Root zone profile
Pitches can be designed and built in different ways. These can be divided into five groups:
Native soil profiles
The most basic and cheap alternative is just shaping the original soil, providing a slope to allow water run-off without any internal improvement of materials, amendments, or drainage. Performance will depend on soil texture and structure (drainage rate) and climate (precipitation), but it is usually low and not suited for stadiums or elite level sports.
Modified soil profiles
Native soils can be improved by incorporating sand, generally with frequent topdressing after core aeration, and by installing some type of drainage system (pipes or sand bands). Sand-amended pitches are common around the world and can produce good results. However, for elite competition, at least in stadiums, they can still present limitations.
This construction model is the most desirable for top-level venues. As it minimises the risk of drainage problems arising. The concept involves replacing native soil with a root zone mix of sand and an organic amendment.
Reinforced sand-based profiles
A hybrid system (natural grass with inclusion of synthetic fibres) can potentially provide more usage and better traction for the players. The suitability of using a hybrid turf system must be discussed with your turf consultant.
Artificial turf fields
A field incorporating a fully synthetic turf stitched into a carpet and filled with performance and stabilising infill. For rugby, these fields will generally require to be installed on a shock pad. All artificial turf fields for use in rugby must comply with World Rugby Regulation 22. Further information on artificial turf fields for rugby and Regulation 22 is available at world.rugby. The rest of this section is primarily focused on natural turf surfaces but will reference artificial turf where appropriate.
Water management is not only important for the turf, but also the environment.
Irrigation design is a specialist business, and it is important to ensure a reputable irrigation designer has been commissioned as part of the project team.
A good irrigation design will enable different areas of the ground to be watered separately. Different sections of the ground, such as sides, centre corridor and in-goals, may require different irrigation scheduling depending on factors such as usage rate, environment, and maintenance programme.
It is highly advisable to install a variable frequency drive to allow the pumps to work in a variable fractional capacity to allow spot irrigation.
Sprinkler heads and other in-ground componentry must be selected based on proven efficiency and player safety. Other devices, such as a rain-sensor, salinity sensor or in-ground moisture sensors, are helpful in fine-tuning the irrigation and agronomic programmes.
Consideration should be given to the feasibility of capturing and reusing rainwater for irrigation purposes as required.
Appropriate natural grass species should be considered which require minimal inputs in that particular climate, e.g. drought tolerance or pest resistance.
Warm season grasses
In warm regions, a rhizomatous and stoloniferous species is preferred, due to its vigour, stability, and recovery capacity. The species of choice if sunlight is abundant is Bermudagrass (Cynodon dactylon), usually as a hybrid (with C. traansvalensis) of which there are many proven varieties.
In some parts of the world, other species might be considered: Seashore paspalum (Paspalum vaginatum) due to its high salinity tolerance, Zoysia species in areas of high disease pressure and Kikuyugrass (Pennisetum clandestinum) which is widely distributed in the southern hemisphere. Climate will be a large factor in determining what turf species to use, although factors such as shade tolerance, ease of maintenance, player preference (fine v coarse leaf) and turf colour should also be considered. For example, paspalum is dark green, medium-textured and looks like some bermudagrasses while kikuyu and zoysia may be light green with coarser leaves and thicker stolons.
Cool season grasses
Cool season grass species not only handle lower temperatures, but they are also better adapted to low light environments, such as shaded stadiums.
Perennial ryegrass (Lolium perenne) is a popular choice as a cool season grass as it offers true winter activity. It flourishes where summers are moderate, and winters are cool. It has rapid establishment and very good wearing qualities. As it is extremely important to have a quality ryegrass surface to play on, a premium perennial ryegrass blend is the preferred choice. Research suggests that perennial ryegrass has the highest wear tolerance of all the cool season grasses and can keep up with more hours of play.
A perennial ryegrass is the better choice over an annual ryegrass mainly because of its slower growth rate and its finer texture. Annual ryegrass grows much faster which creates maintenance problems like having to cut more often. Annual also tends to grow in clumps rather than the uniform pattern achieved by perennial ryegrass.
Mixtures of two compatible cool season species, one rhizomatous and the other bunch-type are used, especially in North and South America. The rhizomateous species (for example, Poa pratensis) aids stability and cohesion while the bunch-type increases traffic tolerance.
Where a hybrid system is installed, there is generally no need to have a rhizomatous species and perennial ryegrass is used alone.
Mixed season grasses
In the transition zone, where warm season grasses enter dormancy during the wintertime, a common approach is to overseed the warm season grass with perennial ryegrass. This would be done every year in the fall to allow play during the cold months. The overseeding and the transition back to the underlying warm season grass are two of the most important management practices in the calendar. It is critical to minimise the duration of shading by the ryegrass once the warm season grass starts budding in spring. Annual ryegrass or intermediate ryegrass must be avoided because they don’t have the same traffic tolerance, they are coarser and aesthetically unpleasant.
