Variable Rate Irrigation

Earlier in December the Bothwell Making Good Better focus group had a session looking at Variable Rate Irrigation (VRI). We visited Richard Hallett's property Llanberis, where Richard has two different systems installed, on two of his centre pivots. Along with Richard, Will Burden (Roberts Irrigation) and Reuben Wells (AgLogic) gave the group an excellent overview on how the VRI works, what is involved, etc. VRI uses GPS technology to control individual sprinklers and/or the speed of the wheels to increase or decrease the amount of water applied to particular sections of paddock. There is a GPS node installed at a control unit at the centre point and at the end of the machine. Soil maps are used as a base to program the machine (maps can be created a number of ways - simply by reveiwing aerial photos of the paddock, by detailed soil surveying on the ground or by EM survey). Once the map is created different programs can be produced for different areas - for example a drainage line may be an avoidance area (no water applied), a wet hollow may get 20% of the rate applied to the rest of the paddock and a sandy bank may get 110% of the standard rate. The programs can be altered as the season progresses, and saved, so they are on file for future years. It is important to put the time in at the start of the season to do the mappng and set up your programs so that it all runs smoothly when you need it to.

A key benefit of VRI is that it can be used to keep water off wet areas, prevent waterlogging, bogging and runoff as well as being able to adjust amounts of water for different soil types. With huge variation in soil types in pivot circles on Llanberis (from sands to black cracking clays), Richard is very happy with his system, which is enabling him to get yields off areas that would never grow anything in the past. However VRI is expensive and not a silver bullet for all problems, so make sure you've got everything else right with your irrigation system first (sprinklers, drainage, etc), and then look carefully at likely returns/payback time.