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‘Reading’ nitrogen on the go still evolving

Ground-based, canopy-reflectance sensors are effective at detecting nitrogen stress in growing corn and other crops. But currently there is what Richard Ferguson calls a stalemate in the adoption of the sensors in variable-rate application systems.

“There has been significant research by UNL and other universities on the sensors and variable-rate, on-the-go application,” adds Ferguson, UNL soils specialist. “From an adoption standpoint, farmers want more education on use of these systems and their components. Farmers want to see more demonstration of the systems.”

Ferguson says the algorithms, or equations, that interpret the sensor plant canopy readings and determine on-the-go rates are a key component of the system and, in some cases, may need refining. Some sensor/algorithm systems on the market use a reference strip, a strip in the field where nitrogen is applied so that crop nitrogen isn’t lacking. Sensors read that nitrogen-rich strip and use it as a reference for adjusting rates in the rest of the field.

At a glance

Canopy sensors are effective in detecting corn nitrogen stress.

Farmers are seeking more information and demonstrations.

UNL specialist says system algorithms may need refining.


“Transferring that difference — from the adequately fertilized reference strip to another part of the field — can be a problem if the reference strip doesn’t actually represent the range of variability present in the field. I encourage farmers to use more than one of the reference strips,” he says.

Ag Leader is one of the three companies marketing sensors, says Ferguson. Its OptRx sensor uses an algorithm that doesn’t require a reference strip. The sensor can use an operator-selected average nitrogen rate to start with, and then will adjust the rate as sensor data is collected.

“If judiciously managed, these systems can apply nitrogen where it will be used most effectively,” Ferguson says. “That may not necessarily always mean lower rates, but it’s more efficient when you can apply the right amount at the right place.”

He cites an environmental benefit when nitrogen is applied where it’s needed most and not applied at a constant rate across the field. “You can avoid losing nitrogen through leaching where it’s been overapplied.”

Snider says the technology is still new. “But I believe it’s the thing of the future in nitrogen use,” says the farmer from McCool Junction. “I am anxious to get more than one year’s experience with it.”

He purchased the sensors, monitor and controller from Crossroads GPS, a precision agriculture company in York that is a dealer for Trimble, which markets the GreenSeeker sensors. Crossroads GPS assisted Snider in setting up the system

His 2011 entry in the National Corn Growers Association Corn Yield Contest benefited from the GreenSeeker system, Snider believes. He earned first-place among Nebraska producers in the strip-till/no-till category with a yield of 291 bushels an acre.

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LIGHT ON NITROGEN: A close-up shows a GreenSeeker optical light sensor on the cultivator used by Tom Snider Jr. of McCool Junction last year.

This article published in the March, 2012 edition of NEBRASKA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.