Sports green areas: trends and technologies
The maintenance of sports fields, especially football fields, represents a considerable commitment, including in economic terms. The operations are complex and frequent, and it is essential to have appropriate mechanical technologies and cultivation techniques. Natural fields, artificial fields and hybrid composition fields have different needs. The latter offer the advantage of the natural turf while at the same time guaranteeing the improvement of the cover. The San Siro stadium is one of the most significant examples of this application
From the “Export” research conducted in view of Expo 2015 by the Master’s in “Sport Management, Marketing and Sociology” we obtained interesting data on the turnover of sports and on the evaluation of national sports structures. There are over 800 Italian companies that produce sporting goods and the turnover that sports generates in the country exceeds 1.5% of GDP. On the other hand, the perception of Italians regarding the quality level of sports facilities in their municipality of residence can be defined as medium-low. Only a little over 40% of those interviewed consider them good, compared with around 40% who consider them adequate and 18% who think they are poor.
The assessment resulting from the survey carried out in 2012 by the Lombardy Region on regional sports facilities, which showed that over 60% of them are considered obsolete and not very usable, is no different. On the other hand, the sports market in Lombardy is very active, with over 3,000 companies operating in the sports sector, 30% of which are in the municipality of Milan.
Focusing on the quality of sports green areas, it should first of all be emphasized that there are two aspects to always keep in mind regardless of the type of green area: the drainage of the ground, which must allow for the rapid permeation of rainwater, avoiding stagnation in all sections of the field even in the event of heavy rains; the turf, which must consist of varieties capable of resisting trampling, responding to the needs of the game and enduring low and frequent cuts.
During the usage phase, the maintenance must be very thorough, otherwise the turf will quickly deteriorate. The quality and durability of a sports field depends largely on these two phases of creation and maintenance.
Innovation and new trends mainly concern sports fields at a professional level, but the effects also involve the amateur sector. In this article we will analyse the topic of turf maintenance for football fields, where the innovation of the structures is particularly significant given the significant turnover that characterizes this sports on a professional level.
Soil preparation and drainage of football fields
The preliminary preparation work is basically the same for the different types of green areas. Since the profile of the ground must be made even, excavators and laser levelling blades are frequently used. The soil drainage must allow the rapid percolation of rainwater, primarily for game-related needs, and secondly for the vegetation’s needs.
The classic draining system was performed with the continuous draining layer technique. In practice a succession of different well-defined layers was created, with a layer of plant soil within which the root system develops (thickness 150-200 mm), a layer of thin filtering material, and a layer of coarse filter material to cover the drainage pipe network located on the bottom. To increase the flow capacity in order to obtain a percolation capacity exceeding 150-200 mm/h (about 40 times higher than that of agricultural land), we have adopted a technique of reinforced surface drainage. It consists in making longitudinal channels 300-350 mm deep at a distance varying from 5 to 10 metres. At the bottom of the channel there is a thin layer of gravel on which perforated pipes are placed, which are then covered with gravel and with sand mixed with peat closer to the surface. The longitudinal channels are then connected by perpendicular channels 150-200 mm deep, which are then filled with a mixture of sand and soil. All these operations are carried out with specific machines that are able to complete the entire work cycle in a single pass (excavation, soil removal, laying the draining pipes and filling). As we will see later in the description of turf with latest generation reinforced natural grass, the drainage system has had further developments.
The preparation of the superficial vegetation layer has also seen improvements aimed at, for example, conserving water. Hence the use of porous materials, such as volcanic sand, pumice and pozzolana combined with material that can increase the exchange capacity. After the soil has been drained and levelled, the vegetation cover is installed, and the choice of the mixture of species and cultivars to be used is of great importance. The types of coverage can be: natural grass, artificial grass, reinforced natural grass.
Fields with natural grass
Microthermal species are used in the north and macrothermal are used in the south. In the intermediate climate regions, the macrothermals, which have their optimal temperature above 30° C, turn yellow during the cold period, at the expense of the aesthetic aspect. Therefore “mixed” covers were obtained by carrying out microthermal overseeding at the first frosts. On the other hand, in northern climates, the practice of heating has been adopted to cope with the winter cold that inhibits grass growth, inserting a network of pipes under the vegetation layer. Electric heating was also used to heat the substrate, installing a dense network of low-voltage electric cables that allows to create a temperature of 12° -14° C in the substrate explored by the roots. However, these solutions do not reconcile well with the necessary vertical drainage interventions carried out with coring and drilling machines. This led to installing heating systems above the grass cover. It is a matter of creating a “roof” of tear-proof and transparent sheeting, automatically moved and anchored in different points in order to guarantee complete coverage of the field. The greenhouse effect that is created is increased with the insufflation of hot air. The height at which the sheets are placed must allow access for normal maintenance operations. Since the 90s of last century, the sowing of turf has been replaced, at least in the professional fields, by “sodding”, i.e. the transplanting of squares or rolls of pre-established turf. Both removing the sods from the nurseries and laying it in place are carried out with specific machines. The maintenance includes the operations of: grass cutting, fertilization, aeration, sanding, pest defence and irrigation. The grass is cut at a height of 30-40 mm, so during the periods of full vegetation it is done twice a week. Both helical blade mowers and horizontal blade mowers, including robotic ones, are used. The frequency of ventilation operations is mainly linked to the intensity of use. In general, coring or drilling machines are used. As an alternative to mechanical drilling, there are machines that make the holes with jets of high-pressure water. The sanding, with silica sand and soil, is performed to fill the holes, to reduce the formation of felt and to fill any irregularities. Another intervention is the partial or total transplantation of clods to replace any degraded ones. Besides the traditional fertilization of the soil with granular fertilizers, carried out with the normal fertilizer spreaders, there is also leaf fertilization, based on hormones (cytokinins) and zinc ammonium acetate, which promote root growth and consolidation. Irrigation performed in a completely automated way is indispensable.
