Once out of the price range of many growers, GPS auto-steer systems for tractors are now more affordable. But don't buy the cheapest system available and expect the pinpoint accuracy that is needed for strip-till and other precise production techniques.

That's the advice of Jerry Brightbill, an innovative Plainview, TX, grower who pursued a GPS system for his operation even before it was available in the late '90s. Brightbill, who mainly produces cotton, now has four 8000 series John Deere tractors equipped with RTK auto-steer systems from Trimble and is consistently reducing his input costs while generating better yields.

RTK, or “real time kinematic,” provides sub-inch accuracy that is often crucial in newer farming techniques. “You can now buy an RTK auto-steer system for less than $30,000,” says Brightbill, who likes his systems so much that he became a Trimble dealer. That price compares to as much as $65,000 for a typical RTK system four years ago and still well over $40,000 in 2004.

For growers who don't require sub-inch accuracy, Trimble, AutoFarm and other precision ag companies now offer auto-steer systems that are as low as $6,500. That type of system will provide 4-8 in. accuracy and the freedom of being able to take your hands off the wheel during trips down the row.

There is less fatigue, the ability to keep an eye on the planter, sprayer or other equipment and freedom to perform more precise tasks at night or during foggy conditions.

“There are about five different levels of accuracy for both guidance and auto-steer systems,” says Viacheslav Adamchuk, agricultural engineer for the University of Nebraska-Lincoln. “Nearly every manufacturer has some downgradable options. Frequently they start with a lightbar type of system that uses a conventional differential GPS signal, then advance all the way to RTK, which is the ultimate solution.”

Brightbill has used computers to control his center pivot irrigation systems for years. He also counts on yield mapping and variable-rate application made from infrared imaging. “We've been in it for enough years to collect enough data to document extreme field variability and where we are wasting inputs in parts of a field,” he says.

He installed his first auto-steer unit in January 2003. He needed a system that could be programmed to steer accurately in circle rows planted beneath irrigation center pivots. “Trimble made the commitment to program the system for circle planting if we agreed to help develop it,” he says. “In 2005 we planted flat in circles with the Trimble the auto-steer system in tractors. We also installed a Trimble on our 4710, our sprayer and cotton strippers for harvesting.”

The 1-in. accuracy is critical because a cotton stripper can't be off much more than about 11/2 in. on row spacing or it will knock the plants down instead of having them go in the stripper row unit.

In a typical RTK system, such as the Trimble AgGPS AutoPilot, the tractor is equipped with a receiver and a navigation control system. A field computer inside the cab controls everything from automated steering and record keeping to field mapping and coverage mapping.

A wheel angle sensor and hydraulic control valve receive electrical signals from an RTK base station that is usually portable. Brightbill also has a set base station network. The base station receives signals from 30 communications satellites circling the globe. Roll, pitch and yaw from the tractor or harvest equipment are automatically controlled according to data entered into the computer for each field.

“The key to our farming with RTK technology is a fixed base network that is tied into the same coordinance system,” says Brightbill, noting that this system prevents the operator from having to move a mobile base station. “A 10-hour day has only 600 minutes. With the network, the farmer doesn't have to waste 20-30 minutes moving the mobile station when he goes to another farm. And time is critical in our operation.”

One huge advantage of Brightbill's auto-steer system is the ability to conduct precise field applications literally 24 hours a day. Darkness is no problem for sub-inch accuracy units.

“We've saved a lot in our herbicide program by being able to spray at night,” he says. “From our research we observed through Texas Tech University, spraying half the rate of Roundup at night can provide as good or better weed control than a full rate application during the day.”

Brightbill uses a particular field's auto-steer coordinates on a 90-ft. wide sprayer. He makes the night application without overlapping or skipping a row. “Without the Trimble's Ag170 Field computer, would you know (exactly) where you've been and where you haven't?” he asks.

He encourages growers to consider the bang for the bucks when adding a GPS auto-steer system to their operations. Less expensive systems can provide the auto-steer hands-off advantages for tractor operators, he says, but the accuracy of the less expensive units is lower.

“A lightbar system doesn't know of the hazards in a field, but a field computer does,” he says.

Adamchuk says base station network systems, like that used by Brightbill, add to the benefits provided by RTK. “Usually, the base station has to be 6-10 miles from the field, depending on terrain,” he says. “But networks can enable the signal to be carried further. Some base stations are being set up through co-ops using grain elevators for data transmission.”

Of course, with more elaborate systems come higher costs. However, there are numerous lower cost GPS auto-steer systems available that can certainly be beneficial to corn, soybean and cotton growers not using strip-till or other precise farming. Planting can be more exact and additional trips through the field made easier.

The AgGPS EZ-STEER unit from Trimble (www.trimble.com) will provide plus or minus 6-8 in. accuracy. Its cost is about $6,500. The tractor driver can be attentive to implement performance and can more easily catch clogs or other problems when planting or making chemical applications. “There is much less fatigue when operating a tractor with an auto-steer system,” notes Brightbill.

StepOne is a lower cost auto-steer system from AutoFarm, a former Integrinautics company that is now a division of Novariant. It delivers 4-in. accuracy for tillage, spraying, spreading and harvesting in broadcast crop operations. Like with RTK units, it eliminates the need for markers and lightbars. And like the Trimble units, it's tractor color-blind, meaning it fits virtually any brand of tractor sprayers, spreaders or combines.

AutoFarm's touchscreen in-cab panel (see “Pinpoint Accuracy” in The Corn And Soybean Digest February 2005 issue) is described to be as easy to use as an ATM machine. StepOne can be upgraded to an RTK if needed. Go to www.novariant.com/agriculture/products for more information on AufoFarm auto-steer systems.

The Arro auto-steer system from BEELINE is another option for growers eager to add auto-steer to their tractors. Arro is available at 1-in. accuracy, or with several other options for 2- to 4-in. or 6- to 12-in. accuracy. Go to http://beeline.ag/products/ for more detailed information.

Information on auto-steer systems available from Case is available at www.caseih.com. John Deere also has a broader line of auto-steer systems available on its equipment. The GreenStar systems link to John Deere's AutoTrac systems for a variety of auto-steer capabilities. In addition to RTK, two levels of satellite-based differential correction services (StarFire 1 and StarFire 2) are available through their private network. Visit www.deere.com for more information.

Adamchuk says Outback eDrive provides fairly effective low-end solutions for growers in search of lower cost auto-steer. Go to www.outbackguidance.com for more information.

He adds that different systems have different capabilities, including special modules that control steer when a tractor or other equipment is tilted on a terrace or hill.

There are new GPS systems for tractors and other agricultural equipment emerging as technological advances are made to further aid farmers, says Brightbill. “We need all the help we can get to reduce our inputs without reducing our production,” he says. “Precision agriculture offers many ways to reach those goals.”