1998 Iowa Turfgrass Research Report
Rubber Tire Particles as a Topdressing Amendment for Intensely Trafficked Grass - 1996-97 data
Jeffrey J. Salmond and David D. Minner
The U.S. discards about 250 million tires a year. The rubber tire recycling industry produces several grades, sizes, and shapes of processed rubber. All recycled rubber is not the same. Suitable materials for athletic field use must be free of all metal fibers and slivers, and must be a size that is compatible with hollow coring and can easily filter into the turf canopy. Some rubber particles may contain nylon strands from "cord reinforced tires". It is doubtful that the nylon will limit plant growth; however, the effect of the nylon on water retention and plant growth is not known. To ensure a consistent rubber product only a trace of nylon should be present.
Two recycled tire products for turfgrass use are crumb and buffing rubber. Crumb rubber is derived from chipping whole tires and is available in screened particle sizes ranging from 2 to 50 mm. The rubber must be screened to remove the metal and nylon cords. Buffing rubber comes from the retread industry, and it originates when tire treads are ground before being recapped. Little effort has been made to commercially produce screened buffing rubber due to the declining number of markets for passenger retreads (U.S. EPA and PES, 1993). Buffing rubber has no metal or nylon because only the tread is recycled. Particles range from 0.25 to 50 mm. Smaller particles are rounded. However, many particles are shreds that have a length-to-width ratio of approximately 7:1.
Materials. Experiments were conducted in 1996 and 1997 at the Iowa State University Horticulture Research Station north of Ames, Iowa, on a mature stand of Kentucky bluegrass. The soil was a Nicolett series (fine-loamy, mixed, mesic Aquic Hapludoll) with a pH of 6.8. On 6 May 1995, before treatment with rubber, the plot was mowed at 1.5 cm, solid-tine core aerified, and topdressed with ten treatments. The topdressing treatments were two types and two depths of crumb rubber, two types and two depths of buffings rubber, sand, and an untreated control. The size description of rubber particles is generally expressed by two sieve numbers. For example, a 10/20 mesh rubber indicates that the rubber passes through a 10 mesh U.S. Tyler sieve and is retained on a 20 mesh U.S. Tyler sieve. The rubber treatments consist of a coarse crumb and medium crumb size, and a coarse buffing and medium buffing size (Table 1). The rubber treatments were topdressed at depths of 1 cm and 2 cm. The sand was topdressed at 2 cm and was 92% 35/100 mesh (Table 1). The treatments were arranged in a randomized complete block design. Each treatment was replicated three times. Overall plot size was 27.5 m x 2.4 m, and the individual plots measured 1.2 m x 1.8 m (4 ft. x 6 ft.). The thirty individual plots were split into two rows along the long axis, so that the traffic treatments could be applied uniformly. The overall plot received 146.7 kg N·ha-1 per year and was not supplied with supplemental irrigation during the traffic periods.
Traffic and evaluations. The Brouwer Traffic Simulator (Brouwer Co., Dalton, Ohio) was used to supply differential-slip type traffic on 0.3-m (1 ft.) centers across the plots. The double-roller, traffic simulator was equipped with 1.5-cm football cleats. The width of each roller was 0.6-m. Traffic was applied on each Monday, Wednesday, and Friday from 31 Mar. through 21 June 1996, to simulate spring athletic activity. This traffic period was followed by a summer no-traffic period for turfgrass recovery, from 21 June to 14 Aug. Traffic resumed on 14 Aug. through 8 Nov., to simulate fall athletic activity. This traffic period was followed by a winter no-traffic period for turfgrass recovery, 8 Nov. 1996 through 31 Mar. 1997, before a new traffic period was to begin. Treatments for a second season resumed on 31 Mar. to 7 June for spring traffic, 7 June through 20 Aug. for spring recovery, 20 Aug. through 20 Nov. for fall traffic, and 20 Nov. 1997 through 31 Mar. 1998 for fall recovery. Assessments of fall recovery were made on 31 Mar. 1998. An average of six passes were performed each traffic day. A pass consisted of driving the simulator down the length of the overall plot along 0.3-m centers over the width of the overall plot. The plots were evaluated after traffic treatments and recovery periods for quality, density, color, percentage living turfgrass cover, percentage topdressing visible, and surface hardness. One traction assessment was taken on 15 May 1997.
Quality, density, and color. Turfgrass quality and density were rated visually on a scale of 1 to 10, where 1 represented the poorest, 6 represented the lowest acceptable, and 10 represented the best for each parameter. Turfgrass color was rated also on a scale of 1 to 10, where 1 represented unresponsive turf (yellow or brown), 6 represented the lowest acceptable color, and 10 represented a dark green color. Turf quality is an overall visual rating of turf color, density, and texture. Turf density and retention of a vegetative mat or thatch were considered more important than color when rating turf quality of treatments that received traffic. Turf density was a visual estimate of plants per individual plot area. Traffic tolerance was assessed by visually estimating quality and percentage turfgrass cover.
Turf cover and percentage topdressing showing. Throughout the traffic and recovery periods, percentages of the following were observed: living turf cover, rubber or sand topdressing, and bare soil. Percentage living turfgrass cover is the most important parameter for evaluating the detrimental effects of traffic on athletic turf. Following traffic treatments, turf begins to decline and the underlying materials, bare soil, sand, or rubber, become visible. The percentage cover values estimate how much grass, bare soil, sand, or rubber is visible on the surface. Treatments with a high percentage of turf cover and low percentage of bare soil, sand, or rubber topdressing visible are more desirable.
