Space-Age Farming

07/01/2009 02:00:00 AM

By Vicky Boyd, Editor

Will Hyatt, owner of Hyatt Farms near Lake Wales, says he’s still an infant when it comes to learning the benefits of a global positioning system, since he just acquired the technology last fall.

Already, though, the producer of vegetables and citrus says he has experienced increased efficiency during land leveling and marking beds.

“The great thing about it is the fuel savings,” Hyatt says of marking vegetable beds. His beds are on 6-foot centers, and he marks four per pass.

“Before, we had to put our tractor tire back in the plow row to keep the distance right. We were only making two new rows per pass. Now we’re getting four rows. With the GPS, we just line up the tractor 6 feet from the last plow mark. It cuts your time in half.”

Hyatt bought the unit originally for its land leveling capabilities. He had been hiring a firm to custom laser level his ground, but found he was on the bottom of the priority list.

Basic GPS units typically have sub-meter accuracy and are designed for uses, such as cultivation and herbicide spraying.

Rather than pay someone else and be tied to their schedule, Hyatt says he decided to make the investment so he could level his ground when he needed to.

Aaron Troyer, general manager of Troyer Brothers Farms near Ft. Myers, also has experienced increased efficiency. For about two years, the operation has been using GPS lightbars on two tractors for field mapping and herbicide spraying.

“When you have larger fields and you have no references, you can kind of wander and meander,” Troyer says of the sprayers.

Before, he says, it wasn’t unusual to have 30 percent to 40 percent sprayer overlap. With the GPS units, that’s been cut to 5 percent to 10 percent.

“You can save on costs [of herbicide] 15 to 20 percent,” he says.

GPS gains popularity

Hyatt and Troyer are two of an untold number of producers in the state who have adopted the satellite-guided technology.

Reza Ehsani, an assistant professor of agricultural and biological engineering at the Citrus Research and Education Center in Lake Alfred, says he doesn’t know how many growers in Florida use GPS. But he says he’d like to conduct a survey to gauge adoption of the technology.

In the meantime, Ehsani says he’s noticed an increased interest among citrus growers, who use handheld units to map citrus groves and assign GPS coordinates to disease-infected trees.

“It used to be used just for variable-rate application and precision ag-types of applications,” Ehsani says. “But now with the diseases we have in citrus, a lot of growers are using it for scouting purposes.”

But not all GPS systems are the same. And matching the correct one to the use is critical if you want to obtain the most out of a system.

Ehsani has conducted several workshops to help citrus growers learn about handheld GPS units, how to use them and how to integrate them with other software.

Photo courtesy of Trimble
An RTK global positioning system provides up to sub-inch accuracy that’s needed for precision planting of crops, such as lettuce.

GPS demystified

GPS receivers use signals from a group of satellites to triangulate the unit’s location. About two dozen satellites orbit the earth twice per day and transmit precise microwave signals. Typically about four to 10 are in view at any one time.

The more satellites on the horizon, the more accurate the collected data, within limits. But a minimum of four are needed to be able to determine exact location.

Basic GPS units—such as the one used in some lightbars—have sub-meter accuracy and are appropriate for uses, such as field cultivation, herbicide spraying and dry fertilizer spreading.

They help prevent overlaps, reduce operator fatigue and increase efficiency. They’re also the least expensive and can be had for less than $1,000 per unit in many cases.

Most GPS units are capable of receiving WAAS—or Wide Area Augmentation System—signals. WAAS is a free differential correction signal that improves the accuracy of GPS systems.

If you farm near a navigable waterway, such as along the Indian River, the Coast Guard maintains beacons that provide similar differential correctional signals.

Growers who use auto-pilot systems or GPS to precisely plant rows or level land use an RTK GPS system. They’ll typically put a portable RTK tower in their fields to fine-tune the satellite signals even further. The result is sub-inch accuracy.

RTK systems also tend to be the most expensive, with systems typically starting at about $35,000.

GPS wins over lasers

Because his fields are contiguous and within a 6-mile radius, Hyatt says he can leave the RTK base station in one place. That’s a time savings compared with laser leveling, where the laser has to be moved from field to field along with the scraper buckets.

Hyatt says he found the system relatively simple to use, citing Trimble’s user-friendly display.

“It’s not a really difficult thing to set up,” he says.

Choose DGPS for citrus scouting

Growers who want the technology to scout citrus groves should use differentially corrected GPS, or DGPS, because of the higher accuracy, Ehsani says.

“If you were in the middle of a row collecting data with a low-cost GPS unit, you would have four or five trees and you couldn’t be sure which tree you were talking about,” he says. “If you’re using one with sub-meter accuracy, such as the [Trimble] AgGPS 132, you’ll definitely need to get close enough to the tree to be able to identify the tree later.”

Even if you’re using a DGPS unit, Ehsani says you have to pay attention to the signal strength to ensure optimum accuracy.

“Sometimes they’ll loose the WAAS, they’re not paying attention and they don’t know they’re not in the differential mode,” he says. “[The unit] will accept the location but it may not be accurate.”



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