Satellite system can control tractors.

Future farmers of America never may have to learn to drive a tractor. A Stanford (Calif.) University research team has equipped a John Deere tractor with a satellite-based automatic control system that can guide the 20,000-pound farm vehicle more precisely than the best human drivers.

Doctoral students Gabriel H. Elkaim and Michael O'Connor report that their team has perfected the system to the point it can maneuver the tractor at all speeds while pulling a variety of implements, with centimeter-level precision. "These guys have done an amazing job in controlling the tractor. They've taken it beyond anything we expected," indicates Gary K. Hendrickson, manager of product testing and reliability for John Deere, who has been working with them.

They achieved this level of control by using the Global Positioning System (GPS), a constellation of 24 satellites operated by the U.S. Department of Defense that circle the Earth every 12 hours. The system originally was designed and constructed primarily for military usage, but has been made available for civilian purposes.

Normal civilian GPS receivers have a precision of about 100 yards. A system called differential GPS, which requires a local base station, can provide meter-level accuracy. At these accuracy levels, the technology has found widespread use in the nation's farmland, as part of a movement called precision agriculture.

In the days before agriculture was industrialized, farmers were familiar with the characteristics of their fields yard by yard, and successful ones adapted their practices--such as seeding, cultivating, and irrigation--to these variations. The advent of industrialization, however, forced farmers to prepare entire...