219.9 232.9 215.2 16.2

8.5 199.2 190.9 205.0 207.0 213.9 211.9 16.2

LSD (0.05) 16.2 16.2 16.2 16.2 16.2 16.2 -

† indicates number of N applications (each at 49 kg N ha-1) made in the spring and fall, respectively

76

Shear strength

Shear strength at the soil surface is not a direct measurement of divot resistance. The

measurement is performed at a slower rate and interacts with the surface differently than

an athlete’s foot. Still, shear strength can be considered a related measurement because it

evaluates the surface’s resistance to mechanical deformation. It is more rapid and less

destructive than divots produced with Pennswing. Differences in shear strength occurred

due to treatments in this research project (Tables 25-27).


The main effect of cutting height on shear strength was statistically significant at VRC.

The 3.18 cm cutting height produced a mean shear strength 10% greater than that of the

3.81 cm height (Table 25).


Topdressing significantly lowered shear strength at VRC. Table 26 contains shear

strength values for topdressed and control plots at VRC. The mean difference due to

topdressing was 1.9 Nm. The reduced shear strength for topdressed plots was probably

related to the addition of non-cohesive sand particles to system.

77


Nitrogen fertilization did not significantly affect shear strength at VRC and there was

little variation among treatments. Data presented in Table 27 suggest that shear strength

is a function of factors other than N supply.

Interactions-

No significant two-way or three-way interactions related to shear strength occurred at

VRC among cutting height, topdressing, and nitrogen treatments.

78

Table 25. Mean shear strength values for the cutting height main effect at VRC.

Cutting height Shear strength Letter grouping

---- cm ---- ---- Nm ----

3.18 29.7 A

3.81 27.0 B

LSD (0.05) 2.3 -

Table 26. Mean shear strength values for the topdressing main effect at VRC.

Topdressing applied Shear strength Letter grouping

---- kg sand m-2 ---- ---- Nm ----

0.0 30.5 A

8.5 26.1 B

LSD (0.05) 0.6 -

Table 27. Mean shear strength values for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Shear strength Letter grouping

---- Nm ----

2-0 28.4 NS

2-1 28.6 NS

3-0 28.4 NS

3-1 27.8 NS

4-0 28.8 NS

4-1 28.0 NS

LSD (0.05) NS -


respectively

79

Shoot density

The number of turfgrass plants per unit area has been related to playing surface

characteristics including divot resistance, shear strength, surface hardness, and traction

(Shildrick and Peel, 1984; McNitt, 1994; Serensits, 2008). Significant differences and

related trends are described in the following paragraphs.


In Experiment 1, significantly higher shoot density was exhibited at the 3.18 cm cutting

height compared to 3.81 cm (Table 28). When averaged across all nitrogen and

topdressing treatments, the mean increase at was 5%.


Topdressing did not influence shoot density at either location. In fact, the mean values for

this main effect were exactly equal at VRC (Table 29).


Nitrogen fertilizer applications strongly affected shoot density (p<0.001). At VRC,

increased total N consistently produced greater density (Table 30). The fall N application

tended to overwhelm any influence from spring N applications. Treatments receiving N

in September had similar density regardless of the spring N rate; the 2-1, 3-1, and 4-1 N

treatments produced densities of 251, 252, and 256 shoots dm-2, respectively. This result

80

is reasonable since the turf had less time to metabolize the N from the fall application and

equilibrate to its prior shoot density.

However when N was not applied in the fall, higher rates of spring N still had a residual

influence on the stand density 5-6 months later. For example the 3-0 N treatment had

10% greater density than did the 2-0 program. Table 31 shows selected contrasts to

compare shoot density among various N treatments and treatment combinations.

Topdressing x nitrogen interaction-

A significant interaction occurred at VRC between topdressing treatments and N

treatments. The statistical significance of the interaction probably resulted mostly from

the behavior of the 3-1 N treatment when not topdressed (Table 32). When topdressing

was applied, shoot density increased by 44 shoots dm-2 with the 3-1 N treatment

compared to the 3-0 N treatment. In contrast, when not topdressed the density increased

by only 2 shoots dm-2 as N applications increased from 3-0 to 3-1.The reason for these

treatments’ behavior is uncertain. Though statistically significant, the interaction

probably has little practical meaning.

Other interactions-

The cutting height by topdressing, cutting height by nitrogen, and cutting height by

topdressing by nitrogen interactions each were not significant at VRC.

81

Table 28. Mean shoot density values for the cutting height main effect at VRC.

Cutting height Shoot density Letter grouping

---- cm ---- --- no dm-2 ---

3.18 244 A

3.81 232 B

LSD (0.05) 8 -

Table 29. Mean shoot density values for the topdressing main effect at VRC.

Topdressing applied Shoot density Letter grouping

---- kg sand m-2 ---- --- no dm-2 ---

0.0 238 -

8.5 238 -

LSD (0.05) NS -

Table 30. Mean shoot density values for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Shoot density Letter grouping

--- no dm-2 ---

2-0 209 C

2-1 251 A

3-0 230 B

3-1 253 A

4-0 229 B

4-1 257 A

LSD (0.05) 15.9 -

† indicates number of N applications (each at 49 kg N ha-1) made in the spring and

fall, respectively

82

Table 31. Selected contrasts comparing shoot density at VRC as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Shoot density

Difference relative


Statistical

Significance ††

--- no. dm-2 --- -------- % --------

A 0 fall vs. 1 fall 223 vs. 253 -12% <.0001 ***

B 3 total vs. 4 total 240 vs. 241 0% 0.939 NS

C 4 total vs. 5 total 241 vs. 257 -6% 0.076 NS

D 3 total vs. all other rates 240 vs. 237 1% 0.558 NS

E 5 total vs. all other rates 257 vs. 234 10% 0.006 **



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0


83

Table 32. Mean shoot density values for the topdressing by nitrogen treatment interaction at VRC.

N treatment

Topdressing applied 2-0 2-1 3-0 3-1 4-0 4-1 LSD (0.05)

---- kg sand m-2 ---- ------------------------------------- no. dm-2 -------------------------------------

0.0 220 261 230 232 235 250 23

8.5 197 241 230 274 223 263 23

LSD (0.05) 23 23 23 23 23 23 -


84

Thatch accumulation

Thatch is of interest to sod growers and athletic field managers for its influence on

playing surface quality and turfgrass health. In this research project, thatch accumulation

was measured from plugs in terms of both mass (via loss on ignition, LOI) and

compressed thickness (with a ruler). Masses and thicknesses were respectively expressed

as grams of oven-dry organic matter per plug and millimeters of thatch thickness. Cutting

height, topdressing treatment, and N treatment all significantly affected thatch levels.

Two significant interactions, between cutting height and nitrogen and cutting height

topdressing, also occurred.

The relative orders of treatment means were similar between the two measurement

techniques; however, the LOI method detected additional main effects and interactions

compared to the thickness method. The greater inference power of the LOI method was

likely due to its greater measurement precision. Since the two methods were generally in

agreement and highly correlated (r=0.86; p<0.0001), only thatch mass data are presented

in this section. Thatch thickness values for all main effects and statistically significant

interactions are presented in the Appendix (Tables 101-105


Cutting height significantly affected thatch mass at VRC. Table 33 presents thatch mass

values for the two cutting heights averaged across all other treatment levels

85

Thatch mass was greater for the higher cutting height. Plots maintained at 3.81 cm

averaged 12% greater thatch mass than those maintained at the 3.18 cm height. Such an

effect has also been observed in other studies (Murray and Juska, 1970; Shearman, 1980)


Topdressing had a highly significant effect on thatch mass at VRC (p<0.0001). Control

plots produced more than double the thatch of those receiving sand topdressing (Table

34). This treatment effect is logical because the primary goal of topdressing is to

dilute/reduce thatch. A very small amount of thatch still accumulated at the surface of

plots receiving topdressing. However in most cases the layer was so thin that it could

have been eliminated simply by making an additional application of topdressing sand.


Thatch levels at VRC were significantly affected by N treatment. The greatest thatch

levels occurred under the highest N treatments (Table 35). This effect was consistent

across other main effects.

Contrast statements revealed other differences based on N rate and timing. By far the

largest single influence among N treatments was the application of 49 kg N ha-1 in

September. This application increased thatch mass by 15% at VRC. This difference was

also reflected in contrasts between the 4-1 N treatment and the mean of all other

treatments. The 4-1 application schedule resulted in significantly greater thatch than N

86

treatments receiving just one fewer application (i.e., average of the 3-1 and 4-0

programs), and also when compared against all other rates averaged together (Table 36).

A large fraction of these differences probably can be attributed to the additional fall

application.

Cutting height x topdressing interaction-

The cutting height by topdressing interaction was statistically significant at VRC (Table

37). A very small increase in thatch was observed in topdressed plots when moving from

the 3.18 to 3.18 cm cutting height. The effect of cutting height was minimal for un-

topdressed plots but greater for plots receiving topdressing.

Cutting height x nitrogen treatment interaction-

A statistically significant interaction occurred between cutting height and nitrogen

treatment at VRC. Experimental units not fertilized in the fall tended to have more thatch

at the higher cutting height compared to the lower height (Table 38). This may indicate

that under very low or very high N the cutting height has less influence on thatch

accumulation than does the N application schedule.

Other interactions-

The topdressing by nitrogen and cutting height by topdressing by nitrogen interactions

were not significant at VRC.

87

Table 33. Mean thatch mass values for the cutting height main effect at VRC.

Cutting height Thatch mass Letter grouping

---- cm ---- --- g sample-1 ---

3.18 1.49 B

3.81 1.67 A

LSD (0.05) 0.17 -

Table 34. Mean thatch mass values for the topdressing main effect at VRC.

Topdressing applied Thatch mass Letter grouping

---- kg sand m-2 ---- --- g sample-1 ---

0.0 2.26 A

8.5 0.90 B

LSD (0.05) 0.08 -

Table 35. Mean thatch mass values for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Thatch mass Letter grouping

--- g sample-1 ---

2-0 1.29 D

2-1 1.58 BC

3-0 1.49 C

3-1 1.70 AB

4-0 1.57 BC

4-1 1.84 A

LSD (0.05) 0.15 -


respectively

88

Table 36. Selected contrasts comparing thatch mass at VRC as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Thatch mass


second value Pr > F

Statistical

Significance ††

----- no. dm-2 ----- -------- % --------

A 0 fall vs. 1 fall 1.45 vs. 1.71 -15% <0.001 ***




E 5 total vs. all other rates 1.84 vs. 1.53 21% <0.001 ***

† Each application supplied 49 kg N ha-1. Labels indicate which N treatment combinations were pooled for the contrast. Nomenclature for

each contrast's null hypothesis is as follows:

A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0


89

Table 37. Mean thatch mass values for the cutting height by topdressing interaction at

VRC.

Cutting height

Topdressing

---- kg sand m-2 ----

0.0 8.5 LSD

(0.05)

---- cm ---- ------ g sample-1 ------

3.18 2.24 0.73 1.14

3.81 2.27 1.07 0.14

LSD (0.05) 0.14 0.14 -

90

Table 38. Mean thatch mass values for the cutting height by nitrogen treatment interaction at VRC.

N treatment †

Cutting height 2-0 2-1 3-0 3-1 4-0 4-1 LSD (0.05)

---- cm ---- --------------------------- g sample-1 ---------------------------

3.18 1.10 1.57 1.36 1.76 1.55 1.58 0.22

3.81 1.48 1.59 1.62 1.63 1.59 2.11 0.22

LSD (0.05) 0.22 0.22 0.22 0.22 0.22 0.22 -


91

Below-ground biomass

Roots and rhizome are of interest in sod production because they anchor the soil together

and permit the sod to be harvested. They also stabilize the surface and prevent divots

from forming during athletic competition. Thus a larger quantity of BGB is desirable. In

this research project, below-ground biomass was considered any plant material growing

beneath the soil surface. The values are expressed in grams to represent the total mass of

BGB obtained from the cylindrical plugs with 5.08 cm diameter and 4.45 cm height.

Roots were not differentiated from rhizomes. Thatch was removed prior to measurement

of BGB and was discussed in the previous section. Due to the large degree of variability

in sub-surface growth and root recovery during analysis, an α-value of 0.1 was used

during the statistical analyses of BGB measurements.


Cutting height significantly affected below-ground biomass at VRC. BGB increased by

11% under the 3.18 cm cutting height compared to 3.81 cm (Table 39).


Topdressing had a large, statistically significant effect on BGB at VRC. Mean BGB

values were 2.628 g for topdressed plots and 1.442 g for control plots (Table 40).

It is critical to note, however, that despite the magnitude of this effect the addition of

topdressing sand did not necessarily cause the turfgrass plants to produce more roots and

92

rhizomes. A much more likely explanation for this effect relates to partitioning of plant

material in the sample plugs. When sand was applied, the new mineral matter

encapsulated any plant material that had begun to accumulate around the crowns,

effectively raising the soil surface. This caused what would have otherwise been thatch to

become below-ground biomass; this effect is essentially the goal of topdressing. Plots

receiving no topdressing continued to accumulate plant debris at the soil surface (thatch).

During plug analysis this material was removed from the plug and processed separately

from the BGB fraction. Thus the thatch: BGB ratio was altered such that a greater portion

of the plug was considered to be below the soil surface in topdressed plots, compared to

those that did not receive sand applications.


Nitrogen fertilization significantly affected below-ground biomass at VRC. The lower N

rates tended to produce more BGB than did the high N rates (Table 41). The greatest

mean BGB (2.187 g) was observed under the 2-1 N treatment while the lowest mean

value (1.914 g) occurred under the 4-1 N treatment.

Contrast statements revealed additional differences considering the effect of N

fertilization on below-ground biomass at VRC (Table 42). Plots receiving 3 total N

applications (either 2-1 or 3-0) had 8% more BGB than those receiving 4 total

applications and 7% more than all other treatments averaged together. The 4-1 N

treatment (5 total applications) had 7% lower BGB than the average of all other N

treatments.

93

Table 39. Mean below-ground biomass values for the cutting height main effect at VRC.

Cutting height Below-ground biomass Letter grouping

---- cm ---- --- g sample-1 ---

3.18 2.14 A

3.81 1.93 B

LSD (0.1) 0.18 -

Table 40. Mean below-ground biomass values for the topdressing main effect at VRC.

Topdressing applied Below-ground biomass Letter grouping

---- kg sand m-2 ---- --- g sample-1 ---

0.0 1.44 B

8.5 2.63 A

LSD (0.1) 0.10

Table 41. Mean below-ground biomass values for the nitrogen treatment main effect at

VRC.

Nitrogen treatment† Below-ground biomass Letter grouping

--- g sample-1 ---

2-0 2.11 AB

2-1 2.19 A

3-0 2.06 ABC

3-1 1.95 BC

4-0 1.98 BC

4-1 1.91 C

LSD (0.1) 0.17 -

94

Table 42. Selected contrasts comparing below-ground biomass at VRC as related to total both total nitrogen applied and

individual nitrogen treatments.

Contrast label Nitrogen applications†

Below-ground

biomass Difference relative to

second value Pr > F

Statistical

Significance ††

--- g sample -1 --- -------- % --------

A 0 fall vs. 1 fall 2.05 vs. 2.02 2% 0.572 NS

B 3 total vs. 4 total 2.12 vs. 1.97 8% 0.037 *


D 3 total vs. all other rates 2.12 vs. 1.99 7% 0.039 *

E 5 total vs. all other rates 1.91 vs. 2.06 -7% 0.070 +



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

†† + significant at 0.1 level, *significant at 0.05 level, **significant at 0.01 level, ***significant at 0.001 level

95


A significant interaction occurred between cutting heights and topdressing treatments at

VRC. When plots were not topdressed, the two cutting heights produced similar BGB.

