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Corn+Soybean Digest

In Pursuit Of Precision

Just a few years ago Gerald Thompson, a cash grain producer near Colfax, IL, began using a global positioning system (GPS) and auto-steer.

He hoped to do a more accurate job of fertilizer and herbicide placement. “Faced with spiraling ammonia costs, something had to change in how we managed crop production more efficiently,” he says.

So, Gerald and his father, Don, and partner, Ron Warfield, of R & S Custom Farming, bought a lightbar guidance system for their John Deere 8200 tractor in fall 2004. They have used it to reduce overlaps and skips.

At that time, the Wide Area Augmentation System (WAAS) was used to guide the equipment. WAAS is a free and widely available signal broadcast from a government satellite.

“The increased accuracy in our fall fertilizer applications was a real eye opener for me,” he says. “That initial start definitely got me hooked on using GPS, and I quickly recognized its potential in helping curb fertilizer costs, especially on the 2,000 acres that we commit to continuous corn. Before, there was a lot of uncertainty in keeping close track of fertilizer placement.”

Thompson also used the lightbar for spraying applications and combining. “I bought the unit new and sold it for only a couple hundred dollars less than the purchase price, but it sure had paid for itself many times over,” he says.

R & S Custom Farming's main focus is growing specialty corn varieties under contract for several processors. They farm 3,000 acres (some owned, some leased) in eastern McLean and western Ford counties. The operation also grows waxy corn under contract.

“Nearly 90% of our total corn acreage is under contract, and we have about a 300,000-bu. storage capacity for handling two kinds of waxy corn varieties, as well as white and yellow food-grade corn varieties,” says Thompson.

Using 15-in. rows at seed populations of nearly 190,000/acre, mid-2 or mid-3 soybeans (either non-biotechs or Roundup Ready) are grown on the remaining acres under no-till.

Also, nearly two-thirds of the corn is grown continually on 30-in. rows, using seed populations of about 28,000-32,000/acre. Thompson has also been experimenting with strip-till, as well as limiting tillage to a single-pass with the chisel plow in fall.

With that many acres and using only a lightbar unit, Thompson and his partner soon faced a real need to upgrade into a more comprehensive system.

For example, the John Deere 9320 is now equipped with a GreenStar guidance system and Auto-Trac.

Instead of using the free WAAS signal, Thompson decided in spring 2005 to subscribe to John Deere's SF2 signal for about $800/year.

“Access to this premium signal also allows for more precise variance corrections that helps keep you on line in the field — within 4 in. or 2 in. either side of the center,” says Thompson. “While precision comes at a price, in the long haul it keeps your equipment on track while traveling at a good clip in the fields.”

For example, Thompson reaches ground speeds of 9 mph with the soil finisher and 7 mph with the chisel plow.

The GreenStar system used in the John Deere 9320 has also been taken out and used in another tractor for post-emergence applications. While this tractor wasn't equipped for auto-steer, the guidance system was used for precise parallel tracking.

This spring, Thompson and his partner also purchased a new John Deere 8330-T, with rubber tracks and a fully equipped GreenStar guidance system and Auto-Trac assisted steering.

“If needed, we have the flexibility to use the guidance system in other tractors,” says Thompson. “This has worked out well especially when we need to use the GreenStar system during post-emergence applications. We can also amortize the cost of the systems over planting, spraying and fertilizer applications.”

The GPS and Auto-Trac has also reduced operator fatigue.

“When using GPS combined with an auto-steer system, you quickly realize just how much time and effort was spent on paying close attention to manually steering the tractor down the rows,” says Thompson. “With the new system you can now pay more attention to what's really going on in the field and even relax a bit.”

Gerald's father Don, 75, agrees. The new technology enabled him to work 300 acres in a day this spring without getting too tired.

In the near future, Thompson plans to translate the variable-rate aspects of precision agriculture into a tidy map program for the equipment to follow.

“The basic idea is to layer the various agronomic data maps to help formulate a composite picture of individual fields,” says Thompson.

Overall, Thompson says that this technology holds great cost- and time-saving potential. He adds, “I think the big challenge will center on how easily it can be interchanged from one tractor to another and remain compatible in handling various cropping operations in cost-effective ways.”

Get More Value From Your Data

Part of the attraction of using a Global Positioning System (GPS) and auto-steer technology is bundling it with yield maps, soil maps and any other field data for more precise crop management.

Dennis Bowman, University of Illinois Extension educator in crop systems, offers the following tips and resources to consider in becoming more comfortable with using field data and mapping:

  • When scouting fields and making other cropping notes, it's useful to have good aerial maps of your farmland. For a small fee, you can acquire these aerial maps as hard copies from your local Farm Service Agency (FSA) office.

    “It's also a good idea to review your Common Land Unit (CLU) boundaries with the FSA,” says Bowman. If you have access to high-speed Internet and a good printer, the CLU GIS layers and the aerial maps of Compressed County Mosaics (CCM) can be downloaded for free, from

    You will also need to download a GIS viewer program from ESRI, as listed later in this sidebar.

    For more information, visit the USDA's Aerial Photography Field Office Web site at: or the FSA's Web site at:

  • Ag Leader Technology, Inc., of Ames, IA, ( offers free 30-day trials of several “SMS” software programs for organizing and crunching field data.

    Raw data from your yield data memory card, for example, can be converted into a shape file (a standard file format used extensively in GIS software) to generate useful maps.

  • The Environmental Systems Research Institute (ESRI), which actually created the shape file format and is considered to be the industry GIS standard, offers programs like ArcExplorer, ArcVoyager and ArcView.

    ArcExplorer software, for example, is a data viewer that offers an easy way to perform basic GIS functions, including display, query and data retrieval applications. It can be used on its own with local data sets or as a client to Internet data and map servers.

    ArcVoyager and ArcView are used by school systems to help students understand geographical maps on computers.

    Environmental Systems Research Institute (ESRI)'s home page is:

  • Yield Editor software offers fairly rapid editing of data from combine yield monitors and the ability to correct errors.

    That free software is downloadable from USDA's Agricultural Research Service (ARS) site at:

    For more information, contact Scott Drummond, USDA-ARS, phone: 573-882-1146 or e-mail:

  • Soil information is available the Natural Resources Conservation Service (NRCS) at:

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