39 RESULTS AND DISCUSSION Evaluation of traffic and disruption of golf putting green Microrelief measurements. The average depth of depression for the heel of a sneaker, heel of a golf shoe, 2.5-cm wide rigid tire wheelchair, and 3.5-cm wide pneumatic tire wheelchair for all putting greens throughout 1996 is shown in Table 4. The lack of significant differences in measurements of surface hardness, surface strength, and gravimetric moisture content for the 0- to 5-cm depth below the turf surface for each form of traffic indicated that the measurements of depression were collected randomly and not biased by conditions. The heel of a golf shoe and sneaker did not differ in the depth of depression caused after applying 30 seconds of static pressure. As expected, the greatest depth of depression occurred with the 2.5-cm rigid tire wheelchair. The 3.5-cm wide pneumatic tire wheelchair caused less depression than the 2.5- cm rigid tire, however, depressions caused by the 3.5-cm wide pneumatic wheelchair were greater than the heel of either shoe (Table 4). The pneumatic tires of single rider carts were not measured on enough occasions to compare with the other forms of traffic over the entire season. Sufficient data were collected on 11 and 18 September and 2 and 28 October 1996 to evaluate the depth of depression caused by the heel of a sneaker and golf shoe combined and the 16.5- and 15.2-cm wide pneumatic tire of the Golf Express and Lone Rider cart, respectively. The average depth of depression for
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39RESULTS AND DISCUSSION
Evaluation of traffic and disruption of golf putting green
Microrelief measurements. The average depth of depression for the heel
of a sneaker, heel of a golf shoe, 2.5-cm wide rigid tire wheelchair, and 3.5-cm
wide pneumatic tire wheelchair for all putting greens throughout 1996 is shown
in Table 4. The lack of significant differences in measurements of surface
hardness, surface strength, and gravimetric moisture content for the 0- to 5-cm
depth below the turf surface for each form of traffic indicated that the
measurements of depression were collected randomly and not biased by
conditions.
The heel of a golf shoe and sneaker did not differ in the depth of
depression caused after applying 30 seconds of static pressure. As expected,
the greatest depth of depression occurred with the 2.5-cm rigid tire wheelchair.
The 3.5-cm wide pneumatic tire wheelchair caused less depression than the 2.5-
cm rigid tire, however, depressions caused by the 3.5-cm wide pneumatic
wheelchair were greater than the heel of either shoe (Table 4).
The pneumatic tires of single rider carts were not measured on enough
occasions to compare with the other forms of traffic over the entire season.
Sufficient data were collected on 11 and 18 September and 2 and 28 October
1996 to evaluate the depth of depression caused by the heel of a sneaker and
golf shoe combined and the 16.5- and 15.2-cm wide pneumatic tire of the Golf
Express and Lone Rider cart, respectively. The average depth of depression for
Table 4. Depth of depression, percent rebound, surface hardness, surfacestrength, and gravimetric moisture content of the 0- to 5-cm depth zone belowthe turf surface measured for each form of traffic averaged over all puttinggreens measured in 1996.
40
Depth of Surface Surface MoistureForm of Traffic nt Depression Rebound t Hardness ~ Strength 11 Content #
*** Significant at the 0.001 probability level.t Number of observations.t Percent rebound of depth of depression after 30 minutes; the number ofobservations for percent rebound data was 18,20,31, and 32 for the heel of asneaker, shoe, 2.5- wide rigid tire, and 3.5-cm wide pneumatic tire wheelchair,respectively.S Surface hardness, maximum deceleration measured in gravities.11 Surface strength measured at the O-to2.5-cm depth zone.# Gravimetric moisture content of the 0- to 5-cm depth zone below the turf surface.
41the pneumatic tires of the single rider carts was greater than the heel of the
shoes (Table 5).
The amount of rebound of the putting green 30 minutes after traffic was
not statistically different for each of the forms of traffic (Table 4 and 5). Thus,
the depth of depression initially caused by wheeled traffic would remain as
deeper depressions 30 minutes after traffic compared to the depression caused
by foot traffic.
Ball roll deflection. Deflection of golf ball roll was evaluated for traffic with
the 2.5-cm wide rigid tire wheelchair in 1996. As evidenced by the data, ball roll
over the path traveled by wheel traffic was altered, however, results were
variable. Results indicated that the lateral position of golf ball roll was
significantly altered 20% of the time when the depth of depression was 1.5 mm
or less after traffic (Table 6). The lateral position of golf ball roll was significantly
altered 60% of the time when the depth of depression was greater than 1.5 mm
after traffic.
The homogeneity of the variances of the forward and lateral positions was
only significant three times during ball roll evaluation in 1996 and did not appear
to be a useful determination of ball roll deflection. The change in lateral position
appears to be the best indicator of ball roll deflection.
The forward position measurement was significantly different after traffic
on seven out of sixteen dates during 1996. The forward position measurement
was not strongly associated with depth of depression caused by wheel traffic.
