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
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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.
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