How Crumb Rubber Particle Size and Depth Impacts Traffic Tolerance of Hybrid Bermudagrass

By Kyley H. Dickson, Ph.D. and John C. Sorochan, Ph.D.

Athletic fields can develop worn areas due to traffic. Finding methods to alleviate traffic is important to improve traffic tolerance of an athletic field. Topdressing is one method that field managers use to mitigate some of the negative impacts of traffic. Topdressing has been identified as a way to reduce undulation, increase water infiltration, aid in thatch decomposition, modify topsoil, and improve surface firmness (Goss, 1977). Crumb rubber generated from recycled automotive tires can be used as a topdressing medium on athletic fields (Rogers et al., 1998). When subjected to traffic, Kowaleski et al. (2011) reported that topdressing with crumb rubber was more effective in increasing Kentucky bluegrass cover and shear strength than topdressing with sand. Additionally, Kentucky bluegrass cover increased with crumb rubber topdressing rate (Rogers et al., 1998).

1– 2 mm particles

Increased wear tolerance and decreased surface hardness and soil bulk density were observed in ‘Tifway’ hybrid bermudagrass as well as ‘Riviera’ and ‘Quickstand’ common bermudagrass when topdressed with one inch (0.04 – 0.09 in particle size range) of crumb rubber (Goddard et al., 2008). Similar results might be achieved using less crumb rubber of a smaller particle size, as they more fully envelop stoloniferous meristems of bermudagrass compared to larger particles. The goal of this study was to determine optimal crumb rubber particle size and topdressing depth combinations for use on hybrid bermudagrass athletic fields.

0.05 – 0.5 mm particles

‘Tifway’ hybrid bermudagrass plots were established at the University of Tennessee Center for Athletic Field Safety (Knoxville, TN) on a leveled Sequatchie silt loam soil. Five crumb rubber topdressing materials were evaluated in this study: Coarse, Medium Coarse, Medium, Fine, and Very Fine. These crumb rubber materials varied in both particle size and uniformity (Table 1). Crumb rubber topdressing was applied in 0.25 in increments seven days apart until desired depths of 0.25 in, 0.50 in and 0.75 in were achieved. A non-topdressed control (0 in) was included for comparison.

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Table 1:

Particle size analysis for five crumb rubber treatments topdressed into hybrid bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt Davy, ‘Tifway’] at various depths in Knoxville, TN, fall 2011 and 2012.

Crumb Rubber Topdressing †

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Particle size ranges: > 2 mm

Coarse ‡: 35%

Medium Coarse: 3%

Medium: 0%

Fine: 0%

Very Fine: 0%

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Particle size ranges: 2-1 mm

Coarse ‡: 58%

Medium Coarse: 97%

Medium: 50%

Fine: 0%

Very Fine: 0%

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Particle size ranges: 1-0.5 mm

Coarse ‡: 7%

Medium Coarse: 0%

Medium: 50%

Fine: 51%

Very Fine: 34%

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Particle size ranges: 0.5 – 0.25 mm

Coarse ‡: 0%

Medium Coarse: 0%

Medium: 0%

Fine: 39%

Very Fine: 57%

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Particle size ranges: 0.25 – 0.15 mm

Coarse ‡: 0%

Medium Coarse: 0%

Medium: 0%

Fine: 8%

Very Fine: 7%

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Particle size ranges: 0.15 – 0.05 mm

Coarse ‡: 0%

Medium Coarse: 0%

Medium: 0%

Fine: 2%

Very Fine: 2%

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† Coefficient of uniformity values for the coarse, medium-coarse, medium, fine, and very fine crumb rubber materials were 1.38, 1.82, 1.79, 2.28, and 1.83, respectively. ‡Names given to particle size distribution range.