The pesticide interventions must be through, especially against possible fungal attacks.
Artificial grass fields
The need to reduce maintenance costs has led to the creation of artificial grass fields, both for football and for other sports activities. These turfs are being increasingly adopted thanks to the improvements in quality. According to an article published in “Il Sole 24 Ore”, the artificial turf market in Italy in 2010 was estimated at 3.5-4 million square metres per year, mainly for football, for a turnover of over 120 million of Euro. Until 2010, the installation of artificial grass concerned solely the amateur sector. Their spread led to the LND publishing the “Regulation for the construction of latest generation artificial turf football fields”, in force since January 2011. From that date, artificial grass in our country has also been used for football fields for professional use, including those of the top league. This growth reflects what has also happened at the international level. According to a review conducted by “Sport industry magazine”, it turns out that “in Europe each year 1.5 billion euros are spent to install more than 2,250 man-made turf mantles, equal to 41.6 million square metres, about half of the global market. And the growth rate is in the double digits”. The latest generation of artificial carpets enable playing conditions and provide performance that is very close to natural grass turf. The grass of these turfs is characterized by a fibre length of 400-600 mm and granules for the infill between the fibres (the task is to support the filaments and allow maximum adherence of the cleats) made with environmentally friendly products. Artificial high filament density grass is made of fibres extruded with polyethylene polymers whose section is furrowed by ribs that allow the immediate return of the filaments in an upright position during and after play.
Ordinary maintenance consists of brushing operations performed with machines equipped with rotating cylinders on a horizontal axis equipped with hard nylon fibres. The operation allows the fibres to be lifted and any foreign elements removed. Periodically check the sheet coupling, the drainage system and the signage. The irrigation interventions are indispensable in the summer months in order not to raise the temperature of the overfill above 35° C. Another operation is represented by the integration and redistribution of the infill material to ensure that the carpet always maintains the same performance. It is also necessary to periodically clean the surface with the use of vacuum cleaners that retain any dirt while the vacuumed infill is dropped back to the ground. Special attention must be paid to reduce the risk of bacterial contamination from the soles of shoes, sweat and saliva of the players. To cope with this, the turf must be disinfected with chemicals. In Italy, unfortunately, there are still no rules set by the Football Federation, while in the USA there are already regulations.
Fields with reinforced natural grass
In the football fields of the top leagues in Italy and abroad, the preference is for natural grass. Hence the birth of grass turf in reinforced natural grass, called “hybrids”, as they consist of natural grass with a portion of artificial grass. The result is a weave that gives greater resistance to wear caused by trampling and play, while maintaining the characteristics of natural grass. We must keep in mind that in order for natural grass turf to maintain optimal or at least good performance, the annual use should not exceed 30-35 matches. In a stadium like San Siro in Milan, where games played mainly during the winter by two teams that are also engaged in international tournaments, this limit is largely exceeded. The San Siro stadium, like others in Italy, was rebuilt for the 1990 World Cup, and is grassed with the “sodding” technique. Furthermore, the third ring was built to increase capacity, which reduced natural light. The combined effect of high use, low lighting and reduced air circulation has led to the need to carry out major maintenance work, including 3-4 “re-soddings” a year, sometimes of the entire field. Naturally this meant high costs in the order of one million euros a year. In 2012, following the example of what was already been accomplished in Europe in important stadiums (Wembley in London, Santiago Bernabeu in Madrid), after 22 years of strife it was decided to install a reinforced natural grass turf at San Siro. Since the time allotted for the execution was short, instead of sowing the natural grass it was necessary to resort to transplanting already grassed sods on a draining base, as if it was a “re-sodding”. Artificial fibres were then injected onto this mantle by means of a special machine equipped with needles which, pushed by compressed air, penetrate the ground by injecting the filaments to a depth of 200 mm and a distance of 20 mm. In total, 20 million injections were made with the use of 43,000 km of artificial filament. The fibres injected this way protrude to the surface by 25 mm, but are not visible and cannot be perceived because they are covered by natural grass 40-45 mm high. The artificial grass injected this way represents 30% of the total grass mantle. Since it is essentially a natural grass field, it must be managed according to the maintenance operations described above, except for the “re-sodding”. The roots of the natural grass are in fact intertwined with artificial fibres, giving the grass a greater resistance to tearing caused by the cleats of footballers’ shoes. On San Siro, however, the serious handicap of the lack of natural light remains. The problem was overcome by resorting to a sort of large steel spider on wheels, which opens up telescopically above the turf at a height of two metres, equipped with sixty 1000 Watt lamps. In addition to providing artificial light, this system also produces heat, thereby overcoming the problems of the winter cold.
Other fields with “hybrid” turf include the Mapei Stadium in Reggio Emilia, built in 2014. After having dismantled the old turf with an excavation to a depth of 350 mm (much less than the 600 mm required by the old techniques), a continuous stratified drainage system was built on which the turf was laid with reinforced natural grass. The radiant heat system was installed at a depth of about 200 mm. The drainage system that has been created enables the recovery of the water percolated on the sides of the field, allowing its reuse, for example, for irrigation. The drainage layer, the heating system and the turf are practically a single integrated system. This stadium too installed a system of artificial lighting modules, to compensate for the lack of light in periods of lower sun radiation.
