2.3.7.3 - Would centre pivot irrigation be a better option?

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One of the key problems faced by the irrigation industry is water availability. Conversion from border-check to centre-pivot irrigation is a potential option to reduce water losses. Centre-pivot irrigators use low-pressure nozzles to irrigate large circular areas. They can be as short as a single-span 35 metre unit or as long as 800 metres with 18 or 20 towers, irrigating approximately 200 Ha.

A well designed and well managed centre pivot should achieve an irrigation efficiency (IE) of 95%, where a well designed and well managed border-check irrigation system on appropriate soils should achieve 90%. On perennial pasture, this 5% difference corresponds to a water saving of about 0.5 ML/ha/year. (IE is the proportion of the applied water used by the crop.)

The improvement in irrigation efficiency associated with conversion from border-check to centre- pivot is likely to be greatest where an existing border-check system cannot capture and reuse surface run-off, or where deep drainage losses are high on light soils.

It is important to note that well managed border-check irrigation on appropriate soils can achieve better IE and productivity than poorly managed sprinkler irrigation. Thus, there are no hard and fast rules on what levels of water saving you should be able to achieve by converting to a centre-pivot irrigator.

A centre pivot may make better use of your water

Productivity

Productivity per hectare increases of up to 10% over border-check irrigation have been observed with sprinkler irrigation on perennial pasture in an ungrazed experiment. However, this has not been confirmed under grazed commercial farming conditions. Any productivity increase under sprinkler irrigation is likely to be the result of irrigating more frequently, at a soil moisture deficit of say 25 mm rather than the 40 mm common with border-check irrigation. That is, the pasture growth is less likely to slow (or stop) because soil moisture has been depleted. However, this has not been demonstrated.

The potential productivity is of course highly dependent upon the management of the system (sprinkler or border-check).

A number of information sources are available:

· DPI Whole Farm Planning officers
- DPI Tatura, ph 03 5833 5932.

· Irrigation designers
- Local irrigation designers are listed in the yellow pages under "Irrigation and/or Reticulation Systems.

· Your bank manager and accountant!

Sprinkler systems are expensive; financial advice should be obtained before proceeding.

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