Irrigation for sports turf
By Laurence Gale
Nowadays, irrigation is an important and integral part of the turf grass management industry, especially as the demand for better quality playing surfaces has increased. This demand has been largely due to extensive televised coverage of major sporting events. Seeing immaculate aesthetically presented golf courses, football, rugby pitches and horse racing courses has increased the expectations of the players and viewers.
Most, if not all, professional sporting facilities have irrigation systems of one sort or another. Without them they would not be able to prepare and maintain their playing surfaces.
Irrigation is essential for a number of reasons:
- for plant survival and growth.
- for soil formation
- for soil strength
- for chemical transport
- for managing playability
- for presentation
Water is influential in all chemical, physiological and biological processes of plant growth. The soil/plant water relationships is critical to the sustainability of any grass plant. Having an understanding of these relationships is critical. All grass plants are a continuum of water movement. Over 90% of the plant's water requirements are transported through the plant from the soil profile, via the roots and stem tissues into the leaves and out into the atmosphere. Knowledge of these relationships is important when designing and operating irrigation systems. The main aim is to achieve a water balance within the soil profile ensuring that the grass plant is able to access available water from the soil.
Detailed information on soil water balance can be seen at: http://www.ces.uga.edu/pubcd/b974-w.html
Irrigation scheduling by the water balance approach is based on estimating the soil water content. In the field, daily evapotranspiration (ET) amounts are withdrawn from storage in the soil profile. Any rainfall or irrigation are added to storage. Should the water balance calculations project soil water to drop below some minimum level, irrigation is indicated. Weather forecasts enable prediction of ET rates and projection of soil water balance to indicate whether irrigation is needed in the near future.
The soil water balance will be affected by a number of factors:
- Soil type and condition; the water holding capacity of soils will vary depending on their classification. Clay soils can hold more water than loamy or sandy soils, therefore soil type will effect and contribute to the amount of water required. Soils are continually going through phases of wetting and drying caused by local weather conditions.
The above diagram demonstrates the ability of the different soils to retain water. The sandy loam has a gentler gradient and is associated with a wider distribution of soil pores, enabling it to dry out more steadily than the sandy soil.
- Turf type and condition; healthy vigorous turf will transpire more water than an unhealthy turf plant.
- Time of the year; there is likely to be more soil water present during the spring, autumn and winter months when temperatures are cooler coupled with higher levels of rainfall.
- Weather; air temperature, daylight hours, solar energy inputs, wind speed and shading are factors that will affect evapotranspiration rates.
- Maintenance regimes; keeping the soil open and aerated will increase the drainage capacity of the soil. On the other hand compacted soils will prevent the movement of water through soils, often creating an environment that prevents water getting down into the soil profile. By carrying out effective regular maintenance regimes that include aeration, scarifying, harrowing, brushing, top dressing all help to keep the soil in good condition.
- Irrigation system; type, capacity, running time, calibration and efficiency.
- Water resources; quantity and quality. The quantity of water available, and the amount licensed for use in any one year, will determine the performance of any system and irrigation capabilities.
- Facility type; design and construction. USGA greens perform differently to pushed up soil greens, each having different water and management requirements. Modern drainage systems also effect soil water conditions. Extensive drainage systems will freely drain water from the soil.
- Groundsman/Greenkeeper knowledge; it is important that there is someone who understands all of the above parameters and can access the water requirements of the turf and correctly implement the right irrigation schedule for the facility.
Water Holding Capacity of Soils:
There are three important levels of soil moisture content that reflect the availability of water in the soil. These levels are commonly referred to as: saturation, field capacity, and wilting point. When a soil is saturated, the soil pores are filled with water and nearly all of the air in the soil has been displaced by water. The water held in the soil between saturation and field capacity is gravitational water. Frequently, gravitational water will take a few days to drain through the soil profile and some can be absorbed by roots of plants. Field capacity is defined as the level of soil moisture left in the soil after drainage of the gravitational water. Water held between field capacity and the wilting point is available for plant use. The wilting point is defined as the soil moisture content where most plants cannot exert enough force to remove water from small pores in the soil. Most turf grasses will be permanently damaged if the soil moisture content is allowed to reach the wilting point. In many cases, yield reductions may occur long before this point is reached.
