Farm tractors steered automatically by signals from advanced solid-state gyros and GPS receivers maintain a +/-0.75-in. row accuracy compared to the typical +/-5 to 8-in. accuracy of hand steering. An onboard computer receives stabilized pitch and roll (artificial horizon) information from a DMU-VGX gyro made by Crossbow Technology, San Jose, and coordinates from satellites and ground-reference stations through a differential GPS. These signals feed either to electrohydraulic steering actuators or to steer-by-wire controls, depending on the tractor model.

Operating the system is straightforward: Drive the tractor to one end of the first row, enter "waypoint 1" on a touch-screen LCD, then drive to the other end and key in "waypoint 2." The beeline -- or shortest distance connecting the two points -- defines the starting row. The computer uses the data to space subsequent rows parallel with it. To begin the later rows, steer the tractor by hand to within 1.5 ft of a row end and press engage. The guidance system drives the tractor to home in on and precisely follow the row until its disengaged.

Tractors equipped with Beeline Navigator Rowcrop guidance systems steer straighter than what's possible by hand. Operators enter commands through a touchscreen LCD. Providing vehicle inclination and acceleration data to the system is a DMU-VGX solid-state gyro from Crossbow Technology.

"Precision guidance permits farmers to work in complete darkness or in fog which can double use of capital equipment and halve payback times," says John Hill, vice president of Business Development at Beeline Navigator Inc., Fresno, Calif. It also eliminates one of the biggest problems in row-crop farming: guess rows. "A guess row is where two adjoining implement (plough) swaths meet. Excessively wide or narrow guess rows made when preparing a field can lead to crop damage during cultivation," explains Hill.

California-based cotton company JG Boswell Co. recently fitted its tractors with the Beeline Navigator Rowcrop systems. Taking the guesswork out of guess rows saves $50/acre/year, or $1.75 million dollars on 35,000 acres, estimates the company.

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