42Table 5. Depth of depression, percent rebound, surface hardness, surfacestrength, and gravimetric moisture content of the 0- to 5-cm depth zone belowthe turf surface measured for foot traffic and single rider carts averaged over allputting greens measured on 11 and 18 Sept. and 2 and 28 Oct. 1996.
Form of TrafficDepth of Surface Surface Moisture
nt Depression Rebound; Hardness9 Strength~ Content#
16.5 and 15.2 cm wide 8 1.1 26 57 12.4 28.7pneumatic tiresingle rider carts
LSD (0.05) 0.4* NS NS NS NSCV; 0/0 34 57 7 10 53
* Significant at the 0.05 probability level.t Number of observations.t Percent rebound of depth of depression after 30 minutes.9 Surface hardness maximum deceleration measured in gravities.~ Surface strength measured at the 0- to 2.5-cm depth zone.# Gravimetric moisture content of the 0- to 5-cm depth zone below the turfsurface.
Table 6. The final resting lateral and forward position of eight golf ball rolls across a putting green at four locations 'before and after traffic with a2.5-cm rigid tire wheelchair in 1996. Ball roll intersected traffic at 30° angle and within the last 0.9 m of the final resting spot.
Lateral Position Forward PositionLocation Date Depth t Before After Vaq: T test~ Before After Var T test
mm ---------- cm ---------- ------------- cm ----------Plainfield
*, **, ***, Significant at the 0.05. 0.01, and 0.001 probability levels, respectively. NS Not significant.t Depth of depression immediately after traffic, 0.0 = no traffic.:I: F test for homogeneity of the variances.~ Probability of a greater t-value.1J Depression made with 3.5 cm wide pneumatic tire wheelchair.
~w
44When differences were observed, the change in forward position resulted in an
increased length of ball roll eight out of nine times. This increase in ball roll
length could be caused by the repeated ball rolls lying down turfgrass blades
along the path of ball travel.
Ball roll deflection was evaluated in 1997 for the heel of a golf shoe, 2.5-
cm wide rigid tire wheelchair, and 3.5-cm wide pneumatic tire wheelchair (Tables
7, 8, and 9). No traffic (0.0 mm of depression) altered lateral position of ball roll
only once (11 % of the time) in 1997. The heel of the golf shoe altered the lateral
position of the golf ball roll 50%) of the time (Table 7). The depth of depression
caused by the heel of a golf shoe ranged from 0.4 to 0.9 mm.
Depressions from wheeled traffic in 1997 produced similar results as in
1996. The 2.5- and 3.5-cm wide wheeled traffic altered ball roll 22% of the time
when depth of depression was 2.0 mm or less (Table 8 and 9). When the depth
of depression caused by wheeled traffic was greater than 2.0 mm, the lateral'
position of ball roll was altered 33% of the time.
Relationship of gravimetric moisture content with depth of depression,
surface hardness, and surface strength
The depth of depression caused by the heel of a golf shoe and sneaker
changed very little over the range of gravimetric moisture content for the 0- to 5-
cm depth below the turf surface on high sand greens and topdressed modified
native soil greens (Figure 3). Conversely, the depth of depression for the 2.5-cm
Table 7. The final resting lateral and forward position of six golf ball rolls across a putting green before and after traffic with theheel of a golf shoe on the Metedeconk National Golf Club nursery green during 1997. Ball roll intersected traffic at 30° angle andwithin the last 0.9 m of the final resting spot.
Lateral Position Forward PositionDate Depth t Before After Var + T test 9 Before After Var T test
mm --------- cm -------- --------- cm ----------21 May
*, **, ***, Significant at the 0.05, 0.01, and 0.001 probability levels, respectively.NS Not significant.t Depth of depression immediately after traffic, 0.0 = no traffic.* F test for homogeneity of the variances.~ Probability of a greater t-value.
Table 8. The final resting lateral and forward position of six golf ball rolls across putting green before and after traffic with a 2.5-cmwide rigid tire wheelchair on the Metedeconk National Golf Club nursery green during 1997. Ball roll intersects traffic at 300 angleand within the last 0.9 m of final resting spot.
------------ Lateral Position ------------ ------------ Forward Position ------------Date Depth t Before After Var t T test ~ Before After Var T test
mm --------- cm -------- --------- cm ----------21 May
*, **, ***, Significant at the 0.05, 0.01, and 0.001 probability levels, respectively.NS Not significant.t Depth of depression immediately after traffic, 0.0 = no traffic.t F test for homogeneity of the variances.~ Probability of a greater i-value.
Table 9. The final resting lateral and forward position of six golf ball rolls across putting green before and after traffic with a 3.5-cmwide pneumatic tire wheelchair on the Metedeconk National Golf Club nursery green during 1997. Ball roll intersects traffic at 30°angle and within the last 0.9 m of final resting spot.
------------ Lateral Position ------------ ------------ Forward Position ------------Date Depth t Before After Var:f: T test 9 Before After Var T test
mm --------- cm -------- --------- cm ----------21 May
*, **, ***, Significant at the 0.05, 0.01, and 0.001 probability levels, respectively.NS Not significant.t Depth of depression immediately after traffic, 0.0 = no traffic.t F test for homogeneity of the variances.~ Probability of a greater t-value.