The soil water on any day may be expressed in terms of a soil water deficit (SWD) this is the defined difference between the present water content and field capacity water content (usually expressed in mm of water)
The principle of good irrigation is to maintain SWD.
Many years ago groundsmen and greenkeepers considered themselves lucky to have a hose pipe and sprinkler available. During 1976, one of the hottest summers on record, whilst working at Cocksmoor Wood golf course, we were barely able to keep the greens alive. We only had a single diesel pump engine that pumped water from a stream, with the capacity to run only four hoses and sprinklers at any one time. Hours were spent moving and transporting the hoses and sprinklers to ensure all the greens received enough water to maintain the grass.
Technology has moved on, and we now see a wide range of irrigation systems from stand alone, self-travelling or boom sprinklers to computer controlled high tech pop up gear driven or jet sprinkler systems able to deliver precise amounts of water. Today many of the top golf courses have what is called wall to wall irrigation systems designed to irrigate greens, tees, approaches and fairways, enabling the course manager to have full control of his watering requirements.
These systems do use a lot of water, albeit more effectively, so consideration needs to be given to the resource available. Is it mains, borehole, well, river or lake water? In most instances an abstraction licence will be required to obtain this water even though the source may be on club owned land. Irrigation constitutes a major user of water resources at times, and in places, when resources are often at their lowest, such as the summer. Incorrect use of irrigation can lead to a waste of water and, in turn, can cause other problems such as increased drainage water, often resulting in the leaching of nitrates into watercourses with the possibility of pollution.
In recent years the Government have brought out a number of laws and regulations regarding the use of water resources. The Water Resources (EIA) Regulations 2003 dictates a number of issues regarding the use of water, of which the Environmental Agency is the main governing body associated with the policing the use of water in the UK. Along with other agencies such as DEFRA Department for Environment Food and Rural affairs. These new laws and regulations will have a significant impact on the way we use and utilise water in the future. Demonstrating water efficiency will be vital to meet the new legislation now being implemented by the . To obtain the necessary extraction licenses,( Water Resources Act 1991) the water authorities will need to see evidence that a club has planned and managed its water requirements effectively. A management strategy for water requirements will involve providing details of the irrigation systems and the capacity and delivery of the systems. There may not be enough water available which may require the building of storage lakes and ponds to supply the capacity of water required. Again, these will require planning permission and evaluation from the local authority.
Irrigation can impact upon the environment in two main ways; by depleting the surface and ground water resources and, secondly, by encouraging the leaching of nitrates from the soil to the ground water. Water used to irrigate crops and turf will often not return to the water course but will be taken up by the plant and returned into the atmosphere. Thus, during dry periods, water ground supplies can be severely reduced. Leaching occurs when the soil is wetted beyond field capacity and water drains from the root zone. This drainage water contains nitrate in solution which will eventually be carried to the drainage ditches or ground water. The main risk periods for leaching are in the spring when nitrogen has been applied to the crop, and in winter when nitrate remains in the soil after harvest, and drainage is at its maximum.
How fast and efficient can it water? To what depth and uniformity? Ensuring the correct application for the particular sport or surface requirement is vital.
Modern irrigations systems do not come cheap. A typical 18 hole golf course irrigation system, catering for greens and tees, will cost anything from £60,000, a single bowling green £6,000 and an artificial synthetic carpet facility £25,000.
Uniformity is the critical design factor of any irrigation system. The position, distance between and working range of the heads is crucial to uniformity. It is important to measure the uniformity of the heads on a regular basis to ensure that the system is operating correctly. This is done by placing receptacles (buckets) in a grid formation at set distances to collect the water. The water in the buckets is measured to see if there has been a uniform distribution to the surface target area.
Irrigation design engineers and manufacturers have now developed and offer a wide range of sprinkler products that can accommodate most facility requirement and applications, (greens, tees, fairways, football/rugby pitches, bowling greens, artificial pitches and horse racing tracks). All facilities require the appropriate system design to maximise the resources available. A poorly designed system cannot be made to work properly with remedial measures at a later date without causing a lot of disruption and cost implications.
