Brazilian football star Vinicius Junior is quite upset with the playing field at the Met-Life stadium, New Jersey (also known as New Jersey-New York stadium). He and his teammates have complained that the field felt dry and is not suited to their style of playing. French player Adrien Rabiot too is not pleased with the touch and feel of the grass. And to think that FIFA worked hard for almost a decade and spent $60 million dollars to lay the perfect the pitch in all the 16 stadiums spread over Canada, USA and Mexico!
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| Courtesy: FIFA |
That has not been an easy task at all. The 16 stadiums are so diverse in terms of weather and geography, that the grass that flourishes in Miami may not grow at all in Seattle. Added to that a few stadiums have their roofs covered while others are open air. Critical to quality is resilience of the grass, the ability of the turf to endure the continuous stomping, kicking, jumping, running and rolling by twenty-two athletic players. Apart from being an excellent shock absorber the turf must ensure consistent mechanical behaviour of the ball such as roll, rebound and bounce. Rolling resistance determines how far the ball travels horizontally on the pitch, which is largely influenced by surface friction which in turn is governed by the grass height and moisture content. According to FIFA regulations, the ball must roll to a distance of 6.0 to 10.6 meters before coming to a halt. Similarly, dropped from 2.0 meters, a ball must rebound to a height between 0.6 to 1.0 meter. When a ball impacts the turf at an angle, the bounce must closely match the impact angle and speed. Unevenness (divots, bald patches) or varying moisture levels interfere with all these parameters.
Search and research for a perfect grass pitch began in earnest in 2018. Turfologists Dr John Sorochan of University of Tennessee and Prof John Rogers III of Michigan State University and their research teams took up the challenge. Commercial growers and stadium groundskeepers were roped in because their field knowledge was essential to choose the right grass type and define the appropriate maintenance protocol (light, watering, ventilation, draining etc) for ensuring grass health throughout the tournament period.
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| Plastic fibres supporting the grass roots Courtesy:Inside FIFA.com |
Aesthetic parameters such as uniformity in color, texture and thickness/density are equally important. A patchy, dried or yellowed turf doesn't match either the professionalism or the standard of FIFA. In color preference, market survey showed that dark green tops the list. Consolidating all the requirements of performance and aesthetics Sorochan and Rogers suggested Hybrid Turfgrass systems. Here natural grass is reinforced with tiny plastic filaments (polyethylene, nylon or polypropylene) as scaffolds. It was presumed that such a turf of 95% natural grass and 5% plastic filament not only enhances the look and feel of the turf but also provides a durable , resilient playing surface that prevents deep divots.
Cool season blend of 84% Kentucky bluegrass and 16% perennial ryegrass was selected for enclosed stadiums and Bermuda grass for warm open-air arenas. The Kentucky Bluegrass- Perennial Ryegrass combination has unique characteristics. Bluegrass is durable and fast spreading while ryegrass sprouts quickly. Bermuda grass grows aggressively, is sturdy, draught resistant and self repairing. The ultimate target was to have a lush green soft turf which can not only withstand a stampede but self-heal as well.
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| Ground preparation for hybrid turf |
The selected species of grass can be grown on a layer of sand spread atop a plastic sheet so that roots grow laterally and intertwine locking the sand bed into a dense, hardy mat. These can then be rolled into bales off the plastic sheet and transported to wherever required. The bales are unrolled over specially prepared ground. The grass mat sits over a layer of several inches of firmly pressed sand. Below that upto a depth of 45 centimeters or more are several layers of soil and gravel mixtures and drainage membranes. An elaborate underground system is in place to ensure aeration, watering, and efficient drainage. In stadiums with domes or limited sunlight arrays of artificial grow lights are provided. Once in place, plastic fibers are stitched into the ground about 18-20 cm deep using special heavy duty sewing machines. These fibres become anchors for the roots below and the blades above. Alternately a meshwork sporting sufficiently long(tall?) polythene fibrils can be laid out at the lower root zone level, filled with soil and sand and then seeded with the selected grass. As the grass grows roots entangle with the plastic filaments and get reinforced.
During the research and development phase Sorochan and Rogers experimented with various types of turfs. Robotic cleats, ball-launching machines, and stadium simulators were used to mimic on-field actions and reactions of the ball. Based on these elaborate and extensive experiments a critical grass height of 22 millimeters was recommended. Even a 5-millimeter variation drastically altered the behaviour of the ball. By the way the alternating light and dark green stripes that we see on the ground is just an optical illusion created by mowing the grass in alternate directions.
TAIL PIECE
Considering FIFA expects to rake up an overall revenue of roughly $10+ billion from this World Cup, the $60 million spent for the perfect pitch seems to be spare change.
REFERENCES:
1. Grasses for Sports grounds and its influence of playing quality : A review
2. FIFA Certified Football Turf: The standard for 2026 World Cup Stadiums
