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.”
- Early Spring 2009
, How To
, Corn College
, Magazine Features
, Test Plots