Background and glossary

Chapters 1 and 3 of the Natural Grass vs. Synthetic Turf Surfaces Study Final Report.

Natural grass

Traditionally sport has been played on natural grass surfaces. As towns and cities were established natural grass sports surfaces were developed on open space sites set aside for recreation. The nature of the sporting activity determined the requirements for the sports ground, in relation to size and surface characteristics.

The construction of natural grass sports surfaces has varied according to the site, and in many cases, sports grounds have been developed either, on original soil, fill sites with poor quality imported soil or in some cases old landfill or drainage sites which can be prone to sinkage. As a result, the quality of natural grass sports grounds is variable, particularly in winter months or following high rain fall events.

In the last 20 years as the profile of sport has increased, particularly at an elite level, the expectation and standards for sports ground quality have also increased. The main drivers for higher standard of sports grounds are;

  • Increased professionalism with significant financial benefit available for elite athletes
  • Increased exposure through media coverage
  • Increased sponsorship
  • Continued technological advancements; and
  • Increased awareness of player safety.

First class and international sports venues must comply with stringent standards in relation to the quality of the sports ground surface. These standards can be accessed on the various state, national and international sporting governing body’s websites (refer to acknowledgments and further information for further details).

The impact of this on local sports grounds is the increased expectation of sporting clubs and associations, in relation to the quality of sports grounds across the sector.  Ground management authorities, including local government, schools, clubs and associations, are under increased pressure to provide high quality sports grounds in an environment where participation rates are increasing for some sports and access to open space is decreasing. Whilst it is not always possible to provide elite standard facilities, sports grounds must be ‘fit for purpose’ for the designated activity.

Whilst specific requirements for individual sporting codes will be discussed later in this report, a general discussion on the major considerations in relation to natural grass sports surfaces follows.

Construction (soil profile)

The aim of natural grass sports ground construction is to produce a turf surface that is ‘fit for purpose’ for the designated activity. Construction standards for elite and premier surfaces are higher than those for local sports grounds.

Elite sports grounds

Elite sports grounds are constructed using an imported sand profile over a drainage layer with sub-surface drainage installed. Such construction is limited to elite venues, which are used for national and international grade sport or smaller areas such as golf or bowling greens.

Premier sports grounds

Premier sports grounds are constructed using an imported sand profile over a natural sub-base with sub-surface drainage installed. Such construction is used for high grade and state level sporting venues.

Local sports grounds

Local sports grounds are constructed using natural soils, where possible, with amendments incorporated if necessary. Generally surface slope is used for surface drainage. Where drainage becomes a problem sand slit drains can be incorporated to improve drainage.

For further information refer to sport specific requirements.

Natural grass species 

The desirable characteristics of grass species for sports grounds are drought tolerance, wear tolerance, a consistent leaf density and good recovery rates.

Natural grass species can be divided into two types;

  • Warm season (Kikuyu – Pennisetum clandestinum/Couch – Cynodon sp.)
  • Cool season (Rye – Lolium sp./Fescue – Festuca sp.)

The warm season grasses have a creeping growth habit with horizontal stems growing above the ground (stolons) and below the ground (rhizomes) which provide good recovery characteristics. Warm season grasses can be established using seed, vegetative cuttings (stolons) or sods. Seed or stolons require several months and up to a year respectively to establish prior to use. Laying of sods, whilst more expensive, is quicker to establish and can be used within weeks of laying given the right conditions. The growing season is spring, summer and autumn with peak growth stages in the hotter summer months. Both Kikuyu and Couch provide a consistent leaf density, they are drought tolerant and have good wear tolerance. However, winter dormancy results in limited recovery from damage or wear during the cooler months, which is the period when grounds are subject to most wear.

