You're listening to Shortwave from NPR.
Short wavers, maybe tall wavers.
I don't know who you are.
What's up?
Nate Rod here.
If you've been watching any World Cup games, and how could you not?
Because they're on everywhere.
There's something you probably haven't appreciated enough.
And no, it's not the players.
So my name's John Sorokin.
I'm a professor at the University of Tennessee, and I
Specialized in turfgrass science.
Turf grass science.
Yes, it's a thing.
And for this World Cup, John had a pretty remarkable mandate from the guy managing the pitches or fields the games are played on.
He wanted consistency, uniformity across the different venues.
Indoor fields and outdoor fields.
The one thing he said is we don't want to have to replace any grass during the tournament.
Which means going in and re-sodding a stadium or even a goal mouth.
We don't want to change any of that.
Meaning the fields had to hold up for 104 matches over six weeks.
16 completely diverse stadiums from Mexico City at really high altitude to the same indoors in Vancouver at sea level.
And the same as in tropical Miami.
How do we get this to be the same?
As close to the same as possible.
After a big gulp, my sleepless nights for the next eight years began.
So today on the show, the science that's gone into the playing fields for this year's World Cup and what it might mean for a community park near you.
You're listening to Shortwave, the science podcast from NPR.
All right, John, I'm kind of tempted to call you Mr.
Turf.
Do your friends call you that?
No, you don't want to know what my friends call me, but yeah, that's okay.
How do you get into something like this?
You've been doing this for 30 years.
Yeah, by accident.
I started off at the University of Calgary thinking I'd be a lawyer in the oil and gas industry, and I did not like it.
So I got a job on a golf course and I fell in love with it.
And I transferred to Michigan State University.
And that's when the World Cup was here.
I started working on that in the late fall of 92 as a student.
And we got to go on the roof of the Silverdome when the whole tournament was over and jump on it like a trampoline.
It was air inflated, right?
And then we laid down and you're like, holy, I'm a couple hundred feet above the ground.
I started looking at the field and you could see after a month indoors with no sunlight, it was showing its wear.
And I was like...
How do I make that better?
How would we make this all uniform?
And so I went on and my PhD was growing grass indoors for dome stadiums and now doing it, you know, 32 years later for the 2026 World Cup.
Is there anything that you guys are doing this year that's different than what's been done in the past?
Yes.
Five of the 16 stadiums are indoors.
First time this happened actually was in 94, 32 years ago when the World Cup was here.
We didn't have the technologies we have today.
So we grew the grass in the parking lot and then we put it inside.
And for the next 30 days, it started declining because there's no sunlight.
Fast forward 32 years, we got five dome stadiums and they've got grow lights in there.
So if you drive by these stadiums at nighttime, they're lit up red because they got these LED grow lights growing the grass indoors to replace the sunlight.
I'm curious, you know, spending three decades in this field, like how has the science evolved from when you first started till now?
Yeah, which makes me feel old when you called it three decades.
We're not aging nobody.
Yes, it's changed a lot.
So FIFA has these requirements.
You have to have a natural grass pitch that has a sand-based root zone, that has an in-ground irrigation system.
And in that sand root zone, they have to be hybrid reinforced with synthetic fibers that go in and kind of act like rebar.
So when you go and you plant, you're not getting a big divot blowout because it stabilizes it below.
But the top you're playing on is all grass, but those fibers are stabilizing that sand below.
Whoa.
It's like mutant grass.
You look like a cyborg grass.
Yes, absolutely.
If you've watched some of the World Cup games that have happened, there's been a lot of rain events.
And that's why they're a sand-based root zone.
So they drain rapidly.
But also they have what's called a vacuum ventilation system where they can actually create a suction and pull water out.
So there's never standing water on these pitches.
England and Mexico, besides being an amazing game.
Yeah, it was.
It had been raining all day and all leading up to the game and even during the game.
And there wasn't a bit of standing water and the pitch was perfect.
So that's because of these requirements that FIFA has.
And these are all new since the 94 World Cup.
