VRI - Helping manage your irrigation use

An estimated 80% of New Zealand’s water use can be attributed to irrigation. 720,000ha of NZ land (or 6% of NZ farmland in 2012) is irrigated. Irrigated land can produce up to three times the output that dryland can achieve. However traditional spray irrigation systems are inflexible, and don’t meet variable water requirements for different soil types or land use. (Yule & Hedley, 2009)

Precision Varitable Rate Irrigation

Precision variable rate irrigation  -  http://www.precisionirrigation.co.nz/en/pages/products/

Variable rate irrigation (VRI) is a technology which provides increased flexibility in irrigation on a single irrigator.  The first system developed in New Zealand was designed by the team at Precision Irrigation (a company later acquired by Lindsay). Commercialised in 2008 the technology was unique due to its ability to control every individual sprinkler along the length of an irrigator.  

VRI was initially developed to meet the need for a more intelligent irrigation system. Since its release the Precision VRI system has been continually refined and enhanced to provide solutions for farmers in NZ as well as abroad. The innovative technology has been recognised with awards including the 2010 “Innovation in Irrigation” award.

By now VRI technology (or similar) is available from a range of companies, such as Lindsay (Growsmart Precision VRI), Valley irrigation and Trimble Agriculture.   

How does it work?

VRI works through the control of individual water valves mounted along the length of the irrigator. These valves can be pulsed on or off to reduce water flow while over an “irrigation management zone”. Some systems also control the travel speed of the irrigator to alter the water application depth.
To identify the irrigation management zones based on varying soil characteristics an electromagnetic (EM) survey can be used. Agri Optics, precision agriculture specialists within NZ, conduct (EM) mapping of the soil under irrigation. This determines the soil texture and can indicate soil available water-hold capacity (AWC) variation of the irrigated area. The EM map and land use features (ie crop types and water exclusion zones such as animal races or waterways) are combined to create a computer modelled plan with specific irrigation management zones. This map is then uploaded to the VRI system and is available for immediate use.

Precision EM Varitable Rate Irrigation

Electromagnetic surveying  (http://www.agrioptics.co.nz/portfolio/em-survey/)

What do you gain with VRI?

Using VRI can reduce water use without reducing crop yields; increasing water use efficiency on farm. A number of studies conducted have indicated that water savings of between 8% and 36% can be achieved without any reduction in crop yield. This translates into money saved- through decreased irrigator and water pump energy costs, as well as less track maintenance due to erosion from irrigation water. This can add up to be a saving of $60-$150/ha/yr (dependent on farm system and soil types). (Hedley, Craigie, & Bradbury, 2013)

Through water scheduling (especially with the use of soil moisture monitoring probes) water runoff and drainage can be reduced by ensuring there is only sufficient water available in the root zone for plant use, rather than saturating the soil. This reduces both the risk of surface soil erosion and nitrate leaching to the groundwater. This, along with the ability to exclude or reduce water application to at risk areas such as swampy areas, water races and areas prone to runoff, can significantly reduce a farms environmental footprint, especially if used in conjunction with good management practises.

Cropping farmers have the ability to irrigate specific to crop requirements - so a barley crop can be harvested in one paddock, while the next paddock over is being irrigated without having to change paddocks around. Stock laneways require less regular maintenance as erosion is reduced with VRI.   

VRI doesn’t come cheap at $100-$140 per metre of irrigator span (depending on quality and specs of VRI parts), but at a reasonable cost savings it can be paid off in 3-5 years.

Craig Blackburn, farmer at Blackhills station near the Rakaia Gorge has had Valley Irrigation VRI for a year now. So far he has found it extremely valuable, and is saving a lot more water than he expected. Craig said that they “had a few teething problems with the irrigation valves not functioning according to the complex paddock design, but will still recommend it to others”. Craig believes that VRI will be valuable leading forward with the increasing environmental regulations, but economically it would depend on your farm system as to the benefit of it. “You would want more than savings on maintenance of stock tracks”.

It seems to me that VRI would be particularly valuable to farmers who have limited or expensive water, have highly variable soil types with very different water holding capacities, or farms which have high leaching rates.

For more information on the Growsmart Precision VRI system visit www.precisionirrigation.co.nz and try the savings calculator (click here) to determine if VRI could be a valuable investment for your farm. You can also check out Valley Irrigation (click here) and Trimble (click here) to suit your VRI needs. For further information on managing irrigation and water use efficiency look into soil moisture monitors such as Aquaflex, by Streat instruments.

Thanks to Don Hunt at Waterforce, Craig Blackburn from Blackhills and Sarah Elliot from Lindsay NZ for your time and information.


Hedley, C., Craigie, R., & Bradbury, S. (2013). Variable Rate Irrigation for improved water use efficiency. Retrieved from maxa.maf.govt.nz/sff/about-projects/search/10-111/report.pdf

Yule, I., & Hedley, C. (2009). Variable Rate Irrigation. In M. University (Ed.). Palmerston North: Massey University.