104 DISCUSSION The results section was divided into seven sections, one section for each of six separate experiments conducted, and one describing turfgrass stand characterization. The results of each individual experiment have been summarized in the results section. This section examines trends or observations across experiments. Topics to be discussed include the effects of: species; soil water content; species and soil water content interaction; verdure wetness; shoe type; shoe type and soil water content interaction; shoe type and species interaction; shoe type and traction measurement type interaction; and turfgrass stand characteristics including cutting height, verdure, tiller density, and below-ground biomass on traction values obtained using PENNFOOT. Species Kentucky bluegrass and tall fescue had higher traction than perennial ryegrass and red fescue at peak traction measurements of 4.4 cm of linear travel in Experiment 2. From 1.3 cm to 2.5 cm of linear travel perennial ryegrass traction was higher than red fescue, though not significantly higher, and from 3.2 cm to 5.1 cm of linear travel perennial ryegrass and red fescue traction values were essentially equal. The effects of four turfgrass species on traction values in Experiment 2 were similar to those obtained by Middour
72
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104DISCUSSION
The results section was divided into seven sections, one
section for each of six separate experiments conducted, and
one describing turfgrass stand characterization. The results
of each individual experiment have been summarized in the
results section. This section examines trends or observations
across experiments. Topics to be discussed include the
effects of: species; soil water content; species and soil
water content interaction; verdure wetness; shoe type; shoe
type and soil water content interaction; shoe type and
species interaction; shoe type and traction measurement type
interaction; and turfgrass stand characteristics including
cutting height, verdure, tiller density, and below-ground
biomass on traction values obtained using PENNFOOT.
Species
Kentucky bluegrass and tall fescue had higher traction than
perennial ryegrass and red fescue at peak traction
measurements of 4.4 cm of linear travel in Experiment 2. From
1.3 cm to 2.5 cm of linear travel perennial ryegrass traction
was higher than red fescue, though not significantly higher,
and from 3.2 cm to 5.1 cm of linear travel perennial ryegrass
and red fescue traction values were essentially equal. The
effects of four turfgrass species on traction values in
Experiment 2 were similar to those obtained by Middour
105
(1992), who reported that Kentucky bluegrass and tall fescue
had the highest traction and red fescue the lowest with
perennial ryegrass having intermediate traction values. In
Experiment 2 these species trends held over soil water values
that ranged from an average of 0.18 to 0.34 kg kg-i.
In Experiment 3, traction values due to species differences
were not significantly different. At peak traction
measurements of 40 degrees of rotation, tall fescue had the
highest traction with a value of 29.8 Nm, perennial ryegrass
had the least with a value of 28.6 Nm, and Kentucky bluegrass
was intermediate with a peak traction value of 29.1 Nm. The
magnitude of these differences is small. Middour (1992) found
statistical differences among species when measuring traction
rotationally although perennial ryegrass did not separate
from red fescue. Both perennial ryegrass and red fescue
showed lower rotational traction than Kentucky bluegrass and
tall fescue. While significant differences were not detected
in Experiment 3 the trends due to species were consistent.
In Experiment 4 linear traction values showed a similar
trend, with respect to species, to the results reported by
Middour (1992) and Experiment 2, although Kentucky bluegrass
was not significantly greater than perennial ryegrass in this
instance. In Experiments 2, 3, and 4, species effects on
traction were confounded by other treatments and fewer
106
significant differences were found than Middour (1992)
reported.
Soil Water Content
Soil water content had a varying effect on traction over the
six experiments. In Experiment 1, the average post-irrigation
soil water content of 0.30 kg kg-1 resulted in significantly
higher traction values than the average pre-irrigation soil
water content of 0.21 kg kg-1. In Experiment 2, the traction
values obtained for post-irrigation treatments were not
significantly different from the pre-irrigation treatments
(average soil water contents were 0.33 and 0.18 kg kg-1,
respectively). In experiment 6, the combined experiment
analysis showed that the pre-precipitation treatment produced
higher traction values than the post-precipitation treatment.