4.0. n e---- High sand greens
...-e--- Topdressed modified native soil greens
5040
Y2=0.4 + 0.001x •r = 0.01 NS
•.•~-eI--&--!_"•••
302010
Y2=0.29 + 0.016xr = 0.09 NS
3.0
2.0
1.0
,0.0o
c:o--InInCDl-e..CDC't-oJ:~e..CDC
Gravimetric Soil Moisture (Ok)
Figure 3. Relationship between gravimetric moisture content of the 0- to 5-cm depth zonebelow the turf surface and depth of depression for the heel of a golf shoe after 30 secondsof static pressure on rootzones of high sand and topdressed modified native soil.NS = Not significant.
49as the gravimetric moisture content for the 0- to 5-cm depth below the turf
surface increased on high sand greens (Figures 4 and 5). The depth of
depression caused by the tire of wheelchairs on topdressed ,modified native soil
greens did not exhibit a clear relationship with the gravimetric moisture content
- 6f the 0- to 5-cm depth below the turf surface (Figures 4 and 5).
Surface hardness measurements increased as the gravimetric moisture
content for the 0- to 5-cm depth below the turf surface decreased (Figure 6). It
was also apparent that two distinct groupings existed within the data which
described the relationship between gravimetric moisture content of the 0- to 5-
cm layer below the turf surface and surface hardness. The two groups were also
described well by the organic matter content at the O-to 5-cm soil depth below
the upper mat layer. One group of data had gravimetric moisture contents below
27%>and organic matter contents below' 2.0% and will be referred to as high
sand greens (Table 1). The other group typically had moisture contents greater
than 27%>and organic matter contents above 2.0%>and will be referred to as
topdressed modified native soil greens.
The relationship between gravimetric moisture content for the O-to 5-cm
depth and surface strength is shown in Figure 7. Surface strength did not exhibit
a significant relationship with gravimetric moisture content of the 0- to 5-cm
depth.
The most obvious deviation from these two groupings was the 12th green
at Pine Valley Golf Club. Although the organic matter level for the 0- to 5-cm
Figure 4. Relationship between gravimetric moisture content of the 0- to 5-cm depth zonebelow the turf surface and depth of depression for 2.5-cm wide rigid tire wheelchair after 30seconds of static pressure on rootzones of high sand and topdressed modified native soil.NS = Not significant. + Significant at the 0.07 probability level.
()'1o
4.0
o
504030
••••........ _ n .. ~ .•
•. - H _
• ••Y2= 1.26 - O.OOlx •r = 0.02 NS
2010
o
---8-- High sand greens
-e-- Topdressed modified native soil greens
ooo ~O00
6 gcP 0Y2= 0.05 + 0.089xr = 0.29 •
o
1.0
2.0
3.0
0.0
r::o.-tntnCDl-e.CDC~o.J:.....e.CDC
Gravimetric Soil Moisture (Ok)
Figure 5. Relationship between gravimetric moisture content of the 0- to 5-cm depth zonebelow the turf surface and depth of depression for 3.5-cm wide pnuematic tire wheelchair after30 seconds of static pressure on rootzones of high sand and topdressed modified native soil.NS = Not significant. * Significant at the 0.05 probability level.
100.,.-... 90C)
~U) 80U)(1) 70c:-c"- 60nsJ:(1) 50(.)
~ 40:::::sen 30
200
--+=-}---- High sand greens
Y2=98.8 - 0.94xr = 0.40 •••
10 20 30 40 50 60Gravimetric Moisture (0/0)
Figure 6. Relationship between gravimetric moisture content of the 0- to 5-cm depth zonebelow the turf surface and surface hardness (maximum deceleration measured in gravities)for rootzones of high sand and topdressed modified native soil.*** Significant at the 0.001 probability level. .
Topdressed modified native soil greens
Y2=20.6 .. 0.11xr = 0.05 NS
•...( ).. ,....
n, • ~_~ •• _ •••
)...•.~-:-I •••
( )
Pine Valley Golf Club
High sand greens
-----e--•
8
24
28
16
20
12---oen4
o 10 20 30 40 50Gravimetric Moisture (0/0)
60
Figure 7. Relationship between gravimetric moisture content of the 0- to 5-cm depthzone below the turf surface and surface strength measured for the 0- to 2.5-cm depthzone for rootzones of high sand and topdressed modified native soil.NS = Not significant. 01
W
54depth below the upper mat layer at Pine Valley was above 2.0%, its values for
gravimetric moisture content of the 0- to 5-cm layer below the turf surface are
similar to high sand greens. The 0- to 5-cm depth below the upper mat layer at
Pine Valley was high in sand content and low in organic matter content
compared to the other topdressed modified native soil greens (Table 2) and may
be responsible for moisture values being similar to greens built using high sand
root zone mixes.
