By Ing W.A. van Mullen, DLV-Adviesgroep, The Netherlands


The goals, when selecting and designing an irrigation system for a nursery container field is to provide a consistent application of water throughout the watering zone, and to choose heads that emit a low volume of water.

     There are many challenges in ensuring even and consistent irrigation coverage, most importantly working with the differences in plant material. Plants differ in size, shape and water requirements. Therefore, a uniform irrigation system is very difficult. Most irrigation systems today in greenhouse situations are pin and bridge nozzles, which emit too much water at once. In addition, plants situated close to walkways are left too dry by most, if not all irrigation systems. It is difficult to combine spring-loaded rotating sprinklers and greenhouse sprinklers as they both operate at different water pressures.

     There are systems available now that provide reasonable coverage, using less water with each application. Capillary mats in the greenhouses and outside container beds have also attracted a lot more attention, and now better quality irrigation systems incorporate sub-irrigation and/or the ability to recycle the irrigation water.


Important factors for choosing irrigation systems
The source of water and its quality is a critical factor to consider when designing an irrigation system. If using ditch and pond water, it is important to consider the salt content. Iron content and bicarbonate (HC03) can also often pose a problem for well water. The best suitable water for plant irrigation is rainwater.

     Good drainage and sloping of the beds is very important when constructing the container beds. Grades must be designed to ensure puddles do not form.

     Recycle irrigation water wherever possible. It is not only important to comply with regulations (water quality regulations are not yet in place in Canada, but are currently under consideration by some provincial governments), but is also a good business practice. For more information on the economics of recycling water and nutrients in nurseries, see the article “Two Chicago nurseries use nutrients and wastewater,” by Dr. Calvin Chong, page 19 of this issue.


TYPES OF IRRIGATION SYSTEMS


Spring loaded circular sprinklers
The spring-loaded circular sprinklers with exchange­able nozzles (2.5 - 5 mm diameter) are very good as they provide a very good spread. The success of this type of sprinkler is very dependent on the water pressure. To perform optimally, spring loaded circular sprinklers must be between 55 and 65 psi. (Some pumps will not deliver that much pressure at the sprinkler head.) The maximum distance that should be allowed between heads with these sprinklers is between 12 and 15 metres. The container beds cannot be more than six to seven metres wide. On small parcels of land, it is difficult to get enough overlapping of the water pattern. Add more sprinklers to ensure full coverage is attained.


Greenhouse and poly house irrigation
The most popular system in a glass or plastic greenhouse is the pin nozzle or spinner nozzle. There is not such a demand anymore for the bridge nozzle.


Pin nozzles
These nozzles work at approximately 30 psi to provide 3.5 to five litres of water per minute. For a good spread, you need three to four lines for every 6.4 metres of width in the greenhouse. The sprinkler distance should be 1.5 metres between heads. The spread attained by these nozzles is good, but they (the nozzles) emit a lot of water in a short time.


Spinner nozzles
Spinner nozzles are frequently used to replace the pin and bridge nozzles. There are a few popular Israelian brand names, such as Eindor, D.A.N. and Naan. The amount of water applied depends on the nozzle (100/200 litre per hour) and the water pressure. The optimum pressure is about 30 psi. The advantage of these spinner nozzles over pin nozzles is that fewer lines are needed (distance 3.20 / 4 metre). In addition, the spinner emits less water than the pin nozzle. Spinner nozzles apply water over a greater distance than the pin or bridge nozzle. One disadvantage lies in the spinner’s wider spray pattern as it is harder to control individual areas that may have differing water requirements. Outside, spinner nozzles are also sensitive to wind variances.


Outside irrigation with smaller sprinklers
Because of the many different irrigation systems used on container beds, there are many different sprinklers coming onto the market. Gaining market share among nurserymen are those sprinklers that work at a low pressure (30 psi, the same pressure as greenhouse irrigation) and apply a smaller amount of water. Brands include: Eindor (900 series), D.A.N., Mankad, Lego and Naan (type 501, 502). All of these brand names can be mounted onto PVC lines or Polyethylene.

     Depending on the type of sprinkler and size of nozzle, as well as the layout of the container field, these sprinklers can be placed at a four to seven metre distance.


Traveling boom
In Belgium and Germany, a large number of tra­veling booms are used in greenhouses, as well as outside on container beds.

     The irrigation goes through nozzles or holes bored in a PVC line. The output depends on the size of the holes, size of nozzle, pressure, the traveling speed, (which can be set between 90 to 900 metres per hour).

     In greenhouses, many traveling booms are hung from the heating pipes and vary in width from six to nine metres. The use of these traveling booms in greenhouses is increasing very rapidly. These booms can also be used as a spray applicator, once nozzles are exchanged.


Drip irrigation
To water very efficiently in big containers, or for plants with dense canopies, drip irrigation with spray stakes or drippers, is another option.

     The application of these drippers, depending on size and water pressure, is between two and eight litres per hour. The spray stakes apply about 30 litres per hour. The disadvantage with drippers, however, is that they are susceptible to rodent damage and subsequent high maintenance requirements. In large containers (7.5 litres or more), one dripper per unit is not sufficient.


Capillary matting
To optimize irrigation and to keep the foliage dry, indoors and outdoors, the capillary matting system is a good alternative. Arguments used in support of capillary mats include:

• No top irrigation, no residue on foliage
• Less fungi problems on foliage
• Better spread of water
• Quality of water is less important
• Plant takes only the amount of water it needs
• Crop stays ‘drier’
• Less water is needed
• Less weeds
• Good water distribution if mat is working properly

     In case of natural rainfall, it is necessary to ensure the capillary mat doesn’t remain saturated too long in outdoor container fields.


Ebb and flow systems
With concrete pads in greenhouses, the effort sand bed system outside and the use of lava, the interest for ebb and flow irrigation is rapidly expanding.

     This system is more expensive than overhead irrigation, but has important cultural advantages; namely, it provides optimal water distribution, moss growth does not occur in containers, the plant only takes amount of water it needs and there are fewer pesticide spray applications needed than with overhead irrigation systems.