Variable Rate Irrigation

Variable rate irrigation allows farmers to set a specific irrigation program for different areas for optimal results. For dairy farms with varying soil and topography across paddocks, this can boost pasture growth, while lowering water and power use.

Understanding variable rate irrigation

Variable rate irrigation (VRI) applies water via a centre pivot irrigator to specific management zones by a control panel loaded with a prescription map. This technology can be retrofitted to centre pivot and linear irrigators and allows delivery of precise amounts of water to different parts of a paddock. It is recommended to use a professional service to assess the variability under each VRI equipped centre pivot and map the specific management zones that will have varied depths applied to them.

EM38 soil mapping is an easy-to-use geophysical surveying instrument that provides a rapid measure of soil electrical conductivity. Estimates of soil type and topography, as well as soil water content derived from EM38 measurements, may be used to generate VRI maps that can be loaded onto the VRI controller on the centre pivot.

Elevation data can be collected using an accurate GPS system or a calibrated drone image – this is often done at the same time as an EM38 survey. The elevation data can be used to produce a model of the surface of the paddock which is then used to predict where water will flow and accumulate. This can also be integrated into the final VRI base map. Soil moisture sensors are also often installed into different zones to monitor real-time soil moisture status. This information is then used to optimise VRI scheduling.

Potential benefits

There are likely to be potential benefits from installing a VRI controller on a centre pivot irrigator, including:

  • Improved crop quality and yield by up to 20 per cent.
  • Savings on water volume for field crops of 20 to 30 per cent.
  • Reduced pumping (energy) costs.
  • Lower soil saturation leading to improved grass growth, and less pugging damage in wetter areas.
  • Reduced muddiness on laneways and easier movement of cows across paddocks.

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