Irrigation New Zealand

Efficient water management plays an important role in irrigated agricultural systems. Under conventional irrigation (Uniform Rate Irrigation or URI), parts of an irrigated paddock are over or under-irrigated due to spatial variability in soil water-holding capacity, infiltration rates and topography. Under-irrigated areas are subject to water stress, resulting in production loss, while over-irrigated areas suffer from poor plant health and nutrient leaching.

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 nozzle and speed control, soil mapping technology, site-specific soil moisture monitoring, and other decision support tools.

INZ has produced a Precision Irrigation Resource Book to aid irrigators in their understanding of VRI systems.

Precision Irrigation Resource Guide