Surface hardness and soil moisture. Surface hardness was measured by using a portable drop-hammer apparatus described by Rogers and Waddington (1990). The 0.5 and 2.25-kg hammers, each with a length of 0.67 m and a missile diameter of 5 cm, were used. Each hammer was fitted with a Brüel and Kj' r Model #4393-1639904 accelerometer (Brüel and Kj' r, Decatur, Ga.). The hammers were dropped from a height of 45.5 cm through a 5.5 cm diameter PVC tube. An accelerometer is mounted inside the hammer. Upon impact, the accelerometer measures the negative acceleration (deceleration, g ) of the hammer. A Brüel and Kj' r 2515 Vibration Analyzer was used to record the impact measurements generated from the accelerometer. A harder, less resilient surface is indicated by a higher gmax (peak deceleration) value. Five individual drops were taken in different locations within each plot, averaged, and stored in the vibration analyzer. Gravimetric soil moisture was measured on two core samples each time hardness was measured.
Traction. Traction measurements, recorded in torque (N·m), were taken with a studded torque wrench device developed by Canaway and Bell (1986). The apparatus was equipped with 45 kg of weight (100 lbs) and dropped from a height of 5 cm. Traction was estimated as the amount of torque required to tear the underlying sod. Three traction assessments were made within each individual plot on 15 May 1997.
Statistical Analyses. The Statistical Analysis System version 6.06 (SAS Institute, 1990) and Analysis of Variance (ANOVA) were used to analyze the data. Least Significant Difference (LSD) means comparisons were made to test between treatments effects on visual quality, density, color, percent turf cover, and percent topdressing showing (Tables 2). LSD means comparisons were also made to test between treatments effects on surface hardness (g-max) (Table 2).
Quality, density, and color. The 2-cm depth of medium buffings rubber provided the best overall visual quality (7.7) and density (7.6) for all the treatments (Table 2). The 2-cm depth of medium crumb rubber compared with the all crumb materials resulted in the best quality (7.0) and density (6.8). We did not find any significant differences in color. A positive correlation (R2 = 0.94) existed between turf quality and turf density. Results for turf density were similar to those found for turf quality. The sand treatment, coarse crumb rubber at the 2-cm depth, and coarse buffing rubber at the 1-cm depth did not increase the quality or density of turfgrass. The untreated control did not improve quality and density, and the coarse crumb rubber at the 1-cm depth and the medium crumb rubber at the 1-cm depth were considered unacceptable for quality and density. No differences were found for quality and density between the control and the 1-cm depth of coarse crumb rubber.
Turf cover and percentage topdressing showing. The 2-cm depth of medium buffings was the best treatment in providing turfgrass cover (87.7%)(Table 2). However, the 2-cm depth of medium buffings rubber showed the least topdressing on the surface (10.2%)(Table 2). The 2-cm depth of medium crumb rubber provided the best cover and least percentage of topdressing showing for the crumb materials. Positive correlations existed between turf cover and quality (R2 = 0.9) and density (R2 = 0.86). The untreated control did not improve. No differences were found for percentage cover and percentage topdressing showing for the control and the 1-cm depth of coarse crumb rubber. A negative correlation existed between topdressing showing and quality (R2 = -0.78) and density
(R2 = -0.76).
Surface hardness. Many of the surface hardness measurements were out of the proposed range suggested by Canaway et al. (1990) for the 0.5-kg hammer. All treatments reduced surface hardness with the 0.5-kg and 2.25-kg hammers compared to the control (Table 2). The 2-cm depth of coarse crumb rubber had the lowest surface hardness for the 2.25-kg hammer (67.7) and the 2-cm depth of medium buffings rubber had the lowest surface hardness for the 0.5-kg hammer (80.3). For the two-year average, the 2.25-kg hammer and soil moisture had a correlation coefficient of -0.704, whereas the 0.5-kg hammer and soil moisture had a correlation coefficient of -0.598. The 2.25-kg hammer was more correlated with soil moisture than the 0.5-kg hammer. A comparison between surface hardness and soil moisture on an annual basis showed strong correlation.
Traction. All of the treatments resulted in traction above the preferred minimum limit of 25 N·m proposed by Canaway et al. (1990). However, only medium buffings rubber at the 1-cm depth (43.9 N·m) and medium buffings rubber at the 2-cm depth (44.0 N·m) had greater traction than the control (38.4 N·m)(Table 2). The 2-cm depth of medium buffings rubber provided the greatest traction at 44.0 N·m (Table 2).
One of the interesting effects from rubber occurred on frozen ground (Table 3). During the winter period, results indicate the sand treatment continued to show a higher, harder g-max with the 0.5 and 2.25 kg hammers. Furthermore, on the totally frozen conditions, the soil control is significantly harder than the high rates of coarse crumb, medium buffing, and coarse buffing and lower rates of the medium crumb and medium buffings with the 0.5-kg hammer. Using the 2.25-kg hammer on totally frozen ground shows a significant difference between the sand and soil control as compared to the high rates of coarse crumb and coarse buffings.
If you are considering using rubber particles for a turfgrass topdressing amendment, Table 4 gives information pertaining to the amount of rubber needed for a particular area.
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ISU Horticulture:Publications:1998 Turfgrass Report | College of Agriculture |