Erwin Beltman was the head groundsman for stadium De Kuip in the Netherlands between 2013 and 2022. In that period, the field was voted the best stadium field in the Dutch Eredivisie eight times in a row. These days, he works as a consultant and shares his experiences about achieving good turf pitches on Sportsfields.info. Today he discusses hybrid turfs.
With leagues considering or deciding to ban synthetic turf fields, the market for hybrid turf surfaces in particular seems to be on the move. You can read here or here and here how new players are trying to gain a foothold in various countries. At the same time, it seems that municipalities are increasingly considering the concept as a more sustainable way to guarantee a higher usage. When playing on a hybrid turf surface, the players will predominantly play on the natural grass blades. The only thing the synthetic yarn does is strengthen the top layer. It contributes to the drainage of the surface and ensures that the field remains flat and stable. However, the synthetic turf yarn is also a concern: when the field is renovated, the top layer will be considered to be contaminated with plastic. Only certified companies will be allowed to remove and process the contaminated soil. The City of Amsterdam is going to investigate whether biodegradable yarns will solve this problem, but until this study has been concluded, we have to abide by the current laws. That is precisely why it is important that clubs or municipalities make a well-considered decision when deciding on a hybrid turf surface for sports.
There are three different types of hybrid sports solutions: injected systems, lay-and-play systems and reinforced soil systems. The latter is a bit of an outsider. This kind of surface is reinforced by mixing small plastic fibres through the subbase. It is a fundamentally different solution from the two other types of hybrid systems that are being offered. Reinforced soil systems use soil and require maintenance practices that are very similar to those used for 100% natural turf. Injected systems and lay-and-play solutions use a subbase that is similar to what is used for synthetic turf surfaces. Injected systems and lay-and-play systems also require more specific maintenance. An investment in one of these solutions requires a clear picture of how the field will be used and utilized in the future.
To look ahead is to govern
Lay-and-play options in particular require a meticulous installation. For this type of surface it is essential that the subbase is flat before the carpet with the synthetic turf fibres is rolled out. If not, you run the risk that the maintenance machine will catch in the backing and rip it out while scalping the surface. Both lay-and-play and injected fields require to have this done regularly to remove any thatch that has been built up in the surface. This thatch accumulates between the synthetic turf fibres and can block the drainage of excess water to the drains in the substructure. Once this happens, this can lead to wet spots or puddles on the field that, in the long term, can result in mould settling in.
Precisely because of the vulnerability of the lay-and-play options with regard to major maintenance, most providers believe that this type of hybrid solution only offers a short-term solution. Think about ten years maximum compared to the 15 to 20 years for an injected solution.
This vulnerability to thatch formation means that both the lay-and-play option and the option with injected fibres should not be mowed with robotic mowers, but rather, by mowers that also remove the clippings. The small pieces of grass that robotic mowers leave behind to serve as nutrients for the soil can encourage thatch formation. Lay-and-play and injected systems don’t require nutrients anyway. The substructure for these systems is deliberately kept lean to prevent the formation of thatch.
An investment in a lay-and-play or injected hybrid sports field solution also means that major maintenance must be carried out almost annually. That will certainly improve the playability, but it is something that must be budgeted for.
Both hybrid solutions also need to be aerated more often to maintain the right growing conditions for the grass. In the past, people complained that often the injected surfaces in particular dried out relatively quickly and became harder. This was due to the rapid drainage of rainwater that travelled along the synthetic turf fibres down. More recent installed injected hybrid surfaces appear not to suffer from this problem.
Types of fibres and density
The list of suppliers of hybrid sports surfaces is long. They mainly distinguish themselves in terms of the type of plastic chosen for the synthetic turf fibres and the length to which they inject the fibres. Almost all suppliers allow the synthetic turf fibres to protrude about two centimetres above ground level. That is just under the 2.5 centimetre length that is recommended for the grass. How deep the synthetic turf fibre must go into the ground depends largely on how the field will be used. Historically, the yarn was injected 18 centimetres deep, but nowadays this can vary up to even 6 centimetres in length.
The type of plastic chosen for the synthetic turf fibres can also differ. Polypropylene (PP) is known for being incredibly strong but less resilient than, for example, polyethylene (PE). However, the latter has become the plastic of choice for synthetic turf carpets, as polyethylene is more forgiving when making a slide.
In addition to the type of plastic, the density with which the fibres are injected varies between the various suppliers. A grid of 2 by 2 centimetres appears to be the standard, but this is something that the installer can deviate from, based on the client’s wishes or local circumstances.
Backing material and backing density
Anyone who chooses a lay-and-play option should also pay close attention to the backing. Historically, these are made of plastic, but nowadays there are more sustainable solutions like woven backings that do not require a coating, or a backing made from paper.
The backing can form a disturbing layer that prevents the roots from growing properly or hinders the drainage of rainwater to the drains.
Hybrid sports field solutions offer a great solution for higher usage intensity for clubs that prefer playing on grass. I predict that they will increasingly become a theme in the coming years in our drive for more natural sports field solutions. But if clubs and municipalities want to get the most out of their investment, it is important that they choose the right product.
Erwin Beltman is a former groundsman of Stadium De Kuip in Rotterdam. Between 2013 and 2022, the stadium field was voted the best stadium field in the Dutch Eredivisie eight times in a row. Today, he is director of Master in Grass and consults and advises fellow groundsmen.
The views or information he shares in his articles are not necessarily the views of the publisher
In my next column I will discuss the problems fungi can cause