Cool season grasses (Rye/Fescue) have an upright tufted growth habit relying on tillering from individual plants for growth and recovery. Cool season grass can be established using seed or sods. Seeded sports grounds require several months and up to a year to establish prior to use. Laying of sods, whilst more expensive, is quicker to establish and can be used within weeks of laying given the right conditions. The peak growth season is spring and autumn with reduced growth in winter. Whilst rye and fescue grass does not actually have a dormant period, they require significantly more water to sustain healthy growth in summer and are not drought tolerant.  Where turf has declined due to wear, recovery requires over sowing as the individual grass plants must be replaced.

Kikuyu or Couch sports grounds can be over sown with rye grass to provide improved winter wear tolerance.  However, it is necessary to eradicate the rye in spring. This practice is costly and is usually done only on premier sports grounds.

At a ‘local’ sports ground level the desired grass species are either Kikuyu or Couch grass. It is important that the grass quality is maintained to a high level with a consistent dense coverage going into winter dormancy so the grass can withstand winter wear. Whilst recovery from excessive wear in winter may be slow, the grass will recover during spring and summer.  Where natural grass quality deteriorates this has an impact on surface quality with the development unstable, loose or uneven areas leading to divots and pot-holes resulting in twisting or trip hazards.

Natural grass turf maintenance

In order to maintain the grass turf to provide an acceptable, ‘fit for purpose’ facility, a sound turf maintenance program should be implemented aimed at maintaining turf health, soil structure, and surface levels. A turf maintenance program includes the following:

Mowing

Turf should be cut with a cylinder mower weekly during spring and summer and fortnightly during the colder months when grass growth is slower. Height of cut should generally be between 15-25 mm for warm season grasses and 25-40mm for cool season grasses.

De-compaction

To maintain soil structure, de-compaction works using a mix of deep coring with hollow tynes in spring (verti-drain) and deep slicing (earthquake) in Autumn. Varying the de-compaction methods will ensure that a hard pan is not created within the profile.

Sodding

Areas that suffer excessive wear may require sodding in order to maintain acceptable turf and surface quality. Areas such as goal squares and cricket pitch run-ups are particularly susceptible. Maxi-sods which are 600mm wide are preferred. Unless sods are grown on a sandy soil they will require coring with the addition of sand top-dressing to ensure drainage through any imported clay loam soil.

Top-dressing

To maintain surface levels, sports turf should be top-dressed, concentrating on heavy wear areas such as the centre corridor and goals, in early spring following the winter competition season. Top-dressing material should be of high medium to coarse sand with hydraulic conductivity of > 100mm/hr and pH of between 6.0–7.0. Top-dressing rates are between 100–150 tonnes per hectare concentrating on the centre corridor and high wear areas. Top-dressing should follow sodding and coring to ensure the sand is incorporated into the root zone of the soil profile.

Weed/pest/disease control

It is generally not necessary to implement a proactive weed, pest and disease control program for local sports grounds. Rather where weeds, pests or disease are identified specific action will be required.

Irrigation

Irrigation schedules over the summer months should replace soil moisture lost through evapotranspiration. A base irrigation schedule is developed using average climatic conditions and irrigation system application rates to ensure adequate irrigation is applied without wastage. The schedule needs to be adjusted for weather variations. As a guide the irrigation requirement for warm season turf using average climatic conditions in Perth is between 5,500kL-6,800kL per hectare.

Thatch control

Excessive thatch can be detrimental to turf health and should be minimised. The usage schedules will thin turf and thatch can be controlled with close mowing and sound irrigation programming. Where thatch levels become a problem dethatching or scarifying is required.

Fertiliser

 Healthy natural grass requires correct nutrition to provide the necessary food for the plant to grow. Laboratory soil tests should be done annually to determine soil nutrient status and enable amendment fertiliser program to ensure chemical balance within the soil. This is coupled with an ongoing maintenance fertiliser program providing the major nutrients of Nitrogen, Phosphorus and Potassium.

A natural grass sports surface provides an asset to a community which is alive and self-renewing given sound management. Being a natural surface it is subject to many variables and the quality of the surface is impacted by the quality of construction, maintenance regimes, weather and usage rates. Full lifecycle costings for specific natural grass sports surfaces for individual sporting codes are provided later in this report. [1] For further information on Natural Grass Surfaces Management refer to acknowledgments and further information.