You were describing the most like complicated, sophisticated field that I more than I could even begin to comprehend.
Right.
Yes.
I just want to know, did I ruin it for you now when you watch the next game?
Are you going to be watching the pitch or are you going to be watching the match?
I mean, since we've been prepping for this story, I've definitely been paying more attention to the pitch.
I think a lot of people watching these World Cup games might be surprised to hear what an important role the grass field plays.
Why is it so important?
Well, when you think of everything that goes into putting on something like this, whether it's the Super Bowl or the World Cup,
You've got these immaculate stadiums.
You've got to make sure you have the hotels for people.
And you've got the concessions and the skyboxes, everything.
$30 hot dogs.
Yeah.
Whatever it is, everyone's there to watch the game.
And what's most important about all of these things is what the game's being played on.
If it was a crappy field, they're going to talk about it.
And if it was bare and the ball was bouncing wrong or a player's going to stop and he blows out a big piece of grass or he slips and falls, that's not good.
We don't want to compromise the outcome of the game because of the surface that they're playing on.
We want those players to have the perfect canvas that they can have to orchestrate their game and demonstrate their abilities at the highest level.
I'd assume it has something to do with player safety too.
Yeah, absolutely.
What we focus for our safety guidelines is consistency and uniformity.
Not too hard and not too soft.
Not giving you way too much traction and not being aware that they're going to slip and fall also.
Because there's three components when it comes to the player safety.
There's the player, there's the surface, and then there's the footwear.
And if you watch F1, they've got hard, medium and soft tires for the F1 car that they race on, depending on the conditions of the track.
And then if it's raining, they put on slicks.
If you think of a World Cup soccer player as an F1 car, depending on the surface, because we have warm season grasses and cool season grasses, because in Miami, they're going to grow warm season grass.
In Boston, they got a cool season grass.
Well, you probably want different tires or treads or cleats on those surfaces.
So you get the same performance on those two surfaces.
It's like you're setting the stage for one step of this process, but then the players and their coaches and their equipment managers are doing the next phase.
Yeah.
And we want to provide evidence-based data.
We developed a machine at the University of Tennessee that actually simulates a foot strike.
And we can get a heat map of a soccer field going up and down it.
And it tells us the
Forces that the athlete's feeling vertically, horizontally, laterally, their level of traction, the time to get to their peak performance, and a rebound effect if there's any bounce back that they're feeling.
And so we can educate players and coaches and equipment managers.
Does this device look like a foot?
I'm imagining like a robot foot.
It is.
Well, the device is big and then inside it's got a 3D printed foot.
And then you put the shoe on it and it strikes down the surface.
Is it like a mock-up of your foot?
Yeah.
No, we want to use elite athletes' feet.
Your foot isn't an elite athlete foot?
That ship has sailed.
Yeah.
Yeah, my ship sailed too.
So from my understanding, the transformation process for each stadium was different.
So what were all the factors that went into determining, you know, which combination of grass was going to be best for each place?
So we know what grasses grow in each region and that's where they're done.
The cool season grasses grow best between 60 to 75 degrees.
So we can look at Seattle.
That's going to be ideal.
We've got five dome stadiums.
They're indoors.
Inside at 70 degrees, we're going to put the cool season grass inside.
But it's 95 degrees in Houston, so you can't grow the sod for Houston in Houston because it's too hot outside.
So we actually grew it in Denver.
What?
And then shipped it to Houston?
The sod was planted a year before in Denver on a sod farm.
It was grown on plastic, and then we shipped it to Dallas, Houston, and Atlanta from Denver.
And they harvest it at nighttime, put them in refrigerated trucks, drive it whatever distance they had to go.
And the nice thing about the sawed-down plastic is it's growing in the exact same sand as what's in the stadium.
So we can come and cut it like a pizza, roll it off of the plastic, and you've got these healthy roots all intact.
And when we go lay it in the stadium…
On the sand that's below, roots grow by gravity.
It's called gravitropism.
And it establishes faster and you've got one less stress that you didn't add by cutting off all of its roots.