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Plots were subjected to traffic using a Cady Traffic Simulator. The Cady Traffic Simulator used was a modified core aerifier (Jacobsen VA-24; Jacobsen, Charlotte, NC) that imparted impact forces equivalent to those generated by American football players (Henderson et al., 2005). Traffic dates coincided with the high school football season in Knoxville, TN. Traffic was applied until all plots received 25 traffic events each year. Hybrid bermudagrass percent green cover was quantified immediately after each traffic. Surface hardness was measured on all plots immediately following traffic using a Clegg Impact Soil Tester. Soil water content (%) data were collected on each date surface hardness was assessed using a time domain reflectometry probe equipped with threeinch tines (FieldScout 300 Probe. Spectrum Technologies, Inc. Plainfield, IL).

Green Cover

All depths of crumb rubber topdressing maintained green cover longer than nontopdressed control plots. Only 12 traffic events reduced green cover below 50% on non-topdressed control plots compared to 20 traffic events for those receiving crumb rubber at 0.5 or 0.75 in. Applying 0.25 in of crumb rubber topdressing improved 50% green cover values compared to non-topdressed control plots but less so than applications at 0.5 or 0.75 in. On Kentucky bluegrass, Rogers et al. (1998) also reported that topdressing crumb rubber to a minimum depth of 0.25 in increased turfgrass cover in response to traffic events and suggested that this response may be a result of crumb rubber particles protecting plant crowns during traffic application (Rogers et al., 1998). The improved traffic tolerance observed herein could be due to crumb rubber protecting hybrid bermudagrass crowns by attenuating impact forces exerted during foot strike with the turf canopy. Regardless of particle size, all plots receiving crumb rubber maintained green cover longer than non-topdressed control plots. Non-topdressed control plots were reduced to 50% green cover after 12 traffic events while those receiving crumb rubber topdressing required 19 to 21 traffic events to be reduced to 50% green cover. However, few differences due to crumb rubber particle size were observed in our study.

Surface Hardness

Crumb rubber topdressing depth impacted surface hardness after application of 25 traffic events. Surface hardness on non-topdressed control plots measured 73 Gmax compared to 52-57 Gmax for plots topdressed to a 0.5 or 0.75 in depth. A similar response was observed in our green cover data with the 0.25 in topdressing depth having a less pronounced effect on hybrid bermudagrass athletic field turf than 0.5 or 0.75 in. Regardless of crumb rubber particle size, every increase in topdressing depth resulted in a significant reduction in surface hardness, similar to responses reported by Rogers et al. (1998) on Kentucky bluegrass. Future studies are warranted to determine optimal crumb rubber topdressing depth to reduce soil bulk density on Tifway hybrid bermudagrass subjected to traffic.

Conclusions

All crumb rubber treatments in this study increased traffic tolerance compared to plots not receiving crumb rubber topdressing. All crumb rubber topdressing depths increased number of traffic events to 50% green cover values more than 50% compared to non-topdressed control plots and reduced surface hardness. Crumb rubber particle size did not have any practically important differences on green cover or surface hardness. Given the responses observed in the current study, depth is a more important factor in selecting crumb rubber topdressing for hybrid bermudagrass athletic fields than particle size.

References

Goddard, M. J.R., J.C. Sorochan, J.S. McElroy, D.E. Karcher and J.W. Landreth. 2008. The effects of crumb rubber topdressing on hybrid Kentucky bluegrass and bermudagrass athletic fields in the transition zone. Crop Sci. 48:2003-2009.

Goss, R.L. 1977. Topdressing your way to better greens. Proc. IL. Turf. Conf. 18:33-37.

Henderson, J.J., J.R. Crum, T.F. Wolff, and J.N. Rogers. 2005. Effects of particle size distribution and water content at compaction on saturated hydraulic conductivity and strength of high sand content root zone materials. Soil Sci. 170:315-324.

Kowalewski, A.R., J.C. Dunne, J.N, Rogers, and J.R. Crum. 2011. Heavy sand and crumb rubber topdressing improves Kentucky bluegrass wear tolerance. App. Turf. Sci. 100:60.

Rogers, J.N., J.T. Vanini, and J.R. Crum. 1998. Simulated traffic on turfgrass topdressed with crumb rubber. Agron. J. 90:215-221.