With auto-steering, a farmer manually drives the perimeter of a field to map its boundaries so the GPS gadget can then direct the tractor to carve near-perfectly straight rows. A few systems will even turn the tractor around at the end of each row. By cutting down on overlap, the system saves fuel, and it means the same ground won't be planted twice or sprayed unnecessarily with fertilizer or pesticides.

Barbre estimates that using auto-steering on his 4,000 acres — split about evenly between soybeans and corn — has cut his fuel costs up to 5 percent.

"That's maybe 30, 50 cents an acre," he said. "Over 4,000 acres, that adds up."

Yield mapping — tracking how much corn or soybeans parts of his fields produce, which he's used for more than 10 years — brings him an extra $30 or $35 on every acre of corn. He figures he's spent about $14,000 on it over the years, buying and upgrading his hardware and software, for a net benefit of $60,000 to $70,000 or more per year on 2,000 acres of corn.

But technology has limits for Barbre. Some of his fields are cut into hilly terrain, while others are near-perfect squares and rectangles of flat prairie.

"This field I'm planting in right now goes all the way from flat, black ground to ridges with terraces in them," he said while taking a break from corn planting.

The auto-steering helps a lot more in fields like that and less on flat, relatively square tracts. Similarly, yield-monitoring can work wonders if you farm across different types of soil, but not so much if all your crops sprout from similar ground.

A lot also depends on how effectively a farmer uses the technology.

Iowa State University agriculture professor Matt Darr said buying and using high-tech gear is a lot like buying exercise equipment.

"Just because you have a treadmill in your basement doesn't mean you're in great shape," he said.

That's why equipment dealers are offering new services.

"They've had to hire consultants. They have to go out to the farm," said Barry Nelson, a spokesman for the agricultural equipment division at Moline, Ill.-based Deere & Co. "There are some extra expenses."

A 2007 survey of farm equipment dealers conducted by Purdue University and CropLife magazine found that 85 percent offered customers custom applications and someone to come out and put in-field technology to work. Only 45 percent reported making money on the services.

Companies like Deere now try to entice farmers to stick with their brand by making their various high-tech devices compatible so a farmer can get more use from data and high-tech parts, like GPS receivers.