GRASS A HEALTHY, HARDER WEARING PLAYING SURFACE
J. W. Hacker Professional Sportsturf Design (N.W.) Ltd, Preston, U.K.
M.K. Harbridge Professional Sportsturf Design (N.W.) Ltd, Preston, U.K.
Recent legislation and increased demand for better sports stadia have led to increased problems in growing a healthy, hard wearing grass playing surface. This paper highlights environmental factors essential for grass growth. It also highlights the need for careful stadia design and discusses some of the ways in which these problems are being addressed by maintenance programmes and newer construction systems.
Key Words: Grass Playing Surfaces, Shade, Construction Systems, Maintenance Programmes.
Implementation of new legislation and the availability of large quantities of monies for stadia improvement have led to many new or reconstructed stadia over the past five years. Many of the new stadia designs do not take into account the requirement to grow grass for a playing surface. This may be down to a lack of knowledge on the part of the Architects concerned, or the fact that, until now, grass growth has been sufficient to enable play year round in most stadia. As might be expected, the desire for improvements in stadia design including seating and covered areas, is mirrored by the requirement of the football club to have as good a playing surface as possible year round. Unfortunately, this is becoming more and more difficult to achieve as the parameters necessary for plant growth are being degraded by large buildings surrounding the pitch.
Research work undertaken by Baker (1) in 1995 showed that the amount of shade on the pitch at mid day in December/early January ranged from 63% of the pitch area for Premier League Clubs to 71% for Scottish Premier League Clubs. 83% of staff at clubs considered shade to be a major or moderate problem. In his companion paper Baker (2) highlighted the need for club officials and Architects to take into account the effects of any new construction work on grass growth. He noted that the main factors of importance were:
a) Avoidance of large stands on the south side of pitches.
b) Maintenance of as much space as possible between the stands and the pitch, especially on the south side but also where possible for the east and west stands.
c) Avoidance of the enclosure of corners by covered stands.
Since Baker's work, many more stadia and stands have been erected, only some of which have sought to address the problems highlighted in his two papers. This paper seeks to highlight the factors necessary for plant growth which must be considered if a satisfactory natural grass playing surface is to be achieved.
FACTORS AFFECTING PLANT GROWTH
There are a number of factors which affect plant growth within any situation. These include the following:
a) Temperature - air and soil b) Soil moisture/humidity c) Nutrient availability and effect d) Light quality and quantity
TEMPERATURE AND PLANT GROWTH
The optimum temperature for plant growth varies from species to species. For most temperate species grass shoot growth will occur at temperatures between 40oF ( 4oC) and 105oF (40oC). Optimum temperatures for shoot growth in temperate species is between 60oF (16oC) and 75oF (24oC). Fluctuating (diurnal) temperatures between day and night (68oF (20oC) day and 37oF (3oC) night) have also been found to enhance tillering in ryegrass. Within the sports stadium there is often little that can be done to control the temperature of the air. Essentially, the optimum temperatures for grass growth occur prior to the winter onset sometime between mid October and mid November, depending upon location. Ideally, grass growth should be maximised during the growing season and maintained as long as possible into the autumn without promoting soft, easily worn growth. Air temperatures will themselves dictate when growth slows and ceases.
It should also be borne in mind that temperature is also closely related to light intensity with high light intensities producing more tillers at higher temperatures. If light levels are low, then the optimum temperature for tiller production is also lower. This is also true of leaf appearance where an increase of light intensity only slightly increases leaf appearance compared with an increase in both temperature and light levels.
Root growth however prefers a lower temperature range than shoots with the optimum temperature range being between 50oF (10oC) and 65oF (18oC) for maximum sustained root growth. Higher rates of root growth can be achieved at higher temperatures but only for a short period of time. Where undersoil heating exists some use can be made of it to maintain soil temperatures. However, care is needed to ensure that roots are not dehydrated and killed. Reduced rooting depth is not immediately obvious and can be the cause of surface divoting in some cases.
Roots have been found to be very sensitive to reductions in light intensity, with less roots being produced at lower light intensities. This is thought to be due to the amount of assimulates reaching the roots being reduced under lower light intensities and high temperatures. This is also true of a grass sward when mowing is undertaken as root growth is reduced by lowering the height of cut. Insistence by some managers on heights of cut below 25mm is often part of the cause for sward thinning and wear.
Provided all other essential elements are present, then light and temperature interact to control growth through the production of assimulates and regulation of growth hormones.
SOIL MOISTURE LEVELS AND HUMIDITY
Moisture levels are not usually a problem in the United Kingdom. After what is the wettest year on record, very few are looking for ways of increasing rainfall. Not only that, most stadia pitches also have installed pop-up irrigation systems which can allow water to be applied at the touch of a switch. The application of water is therefore not a problem. However, getting water away and out of the rootzone is most definitely a problem. This is partly associated with high winter rainfalls as might be expected but also partly due to the insistence of many football club managers to have the pitch watered prior to playing the game. In a wet year such as the last year, this requirement has meant that many pitches have been maintained at field capacity for a large part of the winter and at soil saturation for a significant part. This is particularly true of those pitches which are based on a gravel carpet whereby the carpet is designed to retain water in the base of the rootzone. It would seem that this recent wet year has led to increased water retention in the base of the rootzone thereby discouraging deep root growth and promoting more surface rooting.
