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Putting moisture where it’s needed most

Rain is indiscriminate when it falls from the sky; Mother Nature doesn’t ignore low spots on fields just because they don’t need moisture. But for potato growers, technology is making it possible to even out moisture levels to allow for more equitable crop development. No more do pivots have to circle the field, applying the same amount of water on every sector whether it be a drier hilltop or a moisture retaining former creek bed.

Although not new technology, a Nebraska company’s Variable Rate Irrigation (VRI) system is gaining notice in Canada. Valley Irrigation advertises that VRI will “make all areas in your field profitable, reduce runoff, and increase water and chemical application efficiency.” The company also says the equipment is relatively easy to use and will make managing irrigation less stressful.

However, a grower who has been using the system on his Alliston, Ont. farm for two years now claims there is still much to learn and understand once the equipment is installed. Adequate rain during the two years since he began using the equipment did not give Homer VanderZaag the opportunity to fully experience the VRI technology.

“I know there will be a value in using this system, but the last couple years have been wet, so we didn’t see the full benefit,” VanderZaag admits. “Our first measurement of success should be yield improvements across the field.” He explains the system allows growers to divide a field into zones and a computer program can tell the pivot when to apply moisture in a zone. Fertigation can be controlled in the same manner, and late blight and tuber rot can also be better managed in years when the crop receives irrigation exclusively.

James Wolsky of K & T Irrigation in West Fargo, N.D., sells Valley’s VRI technology and he understands what VanderZaag has been facing, but he also sees the equipment helping in wet years as well. “We’ve been in a wet cycle for many years here, but we see the variable rate irrigation helping to control excess moisture,” he explains. “Our customers are not putting water on where it isn’t needed. We know every field is not the same, so we use the variable rate technology to prevent over-watering potatoes.”

Even in wetter years there might be periods where some moisture is needed on higher zones, and the pivots can be programmed to water where needed while leaving the lower spots alone.

“The hard part with VRI is writing the prescription for the pivot,” VanderZaag admits. “You take what you know about the field and translate it into a map that represents the needs of the field. You can overlay maps to help, but you need good aerial imagery and topography knowledge. It can be daunting.”

VanderZaag says soil test results help with fertigation, but there is no tool that estimates how much moisture is available in the soil. He feels knowing moisture levels for the various zones would make it easier to program the equipment and to manage water more effectively. He also says VRI would be most useful to growers who have many zones across a field, from highs to lows; a perfectly flat field would, conceivably, require the same level of moisture across all zones.

Wolsky agrees. “We have an example of a grower who has a sand ridge in a field, so he’s not putting water on the lower, wetter, heavier soils, but only on that ridge.” By using the variable rate technology, he says, there can be a savings in water use, and the equipment can also be set to a variable frequency drive to put more water where it is needed most.

According to Valley Irrigation, VRI can save water because only the amount of water that is needed will be applied. By changing the application depth, run-off can also be reduced and over-watering will not be an issue. There are two types of VRI available – speed control of the pivot as it crosses the field, and zone control that allows for fine-tuning the amount of moisture given to the crop. The company literature says the zone-control technology is most helpful in challenging fields divided into more than 5000 zones. The speed control programming works best when the field variability can be captured in pie-shaped wedges.

VanderZaag says in his most complex field, he has 2700 zones with his 1100 foot pivot covering an 80 acre circle. He explains he can set the equipment to irrigate more frequently knowing that each acre is getting the correct amount at any given time. High sandy spots receive more water, while low areas can be limited or even left dry as insurance against large rain events. He believes his average yield will improve overall with regulated moisture. Plus, disease and pests will be managed more effectively.

“This is amazing technology and, once the programming is done, it is easy to use,” VanderZaag says. “It was a challenge at first, but it’s a great opportunity to improve our crop output. I like the fact that I can manage my crop’s moisture more effectively.”

VanderZaag did a retrofit on existing equipment to install VRI, but complete systems can be purchased with the technology in place on the pivot. Then, all a grower needs to do is input the field’s “personal” information into the computer program.

Not all fields are the same, but variable rate irrigation technology offers growers multiple options for managing moisture. When Mother Nature isn’t hitting the high spots adequately, VRI can make up the difference.

September 1, 2015  By Rosalie I. Tennison