Science in Action: Synthetic Play Surfaces in the Desert

Artificial turfgrass surfaces, in the past, were viewed as expensive playing surfaces relegated to professional sports fields and not meant for municipal or backyard applications. Now, faced with limited resources and an ever expanding user population, organizations and public entities are interested in finding ways to reduce costs and maximize athletic field capacity. Natural grass playing surfaces are being successfully challenged by these improved artificial surfaces in many different applications.

Golf course turfgrass and irrigation ponds add the equivalent of about a
70 ton air conditioner per acre to the local environment and water loss
from leaf surfaces keep the surface temperature at right around 95F
even when air temperatures hit 120F

            There has been an evolution in synthetic playing surfaces since the 1960’s during which AstroTurf^TM became a household name. Due to clever marketing, AstroTurf^TM was tied to the image of “space age” technology and domed stadiums like the Huston Astrodome for which it was named and Minneapolis’ Metrodome. Untreated nylon and polyurethane grass and mat surfaces were highly susceptible to decomposition by UV light and not very durable, with high maintenance costs. These surfaces were replaced on an average of every five years, certainly not within the budgets of municipalities and homeowners.

            But AstroTurf^TM had numerous other problems as well which included its poor drainage characteristics, impact on ball roll and bounce, alteration in the speed of players on the field affecting play, increase in minor injuries to players and finally the players just didn’t like it. Instead of addressing the problems, Monsanto and other competing firms with similar products, suggested things like elbow pads and special turf shoes when playing on artificial turfgrass.

            The original AstroTurf^TM no longer exists on any NFL fields as these types of products eventually evolved to newer and improved artificial surfaces (AstroPlay^TM, FieldTurf^TM, Sportexe Momentum Turf^TM, RealGrass^TM, and others) or in some cases fields were converted back to natural grass. A quick review of the artificial turfgrass evolution might be interesting.

            During the 1970’s little was done to improve the artificial turfgrass industry as Monsanto dominated the market with the exit of competing products from companies like 3M and Biltrite. AstroTurf^TM was the only artificial turfgrass available, they had captured the market and so R and D came to a standstill.

            During the early 1980’s engineers attempted to correct the problems of ball roll and drainage problems still associated with artificial turfgrass. The ball roll problem was solved by “texturizing” the nylon grass fibers, making them kinked instead of smooth.

            During the late 1980’s new products began to emerge that attempted to combine natural and synthetic surfaces into one playing field hoping to capitalize on the best attributes of both. Surfaces such as the original sportsgrass^TM emerged which used polypropylene grass blades held together with a woven backing that was applied to an amended layer of sand.

            Natural grass was grown by seeding or sprigging into this synthetic layer in hopes of preventing damage to the crown and root systems from heavy play. Roots could grow through the woven backing and into the sand below. Since grass roots grow down through the synthetic fibers and backing, the crown and roots of the plant would be protected. Complaints emerged in some parts of the country that the playing surface became hard from compaction and extensive play damaged the synthetic backing. This type of damage led to an unstable playing surface which in turn hampered regrowth of the natural grass.

            Engineers in the sports field industry also tackled the player injury and stability problem by paving the soil under the turfgrass with asphalt and adding a layer of PVC foam for cushioning. Outside fields subjected to heavy rains were “crowned”, making the center of the field 16 to 25 inches higher than the sides so that water would surface drain off of the field.

            Porous asphalt, a technology developed in England, was incorporated into the engineering of artificial turfgrass to improve internal drainage. First the soil of the field was leveled and then covered with a layer of crushed rock several inches thick. A layer of porous asphalt was laid on top of the gravel followed by a shock-absorbing pad and finally followed by the turf. After installation, the turf was glued to the pad and holes were punched through the foam pad for drainage.

            Things changed in the 1990’s when strong and soft polyethylene was chosen by artificial turfgrass manufacturers to replace the stiff but durable nylon of the past. The fibers were UV resistant and long compared to previous artificial turfgrass fibers. These fibers were “tufted” into a mat in a process similar in appearance to a shag rug. Once the “sod carpet” was in place, it was topdressed with “infill” which could be recycled rubber called “crumb” or a mixture of this rubber and sand. Recycled rubber has been a source of controversy as to its potential for damaging the environment and human health concerns. An average football field might require up to 400 tons of infill applied to its surface.

In most recent years, two groups of artificial turfgrasses have emerged with infill systems (NeXturf^TM, AstroPlay^TM and FieldTurf^TM). These products carried claims that they realistically duplicated natural grass color and playability, allowed for more play, and provided a ten year life before replacement. If true, this was a significant improvement over previous generations of artificial turf and placed it with the budgetary reach of nonprofessional sports turf and municipal budgets. But the part that caught the eye of municipalities and managers of nonprofessional sports fields with smaller budgets were the claims that these surfaces lowered long term maintenance costs (no water, no chemicals, decreased labor), were more environmentally friendly (no pesticides or fertilizers) while at the same time reduced major injuries to players.

            During the early years of AstroTurf^TM, players complained of numerous minor injuries such as "turf toe" (a ligament sprain in the big toe that was exacerbated by artificial turf), “turf burn” (skin abrasions like rug burn), foot blisters, and bruised toes. Since then numerous studies have been conducted to evaluate the safety and playability of synthetic surfaces. Mechanical devices have been devised to simulate human movement across a playing surface, injury from concussions, and the type and number of injuries occurring to athletes during events were counted and recorded.

Reports and studies are numerous that demonstrated fewer serious player injuries on artificial turfgrass compared to natural grass (NFL, NCAA, reports by the University of Nebraska, and the Amarillo Independent School District) while claims of minor injuries (such as “turf burn”) still persisted.  Researchers have suggested that the reason for fewer player injuries on artificial grass might be due to a more even and predictable playing surface and the accessibility of these fields to frequent and timely practices which were not possible on natural grass surfaces that needed repair after heavy play.

The rationale for switching to artificial turfgrass since that first installation has varied based on site location and user needs. Reasons have included: increasing playability during inclement weather, lower maintenance costs, and perhaps most relevant to the southwestern United States, the conservation of water. However, a potentially significant undesirable characteristic of artificial turfgrass is the elevated surface temperatures (approaching 170 F) which restricts play during the summer months and human health concerns for players.

Communities like Las Vegas have spent millions of dollars replacing turfgrass on recreational sporting fields with artificial turfgrass, with the goal of reducing maintenance costs, increasing play time while saving significant amounts of money by eliminating irrigation. Although the rapid increase in surface temperature in the presence of sunlight has been known for decades little research has been published on the subject, especially related to the controlling forces behind the rise in temperature. The majority of information currently available on elevated surface temperature of artificial turfgrass has come from unpublished studies available from internet web sites.

Research at the University of Nevada in Las Vegas examined the factors that influence surface temperature rise of artificial turfgrass. The data collection included surface temperatures, spectral reflectance, solar radiation and air temperatures associated with different landscape covers and artificial turfgrass components; and, an assessment of energy balance and heat transport through artificial turfgrass.