Synthetic turf

History of synthetic turf

Synthetic turf was first invented in the mid 1960’s in America.  It originally came into existence in the market place to replace natural grass that had difficulty growing in indoor stadiums. The Houston Astrodome was the world’s first fully enclosed stadium with a synthetic turf field. This field was not much more than green plastic indoor-outdoor carpet, however, it was praised for its visual appeal and playability and as a result, synthetic turf fields were soon under construction across America.

Despite a growing number of complaints from teams and players about various injuries occurring on the fields for most of the next decade, little change was made to the original turf design. Many of the USA stadiums that tried synthetic turf around this time, including the Houston Astrodome, all eventually returned to natural grass.2

However by the mid-1970s these first generation synthetic turf pitches (low-pile height, high-density of fibres) had improved to the point where a synthetic turf pitch was successfully used for the hockey tournament at the 1976 Olympic Games in Montreal.  Made of nylon (polyamide) yarns, first generation pitches were coarse and capable of causing friction burns and wounds unless they were played on when they were wet - as per the hockey model.  This model did not suit a number of sports including soccer, baseball and American football3 so the uptake of synthetic surfaces in these sports was slow.

Improvements in synthetic turf technologies continued over the next decade but it wasn’t until the early 1990’s that significant changes were seen, with the introduction of the third generation turfs. New, revolutionary improvements were happening.  Various mixtures of silica sand and/or recycled tires (granulated crumb rubber) were now being incorporated into extremely well-drained synthetic turf fields. The overall playability of the fields was becoming more and more similar to natural grass surfaces.2

The use of a softer polyethylene based fibre and the ability of the surface to take a normal stud has resulted in it becoming an acceptable surface for sports such as soccer and rugby. The rubber infill, sometimes with a shock pad for added safety, have made third generation synthetic turf more acceptable for most of the sports where a player might occasionally slide, fall to the ground, or land from height. These third generation pitches are now becoming popular in Australia, and will increasingly be seen in the future being used for Australian Rules football and cricket (outfields), and for multi-sport usage.3

Types of synthetic turf

Type according to infill content:

Unfilled

Unfilled pitches were the first type of system implemented for sport. They had short pile height, were dense in quantity and had no infill material. They were often made of nylon, which meant the prototypes were often tough and abrasive. Partly due to the abrasiveness, watered unfilled surfaces were developed and have since been popular for elite levels of hockey.

Filled

With filled synthetic turf systems, the synthetic turf fibres or blades are fully supported or stabilised by the addition of a filling material, such as sand, clay and rubber granules, or a mix of sand and rubber granules. The sand and fibres combine to form the characteristics of the playing surface. Synthetic turf surfaces which are filled with sand only are generally suitable for hockey, tennis, lawn bowls, touch rugby, lacrosse, and soccer (training) and multifunction use.

Dressed

Dressed systems are a derivative of the sand-filled system, and intermediate in their properties and playing characteristics between the traditional filled and unfilled carpets. They can have either:

  • a shorter, denser pile than the standard filled system which are considered suitable for hockey, soccer (training), touch rugby, lacrosse and cricket (fielding practice).
  • a longer pile which is suitable for soccer, rugby, Australian Rules football and cricket.

Types according to pile height:

Short-pile turf

Short-pile turf is made up of high-density short fibres (between 8-12mm in length) and is used predominantly for cricket pitches or for elite level hockey pitches. The unfilled hockey pitches have, until now, had to be kept wet to improve foot traction, ball speed and heat suppression.

Medium-pile turf

Medium-pile turf (between 20-35mm in length) has traditionally been the hard-wearing sand-filled carpets used for hockey, tennis, lawn bowls and for training level activities in a variety of other sports.