However when sand was applied, the 3.18 cm height produced more BGB per core than

did the 3.81 cm height. Table 43 presents values for each combination in this interaction.

This interaction is difficult to explain but conceptually could be a function of root density

with depth. It is possible that plots mowed at 3.18 cm produced most of their roots in the

very top portion of the soil profile. When topdressing was applied, the effective rise of

the soil surface moved the bottom of the sod layer closer to the zone of high root density

for the 3.18 cm plots. The 3.81 cm plots would have had no such zone if their roots were

distributed more evenly with depth. Thus the amount of soil sampled beneath the

topdressing layer would contain fewer roots and rhizomes for the 3.18 cm plugs (see

conceptual model in Fig. 16).

96

Table 43. Mean below-ground biomass values for the cutting height by topdressing

interaction at VRC.

Cutting height

Topdressing

---- kg sand m-2 ----

0.0 8.5 LSD (0.1)

---- cm ---- -------- g sample-1 --------

3.18 1.44 2.83 0.16

3.81 1.44 2.42 0.16

LSD (0.1) 0.16 0.16 -

97

Figure 16. Conceptual model depicting a possible explanation for the cutting height by

topdressing interaction in Experiment 1. Plugs on left have varying BGB density with

depth but contain essentially the same total amount of BGB. Plugs on right have been

topdressed, reducing the fraction of the plug sampled from original soil. Less native soil

is incorporated, resulting in the lower CH plots having greater BGB per plug. Cartoon is

for conceptual purposes only and is not drawn to scale.

98

Cutting height x N treatment interaction-

A significant interaction occurred between cutting heights and N treatments at VRC.

Table 44 contains below-ground biomass for each combination treatment present in this

interaction.

At moderate N levels, the two cutting heights performed similarly. BGB for the cutting

heights was not significantly different under the 3-0, 3-1, and 4-0 N application

schedules. At the very low or very high N levels, the two cutting heights behaved

differently. At two of the lowest N levels (2-0 and 2-1 programs), and the highest N

treatment (4-1) the 3.18 cm cutting height produced more BGB than did the 3.81 cm

height. BGB was reduced by the highest N treatment regardless of the cutting height,

consistent with the N main effect described earlier in this section.

The lower cutting height produced slightly greater BGB irrespective of N rate (CH main

effect). This may have occurred due to the roots being concentrated in the top portion of

the profile for the shorter cutting height. The lower N rates produced greater BGB than

higher N (N main effect). It is possible that a synergistic effect occurred between these

factors- by mowing lower and also applying less N, the benefits of both practices

combined to produce greater BGB than the combined effects of higher cutting height and

also higher N.

99

Table 44. Mean below-ground biomass values for the cutting height by nitrogen treatment at VRC.

N treatment †


---- cm ---- ------------------------------------- g sample-1 -------------------------------------

3.18 2.38 2.36 2.10 2.00 1.88 2.10 0.30

3.81 1.84 2.02 2.01 1.91 2.09 1.73 0.30

LSD (0.1) 0.30 0.30 0.30 0.30 0.30 0.30 -


100

Other interactions-

The topdressing by nitrogen treatment and cutting height by topdressing by nitrogen

treatment interactions both were non-significant at VRC.

101

Tuckahoe Turf Farms (TTF) Location

At the TTF location all dependent variables were significantly affected by at least one

treatment, with the exceptions of divot length and shoot density (Tables 45-46). The

following subsections present data from Experiment 1 at the TTF location.

Divot length


At the TTF location divot length was not significantly affected by cutting height (Table

47). The trend was slightly larger divots at the lower height of cut.


Topdressed plots had a very slight decrease in divot length at TTF, but the effect was not

significant. Mean divot lengths for both topdressing treatments are presented in Table 48.


At TTF, the main effect of nitrogen treatments on divot length was non-significant. Mean

divot lengths for each N treatment appear in Table 49.

Interactions-

No significant two-way or three-way interactions on divot length occurred at TTF among

cutting height, topdressing, and nitrogen treatment treatments.

102

Table 45. Summary of treatment effects on field parameters in Experiment 1 at TTF.

NS = not significant, * = Significant at 0.05 level,** = significant at 0.01 level

Source

Degrees of

freedom

Divot

Length

Divot

Width

Divot

Depth

Sod

Strength

Shear

strength

Cutting height ( C ) 1 NS * * NS *

Block (B) 2 N/A N/A N/A N/A N/A

CB (Error 1) 2 NS N/A N/A N/A N/A

Topdressing (T) 1 NS NS * * **

Nitrogen treatment (N) 5 NS * * * NS

CT 1 NS NS NS NS NS

CN 5 NS NS NS * NS

TN 5 NS NS NS NS NS

CTN 5 NS NS NS NS NS

Volumetric water content 1 ** ** NS NS **

Residual error 43

Total 71

103

Table 46. Summary of treatment effects on laboratory parameters in Experiment 1 at TTF.

Source

Degrees of

freedom

Shoot

density

Thatch

Mass

Thatch

Thickness

Below-ground

Biomass

Cutting height ( C ) 1 NS NS NS +

Block (B) 2 N/A N/A N/A N/A

CB (Error 1) 2 N/A N/A N/A N/A

Topdressing (T) 1 NS ** ** **

Nitrogen treatment (N) 5 NS ** ** NS

CT 1 NS * NS NS

CN 5 NS ** NS NS

TN 5 NS * NS NS

CTN 5 NS * NS *

Residual error 44

Total 71

NS = not significant, + = significant at 0.1 level * = Significant at 0.05 level,** = significant at 0.01 level

104

Table 47. Mean divot lengths for the cutting height main effect at TTF.

Cutting height Divot length Letter grouping

---- cm ---- ---- cm ----

3.18 33.6 -

3.81 29.6 -

LSD (0.05) NS -

Table 48. Mean divot lengths for the topdressing main effect at TTF.

Topdressing applied Divot length Letter grouping

---- kg sand m-2 ---- ---- cm ----

0.0 32.5 -

8.5 30.8 -

LSD (0.05) NS -

Table 49. Mean divot lengths for the nitrogen treatment main effect at TTF.

Nitrogen treatment† Divot length Letter grouping

---- cm ----

2-0 31.2 -

2-1 32.5 -

3-0 33.7 -

3-1 31.1 -

4-0 30.7 -

4-1 30.6 -

LSD (0.05) NS -


respectively

105

Volumetric water content as a covariate with divot length-

Volumetric water content (VWC) was measured with a 3.81 cm time domain

reflectometry probe concurrently with divot production. VWC was used as a covariate

during the analysis of variance for field data. Smaller divots were produced with greater

VWC, though the coefficient of determination was relatively small (r2=0.17) (Fig. 17).

The maximum VWC value was less than 25%. It is unclear why the turf was more divot

resistant under higher moisture contents, as soil cohesion tends to decrease with

increasing moisture content (Dafalla, 2013). However as described in the literature

review section of this thesis, in vegetated soils electrostatic cohesion and friction among

soil particles is considered to be of minimal influence on shear strength compared to root

stabilization. Perhaps this covariance is actually related to another property of the turf

which separately affected both moisture retention and divot resistance. One example is

thatch. The influence of thatch on divot resistance is discussed is discussed in subsequent

portions of this thesis.

106

Figure 17. Scatter plot of divot lengths plotted against volumetric water content in Experiment 1 at TTF.

y = -1.5227x + 63.877

R² = 0.1727

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

15.0 17.0 19.0 21.0 23.0 25.0 27.0

Div

ot

len

gth

(cm

)

Volumetric water content (%)

107

Divot width


Cutting height significantly affected divot width. Wider divots were produced under the

3.81 cutting height than the 3.18 cm height (Table 50)


Topdressing did not significantly affect divot width. Mean divot widths for each

topdressing treatment are shown in Table 51.


The effect of nitrogen on divot widths was statistically significant at TTF (Table 52; Fig.

18). These differences were relatively small (less than 10%). Experimental units

receiving less nitrogen tended to have smaller divots. Table 53 presents contrast

statements comparing the divot widths for individual treatments of interest and selected

treatment groups. These contrasts revealed that treatments including a fall N application

produced wider divots. In addition the divots produced under the 4-1 N treatment were

the widest of any treatment.

Interactions-

No significant two-way or three-way interactions on divot width occurred at TTF among


108

Table 50. Mean divot widths for the cutting height main effect at TTF.

Cutting height Divot width Letter grouping

---- cm ---- ---- cm ----

3.18 7.4 A

3.81 6.8 B

LSD (0.05) 0.4 -

Table 51. Mean divot widths for the topdressing main effect at TTF.

Topdressing applied Divot width Letter grouping

---- kg sand m-2 ---- ---- cm ----

0.0 7.0 -

8.5 7.2 -

LSD (0.05) NS

109

Table 52. Mean divot widths for the nitrogen treatment main effect at TTF.

Nitrogen treatment† Divot width Letter grouping

---- cm ----

2-0 6.8 B

2-1 7.2 AB

3-0 6.9 B

3-1 7.1 B

4-0 7.2 AB

4-1 7.7 A

LSD (0.05) 0.5 -


respectively

Figure 18. Mean divot widths for the nitrogen treatment main effect at TTF. Treatments


5.0

5.5

6.0

6.5

7.0

7.5

8.0

2-0 2-1 3-0 3-1 4-0 4-1

Div

ot

wid

th (

cm)

Nitrogen treatment


110

Table 53. Selected contrasts comparing divot widths at TTF as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Divot width


second value Pr > F

Statistical

Significance ††

------ cm ------ -------- % --------

A 0 fall vs. 1 fall 6.94 vs. 7.29 -5% 0.023 *


C 4 total vs. 5 total 7.11 vs. 7.65 -7% 0.015 *


E 5 total vs. all other rates 7.65 vs. 7.01 9% 0.002 **



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

†† *significant at 0.05 level, **significant at 0.01 level, ***significant at 0.001 level

111

Volumetric water content as a covariate with divot width-

Smaller divots were produced with greater VWC, though the coefficient of determination

was very small (r2=0.04) (Fig. 19). The maximum VWC value was less than 25%. It is

unclear why the turf was slightly more divot resistant under higher moisture contents;

however this degree of association is minimal even though it was statistically significant.

.

112

Figure 19. Scatter plot of divot widths plotted against volumetric water content in Experiment 1 at TTF.

y = -0.0768x + 8.7401

R² = 0.038

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

15.0 17.0 19.0 21.0 23.0 25.0 27.0

Div

ot

wid

th (

cm)


113

Divot depth


Cutting height significantly affected divot depth. Divots were deeper under the 3.18 cm

cutting height than the 3.81 cm cutting height (Table 54).


Topdressing significantly affected divot depth. Experimental units receiving topdressing

produced slightly deeper divots compared to the control (Table 55).

114

Table 54. Mean divot depths for the cutting height main effect at TTF.

Cutting height Divot depth Letter grouping

---- cm ---- ---- cm ----

3.18 1.8 A

3.81 1.6 B

LSD (0.05) 0.2 -

Table 55. Mean divot depths for the topdressing main effect at TTF.

Topdressing applied Divot depth Letter grouping

---- kg sand m-2 ---- ---- cm ----

0.0 1.6 B

8.5 1.8 A

LSD (0.05) 0.1 -

115


The effect of nitrogen on divot depths was statistically significant and had an influence

similar to that for divot widths, though less pronounced (Table 56; Fig. 20). Mean divot

depths ranged from 1.5-1.9 cm for the various N treatments. Divots were deeper under

higher N.

Contrast statements revealed additional differences among N treatments (Table 57). The

higher N treatments resulted in the deepest divots at TTF. The 4-1 N treatment produced

divot depths 11% greater than the mean of all other rates. The fall N application increased

divot depth by 12% regardless of the spring application schedule.

Interactions-

No significant two-way or three-way interactions on divot depth occurred at TTF among


116

Table 56. Mean divot depths for the nitrogen treatment main effect at TTF.

Nitrogen treatment† Divot depth Letter grouping

---- cm ----

2-0 1.5 B

2-1 1.7 AB

3-0 1.6 B

3-1 1.9 A

4-0 1.7 AB

4-1 1.9 A

LSD (0.05) 0.2 -


respectively

Figure 20. Mean divot depths for the nitrogen treatment main effect at TTF. Treatments


0.0

0.5

1.0

1.5

2.0

2.5

2-0 2-1 3-0 3-1 4-0 4-1

Div

ot

dep

th (

cm)

Nitrogen treatment


117

Table 57. Selected contrasts comparing divot depths at TTF as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Divot depth

Difference relative


Statistical

Significance ††

------ cm ------ -------- % --------

A 0 fall vs. 1 fall 1.6 vs. 1.8 -12% 0.001 ***


C 4 total vs. 5 total 1.8 vs. 1.9 -4% 0.393 NS


E 5 total vs. all other rates 1.9 vs. 1.7 11% 0.032 *



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

†† *significant at 0.05 level, **significant at 0.01 level, ***significant at 0.001 level

118

Sod strength


A slight decrease in SS was observed at TTF under the higher cutting height compared to

the lower height, but the effect was not significant (Table 58).


SS was significantly lower for plots receiving sand applications compared to the

untreated control plots at TTF. Mean SS values are presented in Table 59.


Nitrogen treatments significantly affected SS at TTF. Sod strength values by N treatment

ranged from 144.1 kg to 170.2 kg. Mean sod strength values for each N treatment are

presented in Table 60.

The lowest sod strength was produced with the 2-0 and 2-1 N treatments. Sod strength

was increased by additional N applications (i.e. the 3-0, 4-0 or 3-1 treatments), but tended

to decline again under the 4-1 program (highest N). The differences between the 3 best-

performing treatments were not significant.

119

Selected contrasts were computed to compare the effect of total N rate on SS and make

specific comparisons among specific N treatments and treatment combinations. These

contrasts appear in Table 61. The only significant contrast was between treatments

totaling three N applications (2-1 and 3-0) with those including four total applications (3-

1 and 4-0). Making a fourth application increased SS on average by 9% compared to

experimental units receiving only three total N applications.

120

Table 58. Mean sod strength values for the cutting height main effect at TTF.


---- cm ---- ---- kg ----

3.18 160.9 -

3.81 150.8 -

LSD (0.05) NS -

Table 59. Mean sod strength values for the topdressing main effect at TTF.

Topdressing applied Sod strength Letter grouping

---- kg sand m-2 ---- ---- kg ----

0.0 162.3 A

8.5 149.5 B

LSD (0.05) 8.9 -

Table 60. Mean sod strength values for the nitrogen treatment main effect at TTF.

Nitrogen treatment† Sod strength Letter grouping

---- kg ----

2-0 144.1 C

2-1 147.8 BC

3-0 152.2 BC

3-1 170.2 A

4-0 158.1 ABC

4-1 162.8 AB

LSD (0.05) 15.5


respectively

121

Table 61. Selected contrasts comparing sod strength at TTF as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast

label Nitrogen applications† Sod strength


second value Pr > F

Statistical

Significance ††

------ kg ------ -------- % --------


B 3 total vs. 4 total 150.0 vs. 164.1 -9% 0.022 *



E 5 total vs. all other rates 162.8 vs. 154.5 5% 0.234 NS



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0


122

Cutting height x N treatment interaction-

Thus the N treatments did not behave the same way under each cutting height. SS values

for each CH-N combination are presented in Table 62. The statistical significance

resulted from the different trends across nitrogen combinations within each cutting

height. A fairly consistent SS increase was attributed with fall fertilization under 3.81 cm

height of cut. All three levels of spring fertilization (2, 3, or 4 applications), exhibited

greater SS when a fall application was also made. For example, the 2-1 treatment had

26.8 kg stronger SS than the 2-0 treatment. However at the 3.18 cm height this trend was

not evident.

