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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%