The employment of experienced irrigation specialists/consultants will ensure that the right system is employed and, in the long term, will save time and money.
Designing an effective system requires knowledge of pipe hydraulics, zoning techniques, head spacing, wiring, efficiency features, and the reliability of various manufacturers' rotary sprinklers, valves, and controllers. Designers give a great deal of consideration to choosing the most appropriate equipment, since each project will have its own specific product and budget requirements.
Running times and system output capacities are very important. Many golf course often have to run for 6-8 hrs to complete a watering cycle. Does the system have the capacity or flow to change the quantities required? Is there enough running time available to achieve the aims and objectives?
The optimum time for watering is from 8pm through to 8am. Watering at other times may cause inconvenience to players and affect surface playability. Watering during the day, especially in hot weather, may lead to scorching of the turf and loss of water by evaporation.
All irrigations systems are driven by water pressure. It is important that the correct specification of piping is used to conform to the pressure requirements of the system being employed. Using the wrong size piping materials and UPVC joints could result in leakage problems once the system is up and running. Leaks and loss of pressure will have a dramatic effect on the performance of the system, with the added problem that the water will be going somewhere else!
Also, the quality of your water may effect the performance of your system. Sites in areas with heavy lime deposits may require filtration systems. Similarly, recycled water (grey water systems) will require an effective filtration system employed to clean the water prior to use on natural turf surfaces.
The building of water storage facilities can enhance the landscape, producing a haven for wild life and changing the aesthetic look of your facility.
Finally on the design front, does the system have the capability to be upgraded in the future?
Types of irrigation Equipment:
Hose pipe and sprinklers (oscillating/impact)
Boom sprayers, static line and travelling
Self travelling Sprinklers
Automated Pop up systems
Portable, stand alone sprinkler systems require regular moving and monitoring, often a time consuming operation. These are now considered an inefficient means of irrigation, however they are still widely used on small scale facilities.
Portable systems are cheaper to install than automatic ones. However, because of their many disadvantages, portable systems are viable alternatives only where budget limitations prohibit the installation of automatic irrigation. It should also be noted that portable systems being installed today must have the same type of backflow prevention device required for installed systems.
The desired application of water from any irrigation system will be fully dependant on irrigation scheduling. Proper irrigation scheduling is a difficult skill that surprisingly few groundsmen and greenkeepers have mastered. By far the largest loss or decline of turf grass quality on playing surfaces is the direct result of improper irrigation scheduling. You may be surprised to learn that the most common irrigation scheduling problem is not too little water, or even too much water, it is watering too frequently. Many of the common turf grass diseases are made worse by, or even may be the result of, watering too frequently. It is vitally important to understand the water needs of the plants and soil rootzone.
Even with the most technological systems there will have to be some input from the groundmans/greenkeeper in regard to monitoring and managing these systems. Therefore, plant and soil water knowledge is important. This information will help set the parameters for the system to operate.
Irrigation scheduling is simply a matter of close observation and dedication.
All irrigation scheduling procedures consist of monitoring indicators that determine the need for irrigation.
