Gear Up for VRT

March 28, 2009 07:40 AM

Spurred by high input prices, variable-rate technology (VRT) application of phosphorus and potassium is becoming common. VRT application of seed and nitrogen (N) has been slower to catch on. Brad Beutke, who works alongside Farm Journal Field Agronomist Ken Ferrie at Crop-Tech Consulting, estimates about 10% of the firm's clients are varying either the rate of N, plant population or both.

But Beutke believes VRT application of N and seed is poised for takeoff because new affordable technology puts the concept within reach of any farmer. At last year's Farm Journal Corn College, Beutke told attendees how to get started.

First, lay the groundwork. For variable-rate N and population to pay back, other building blocks must be in place. "You need to have a comprehensive fertilizer plan,” Beutke says. "Keeping pH in balance is the big thing. Along with a nitrate test, we use the Illinois Soil Nitrogen Test to measure the nitrogen-supplying capacity of the soil, but th at test isn't applicable unless you have a stable pH.

"If you have soil density problems, correct them by doing vertical tillage. Know your pests and diseases; if you push population, you'll change the
environment, and that's where you run into pest and disease problems.

"Next, map your management zones,” Beutke says. "These are the areas where you will bump population and nitrogen rates up or down, depending on the productive capacity of the soil. Management zones may result from different soil types, poor drainage, natural or man-made problems or other factors.”

VRT capability usually begins with a yield monitor. "Your yield monitor collects data we can use to develop yield zones,” Beutke says. "Many yield monitors are VRT-capable.

"Calibrating your yield monitor is important,” Beutke adds. "It should be within 3% of the scale weight. Most of our growers calibrate with 1% or 1.5%. We recommend they calibrate at least twice, maybe three times, in corn—every time moisture drops by five points. It makes a more accurate map.”

All monitors on the market today are capable of producing yield maps, Beutke notes. However, some produce better maps than others. "For management zones, we want yield maps that show spatial variability,” he says. "For mapping, we are not as concerned with total bushels produced but with where the bushels came from in the field.”

Other components may include GPS receivers, VRT controllers, hydraulic drives and prescription maps.

GPS receivers. To make a VRT application, you will need a GPS receiver. "Your receiver doesn't have to be expensive,” Beutke says. "Half of our VRT nitrogen applications are made using a $250 receiver with three-meter accuracy. The thing to keep in mind is whether you are going to use the GPS signal for something else, such as auto-swath, auto-steer or mapping. In that case, you would be better off with a more accurate receiver.”

VRT controllers. "VRT controllers tie everything together,” Beutke explains. "They use data from your GPS receiver and your prescription map to tell your hydraulic drive or flow controller what rates to apply and where.”

Controllers fall into two groups. Those that come as standard equipment on tractors are called OEM (original equipment manufacturer) controllers. The second option is aftermarket controllers, which are made by a number of manufacturers.

"OEM controllers have wiring integrated into the equipment, so there's less cab clutter,” Beutke says. "You can transfer a monitor between tractors just by unbolting it from the first one and plugging it into the second. Many of the components are included with the tractor. The up-front cost is less. They usually are multifunctional—for example, the same monitor display may be used for VRT and for tractor functions, such as hydraulic flow.”

The downside of OEM controllers is limited compatibility with other manufacturers' components. "It's getting better,” Beutke says, "but it's still limited compared with controllers available on the aftermarket.

"OEM desktop software to support these controllers is also limited. The software from equipment manufacturers usually is not geared toward creating management zones. However, aftermarket solutions are available.”

Aftermarket controllers can be as simple as handheld personal digital assistants (PDAs). "For a simple system, you can load programs, such as FarmWorks VRT software, into a PDA, plug it into a flow controller and you're ready to go,” Beutke says.

Aftermarket controllers usually are the most user-friendly, he says. "They are less brand-specific and usually can be made to work with any tractor or implement. The aftermarket controllers usually are multifunctional. The most common one is a yield monitor.

"Support from aftermarket manufacturers tends to be good,” Beutke says. "Most of them accept standard file types, or they have easy file conversion software. On the other hand, they require their own wiring, so you have a little more cab clutter.”

VRT planting equipment. The majority of the variable-rate planter drives are hydraulic-based and require an adequate amount of hydraulic flow from your tractor.

"Hydraulic drives must be calibrated before you go to the field,” Beutke says. "Some aftermarket hydraulic drives let you shut down the controller and go back to ground-drive if anything goes wrong.”

VRT nitrogen equipment. With liquid N fertilizers, variable-rate can be accomplished with a flow controller, a control valve and meter and a hydraulic-driven centrifugal pump. Another system uses a ground-driven variable-rate piston pump. "It drives like a regular pump,” Beutke says. "It has an electric servo, which attaches to the pump stroke adjuster and adjusts the piston pump on the go.”

