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Irrigation

A mature orchard in a 500mm rainfall area will need at least 5 megalitres of good irrigation water per hectare.

Applying one mm of water on to one hectare uses 10 kilolitres of irrigation water.

Important factors affecting irrigation are:

• Soil type.
• Slope of land.
• Local climate.
• Annual rainfall.

Critical times when water shortage could affect growth or production are:

• Planting.
• Flower formation in early summer.
• Fruit setting.
• Frosts.

Water requirements will vary according to soil type and slope. As a guide estimated requirements for a tree growing in a 5 x 8m layout grove, including rainfall, are given in The Olive Handbook.

OPTIONS FOR IRRIGATION

• Hand-watering:

* labour intensive.

• Flood irrigation:

* uneven water application
* often wasteful.

• Drip irrigation:

* higher set-up costs
* reduced evaporation losses
* good filtration needed
* can restrict root development
* can be buried
* easiest to manage for saline water.

• Micro-sprinkler irrigation/overhead irrigation:

* higher set-up costs
* good filtration needed
* encourages wider root formation
* higher evaporation losses than drip irrigation
* can be buried.

Application efficiency of irrigation systems

Irrigation System	Efficiency
Furrow/Flood	Less than 50%-90% (depends on soil and slope)
Overhead Sprinkler	65%-75%
Micro sprinkler	75%-85%
Drip	Greater than 85%

Other factors to consider when selecting an irrigation system:

• Ease of use and maintenance.
• Cost.
• Water quality and quantity (including salinity).
• Ability to incorporate chemicals and fertiliser.
• Frost protection.
• Irrigation of cover crops.
• Environmental conditions such as wind.
• Topography.
• Ability to supply sufficient volume of water.

Irrigation System Design

It is recommended that you have the irrigation system designed professionally to industry standards by a designer accredited by the Irrigation Association of Australia.

Design should cover:

• Mains, sub-mains and lateral piping.
• Application rate of system (mm/h).
• Pumping rate for total system flow rate.
• Percentage of wetted area.

IRRIGATION OF YOUNG TREES

The following is a rule of thumb for the application of irrigation to young trees.

Area of grove floor shaded by tree canopy at midday	% of irrigation for mature grove to be applied
10%	20%
20%	40%
50%	100%