One possible explanation for this phenomenon is that the high CH area responded less

favorably to N applications throughout the year than did the low CH area. As a whole the

area had reduced color and vigor compared to the 3.18 cm area despite receiving an

identical treatment array (Fig. 21; visual quality data presented in Tables 96 and 99 in

Appendix). Thus these plots may have been more deficient throughout the season and

strongly benefited from additional N applied in the fall, whereas the lower CH area was

generally less deficient and failed to show as dramatic a response to additional N in the

fall. The reason for the striking difference in turf quality among CH areas is unclear, and

is not likely to have occurred solely due to cutting height. The reduced quality may have

resulted from irregular plot maintenance, misapplication of a chemical, or other unknown

factors.

123

Table 62. Mean sod strength values for the cutting height by nitrogen treatment interaction at TTF.

N treatment †


---- cm ---- ---------------------------------------------- kg ---------------------------------------------

3.18 160.4 145.4 164.2 173.4 166.5 155.7 30.1

3.81 127.8 150.2 140.2 167.0 149.7 169.9 30.1

LSD (0.05) 30.1 30.1 30.1 30.1 30.1 30.1 -


124

Figure 21. Comparison of the 3.81 cm area (top) and 3.18 cm area (bottom) at TTF.

125

Other interactions-

The cutting height by topdressing, topdressing by nitrogen, and cutting height by

topdressing by nitrogen interactions on sod strength each were not significant at TTF.

126

Shear strength


The main effect of cutting height was statistically significant at TTF. The higher CH

(3.81 cm) produced greater shear strength (Table 63).


Topdressing significantly lowered shear strength at TTF. Table 64 contains shear strength

values for topdressed and control plots at TTF. The mean difference due to topdressing

was 1.9 Nm. However the decrease in shear strength for experimental units receiving

topdressing was relatively small and of questionable practical value.


Nitrogen fertilization did not significantly affect shear strength at VRC and there was

little variation among treatments. Data presented in Table 65 suggest that shear strength

is a function of factors other than N rate.

127

Table 63. Mean shear strength values for the cutting height main effect at TTF.


---- cm ---- ---- Nm ----

3.18 23.1 B

3.81 25.6 A

LSD (0.05) 2.4 -

Table 64. Mean shear strength values for the topdressing main effect at TTF.

Topdressing applied Shear strength Letter grouping

---- kg sand m-2 ---- ---- Nm ----

0.0 25.2 A

8.5 23.5 B

LSD (0.05) 1.0 -

Table 65. Mean shear strength values for the nitrogen treatment main effect at TTF.

Nitrogen treatment† Shear strength Letter grouping

---- Nm ----

2-0 24.3 NS

2-1 23.5 NS

3-0 24.5 NS

3-1 24.6 NS

4-0 25.3 NS

4-1 24.0 NS

LSD (0.05) NS -

† indicates number of N applications (each at 49 kg N ha-1 made in the spring and fall,

respectively

128

Volumetric water content as a covariate with shear strength-

Shear strength tended to increase with moisture content. The coefficient of determination

for this relationship was 0.30 (Fig. 22). As inherent soil cohesion and shear strength of

un-vegetated soil tend to decrease with increasing water content, the relationship

observed here is somewhat puzzling. It is possible that this relationship is actually

capturing a separate property of the experimental units – one which separately increased

both moisture retention and shear strength. One potential property could be thatch

accumulation, as turf with a thicker thatch layer may retain more moisture and was also

positively related to shear strength (see Correlations section below). Thatch also

positively correlated with water content (Fig. 23).

Interactions-

No significant two-way or three-way interactions related to shear strength were detected

at TTF among cutting height, topdressing, and nitrogen treatments.

129

Figure 22. Scatter plot of shear strength plotted against volumetric water content in Experiment 1 at TTF.

.

y = 0.6017x + 12.424

R² = 0.2983

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

15.0 17.0 19.0 21.0 23.0 25.0 27.0

Sh

ear

stre

ngth

(N

m)


130

Figure 23. Scatter plot of thatch thickness plotted against volumetric water content in Experiment 1 at TTF.

y = 0.5594x - 5.9717

R² = 0.1586

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

15.0 17.0 19.0 21.0 23.0 25.0 27.0

Th

atc

h t

hic

kn

ess

(mm

)


131

Shoot density


Shoot density was not significantly affected by cutting height at TTF, although a trend of

higher density at the lower cutting height was observed (Table 66). Experimental units at

the lower height of cut were 9% denser on average.


Topdressing did not affect shoot density at TTF. Mean density values were within 1 tiller

dm-1 (Table 67).


Nitrogen treatment did not significantly affect shoot density at TTF. However a trend was

evident toward greater density values for plots fertilized in the fall (Table 68).

Interactions-

No significant two-way or three-way interactions related to shoot density were detected at

TTF among cutting height, topdressing, and nitrogen treatments.

132

Table 66. Mean shoot density values for the cutting height main effect at TTF.


---- cm ---- --- no dm-2 ---

3.18 231 -

3.81 212 -

LSD (0.05) NS -

Table 67. Mean shoot density values for the topdressing main effect at TTF.

Topdressing applied Shoot density Letter grouping

---- kg sand m-2 ---- --- no dm-2 ---

0.0 221 -

8.5 222 -

LSD (0.05) NS -

Table 68. Mean shoot density values for the nitrogen treatment main effect at TTF.

Nitrogen treatment† Shoot density Letter grouping

--- no dm-2 ---

2-0 216 -

2-1 232 -

3-0 220 -

3-1 222 -

4-0 212 -

4-1 227 -

LSD (0.05) NS -

133

Thatch accumulation

The two measurement techniques used to quantify thatch in this project (mass and

thickness) produced similar results. Since the two methods were generally in agreement

and highly correlated (r=0.86; p<0.0001), only thatch mass data are presented in this

section. Thatch thickness values for all main effects and statistically significant

interactions are presented in the Appendix (Tables 106-109).


Cutting height did not significantly affect thatch mass at TTF. Table 69 presents thatch

mass values for the two cutting heights averaged across all topdressing and N treatments.


Topdressing had a strongly significant effect on thatch mass at TTF (p<0.0001). Control

plots produced more than double the thatch of those receiving sand topdressing (Table

70). This treatment effect is logical because the primary goal of topdressing is to

dilute/reduce thatch. A very small amount of thatch still accumulated at the surface of

plots receiving topdressing. However in most cases the layer was so thin that it could

have been eliminated simply by making an additional application of topdressing sand.

134


Thatch levels at TTF were significantly affected by N treatment. The greatest thatch

levels occurred under the highest N treatments (Table 71). This effect was consistent

across other main effects.

Contrast statements revealed other differences based on N rate and timing (Table 72). By

far the largest single influence among N treatments was the application of 49 kg N ha-1 in

September. This application increased thatch mass by 18% at TTF. This difference was

also reflected in contrasts between the 4-1 N treatment and the mean of all other

treatments. The 4-1 application schedule resulted in significantly greater thatch than N

treatments receiving just one fewer application (i.e., average of the 3-1 and 4-0

treatments), and also when compared against all other rates averaged together. A large

fraction of these differences probably can be attributed to the additional fall application.


The cutting height by topdressing interaction was statistically significant at TTF. A very

small increase in thatch was observed in topdressed plots when moving from the 3.18 to

3.18 cm cutting height. A decrease in thatch was observed at the higher cutting height.

This decrease was likely due to reduced plant vigor rather than a physiological change

associated with the higher cutting height. Mean thatch mass values for all combinations

of the cutting height by topdressing interaction are presented in Table 73.

135

Cutting height x nitrogen treatment interaction-

A statistically significant interaction occurred between cutting height and nitrogen

treatment at TTF. Plots not fertilized in the fall tended to have greater thatch at the 3.18

cm cutting height compared to 3.81 cm. However this effect may have been related to the

reduced vigor of the 3.81 cm area rather than an effect due to cutting height. Table 74

contains thatch mass values for all combinations of the cutting height by N treatment

interaction.

136

Table 69. Mean thatch mass values for the cutting height main effect at TTF.


---- cm ---- --- g sample-1 ---

3.18 1.66 -

3.81 1.49 -

LSD (0.05) NS -

Table 70. Mean thatch mass values for the topdressing main effect at TTF.

Topdressing applied Thatch mass Letter grouping

---- kg sand m-2 ---- --- g sample-1 ---

0.0 2.18 A

8.5 0.97 B

LSD (0.05) 0.15 -

Table 71. Mean thatch mass values for the topdressing main effect at TTF.

Nitrogen treatment† Thatch mass Letter grouping

--- g sample-1 ---

2-0 1.29 D

2-1 1.58 BC

3-0 1.49 C

3-1 1.70 AB

4-0 1.57 BC

4-1 1.84 A

LSD (0.05) 0.146 -


respectively

137

Table 72. Selected contrasts comparing thatch mass at TTF as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Thatch mass


second value Pr > F

Statistical

Significance ††

--- g sample-1 --- -------- % --------

A 0 fall vs. 1 fall 1.43 vs. 1.73 -18% <0.001 ***







A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0


138

Table 73. Mean thatch mass values for the cutting height by topdressing interaction at TTF.

Cutting height

Topdressing

---- kg sand m-2 ----

0.0 8.5 LSD (0.05)

---- cm ---- ------ g sample-1 ------

3.18 2.40 0.92 0.21

3.81 1.97 1.02 0.21

LSD (0.05) 0.21 0.21 -

Table 74. Mean thatch mass values for the cutting height by nitrogen treatment interaction at TTF.

N treatment †


---- cm ---- ------------------------------------------- g sample-1 -------------------------------------------

3.18 1.72 1.55 1.65 1.69 1.47 1.90 0.36

3.81 1.08 1.59 1.24 1.76 1.40 1.90 0.36

LSD (0.05) 0.36 0.36 0.36 0.36 0.36 0.36 -


139

Topdressing x nitrogen treatment interaction-

A statistically significant interaction occurred at TTF between topdressing treatment and

N treatment (Table 75). The relative performance of all N treatments was similar across

topdressing treatments, with the exception of the 4-1 treatment. When topdressed, this N

treatment produced more thatch than other N treatments receiving topdressing. This may

indicate that topdressing was less effective at controlling thatch buildup when plots were

subjected to the highest N level, although it is unclear why this N treatment did not also

produce more thatch than all other N treatments when no sand was applied.


A significant three-way interaction on thatch mass occurred at TTF among cutting height,

topdressing treatment, and N treatment. Table 76 presents thatch mass values for each

three-way treatment combination. Several treatment combinations produced nearly

identical amounts of thatch. All of the highest-thatching combinations did not receive

topdressing (as expected), and the least thatch tended to occur under low N regardless of

cutting height. The statistical significance appears to have resulted from the lesser

separation of N treatments at the 3.18 cm cutting height compared to the 3.81 cm height.

A considerable increase in thatch production was also observed under the 4-1 N treatment

at 3.18 cm cutting height. This trend was not observed at the higher cutting height,

although the 4-1 N treatment still produced the most thatch. While statistically

significant, there was no synergistic trend among cutting height, topdressing, and

nitrogen, so the practical importance of the interaction probably does not supersede the

main effects of each main effect taken individually.

140

Table 75. Mean thatch mass values for the topdressing by nitrogen treatment interaction at TTF.

N treatment

Topdressing applied 2-0 2-1 3-0 3-1 4-0 4-1 LSD (0.05)

---- kg sand m-2 ---- --------------------------- g sample-1 ---------------------------

0.0 2.07 2.29 2.11 2.42 2.00 2.22 0.36

8.5 0.73 0.85 0.78 1.03 0.87 1.58 0.36

LSD (0.05) 0.36 0.36 0.36 0.36 0.36 0.36 -


Table 76. Mean thatch mass values for the cutting height by topdressing by nitrogen treatment interaction at TTF.

N treatment


---- cm ---- ---- kg sand m-2 ---- --------------------------- g sample-1 ---------------------------

3.18 0.0 2.61 2.22 2.42 2.52 2.37 2.60 0.50

8.5 0.82 0.89 0.88 0.85 0.57 1.54 0.50

3.81 0.0 1.53 2.36 1.79 2.31 1.62 2.19 0.50

8.5 0.64 0.81 0.68 1.20 1.18 1.62 0.50

LSD (0.05) 0.50 0.50 0.50 0.50 0.50 0.50 -


141



Cutting height significantly affected below-ground biomass at TTF (Table 77). BGB

increased under the 3.18 cm cutting height compared to 3.81 cm. At TTF, plots

maintained at the lower cutting height had 11% greater BGB than those maintained at the

higher height It is possible that this effect occurred solely due to cutting height, although

the 3.81 cm area had reduced vigor which may have also contributed to the difference.


Topdressing had a statistically significant effect on BGB at TTF. Experimental units

receiving topdressing averaged 2.069 g compared to 1.118 g for the non-topdressed

control (Table 78).

It is critical to note, however, that despite the magnitude of this effect the addition of

topdressing sand did not necessarily cause the turfgrass plants to produce more roots and

rhizomes. A much more likely explanation for this effect relates to partitioning of plant

material in the sample plugs (c.f. p. 93-95 and Table 40).


Nitrogen fertilization did not significantly affect below-ground biomass at TTF. The 4-1

N treatment (most applied nitrogen) produced the lowest BGB, although the magnitude

142

of the difference between this and other treatments was small. Greatest BGB resulted

from the 4-0 N treatment. The second most effective treatment in terms of BGB was the

2-1 schedule. Other N treatments performed similarly (Table 79).


A significant three-way interaction occurred among cutting height, topdressing, and N

treatment (p=0.03). The statistical significance probably resulted mostly from the unusual

pattern exhibited by topdressed plots maintained at 3.18 cm (Table 80). Under lower N

treatments, these plots performed similarly to other CH/T combinations. However their

BGB increased appreciably under higher N, which was contrary to other treatment

schemes. At the highest N level (4-1 treatment) these plots did show a decline in BGB.

The three-way combination of cutting height, topdressing, and N fertilization producing

the most BGB was a 3.18 cm height of cut, with topdressing and the 4-0 N treatment

applied. The combination producing the least BGB was a 3.81 cm cutting height with no

topdressing and the 3-0 N treatment.

As this interaction involves three variables, the mechanisms behind its occurrence are

probably complex. Perhaps the increased vigor of the 3.18 cm area (described earlier in

the SS portion of the Results section) was further stimulated by additional N applications.

The practical implications of the interaction are somewhat unclear, although it does

permit certain treatment combinations to stand out as particularly effective or ineffective

at the TTF location.

143

Other interactions-

The cutting height by topdressing, cutting height by nitrogen, and topdressing by nitrogen

interactions each were not significant at TTF.

144

Table 77. Mean below-ground biomass values for the cutting height main effect at TTF.


---- cm ---- --- g sample-1 ---

3.18 1.67 A

3.81 1.51 B

LSD (0.1) 0.15 -

Table 78. Mean below-ground biomass values for the topdressing main effect at TTF.

Topdressing applied Below-ground biomass Letter grouping

---- kg sand m-2 ---- --- g sample-1 ---

0.0 1.12 B

8.5 2.07 A

LSD (0.1) 0.12 -

Table 79. Mean below-ground biomass values for the nitrogen treatment main effect at

TTF.

