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Smart spreaders

When it comes to doing any job with precision, you're only as exact as your tools. And ag engineer Tony Grift says producers need more accurate feedback tools for precision agriculture.

Fertilizer spreaders are a good example. “Traditional spinner-type spreaders have a high degree of variation in rate and pattern,” says the University of Illinois professor and extension researcher. “There are lots of peaks and valleys. Peaks mean you're over-applying and there is economic loss. Valleys mean you are under-applying and the crop is not getting as much as it needs.

“Proper equipment calibration is the key to accurate application,” Grift continues. “But anyone who's ever calibrated a spinner-type fertilizer spreader will tell you it's no fun. Driving the spreader over a row of 25 collection trays to collect the fertilizer and then weighing each tray's content to determine the spread pattern is a lot more work than most producers care to go through, or should have to.”

The alternative is to pad the application rates, he says, “which is what most producers do, but then you lose the efficiencies of precision ag.”

Challenge of calibration

The problem with trying to keep a spinner fertilizer spreader calibrated is that there are too many variables, Grift says. The constantly changing level of the hopper affects calibration, as does the segregation of the smaller and larger particles and the constant wear on the parts. “Even pneumatic systems don't provide the degree of accuracy that we should be getting for true precision farming,” he says.

The solution is to develop machines with sensors that provide accurate, real-time feedback on what's being applied, Grift says. He has been collaborating with colleagues at the U of I and from around the world to develop several approaches to accomplishing this.

His first device, called the Smart Spreader System, uses optical sensors installed on a spinner-type spreader to measure the velocity and size of particles as they pass by. This information is then used to calculate where the particles will land, which translates into a spread pattern.

Working with a graduate student, Grift has refined a design, which places three moveable “fingers” in front of the spreader's two feed holes. “By varying the position of those fingers, we can put the fertilizer wherever we want to,” he explains. “A tractor operator could simply watch a cab-mounted screen to see the calibration information collected by these sensors and adjust the application rate on the go.”

Fire the cannons

The idea for one of Grift's most recent alternative application systems came from his interest in cannons (he builds small air versions for a hobby). Rather than throw the fertilizer particles, as a spreader does, this device would blast them out through several little cannon-like barrels that would move rapidly back and forth. “We could control the amount of air pressure used to project the particles and the angle of the barrels,” Grift explains. “Every cannon would have a feedback sensor at the end to measure how much material was flying out.

“Whatever the applicator design, it needs to provide greater control over uniformity and rate; that's what we are working toward,” he says.

Both units need more refinement before they are marketable, Grift says, but they represent what he envisions as the next era in machinery development for precision agriculture. “Many of these sensors are fairly inexpensive and could be incorporated into systems that provide more real-time feedback about what's happening in the field. That's critical to improving our precision, for both economic benefit and environmental concerns,” he says. “At some point, the EPA may require greater accountability and more precise application. We've got to be working now on the machines that can do that.”

To read more about Grift's research, visit his Web page at

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