That's how it gets its water and nutrients.
The amount of thought that goes into this is, you've blown my mind like 42 times already.
So John, like you've described needing different types of grasses for different climates, which makes sense.
But if the goal is uniformity, how do you make sure that one type of grass performs at the same level as another?
I had a grad student that did work where we launched soccer balls at an angle at like 50 miles an hour, and then it bounces.
And we had high speed cameras and we tracked it.
And we found what's the mowing height for the cool season grasses versus the warm season grass.
So that when the ball comes in, it's going to bounce at the same angle and the same coefficient of restitution.
I had my students, undergrads, putting on soccer cleats and running back and forth, doing high steps.
If we're not abusing the grass and killing grass, we're not testing its limits.
And so we do a lot of that simulation of traffic and abuse.
And then we look at just things like plant growth regulators to
To slow the vertical growth, but increase the density and the rigidity of the grass.
And we look at different nutrition of nitrogen fertilizer balances because that's what's the driving force.
We don't want to grow too fast because it makes it more lush, but we don't want to grow so little that...
It's not going to recover when it does because you abuse it.
It's a living organism.
It will die and it needs to recover.
And so we're looking at that balance.
Like the Goldilocks amount of nitrogen.
Exactly.
It sounds all really complex, but it's actually really simple.
Don't mow it too infrequently.
Don't mow it too short and don't mow it too high.
And the nice thing about grasses is when you mow it, like
Any other plant in the world, you can't do this to.
The grass family is the most important family of plants in the world.
I would say because of turf grass.
Objectively, you would say.
Yes, objectively.
Nate, I'm 100% objective of it.
Of those grasses, we've got rice, corn, wheat, millet.
Those are the main staples of the world's diet, right?
You can't go and cut off...
A wheat field every day.
It's not going to grow back or cornfield, but you can with the turf grasses and that just gets them to actually grow up and put new leaves.
So it's that's what's unique about turf grasses.
Man, I want to be a grad student for you.
Can I come do that?
Absolutely.
What impact do you hope that this will have on future World Cups and like other sporting events?
Because turf is important in just about every sport we play as humans.
Yeah.
So I think it's increased the awareness of what goes behind it.
A lot of the research we've done that FIFA did wasn't even used in this World Cup, but it's done a lot of innovative things.
We developed and we worked and we proved the concept of what's called a shallow pitch profile, where we just now showed that you can come in in a short period of time and put a nice natural grass field in, play a game in, take it out.
And you can get ready for motocross or the truck and tractor pull or Taylor Swift or whatever you want.
That's really cool.
And then just some of the other stuff that's going to have the legacy and trickle down.
There's all sorts of things that,
How do we help the average city park and rec field to get better and safer for maybe what we might consider the most important athletes, which is our children that are playing on them, right?
I think that's, to me, one of the great outcomes that's come from this and that will continue to go as we...
Disseminate the information that we've gained over these last several years of doing research.
Yeah.
John, we're taping this before we know who's in the final, but by the time this airs, we should know who the final two teams are.
Are you pulling for anybody in particular?
You know, as a Canadian, I was obviously cheering for Canada, but I love all the teams.
I'm cheering for the pitches now.
First and foremost.
Well, I'm going to take a note from your book, John, and I'm going to just cheer for the grass.
Yeah.
Well, John, thanks so much for doing this, man.
It's really cool.
I've learned a lot and I have a whole new appreciation for what I'm watching on TV now.
Absolutely.
Thank you for reaching out and wanting to do this.
This has been a lot of fun.
If you're a soccer fan who just listened to this episode because it's about the world cup or you're a fan of sports, I think you'd love some of our other stories on the science behind your favorite athletics, like our story on the physics of ice skating
For more science stories, just like these follow shortwave on the NPR app or wherever you're listening from.
This episode was produced by Aru Nair.
It was edited by our showrunner, Rebecca Ramirez.
Tyler Jones checked the facts.
Robert Rodriguez was the audio engineer.
I'm Nate Rott.
Thanks for listening to Shortwave, the science podcast from NPR.