Test methods for determining bearing strength of golf greens
Surface hardness and surface strength measurements were compared to
depth of depression measurements to evaluate if these quantitative tests could
describe the bearing strength of golf greens. The organic matter content at the
0- to 5-cm soil depth below the upper mat layer was strongly correlated with
surface hardness, surface strength, and depth of depression data. Therefore,
surface hardness and strength measurements were regressed separately with
depth of depression measurements on high sand and topdressed modified
native soi I greens.
Surface hardness and strength were more strongly correlated to depth of
depression on high sand greens than topdressed modified native soil greens
over all forms of traffic (Table 10 and 11). The depth .of depression caused by
the heel of the golf shoe and sneaker changed very little over the range of
surface hardness and strength measurements on high sand greens (Figures 8
and 9). However, the depth of depression created by the tires of the wheelchairs
55Table 10. Coefficient of determination (r2)J model significance (P > F), andnumber of observations (n) for simple linear regression of the depth ofdepression of the forms of traffic with surface hardness and ,strength values onhigh sand greens.
Form of Traffic Variable t n P>F
Heel of golf shoe Hardness L 21 0.39 0.003and sneaker HardnessQ 0.50 0.002
Strength L 19 0.21 0.05Strength Q 0.29 0.06
2.5 cm wide rigid Hardness L 16 0.44 0.005tire wheelchair HardnessQ 0.46 0.02
Strength L 14 0.43 0.01Strength Q 0.46 0.03
3.5 cm wide pneumatic Hardness L 17 0.40 0.006tire wheelchair Hardness Q 0.67 0.001
Strength L 15 0.22 0.07Strength Q 0.50 0.01
16.5 and 12.7 cm wide Hardness L 6 0.23 0.34pneumatic tire HardnessQ 0.77 0.11single rider carts
Strength L 6 0.00 0.97Strength Q 0.24 0.65
t L = linear equation and Q = quadratic equation.
56Table 11. Coefficient of determination (~)t model significance (P > F), andnumber of observations (n) for simple linear regression of the depth ofdepression of the forms of traffic with surface hardness and strength values ontopdressed modified native soil greens.
Form of Traffic Variable t n P>F
Heel of golf shoe Hardness L 21 0.01 0.67and sneaker Hardness a 0.07 0.50
Strength L 20 0.15 0~09Strength a 0.27 0.07
2.5 cm wide rigid Hardness L 19 0.18 0.07tire wheelchair Hardness a 0.23 0.12
Strength L 18 0.11 0.17Strength a 0.23 0.13
3.5 cm wide pneumatic Hardness L 16 0.03 0.52tire wheelchair Hardness a 0.09 0.53
Strength L 15 0.03 0.55Strength a 0.12 0.47
16.5 and 12.7 cm wide Hardness L 3pneumatic tire Hardness asingle rider carts
Strength L 3 0.75 0.33Strength a
t L = linear equation and Q = quadratic equation.
90
••H
~ = 5.6 - 0.05xr = 0.44 **
l-:J
•[J
[]LJe [1
••[J- .
o [J• [J•"--A-- ••
• -A-- 'A-A.".•
50 60 70 80Surface Hardness (g)
-----e-- Rigid tire wheelchair
----EJ--- Pnuematic tire wheelchair
---A---- Heel of golf spike and sneaker••i:,"--~. __\2[]
~ = 26.2 - 0.689x + 0.005x ""r = 0.67 .. * "
~= 6.8 - 0.169x + 0.001x2 •r = 0.50 **
3
1
o40
4
c::o.-UJUJCD'- 2c.CDC'I-o.t:......C.CDC
Figure 8. Relationship between surface hardness (maximum deceleration measured ingravities) and the depth of depression caused by 30 seconds of static pressure from theheel of a sneaker and golf shoe, 2.5-cm wide rigid tire wheelchair, and 3.5-cm widepnuematic tire wheelchair on high sand greens located in New Jersery during 1996.**, *** Significant at the 0.01 and 0.001 probability levels, respectively.
3
1/.
[J
r J
[I
A
..,A--.----A
•
-e-- Rigid tire wheelchair
-E-]-- Pnuematic tire wheelchair
.~-- Heel of sneaker and golf shoe
••
••••[J
[l
Y = 61.2 - 27,7x'" 3.j~~r2 = 0.50 .... •
[]
[] .' []LJ
I] 0A A [1
A -', -, ,-,~_ ..A ,.'.~--,t-._-;&---.t .'---. __'n A-
Y = 11.9 _4.6x + 0.53i A A '.i- '.'. ---'.r2 = 0.29~' A
Y2=19.2 - 3.1xr = 0.43" •
o
4
c:o.-tntnCD~ 2c.CDC"-o.c:.....0-CDC
12 16 20-2Surface strength (kg cm )
Figure 9. Relationship between surface strength measured for the 0- to 2.5-cm depthzone and the depth of depression caused by 30 seconds of static pressure from the heelof a sneaker and golf shoe, 2.5-cm wide rigid tire wheelchair, and 3.5-cm wide pnuematictire wheelchair on high sand greens located in New Jersey during 1996.+, ** Significant at the 0.06 and 0.01 probability level, respectively. (J'1
Figure 10. Relationship between surface hardness (maximum deceleration measuredin gravities) and the depth of depression caused by 30 seconds of static pressure fromthe heel of a sneaker and golf shoe, 2.5-cm wide rigid tire wheelchair, and 3.5-cm widepnuematic tire wheelchair on topdressed modified native soil greens located in NewJersey during 1996. NS = Not significant. + Significant at the 0.07 probability level. m
a
12 16 20-2Surface strength (kg cm )
24
•--
---e- Rigid tire wheelchair
_n_[] __ Pnuematic tire wheelchair
,'.', l'-'.