|Different methods for determining irrigation scheduling.|
|Method||Measured parameter||Equipment needed||Irrigation criterion||Advantages||Disadvantages|
|Hand feel and appearance of soil.||Soil moisture content by feel.||Hand probe/trowel.||Soil moisture content.||Easy to use; simple; can improve accuracy with experience.||Low accuracies; field work involved to take samples.|
|Local facility experience||Local knowledge of facility construction and topography of site.||Past experiences.||Soil and plant conditions||Dependant on experience and knowledge of soils and plant||Poor judgements could influence the inaccuracy of water application|
|grass indicators||plant growth rate||ruler/ visual||plant appearance||Easy to use; simple; can improve accuracy with experience.||Confusing signals the plant may be suffering from stress already?|
|Gravimetric soil moisture samples||Soil moisture content by taking samples.||Auger, oven.||Soil moisture content.||High accuracy.||Labour intensive including field work; time gap between sampling and results.|
|Soil moisture tension.||Tensiometers including vacuum gauge.||Soil moisture tension.||Good accuracy; instantaneous reading of soil moisture tension.||Labour intensive to read results. prone to vandalism|
|Electrical resistance/ gypsum blocks||Electric resistance of soil moisture.||Resistance blocks AC bridge (meter).||Soil moisture tension.||Instantaneous reading; works over larger range of tensions; can be used for remote reading.||Affected by soil salinity; not sensitive at low tensions; needs some maintenance and field reading.|
|Theta probe||Electric resistance of soil moisture.||Hand held reader that measures soil moisture at 5-10cm depths||Soil moisture tension.||instant reading ,easy to use||limited depth reading of up to 10cms.|
|Neutron probe||aluminium access tubes||Neutron probe using radioactive properties to measure soil moisture.||Soil moisture content.||Produces very accurate data||A radiation hazard and expensive to buy, requires a licence to use.|
|Water budgeting||Climatic parameters: temperature, radiation, wind, humidity and expected rainfall, depending on model used to predict ET.||Weather station or available weather information.||Estimation of moisture content.||No field work required; flexible; can forecast irrigation needs in the future; with same equipment can schedule many fields.||Needs calibration and periodic adjustments, since it is only an estimate.|
|Modified Atmometer||Reference ET.||An atmometer (ET gauge) measures the amount of water evaporated to the atmosphere from a wet, porous ceramic surface.||Estimate of moisture content.||Easy to use, direct reading of reference ET.||Needs calibration; it is only an estimation.|
Advantages of Irrigation Scheduling:
Irrigation scheduling offers several advantages:
- It enables the groundsman/greenkeeper to schedule water rotation among the various facilities to minimise turf grass water stress and maximise growth.
- It reduces costs of water and labour through fewer irrigations.
- It lowers fertiliser costs by holding surface runoff and deep percolation (leaching) to a minimum.
- It increases net returns by increasing turf grass yield and quality.
- It minimises water-logging problems by reducing drainage requirements.
- It assists in controlling root zone salinity problems through controlled leaching.
- It results in additional returns by using saved or grey water to irrigate.
Maintenance of Irrigation equipment:
Like all mechanical and electrical equipment there is a need for maintenance. Regular inspections should be carried out to installations, man hole covers and pop up sprinkler heads looking for any damage or leaks. It is also important to periodically calibrate the system, checking the uniformity of the irrigation and ensuring that all sprinklers are working. Drops in water pressure or leaks will effect the delivery of the system, often leading to non-uniform watering, which may lead to dry spots and inconsistent surface playability.
At the end of the season, close and drain down the irrigation system to prevent any frost damage.
It may also pay to implement a service agreement with the company that installed the system.
Keep records and diaries of irrigation scheduling, running/operating times and performances of the facility. Records will play an important part in the future use of water, especially as this resource may become scarce or restricted. The environment agencies will only look favourably on business that have managed and maintained their water budgets efficiently and have evidence of a irrigation strategy.
The main aims of the strategy are:
- Correct choice of irrigation equipment and system that is most appropriate for the facility.
- Irrigation scheduling; applying the right amount of water at the right time e.g. irrigating at night to prevent water losses by evaporation.
- Consider use of wetting agents to help promote water infiltration into the soil profile.
- Maintain a water balance within the spoil profile.
- Consider choice of drought tolerant grass species.
- Maintain an acceptable level of organic matter; will help the soil's water holding capacity.
- Implement cultural maintenance programmes aimed at establishing healthy deep rooting grass plants.
- Attendance on training courses and seminars on water resource management and complying with all water use legislation as promoted by the Water resources act 1991
- Set up and carry out regular maintenance checks on the irrigation systems, which also involves checking water quality.
- Keep maintenance and scheduling records for the systems employed.
- Keep records of weather data, recording rainfall, sunshine hours, air temperatures, and make use of local weather station information.
Irrigation management and the optimisation of watering strategies are important to the proper maintenance of sports facilities. Insufficient moisture when soils reach soil water deficit will result in a declining quality of sward, or even death. Legislation is going to force the industry to control and manage this scarce resource, therefore the understanding and implementation of an irrigation strategy is a must for all clubs and organisations.
References Irrigation Management and Optimisation by TM Hess March 2000 Cranfield University
Irrigation scheduling by I Broner http://www.ext.colostate.edu/PUBS/crops/04708.pdf 2004