Nitrogen treatment† Below-ground biomass Letter grouping

--- g sample-1 ---

2-0 1.51 -

2-1 1.67 -

3-0 1.53 -

3-1 1.58 -

4-0 1.78 -

4-1 1.50 -

LSD (0.1) NS -

† indicates number of N applications (each at 49 kg N ha-1) made in the spring and

fall, respectively

145

Table 80. Mean below-ground biomass values for the cutting height by topdressing by nitrogen treatment interaction at TTF.

N treatment


---- cm ---- ---- kg sand m-2 ---- --------------------------- g sample-1 ---------------------------

3.18 0.0 0.94 1.24 1.07 0.95 1.32 1.52 0.40

8.5 2.15 2.32 1.93 2.44 2.55 1.66 0.40

3.81 0.0 1.14 1.12 0.94 1.09 1.13 0.97 0.40

8.5 1.80 2.02 2.17 1.86 2.10 1.84 0.40

LSD (0.1) 0.40 0.40 0.40 0.40 0.40 0.40 -


146

Variability across locations

Sod performed better at the VRC location than the TTF location with respect to nearly all

measured parameters (Tables 81-82). In the cases of divot length, width, and depth, the

values were larger at TTF than at VRC. Sod strength, shear strength, shoot density, and

below-ground biomass were all greater at VRC than at TTF. An exception to this trend

was thatch development, which was more extensive at VRC than at TTF. This can

probably be attributed to greater total biomass production at VRC due to the more

favorable weather conditions at this location.

Treatment effects were not always equivalent between the locations. For example, the

main effect of cutting height on shear strength was statistically significant at both TTF

and VRC. However at VRC the trend was greater shear strength under the 3.18 cm

cutting height, while the opposite was true at TTF (greater shear strength at the 3.81 cm

cutting height). The cause of this reversal is unclear; in any case, the small differences

due to mowing treatment are probably of little practical value.

In many cases the relative difference between the locations was larger than differences

ascribed to the experimental treatments. This observation highlights the importance of

weather conditions and other turf management practices in addition to the experimental

treatments. In November 2013, measurements were also recorded on sod harvested from

the actual 2013 thick-cut sod production field at TTF. The values obtained from the

147

production field were similar to mean values (averaged across all treatment levels) from

the TTF research plots. These data are presented in the Appendix (Table 91).

Weather conditions

Air temperatures were generally higher at TTF, especially during the months of July and

August (Fig. 24). These conditions were expected due to the more southern latitude of the

TTF location (39.68 deg. N) compared with the VRC location (40.81 deg. N).

During the summer months, high temperatures and humidity are stressful to cool-season

turfgrasses. The higher air temperatures may have contributed to the diminished sod

quality at the TTF location.

148

Table 81. Mean values for field-measured parameters at each location when averaged across all treatment levels.

Divot Sizes

Location Length Width Depth Sod strength Shear strength

-----------------cm----------------- -----kg----- -----Nm-----

VRC 24.2† 5.6† 1.6† 211.5† 28.3†

TTF 31.6 7.1 1.7 155.9 24.4

% change from VRC to TTF +30.6% +26.8% +6.2% -26.3% -13.8%

† denotes the more “preferred” value between the two locations

Table 82. Mean values for laboratory-measured parameters at each location when averaged across all treatment levels.

Location Shoot density Thatch mass Thatch thickness Below-ground biomass

-----no. dm -1----- ----g sample -1---- ------mm------ ----g sample -1----

VRC 238† 1.578 7.3 2.035†

TTF 221 1.578 5.2† 1.594

% change from VRC to TTF -7.1% 0.0% -28.8% -21.7%

† denotes the more “preferred” value between the two locations

149

Figure 24. Mean air temperatures at both locations over the duration of Experiment 1. Lines represent a 5-day moving average of

the mean between daily high and low temperatures. Black bold line at 20 °C represents the temperature considered optimal for

cool-season turfgrasses (Turgeon, 2012). Green arrows represent treatment application dates.

0

5

10

15

20

25

30

35M

ean

dail

y t

emp

era

ture

(d

eg. C

)

Calendar Date

daily mean temperature- TTF

daily mean temperature-VRC

150

Correlations

By measuring the degree of association among dependent variables, ideas can be formed

about which traits are most important in producing sod with excellent athletic playing

quality. Table 83 presents correlation coefficients between each combination of

dependent variables measured in this project.

Numerous significant correlations were detected among plot characteristics. Divot length,

width, and depth were all positively related to one another. This relationship is not

surprising because it is logical that less divot-resistant turf impacted by Pennswing would

be more severely damaged in all dimensions.

All other significant correlations related to divot length were negative. This indicates

plots with smaller divots also tended to have higher sod strength (r= -0.38) and shear

strength (r= -0.47). Divot length also had a significant, negative correlation with thatch

thickness (r= -0.26). In other words, plots with more thatch had larger divots.

The low magnitude and non-significant p-value of the correlation between divot length

and below-ground biomass is somewhat surprising. It might be expected that more

below-ground biomass would be associated with shorter divots. In this experiment thatch

appears to have played a larger role in divot size than did below-ground biomass.

151

Table 83. Spearman correlation coefficients among parameters measured in Experiment1

* = Significant at 0.05 level,** = significant at 0.01 level, *** = significant at 0.001 level

Divot

length

Divot

width

Divot

depth

Sod

strength

Shear

strength

Shoot

density

Thatch

thickness

Thatch

mass

Below-

ground

biomass

Divot

length -- 0.66 *** 0.33 *** -0.38 *** -0.39 *** - 0.09 -0.26 ** -0.11 -0.08

Divot

width -- 0.49 *** -0.52 *** -0.47 *** -0.10 -0.23 -0.05 -0.14

Divot

depth -- -0.04 -0.12 0.07 0.02 0.06 * -0.14 **

Sod

strength -- 0.67 *** 0.30 *** 0.40 *** 0.21 ** 0.19 **

Shear

strength -- 0.26 *** 0.62 *** 0.51 *** -0.24 ***

Shoot

density -- 0.07 0.16 * 0.10

Thatch

thickness -- 0.86 *** -0.64 ***

Thatch

mass -- -0.75 ***

Below-

ground

biomass

--

152

Shear strength and sod strength were highly correlated (r= 0.67) and also had similar

relationships with other properties. High shoot density and greater thatch thickness were

associated with higher shear strength (r=0.26 and r=0.62). Similarly, shoot density and

thatch thickness were positively correlated with greater sod strength (r=0.30 and r=0.40).

Thatch thickness was highly correlated with thatch mass (r= 0.86). This is logical because

the two techniques measure the same property.

Thatch measurements were negatively correlated with below-ground biomass (r=-0.64 for

thatch thickness and r= -0.75 for thatch mass). This could be a function of the plants

partitioning biomass above or below the surface based on cultural and environmental

factors. This strong relationship also could be related to the method in which the sod was

harvested. For all sod strips, the profile was 4.45 cm thick. Thus plots with thicker thatch

layers also had less soil in the sod profile and would tend to also have less below-ground

biomass.

153


cut Kentucky bluegrass sod

Research and anecdotal reports indicate cutting height may influence divot resistance, sod

strength, and related characteristics. The goal of Experiment 2 was to further elucidate

the influence of cutting height on the same parameters measured in Experiment 1. In

Experiment 2, four cutting heights were evaluated under identical fertilization and

topdressing regimes. All plots in Experiment 2 were identically fertilized with the 3-0 N

treatment and were topdressed three times during the season, on the same dates as

Experiment1 plots.

Divot length, width, and depth

Divot sizes were not significantly affected by cutting height in Experiment 2 (Table 84).

The smallest divots were produced under the lowest cutting height of 2.54 cm while the

largest divots were produced under the 3.18 cm cutting height. It is not clear why this

treatment performed so poorly; the same treatment combination in Experiment 1

produced a mean divot length of 24.2 cm and width of 5.0 cm. Perhaps the small number

of experimental units in the experiment was insufficient to obtain a representative divot

size for each cutting height.

154

Table 84. Mean divot dimensions for the four cutting heights evaluated in Experiment 2.

Divot Dimensions

Cutting height Length Width Depth

---- cm ---- --------------------- cm ---------------------

2.54 27.0 5.8 1.5

3.18 34.3 7.4 1.7

3.81 29.2 6.5 2.1

4.45 30.7 7.0 2.2

LSD (0.05) NS NS NS

155

Sod strength

The cutting height treatment significantly affected SS in Experiment 2, with the 4.45 cm

cutting height producing higher SS than all other cutting heights (Table 85). The overall

trend was greater SS under higher heights of cut, but the greatest jump in SS occurred

between the 3.81 cm and 4.45 cm treatments (Fig. 25).

Shear strength

Shear strength was not affected by the cutting height treatments in this experiment (Table

86) although the trend was greater shear strength for lower heights of cut. It should be

noted that the shear strength values obtained in Experiment 2 were similar to those from

plots receiving the corresponding T - N maintenance regime in Experiment 1 (26.7 Nm).

156

Table 85. Mean sod strength values for the four cutting heights evaluated in Experiment

2.


---- cm ---- ---- kg ----

2.54 193.5 B

3.18 203.6 B

3.81 207.8 B

4.45 234.5 A

LSD (0.05) 21.6 -

100.0

120.0

140.0

160.0

180.0

200.0

220.0

240.0

260.0

2.54 3.18 3.81 4.45

Sod

str

ength

(k

g p

eak

forc

e)

Cutting height (cm)

Figure 25. Mean sod strength values for the four cutting heights evaluated in


different using Fisher’s Protected LSD.

157

Table 86. Mean shear strength values for the four cutting heights evaluated in Experiment

2.


---- cm ---- ---- Nm ----

2.54 25.3 -

3.18 24.8 -

3.81 24.5 -

4.45 23.0 -

LSD (0.05) NS -

158

Shoot density

Shoot density was not significantly affected by cutting height in Experiment 2. However

shoot density increased with each incremental decrease in canopy height, showing a 22%

increase from the highest to lowest heights of cut (Table 87; Fig. 26). An analogous trend

was observed in Experiment 1. Increased density under closer mowing is a well-

substantiated phenomenon in turfgrass culture. The lack of a statistical difference among

cutting heights in Experiment 2 probably can be attributed to the small number of

experimental units in this study.

Thatch accumulation

Thatch accumulation was not significantly affected by cutting height in Experiment 2

(Table 88). It is likely that the applied topdressing was sufficient to dilute most of the

thatch, overwhelming any cutting height effect that may have occurred.


Below-ground biomass was not significantly affected by cutting height in Experiment 2

(Table 89). The lack of a statistical difference could be attributed to the small number of

experimental units in this study, or to the application of sand topdressing to all plots

muting the cutting height effect.

159

Table 87. Mean shoot density values for the four cutting heights evaluated in Experiment

2.


---- cm ---- --- no. dm-2 ---

2.54 243 -

3.18 223 -

3.81 214 -

4.45 200 -

LSD (0.05) NS -

Figure 26. Mean shoot density values for the four cutting heights evaluated in Experiment

2. Treatments with overlapping error bars are not significantly using Fisher’s Protected

LSD.

100

120

140

160

180

200

220

240

260

280

2.54 3.18 3.81 4.45

Sh

oot

den

sity

(n

o. d

m-2

)

Cutting height (cm)

160

Table 88. Mean thatch mass values for the four cutting heights evaluated in Experiment

2.


---- cm ---- --- g sample-1 ---

2.54 0.94

3.18 1.13

3.81 0.92

4.45 1.08

LSD (0.05) NS -

Table 89. Mean below-ground biomass values for the four cutting heights evaluated in

Experiment 2.


---- cm ---- --- g sample-1 ---

2.54 2.65 -

3.18 2.61 -

3.81 2.62 -

4.45 2.53 -

LSD (0.1) NS -

161

DISCUSSION

The primary objective of this research project was to maximize divot resistance of thick-

cut KBG sod through manipulation of pre-harvest cultural practices, while maintaining

adequate sod strength for harvesting and installation. Data from each measured parameter

were presented in the Results section. In addition, a number of morphological

characteristics of the Kentucky bluegrass were measured and correlated to the divot

resistance and sod strength resulting from the varying treatments. This section

synthesizes these data and interprets their practical meaning within the context of sod

production and surface performance.

The Discussion section first addresses how the experimental treatments affected divot

resistance, shear strength, and sod strength which are the foci of this research project. A

discussion of the changes in morphological characteristics of the Kentucky bluegrass

resulting from the various treatments and their relationship with divot resistance and sod

strength follows. The section ends with a discussion of future research opportunities and

suggestions.

162

Field Evaluations

Divot Resistance

Cutting height effect on divot resistance

It was somewhat surprising that cutting height had no significant effect on divot

resistance as measured by the length of divots produced with Pennswing. As regular

cutting is the most fundamental practice to turfgrass culture, cutting height has a central

influence on the growth habit and morphology of a sward (Turgeon, 2012). In

Experiment 1, two relatively similar cutting heights were evaluated. The small difference

in cutting heights may have contributed to the lack of a difference in divot length

measurements. Experiment 2; however, contained a wider range of cutting treatments

from 2.54 to 4.45 cm which also had no significant effect on divot length. A slight trend

of smaller divots under lower cutting heights was evident. The shortest cutting height of

2.54 cm produced a mean divot length of 27.0 cm compared with 30.7 cm for the tallest

height of cut (4.45 cm). Experiment 2 contained only 12 total experimental units. Due to

the large degree of variability in the size of divots produced by Pennswing, it is possible

that the number of experimental units in Experiment 2 was too small to accurately

capture the differences in divot resistance.

Aside from the experimental design, cultivar influences and TE-induced growth

regulation may have also masked cutting height effects on divot length. Unpublished data

from research at The Pennsylvania State University suggested very low cutting heights

163

(<2.5 cm), improved divot resistance in Kentucky bluegrass (McNitt, 2014, personal

communication). However this effect occurred only for certain cultivars, while other

cultivars were either not influenced or performed better at higher heights of cut (Fig. 27).

Marked genetic diversity exists among KBG cultivars and other studies have also shown

the cultivar influence to play an integral role in divot resistance (Murphy et al., 2004;

Serensits, 2008; Trappe et al., 2011).

The cultivars used in Experiments 1 and 2 are considered to have compact (‘Everest ‘and

‘Boutique’) and laterally aggressive (‘P-105’) growth habits (Murphy et al., 2004).

Because all plots in Experiments 1 and 2 contained the same cultivar blend, the cutting

height effect could have been muted.

Growth regulation is an additional factor which may have masked potential cutting height

effects on divot resistance. All the turf in both Experiments 1 and 2 was maintained under

growth regulation with trinexapac-ethyl (TE). TE has been shown to produce

morphological effects similar to those observed under close defoliation. For example,

TE-treated plants exhibit a more rapid tillering rate and greater shoot density (Ervin and

Koski, 1998, 2001a). Additionally, TE reduces elongation of leaf blades and sheaths,

producing a compact or “miniature” growth habit (Ervin and Koski, 2001b; McCarty,

2014). It is possible that the growth-regulating effects of TE masked any effects on divot

size which would have otherwise occurred due to cutting height treatments.

164

Figure 27. Divot lengths as affected by a cultivar by cutting height interaction; the unpublished data were provided by McNitt

(2014, personal communication).

0.0

5.0

10.0

15.0

20.0

25.0D

ivot

len

gth

(cm

)

Cultivar

2.22 cm CH

3.49 cm CH

165

Topdressing effect on divot resistance

A potential concern in applying sand topdressing to young sod is the possible decrease in

divot resistance and sod strength. Sand particles possess little inherent cohesion, so if

more sand is applied than can be encapsulated by turfgrass stems and roots, the surface

can become unstable and prone to scuffs and divots.