--- ..--
Heel of sneaker and golf shoe
••••1[1 ••
• [J 1.1-[J----- -Tr-"--
[J 0 CJ t'~•6. {\ L
L~ _D.-----------.- ... '---ZS-TJ 6
••
/\
•'2= 11 .4 - 1.~xr = 0.11 NS
~= 5.0 - 0.28£L-r = 0.03 NS
~= 0.30 ~ 0.41xr = 0.15
3
o8
1
.--....4EE
~
co--enen(1)...2c.(1)C....o.c::..,Q.(1)C
Figure 11. Relationship between surface strength for the 0- to 2.5-cm depth zone anddepth of depression caused by 30 seconds of static pressure from the heel of a sneakerand golf shoe, 2.5-cm wide rigid tire wheelchair, and 3.5-cm wide pnuematic tirewheelchair on topdressed modified native soil greens located in New Jersey during 1996.NS = Not significant. + Significant at the 0.09 probability level, respectively.
62The depth of depression caused by the different forms of traffic on high
sand greens was associated with the factors of depth and organic matter content
of the upper mat layer and organic matter content of the topdressing material
(Table 12). The depth and organic matter content of the upper mat layer were
contained in the best single variable equations. The depth and organic matter
content of the upper mat layer was negatively correlated to the bulk density of
the upper mat layer (data not ~ho~n). The compactibility of a soil depends on
the initial compactness of the soil (Hakansson et. al. I 1988), therefore, the depth
and organic matter content of the upper mat layer may indicate the compactibility
of the turf surface and associated to the depth of depression caused by traffic.
Equations describing depth of depression on the topdressed modified
native soil greens did not have a single unique edaphic property that remained
in the best fit models for all forms of traffic. Depth of depression did not vary
with surface hardness and strength values on topdressed modified native soil
greens (Figures 10 and 11). The topdressed modified native soil greens may
have rootzones with a great amount of variation and the depth of depression
caused by traffic can not be accurately described by anyone edaphic property
or surface measurement. Apparently the bearing strength or 'resiliency' of
topdressed modified native soil greens was similar over a broad range of
conditions.
The organic matter content of the upper mat layer remained in all three
best single variable equations that were significantly associated with the percent
Table 12. Regression equations, coefficient of multiple determination (R2), model significance (P > F), coefficient
of simple determination (r2) of best single variable model, and number of observations (n) for edaphic properties of
golf putting greens associated with the depth of depression (Y) of the forms of traffic on high sand greens andtopdressed modified native soil greens.
Construction Type Best Multipleand Form of Traffic + Variable Equation 9
t * ** All variables in the model significant at the 0.10,0.05 and 0.01 level, respectively.t 2.5 cm tire = 2.5 cm wide rigid tire wheelchair, 3.5 cm tire = 3.5 cm wide pneumatic tire wheelchair, and heel = heel of sneaker andgolf shoe for 30 seconds of stationary pressure.~ X1 = height of cut, X2 = depth of upper mat layer, X3 = organic matter content of the upper mat layer, X4 = organic matter content of theo to 5 cm depth below the upper mat layer, Xs = organic matter content of the topdressing material, ~ = soil temperature at the 5-cmdepth, and X7 = gravimetric moisture content of the 0 to 5 cm depth below the green surface.
0>w
64rebound of a depression 30 minutes after traffic with the 2.5- and 3.5-cm wide
tire wheelchairs (Table 13). Thomas and Guerin (1981) developed a method to
measure the elasticity of sports turf, elasticity measurements were time intervals
required for the compacted area to closely return to its original state. They
observed differences in elasticity for growing media of different soil textures.
The organic matter content of the upper mat layer, like soil texture, may affect
the elasticity or rebound of a depression by wheeled traffic.
The percent rebound of a depression 30 minutes after foot traffic did not
show a strong association with any of the edaphic features studied (Table 13).
Although the percent rebound of a depression for foot traffic is similar to rebound
for wheeled traffic, the depth of depression was greater for the wheeled traffic.
The depth of depression for foot traffic may be to small to observe an
association of edaphic properties with the percent rebound of a depression.
Edaphic properties associated with surface hardness and strength
Multiple regression analysis for edaphic properties associated with
surface hardness and strength was performed over all green types (high sand
and topdressed modified native soil greens combined). The organic matter
content of the 0- to 5-cm depth below the upper mat layer and the gravimetric
moisture content of the 0- to 5-cm depth below the surface remained in the best
multiple variable equation fQr both surface hardness and strength (Table 14).