Ferrie's staff has worked with several fertilizer dealers to equip rented toolbars for VRT application of UAN solution. "The grower owns a flow controller and pressure relief valve, which he swaps out with equipment on the toolbar, using quick-attach connectors,” Beutke says. "The operator sets the ground-driven pump for the maximum rate he wants to apply. When the controller calls for a lower rate, a control valve closes to feeds extra solution back through the pressure-relief valve.”

A system from Capstan Ag Systems ( uses a Redball monitor-type manifold with a solenoid control for every knife. "It can hit a wide range of rates over a wide range of pressure and speed,” Beutke says. "But it is more expensive and complex than other systems.”

"With liquid VRT, remember that pressure increases four times as the rate doubles,” Beutke says. "So you need to use VeriFlow nozzles (from SprayTarget, if you don't want to change groundspeed as the rate changes.”

Capstan also makes a model for VRT anhydrous ammonia. "It can handle ammonia rates below 60 lb. per acre, which you sometimes want when sidedressing VRT nitrogen,” Beutke says.

Most ammonia bars are set for higher application rates, he notes. In a VRT N system, you can get around that by applying more ammonia at sidedressing and less at preplant.

Before you move. Take time to think about your long-term plans before you invest in a VRT system. "If all you want to do is VRT application, you can get by with a used PDA, WAAS GPS and VRT software,” Beutke says. "But if you decide later to add features, such as auto-steer, automatic swath control and remote sensing, it can be expensive, and you may end up with multiple monitors in the tractor cab.”

Evaluate the equipment you already have, such as GPS receivers. "A lot of it is already VRT-capable if you just add a couple components,” Beutke says.

"Consider the longevity of your current equipment. It makes no sense to spend a lot to buy this technology for a planter or sidedress bar you're going to trade off next year. Wait until you're buying a new applicator or planter.”

Smart advice. Discuss your plans with whoever will be making your VRT maps. "Each brand of controller usually requires a different file type,” Beutke says. "The shapefile is an
industry standard file type for GPS mapping. The cost of VRT prescription maps usually depends on the time and software needed to convert shapefiles to the file type required by your VRT controller.”

Ask VRT equipment dealers for references. "Make sure you buy a system based on what it can do now, and not what it will be capable of with an update in the future,” Beutke says.

"Too often those updates never show up. Talk with other growers who are using the equipment. Ask what problems they have had and what shortcomings they have discovered.”

Ask about the quality of local support your dealer will provide. "Good support is more important than a cheaper price,” Beutke cautions. "Also, call the manufacturer's support hotline. Find out how long you're going to be on hold when you have a question. In 2008, we usually didn't get more than 1½ days of good planting weather at a time. If you can't get your equipment to work, you can lose out big time.”


How to Make Management Zones

Management zones are areas within a field with similar productive capacity—maybe high and maybe low. "To make a management zone map, we start with a soil map,” explains Brad Beutke, who works with Farm Journal Field Agronomist Ken Ferrie. "Soil maps contain lots of valuable information, such as slope, drainage, waterholding capacity and erosion, all of which provide insight about fertility and yield potential.

"GPS-referenced soil maps are free on the Internet, from a USDA Natural Resources Conservation Service Web site,” Beutke adds. "The URL is”

"We try to keep management zones from three to seven acres, or sometimes a little smaller,” Beutke says. "You can divide soil types into smaller zones based on slope, elevation or other natural breaks. To break zones down further, lay the soil map over a yield map and create zones based on yield. If yield maps aren't available, you can use Normalized difference Vegetation Index (NDVI) maps and create zones based on crop health.(For more information about NDVI maps, see "New Yield-Boosting Tool” in the Mid-February 2009 issue of Farm Journal)

"When you overlay a soil map over a yield map, you will find that most areas respond by soil type,” Beutke continues. "But there are exceptions; when we find an exception, we try to figure out what's going on. For example, a low-yielding area may be wetter than other soil in the field or it may contain nematodes.”

"We wait until we see a problem repeat itself on a yield map before we designate an area as a management zone. If a problem only shows up once, the low yield may have been caused by an insect or disease problem that is only present for one year. We also want to see which crops are affected because some problems are crop-specific. Finally, we visit the area and ground-truth the problem—you can't leave it up to your software to make the decision.”

After you have established management zones, you can begin soil testing by zone and you can seek recommendations from seed and fertilizer dealers about the best rates and management techniques for each zone.

For more information about creating management zones, visit, and click on the Corn Navigator icon. Then click on "Route 10: Road Map to Bigger Yields.”

For additional information on variable-rate nitrogen, visit, and click on the Corn Navigator icon. Read Route 4 "On The Road To Variable-Rate Nitrogen.”
For tips on calibrating yield monitors, click on Route 1 "Yield Monitor Secrets.”

You can e-mail Darrell Smith at

Back to news


Spell Check

No comments have been posted to this News Article

Corn College TV Education Series


Get nearly 8 hours of educational video with Farm Journal's top agronomists. Produced in the field and neatly organized by topic, from spring prep to post-harvest. Order now!


Market Data provided by
Brought to you by Beyer