What is natural turf?
Natural turf fields are becoming increasingly complex and engineered to:
Drain more effectively while maintaining sufficient moisture content.
Reduce reliance on water for irrigation.
Tolerate more use.
Be available during or immediately after bad weather.
To respond to these requirements, the designs are becoming more complex with highly specified materials and full engineering specifications and drawings which is a great move for the industry.
However, we’re seeing poor designs not adequately addressing these requirements resulting in increased maintenance costs and operations costs and we also see local facilities built using low-cost options that are ineffective and a waste of money.
This series addresses the most common questions we get asked about natural turf surfaces, from ‘isn’t it just dirt and grass?’ to ‘how do I maximise playing surface quality through maintenance?’. We’ll answer a couple of those questions in each blog post, so check back in regularly, or follow us on LinkedIn or Instagram to get notified of the next post. Let’s get started…..
Introduction to natural turf surfaces and upgrade options
Understanding more about natural turf Fields of Play will change the way you watch sport – for many of us here at SPORTENG we watch the turf as much as the action! Most people don’t realise how complex natural turf surfaces can be, so this blog series kicks off with a long post, answering two questions that we get asked a lot……
What do we mean by natural turf surfaces; it’s just dirt and grass, right?
Natural turf surfaces used for sport can indeed be just dirt and grass, but that’s becoming less and less common for any surface that needs to support regular use and be resilient to weather conditions such that training or match cancellations are avoided. Since the 1920s, research has been happening around the world to investigate ways of improving the performance of natural turf Fields of Play and almost universally, this resulted in the use of coarse-grained, free-draining materials, such as sand, being used to build sports fields.
Low-cost improvement works, such as re-grading to optimise water run-off, do not produce widespread improvements: Producing a surface that sheds water is only useful in prolonged rainfall events where the overland flow is likely. During less intensive rainfall events, rainwater will infiltrate into the soil and the upper layers will remain wet creating a ‘boggy surface’. The use of the surface in that condition destroys soil structure at the immediate surface which then causes the field to become boggy after smaller and smaller rainfall events. Then, during warmer times of the year, the structureless soil will become dry and hard.
Maintenance and field closures can be used to combat this: carrying out physical works to decompress the surface and 'resting' the fields, allowing the grass to grow over the surface which acts to protect it. In reality, extra maintenance and field closures fail to meet budget and usage expectations.
So what are the options for improving natural turf playing quality?
Once minor works are ruled out, all other options are disruptive, require specialist equipment and skills, and will remove the Field of Play from use until the new turf surface is fully established. We’ve produced a cheat sheet (available here [link to cheat sheet landing page]) of the typical surface upgrade options and the ones we see most commonly in Australia are summarised below:
The ‘Sandy Loam’ option. Excavate existing soil and replace it with sandy loam (with or without drains). A relatively low-cost option but minimal improvement in usability as the rate of water infiltration into the profile is only marginally better than what it replaced.
The ‘Slit Drain-Sand Carpet’ system. A low-cost option that retains the existing surface but installs a three-tier drainage system of subsoil drains, slot drains and a sand layer to provide a hydraulic connection from the surface to the subsoil drains. Not as effective as a fully reconstructed profile, but less expensive and well-proven around the world.
The ‘Rootzone Sand’ option. The existing soil is excavated, the subgrade levelled, drains installed and rootzone sand (possibly amended with various additives) installed. A mid-cost option that provides a highly permeable surface that is not susceptible to compaction. However, drains need to be closely spaced and amendments will be required to assist with moisture retention.
The ‘Sand-over-Gravel’ option. In reality, there are two variants to this. Both require the existing surface to be excavated and the subgrade levelled. And both also include the installation of drains, a gravel layer, and a layer of highly specified rootzone sand. The two options differ in the materials being used. In the conventional option, materials are selected that permit a free-flowing connection between the sand layer and the gravel layer, allowing water to drain away completely. The second option is to select materials that permit some drainage and then causes the remaining water to perch on top of the gravel layer, creating a saturated zone at the base of the sand layer. This is called a Perched Water Table and is generally preferred as it provides a small reservoir of water for plant roots to us and captures some ‘free’ rainwater. These systems are the most expensive and disruptive to install but are the premium natural turf surface upgrade options.
The weak link in all the above systems is the grass itself. Turfgrass differs from just ‘grass’ in that it has been selected and bred based on its research-proven tolerance to high levels of use and its rapid recovery from wear. Other factors such as aesthetics, growth habit, and density also form part of the selection criteria. Future posts in this series will consider the importance of the turfgrass itself in more detail.
Suffice to say that even the hardiest grasses have a maximum amount of use they can tolerate per week. Once this is exceeded, ground cover will be lost and a sandy surface easily damaged; disrupting surface levels and exposing a surface with low traction that may result in player injury. In the next blog post, we’ll take a look at options for increasing the resilience of a natural turf surface.
We hope you’ve enjoyed reading our natural turf series blog. Check out our other posts and if you’d like to discuss anything covered in this series in more detail, contact us.
For more information about natural turf upgrade options, sign up for our Field of Play Playbook here.
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