Cost effective technological advances in recent years have allowed the uptake of variable rate irrigation (VRI) systems in New Zealand. Typically an existing sprinkler irrigator is modified for variable rate irrigation, irrigation management zones are defined using EM (electromagnetic) soil survey data, and soil moisture monitoring is conducted within each management class for precision irrigation scheduling.

Results will be presented from three farms (110 ha arable with linear move sprinkler; 170 ha dairy with centre pivot; 75 ha arable with centre pivot) where VRI is being used, and trials are being conducted, to compare uniform rate irrigation (URI) with VRI. URI schedules a uniform irrigation event to the whole irrigated area when the most droughty soil class requires irrigation. VRI schedules different amounts of irrigation to different soil classes, based on soil water status and crop requirement. It also shuts off irrigation to exclusion zones and eliminates areas of overlap. Irrigation schedules and yield are being monitored at all sites, and preliminary results show up to 20% water saving with no reduction in yield, increasing irrigation water use efficiency.