A Wearing Subject
Tips for maintaining safety and functionality on recreational turf
By J. Scott Ebdon and William M. Dest
Recreational turf provides for healthy activities and important entertainment value to society. Unlike ornamental turfgrass on residential and commercial properties, recreational surfaces are exposed to different stresses and provide a uniquely different function.
Recreational turf--such as on athletic fields--requires a smooth, uniform and firm surface that allows for true ball roll, as well as influencing the distance the ball rolls over the surface. These qualities, along with shoot density, provide adequate footing and cushioning to reduce the potential risk of injury to athletes. In a recent study that included varsity fields from nine high schools and three university fields in four New England states, we found that a dense turfgrass stand accounted for 39 percent of field-related injuries. Higher shoot densities were associated with fewer reported player-to-surface injuries. Additionally, research has shown that the potential for movement of nutrients and pesticides into surface and ground water is greatest under low vegetative cover. A high-density turf is important to preserve water quality and maintain safe playing surfaces.
Stressful Situations
The two principal stresses on recreational turf are wear and soil compaction--collectively referred to as traffic stress. Wear stress is bruising injury targeted at the aerial shoots with the loss of plant density, which effects traction, ball-bounce resiliency and ball roll. Soil compaction (soil hardness) alters the soil’s physical properties, which further affect surface hardness, traction, ball-roll distance and turfgrass rooting. Intensely trafficked grassy surfaces result in a loss of shoot density and function, leading to poor and unhealthy playing surfaces. High turf density increases the energy-absorbing qualities (resiliency) necessary for promoting better overall field conditions.
However, safe and durable recreational turf is not free. It requires:
· Regular maintenance
· Proper selection of turfgrass species and cultivars (varieties)
· Regular fertilization
· Frequent mowing
· Timely pest control (biological or chemical weed, insect and disease controls).
Therefore, education is key for administrators, directors and practitioners responsible for field maintenance. Most states have well-developed turf extension programs, which are the research-based community education arm of a university system. For example, as part of the University of Massachusetts-Amherst Turf Program, educational workshops, seminars and field days that are specific to athletic-field maintenance are available to the public (visit www.umassturf.org/).
Picking And Choosing
Proper turfgrass selection is the foundation of maintaining healthy and functional turf. In cool-season growing regions, such as the northern half of the United States, only a few grasses are suitable for athletic turf. Kentucky bluegrass (Poa pratensis) and perennial ryegrass (Lolium perenne) are the principal components of athletic-field mixtures in many locations, along with tall fescue (Festuca arundinacea). These species--when properly maintained--are able to sustain the density and vigor needed for optimum wear-tolerance and recovery from wear.
Cultivar Conundrum
While proper turfgrass selection at the species level is important, it is equally important to select the most traffic-tolerant cultivar. There are numerous cultivars (genetic variations within the species) that are commercially available. Perennial ryegrass and Kentucky bluegrass as species are two of the most wear-tolerant, cool-season turfgrass. However, some cultivars of these species have shown to be intolerant of wear due to the significant genetic variation that is observed at the cultivar level (Figures 1 and 2). Selecting wear- and compaction-tolerant cultivars within these species is a real dilemma because unlike species, hundreds of cultivars of Kentucky bluegrass, perennial ryegrass and tall fescue are available (Figure 3). Furthermore, not all cultivars have been tested for traffic tolerance at university field-experiment stations, so there may not be any scientific data available.
As a general rule, a blend of two to three cultivars that have been shown to be tolerant of traffic should be selected for each species-component of the mixture. Such traffic-tolerant species and cultivars will be best for maintaining the highest density under traffic while at the same time helping to keep weeds, diseases and pesticides to their lowest possible levels (Figure 4).
The National Turfgrass Evaluation Program (NTEP), however, provides reliable data for selecting cultivars. NTEP cooperates with university-based turf researchers to collect data and make the results available to the public for free (visit www.ntep.org).
Don’t Forget The Fertilizer
Most turfgrass species recommended for athletic-field use have a moderate-to-high requirement for fertilizer, particularly the need for fertilizer nitrogen (N). As traffic intensity and the number of game events increase, the need for fertilizer N increases. Recently published research conducted at the University of Massachusetts-Amherst shows that optimum N for maximum wear-tolerance and recovery was obtained when these grasses were fertilized with 3 to 5 pounds of N per 1,000 square feet per year. This yearly rate equates to three to five fertilizations per year. Other primary nutrients, such as potassium (K) and phosphorous (P), play a secondary role to N in vigor and density. However, regular soil testing is highly recommended for identifying soil P and K deficiencies.
Nitrogen is critical to maintaining shoot density. Generally, shoot density and leaf-growth rates increase with higher N. Turf under-fertilized at less than 3 pounds of N per 1,000 square feet per year can cause significant thinning and loss in density, vigor and traffic tolerance. Excessive N beyond 5 pounds per 1,000 square feet per year may increase shoot density, but this comes with diminishing returns because disease activity, mowing and irrigation frequencies and wear injury can increase (Figure 5). Balanced N fertility is critical!
Best Practices
Frequent mowing at a reasonable height (1.5 to 2.5 inches) promotes greater shoot density because turfgrass plants are able to adapt to mowing and defoliation by increasing leaf and shoot density. It is strongly recommended that intensely trafficked fields be mowed often to help maintain a dense and uniform appearance (Figure 6), and to avoid excessive clipping accumulations, which can promote disease and thinning of turf stands. Slower-growing varieties have been identified that may allow managers to reduce mowing frequency as well as fuel and labor costs, but these varieties may reduce wear-tolerance and recovery. Also, slow-release N (SRN) fertilizers are available that can reduce vertical leaf-growth rates and lower mowing requirements. The use of SRN is especially important in the spring when grasses are growing under long days and favorable temperatures, which are conditions that promote more rapid leaf-growth rates compared to the short days of fall. Approximately 25 to 50 percent of the total N in a fertilizer container should be derived as SRN. This information is readily available on the fertilizer label.
J. Scott Ebdon received a Ph.D. in horticulture from Cornell University and is Associate Professor of Turfgrass Science at the University of Massachusetts-Amherst. He can be reached via e-mail at sebdon@pssci.umass.edu.
William Dest received a Ph.D. in soils from Rutgers University and is Professor emeritus at the University of Connecticut-Storrs and Adjunct Professor at the University of Massachusetts. Their research focuses on the influence of plant-soil interaction on turfgrass stress.