Irrigating in the zone
In 2010, J.J. Long joined the small but emerging variable-rate irrigation club to manage a pivot circle with “wildly varying soil types.” Half of the circle seldom reached his yield expectations. “It never seemed to get enough water,” he says.
He believes he’s fixed that yield challenge by equipping the pivot with a CropMetrics precision ag package for VRI. It was one of 100 systems in Nebraska and Kansas last year varying water rates based on a VRI prescription generated by a new agronomic tool.
Long, who farms near Grant, intends to add the program to two additional pivots this season. “I basically have irrigated by the ‘guess method,’” he says. “My goal now is not uniform water application, but uniform yield instead by matching the water rates to soil types and their water-holding capacities.”
He accomplishes this by delivering the VRI prescription, generated by what CropMetrics calls its Virtual Agronomist (VA) software program, to a GPS-based AgSense Field Commander remote controller installed at the pivot’s end tower. The water prescription is wirelessly transmitted from the VA program to the AgSense unit that ultimately controls the pivot’s variable speed.
At a glance
• Variable-rate irrigation may conserve water and raise yields.
• CropMetrics service divides the field in different zones.
• The irrigation service is provided through agronomists and consultants.
VRI speed control varies irrigation application rates in up to 60 different management zones, or pie slices, in the circle by speeding up or slowing down the pivot, says Kevin Abts, head of CropMetrics sales and marketing.
To create the water prescription, the VA software automatically analyzes the soil types and water-holding capacities, field topography and yield data. Long also installed a soil moisture probe in an area determined by the VA program as representative of the field’s overall majority soil type, and he relies on the probe’s reading to determine both the optimal base application rate and exactly when to irrigate.
“Then the water prescription determines how to vary the rates. If I decide to apply a base rate of an inch of water, the pivot may apply 0.80 to a wetter zone and 1.20 inches to a drier zone,” he says.
In Long’s case, the VA program uses high-resolution soil maps in the form of data layers to create prescriptions that slow down the system over sandy soils to deliver more water and speed it up over heavier clay-type soils that have a higher water-holding capacity.
Crafting a prescription
Building the water prescription with the VA program is the foundation of CropMetrics. Nick Emanuel of North Bend, company president, says three categories of information are collected and layered: an EM (electromagnetic) survey of the field to map soil types and water-holding capacities, an RTK elevation map of field topography, and yield history for at least three years. The EM survey is made with an implement pulled through the field by an all-terrain vehicle.
CropMetrics contracts with Midwest Independent Soil Samplers, a Minnesota company, to make the EM and field topography surveys.
“We come up with site-specific yield optimization opportunities,” Emanuel says. “With our program, the data is available for not only variable-rate irrigation, but also VR seeding and nitrogen.”
The majority of CropMetrics pivots in 2010 were outfitted with the Field Commander, a GPS-based, remote-telemetry unit from a South Dakota company called AgSense. The unit receives prescriptions created by the VA program and then automatically relays them to the pivot.
CropMetrics markets its VA program to agronomists and crop consultants who are trained and certified as VRI specialists, and they in turn offer it to farmers as part of their precision ag services.
Costs for a three-year CropMetrics program is $8 an acre per year. For more information, go to www.cropmetrics.com.
This article published in the March, 2011 edition of NEBRASKA FARMER.