A new school year is near and the fall sports season is upon us. For all sports, we are entering into the concussion awareness era. It is a huge object of discussion and has been covered significantly in mass media. Field hardness issues, as well as field safety in general, will continue to grow in importance. My guess is that field hardness testing will be coming to a field near you soon, if it hasn’t already. Issues like this can get pretty emotional, but a rational approach rooted in science and fact is always best. As sports field managers, we must educate ourselves on the science and embrace this as part of our field management program.
Dr. Braden Clegg (1925-1999) first conceived of the device that would become the Clegg Impact Soil Tester (a.k.a. the Clegg Hammer) in the 1960s as a lecturer in the civil engineering department of Western Australia University. Early applications were mostly in research and road-base construction testing. By the early 1990s it became commercially available, and soon several models were developed for differing applications, but until recently, the units available were quite expensive, in the $20,000 to $30,000 range. Lighter units designed for sports field testing have recently become available for around $3,700 (2.25 kilogram weight).
The basic concept is that a weighted, hard, rubber-like mallet is dropped down a vertical tube from a height of about 18 inches. Instruments on the “hammer” measure its deceleration (or negative acceleration if you prefer) as it strikes the ground. Harder surfaces will stop the hammer faster when it strikes, compared to softer surfaces. This value is reported in units of gravities, also referred to as G-Max, or in tens of gravities, called CIT units. Each test site is recorded in a data logging unit, which can be directly downloaded to an Excel spreadsheet on your computer. The unit is light and easy to use, allowing for tests on many different sites or fields. There are certain protocols developed by the ASTM for different units and different applications. These protocols allow data collected from different users to be correlated better. (ASTM test method D5874 and F1702).
Up to this point the science is clear and well developed. Perhaps less well developed is the science to turn these G-Max values into field safety standards. It seems that it has been generally accepted in this country that a G-Max reading over 100 is cause for concern in terms of field hardness, but we have no national institute of sports in this country, unlike most others. Who can set this standard here? There is science behind this 100 G-Max number, but from what I can tell this has been developed from some work done by GM and Ford in the ’60s and ’70s using crash test dummies against dashboards in a crash. Newer research is ongoing, and the science will mature.
For us sports field managers, it means learning how maintenance and cultural practices on a field can help keep it within acceptable ranges. Once standards have been set, best practices must be developed. On an artificial infill field, we look at grooming and/or brushing, as well as adding rubber to the infill where it is low, always within the manufacturer’s warranty specifications. As an infill field ages, it may become more difficult to manage field hardness, signaling the need for replacement. A well-designed, well-built and well-managed natural grass field has an unlimited life span, but managing field hardness with corrective measures is more complex. Core aeration and field moisture are most touted as remedies. I believe verticutting will become a useful tool in managing field hardness, but like coring, it’s a little invasive and requires a healing period before play. We are taught not to core aerify or otherwise significantly disrupt the surface of a field unless there is enough time for the grass and surface to heal. It tends to loosen a field surface, potentially lowering traction. I wouldn’t want to core aerify a fully painted and prepped football field a day or two before the big game, especially since it must take time for the soil to loosen up into the core holes. Increasing soil moisture with irrigation may soften a field, but will this adversely impact traction and divot resistance and thereby diminish field safety? Learning how to better manage for hardness on a grass field will take time as more of us test our fields regularly and try to correlate the results with environmental conditions, field use, and certain field maintenance procedures and treatments.
Grass cover is another important factor. Nothing softens a Clegg drop like good, thick, tight grass cover. Most sports field managers can give you a great stand of turfgrass if you give them a reasonable budget and a reasonable game/event schedule. I’ve always said that one of the benefits of field performance testing is that we can begin to chart the effects of event uses (games and other) on field quality. It can also help us determine how our maintenance vehicles (mowers and others) and our management decisions impact field hardness.
No doubt there is a lot of wood to chop, even on just one of the many aspects to field safety. There are a lot of smart and reasonable people working on this issue. Everyone in sports is involved, and sports field managers must be in the room for these discussions. That means we need to be smart and reasonable too. There are many issues to be worked out. Protocols have to be set before any programs are initiated. Who sets the standards and protocols? We will all have to look seriously at how many games/practices/events we are scheduling on our athletic fields, both natural grass and artificial turf. What are the impacts on facility economics? Who performs the tests? When and where should the tests be done? Let’s start chopping.
However you feel about the subject, it’s coming soon to a field near you.
Back to school time …
Ross Kurcab, who holds a bachelor’s in landscape horticulture/turfgrass management from Colorado State University, has 26 years of turf management experience and is the first Certified Sports Field Manager. You may reach him at email@example.com