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Variable Rate Field day - a success!

23 February 2012

On the 16th of February Dairy NZ held a Variable Rate Irrigation (VRI) field day at John Wrights farm (Wainono). Approx 100 people spent several hours listening to those involved in the project. 

The field day was run by Dairy NZ as an overview of the ongoing work supported by the MAF sustainable farming fund project.(MAF SFF). Variable rate irrigation has been an on going development on this property as a way to better utalise their available ground water and stored water consents through the use of precision irrigation and farming techniques. 

The property is a well run dairy block, whose land area exceeds their available instantaneous water rights.  To increase yield potential it was decided to expand the existing irrigation system (which includes 2 x Valley Centre pivot irrigators) to utilise stored water and incorporate precision farming techniques.  This included the introduction of Variable Rate Irrigation technologies leading to better use of the water rather than applying all of their water under a uniform rate irrigation (URI) methododology (applying a uniform amount i.e. mm/day over an entire area).

The Variable Rate systems were installed on the pivot to allow increased control and better utilization of water. Further alterations were required to the original infrastructure including:

  • significant upgrades and alterations to pumping,
  • mainline and electrical controls to allow the entire system to function, and
  • an adaption to the farm management techniques. 

The farm has been under development since 1999 and is now developed to a stage where water utilization is allowing best farming practice to be a reality for the owners with lower pumping costs, less fertiliser leaching and increased yield through the greater spread of water over area. The VRI system is being used as a test system with field trial blocks being monitored by Landcare research as part of the MAF sustainable farming fund project.

Several key items have been employed in the development to allow the maximisation of the Variable rate irrigation hardware:

  1. EM mapping:  Electro-magnetic Mapping technologies which are used to create water holding capacity mapping profiles for each area under the pivots. This farm has four areas of soil division which have been used as the control zones for the Variable Rate Irrigation (as well as field trial blocks for strategic testing of effectiveness). EM mapping is available through AgriOptics- Craige MacKenzie spoke about this technology and its applications. (
  2. Soil moisture monitoring equipment:  A critical part of the on going utalisation for the Variable Rate system has been the on farm monitoring and reference checking of there telemetered soil moisture hardware. Several soil moisture strips have been installed and are monitored regularly over the the four soils by the farm management, alongside this Hydroservices are engaged to check and advise re soil moisture scheduling. (
  3. On going monitoring:  As part of the system on going monitoring, checking and altering of the systems functional components takes place by a range of resources from Landcare research, Hydro services, farm management, installation contractor, and farm consultants (Jeremy Savage- McFarlane Rural Business) to ensure the practical aspects of the system are being managed to the season and that the theoretical aims of the study are being answered.

Areas of benefit on this property for Variable rate irrigation (VRI) technologies and management systems are seen as:

  1. Better water utalisation- lower water applications on heavy soils, and quicker rotation periods for lighter soils.
  2. Better water utalisation- Removing water applications from tracks, gateways, over stock troughs and other non productive areas.
  3. Healthier soil structures due to less overwatering of heavy ground.
  4. Lower track maintenance due to lower watering/ non watering of tracks and other non grassed areas.
  5. Expansion of irrigation areas due to controlled applications resulting in higher overall farm yield.
  6. Higher level of farmer understanding- the introduction of advanced technologies has engaged the farm manager to a higher level of irrigation management.


Variable rate irrigation (VRI) through precision irrigation farming techniques has added significant improvement to the centre pivot irrigation systems on this South Island farm. The principles shown on this farm although specific to this block can often be applied to other centre pivot irrigation developments. 

Each property should be assessed as to what form of Variable rate irrigation technologies is required - Zone control or Speed control (see VRI News link or Valley VRI Brochure for further information), assessing the cost of a system versus the initial benefits and the future opportunities.

A copy of the Field Day handout is available by clicking here

For further information on Variable rate irrigation and precision farming technologies on Centre Pivot irrigators contact WaterForce.

Article notes: This is an opinion piece by Quinn Elstone of ValleyNZ.