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Types of Playing Fields

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Natural, reinforced, natural hybrid, synthetic hybrid, or synthetic. Five types of playing fields have been developed in recent years according to FIFA. Let’s delve into the details to understand the advantages of each type.

Summary

Benefits of natural grass with synthetic reinforcementBenefits of natural grass with synthetic reinforcement

In the quest for increasingly high-performance surfaces, at a time when stadiums are used several times a week and provide challenging conditions for the growth of natural grass, various innovations have emerged in the market. In addition to traditional natural grass and the established third generation of artificial turf, the popularity of a new generation of playing surfaces is growing: often simply referred to as hybrid systems, these actually involve various combinations of materials and types of construction. For this reason, following the document produced by FIFA, we aim to provide an overview of the various types of sports surfaces used in football, with some guidelines on technical aspects and performance, also in relation to the innovative POWERgrass hybrid system.

Types of Playing Fields According to FIFA

Since many different terms are used to qualify surfaces as “hybrid”, “reinforced”, or “mixed”, the following table aims to provide a clearer overview of the different categories, placing them within the natural-synthetic continuum. The table should be regarded as a generalisation of current products. As innovations and technologies evolve, updating classifications may become necessary. In 2017, FIFA proposed the following classification:

Playing field classification - FIFA 2017Playing field classification - FIFA 2017

The differentiation is based on the organic/inorganic nature of the materials used, the impact of materials on the final product, and typical maintenance required for each category. Natural grass is a living organism that can grow and regenerate, whereas synthetic grass does not.

  1. The category of “natural grass turf” includes all cultivated or laid grass surfaces that do not involve other materials.
  2. “Reinforced surfaces” include additional support in the root zone construction, aimed at strengthening the hold of the grass. For the user, the surface does not look different, as it is essentially just natural grass.
  3. “Natural hybrid surfaces” are those most commonly referred to when using the term "hybrid". These are natural surfaces cultivated within a base of synthetic fibres. The synthetic fibres are visible but typically constitute less than 5% of the total grass cover, which is why these surfaces are classified as “natural”.
  4. “Synthetic hybrid surfaces” are based on artificial grass with sand but may use natural organic materials as so-called performance infill (typically instead of rubber infill). This category is considered synthetic turf as it essentially requires the maintenance of an artificial grass field.
  5. “Synthetic surfaces” consist of artificial materials (manufactured or fabricated by humans), typically artificial grass carpet, sand infill, and rubber infill, with the possible addition of an elastic shock-absorbing underpad.

Please note: Hybrid grass systems, for certification purposes, belong to the category of natural grass playing fields.

The Significant Differences Between Hybrid Systems

With the development of innovative technologies, further classification is possible as the choice between different hybrid systems and the installation method can significantly influence field usability during the week, construction and maintenance costs, and the possibility of renewing the system multiple times, thus affecting its longevity. For instance, among a vertically injected in situ hybrid system, a horizontally transplanted in sod hybrid system, and a horizontally installed in situ hybrid system, there are many variables that can easily constitute three subtypes of natural hybrid fields.

differences between hybrid systemsdifferences between hybrid systems

3.1 In the case of the natural vertical hybrid system, there is no support to which roots can cling. The system requires a special machine for installation, and the fibre retention to the ground depends on the sand layer's consistency and working depth. Generally, fibres are planted to a depth of 18 cm and form a very solid surface. During play, there are fewer holes forming on the surface, but the ground tends to harden quickly. Post-match restoration and frequent aeration are needed to maintain the surface softness in the optimal range of 65-85 g with the Clegg hammer. The difference between one vertical system and another lies in the quality of fibres and their number per square metre, which generally hovers around 2500 points per square metre.

3.2 In the case of the natural horizontal hybrid system, this refers to all types made with artificial carpets with an open horizontal support, easily penetrable by roots that anchor there. The fibres need to be welded to the horizontal support in the factory with a force exceeding 30 N. Differences between one system and another relate to the type of support, fibre quality, and number per square metre, which should not exceed 5% of the surface, to leave ample room for natural grass. We won't delve into the technical details between systems, but we can make a large distinction for those transplanted on large field turf. This type of installation necessarily implies a nursery cultivation period of between three to six months. Often, hybrid sods are cultivated far from the final installation field, which entails adaptation to a different climate. In any case, special machinery, numerous transports, and precise organisation are required for harvesting, transporting, and laying hybrid sods. Moreover, transplanting is itself a significant stress for the lawn, creating more thatch, while differences between sod joints often require overseeding and sanding that tends to bury the synthetic fibres. During the renovation phase of natural grass (required at most every 3 years), the operation is complicated, if not impossible, to remove natural grass without lifting artificial grass or damaging synthetic fibres.

3.3 In the case of a natural horizontal hybrid system installed in situ, however, these issues are less present because the artificial grass rolls with open backing are sewn together. Many believe that the lawn must grow for at least 6 months to attain proper maturity. However, through optimised cultivation methods, it is possible to provide a ready-to-use horizontal hybrid turf within 4 weeks of seeding, a period consistent with the summer break in play. In the case of intensively used fields, favouring systems with more fibres, it is possible to have a field always playable even during winter, and then plan for reseeding during the ideal growing season. Sewing the rolls together allows easy system renewal every 2 or 3 years without damaging fibres or lifting artificial grass, thus providing a field that can last beyond 20 years, like the POWERgrass field.

4.1 and 4.2 In the case of synthetic hybrid systems and synthetic hybrid refill systems, it should be clarified that in neither case do we have natural grass, except when weeds grow. The main difference between the two is that the first has two types of infill: a stabilising infill (dried sand) and a performance infill with natural organic grains. Both infills must be removed when the system is replaced at the end of its lifecycle and possibly recycled for other uses. The synthetic hybrid refill system, however, does not use sand to stabilise the artificial turf, as the performance infill is heavy enough to perform both functions. In this case, the infill can be partially reworked, cleaned, and reused at the end of the artificial grass lifecycle.