18 SportsTurf | July 2013 www.sportsturfonline.com

FieldScience | By Andy McNitt, PhDmela J. Sherratt

I’VE HEARD IT OVER ANDOVER AGAIN from those in theturf business: “If I could mow atone inch, I’d be able to have pris-tine looking turfgrass like in all

these NFL stadiums.” I politely reply that ifthose kinds of skills and knowledge existedanywhere, there would already be lots ofsmart people using them to improve thesesurfaces.

Let’s review a few facts that aren’t alwaysin our frontal lobe while we watch an NFLgame from the comfort of our homes on alate November Sunday.

First, it’s November. It’s getting seriously

cold now and the light levels are extremelylow. Think about the effects of “winterplay” on a golf course.

Yes, most of the NFL’s northern fieldshave an ethylene glycol heating system run-ning under the sand rootzone. The heatingsystems provide some benefit by extendingthe growing season further into the fall andlimiting frost development on areas that re-quire painting; however, light is still limit-ing. The sun is low in the sky and thestadium seating is being placed as close tothe playing surface as possible. This meansvery steep seats and significant shade. Yes,south facing endzones are sometimes built

lower or more open but there are manyfields where the sun never hits the fieldfrom the endzone through the 20 yard linein November.

In the fall direct sunlight is very limitingand if the heating system is used to pushthe turfgrass excessively, the turf becomesseverely etiolated. Also, the heating systemcan push moisture to the soil surface. Intheory, the ideal set up for an NFL footballgame on a sand rootzone is to have amplemoisture in the rootzone but have it a littledry in the top half inch or so. When theheating system is running during coldweather, moisture in the rootzone is vapor-

Issues and technologies usedon NFL playing surfaces

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ized. It moves up through the sand andeventually encounters the cold air tempera-ture where it condensates. This flips themoisture strata where now it is wet on thesurface and dryer further down in the root-zone.While a tremendous help, the heating

systems are not a silver bullet for growingturf in cold conditions. Light is a truly limiting factor in the fall

and in some stadia throughout the season.Artificial lighting systems have been devel-oped and are being used in Lambeau Fieldin Green Bay. Here at Penn State, we’vebeen experimenting with a rollable lighttarp. This system contains a series of LEDlights in the wavelengths needed for opti-mal growth. The wavelengths can be variedto provide optimal growth conditions forparticular species and in some instances forparticular cultivars. We continue to work toget this system commercialized. Besides limitations of light and heat well

into the fall and winter, it’s important to re-alize the tremendous amount oftraffic/damage that occurs to these surfaces.Football fields look big when watching thegame on TV. When you attend an NFLgame the stadium is large and bigger thanlife. This subconsciously makes us multiplythe size of the field. The field looks im-mense. Really, the majority of the game isplayed on a small area. Research has shownthat for most games about 80% of the traf-fic occurs between the numbers and be-tween the 20-yard lines. The area receiving80% of the damage is about 15,800 squarefeet, or the size of about two and a half golfgreens. Think about that for a moment. Most stadia, save three, in the NFL are

used for multiple and varied revenue gener-

ating and charity events. There are the NFLevents, college football games, high schoolfootball games, the FOP versus the FOFcharity event. Lacrosse championships, soc-cer tournaments and professional soccerevents dot the schedule. Then in summerwhen the temperatures are sometimes ex-treme, the stadium hosts between one andthree summer concert events and/or mon-ster truck rallies where at least parts of theturfgrass may be covered for up to 7 days

and other parts must accommodate largecranes, and countless passes with forklifts,trucks and other utility vehicles.Considering the amount and kinds of

events held on these surfaces, it’s a testa-ment to the field managers that they areable to provide a safe and playable surfaceweek in and week out. Remember, there areno frost delays. Unlike baseball nobody stopsplaying for a little rain or even snow. For those of you managing high school

Left: THE SUN is low in the sky and the stadium seating is being placed as close to the playing surface as possible. This means very steep seats andsignificant shade. Middle: Artificial lighting systems have been developed and are being used in Lambeau Field in Green Bay. Right: Most stadia, savethree, in the NFL are used for multiple and varied revenue generating and charity events that can find parts of the turfgrass covered for up to 7 days.

