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.

• 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.

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.

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