Long-pile turf

Long-pile turf has long blades of fibre similar in height to some natural grass playing surfaces. The long fibres (between 40-65mm in length) provide cushioning and allow for a great amount of infill to be integrated into the pitch adding to the shock absorbency and force reduction characteristics of the ground, and plays more like grass. These fibres can be single fibre or multi-ended yarns (brush-like at the tip), and are proving to be popular for soccer, rugby, Australian Rules football/cricket and golf. The latest development with long-pile turf is the development of even longer fibre carpet (80-85mm, with approximately 60mm of infill material). This is being hailed as the first suitable synthetic turf system for athletics field events including hammer, shot put, discus and javelin.4

Maintenance practices for synthetic turf

It is often widely believed that synthetic turf fields require less ongoing maintenance than natural grass. Even though they do not require watering and mowing they do have an extensive maintenance protocol, particularly if used regularly for a multitude of sports events or for elite level sport.

Such maintenance is critical if the surface is to achieve its optimum performance, and full lifespan. Usually the installer’s guarantee or warranty will usually be conditional on the recommended maintenance requirements being carried out.

Maintenance practices differ depending on the type of synthetic turf surface installed and it is important to follow the manufacturer’s instructions and guidelines.  Below is a list of common maintenance practices that are undertaken for synthetic turf.

Cleaning

Sweeping of leaves and other debris from the surface generally needs to be done weekly.  If leaves, tree flowers, pine needles and other debris are left on the surface for any length of time they rapidly rot down and form a drainage-inhibiting skin within the surface which can encourage the growth of algae and moss.

Grooming

Grooming the surface is a crucial operation aimed at keeping the mat and texture of the synthetic turf as even and uniform as possible, so as to prevent the deterioration of play characteristics, appearance and drainage properties.  Grooming the surface through brushing and/or drag matting lifts the fibres at the surface.  It redistributes evenly any sand or rubber that has been disturbed, and counteracts any compaction of the sand and any tendency to form an impervious surface skin which might impair drainage (filled surfaces only).

Moss and algae

In certain situations and in some seasons, algae or moss can become established on the surface. This only becomes a serious problem if it is allowed to become established.  Prevention is more effective than cure, therefore, an annual application of moss-killer and/or algaecide is recommended.  It is important to check the surface regularly for any signs of moss or algae growth and imperative that affected areas are treated as soon as they become present.

Weed removal

Weeds are not as prevalent in synthetic turf as they are with natural grass but, they do still appear from time to time.  It is important to remove weeds as soon as they are noticed to prevent them from spreading.  They can either be removed by hand or local areas of infestation can usually be treated with domestic weed killer, however, always check with the manufacturer before using any chemical sprays on the surface.

Stain removal

Most stains can be removed easily with a solution of warm (not boiling) water and a household detergent such as dishwashing liquid. Before attempting to remove heavy soiling and stubborn stains it is important to seek the surface supplier’s advice.

Joints and Seams

It is important to check all joints and seams on a regular basis and repair any failures promptly, before loss of any synthetic surface pile or risk to users.

Check and top-up infill levels (filled surfaces only)

High traffic areas such as penalty spots and short corners should be checked daily or weekly, but other areas of the ground infill levels should be checked monthly.

Power brushing

Many (but not all) manufacturers of third generation rubber-filled surfaces now recommend the use of powered brushing machines to ensure that the rubber particles remain mobile and the carpet fibres upright.  This operation is recommended at least every 6 months.

Deep cleaning

Both sand filled, dressed and rubber filled surfaces may in time require a degree of deep cleaning. This will depend largely on the environment and usage levels and should only be performed if surface contamination is suspected, and then only by specialist contractors.5