In this experiment the topdressing treatments did not cause significantly larger or smaller

divots. This result was consistent across all cutting and N treatments, suggesting that 8.5

kg sand m-2 yr-1 is an acceptable topdressing rate under the other cultural circumstances

of this project. In other words it is apparent that when 14-month old KBG sod is

maintained under this range of cutting heights and N rates, applying 8.5 kg sand m-2 will

not influence the sod’s divot resistance when harvested at 4.45 cm depth. The total sand

rate was split over three applications to progressively dilute the organic matter

accumulation and avoid creating a layered profile. Since the application of 8.5 kg sand

m-2 had no effect on divot resistance compared to no topdressing, other rates should be

investigated. Perhaps a lower rate would improve divot resistance or at a minimum

produce similar results to the rate used in this project. The cost of sod production may be

lowered with a lower topdressing rate.

While the results of this project did not indicate a strong relationship between topdressing

and divot resistance, sand topdressing is still recommended to sod growers who produce

166

thick-cut KBG for in-season football field replacements. The current market for thick-cut

in-season sod replacement demands little to no thatch and topdressing is currently the

only effective, non-mechanical method to mitigate thatch accretion. Topdressing is

performed ubiquitously by golf and sports turf managers, especially following core

cultivation, but topdressing during sod production is a relatively new practice. In most

cases the material costs are prohibitive, and benefits of topdressing are not evident when

the sod is produced for applications other than high-end athletic fields. On such fields, the

presence of thatch has been observed to cause more prevalent ‘scuffs’ and sometime

more prevalent divots. Scuffs are defined as when the surface portion of the plant (and

often the thatch) is torn out by athletes maneuvering on the surface wearing cleated

footwear. Typically, scuffs are primarily only an aesthetic concern as grass crowns

remain and regrowth is relatively rapid. However, some observations suggest that thatch

leads to an increase in divots where crown material is also removed. Since a slight

relationship between thatch thickness and divot size was indicated in this research, and

topdressing had no negative effect on divot size, it is suggested that topdressing practices

are continued and more research be conducted to further investigate the effect of various

topdressing types, rates, and timings on divot resistance.

Nitrogen treatment effect on divot resistance

Nitrogen fertilization was the only treatment with a significant influence on divot sizes at

both locations. The highest N treatment (4 applications in spring and 1 in fall, totaling

244 kg N ha-1) produced the largest divots by a wide margin; the mean divot length for

167

this program was 21% greater than the average of all other N treatments and 37% greater

than the most effective treatment (3 spring applications; no fall N). Divot depths were

affected similarly, with the 4-1 treatment producing depths 19% greater than the average

of all other treatments and 29% greater than the most effective treatment (again the 3-0

schedule). At the TTF location no effect occurred on divot lengths, but divot widths and

depths were significantly larger under high N. The 4-1 N treatment produced 9% wider

divots than the mean of all other treatments, and a 12 % reduction in divot depth was

produced by withholding the September N application. High-N plots exhibited darker

green color (data presented in Appendix; Tables 92-100) and had excellent shoot density.

However these traits may come at the cost of reduced divot resistance, which is of greater

consideration than aesthetic appeal on American football fields.

The 4-1 N treatment was the treatment most similar to the fertilization schedule actually

used by TTF in current production of thick-cut sod for NFL stadia. This research project

suggests N rates below the current standard may be advantageous with regard to divot

resistance. During seedling establishment, N was applied on two dates to total 84 kg N

ha-1. After the precursory 98 kg N ha-1 was applied in spring of 2013, the turf had

established 100% ground cover and N treatments began. In this project the smallest

divots were produced with just one additional N application, for a total of 146 kg N ha-1

over the 2013 growing season. This rate is lower than those commonly suggested for

maintenance of Kentucky bluegrass, which are 196-294 kg N ha-1 yr-1 (c.f. Carrow et al.,

2001; Puhalla et al., 2010). Kentucky bluegrass is widely considered by turf managers to

have an N requirement among the highest of all cool-season turfgrass species. A

168

perception also exists among some sod growers that a high N supply can “push” the turf

to accelerate sod development. This perception likely stems from the positive color,

density, and vigor responses to additional N. In the past these sod growers have applied

as much as 400 kg N ha-1 yr-1 to young Kentucky bluegrass sod (McNitt, 2014, personal

communication). No research data are available on the effects of increasing N rates in an

attempt to accelerate sod harvest. However reports from sod industry representatives

indicate such attempts usually fail (Charbonneau, 2000; Cisar, 2000).

Once a new turf reaches a maximum leaf area index, shoot density does not respond to

additional N (Simon and Lemaire, 1987). Furthermore, below-ground responses are

critical for a successful sod harvest and are likely to be hampered by over-fertilization

with N (Badra et al., 2005). Thus a successful post-seeding strategy may be to apply

sufficient N to quickly reach a maximum leaf area index, before “hardening off” the turf

during the summer months. The greater number of individual plants produced during the

spring can then produce more roots and rhizomes as the N supply is subsequently

depleted.

Larger divots under higher N may be attributable to factors including reduced below-

ground biomass, greater thatch, and/or plant succulence. In this project, below-ground

biomass was not significantly correlated to divot length (see Correlations section below),

although smaller divots and greater BGB were both observed under low N treatments.

This effect can likely be attributed to shoot priority, which dictates that as N becomes less

limiting, turfgrasses will preferentially allocate energy to leaf and tiller production rather

169

than growth of subterranean stems and roots (Carrow et al., 2001; Badra et al., 2005;

Bell, 2011).

It must be acknowledged that other benefits to the sod grower are associated with rapid

establishment of contiguous ground cover through high N rates. Perhaps the most notable

are reductions in soil erosion and weed encroachment. In the case of thick-cut sod

production for NFL stadia, the production interval is relatively fixed, so rapid harvest

potential is not a concern. The seeding date is constrained by favorable growing

conditions in late summer the year before the sod harvest, and the harvest date is dictated

by the NFL playing season.

Sod Strength

Estimation of minimum acceptable sod strength

Harvesting and installation of sod requires a minimum level of sod strength. If not

sufficiently knitted, the strip cannot be removed from the sod field and transplanted to a

site without falling apart. Thus SS must exceed a minimum threshold to be considered

harvestable. The minimum acceptable SS for thick-cut sod is higher than for standard-

depth sod due to the greater soil weight; however this value has not been estimated in

prior studies. Published values for minimum acceptable sod strength range from 20-50

kg. These values do not account for varying thicknesses or widths of the sod strips tested

170

in such studies. Additionally the values are applicable to standard-size palletized sod

rather than thick-cut big rolls.

SS can instead be expressed as a function of cross-sectional area to standardize values

across studies and predict SS values for various sod strip dimensions. A minimum

acceptable SS value for thick-cut sod could then be estimated by calculating the cross-

sectional area of a thick-cut, big roll strip and multiplying by the sod strength per unit

area obtained in other studies (Table 90). However this approach would assume SS to be

equal at all vertical positions of the sod strip. As root and rhizome mass nearly always

declines with depth, the bottom portion of the sod strip might be expected to have

relatively lower SS than the upper portions, where more roots and rhizomes reside. Since

all published studies have tested sod with appreciably thinner sod, this method could

underestimate the actual minimum value needed for the harvest.

As opposed to the calculation described above, an estimate for the minimum acceptable

SS for thick-cut, big-roll sod was obtained through direct SS measurements taken at the

TTF location (see Table 91 in Appendix). Three-month old Kentucky bluegrass sod was

harvested at 4.45 cm soil depth, as for Experiments 1 and 2. At the date of testing, TTF

personnel considered this sod to be slightly below the minimum strength needed to

harvest it in big rolls at 4.45 cm depth. The mean SS for this sod field was 39.0 kg. Thus

a very conservative estimate of 100 kg was chosen as the minimum SS needed to

successfully harvest, transport, and install thick-cut, big-roll sod in this research project.

171

Sod strength was significantly affected by all three treatments: cutting height,

topdressing, and nitrogen fertilization. The following subsections relate these effects to

related literature and practical considerations.

172

Table 90. Comparison of data collected in Experiment 1 with selected published values for KBG sod strength on a per-unit-area

basis.

Reference Sod age Sod strength† Sod strength

per unit area Comments

mo. after

seeding ---- kg ---- ---- kg dm-2 ----

Experiment 1- VRC location 14 232.9 114.6 -

Experiment 1- TTF location 14 173.4 85.3 -

Ross et al., 1991 7 30.1 154.4 greenhouse experiment

Heckman et al., 2001 27 65.8 101.8 sod heating study

Shearman et al., 2001 12 62.0 172.2 cultivar evaluation

Kowalewski et al., 2008 11 84.1 96.6 field experiment

Li et al., 2011 14 27.1 71.0 conducted on high clay soil

173

Cutting height effect on sod strength

Cutting height had only a small influence on sod strength. No significant effect was

detected in Experiment 1, which tested heights of 3.18 and 3.81 cm. In Experiment 2, sod

tensile strength increased with cutting height, but the highest cutting height of 4.45 cm

was the only treatment statistically different from the others. While sod strength was

slightly reduced for the lower cutting heights, 2.54-3.81 cm heights still produced

adequate tensile strength for a thick-cut, big-roll harvest (well above 100 kg). These data

dispute prior anecdotal concern that maintaining the sod under cutting heights less than

3.81 cm could weaken the root system and result in unharvestable sod. Cutting height

should instead be chosen to match the eventual maintenance cutting height chosen by the

football field manager. This CH is typically between 2.54 and 3.81 cm. Cutting height

should therefore fall within this range, which falls on the low end of cutting heights to

which KBG is adapted (Turgeon, 2012). Producing sod for in-season replacements at a

CH greater than 3.81 cm is not recommended since the canopy height will be likely be

lowered at the stadium to about 3.18 cm. This severe reduction could weaken the turf by

compounding the stressful conditions imposed during the sod harvest and transport

process (Crider, 1955). The lower cutting height would also aid in more rapid

establishment from seed (Brede and Duich, 1984).

174

174

Topdressing effect on divot resistance

Topdressing reduced sod strength by 6% on average. The mean sod strength for

topdressed experimental units was 149.5 kg at the TTF location and 206.8 kg at the VRC

location. These values would still be considered more than adequate for a thick-cut big-

roll harvest sod strength (>100 kg). Care should still be taken to avoid over-application of

sand, as this could reduce SS below critical levels.

Nitrogen treatment effect on divot resistance

Highest sod strength was obtained with 196 total kg N ha-1. At the TTF location the

greatest sod strength was 375 kg under the 3-1 N treatment. At the VRC location the

highest SS was 483 kg under the 4-0 N treatment. At both locations these “optimum”

treatments were not statistically different from any other N treatments receiving 144 or

196 kg total N (3-1, 4-0, or 4-1 treatments). No N treatments produced unharvestable sod;

consequently, growers can apply N at the rates which optimize divot resistance without

fear of deleterious effects on sod strength.

Other recent work with KBG suggested slightly lower N (120 kg N ha-1) produces

optimum sod strength (Li et al., 2011). However the study by Li et al. (2011) was

specifically conducted to evaluate sod production on clayey soil. The soil used in their

experiment contained 52% clay and 46% silt, and also contained 4.2% organic matter by

mass. The soil in this research project was a loamy sand with nearly 90% sand and just

175

175

1.2% organic matter. It might be hypothesized that the clayey soil used by Li et al. (2011)

would have had less N leached from the profile, as well as more microbial mineralization

of organic N during the season. These differences in soil properties may help explain why

higher N rates produced greater sod strength in the current research project.

Shear Strength

Shear strength was measured with the Turf-Tec Shear Strength Tester, the same device

currently utilized by the NFL in their Game Day Certification program. The device does

not measure divot resistance, but is a related measurement and is more portable and less

destructive than Pennswing. It was used in Experiments 1 and 2 to compare shear

strength values with the divot sizes produced using Pennswing.

Cutting height effect on shear strength

Cutting height had a varied effect on shear strength. In Experiment 1 at VRC, shear

strength was significantly greater under higher cutting heights, while at TTF the opposite

occurred. No significant difference occurred in Experiment 2 across the four cutting

heights, although the trend was greater shear strength for higher heights of cut.

Regardless of the statistical outcome, all these differences were small and of little

consequence. Nearly all shear strength values were above 20 Nm, considered

“exceptional” by the shear strength device’s manufacturer (Mascaro, 2013). Typically,

the shear strength of all newly installed sod in NFL stadia measure high in shear strength.

176

176

The shear strength is diminished as the above-ground verdure and below-ground biomass

are reduced by traffic (Serensits, 2008; Kowalewski et al., 2011). Most research on shear

strength therefore includes a simulated wear component to better elucidate the treatment

responses. As no wear was applied in this project, it is likely that any cutting height

effects on shear strength were less important than the fact that all plots had 100%

vegetative cover.

Topdressing effect on shear strength

Topdressing significantly reduced shear strength at both locations. The engineered sands

used for topdressing have little cohesion and this property is likely responsible for the

reduction in shear strength observed for topdressed sod. This is probably the same

phenomenon responsible for slightly lowered sod strength due to topdressing. The

magnitude of the shear strength differences were small, and the benefits of topdressing in

order to offset thatch buildup probably outweigh any marginal decreases in shear

strength.

Nitrogen treatment effect on shear strength

When averaged across all other treatment levels, nitrogen treatments had no statistical

effect on shear strength, nor did they result in any discernable trend. All mean shear

strength values were very similar among nitrogen programs. This result was somewhat

177

177

surprising given that divot sizes were larger with the highest N inputs. While shear

strength and divot resistance may be considered related properties, the direction and

magnitude of the force created by Pennswing is quite different from that of the shear

vane. In addition, the shear vane was designed as a simple device for rapid field

measurements, rather than a precise research tool. Serensits (2008) found that the shear

vane was less sensitive than Pennswing in detecting differences among treatments.

Turfgrass morphological characteristics

Various morphological characteristics of the turf that have been previously described

were measured for each plot in these experiments. These characteristics were evaluated

for their known or purported relationships to divot resistance. This section discusses the

effect of the cutting height, topdressing, and nitrogen fertilization regime on these

morphological characteristics in November 2013, when divot size and sod strength was

measured.

Shoot density

Cutting height effect on shoot density

Shoot density was significantly affected by cutting height. As commonly reported, the

lower height of cut produced greater density at both locations. This phenomenon occurs

as the turfgrass plants attempt to maintain a constant total leaf area under more severe

defoliation (Eggens, 1981). However the small increase in density may be solely of

178

178

aesthetic value, as the increased density did not correlate to divot size (see Correlations

sub-section below).

Topdressing effect on shoot density

Topdressing had no significant effect on shoot density at either location. Shoot density

was essentially equal for topdressed and untreated plots.

Nitrogen treatment effect on shoot density

Nitrogen treatment significantly affected shoot density. Higher spring N rates resulted in

higher November shoot density if no N was applied beyond June. This difference was

observed in November - several months after the last spring N application. However,

when a September N application was made, any influence from spring fertilization rate

was masked. Each of the three treatments receiving a fall N application had statistically

equal density regardless of differences in spring application rate. A practical implication

of this finding is that even under low total N (desirable for greater divot-resistance), high

November shoot density could be achieved by using little N in the spring and making a

single N application in the fall. This could produce denser, more aesthetically pleasing

turf without compromising divot resistance.

179

179

Thatch

Cutting height effect on thatch

At the VRC location, a small but statistically significant difference in thatch

accumulation was detected among cutting height treatments. Thatch mass was 12%

greater at the higher CH of 3.81 cm. Such an effect was not observed at TTF. A positive

relationship between height of cut and thatch accumulation is consistent with prior

research (Murray and Juska, 1970; Shearman, 1980). The practical value of this

difference is unresolved, as the integration of other cultural practices (specifically

nitrogen management and topdressing) and turfgrass genotype can complicate the cutting

height influence (see Results section; c.f. Shearman, 1980).