Soil water contents averaged '0.17 for the post-precipitation
treatment and 0.13 kg kg-1 for the pre-precipitation
treatment, on this sandy soil. Soil water contents were
measured in Experiments 3, 4, and 5 but were not a treatment.
There was no significant correlation between traction values
and soil water content in Experiment 3. In Experiment 4,
traction values obtained from individual shoes did positively
correlate with soil water contents; however, this result was
confounded by varying water contents among species and is
addressed in the section entitled Species and Soil Water
Content Interaction. Correlation coefficients could not be
107
calculated for Experiment 5 due to experimental design. A
further examination of the effect of soil water content on
traction is discussed in the sections entitled Species and
Soil Water Content Interaction and Shoe Type and Soil Water
Interaction.
Species and Soil Water Content Interaction
No significant statistical interaction between species and
irrigation treatments occurred in Experiment 2. Each species
in Experiment 2 had lower traction values 20 minutes after an
irrigation treatment consisting of 5 cm of water. At 4.4 cm
of linear travel, Kentucky bluegrass traction dropped 43 N
after irrigation was applied, tall fescue dropped 122 N,
perennial ryegrass dropped 120 N, and red fescue dropped 102
N. While the interaction was not statistically significant in
this experiment, Kentucky bluegrass appeared to be less
affected by high soil water conditions than the other
species. Species other than Kentucky bluegrass had a
significant negative correlation with soil water (red fescue,
r = -0.96, perennial ryegrass, r = -0.91, tall fescue, r =-0.93) while Kentucky bluegrass (r = -0.76) did not have a
significant correlation with soil water.
It may be that the rhizomonous growth habit of Kentucky
bluegrass enables it to provide higher traction values under
high soil water condition where soil strength decreases and
108
the morphological characteristics of the grass become more
important. Kentucky bluegrass had significantly more below-
ground biomass than the other species. However, below-ground
biomass alone cannot explain this trend with Kentucky
bluegrass because there was a low correlation between
traction and below-ground biomass. More likely this result is
due to a combination of effects due to both plant and soil
interactions. More work needs to be done on plant
morphological characteristics and their effect on traction
under various soil water contents and soil textural classes.
Verdure Wetness
Experiment 3 was designed to investigate the effects of
moisture on verdure with respect to traction. No significant
traction differences were found between dry and wet verdure
at peak traction values of 40 degrees of rotation; however,
dry verdure had consistently higher traction values under
both loading weights. Due to statistical design, traction
differences due to verdure wetness were tested with an error
term that has only two degrees of freedom. This experiment
should be repeated using a different experimental design. It
can be theorized that dew or gutation water has little effect
on traction until it becomes dislodged and wets the soil
surface. The act of placing a studded foot on the turf can
dislodge the water.
109
Shoe Type
Experiment 4 was designed to compare traction values obtained
using the two shoe types described previously, across species
and cutting heights. The studded shoe had consistently
higher, but not statistically significant, linear traction
values when averaged across species and cutting heights than
did the molded shoe. Traction differences due to shoe types
were tested with an error term that has only 2 degrees of
freedom. The magnitude of difference between peak traction
values obtained with the different shoes was 148 N and is
considered large when compared to other differences that have
been found to be statistically different by this and other
researchers. Significant shoe by species interaction
(discussed later) did show significant shoe differences with
three of the four turfgrass species. It can be assumed that
by using a different statistical design these shoe types
would yield statistically different traction values.
In Experiment 5 there was virtually no difference between the
peak traction values obtained with the molded and studded
shoes when averaged over all loading weights. Although the
difference was not significant, the studded shoe gave
slightly greater traction than the molded shoe at peak
traction values occurring at 4.4 cm of travel for only the
116 kg loading weight. Lighter loading weights of 88 and 59.9
kg showed the molded shoe to 'have higher traction than the
110studded shoe. Why this particular stand of bluegrass yielded
results in which there was little difference between linear
traction values using the different shoes is not clear. The
soil water contents in Experiment 5 averaged approximately
0.24 kg kg-1 for plots on which linear traction was measured
as compared to an average of 0.19 kg kg-1 for Experiment 4.