The height of cut and organic matter content of the upper mat layer also
remained in the best multiple variable equation for surface hardness and surface
Table 13. Regression equations, coefficient of determination (R2), model significance (P > F), coefficient of simple
determination (r) of best single variable model, and number of observations (n) for edaphic properties of golfputting greens associated with the percent of rebound of a depression (Y) 30 minutes after different forms of trafficon high sand and topdressed modified native soil greens.
t * ** All variables in the model significant at the 0.10,0.05,0.01 level.:J: 2.5 cm tire = 2.5 cm wide rigid tire wheelchair, 3.5 cm tire = 3.5 cm wide pneumatic tire wheelchair, and heel = heel of sneaker andgolf shoe for 30 seconds of stationary pressure.9 X1 = height of cut, X2 = depth of upper mat layer, X3 = organic matter content of the upper mat layer, Xt = organic matter content of theo to 5 cm depth below the upper mat layer, Xs = organic matter content of the topdressing material, Xa = soil temperature at the 5-cmdepth, and X7 = gravimetric moisture content of the 0 to 5 em depth below the turf surface.
m()1
Table 14. Regression equations, coefficient of determination (R2), model significance (P > F), coefficient of simple
determination (r2) of best single variable model, and number of observations (n) for edaphic properties of golf
putting greens associated with surface hardness and strength (Y).
Surface Measurement
Surface Hardness
Best MultipleVariable Equation t n P>F
Best SingleVariable Equation t r2 P>F
Y = 103 + -5.9*X1 + 2.5*X4 - O.9*X7 99
Surface Strength
0.52 0.001* Y = 76 - 0.41*X7 0.33 0.001
Y = 13.5 + 0.46*X3 + 0.58*X4 - 0.15*X7 94 0.44 0.001 * Y = 11.7 + 0.43*X3 0.34 0.001
* All variables in the model significant at the 0.05 level.t X1 = height of cut, X2 = depth of upper mat layer, X3 = organic matter content of the upper mat layer, X4 = organic matter content of theo to 5 cm depth below the upper mat layer, Xs = organic matter content of the topdressing material, ~ = soil temperature at the 5-cmdepth, and X7 = gravimetric moisture content of the 0 to 5 cm depth below the green surface.
0>0>
67strength, respectively. The association of the height of cut and organic matter
content of the upper layer with surface hardness and strength will be discussed
later with the analysis at specific gravimetric moisture levels.
As discussed previously, surface hardness and strength were separated
into two groups based on gravimetric moisture content of the 0- to 5-cm depth
below the turf surface (Figures 6 and 7) and organic matter content of the 0- to
5-cm depth below the upper mat layer (Table 2). The factors of gravimetric
moisture content of the 0- to 5-cm depth below the turf surface and organic
matter content of the 0- to 5-cm depth below the upper mat .layer separated the
rootzones into high sand and topdressed modified native soil greens. Thus the
type of root zone was consistently associated with surface hardness and
strength and is an important consideration when evaluating the bearing strength
of putting greens.
The examination of the relationship between surface hardness and
edaphic properties at specific gravimetric moisture levels was performed to
identify edaphic characteristics other than gravimetric moisture which influenced
surface hardness measurements. Surface hardness measurements were
grouped into four levels of gravimetric moisture content: 10 to 15, 15 to 20, 35 to
40, and 40 to 45%). The 10 to 150ft,and 15 to 20% levels of gravimetric moisture
consisted of high sand greens and the 35 to 400ft,and 40 to 45% were
topdressed modified native soil greens.
68The best single variable model associated with surface hardness at the
10- to 15- and 15- to 20-0/0levels of gravimetric moisture cqntent of the O-to 5-cm
depth below the turf surface included the variable of depth of the upper mat layer
(Table 15). Rogers et al. (1988) found that lack of turf cover inside the
hashmarks of high school athletic fields contributed to higher surface hardness
measurements. The depth of mat layer could provide a cushioning effect similar
to turf cover for surface hardness measurements on high sand greens.
At the 35 to 40% gravimetric moisture range, the height of cut remained in
the best fit single variable model accounting for the largest percentage of the
variation of surface hardness (Table 15). While the relative change in the height
of cut between putting greens does not appear to be large enough to change
readings of surface hardness, the factor of height of cut is likely associated with
other management practices (i. e. I rolling, topdressing, irrigation, etc.) which
influence surface hardness.
The organic matter content of the upper mat layer was in the best single
variable equation of surface hardness at the 40 to 45 0;0range of gravimetric
moisture content. Surface hardness would be expected to decrease as the
organic matter content of the upper mat layer increased, increased organic
matter content would reduce bulk density and lower surface hardness values
(Rogers et. aI., 1988). However, the equation indicates a positive relationship,
that as organic matter content increases, surface hardness increases. Possibly,
Table 15. Regression equations, coefficient of determination (R2), model significance (P > F), coe.tficient of simpledetermination (r2
) of best single variable model, and number of observations (n) for edaphic properties of golfputting greens associated with surface hardness and strength (Y) at four distinct moisture ranges.