Topdressing effect on thatch

Topdressing significantly reduced thatch levels; an expected result, as thatch dilution is a

primary goal of topdressing (Turgeon, 2012). The total sand rate of 8.5 kg m-2 reduced

the mean thatch mass to 0.94 g per plug, compared 2.23 g for the control plots. It is

important to apply the sand in light, frequent doses to incorporate the material evenly and

avoid creating layers in the soil profile. Such layers could become shear planes along

which divots could form due to restricted drainage and rooting.

180

180

Nitrogen treatment effect on thatch

Greater N rates significantly increased thatch in Experiment 1. This result is consistent

with some prior thatch research (Duncan and Beard, 1975; Weston and Dunn, 1985)

although such a result is not always obtained under higher N (Shearman, 1980; Carrow et

al., 1987). The discordance among research trials can probably be associated to the

complexity of the thatch system, which contains many interacting components including

species/cultivar, weather, irrigation frequency, and soil conditions (Waddington, 1992).

The simplest explanation for increased thatch under high N is greater total biomass

production. The turfgrass plants grow more vigorously, thus fixing carbon at a greater

rate than microbial organisms can decompose the biomass. However, a complication in

ascribing thatch levels solely to N supply is that most N fertilizers are weak acidulants.

Soluble ammonium N sources (such as the ammonium sulfate used in this study) tend to

decrease soil pH and slow microbial breakdown of thatch with greater application rates.

This process may occur over longer time scales than the 14 months spanned by this

project, although the coarse texture and low buffering capacity of the soil would indeed

be conducive to rapid pH shifts. Prior to the initiation of treatments, a composite sample

from each location indicated pH values of 6.4 and 6.5 at TTF and VRC, respectively. Soil

pH was not measured in Experiments 1 or 2 following the initiation of treatments.

181

181


Cutting height effect on below-ground biomass

In Experiment 1, the lower cutting height (3.18 cm) produced significantly higher below-

ground biomass in the 4.45 cm-thick sod profile than did the higher cutting height (3.81

cm). This result was observed at both TTF and VRC. This effect was not observed in

Experiment 2, although the small number of experimental units may have contributed to

the lack of a trend.

It is well-understood that gross root mass is diminished by closer cutting (Juska and

Hanson, 1961; Eggens, 1981; Shearman, 1989). However, divot resistance and sod

strength are not influenced by roots deep in the profile. It is thus desirable to maximize

BGB within the 4.45 cm sod layer. Unpublished research has suggested that while close

cutting reduces overall BGB production, root and rhizome density in the uppermost

portion of the profile is actually increased. (McNitt, 2014, personal communication).

Data from this project would support such a phenomenon, as the 4.45 cm sod profile

contained greater BGB under the lower of the two heights. The reduced vigor of the 3.81

cm area at TTF could also have contributed to the significant difference at TTF.

Topdressing effect on below-ground biomass

Topdressing significantly increased below-ground biomass. However this effect was most

likely due to the sampling method rather than the grass actually producing more BGB as

182

182

a result of sand applications. Topdressed plots had sand incorporated among the majority

of their rhizome and crown tissues, while this same material became thatch for control

plots. Thus similar plant material was classified differently among topdressing

treatments, and the literal result of this effect does not have a practical meaning.

Nitrogen treatment effect on below-ground biomass

Nitrogen treatment significantly affected below-ground biomass at the VRC location,

though this trend was not observed at the TTF location. Higher N rates decreased below-

ground biomass. This result is consistent with the volume of research showing higher N

decreases root: shoot ratios and favors partitioning of axillary buds to tillers rather than

rhizomes (McIntyre, 1964; Goss and Law, 1967; Adams et al., 1974).

Correlations among measured parameters

While statistically significant correlation among the various parameters were found, few

very strong and meaningful relationships were detected. Divot length was perhaps the

most important characteristic measured in this experiment. Divot length significantly

correlated with divot width and depth (r=0.66 and 0.33 respectively). It is logical that for

a less divot-resistant plot, divots would be larger in all three dimensions. Divot length is

considered the best indicator of divot resistance and had the strongest relationships with

other measured parameters.

183

183

Curiously, divot length was negatively correlated with thatch thickness (r=-0.26). This

finding is contrary to the prevailing opinion among turf managers that thatch increases

divoting. In this project experimental units with greater thatch levels tended to produce

smaller divots, although such an association does not necessarily reflect a causal

relationship. It is possible that the perceived association between thatch and more

divoting is related to the scuffing effect previously described in this Discussion section.

During competition, athletes’ cleated footwear tends to tear the turfgrass shoots and small

portions thatch from the surface, colloquially termed “scuffs.” Scuffs differ from divots

in that after a scuff forms the turfgrass crowns remain intact and little soil is removed.

Scuffs therefore pose little threat to player safety and performance, yet the prevalence of

scuff debris across the surface is unsightly and can contribute to perception that the

surface is unstable. While Pennswing simulates the severe impact energy of a large

athlete contacting the surface at high speed, it does not capture the surface disruption

caused by frequent, less intense athletic maneuvers also performed during competition.

Informal observations during data collection indicated that upon impact the club head

tended to “bounce” on plots with greater thatch while on plots with less thatch the club

was more likely to penetrate through the thatch and into the underlying soil to produce a

divot. The relationship between thatch and divot resistance is not fully resolved and

merits further study. A device which more accurately simulates athlete-to-surface contact

should be developed.

184

184

Thatch mass and thickness were each positively correlated with sod strength (r=0.21 and

0.40 respectively). The experiences of TTF growers corroborate the notion that a thatch

layer increases sod strength (J. Betts, 2013, personal communication). Increased N levels

tended to produce more thatch, less below-ground biomass, and also greater sod strength.

Perhaps the thicker thatch layer helped prevent a decrease in SS, which would have

otherwise been expected with reduced below-ground biomass. A similar relationship was

observed for shear strength (r=0.62 with thatch mass; r= 0.51 with thatch thickness).

These correlations probably resulted from the looser surface produced by topdressing

treatments, which simultaneously reduced thatch levels. Greater thatch levels have been

previously related to increased surface shear strength (Shildrick and Peel, 1984; Chivers

et al., 2005)

Shoot density was positively correlated with sod strength (r=0.30) but not significantly

related to divot resistance. Other research has related shoot density to divot resistance on

a trafficked football field (Serensits, 2008). However, the current study did not include a

simulated wear treatment to thin plots. The absence of traffic may account for the lack of

a significant correlation between density and divot resistance. The fact that all

experimental units had 100% turfgrass cover may have diminished the importance of

density.

Shoot density was significantly correlated with shear resistance, although the correlation

was not strong (r=0.26). Contrary to Pennswing, this relationship indicates the Turf Shear

Tester still detected density differences under conditions of 100% ground cover. Shoot

185

185

density was also positively correlated with shear strength in other studies (Shildrick and

Peel, 1984; Serensits, 2008).

Potential for related future research

Fraise cutting

Minimizing thatch buildup is a common objective of turf managers. In this project light,

frequent topdressing applications mitigated thatch. Other means of thatch control are

available. A novel method of thatch removal is colloquially known by practitioners as

fraise cutting or “KORO-ing,” in reference to inventor Ko Rodenburg (KORO by Imants,

2014). KORO machines utilize an array of toothed, helical blades to grind away the green

verdure and thatch, leaving only rhizomes and crowns intact. The waste debris is

deposited into a hopper via conveyor belt and removed from the system. With proper

management the turf will regenerate from the remaining meristems.

Mechanical thatch control methods are not usually practiced by sod growers due to their

expense and negative impact on sod strength. If used to control thatch in sod fields, the

turf would need time to regenerate before being harvested- extending the production

period and raising the production cost. However if fraise cutting or related practices were

able to produce a marked increase in divot resistance, it is likely sod growers would adopt

these practices for high-end thick-cut sod. Customers would be willing to bear the

increased cost in exchange for the increase in quality.

186

186

Anecdotal evidence suggests that following fraise cutting, regenerated turf has intact

rhizomes and excellent stability (Minnick and Reed, 2013). Perhaps these observations

are related to an apical dominance phenomenon, which is described in the following

section on verticutting. The observations may also result from abundant generation of

young, very photosynthetically active leaf tissue (Dunn and Engel, 1971), or simply to a

reduction in thatch. Research is needed to determine the value of fraise cutting during

production of thick-cut KBG sod.

Verticutting

Practitioners have reported greater divot resistance following mechanical cultivation and

attribute it to increased rhizome production. Divot resistance was in fact improved by

cultivation in the work by (Serensits, 2008) despite no measured change in root or

rhizome mass due to aerification and vertical mowing. Greater rhizome production

following verticutting has not been substantiated in field research trials, but the

phenomenon would agree with fundamental experiments on rhizomatous grass plants

(McIntyre, 1970; Mcintyre and Cessna, 1998). Several experiments with quackgrass

(Elytrigia reptans) showed that by severing rhizomes, undeveloped rhizome buds were

released from apical dominance and developed as new rhizomes and aerial shoots.

Dominance of rhizome apices and parent shoots over rhizome lateral buds by is a

complex phenomenon also governed by temperature, photoperiod, and N availability.

These environmental signals moderate various hormonal feedback loops involving

187

187

auxins, abscisic acid, gibberellins, and ethylene (Gang, 2013). More research is needed to

better understand these processes and whether they occur with KBG in a field setting,

where significant interplant competition exists for light, water, nutrients, and physical

space.

TTF has in fact attempted to verticut KBG for thatch control prior to a thick-cut sod

harvest. The subsequent harvest failed due to insufficient sod strength. A post-verticut

addition of sand topdressing buried the remaining thatch layer, which coupled with

unfavorable weather conditions may also have contributed to the failed harvest.

Verticutting warrants a more controlled evaluation with regard to timing and intensity of

cultivation events before definitive claims can be made about its influence on sod

strength and divot resistance.

Nitrogen and divot resistance on established turf

This study tested divot resistance of immediately after sod installation. Nitrogen had an

influence on divot resistance in this project and has previously been shown to impact

wear resistance and subsequent recovery (Canaway, 1984; Carroll and Petrovic, 1991;

Hoffman et al., 2010). Thus a study could test N treatments during sod production, with

the addition of a simulated wear component following installation. Such an experiment

would help evaluate the pre-conditioning N programs’ efficacy over the duration of the

sod’s lifetime (typically 4-6 NFL games). However, it should be noted that during the

188

188

time of year when thick-cut sod is typically installed, turf recovery is minimal due to low

light and temperature conditions. Thus wear tolerance is mainly a function of divot

resistance immediately after harvest (as tested in this project) and N supply would be

expected to have a lesser effect due to reduced growth potential.

Nitrogen effects on divot resistance for established turf

Voluminous research data exist with regard to the effects of nitrogen fertilization on

athletic field wear tolerance. However these studies have used percent ground cover,

turfgrass color, or other visual ratings to evaluate wear tolerance (e.g. Canaway, 1984;

Carroll and Petrovic, 1991; Sorochan et al., 2001). In the case of NFL or facilities with

infrequent yet intense usage, divot resistance may be a more important response variable.

Nutrient requirements can vary considerably between newly established and mature turfs.

Since the current experiments geared toward sod production showed N to be important in

optimizing divot resistance, the effects of N on the divot resistance of established turf

warrant study.

Improved research tools for evaluating divot resistance

In this project, both Pennswing and the Shear Strength Tester detected differences among

treatments, although different treatments affected the two measurements. Nitrogen

treatment was the only factor to affect divot sizes produced by Pennswing, but the two

other treatments (cutting height and topdressing) affected shear strength. The shear vane

189

189

probably does not simulate a divot-forming impact as well as the pendulum device, but it

was still able to detect treatment effects of cutting height and topdressing in this project.

In the work by Serensits (2008) the shear vane was less sensitive in detecting differences

among treatments than Pennswing.

While significant differences in the size of divots produced by Pennswing were detected

in this study, turfgrass researchers would benefit from an improved divot production

device. Most devices designed to test divot resistance are inserted into the turf at a

specified depth before being activated in order to produce a divot. An example is the

Clegg Turf Shear Tester. This device utilizes a paddle inserted into the soil, which is then

rotated about a horizontal axis to produce surface disruption. Pennswing forcefully

impacts the surface from above without prior insertion, as is the case during actual

athletic competition. However Pennswing may not accurately simulate the actual

magnitude or direction of forces imparted to the surface by athletes with studded

footwear. A divoting device which better simulates these forces should be developed for

future studies and compared to the current methodology. Ideally such a device would use

the actual studded footwear used by professional athletes, a feature of the traction testing

device described by McNitt et al. (1997). An improved divoting device should also utilize

various loading weights and permit significant flexure upon impact with the surface in

order to allow divot size to be more sensitive to the turf properties than the device’s

dimensions. Finally it would be advantageous if the device were more portable, in order

to permit measurements to be taken at various sites.

190

190

SUMMARY AND CONCLUSIONS

The goal of this project was to optimize the divot resistance of newly installed thick-cut

Kentucky bluegrass sod. Data from the experiments can inform cultural management

strategies during the sod production period, prior to harvest and installation.

Cutting height did not significantly affect divot resistance. The uniform blend of cultivars

and application of trinexapac-ethyl to all experimental units may have overshadowed the

influence of cutting height on plant morphology and divot resistance. Of the two heights

evaluated in this study, the shorter cutting height of 3.18 cm is recommended on the basis

of its similarity to actual cutting heights used on professional American football fields.

By keeping the canopy at a consistent height, the stress from a reduction in cutting height

following the sod harvest can be eliminated. Lower cutting heights also tend to produce

greater linear traction, a surface characteristic desired by most athletes (McNitt, 1994).

The 3.18 cm cutting height also produced better shoot density, although this density

increase may be only of nominal aesthetic value with little value towards playability.

Closer clipping did not prevent a successful sod harvest, despite prior concern by

practitioners.

A topdressing rate of 8.5 kg sand m-2 was sufficient to essentially eliminate thatch

accumulation. Applying sand at this rate did not increase or decrease divot resistance. In

the future other rates of topdressing should be evaluated to further elucidate the effects of

sand topdressing on divot resistance. A very small reduction in sod strength was observed

191

191

with topdressing, but the sod was still harvestable, as all sod strength values were well

above the 100 kg threshold.

Nitrogen had the greatest influence on divot resistance of any experimental treatment.

Divot resistance was negatively impacted by greater N supply. At the VRC location, the

highest N rate (4-1 treatment; 244 total kg N ha-1) produced 37% larger divots than the

most effective N rate (3-0 treatment; 144 total kg N ha-1) and 27% larger than the average

divot length of all other N treatments. The 4-1 N treatment also produced the least below-

ground biomass and the most thatch. This treatment was most similar to actual

fertilization programs in place at TTF during the experiments. These data suggest a

reduction in the N input will improve divot resistance.

Divot length was not affected by N treatment at TTF, but divot lengths and depths were

larger under higher N treatments. N treatment effects may have been partially muted at

TTF by the overall deterioration of the plots. Supervisors of the TTF facility were unable

to pinpoint the cause of decline. The reduced turf quality may have resulted from

inadequate irrigation, a faulty pesticide application, insufficient N prior to the

experiment, or other unknown factors.

The lack of simulated traffic in this project may account for the small number of

significant treatment effects on divot resistance. In prior studies of divot resistance, plots

receiving different treatments but not exposed to traffic showed only small differences in

divot resistance (Serensits et al., 2011). Although nitrogen did significantly affect divot

192

192

resistance, all experimental units had 100% turfgrass cover which may have diminished

the magnitude of nitrogen and other treatment effects.

