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Variable Rate Irrigation

Why this alternative to conventional irrigation techniques is getting a lot of attention in potato production circles.

In recent years, the concept known as variable rate irrigation or VRI has become a catchphrase among irrigation specialists and growers alike. Some would even describe it as precision agriculture applied to irrigation.

In essence, VRI is the process of applying differing irrigation amounts to match crop water demands at a small scale within a particular field. Most irrigation equipment manufacturers in Canada nowadays offer systems that are or can be retrofitted with the necessary technology needed to enable these systems to be used for VRI.

Variable Rate Irrigation: The Next Big Thing in Irrigated Agriculture?, a paper published last year by irrigation specialists with Agriculture and Agri-Food Canada and Alberta Agriculture and Rural Development, notes the following components of VRI technology:

  • Sprinkler control valves — water valves that open and close in response to a control signal, controlling individual sprinklers or defined banks of sprinklers
  • A pivot positioning system — usually a global positioning system, this locates the exact position of the pivot system within the field
  • An electronic control panel — this processes the information uploaded by the operator and sends control signals to the sprinkler valves in accordance with the pivot location in the field and the desired water application depth along the system

VRI system users are provided with software that creates a “prescription” indicating the desired application depths for defined areas beneath the irrigation system. The prescription is then uploaded to the centre pivot’s electronic control panel, which references the prescription when sending out control signals and cycles the signal to associated control valves to achieve the desired water application amount for that particular area of the field.

Benefits of VRI

Proponents of VRI provide several reasons for it being beneficial. Among the benefits listed in the AAFC and AARD report:

  • Stresses due to drought and excess moisture are avoided, reducing the incidence of crop disease and stress-related crop quality problems
  • Reduced water use (up to 15 per cent, according to some estimates)
  • Reduced energy use, as a result of reduced pumping at the field level as well as from the water source to the field
  • Potential for the precision application of nutrients through fertigation

VRI enthusiasts often point out that if areas of a particular field are either under-irrigated or over-irrigated, yield potential will not be maximized no matter at what rate other inputs are applied.

VRI technology and its application have been put to the test by Canadian potato researchers and growers alike over the past few years. During the Manitoba Potato Production Days event in Brandon, Man., earlier this year, Jeff Bronsch of Sunrise Ag, a farm production management company in Taber, Alta., talked about a VRI project he conducted along with a couple of Alberta potato growers in 2012.

In an interview with Spud Smart magazine during the conference, Bronsch said that he’s been involved in trials with VRI technology at the grower level for the past three years. What he and his research team are investigating is how VRI techniques can be used to help develop field prescriptions that address soil variability.

According to Bronsch, the outstanding value of VRI for potato production is “minimizing that production variability so that the grower at harvest would have a uniform crop across the field and minimize waste.”

Bronsch further pointed out that from a production standpoint, “there is a maturity aspect that comes into play where part of the crop would not be mature while other parts of the same crop would still be immature. Variability in maturity of a crop always creates problems in storage for one, while there is also the matter of differences in size profile because of variability in maturity across certain sectors of the field.”

According to Bronsch, “Ultimately the goal is to minimize that variability within a field to maximize the economics so there is more product in the bag, thus minimizing waste and maximizing the input cost.”

Although he believes that VRI can play a role in yield improvement, Bronsch sees the most important benefit as improved product quality. One example of enhanced quality, he said, “is being able to develop a unified crop profile within the parameters of processor specifications.”

Bronsch stressed an improvement in quality leads to higher economic yield, since there is less grading required after harvest and not as much product is thrown away because there’s a more uniform crop.

Bronsch acknowledges that VRI currently costs more than traditional irrigation techniques but stresses, “there is a payback or there wouldn’t be much interest.” These paybacks include increased economic yields resulting from higher crop yields and quality and less waste, he says, adding that VRI can help growers harvest every planted acre and capture the investment of every acre, both in terms of fixed costs and crop inputs.

Bronsch maintains VRI can also help farmers maximize the benefits of a fixed water location. “In some areas like Manitoba, water is captured in the spring at high flows and diverted into storage ponds. Maximizing the efficiency and delivery of this fixed allocation to the crop is valuable,” he says.

Canadian researchers studying variable rate irrigation technology and its applications in potato production include Manitoba agronomist Alison Nelson.

Manitoba Study

During a field trial tour at the Canada-Manitoba Crop Diversification Centre near Carberry, Man., in August, agronomist Alison Nelson spoke to Spud Smart about a variable rate irrigation research project that the CMCDC started this year.

VRI can help growers harvest every planted acre and capture the investment of every acre, both in terms of fixed costs and crop inputs.

– Jeff Bronsch

The work is currently in a fact-finding phase and the plan is get a VRI system up and running soon. It’s hoped the comparative study will be completed within two years of VRI installation. Nelson said the project was spurred on by requests from Manitoba producers for the CMCDC to help come up with ways to help reduce soil moisture variation within potato fields in the province.Nelson indicated that the project is aimed at comparing the benefits of a VRI system with those of a conventional irrigation system on potato crops, to see how the two systems differ in terms of quality and yield at the end of the season.

Research in Ontario is also underscoring the benefits of VRI in potato production.  A study by the Water Resource Adaptation and Management Initiative entitled Showcasing variable rate irrigation technologies in the Ontario potato industry has shown this irrigation technique requires substantially less irrigated water (between nine and 26 per cent) and there are associated energy savings as well. There was also a significant reduction in field runoff and drainage, reducing the risk of nitrate leaching with VRI.

A big obstacle to the widespread adoption of VRI is of course the cost. However, improvements in the technology are narrowing the gap between it and traditional irrigation methods. Only time, ongoing research trials, and the nature of grower experiences at the field level with this technology will establish in the long run whether variable rate irrigation in potato production is here to stay.

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