Variable Rate Irrigation

Variable-Rate Irrigation (VRI) is a tool of precision agriculture that optimizes irrigation water application. Most fields are not uniform due to natural variations in soil type or topography, but center pivot irrigation systems still apply a singular rate across the field without sensitivity to these variations. VRI technology enables farmers to more easily apply customized rates of irrigation water based on individual management zones within a field. Developed by researchers from the University of Georgia, VRI is now commercially available as a modular component retrofit on existing center pivots or as a component of new systems. Research shows that implementing a VRI system can result in water savings of up to 15%.

Potential management zone conditions

  • Non-cropped areas
  • Overlap with adjacent pivots
  • Topographic variability
  • Soil variability
  • Hydrologic variability (boggy or dry areas)
  • Multiple crops/crop stages
  • Irregularly shaped fields
  • Environmentally sensitive areas

Advantages of VRI

  • Reduced input costs (pumping, chemigation)
  • Enhanced yields and profitability
  • More accurate water application
  • Improved water use efficiency
  • Water conservation
  • Reduced weed and/or disease pressure
  • Reduced runoff


FirstWater Ag


The FirstWater Ag VRI system consists of multiple components. The Master Controller acts as the brain of the system. This controller is where irrigation rate maps are loaded, deleted, changed and/or executed. The Master Controller allows for up to five zones (each zone is made up of a pre-determined number or “bank” of sprinklers). To add more zones, an expansion node is necessary. Each expansion node allows for the addition of eight more zones for a maximum of forty-eight zones. Solenoid valves send pressurized water from the mainline to activate flow control valves on each sprinkler when needed. The solenoid valves along with flow control valves allow each bank of sprinklers to be shut off over non-cropped areas or allow for cycling (for less than full amount) when necessary. The 100% rate is the base rate of application set by the user on the manufacturer’s control panel. Cycling refers to turning a sprinkler bank on and off based on percent of a minute (for example, 40% refers to sprinklers on for 40% of a minute and off for 60% of a minute to achieve 40% of the base rate). The GPS receiver located on the end of the center pivot mainline allows for the rate map to be applied to the correct locations on the field. A pressure reducing valve is usually added between the water source and the pivot point to allow the pivot to enable sprinkler cycling (or shut off sprinklers) without excessive pressure buildup which could lead to damaged pipes.

How it Works

In the Super Duper PC software, the center pivot system dimensions, sprinkler banks/groupings, and sectors are defined. A bank of sprinklers can range from a single sprinkler to as many as 7-10 sprinklers. A sector represents the division of the pivot circle from 1-10 degrees of travel. A water application map is then configured in the software (by combining the banks and sectors with percent application) which establishes special management zones throughout the field. Management zones are the areas of the field requiring more, less, or no water application, such as non-cropped areas or boggy areas. The water application map can also be programmed to control the end gun and speed of the pivot system. The sprinkler banks that correspond to each designated management zone will apply the desired amount of water to each zone in the field, using GPS. Once the field management zones have been established, they are then digitally drawn in a grid system over a background image of the field. Once this map building process is complete, the file is uploaded to a USB drive and transferred to the Master Controller on the pivot. The Master Controller then manages the sprinkler banks so the pivot applies water at the desired rate across the field, maneuvering through each variation or zone with the specified amount of water being applied.


The development of VRI began around 1993 when The University of Idaho received a US Patent No. 5,246,164 for the “Method and Apparatus for Variable Application of Irrigation Water and Chemicals.” However, there is little evidence of actual development of a University of Idaho-based VRI system In 1999, The University of Georgia via the College of Agricultural & Environmental Sciences’ NESPAL group acquired a “prototype” VRI system developed by Greg Harting, who at the time was an irrigation manager for R.D. Offut Northwest (Boardman, OR). The following year UGA approached Ole Hansen with Computronics/Farmscan (Perth, Australia) to provide a more simplified electronic control system for VRI. The first Farmscan system was installed in February 2001 in Tifton at the UGA-Tifton campus. Computronics/Farmscan secured exclusive worldwide license from the University of Idaho in 2004. The same year, Hobbs & Holder LLC (Ashburn, GA) became the US dealer for Farmscan VRI. Using USDA-NRCS funding, the Flint River Basin Partnership installed twenty-two VRI systems in 2004-05. Another twelve systems were installed by UGA and Clemson under a NRCS CIG-funded grant project. Advanced Ag Systems (Dothan, AL) became the sole US dealer/distributor for Farmscan VRI in 2010. To increase distribution of its patented Farmscan VRI technology globally, Computronics/Farmscan signed an agreement with Valmont Industries Inc. (Valley Irrigation). Over the last few years, the major pivot manufacturers, Lindsay (2010), Valley (2010), Reinke (2013), and T-L (2013), have brought their own VRI products to the market. More recently, Trimble announced the acquisition of a New Zealand irrigation company that specializes in VRI (IQ Irrigation), adding another major player to the market. Since 2010, numerous grants and cost-share funding opportunities have led to the expansion of VRI installations. In October of 2013, Advanced Ag Systems announced. VRI is one of the main tools of agricultural water conservation, and as the technology continues to grow and improve, more farmers will adopt this irrigation tool.