To truly understand a field’s variability, Isaac Ferrie advocates layering yield maps from a well-calibrated yield monitor with other field maps, such as soil type maps, soil test maps and tile maps, and observations from the field.
Map field variability for zone management
The data you gather at harvest can be the building blocks for adopting variable-rate technology (VRT). The first step is to understand variability in your fields.
"Yield maps are the report card for farm operations and are an excellent source to determine where variability exists," says Matt Darr, assistant professor, Department of Agricultural and Biosystems Engineering, Iowa State University. "Yield maps enable growers to put a real dollar value on the cost of variability and help them identify high-impact or return areas to
focus their attention."
VRT (also called variable-rate application, or VRA), is a growing technology that allows farmers to define management zones where input rates can be refined. With today’s technologies, farmers can vary the rate at which they apply dry fertilizer, seed, liquid nitrogen and lime across the field.
Darr says the stage is set for more farmers to practice VRT, thanks to the high adoption of hydraulic drive planters and section control on sprayers.
The investment to make VRT work on the farm goes beyond just outfitting your equipment and getting set up with the software.
"To correctly use VRT, it takes time and knowledge," says Isaac Ferrie, who works in the Farm Journal Test Plots and at Crop-Tech Consulting in central Illinois.
A map to more profit. When farmers are gearing up for VRT, Ferrie says, a yield map can be the best guide for pinpointing the current and potential problem areas in your fields.
"We start by making sure our customers have well-calibrated yield monitors with good spatial variability," Ferrie says. "If the yield monitor isn’t set up correctly, you’ll end up with falsified data that will lead you down the wrong road."
The quality yield map serves as the foundation for information on your fields. The established management zones will only be as accurate as the quality and scope of the data used as source material.
"Farmers should collect at least three years of yield maps to define management zones, because any one year could be an anomaly," Ferrie explains. "However, to refine those zones, a map from a wet or dry year could be the most valuable."
For example, a lighter-soil hilltop might show a 3 bu. to 4 bu. yield difference in an average year, but in a dry year, that zone could show a 10 bu. to 20 bu. yield difference.
"The variability is there from year to year, but it’s more prevalent in a stressed environment," Ferrie says. "The maps will help you better define those boundaries."
- October 2011