Increased irrigation or rainfall and prolonged periods of surface wetness are also a major factor in disease promotion. A number of diseases are increased by a high atmospheric water vapour content including the two most common diseases as identified by Raikes Lepp and Canaway (3), that being fusarium patch disease and red thread disease. Other diseases encouraged by these conditions include powdery mildew and dollar spot. Disease normally found in warmer climes such as brown patch and pythium are also encouraged by a high humidity.
In addition to a high humidity above the grass, a depletion in nutrient levels has also been associated with diseases such as leafspot and red thread. Sand based pitches are designed to be free draining and are therefore subject to ready leaching of nutrients, especially nitrogen.
NUTRIENT AVAILABILITY AND EFFECT
Sand based rootzones are notoriously low in exchange capacity. Their ability to hold onto nutrients is reduced due to the small amounts of organic matter and clay within the rootzone, which is primarily designed to be free draining. As the rootzone ages so the amount of organic matter increases thereby helping nutrients to be retained. However, sand based pitches are more dependent upon the groundsman for regular nutrient applications and their management needs to be learnt and fine tuned on a day by day basis by the groundstaff. This is not by any means impossible and many groundstaff are now very adept at knowing just when they need to apply additional fertiliser in order to maintain the appropriate growth.
The effects of reduced or enhanced nutrient levels is one of the factors which is closely involved in disease susceptibility or resistance. Raikes, Lepp and Canaway (3) in 1994 undertook a survey of professional football clubs and noted the importance of disease management using both chemical and cultural methods in an Integrated Pest Disease Management Strategy. They found that the most common diseases were red thread disease and fusarium patch disease. However, the management of nutrients in order to discourage disease is not always as clear as it might seem. Tables within that paper clearly highlighted this by showing that red thread is promoted by low nitrogen, while fusarium patch disease is promoted by excessive nitrogen. Getting the balance right is, of course, part of the skill of being a good groundsman. This is just one example of how nutrients are closely involved in healthy plant growth.
Getting the amount of nutrients right is also important in terms of wear resistance. Canaway (4) in his paper in 1985 found that nitrogen levels were directly related to wear resistance. Too little or too much and the pitch grass cover reduced. This was supported by work undertaken by Canaway and Hacker (5) in 1988 when similar trials were undertaken on a PM sand carpet construction.
Clear evidence exists therefore for the need to maintain the correct level of nutrients to achieve the healthiest sward available which is both wear and disease resistant. Other work, not mentioned here, identifies the need for a balanced nutrition and the effect of other major and minor plant nutrients on growth and disease resistance.
LIGHT QUALITY AND QUANTITY
So far this paper has discussed some of the factors which can be controlled by the goundstaff after construction has taken place. Unfortunately, increasing light levels is usually not an option. Light is essential for plant growth in that it is the means by which plants receive the energy to convert carbon dioxide and water into energy rich organic compounds. This process takes place primarily in the presence of two pigments chlorophyll a and chlorophyll b. These compounds exist in the chloroplasts which are found in the living cell. In simple terms photosynthesis turns light energy into sugars and starches which are then broken down by the plant in the process of respiration releasing energy for plant growth.
The three major requirements for the photosynthetic process are light, water and carbon dioxide. Both the quantity and quality of light are important in the photosynthetic process. The quality of light is important as chlorophyll absorbs light in two major bands: red light (580-690 nm) and blue light (350-530 nm). Such active light is referred as photosynthetically active radiation (PAR) or physiologically active irradiation (PAI) and is approximately 44% of daylight.
While the quality of light for photosynthesis is well defined, the quantity of light needed for maximum growth cannot be determined on its own. This is because it is closely related to other factors such as temperature.
Natural light levels will vary from place to place in the United Kingdom, but the daily averages were found to be as follows in London and Aberdeen:
December June Peak MJ/m2 MJ/m2 MJ/m2
London 1.82 18.28 29.38 (June)
Aberdeen 1.06 17.60 31.02 (June)
This gives a figure of 0.8 MJ/m2 PAR for London and 0.45 MJ/m2 PAR for Aberdeen in December.
Most energy absorbed however is re-radiated at longer wave lengths with the release of heat. The compensation point, the point where photosynthesis equals respiration, for most grass is between 2 and 5% of full sunlight.
The maximum photosynthetic rate of individual turf grass leaves occurs at light intensities of about one third of full sunlight. Indeed, the photosynthetic response rate is considered to be directly proportional to radiant flux values under U.K. winter daylight conditions. Under summer daylight conditions the photosynthetic response rate diminishes due to light saturation.