Glossary

Clegg Hammer
Simple to use device consisting of two basic components: a flat-ended cylindrical mass and a guide tube. The mass, i.e. the hammer, is manually dropped from a predetermined height to measure the "stiffness" of natural or constructed soil conditions.
Crumb rubber
Granules of new or recycled rubber materials used for infill or for top dressing on synthetic grass materials.
Dressed pitches
Pitches using a carpet of woven, tufted or knitted synthetic yarn partly supported or stabilised by the addition of filling material (eg. sand and/or rubber granules – generally filled to around 60% of the pile height and therefore sometimes referred to as a sand-dressed pitch).
Evapotranspiration
Loss of water from a land area through evaporation from the soil and through plant transpiration.
Filled pitches
Pitches using a carpet of woven, tufted or knitted synthetic yarn fully supported or stabilised by the addition of filling material (e.g. sand and/or rubber granules). Generally loose laid, not stuck to the layers below (except at the seams).
Impermeable surfaces
Surface that does not allow water to soak through.
Impervious surfaces
Artificial structures such as pavements, roads, sidewalks, driveways and parking lots that are covered by impenetrable materials such as asphalt, concrete, brick, and stone and rooftops.
In-fill
Generally silica sand, rubber granules, or a combination of both, and its function is to support the pile of the carpet, help the pile to remain vertical and contribute to the playing and cushioning qualities of the surface (ball rebound, shock absorption and vertical deformation).
Natural Grass
Natural turf species used for sports ground construction i.e. Kikuyu, Couch and Rye grass.
Pile
The full depth of tufts or loops of yarn which form the carpet.
Pile length
The length of the extended tufts measured from the primary backing top surface to their tips. Pile tuft should be gently extended but not stretched during this measurement.
Polyethylene
Softer type of plastic used for the new generation synthetic turf yarn. It is durable, resistant to staining, can be U.V. stabilised and is currently the most suitable material for synthetic turf yarns.
Polypropylene
Type of plastic predominately used for synthetic turf backing and can also be used for synthetic turf yarn.
Seams
The line formed where two pieces of turf are joined. The action of setting the turf and seaming using one or more methods; adhesives, sewing or tacks.
Shock pad
If required, a shock-absorbing layer is placed over the base, directly under the carpet. It is used to provide a degree of comfort to players underfoot, but also to reduce peak forces for head impacts, and to create defined playing characteristics for specific sports.
Surface run-off
The water flow that occurs when soil is infiltrated to full capacity and excess water from rain or other sources flows over the surface.
Synthetic Turf
Refers to any artificial turf surface used in sports ground construction including unfilled, filled and water-based surfaces.
Third Generation (3G) turf
Introduced in the late 1990s – comprising a longer pile (35-65mm), lower density of fibres infilled with sand/rubber granules or both. Generally loose laid, not stuck to the layers below (except at the seams).
Unfilled pitches
Pitches using a carpet of woven, tufted or knitted synthetic yarn in which the density of the pile is sufficient to maintain yarn vertically without support or stabilisation by other materials, usually needs to be wet to achieve playability.
Volatile organic compounds
Organic chemicals that have a high vapor pressure at ordinary, room-temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate from the liquid or solid form of the compound and enter the surrounding air. Many VOCs are dangerous to human health or cause harm to the environment.
Water-based pitches
An unfilled pitch (generally low-pile height, high-density of fibres) most often used for hockey, that is played on ‘wet’ to help keep the ball on the carpet surface, provide some controlled foot-slide when players need to stop/turn, and to allow players to fall on the surface without risking friction burns.
Yarn
A continuous strand of twisted fibres. 

Footnotes

  1. Handreck, K. A. and Black, N. D. (2001) Growing Media for Ornamental Plants and Turf, 3rd Edition, NSW University Press, Kensington, Australia 2001
  2. Target Technologies, 2011. A Brief History of Artificial Turf, http://www.ttiionline.com/turf_industry_history.htm viewed August 2011.
  3. State Government Victoria, 2011.  Artificial Grass for Sport, Sport and Recreation Victoria
    Department of Planning and Community Development, Melbourne, Victoria.
  4. State Government Victoria, 2011.  Artificial Grass for Sport, Sport and Recreation Victoria
    Department of Planning and Community Development, Melbourne, Victoria.
  5. State Government Victoria, 2011.  Artificial Grass for Sport, Sport and Recreation Victoria
    Department of Planning and Community Development, Melbourne, Victoria