Establishing a turf cover is the final step in the construction process. There are several techniques used to establish a natural turf surface, including:
- Turfing or sodding
The choice of technique will involve weighing up several key factors including:
- Type of grass species selected
- Timeframe before use
- Availability of resources
- Material supply
- Specialist machinery
Before planting ensure the growing medium is 100 per cent ready. It is critical to get the surface as level as possible before any re-grassing. It is difficult and costly to address poor levels after the turf is established.
For new constructions ensure the root zone and sub-grade are properly consolidated. Future sinkage of unconsolidated spots will mean having to sand top-dress to restore levels.
Make sure the root zone is satisfactorily loosened so that there is no restriction for root development.
As a final step before grassing, apply starter fertiliser to the surface and lightly rake in. Ensure the surface is in a moist (and non-repellent) condition before re-grassing.
Seeding has historically been the preferred method of establishing cool season grasses and sometimes warm season grasses. It is the most economical way to establish turf but requires longer to be match ready. Generally, allow 12 weeks minimum establishment time, although this can vary depending on climate and construction type (could be shorter with hybrid systems).
Seeding is not a viable option where the desired turf species, such as many Bermuda grasses and other warm season species, can only be propagated vegetatively. The following points should be considered for successful establishment from seeding:
- Use a specialist seeder to ensure even application and incorporation of the seed into the soil. It is important to maintain good soil/seed contact to help to conserve moisture and prevent seed desiccation.
- Apply the seed evenly for best results and use the correct seed rate. A high seeding rate does not always result in a better turf surface and may lead to the development of spindly, immature plants less able to cope with wear or disease. In contrast, low seeding rates may provide greater opportunity for weeds to invade.
- Maintain a high surface moisture level for the initial two or three weeks, until the root system has started to develop. It may be necessary to water several times (lightly) throughout the day in hot dry conditions.
- Keep all traffic (including mowers) off the seedlings until they are strong enough to take traffic. This is likely to take at least three weeks after germination.
Sprigging, sometimes called stolonising, involves using plant material to vegetatively propagate and establish a new turf surface. The sprigs, or stolons, are usually derived from shredding harvested turf. The shredded turf is then either spread evenly across the surface, or it can be inserted into the ground using specialist machinery. The term “line planting” is often used to refer to insertion of sprigs in rows.
Sprigging is commonly used for establishing warm season grass species that cannot be successfully established from seed. The cost of sprigging is generally greater than for seed but considerably less than for turf sod, especially if specialist equipment is on hand. However, it generally takes longer to establish turf by sprigging (allow a minimum of 12 weeks in good growing conditions) and it generally takes more water over the first few weeks. There is also a greater risk of failure through washouts in the event of storms.
The following points should be considered when establishing a turf surface from sprigging:
- Important to access and use good quality sprigging material. Material should be fresh and have rhizomes ready to bud.
- Sprigs must be planted within the soil profile then kept moist. Spreading the sprigs on the surface is less likely to be successful than if the material can be pressed into the soil or buried with topdressing.
- Use sprigs at a generous rate to ensure full and even coverage. Depending on the species typically sprigs would be planted at a ratio of around 1:6 (one unit area of harvested sprigs would be spread over six units of area).
Sodding or turfing is the laying of mature turf that is grown and transported from a turf sod nursery. Although a costly option, it is the only technique that results in an instant turf cover and hence reduces the time taken before the turf surface can be used. It also reduces the risk of a washout in the event of a storm. Often the decision to turf rather than sprig or seed comes down to the pressure of having the playing surface available as quickly as possible.
Sod can be used either washed or with a thin layer of the soil where the turf was grown. Washed turf is preferred, especially if dealing with sandy profiles, because it eliminates any issues associated with introducing a poor quality soil layer within the sand root zone profile. A common practice with major stadiums is to have a nursery of “instant play” turf available in the event a surface needs to be re-turfed and played on within a short timeframe (often a couple of days).
Instant play turf is generally thicker (maybe 40mm thick) and is often grown on plastic sheeting in the nursery in order to aid rapid establishment and easier transport.
The following is the general procedure when using turf sod:
- Check that the turf is healthy and weed-free when delivered and before it is used
- Water the underlying soil prior to laying to ensure rapid transplant rooting
- Avoid damaging the surface or surface levels when laying the turf
- Lay the sod in a brickwork pattern initially along a straight edge and ensure it is butted tightly into the adjoining sods for a good stable and firm finish
- Lightly consolidate by rolling
- Topdress with a light application of sand root zone material
- Water immediately after laying. Instant turf should show new root growth within days of laying and be well established within weeks depending on the grass species and the time of year.
Pitches that have been turfed should be ready for use within six-eight weeks of laying, however this should only be used as a guide. Time is still needed with traditional turf sod for the roots of the turf to establish before it is used for play. Where the surface is to be used immediately after sodding, a deeper sod containing a compatible sand root zone material must be used. This will minimise any transplant shock and ensure a stable surface that can be played on immediately.