More soil water in Experiment 5 may have allowed greater
cleat penetration than in Experiment 4; however, cleat
penetration was not determined and differences due to
penetration is only speculation. Kentucky bluegrass tiller
densities were not appreciably different with averages of 168
tillers per plug in Experiment 4 and 167.6 tillers per plug
in Experiment 5. The 'Kentucky bluegrass plots' in Experiment
5 did have a small amount of thatch present, while the
'species plots' had virtually no thatch. The effects of
various levels of thatch have not been investigated; however,
it is possible that thatch would prevent or lessen stud
penetration into the soil. Also it is conceivable that
differences in stand age or degree of wear on a species could
alter its responsiveness to a given shoe type.
In Experiment G.b, rotational traction values obtained with
the molded shoe were significantly higher than those obtained
with the studded shoe at each 10 degree increment of
rotation.
111Shoe Type and Soil Water Content Interaction
Experiment 1 and 2 included similar irrigation treatmentswith the exception that linear traction measurements weremade 20 hours after irrigation was applied in Experiment 1 asopposed to 20 minutes after irrigation was applied inExperiment 2. Experiment 6 was conducted on a sand-modifiedsoil with rotational traction measurements taken before and
immediately after a rainfall.
In Experiment 1, traction values due to irrigation treatmentswere statistically different at 4.4 and 5.1 cm of lineartravel, with the post-irrigation treatment having highertraction values than the pre-irrigation treatment. Althoughnot statistically significant, post-irrigation traction waslower than pre-irrigation traction in Experiment 2 by thesame magnitude difference as in Experiment 1 (114 and 115 Nmrespectively). Experiment 1 and 2 were conducted on differentplot areas, but both were a Hagerstown silt loam soil (seeMaterial and Methods). A loading weight of 102 kg was used inboth Experiment 1 and 2, whereas a 116 kg loading weight wasused in Experiment 6. The molded shoe was used in Experiment1 and 6, whereas the studded shoe was used in Experiment 2.
In practice, the molded shoe is used by athletes on dry soilsand the studded shoe is used when there is more soil waterpresent. The molded shoe has 18 triangular studs (12 rom long)
112
around the perimeter of the sole and 35 smaller studs (9 rom
long) in the center. The studded shoe contains 12 cylindrical
studs, each 12 rom long and 11 rom in diameter. The molded shoe
used in Experiment 1 has more stud surface area than the
studded shoe. Gravimetric soil water values for Experiment 1
averaged 0.21 kg kg-1 pre-irrigation and 0.30 kg kg-1 post-
irrigation. Soil water correlated significantly (r = 0.71)
with traction values when compared across all treatments in
Experiment 1. The increase in traction 20 hours after the
irrigation treatment may be due to increased stud penetration
of the molded shoe. In Experiment 6, significantly lower
traction was obtained on the sandy soil post-precipitation
using the molded shoe. Experiment 6 differed from Experiment
1 in that a heavier loading weight was used to measure
rotational rather than linear traction. Traction values did
not correlate significantly with soil water values in
Experiments 6. A study in which varying water content, shoe
type, soil textural class, and measurement type (rotational
or linear) should be conducted and stud penetration into the
soil should be measured.
In Experiment 3, rotational traction values did not
significantly correlate with soil water content values. Soil
water was not a treatment in Experiment 3 and as a result the
range of soil water values was small, ranging from 0.20 to
0.24 for Kentucky bluegrass, 0.22 to 0.29 for tall fescue and
0.21 to 0.28 for perennial ryegrass.
113
In Experiment 4 there was no significant correlation between
traction on individual species and soil water content.
