By Kyley Dickson, Ph.D., and John Sorochan, Ph.D.
Athletic fields require maintenance whether they are natural or synthetic. The challenging aspect for athletic fields is that they change as a season progresses. One of the best ways to reduce injuries and increase performance is to have a consistent playing surface that is within acceptable ranges for athlete safety. Without regular field testing, it is hard to determine variances in playing surface consistency as use/wear increases. Knowing how a field is changing throughout the year can help field managers make data-driven decisions to optimize the performance of the playing surface and, in turn, the safety of the surface for the athlete. Keeping records of different field properties throughout a season and years can help paint the picture for the field managers on what is also going on below the surface. Unfortunately, testing takes time and can be expensive, and these drawbacks can lead to many overlooking the need to test a field. However, testing is another important tool to have in the field manager’s toolbox.
One of the main benefits of testing a field is it indicates consistency and characteristics of a field’s impact on athletes. Tests that are conducted give clues to the health of a field and help identify maintenance practices that are needed. Although there are different testing criteria for natural and synthetic surfaces, there are shared tests beneficial for both. However, not all tests can be used on both types of fields. In determining what tests are needed for a surface, a few questions need to be answered:
- Is it natural or synthetic?
- What sport or sports are played on the field?
- What is the budget and time available for testing.
This information will help determine what tests would be the most beneficial information for a surface. To start, some basic tests need to be established for field managers as a base.
The University of Tennessee Center for Athletic Field Safety (UTCAFS) has a suggested basic kit for natural and synthetic fields. A natural field basic test kit should include a soil moisture probe, a side soil profiler, and a rotational traction testing device. The cost for the components to buy new will range from $2,500 to $5,000, depending on which products are selected. On a synthetic surface, the basic kit recommended is an infill depth gauge, surface temperature measuring device, and some type of rotational traction device. The cost for a synthetic turf test kit ranges from $850 to $1,000. (Note: All kit estimates are from price researching different suppliers’ websites and totaling the cost. The purpose of this article is not to promote one specific brand of testing equipment, as there are a variety of products available.)
All testing done is a snapshot of that field at that particular time, the same test could be conducted the following week with different results being observed. That is why taking multiple readings in a year will give a more detailed picture of what is happening. The other key to getting a good snapshot is testing for the variables that have the greatest impact. Published research has identified a few variables that have been found to influence many parts of the field (Baker, 1991; Dickson et al., 2018). For natural grass fields, the soil moisture content of the field has been found to impact surface hardness, traffic tolerance of grass, rotational traction/resistance, increase in soil bulk density when trafficked, head injury criterion, and translational traction (Baker and Gibbs, 1989; Baker, 1991; Dickson et al., 2018a, Dickson et al., 2018b). Soil type of a field is important, because soil moisture content will have a greater influence on the playability of a soil that is higher in silt plus clay than a sand-based field (Dickson et al., 2018). Although there are a multitude of tests for additional field performance parameters, getting the soil moisture content right could improve safety, longevity and performance of a field, in addition to improving the overall quality of the grass. There are several different kinds of devices that measure soil moisture, and most of them can test fields relatively quickly.
Another tool for natural grass is a side soil profiler. This is a device that lets the user take a side cut out of the field to see what is really going on below the surface (Figure 1). This device can be used to determine root depth, layering issues, black layer and buried objects, just to name a few. Figure 2 shows a sand-based rootzone that has a pocket of clay preventing consistent grass growth. The grass above the clay was worse than the surrounding areas, and a soil profiler revealed the problem. After a soil profile is taken, it can be reinserted back into the area tested with minimal surface disruption.
Rotational traction is an additional tool that is very useful for both natural and synthetic surfaces. These testing devices give more of a performance and safety standpoint for the athletes on the field. Trying to keep a field consistent for rotational traction is helpful in providing consistent footing and potentially safer playing surfaces. Rotational traction has been associated with both lower extremity injuries and grass health (Orchard et al., 1999; Stier et al., 1999). The smaller portable devices are relatively easy to use and quick. These devices will slightly disrupt the playing surface where tested, but is still considered minimal surface disruption.
For synthetic turf, infill depth can be just as important as soil moisture is for natural grass. The infill depth is something that is taken for granted on many synthetic fields. As seasons progress on synthetic turf, infill can be moved around and create spots on the field that are lower/higher than other areas. Variances in infill depth have been found to impact surface hardness, surface temperature and rotational traction (Center for Athletic Field Safety Reports). Infill depth is a very easy measurement, and can be done very quickly. This test lets the field manager know infill is needed because the levels are too low, or if the infill simply needs to be redistributed from areas that are too high to areas that are too low. The goal is keeping the infill depth as close to manufacturer’s recommendation as possible.
Surface temperature is another important variable. Synthetic turfs have temperatures that can be much higher than natural grass fields during full-sun conditions (Lim and Walker, 2009; Thoms et al., 2016). As heat increases, it has a detrimental impact on athletes, decreasing performance and increasing the need for breaks and rehydration (Charalambous et al., 2016). Surface temperatures can be taken with a variety of tools, but the temperature gun used by most automotive repair shops is a fast and easy device to determine the surface temperature. While little can be done to reduce synthetic turf temperature after a system is installed, educating field stakeholders of potential heat concerns is one potential plan of action.
Difficulty comes in choosing what tests have time and the budget to be completed. The last thing a field manager needs is tests that take a long time to complete. Some of the tests do not need to be collected before every game – some could be done once a year. In addition, the cost of testing devices has a wide range from affordable to very expensive. Each additional test can increase the cost and time to complete, but provide greater detail about the field. There are companies that test both natural and synthetic athletic fields, and can provide a summary of their findings and recommendations for any actions needed. Although more information is always desired, selecting the most important tests can save time and money.
The tests described above are just the basics, and there are many more tests available if budget and time permit. Another consideration is what sport/sports are played on the field. In soccer, FIFA has requirements about ball roll and ball rebound that take place on a field; while in football, knowing surface hardness and rotational traction are of greater importance than ball-to-surface interaction questions. One way to help determine which tests are important for a particular sport are generally listed by a professional sports governing body (i.e., the FIFA handbook). Currently, most field testing is only required at the professional level and some sports do not have sport-specific tests. However, there are universal tests such as surface hardness and rotational traction on most surfaces that can be completed.
Another key in field testing is being able to interpret the results in a meaningful way, and have a record of the testing. It is recommended to test the same 8 to 12 spots (example, Figure 3) on a field each time while testing additional areas that may be of concern. Testing the same spot will tell you how it is changing each time testing is completed. The more locations that can be tested on a field, the better. A representative sample of the field is desired for testing. Keeping data in a spreadsheet or some type of record-keeping system to go back and review is vital. If comparing multiple fields in a complex, the fields will have some variation from each other due to soil type, construction, grass, infill, etc. Focusing on the testing within each field shows variability that can be addressed to improve safety and performance.
The basic tests suggested can potentially increase the performance and eventual safety of an athletic field, and can be completed quickly with minimal expense. These quick data snapshots throughout a season would take less than an hour to complete per field, and would provide extremely useful information for the field manager. When you put the snapshots together for the entire year, you get a pretty clear picture of the changes that occur throughout the season. Ultimately, these data will also aid in maintenance decisions needed to provide a consistent playing surface. When it comes to field testing, start with the basics and work out from there.
Kyley Dickson, Ph.D., is a turf researcher at the University of Tennessee; John Sorochan, Ph.D., is a professor of turfgrass science at the University of Tennessee and director of the University of Tennessee Center for Athletic Field Safety in Knoxville.
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