By Sharon Omahen University of Georgia
Most farmers know that different areas of their fields produce better crops than others. Now yield maps can tell them exactly where these areas are and how to improve or avoid them.
"One farmer called it his entrance and exit exam," said Calvin Perry, an agricultural engineer with the University of Georgia College of Agricultural and Environmental Sciences.
"When you show farmers yield maps," Perry said, "most of them can tell you why the yield differs across the field."
Software and yield monitors create map
To make a yield map, specialized software converts raw data collected by a yield monitor into an easy-to-read image of the field. The yield monitor consists of a yield-sensing device, a Global Positioning System receiver and a computer console attached to a harvester.
"The console reads the yield sensor every second and gets a value for yield," Perry said. It matches the yield data with the location with GPS, then stores and uses both to create the yield map.
"A yield map has colored pixels that represent where the yield data point was collected and how much yield occurred at that spot," he said.
Yield monitors are available for cotton, root crops and grain crops like corn, wheat and soybeans. Cotton farmers have just begun using them, since cotton yield monitors are fairly new, Perry said.
As many as 30 percent of grain farmers use them. "Grain yield monitors have been around 15 years," Perry said.
A prototype peanut yield monitoring system was developed by the UGA precision agriculture team at the National Environmentally Sound Production Agriculture Laboratory in Tifton, Ga.
"The system was licensed by a company to begin marketing it to farmers," Perry said. "But the company encountered financial difficulties and will not be able to produce the yield monitor."
Effective, but pricey
Yield monitoring isn't the cheapest tool farmers have. "A yield monitor for a typical grain combine would cost about $4,500," Perry said. "A four-row cotton picker yield monitor would cost around $6,500 and a six-row system about $8,000." These prices don't include the GPS receiver, another $800 or so.
"Large farmers can afford to invest in technology like this," he said. "It's harder for smaller farmers to do the same. ... It's hard for them to justify spending money for gear that produces a map."
But the maps can help farmers manage future inputs.
"In one case, a yield map showed a farmer he actually had a higher yield where he didn't spray herbicides," Perry said. "The yield map definitely made him pay more attention to his herbicide spraying."
Yield maps have pointed out equipment errors, too, like malfunctioning or overlapping sprinklers.
"A lot of things pop out in yield maps that would otherwise go unnoted," Perry said. "It really hits home to a farmer when you show them an area where they're losing money. It makes the farmer take notice and make changes."
Besides their main uses, yield maps can be useful in placing value on land. "They come in handy for land value negotiations, estate and will issues and assessing management decisions," Perry said.
New tool, not replacement tool
Perry said yield maps should be used as another farming tool, not a replacement tool.
"Yield maps are by no means meant to replace scouting (for insects and diseases) and sampling," he said. "They're just one tool of many that farmers should be using."
As with other tools, yield maps have to be used right.
"You can't just have one yield map and think you can use it for a long time," Perry said. "Yield maps will be different on the same field in different seasons because the weather patterns are different."
As more farmers use yield maps, county Extension agents are fielding more questions. Perry and other UGA, Auburn University and U.S. Department of Agriculture researchers train agents to answer them. The most recent training, sponsored by the NASA National Space Grant Program, was held at UGA's Griffin campus last month.
