Crop sensors work

The Skinner family has been working to tighten nitrogen rates ever since they started using precision agriculture techniques some 15 years ago. It’s not just the rising cost of N, says Darin Skinner. “We want to be good environmental stewards,” he says. “We want to be on top of fertilizer rates for both reasons. It’s in the news. The public is paying more attention.”

At Hardscrabble Farms near Kilbourne, Gary, Brian and Darin Skinner soil sample in 2.5-acre grids, and use a variable-rate spreader to apply fertilizer and lime based on the grids. From the soil analysis, Tim Norris with Ag Info Tech in Gambier writes prescriptions for them to vary the applications of nutrients and lime.

Key Points

Infrared sensors enable farmers to apply nitrogen as needed.

The system both saves on N and ensures optimal rates.

Despite a wet spring, sensors proved profitable for Skinners.


The system works well, and when combined with a yield monitor, gives plenty of information about the productivity of the soils in the field, Norris says. But imagine if you could measure the in-season fertility needs of the growing plant and apply as much N as needed to make the plant as healthy as possible.

Light waves

Last spring Norris showed the Skinners an OptRx crop sensor by Ag Leader. The infrared sensor gathers and records data about plant health. By shining a red-edge light wave on plants’ leaves, the sensor measures the reflected light to determine how healthy plants are. The amount of N applied by the spray boom is based on the plant’s direct requirements. Healthier corn plants get less N — saving the farmer money. Less robust plants get an extra shot of N based on their color — adding bushels to the bin.

“It’s extremely easy to set up,” says Darin Skinner. He knows, because the family has upgraded from a high-clearance sprayer and moved the system to the new sprayer. There are two sensors on each side of the 90-foot boom, and the sprayer rates are displayed on the Ag Leader Integra screen in the cab. Rate and swath control are reported, and there’s an on-screen application map.

To start, Skinner makes a five-minute pass over some of the healthiest-looking corn to set a “virtual reference strip.” The strip calibrates a zero, or “vegetative reference point” for application.

The best time to apply the sidedress N is between V-6 and V-8, Norris says. “That’s a tight window,” notes Skinner.

The Skinners tested the system on 1,140 acres last summer. “As I was applying it, we thought we were looking at a 100-bushel-per-acre crop,” Skinner says. Yields came in much better than that, and using the sensor paid off — both in fields where it reduced the average rate and saved dollars, and in fields where it added more N and pushed yields higher.

“In hindsight, I think we wish we had used it on more acres,” Skinner says.

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STRAIGHT AND NARROW: Although Darin Skinner does not use RTK to guide his sprayer, he has gotten used to driving the high-clearance coupe down 20-inch rows as he dribbles 28% N into the fast-growing corn crop based on readings from the OptRx sensor.
Photo courtesy Chris Light

This article published in the February, 2012 edition of OHIO FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.