Efficient water management plays an important role in irrigated agricultural systems.
Under Uniform Rate Irrigation (URI), parts of an irrigated paddock can be over or under-irrigated due to spatial variability in soil water-holding capacity, infiltration rates, and topography.
Variable Rate Irrigation (VRI) systems are designed to address the need to better achieve irrigation efficiency, aiming for the best conversion of each millimetre of irrigation water to plant growth. Irrigation efficiency is commonly referred to as application efficiency and depends on three main factors:
- Applying the correct depth of water.
- A uniform application.
- The application rate being less than the soil’s infiltration rate.
Application efficiency is the percentage of applied water that is retained in the root zone (or target area) after an irrigation event. VRI allows for maximum application efficiency of centre-pivot or lateral-move irrigators.
VRI systems achieve this by utilising a nozzle and speed control, soil mapping technology, site-specific soil moisture monitoring, and other decision support tools.
IrrigationNZ has produced a Precision Irrigation Resource Book to aid irrigators in their understanding of VRI systems.