Individual shoe types did significantly correlate with soil
water content when considered across all treatments. This
result is confounded by varying water contents across
species. Tall fescue and Kentucky bluegrass had average soil
water contents of 0.21 and 0.19 kg kg-i and have been shown to
have higher traction values than perennial ryegrass and red
fescue which had average soil water contents of 0.17 and 0.14
kg kg-i, respectively. It is interesting to note that the
molded shoe was significantly correlated to soil water
content at the 0.01 level (r = 0.88) while the studded shoe
was significant at only the 0.05 level (r = 0.62) and that
traction values obtained with the studded shoe were
significantly correlated with below-ground vegetation (r =0.62) while those obtained with the molded shoe were not (r =0.27). Although soil water contents may have had a greater
effect on the studded shoes' ability to penetrate into the
soil versus the higher stud surface area molded shoe, without
measuring stud penetration this can only be speculated.
Taking all six experiments into consideration it can be said
that although soil water extremes do affect traction, soil
water alone cannot describe varying traction results. In
these studies, it appears that soil water differences not
114
resulting from soil water treatments were confounded with
cutting height and species, which also affect traction.
Conclusions about soil water's effect on traction cannot be
made when data are collected from plots where soil water is
not a treatment or a significant range of soil water levels
does not exist. Since Experiment 2 represents the only
traction measurements taken on plot areas where soil water
was approaching saturation, the possibility that under these
correlated positively (r = 0.62) with traction when using the
studded shoe, but had low correlation (r = 0.27) with
traction when using the molded shoe (Table 13). These results
support the supposition that under certain conditions the
lower stud surface area studded shoe will penetrate deeper
into the surface than the molded shoe and allow below-ground
vegetation to affect traction values to a greater degree.
Vegetative characteristics of turfgrass and their
relationship to traction values obtained using PENNFOOT are
inconclusive, with the exception of verdure effects. The
effects of verdure were directly investigated in Experiment 1
and found to have little effect on traction values. In future
121
experiments, vegetative characteristics should be better
controlled so their individual effects can be discerned.
Traction values should be obtained from turfgrass stands
exposed to various levels of wear. Under these conditions a
wider range of vegetative characteristics may occur and any
differences in traction values would be more appropriate when
compared to actual athletic fields.
122
SUMMARY AND CONCLUSIONS
This thesis includes a review of methods developed to measure
traction of natural turfgrass surfaces, a review of the
relevancy of these methods to the actual athlete to shoe to
surface interaction, and a review of turfgrass vegetative and
soil conditions that affect traction.
An apparatus (PENNFOOT) was developed at The Pennsylvania
State University to measure traction. PENNFOOT is a device
that more closely meets the requirements for valid traction
evaluation set forth by Nigg (1990). This device has the
advantage of measuring traction both rotationally and
linearly, accommodating various athletic footwear, and using
loading weights similar to those exerted by athletes. The
device is portable and measurements can be made in situ.
In order to more fully test PENNFOOT over a wider range of
conditions and to evaluate the turfgrass and soil
characteristics that affect traction values obtained with
this device, more research was required.
PENNFOOT was used in six experiments to determine the effects
of various factors on traction. These factors included
turfgrass species (Kentucky bluegrass, tall fescue, perennial
ryegrass, red fescue), cutting heights (ranging from 2.3 to
7.6 cm), verdure (present or removed), soil water contents
123
(averaging from 0.20 to 0.30 kg kg-1 and 0.18 to 0.34 kg kg-1
on silt loam soils and 0.13 to 0.17 kg kg-1 on a sandy loam
soil), loading weights (ranging from 47.6 to 116 kg), and
shoe types (molded and studded sole) .
Species differences were detected with the molded shoe but
not the studded shoe. In general, traction on species
followed the order tall fescue ~ Kentucky bluegrass >
perennial ryegrass ~ red fescue. Shoe type did not
significantly affect traction on tall fescue, but with the
other species traction was greater with the studded shoe.