fields that host well over 100 events peryear, the pure number of events may lookunimpressive. You should realize that thekinds of events do differ. To give you apoint of reference, when I evaluate theamount of damage caused by a Division Ifootball game on a Saturday to an NFLgame on a Sunday, it like the difference Iobserve on a high school field between a7th grade game and a varsity football game.Seriously, the difference is dramatic. It’s thesize and speed of the players (Energy =Mass x Velocity). It’s not how strong theplayers are, it’s how fast they can move verylarge bodies. And when these large bodieshave momentum and want to change direc-tion, the shear forces on the turf system aretremendous. On these higher-end sand-based sys-

tems, grinding out of the turf through abra-sion is a secondary damage of the turfbehind divoting. So the management phi-losophy of an NFL field manager and ahigh school field manager are different.A high school turf manager caring for a

native soil field receiving many, many eventsper week is trying to limit, and more impor-tantly trying to constantly recover from weardue to abrasion and soil compaction. Thus,the turfgrass needs ample nitrogen to help itrecover and should have a higher cuttingheight to help reduce the effects of abrasion.Aeration is done to reduce soil compaction. On these higher-end NFL and college

fields that have lower numbers of events, per-

haps only two per week, but where the eventsare at a much higher intensity, maintenancepractices vary. Research on Kentucky blue-grass grown on sand indicates that withinreason a lower mowing height results in lessdamage due to divots. In the past, Beaver Sta-dium at Penn State was mowed as low as7/8” and typically exhibited a low amount ofdivoting. A common mowing height forKentucky bluegrass in the NFL is 1.25 inchesalthough some are mowed at a lower heightyear round.During summer months, before the begin-

ning of the football season, some nitrogen andwater is withheld in order to “harden off” thebluegrass. Stressing the plants somewhat hasproven to reduce divots compared to havingsucculent plants heading into the season.When the weather cools, additional nitrogenis applied in order to stimulate growth. Also,significant spring nitrogen applications aresuggested during any cultivation or renova-tion procedures. Cultivation followed by coreharvesting on sand rootzones is done to re-duce organic matter buildup in the rootzone.

20 SportsTurf | July 2013 www.sportsturfonline.com

FieldScience

ORGANIC MATTER accumula-tion in the top couple inches ofthe surface can begin to act likesilt and clog the macropores thatconduct air and drainage water.

ALL BUT A HANDFUL of natural grass NFLstadia resod at least 1.5 times per year and asmany as four times per year, bermudagrassfields included.

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Organic matter accumulation in the top cou-ple inches of the surface can begin to act likesilt and clog the macropores that conduct airand drainage water.

Tom Serensits, manager of Penn State’sSports Surface Research Center, has done sig-nificant work using Primo on these sand-based fields. His research showed that ifPrimo is applied all growing season stoppingsometime in early August, that a field can ex-perience as much as a 20% reduction in div-oting into November. You can watch a videoof Tom’s work by going to ssrc.psu.edu and se-lecting ‘SportsTurfScoop’ in the left handmenu.

Using all of these techniques often isn’tenough to allow the turf manager to maintaina consistent turf stand. Thus all but a handfulof natural grass NFL stadia resod at least 1.5times per year and as many as four times peryear, bermudagrass fields included. We havebeen working with sod companies to improvethe quality of their sod for these in-seasonresod jobs. This has truly become a science.The team is on the road next week, so it is de-

cided that the old sod will be stripped, newsod will be harvested and laid, and a game willbe played on it 10 days later. Many of thetechniques suggested above are employed inthe sod field, before harvesting, to reduce thedivot potential of newly laid sod.

Kentucky bluegrass cultivar selection isalso a factor. Personally, I believe that Ken-tucky blue breeding is moving away fromwhat sports fields need. I believe that thecultivars we used 20 years ago were moredivot resistant than the cultivars today. Weare looking for aggressive rhizome produc-ers and typically those cultivars are poorseed producers and have been abandonedby growers in Oregon due to the low yieldsper acre during seed production. Whiletoday’s cultivars are more attractive andmore disease resistant, they are also moreprone to divoting. We have begun to playwith some old cultivars to determine theirdivot resistance and see if selections can bemade in order to breed grasses specificallyfor these high-end sand-based fields.

Evan Mascitte, an MS candidate working

in our project, has decided to seriously inves-tigate the preharvest conditioning of sod tobe used for in-season resodding. We’ll be re-porting on that work in another issue.

And remember: some of the best, in anybusiness, are so good they make their jobslook easy, when in reality they are hard-work-ing professionals performing well. n

Dr. McNitt has been with The PennsylvaniaState University for 30 years. Presently he is Di-rector of Penn State’s Center for Sports SurfaceResearch (ssrc.psu.edu) where he conducts re-search relating to athletic field surface character-ization and golf green construction andmaintenance. Dr. McNitt is also the ProgramCoordinator for the 4-year turfgrass sciencemajor and the Basic & Advanced Certificate aswell as the Associate, Bachelors, and Masters ofProfessional Studies Programs offered throughPenn State’s World Campus Online Learning.In 2010 he was inducted into Penn State Uni-versity’s College of Agricultural Sciences Acad-emy of Teaching Excellence.