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."
With a quality yield map in hand, the next step is to understand the reason for the variability.
"A yield map tells you where to look for variability, but farmers need to gather other data to confirm the cause of variability that the yield map shows," Darr says. "If you have a drainage problem, varying the rate of any input won’t fix the problem."
He says VRT should address the root cause of the variability. Additional data beyond the yield map is necessary. Other sources can include soil type maps, elevation maps, soil testing maps, Normalized Difference Vegetation Index maps and tiling maps.
"It’s also imperative to ground-truth maps and include observations and field notes," Ferrie says.
With these layers of data, farmers can start to make more well-informed management decisions.
"Putting these maps side by side and over the top of each other, we evaluate the management zones to see where VRT can be a tool to fine-tune a management practice," Ferrie says. "When farmers are able to see variation in the same management zone from year to year, decisions can be made based on multiple growing seasons."
Maximize your investment. Darr notes that more than 40% of farmers own yield monitors, but stresses that that is only the number who own them, not who really use them.
"With VRA, we aren’t interested in just the data—we’re interested in the knowledge that can be applied from that data," Darr says. "Then farmers can start to change the way they farm. It’s just as if you buy a treadmill. To get any benefit from a treadmill, you need to use it. Yield maps fall into the same category. If you don’t analyze your yield data, you’ll never get a positive return from your yield monitor. Put in the time, and you’ll see progress."
After collecting and evaluating data, not all farmers come to the conclusion that implementing VRT is the best way to increase yields.
"Before you can figure out how you should variable-rate, you better know what’s the best standard rate for your farm," Darr says. "Some producers jump into variable-rate seed populations only to find that their typical planting rates were too low. At the very least, their exploration of VRA prompted good on-farm research and increased yield potential."
Ferrie agrees that on-farm research is an invaluable tool to ensure you are implementing VRT correctly.
"We require all of our farmers who are going into variable-rate to conduct strip trials with population and nitrogen rates," he says. "Then they evaluate yields within the management zones, not the entire field."
Data management. With multiple layers and years of data, farmers need to establish a way to organize and store the information.
"In general, data management is very difficult," Ferrie says. "There are a lot of chances for data to be lost or get corrupted, and every year, the problem gets bigger and bigger."
Harvest is not only a good time to collect the data necessary for VRT, but it provides time leading up to planting to gear up for heading to the field with your prescription maps.
Darr agrees that farmers need to establish a plan for data management before they commit to VRT.
"If there is a real gap in applying precision ag, it’s simple data management. Farmers have to keep software updated and keep their computer up to date, which is a challenge. But the software tools are out there to make VRA a reality," Darr says.
Even though not every farmer has an on-staff computer guru, Darr points out, there are many opportunities to partner with crop consultants, precision ag specialists and co-ops.
One way to simplify data management is to change your approach to yield map organization.
"When you print your yield maps, organize by field rather than year," Darr suggests. "It’s easier to see trends in variability and to know the history of the field to identify what might be driving that variability."
It all adds up. Adopting VRT is an ongoing process. "Farmers should realize that over time their management zones may need to evolve to stay current with their operation," Ferrie says.
With their investment of time, technology and machinery, farmers can expect a payback from VRT. As with other precision ag technologies, the return on investment can be realized more quickly when the technology is scaled to the size of the farm.
"VRT takes more than just money," Ferrie says. "It takes time to set up your farm for a successful adoption of the technology, and it takes time to use the data collected to make knowledgeable management decisions."
- October 2011