GRASSES GROWN IN SHADE
Studies on shaded turfgrasses show that such grasses have a more delicate structure and are more succulent than non-shaded turfgrasses. This results in reduced tolerance to heat, cold, drought and wear. In addition, shaded turfgrasses are likely to be more susceptible to pests and diseases.
It has been found that plants at low light intensities have a lower compensation point than those grown at high light intensities. Such shade grown plants also become light saturated at considerably lower light intensities than when grown in full sunlight. Tillering, the production of side shoots, is primarily controlled genetically. Studies found that perennial ryegrass had 6.2 tillers compared with 3.3 tillers for Timothy when grown in similar conditions. Timothy may have five leaves before the first tiller appeared, while in perennial ryegrass a tiller may emerge as soon as the leaf above it is fully expanded. High light intensities however favour tillering provided that the saturation point has not yet been reached, the temperature is adequate and all other factors are not limiting.
GRASSES AND PHOTOPERIOD
The term photoperiod refers to the day length or, more importantly, the length of the dark period or night. It is most significantly found to act as a stimulus for flowering and most temperate grasses flower under a long day stimulus (greater than 12 hours of light). In many grass species, however, tillering is encouraged under short days. Short days in this instance being day lengths less than 12 hours. On the other hand, stolon growth of creeping bentgrass has been found to be enhanced by day lengths in excess of 13 hours. Generally speaking, once a plant has been triggered to flower, then leaf growth reduces or ceases thereby reducing the density of the sward. It is therefore very important that any attempt to enhance light levels do not induce photoperiodic reactions which might trigger the plant to move from a vegetative state to a flowering state and thereby affect its wearability and density.
DISCUSSION AND CONCLUSIONS
There are many factors therefore that affect grass growth, disease resistance and general wearability. Temperature and light however are probably the two most important factors which are often difficult to control during the winter period and sometimes totally out of the groundsman's control due to stadia design. For architects designing stadia these factors ought to be taken into account at the design stage. It is pleasing to see that this is becoming more and more commonplace. The particular factors which need to be addressed in the design stage would include the following:
a) Light Distribution and Quality
Ability for the playing surface to receive light ideally all day all year, but where possible as much as possible for as long as possible. This will involve making sure that the stands are not too close to the playing surface (often easier to say than to achieve), or that stands on the south and or west and east sides are further back than the north stand. In addition, transparent or translucent light panels in stand roofs are also beneficial on stands which will be causing shade during the winter period. The light quality transmitted by such material is also important. It is essential that these products are able to conduct the red and blue light required for the photosynthetic process. Examples of stadia which seem to be well back from the playing surface include the McAlpine stadium at Huddersfield.
b) Air Circulation
In order to maintain humidity at acceptable levels, it is important that there is air flow around the ground. The practice of filling in the corners to the stands has often been detrimental to maintaining air flow. Careful design is needed to maintain air flow, ideally without the need for electric fans. Recent developments such as the SubAir system which enables air to be pulled or pushed through the undersoil drainage system may be beneficial in maintaining an acceptable micro climate around the grass plant itself. In addition, maintenance operations such as reducing irrigation and fertiliser application in shaded areas along with raising the height of cut may also be beneficial (Baker (1)).
Provided these major constraints are addressed in the design stage, then the agronomist has a chance of maintaining the best possible playing surface year round. Recent pitch developments which also help achieve this include improved construction systems, surface reinforcing material, undersoil heating systems, undersoil aeration systems and, of course, better knowledge of nutrition, improved grass cultivars and general maintenance.
1. Baker S.W., The Effects of Shade and Changes in Micro Climates on the Quality of Turf at Professional Football Clubs I. Questionnaire Survey. J.Sportsturf Res. Inst. Volume 71 June 1995
2. Baker, S.W., The Effects of Shade and Changes in Micro Climates on the Quality of Turf at Professional Soccer Clubs II Pitch Survey. J.Sports Turf Res. Inst. Volume 71 June 1995
3. Raikes, C. Lepp, N. W., and Canaway, P. M. Major Diseases, Pests and Weeds of Winter Sportsturf. I Results of a Questionnaire Survey of Professional Football Clubs. J.Sports Turf Res. Inst. Volume 70 1994.
4. Canaway, P. M. The Response of Renovated Turf of Lollium Perenne (Perennial Ryegrass) to Fertiliser Nitrogen I. Ground Cover Response as Affected by Football-Type Wear. J. Sports Turf Res. Inst. Volume 61 1985.
5. Canaway, P. M. and Hacker, J.W. The Response of Lollium Perenne L. Grown on a Prunty-Mulqueen Sand Carpet Rootzone to Fertiliser Nitrogen I. Ground Cover Response as Affected by Football-Type Wear. J. Sports Turf. Res. Inst. Volume 64 1988.