Surface Me~surementand Moisture Content t
Best MultipleVariable Equation 9 n P>F
Best SingleVariable Model P>F
Surface Hardness:----%----
10 to 15 Y = 109 - 2.5*X2 + 1.4*X3 -12.5*X4 - 17.9*Xs 20 0.53 0.02* Y = 87.7 - 1.28*X2 0.24 0.0315 to 20 Y = 103 - 2.0*X2 - 9.5*X4 -10.8*Xs 19 0.47 0.02t Y = 77.3 - 0.97*X2 0.26 0.0335 to 40 Y= 72 - 7.5*X1 + 1.7*X2 + 3.3*Xs 11 0.70 0.03t Y = 79.2 - 4.05*X1 0.32 0.0740 to 45 Y= 8 + 1.6*X3 + 4.6*X4 17 0.77 0.001 ** Y = 36.9 + 1.79*X3 0.46 0.03
Surface Strength:---- % ----
10 to 15 Y = 6.2 + 0.42*X3 + 0.09*X6 19 0.53 0.003* Y = 11.0 + 0.56*X3 0.41 0.00215 to 20 Y = 9.7 + 0.60*X3 13 0.37 0.009** Y = 9.7 + 0.60*X3 0.37 0.00935 to 40 Y = 9.6 + 0.65*X3 11 0.70 0.001 *** Y = 9.6 + 0.65*X3 0.70 0.00140 to 45 Y = 3.4 + 0.41 *X2 + 0.66*X3 17 0.76 0.001 ** Y = 8.2 + 0.60*X3 0.60 0.001
t * ** *** All variables in the model significant at the 0.10, 0.05, 0.01, and 0.001 levels, respectively.:I: Gravimetric moisture content for the 0- to 5-cm depth below the turf surface.~ X1 = height of cut, X2 = depth of upper mat layer, X3 = organic matter content of the upper mat layer, X4 = organic matter content of theo to 5 cm depth below the upper mat layer, Xs = organic matter content of the topdressing material, and ~ = soil temperature at the 5-cmdepth.
m<0
70when upper mat layers are at high moisture contents, increased organic matter
content of that layer may increase surface hardness.
Factors associated with surface strength other than gravimetric moisture
content of the 0- to 5-cm depth below the turf surface were determined using
best fit multiple regression models similar to surface hardness (Table 15). The
organic matter content of the upper mat layer was in all best fit multiple and
single variable models for the four narrow moisture ranges. Penetration
resistance increased as percentage of organic matter in the soil mixture and
amount of rooting increased (van Wijk and Beuving, 1980). The organic matter
content of the mat layer was measured by loss on ignition, this loss can be
associated with either plant debris or organic humus, an increase in either of
these would be expected to be associated with increased surface strength.
71SUMMARY
A traffic event exerts a force on a surface that results in pressures being
distributed to the surface and down through the soil below. The magnitude of
the forces exerted and the condition of the surface being trafficked will determine
the amount of deformation of the surface after a traffic event.
The amount of depression was measured immediately after 30 seconds of
static pressure from the heel of a shoe, a 2.5-cm wide rigid tire wheelchair, and a
3.5-cm pneumatic tire wheelchair on golf putting greens. A change in microrelief
was used to measure the depth of depression occurring after 30 seconds of
static pressure for each form of traffic. The depth of depression was different for
the forms of traffic evaluated; the wheeled traffic was associated with greater
depth of depression compared to foot traffic.
The 0- to 5-cm depth zone below the upper mat layer is composed of
material used during construction and/or topdressing of a putting green. The
organic matter content and gravimetric moisture content of the 0- to 5-cm depth
zone below the upper mat layer characterized two distinct group of the putting
greens studied. One group, designated as high sand greens, had organic
matter levels below 2%)and gravimetric moisture contents less than 27%. The
other, referred to as topdressed modified native soil greens, had organic matter
levels above 2°1«> and gravimetric moisture content greater than 27°1«>.
Surface hardness and surface strength measurements were used to
characterize putting green surfaces. Surface hardness was measured with the
72Clegg Impact Soil Tester. Surface strength was measured for the 0- to 2.5-cm
depth of putting greens with a hand held penetrometer.
The depth of depression caused by traffic on high sand greens was lower
when surface hardness was higher. The depth of depression for the heel of a
16 kg cm-2 on high sand greens would be associated with depth of depression
measurements that altered bal/ rol/lateral distance 220/0of the time in 1997.
74Edaphic properties of putting greens were examined for relationships with
depth of depression and percent rebound of a depression .. Multiple regression
best fit equations indicated that the depth of the upper mat layer was an
important factor associated with the depth of depression on high sand putting
greens. Greater rebound of a depression 30 minutes after traffic was associated
with higher organic matter content of the upper mat layer on high sand and
topdressed modified native soil greens.
Surface hardness measurements decreased with increasing gravimetric
moisture for both green construction types. Rogers and Waddington (1990)
similarly found impact absorption decreased with increased gravimetric moisture
for high school athletic fields. Multiple regression analysis was used to help
identify the most important variables controlling surface hardness at narrow
ranges of gravimetric moisture. The depth of the upper mat layer was included
in the best fit models of surface hardness at the selected moisture ranges of high
sand greens.
