Sprinkler or drip irrigation for shrubs

Ran Pauker

The purpose of this type of irrigation (drip or sprinkler) is to supply water to the required area without loss to areas outside the desired irrigation zone.
It is important to note that water should be spread evenly across the entire soil surface, not just at the base of the plant, to encourage the root system to spread so that it can fully exploit the soil resources (water, minerals and organic nutrients). This can also be achieved with drip irrigation systems by regulating the spacing of the drippers so that the diameter of the wetting fronts will slightly overlap, ensuring an even spread of water. The wetting diameter depends on the water dosage and soil type – noting soil type is important as water flows differently in different soils.
The irrigation method, whether sprinkler or dripper, has to address several key issues (Table 1):

Table 1. Advantages and disadvantages of spray and drip irrigation.

As small droplets are sensitive to wind blow this type of sprinkler should be used on quiet, windless times of the day (often early morning or evening).
No problem
Water distribution
Different areas require different water dosages. Modern sprinkler systems can accommodate this by adjusting the watering segment (3600 to 900, distance from sprinkler head) and accordingly, the dosage. The larger the irrigation area, the easier it is to irrigate equally with sprinklers.
Equal water distribution can be achieved in awkwardly shaped areas by individual placement of drippers.
Salts in the water supply
Over-irrigate to wash salts from root systems. With sensitive plants salts drying on foliage cause problems.
Mulch well the entire area to prevent water evaporation and salt accumulation at the soil surface.
No problem with salt accumulation on leaves.
Over-irrigate to wash salts from root systems.
Dust and soot on the foliage
Sprinklers can wash dust and soot from foliage making a more attractive garden (see Figure 1).
Not relevant.
Foliar diseases
Foliar infection generally needs water droplets on the leaves allowing spore germination and penetration of the leaf surface. Above-foliage sprinkler irrigation will not enhance infection rates in areas susceptible to dew fall if you irrigate at dew times.
In dry, non-dew areas sprinkler irrigation may enhance disease.
Not relevant.
Easy to see broken or malfunctioning sprinklers.
Rodent damage is unusual with this system but if it does occur it is easy to observe.
More difficult for long-term maintenance because of:
·         dripper clogging by salt accumulation, ingress of fine soil particles, biofilm accumulation,
·         rodent and bird damage,
·         root and branch blocking drip line,
The above problems tend to only be visible when the plants start showing water stress.
Figure 2. Myoporum parvifolium cv. Carmalit, one year after planting, irrigated 60 mm every 30-35 days. In summer 2012 we irrigated 360 mm per season. In a nearby area is the same plant grown under drip irrigation (356 mm)
Figure 1. Drip irrigation vis sprinkler irrgation
In field crops irrigation with drippers saves water compared to sprinklers (although I found an experiment with sweet potatoes where sprinklers were shown to have a water saving advantage over drippers (see URLs below – Hebrew only).
 So why not use drippers exclusively? The answer is that there are agro-technical and economic considerations that justify the use of sprinklers.
In Green Point and other experiments we found:
– In lawns and shrubs watered every 30 we found equal water use between dripper and sprinkler irrigation.
We set up an experiment to compare water needs between six species using either sprinkler or dripper irrigation. We found that drippers saved approximately 10% water but this was not a significant difference.
The conclusion, in discussion with plant-water-soil experts is that, in agriculture we expect maximum yield and the irrigation regime has to be as close to 'perfect' as possible and we need a very low soil water tension. This is easier to achieve with drip irrigation. Conversely, in the garden, we may not want maximum yield (excluding sport lawns and fruit trees/special plants that need better irrigation). For water saving it is worthwhile increasing the irrigation interval (http://english.eco-garden.co.il/uploadFiles/Mantell%20&stanhil%201966%20465.pdf ) and therefore the root systems grow deeper and the plants find it easier to manage non-equal water distribution as can be found with sprinkler irrigation.
In conclusion, for our gardens, we have moved more and more towards overhead, sprinkler irrigation for shrubs because of the aesthetic effects of dust and soot removal

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