The sod produced at the VRC location measured considerably higher in divot resistance

and sod strength compared to sod at the TTF location (31% and 26%, respectively). As in

all agricultural endeavors, climatic and edaphic conditions play a central role in the sod

production process. Higher air temperatures at TTF were less conducive to healthy cool-

season grass than the temperatures at VRC. Greater heat and humidity could have

stressed the turf and prevented maximum root and rhizome growth. While treatments

such as reduced nitrogen inputs were beneficial in this project, perhaps the greatest

improvement to the quality of the thick-cut sod produced at TTF would be attention to

detail. The overall level of cultural intensity was probably lower at TTF due to the plots’

location in a production field, rather than a more controlled research facility. Diligent

cutting and ample yet judicious irrigation are two such examples of basic practices

essential to successful turfgrass culture.

Data from this research project can provide sod growers with a deeper understanding of

their product. These data also will help refine the cultural practices used during

production of thick-cut sod. Such knowledge can ultimately improve the safety and

playability of professional football surfaces.

193

193

REFERENCES

Adams, W.A., P.J. Bryan, and G.E. Walker. 1974. Effects of cutting height and nitrogen

nutrition on growth pattern of turfgrasses. pp. 131–144. In: E.C. Roberts, ed., Proc.

2nd Int. Turfgrass Res. Conf., Blaksburg, VA. July 1969. International Turfgrass

Society, American Society of Agronomy, and Crop Science Society of America,

Madison, WI.

Adams, W.A., and R.L. Jones. 1979. The effect of particle size composition and root

binding on the resistance to shear of sportsturf surfaces. Rasen, Grunflachen,

Begrunungen. 10(2): 48–53.

ASTM Standard D2573-08, 2008. Standard Test Method for Field Vane Shear Test in

Cohesive Soil, ASTM International, West Conshohocken, PA. DOI:

10.1520/D2573-08.2. www.astm.org

ASTM Standard D3080-11, 2011. Standard Test Method for Direct Shear Test of Soils

Under Consolidated Drained Conditions. ASTM International, West Conshohocken,

PA. DOI: 10.1520/D3080. www.astm.org.

ASTM Standard D653-14, 2014. Standard Terminology Relating to Soil, Rock, and

Contained Fluids. ASTM International, West Conshohocken, PA. DOI:

10.1520/D0653-14.2. www.astm.org.

ASTM Standard D7181-11, 2011. Method for Consolidated Drained Triaxial

Compression Test for Soils. ASTM International, West Conshohocken, PA. DOI:

10.1520/D7181-11. www.astm.org.

ASTM Standard F1632-10, 2010. ASTM Standard F-1632-10 Standard Test Method for

Particle Size Analysis and Sand Shape Grading of Golf Course Putting Green and

Sports Field Rootzone Mixes. ASTM International, West Conshohocken, PA. DOI:

10.1520/F1632-03R10.2. www.astm.org.

Anderson, J.D. 2012. Establishment Method and Cultural Practice Effects on Sports Turf.

M.S. Thesis, Univ. of Arkansas., Fayetteville, AR.

Badra, A., L. Parent, Y. Desjardins, G. Allard, and N. Tremblay. 2005. Quantitative and

qualitative responses of an established Kentucky bluegrass (Poa pratensis L.) turf to

N , P , and K additions. Can. J. Plant Sci. 85: 193–204.

Barton, L., G.G.Y. Wan, R.P. Buck, and T.D. Colmer. 2009. Effectiveness of Cultural

Thatch-Mat Controls for Young and Mature Kikuyu Turfgrass. Agron. J. 101(1): 67.

http://www.astm.org/





194

194

Beard, J.B. 1973. Turfgrass, science and culture. 1st ed. Regents/Prentice-Hall,

Englewood Cliffs, N.J.

Beard, J.B., P.E. Rieke, and J.W. King. 1969. Sod production of Kentucky bluegrass. pp.

509–513. In: Sports Turf Research Institute, ed., Proc. First Int. Turfgrass Res.

Conf., Harrogate, England. 15-18 July, 1969. Sports Turf Research Institute,

Bingley, England.

Beasley, J.S., G.C. Munshaw, R.E. Strahan, and K. Fontenot. 2013. Influence of sand

topdressing on thatch decomposition of two bermudagrass species. Int. Turfgrass

Soc. Res. J. 12: 223–230.

Bell, G.E. 2011. Turfgrass Physiology & Ecology. 1st ed. CABI, Cambridge, MA.

Bowman, D.C. 2003. Daily vs. Periodic Nitrogen Addition Affects Growth and Tissue

Nitrogen in Perennial Ryegrass Turf. Crop Sci. 43: 631–638.

Brady, N.C., and R.C. Weil. 2007. The Nature and Properties of Soils. 14th ed. Prentice

Hall, Upper Saddle River, NJ.

Brede, A.D., and J.M. Duich. 1984. Initial Mowing of Kentucky Bluegrass-Perennial

Ryegrass Seedling Turf Mixtures. Agron. J. 76(5): 711–714.

Burns, R.E. 1980. Techniques for Rapid Sod Production. pp. 361–366. In: J.B. Beard,

ed., Proc. Third Int. Turfgrass Res. Conf., Munich, West Germany. 11-13 July 1977.

American Society of Agronomy, Crop Science Society of America, Soil Science

Society of America, and Int. Turfgrass Soc., Madison, WI.

Burns, R.E., and G. Futrap. 1979. Measuring sod strength with an instron universal

testing instrument. Agron. J.: 571–573.

Canaway, P.M. 1975. Fundamental techniques in the study of turfgrass wear: an advance

report on research. J. Sport. Turf Res. Inst. 51: 104–115.

Canaway, P.M. 1983. The effect of rootzone construction on the wear tolerance and

playability of eight turfgrass species subjected to football-type wear. J. Sport. Turf

Res. Inst. 59: 107–123.

Canaway, P.M. 1984. The response of Lolium perenne (Perennial ryegrass) turf grown on

sand and soil to fertilizer nitrogen I. Ground cover response as affected by football-

type wear. J. Sport. Turf Res. Inst. 60: 8–18.

195

195

Carroll, M.J., and A.M. Petrovic. 1991. Wear Tolerance of Kentucky Bluegrass and

Creeping Bentgrass Following Nitrogen and Potassium Application. HortScience

26(7): 851–853.

Carrow, R.N., B.J. Johnson, and R.E. Burns. 1987. Thatch and Quality of Tifway

Bermudagrass Turf in Relation to Fertility and Cultivation. Agron. J. 79: 524–530.

Carrow, R.N., D.V. Waddington, and P.E. Rieke. 2001. Turfgrass Soil Fertility and

Chemical Problems: Assessment and Management. 1st ed. Ann Arbor Press,

Chelsea, MI.

Charbonneau, P. 2000. To Harvest or Not to Harvest Cool Season Grasses. Turfgrass

Prod. Int. Turf News (November/December): 27–29.

Chivers, I.H., D.E. Aldous, and J.W. Orchard. 2005. The relationhship of Australian

football grass surfaces to anterior cruciate ligament injury. Int. Turfgrass Soc. Res. J.

10: 327–332.

Cisar, J.P. 2000. To Harvest or Not To Harvest...That is The Question. Turfgrass Prod.

Int. Turf News (November/December): 25–27.

Cockerham, S.T., and D.J. Brinkman. 1989. A simulator for cleated-shoe sports traffic on

turfgrass research plots. Calif. Turfgrass Cult. 39(3/4): 9–10.

Crider, F.J. 1955. Root-growth Stoppage Resulting from Defoliation of Grass. USDA

Tech. Bull. 1102: United States Department of Agriculture, Washington, D.C.

Dafalla, M.A. 2013. Effects of Clay and Moisture Content on Direct Shear Tests for

Clay-Sand Mixtures. Adv. Mater. Sci. Eng. 2013: 1–8. doi: 10.1155/2013/562726

Duncan, D., and J.B. Beard. 1975. Measurement techniques, wear tolerance, and

nutritional relationships as related to turfgrass thatch. pp. 15–17. In: Proc. 45th

Annual Michigan Turfgrass Conf. 14-15 Jan., 1975. Michigan State Univ. East

Lansing, MI.

Dunn, J.H., and R.E. Engel. 1971. Effect of Defoliation and Root-Pruning on Early Root

Growth from Merion Kentucky Bluegrass Sods and Seedlings. Agron. J. 63(5): 659–

663.

Dunn, J.H., K.M. Sheffer, and P.M. Halisky. 1981. Thatch and Quality of Meyer Zoysia

in Relation to Management. Agron. J. 73: 949–952.

Eggens, J.L. 1981. Response of Poa pratensis L. (Kentucky bluegrass) and Poa annua L.

(Annual Bluegrass) to Mowing and Plant Competition. pp. 123–128. In: Sports Turf

196

196

Research Institute, ed., Proc. First Int. Turfgrass Res. Conf., Harrogate, England. 15-

18 July, 1969. Sports Turf Research Institute, Bingley, England.

Eggens, J.L. 1982. Influence of mowing on leaf and tiller orientation of turfgrasses. Can.

J. Plant Sci. 62(4): 979–982.

Ervin, E.H., and A.J. Koski. 1998. Growth Responses of Lolium perenne L. to

Trinexapac-ethyl. HortScience 33(7): 1200–1202.

Ervin, E.H., and A.J. Koski. 2001a. Kentucky Bluegrass Growth Responses to

Trinexapac-Ethyl, Traffic, and Nitrogen. Crop Sci. 41: 1871–1877.

Ervin, E.H., and A.J. Koski. 2001b. Trinexapac-ethyl Increases Kentucky Bluegrass Leaf

Cell Density and Chlorophyll Concentration. HortScience 36(4): 787–789.

Fermanian, T.W., J.E. Haley, and R.E. Burns. 1985. The effects of sand topdressing on a

heavily thatched creeping bentgrass turf. pp. 439–448. In: F. Lemaire, ed., Proc.

Fifth Int. Turfgrass Res. Conf. Savignon, France. 1-5 July, 1985. 1st Nat de la

Recherche Agron., Paris, France.

Gang, D.R., ed.. 2013. Phytochemicals, Plant Growth, and the Environment. Springer,

Pullman, WA. doi: 10.1007/978-1-4614-4066-6_7

Goss, R.L., and A.G. Law. 1967. Performance of Bluegrass Varieties at Two Cutting

Heights and Two Nitrogen Levels. Agron. J. 59: 516–518.

Handin, J. 1969. On the Coulomb-Mohr Failure Criterion. J. Geophys. Res. 74(22):

5343–5348.

Heckman, N., G. Horst, R. Gaussoin, and K.W. Frank. 2001. Storage and Handling

Charateristics of Trinexapac-ethyl Treated Kentucky Bluegrass Sod. HortScience

36(6): 1127-1130.

Hoffman, L., J.S. Ebdon, W.M. Dest, and M. DaCosta. 2010. Effects of Nitrogen and

Potassium on Wear Mechanisms in Perennial Ryegrass: I. Wear Tolerance and

Recovery. Crop Sci. 50(1): 357

Jagschitz, J.A. 1980. Development and Rooting of Kentucky Bluegrass Sod as Affected

by Herbicides. pp. 227-235. In: J.B. Beard, ed., Proc. Third Int. Turfgrass Res.

Conf., Munich, West Germany. 11-13 July 1977. American Society of Agronomy,

Crop Science Society of America, Soil Science Society of America, and Int.

Turfgrass Soc., Madison, WI.

197

197

Juska, F.V., and A.A. Hanson. 1961. Effects of Interval and Height of Mowing on

Growth of Merion and Common Kentucky Bluegrass (Poa pratensis L.). Agron. J.

53(6): 385–388.

KORO by Imants. 2014. Koro Story. 30 pp. Available at

http://www.campeyturfcare.com/exclusiveproducts/koro-field-topmaker-1200.html

(accessed 28 Apr. 14).

Kowalewski, A.R., J.C. Dunne, J.N. Rogers III, and J.R. Crum. 2011. Heavy Sand and

Crumb Rubber Topdressing Improves Kentucky Bluegrass Wear Tolerance. Appl.

Turfgrass Sci. (December): 1–9. doi: 10.1094/ATS-2011-1223-01-RS

Kowalewski, A.R., J.N.R. III, and D. Timothy. 2008. Pre-harvest Core Cultivation of Sod

Provides an Alternative Cultivation Timing. Appl. Turfgrass Sci. (April). doi:

10.1094/ATS-2008-0421-01-RS

Kowalewski, A.R., J.N. Rogers, J.R. Crum, and J.C. Dunne. 2010. Sand Topdressing

Applications Improve Shear Strength and Turfgrass Density on Trafficked Athletic

Fields. HortTechnology 20: 867–872.

Kurtz, K.W. 1967. Effect of Nitrogen Fertilization on the Establishment, Density, and

Strength of Merion Kentucky Bluegrass Sod Grown on a Mineral Soil. M.A. thesis.

Michigan State Univ. East Lansing, MI.

Kussow, W.R., D.J. Soldat, W.C. Kreuser, and S.M. Houlihan. 2012. Evidence,

Regulation, and Consequences of Nitrogen-Driven Nutrient Demand by Turfgrass.

ISRN Agron. 2012: 1–9. doi: 10.5402/2012/359284

Li, D., W. Fang, and L. Han. 2011. Nitrogen Fertilization Influences Shear Strength and

Quality of Kentucky Bluegrass Sod Grown on Clay. Agron. J. 103(3): 751.

Li, D., J. Henderson, J.T. Vanini, and J.N. Rogers III. 2013. Research Tools and

Technologies for Turfgrass Establishment. In Stier, J.C., Horgan, B.P., Bonos, S.A.

(eds.), Turfgrass: Biology, Use, and Management, Agron. Monograph No. 56.

American Society of Agronomy, Madison, WI.

Marschner, H. 2012. Mineral Nutrition of Higher Plants. 3rd ed. Academic Press, San

Diego, CA.

Mascaro, T. 2013. Turf-Tec Shear Strength Tester. Available at http://www.turf-

tec.com/TSHEAR2.html. Accessed 12 November 2014.

198

198

Mccalla, J., M. Richardson, and D. Karcher. 2008. Sod Production Utilizing an Improved

Seeded Bermudagrass Cultivar. Appl. Turfgrass Sci. (January). doi: 10.1094/ATS-

2008-0118-01-RS

McCarty, B. 2014. Plant Growth Regulators for Fine Turf. Clemson University Extension

Publication. Available at

http://www.clemson.edu/extension/horticulture/turf/pest_guidelines/growth_regulato

rs.html. Accessed 19 November 2014.

McCarty, L.B., M.F. Gregg, and J.E. Toler. 2007. Thatch and Mat Management in an

Established Creeping Bentgrass Golf Green. Agron. J. 99(6): 1530-1537.

McIntosh, M.S. 1983. Analysis of combined experiments. Agron. J. 75(1): 153–155.

McIntyre, G.I. 1964. Influence of Nitrogen Nutrition on Bud and Rhizome Development

in Agropyron repens L. Beauv. Nature 203(4949): 1084–1085.

McIntyre, G.I. 1970. Studies on bud development in the rhizome of Agropyron repens I.

The influence of temperature, light intensity, and bud position on the pattern of

development. Can. J. Bot. 48: 1903–1909.

McIntyre, G.I., and A.J. Cessna. 1998. Studies on the growth and development of the

rhizome and lateral rhizome buds in Elytrigia repens: some effects of parent shoot

excision. Can J. Bot. 776: 769–776.

