Thursday January 29th, 2015

Retractable roofs have become commonplace in professional sports. But Glendale's University of Phoenix Stadium did the rest of North America's stadiums one better by introducing us to the world of retractable fields.

And for the Super Bowl, the NFL had its very own retractable natural-grass turf installed. With the pounding the turf takes from Arizona Cardinals home games and the VIZIO Fiesta Bowl at the 65,000-seat University of Phoenix Stadium, the NFL ensured it had a fresh carpet of highly greened grass ready to go for the Pro Bowl and Super Bowl, even if that meant moving it in from Alabama and shuttling it in and out of the stadium.

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The Tifway-419 Bermuda hybrid grass that will be used in Sunday's Super Bowl received its first major use during last Sunday’s Pro Bowl. After that, though, the grass was moved back outside for Monday’s sunshine.

Built as the first retractable field in North America in 2006, the nearly 19 million pound tray holds 92,000 square feet of turf, drainage and even its own irrigation system. Due to the configuration of the stadium, which was designed to resemble a barrel cactus wrapped by a snake, a natural grass field wouldn’t have received enough sunshine to survive surrounded by the seating bowl, even with the stadium's retractable roof.

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So architects Peter Eisenman and a team from Populous created a tray 40 inches deep that rests on 13 railroad-like tracks and moves through an opening four and a half feet tall beyond the end zone to the southeast. A total of 546 steel wheels -- 76 of those powered by a one-horsepower motor for a top speed of one-eighth of a mile per hour -- help expose the grass to the waiting desert sunshine.

The process is started simply by pulling a giant lever on the concourse level, and the field takes about an hour to travel 741 feet.

The arrangement takes up over two acres and includes an irrigation system that works on customized timers, with a one-inch-deep mat and piping for drainage. The grass stands two inches tall. A few inches of water are retained to keep the grass moist in the Phoenix air.

By moving the field outdoors, the stadium can have a luscious green carpet for football along with an easy-to-use floor for concerts and conventions.

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After sliding outside on Monday, the field received new grass for the end zones to rebrand it for the Super Bowl and was doused with a product to help it retain its green color through Sunday.

Generally, the Cardinals move the field indoors two days before a game, but the Super Bowl field has more responsibilities than most turf, requiring its presence inside the venue on Wednesday. With Super Bowl pregame and halftime rehearsals planned, plus player workout time, the field will go from nearly no foot traffic in the first half of the week to plenty of use in the final days leading up to Sunday.

Tim Newcomb covers stadiums, design and gear for Sports Illustrated. Follow him on Twitter at @tdnewcomb.

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