Linear traction was usually higher with lower cutting
heights. Rotational traction was not significantly influenced
by cutting height, but a trend for greater traction with
lower cutting height was present. Removal of verdure on tall
fescue maintained at three cutting heights did not influence
traction. Soil water content affected traction, but the
effect was not consistent across experiments, apparently due
to differences such as range of soil water contents, and type
of traction measurements used. Traction increased with
increasing loading weight.
Although traction on natural surfaces was affected by turf
species, cutting height, soil water content, and shoe type,
it is difficult to generalize about these effects due to
interactions among these factors and the influence of other
factors not measured.
124
This research has raised questions that should be addressed
in future research. For example, why did a shoe by species
interaction exist, how does varying soil water content
interact with soil texture to affect traction, and what
relationship exists among compaction, turfgrass cover, and
traction? The depth of stud penetration into the turf could
explain some differences in traction, but it was not
measured. This factor should be taken into consideration in
future work.
Under the conditions of these experiments, it appears that
recording peak values, rather than the entire curve, would be
sufficient to assess the effects of the various treatments.
In this and previous experiments the peak traction values
generally occurred at 30 or 40 degrees rotation and at 3.8 or
4.4 cm of linear travel. However, in future work on areas
having somewhat different surface characteristics, the
incremental values should be observed to determine
similarities or differences in values throughout the entire
range of motion.
A much more extensive data base is needed to provide
guidelines for maximum playability and to predict the
influence of management practices on traction. Within this
data base an evaluation of human performance as it relates to
traction measurements should be included.
125Bibliography
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Proc. 5th Int. Turfgrass Res. Conf., Avignon, France(Ed. F. Lemaire), INRA, Paris, p. 391-399.
American Society for Testing and Materials. 1990. Annual Bookof ASTM Standards-Soil and Rock; Dimension Stone;Geosynthetics. Standard test method for moisture, ash,and organic matter of peat and other organic soils. D2974-87. American Society for Testing and Materials,
Philadelphia, PA.Baker, S.W. 1989. Technical Note: A standardized sole for
evaluating the' traction and sliding resistanceproperties of artificial turf. J. Sports Turf Res.
Inst. 65:168-170.Baker, S.W. 1991. Temporal variation of selected mechanical
properties of natural turf football pitches. J. Sports
Turf Res. Inst. 67:83-92.Baker, S.W. and M.J. Bell. 1986. Playing Characteristics of
Natural and Synthetic Turf. J. Sports Turf Res. Inst.
62:9-36.Baker, S.W. and P.M. Canaway. 1991. The cost-effectiveness of
different construction methods for Association Footballpitches. II. Ground cover, playing quality and costimplications. J. Sports Turf Res. Inst. 67:53-65.
126Baker, S.W. and P.M. Canaway. 1993. Concepts of playing
quality: Criteria and Measurement. Int. Turfgrass Soc.Res. J. 7:172-181.
Baker, S.W. and S.P. Isaac. 1987. The effect of rootzonecomposition on the performance of winter games pitches.II. Playing quality. J. Sports Turf Res. Inst. 63:67-
affecting the surface stability of a sand rootzone. In:Proc. 6th Int. Turfgrass Res. Conf,. Tokyo, Japan (Ed.
H. Takotoh), p. 189-191.Gramckow, J. 1968. Athletic field quality studies. Cal-Turf
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128Harper, J.C., C.A. Morehouse, D.V. Waddington, and W.E.
Buckley. 1984. Turf management, athletic-fieldconditions, and injuries in high school football.Pennsylvania Agri. Exp. Stn. Prog. Rep. 384. 9 pp.
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Paper. University Park, PA 16802.Holmes, G. and M.J. Bell. 1986. A pilot study of the playing
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62:74-91.Holmes, G. and M.J. Bell. 1987. Standards of playing quality
for natural turf. The Sports Turf Research Institute.
Bingley, West Yorkshire.Lush, W.M., and P.R. Franz. 1991. Estimating turf biomass,
tiller density, and species composition by coring.