McNitt, A.S. 1994. Effects of turfgrass and soil characteristics on traction. M.S. thesis.

The Pennsylvania State Univ. University Park, PA.

McNitt, A.S. 2000. The effects of soil inclusions on soil physical properties and athletic

field playing surface quality. PhD. diss. The Pennsylvania State Univ. University

Park, PA.

McNitt, A.S., and P.J. Landschoot. 2001. Evaluation of a modular turfgrass system

ammended with shreedded carpet. Int. Turfgrass Soc. Res. J. 9: 559–564.

McNitt, A.S., R.O. Middour, and D.V. Waddington. 1997. Development and Evaluation

of a Method to Measure Traction on Turfgrass Surfaces. J. Test. Eval. 25(1): 99–

107.

Minnick, J., and A. Reed. 2013. Concept to active practice: fraze mowing bermudagrass

makes debut. SportsTurf (August): 26–29.

Mitchell, C.H., and R. Dickens. 1979. Nitrogen fertilization and mowing height effects

on tensile strength of bermudagrass sod. Agron. J. 71(6): 1061–1062.

199

199

Morris, K.N., and R.C. Shearman. NTEP turfgrass evaluation guidelines. Online. Nat.

Turfgrass Eval. Prog., Beltsville, MD (2008). Available at www.ntep.org/pdf/ratings.pdf.

Accessed 5 June 2013.

Murphy, J.A., S.A. Bonos, and B.S. Park. 2004. Kentucky Bluegrass Varieties for New

Jersey Sports Fields. Rutgers University Extension Publication. Available at

http://njaes.rutgers.edu/pubs/publication.asp?pid=FS545. Accessed 4 April 2014.

Murray, J.J., and F.V. Juska. 1970. Management Practices on Thatch Accumulation,

Turf Quality, and Leaf Spot Damage in Common Kentucky Bluegrass. Agron. J. 69:

365–369.

National Resource Conservation Service (NRCS). 2014. Web Soil Survey. Online

Resource .Available at http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm.

Accessed 29 Jan 2014.

Nyahoza, F., C. Marshall, and G.R. Sagar. 1974. Some aspects of the physiology of the

rhizomes of Poa pratensis L. Weed Res. 14: 329–336.

Parish, R.L. 1995. A Simple Device to Measure Sod Strength. HortTechnology 5(4): 308-

309.

Parker, D.S. 2011. Influence of sand topdressing on bermudagrass thatch decomposition.

M.S. thesis. Louisiana State Univ. Baton Rouge, LA.

Puhalla, J.C., J. V. Krans, and J.M. Goatley Jr. 2010. Sports fields: design, construction,

and maintenance. 2nd ed. Wiley, Hoboken, NJ.

Rieke, P.E., and J.B. Beard. 1969. Factors in Sod Production of Kentucky Bluegrass. In:

Sports Turf Research Institute, ed., Proc. First Int. Turfgrass Res. Conf., Harrogate,

England. 15-18 July, 1969. Sports Turf Research Institute, Bingley, England. 1:

514–521.

Rieke, P.E., J.B. Beard, and C.M. Hansen. 1968. A Technique to Measure Sod Strength

for Use in Sod Production Studies. Agron. Abstr. 60: 20.

Ross, S.J., A.R. Ennos, and A.H. Fitter. 1991. Turf strength and root characteristics of ten

turfgrass cultivars. Ann. Appl. Biol. 118(2): 433–443.

Sartain, J.B. 1985. Effect of Acidity and N Source on the Growth and Thatch

Accumulation of Tifgreen Bermudagrass and on Soil Nutrient Retention. Agron. J.

77: 33–36.

200

200

Satari, A.M. 1967. Effects of various rates and combinations nitrogen, phosphorus,

potassium and cutting heights on the development of rhizome, root total available

carbohydrate and foliage composition of Poa pratensis L. Merion grown on

Houghton muck. PhD diss. Michigan State Univ. East Lansing, MI.

Serensits, T.J. 2008. The effects of trinexapac-ethyl and cultivation on the divot

resistance of Kentucky bluegrass cultivars. M.S. thesis. The Pennsylvania State

Univ. University Park, PA.

Serensits, T.J., A.S. McNitt, and D.M. Petrunak. 2011. Improving surface stability on

natural turfgrass athletic fields. Proc. Inst. Mech. Eng. Part P: J. Sports Eng.

Technol. 225(2): 85–92.

Shearman, R.C. 1980. Thatch accumulation in Kentucky bluegrass as influenced by

cultivar, mowing, and nitrogen. HortScience 15(3): 312–313.

Shearman, R.C. 1989. Physiology of turfgrass mowing. p. 46–48. In Conference

Proceedings: 60th International Golf Course Conference and Show. Anaheim, CA.

6-13 Feb. 1989. Golf Course Superintendents Association of America. Lawrence,

KS.

Shearman, R.C., T.R. Turner, K.N. Morris, R.E. Gaussoin, M.R. Vaitkus, and L.A. Wit.

2001. Sod strength and lateral spread of Poa pratensis cultivars and experimental

lines. Int. Turfgrass Soc. Res. J. 9: 928–933.

Sherratt, P.J., J.R. Street, and D.S. Gardner. 2005. Effects of Biomass Accumulation on

the Playing Quality of a Kentucky Bluegrass Stabilizer System Used for Sports

Fields. Agron. J. 97(4): 1107-1114.

Shildrick, J.P., and C.H. Peel. 1984. Shoot Numbers, Biomass, and Shear Strength in

Smooth-stalked Meadow-grass (Poa Pratensis). J. Sport. Turf Res. Inst. 60: 66–72.

Simon, J.C., and G. Lemaire. 1987. Tillering and leaf area index in grasses in the

vegetative phase. Grass Forage Sci. 42: 373–380.

Sorochan, C., N. Rogers, C. Stier, and D.E. Karcher. 2001. Fertility and Simulated

Traffic Effects on Kentucky Bluegrass/Supina Bluegrass Mixtures. Int. Turfgrass

Soc. Res. J. 9: 941–946.

Tesfamariam, E.H., J.G. Annandale, J.M. Steyn, and R.J. Stirzaker. 2009. Exporting large

volumes of municipal sewage sludge through turfgrass sod production. J. Environ.

Qual. 38(3): 1320–1328.

201

201

Trappe, J.M., D.E. Karcher, M.D. Richardson, and A.J. Patton. 2011. Divot Resistance

Varies among Bermudagrass and Zoysiagrass Cultivars. Crop Sci. 51(4): 1793–

1799.

Trulio, M. 1994. Thick-cut sod: Weight for Stability. SportsTurf (January): 18–19.

Turgeon, A.J. 2012. Turfgrass Management. 9th ed. Prentice Hall, Upper Saddle River,

NJ.

United States Golf Association (USGA) Green Section Staff, 2004. USGA

Recommendations for a Method of Putting Green Construction. United States Golf

Association, Far Hills, NJ. http://www.usga.org/Content.aspx?id=26124 (accessed

19 December 2014).

Vietor, D.M., E.N. Griffith, R.H. White, T.L. Provin, J.P. Muir, and J.C. Read. 2002.

Export of Manure Phosphorous and Nitrogen. J. Environ. Qual. 31: 1731–1738.

Waddington, D.V. 1992. Soil Mixtures & Amendments. p. 331–383. In Waddington,

D.V., Carrow, R.N., Shearman, R.C. (eds.), Turfgrass, Agron. Monograph no. 32.

American Society of Agronomy, Madison, WI.

Watson, J.R., H.E. Kaerwer, and D.P. Martin. 1992. The Turfgrass Industry. p. 29–88. In

Waddington, D.V., Carrow, R.N., Shearman, R.C. (eds.), Turfgrass, Agron.

Monograph no. 32. American Society of Agronomy, Madison, WI.

Weston, J., and J.H. Dunn. 1985. Thatch and quality of Meyer zoysia in response to

mechanical cultivation. pp. 449–458. In: F. Lemaire, ed., Proc. Fifth Int. Turfgrass

Res. Conf. Savignon, France. 1-5 July, 1985. 1st Nat de la Recherche Agron., Paris,

France.

Yokoi, H. 1968. Relationship between soil cohesion and shear strength. Soil Sci. Plant

Nutr. 14(3): 89–93.

202

APPENDIX

Additional Materials

Table 91. Properties of sod from this research project compared with actual sod produced

by TTF and installed at NFL stadia in November 2013. All sod tested was harvested at

4.45 cm profile thickness.

Sod type

Divot dimensions

Sod strength Shear strength length width depth

-------- cm -------- -- kg peak force -- --- Nm ---

VRC research plots 24.2 5.6 1.6 211.5 28.3

TTF research plots 31.6 7.1 1.7 155.9 24.4

3.81 cm† NFL sod at TTF 31.0 7.5 2.0 135.6 23.9

3.18 cm† NFL sod at TTF 30.0 7.7 1.5 138.7 22.0

Standard KBG sod at TTF* - - - 177.7 26.9

3-month old KBG sod* - - - 35.0 -

† indicates cutting height at which tested sod was maintained throughout the 2013 growing season

* indicates sod was tested from a standard production field, rather than one selected for thick-cut

NFL sod.

203

Table 92. Mean visual color ratings for the cutting height main effect at VRC.

Cutting height Color rating Letter grouping

---- cm ---- ------------

3.18 6.0 B

3.81 7.1 A

LSD (0.05) 0.7 -

Table 93. Mean visual color ratings for the topdressing main effect at VRC.

Topdressing applied Color rating Letter grouping

---- kg sand m-2 ---- ------------

0.0 6.4 -

8.5 6.6 -

LSD (0.05) NS -

Table 94. Mean visual color ratings for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Color rating Letter grouping

--------

2-0 4.9 D

2-1 7.6 A

3-0 5.5 C

3-1 7.6 A

4-0 6.0 B

4-1 7.6 A

LSD (0.05) 0.5 -

204

Table 95. Selected contrasts comparing visual color at VRC as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Color rating

Difference

relative to

second value

Pr > F Statistical

Significance ††

--------------

-------- % -------

-

A 0 fall vs. 1 fall 5.5 vs. 7.6 -28% <.0001 ***


C 4 total vs. 5 total 6.8 vs. 7.6 -10% 0.001 ***

D 3 total vs. all other rates 6.5 vs. 6.5 0% 0.890 NS

E 5 total vs. all other rates 7.6 vs. 6.5 +16% <.0001 ***



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0


205

Table 96. Mean visual color ratings for the cutting height main effect at TTF.

Cutting height Color rating Letter grouping

---- cm ---- ------------

3.18 5.8 B

3.81 4.4 A

LSD (0.05) 1.3 -

Table 97. Mean visual color ratings for the topdressing main effect at TTF.

Topdressing applied Color rating Letter grouping

---- kg sand m-2 ---- ------------

0.0 5.1 -

8.5 5.1 -

LSD (0.05) NS -

Table 98. Mean visual color ratings for the nitrogen treatment main effect at TTF.

Nitrogen treatment† Color rating Letter grouping

------------

2-0 4.2 D

2-1 5.4 A

3-0 4.5 C

3-1 5.9 A

4-0 4.6 B

4-1 5.9 A

LSD (0.05) 0.6 -


206

Table 99. Mean visual color ratings for the cutting height by nitrogen treatment interaction at TTF.

N treatment †


---- cm ---- ---------------------------------------------------------------------

3.18 5.0 5.8 5.7 6.2 5.5 6.3 1.0

3.81 3.3 5.0 3.3 5.7 3.7 5.5 1.0

LSD (0.05) 1.0 1.0 1.0 1.0 1.0 1.0 -


207

207

Table 100. Selected contrasts comparing visual color at TTF as related to total both total nitrogen applied and individual nitrogen

treatments.

Contrast label Nitrogen applications† Color rating

Difference

relative to

second value

Pr > F Statistical

Significance ††

-------------- ------- % -------

A 0 fall vs. 1 fall 4.4 vs. 5.8 -23% <.0001 ***




E 5 total vs. all other rates 5.9 vs. 5.1 +16% <.0001 ***



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0


208

Table 101. Mean thatch thickness values for the cutting height main effect at VRC.

Cutting height Thatch thickness Letter grouping

---- cm ---- ---- mm ----

3.18 6.8 B

3.81 7.7 A

LSD (0.05) 0.8 -

Table 102. Mean thatch thickness values for the topdressing main effect at VRC.


---- cm ---- ---- mm ----

3.18 6.8 B

3.81 7.7 A

LSD (0.05) 0.8 -

Table 103. Mean thatch thickness values for the nitrogen treatment main effect at VRC.

Nitrogen treatment† Thatch thickness Letter grouping

---- mm ----

2-0 6.3 B

2-1 6.0 B

3-0 6.6 B

3-1 7.0 B

4-0 8.6 A

4-1 9.0 A

LSD (0.05) 1.0 -


respectively

209

Table 104. Selected contrasts comparing thatch thickness at VRC as related to total both total nitrogen applied and individual

nitrogen treatments.

Contrast label Nitrogen applications† Thatch thickness

Difference relative


Statistical

Significance ††

------ mm ------ -------- % --------


B 3 total vs. 4 total 6.3 vs. 7.8 -19% <.0001 ***


D 3 total vs. all other rates 6.3 vs. 7.7 -19% <.0001 ***

E 5 total vs. all other rates 9.0 vs. 6.9 30% <.0001 ***



A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

††


210

210

Table 105. Mean thatch thicknesses for the cutting height by nitrogen interaction at VRC.

N treatment †

Cutting

height 2-0 2-1 3-0 3-1 4-0 4-1 LSD (0.05)

---- cm ---- --------------------------------- mm --------------------------------

3.18 5.5 6.2 5.3 7.2 8.8 7.7 1.5

3.81 7.2 5.8 7.8 6.8 8.3 10.3 1.5

LSD (0.05) 1.5 1.5 1.5 1.5 1.5 1.5 -


211

Table 106. Mean thatch thickness values for the cutting height main effect at TTF.


---- cm ---- ---- mm ----

3.18 5.2 -

3.81 5.3 -

LSD (0.05) NS -

Table 107. Mean thatch thickness values for the topdressing main effect at TTF.

Topdressing applied Thatch thickness Letter grouping

---- kg sand m-2 ---- ---- mm ----

0.0 8.2 A

8.5 2.3 B

LSD (0.05) 0.9 -

Table 108. Mean thatch thickness values for the nitrogen treatment main effect at TTF.

Nitrogen treatment† Thatch thickness Letter grouping

---- mm ----

2-0 3.8 C

2-1 4.7 BC

3-0 4.5 BC

3-1 5.8 B

4-0 4.7 BC

4-1 8.0 A

LSD (0.05) 1.6 -


respectively

212

Table 109. Selected contrasts comparing thatch thickness at TTF as related to total both total nitrogen applied and individual

nitrogen treatments.

Contrast label Nitrogen applications† Thatch thickness

Difference relative


Statistical

Significance ††

------ mm ------ -------- % --------

A 0 fall vs. 1 fall 4.4 vs. 6.1 -29% <0.001 ***


C 4 total vs. 5 total 5.2 vs. 8.0 -34% <0.001 ***

D 3 total vs. all other rates 4.6 vs. 5.6 -18% 0.040 *




A H0: μ 2-0, 3-0, 4-0 = μ 2-1, 3-1, 4-1

B H0: μ 2-1, 3-0 = μ 3-1, 4-0

C H0: μ 3-1, 4-0 = μ 4-1

D H0: μ 2-1, 3-0 = μ 2-0, 3-1, 4-0, 4-1

E H0: μ 4-1 = μ 2-0, 2-1, 3-0, 3-1, 4-0

††


effects of pre-harvest cultural practices on the …

Documents