Whatever material they are made of, sports fields need irrigating; whether they are used for football or rugby matches (on natural grass, stabilised surfaces or synthetic turf), grass or clay tennis courts, race courses and equestrian centres (grass or sand) or natural grass golf courses, an efficient irrigation system is essential for the good health of the plants and the quality of the performance of the riders and players.
The reason for irrigating differs according to the composition of the sports surface; synthetic surfaces are irrigated to improve the playing area (quality of play) and cool them down because they tend to overheat under the sun and give off a bad odour. Wetting cools them down and reduces the smell. The irrigation of hard surfaces (stabilised or hard-packed surfaces) allows for the dust to be settled and the ground softened. Finally, natural grass surfaces are watered to help the plants become established, maintaining them and providing a better playing surface (softness of the soil). The irrigation of the sports fields is indispensable because it allows:
• The athletes to withstand shocks and knocks (softness of the soil).
• An optimum quality of play
• An increase in ground attendances.
• The creation of comfort zones within the heat islands (cooling through the transpiration of the plants).
• An aesthetic improvement of the fields, in the case of televised matches, or simply for the well-being of the users.
In order to ensure optimum irrigation, the site managers will have the use of an efficient irrigation system with a number of advantages:
• financial, on account of a saving on the time deployed by the labour force and reductions in the water bill,
• Environmental because of the savings on water (irrigating at night, controlling the irrigation run time), a reduction in chemical inputs (fertilisers and plant-health products) and less maintenance required.
What irrigation system can be used on a sports field?
A well thought out irrigation system allows for exactly the correct amount of water to reach the plant, not too much and not too little; in fact, a lack of water leads to water stress and consequently a deterioration in the structure of the soil and plant health. In the same way, too much water attracts pests and leads to diseases; furthermore, leaching causes the soil to lose nutrients and this results in too much fertiliser being used.
The sprinkler layout plan is very important (see diagram on page 44).
In fact, spacing the sprinklers closer together allows for finer droplets and a better soil water distribution.
One of the difficulties is finding a sprinkler arrangement that is consistent with the dimensions of the field (length and width) so as to get as close as possible to a square sprinkler pattern.
The ideal situation is to use the same nozzle-type throughout, for all the sprinklers, using a weather-based approach to manage its sprinkler rate. Ideally there should be one solenoid valve per sprinkler so as to be able to manage each zone individually. For example, it could be the case that a part of the field is more shaded from the sun and thus it does not require as much water as the rest of the field. This system means that there will be no over-watering of certain zones.
The notion of irrigation uniformity is very significant because it allows us to see whether our irrigation is optimal. Even with an optimum sprinkler layout, the distribution is not regular for each m2 of irrigated surface because the application rate received is equal to the sum of the application rates applied by the nearest sprinklers. However, these application rates depend on the distance from that point to the different sprinklers and depend on the water distribution curve of the chosen sprinkler, operating with one or several nozzles with a defined diameter and a specific pressure. Depending on the make and type of sprinkler, as well as the diameter of the nozzles and the operating pressure, the water application curve will differ. Therefore, the variability of the application rate differs according to the sprinkler chosen and the “nozzle-pressure” combination. The different kinds of measurements are as follows:
• Coefficient of uniformity CU, originally created to measure the uniformity of agricultural irrigation,
• Distribution uniformity, DU, which corresponds to field measurements taken in the field,
• The scheduling coefficient SC, a multiplying coefficient for applying the amount of water required by the plant.
The results are considered to be satisfactory when the CU is 93%, the DU is 90% and the SC is 1.1.
Furthermore, there are tools available to the users for optimising their irrigation, such as centralised control, programmers and sensors. Nowadays, it is hard to imagine having an irrigation controller that is not connected to a rain gauge at the very least.
In order to optimise irrigation, the site manager must also have a good understanding of his or her sports field
Knowledge of the soil properties: the sports field manager must know whether the soil is sandy, loamy or clayey. The volumetric water content of the soil depends on its porosity and permeability. Each soil type has its advantages and disadvantages. Thus, clayey soils are rather heavy and difficult to till, but they have a good water holding capacity. Loamy soils are relatively light and easy to till, but they have a tendency to form a hard crust, which can impair the growth of young seedlings. A sandy soil can hold little water but drains naturally (easy rooting) and it is not affected by movement or traffic above ground. It is not very fertile because it contains coarse particles.
Understanding the plant metabolism: each type of turf has its own characteristics. The manager has to know the type of turf, its water requirements, sensitivity to heat, drought, pests… for example, the tall fescue is tolerant to heat but it is susceptible to Pyricularia, a pathogen that goes unnoticed for the first few days and then causes tremendous harm. In the same way, Kentucky blue grass is tolerant to heat but, on the other hand, Pao Annua and Poa Trivalis have a very low heat tolerance. If it is observed that a planted species does not adapt to its surroundings, then it must be replaced by a more tolerant variety. To create a grass surface, the ideal solution would be to plant a mixture of different grass species, selected for their complementary qualities and suitable for the sports ground.
Understanding the external factors: evaporation is not the same in a Mediterranean climate as it would be in an oceanic climate, so the water requirements are not the same. Thus, it is necessary to have climatic data (Potential Evapotranspiration ETP) provided by a weather station nearby or on the site itself.
Saving on water is part of the learning process
To ensure that the tools are managed properly, training of the personnel is necessary. The National Association of Automatic Irrigation professionals (Synaa) offers training in irrigation :
• Short Expert’O courses (8 modules) run in partnership with the Léa-Tecomah school: they are aimed at all players in the irrigation sector (installers, public or private decision-makers, designers and users). These training courses enable those taking part to obtain the practical and theoretical knowledge required to design, install and use an irrigation system while optimising water consumption.
• extended training courses leading to a diploma (Ministry of Agriculture): at the end of this training, the young professionals, holders of the CSAI (Specialisation Certificate in Integrated Irrigation), will have a skilled trade specialising in automatic irrigation systems (design, implementation and management of the installation), enabling them to work on different types of installation, including sports fields and recreational grounds. Accessible after completing a vocational or technical sbaccalaureate, this is a Level IV training programme completed in one year via sandwich courses.
Furthermore, the professional guidelines for integrated irrigation systems can be downloaded from the Synaa site www.synaa.com.
The sound management of a sports field requires a lot of attention: you need to have an optimal irrigation system and also know how to use the equipment. It is also essential to have an excellent understanding of the sports field, its components, soil type and the climate.