Agron. J. 83:800-803.Middour, R.O. 1992. Development and evaluation of a method to
measure traction on turfgrass surfaces. M.S. Thesis.Pennsylvania State Univ., University Park, PA.
Nigg, B.M. 1990. The validity and relevance of tests used forthe assessment of sports surfaces. Med. Sci. in Sports
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129Powell, J.W. and M. Schootman. 1993. A multivariate risk
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130Stanitske, C.L,. McMaster, J.H. and Ferguson, R.J.
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APPENDIX
ADDITIONAL MATERIALS
131
...;..,~:....
:;(~{)~~${~~r.iii::'
Fig. 19. PENNFOOT traction measuring device.
132
133
Fig. 20. Studded and Molded shoes used with PENNFOOTtraction measuring device.
Table 26. Mean traction values for the designated variable in Experiment 1.
Table 33. Mean weight of below-ground vegetation per sample plug(81 cm2 by 2 cm depth) for each species x cutting heightplot in Experiments 2, 3, and 4.
----- Replications -----Species Cutting I II III Average
10 to 15 15.3 18.9 21.2 21.215 to 20 14.7 18.2 20.8 21.020 to 25 14.2 18.0 20.4 20.7
Isd (0.05) NS NS NS NS .
Outside hashmark
10 to 15 14.2 17.6 19.5 19.815 to 20 14.4 18.3 20.0 20.420 to 25 14.2 17.7 20.0 20.4
Isd (0.05) NS NS NS NS
Table 62. Mean rotational traction values for blocks acrossshoe types in Experiment 6.b, inside and outside thehashmark, using a 116 kg loading weight.
Yard ------ degrees of rotation ------lines 10 20 30 40
10 to 15 20.5 26.5 30.1 29.915 to 20 20.3 26.0 29.5 29.720 to 25 19.1 24.9 28.5 29.3
lsd (0.05) NS NS NS NS
Outside hashmark
10 to 15 19.5 25.1 27.1 27.915 to 20 20.5 27.1 29.9 29.420 to 25 20.3 26.0 28.8 30.8
lsd (0.05) NS NS NS NS
...........o
Table 63. Mean rotational traction values for blocks acrosssoil water treatments in Experiment 6.c, inside andoutside the hashmark, using a 116 kg loading weightand the molded shoe.
Yard ------ degrees of rotation-------lines 10 20 30 40
10 to 15 22.3 29.4 33.1 33.115 to 20 21.9 0.0 32.2 32.220 to 25 21.0 28.7 31.8 32.4
lsd (0.05) NS NS NS NS
Outside hashmark
10 to 15 21.2 27.8 30.8 31.715 to 20 21.9 28.5 32.9 33.620 to 25 22.3 28.8 32.2 32.4
lsd (0.05) NS NS NS NS
-"-
172
Table 64. Mean rotational traction values for the designatedvariables for the ~ombined Experiments, inside andoutside the hashmarks, for loading weightsin Experiment 6.a.
Variable ------ degrees of rotation ------10 20 30 40
Loading weight---------------- Nm ---------------
116 kg 16.9 21. 6 24.4 24.888 kg 14.8 18.5 20.8 21.1
59.9 kg Inside 12.1 14.6 16.2 16.259.9 kg Outside 11.3 13 .8 15.3 15.488 kg Inside 15.3 19.0 21.2 21.588 kg Outside 14.3 18.0 20.4 20.8116 kg Inside 16.7 21.5 23.6 25.3116 kg Outside 17.1 21.7 23.8 24.4
lsd (0.05) NS NS NS NS NS
173
Table 65. Mean rotational traction values for the designatedvariables, for the combined experiments, inside andoutside the hashmark, for shoe types inExperiment 6.b.
Variable ------ degrees of rotation ------10 20 30 40
Table 66. Mean rotational traction values for the designatedvariables, for the combined experiments, inside andoutside the hashmark, for soil waterin Experiment 6.c.
Variable ------ degrees of rotation ------10 20 30 40