The search for ways to make precision ag actually pay has led University of Illinois (UI) researchers to develop a liquid nitrogen applicator that can read the needs of a corn crop and adjust rates on the go.

Using “off-the-shelf” technology, UI scientists built an applicator that uses a multispectral camera mounted 1 ft. in front of the machine to detect nitrogen stress. It's accurate enough to provide analysis similar to leaf tests using a SPAD meter. Those data are sent to a computer that controls a variable rate applicator.

Infinite variation

The 25-row applicator uses individual row drops, and each nozzle is controlled based on the reading taken by the high-tech eye mounted in the camera. “We can infinitely vary application rates from 0 to 100%,” says Qin Zhang, UI ag engineer. “For our tests, we're using 28% N, but you could use any blend you wanted.” During tests, the applicator used rates from 0 to 100% and many levels in between, according to Zhang.

“In our plots, we preplant-applied fertilizer at rates that ranged from 0 to 100% of the corn crop's predicted needs,” he says. “When we used the applicator, it responded with application rates that matched the preplant applications. At harvest, the yields from the different plots showed little variation.”

The applicator works at speeds of 5 to 6 mph and can be used for multiple trips, if that's desired. “You could use it as early as the two-leaf stage up until the corn is approximately 5 ft. tall,” Zhang says. “While multiple trips can be used, our data suggest that a single pass should be able to apply the needed N.”

Because the applicator's sensor uses light reflectance to analyze nitrogen needs, it must be able to see the difference between plant reflectance and soil reflectance. And it needs to be able to do its job under different environmental conditions.

Two-step process

The science works, but it was a two-step process this summer for the UI scientists. It took one pass through the field to map the plants and a second pass to actually apply the nitrogen. The researchers' goal for 2003 is to integrate the process into a single pass.

“The system can work one of two ways,” Zhang explains. “If farmers already have their fields computer mapped, they can run their own variable rate nitrogen program using this machine. But with the sensor mounted in front of the machine, you don't need a computer map to make real-time adjustments on the go.” Regardless of which way the machine is used, the data are recorded and can be downloaded for use as an information layer on computer field maps.

Multiple uses

Adjusting nitrogen rates on corn is just the beginning for this technology, according to Zhang. “With different sensors we can use the same technology to recognize weeds and adjust herbicide applications,” he says.

“There's still some skepticism as to the economic benefits of this variable rate application technology,” says UI ag engineer Alan Hansen. “Some of the original enthusiasm over variable rate application has waned because of economic consideration.”

But since those early days, the technology has become more reliable and computing power has soared, according to Hansen. He believes that the new advancements in sprayer technology may revive interest in variable rate applications.