Surface strength measurements were evaluated at different moisture
ranges similarly to surface hardness. The organic matter content of the upper
mat layer remained in the best single variable equation for edaphic features
associated with surface strength at all four narrow gravimetric moisture ranges
evaluated.
The depth and organic matter content of the upper mat layer was
associated with the depth of depression, percent rebound of a depression,
75surface harness, and surface strength, These edaphic characteristics along with
gravimetric moisture content of the 0- to 5-cm depth zone below the turf surface
and organic matter content of the 0- to 5-cm depth zone below the upper mat
layer are important factors affecting the bearing strength of putting greens.
The results indicate that the depth of depression after traffic with a 2.5-
and 3.5 cm wide tire wheelchairs was dependent on surface conditions
(hardness and strength) for high sand greens, whereas the depth of depression
caused by foot traffic did not change under varying surface conditions. The
edaphic properties associated with depth of depression, surface hardness, and
surface strength were depth and organic matter content of the upper mat layer.
The evaluation of depth and organic matter content of the upper mat layer in
designed replicated experiments would provide a better understanding of the
effect these factors have on the depth of depression after traffic events.
Ball roll deflection needs further study if depth of depression
measurements are to be clearly interpreted for acceptable limits of depression
and interference with play. Further investigation is necessary to determine if
values of surface hardness and strength represent the entire range of surface
conditions found on topdressed modified native soil greens.
Future work might also include the following. The evaluation of different
width pneumatic tires (6.4, 7.6, 10.1 cm) for depth of depression and ball roll
deflection. The examination of surface hardness between 65 and 75 gravities
and surface strength values between 13 and 16 kg cm-2 for depth of depression
76of different forms of traffic and associated edaphic features. The evaluation of
traffic on putting greens with different grass species including bermudagrass
(Cynodon dactylon), overseeded perennial ryegrass (Lolium perenne) and rough
bluegrass (Poa trivialis).
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83Appendix 1. Date of evaluation, surface hardness, surface strength, gravimetric moisturecontent of the 0- to 5-cm depth below the turf surface, and soil temperature at the 5-cm depth ofhigh sand greens evaluated during 1996.
Putting Green Surface Surface GravimetricLocation 1996 Hardnesst Strength; Moisture Temp
Pine Valley 12th Apr 22 56 19.6 20.4Jul29 72 15.6 20.3 24Oct 7 78 18.8 24.9 13
t Surface hardness is maximum deceleration measured in gravities.:; Surface strength measured at the 0- to 2.5-cm depth zone.- Measurement not taken.
85Appendix 2. Date of evaluation, surface hardness, surface strength, gravimetric moisturecontent of the 0- to 5-cm depth below the turf surface, and soil temperature at the 5-cm depth oftopdressed modified native soil greens evaluated during 1996.
Putting Green Surface Surface GravimetricLocation 1996 Hardnesst Strength; Moisture Temp
t Surface hardness is maximum deceleration measured in gravities.; Surface strength measured at the 0- to 2.5-cm depth zone.- Measurement not taken.
Appendix 3 (continued).
putting Green 1996Location
Galloway 18th Jul 9Aug 6
Blue Heron Pines 1st Jul 9Oct 1
t Number of observations.t Depth of depression.9 Percent rebound of depression 30 minutes after traffic.~ Pneumatic tire of 16.5 cm wide pneumatic tire single rider cart.
t Number of observations.:j: Depth of depression.~ Percent rebound of depression 30 minutes after traffic.11 Pneumatic tire of 16.5 cm wide pneumatic tire single rider cart.
mm %
1 0.5 40
2 0.5 40
mm %
(!)a
8created to distribute the load (Chancellor, 1976). A firm surface trafficked by a
rigid wheel will have a smaller contact area than the same wheel load on a softer
surface. If a load is increased, the tendency is for the wheel to sink more
deeply, spreading the load over a larger contact area. The pressure distribution
is not uniform under a rigid wheel; pressures under the edge of the wheel are
less than those under the center (Liston & Martin, 1968).
The pressure exerted on a surface by a traffic event will distribute
stresses through the soil profile below. Most pressure distributions resulting
from traffic on turfgrass surfaces occur in the upper 8-cm of soil (Beard, 1973).
Burton and Lance (1966) studied the affects of golf car traffic on bermudagrass
turf, and found that soil physical properties were affected in the upper 10-cm
zone. The physical properties in the upper 3-cm of a soil below Kentucky
bluegrass was altered by compaction treatment that simulated foot traffic and turf
equipment, whereas the 3- to 6-cm zone changed very little (0' Neil and Carrow,
1983).
The pattern of surface pressure determines how the pressure is
transferred within a soil (Chancellor, 1976). Pressure distributions in soils under
a concentrated load have been described by a set of equations known as the
Boussinesq equations (Hillel, 1980). The equations are intended for uniform
elastic materials and disregard horizontal components of stress placed on a