What You Should Know About Nitrogen Sensor Issue

Precision panel discusses nitrogen sensing idea.

Published on: Dec 14, 2009
You're going to see promotion of possibly three nitrogen sensors for use in postemergence corn that are geared to helping you decide if you need to add extra nitrogen, or how much extra you should add. Bob Nielsen, Purdue University corn Extension specialist, addressed the issue during questions and answers at the Bi-State Corps Forum held near Covington recently. He was a member on a panel talking about how to make a profit using the tools of precision farming.

Here's the lead-in to the question. GreenSeeker has marketed a technology for some time that uses optic sensors and then tells a computer on-board the application rig how much nitrogen to apply. The company claimed good success using it on wheat in the western U.S., but it has caught on much more slowly in the Corn Belt. Last year Trimble acquired rights to the product. Meanwhile, Ag Leader bought rights to a sensor designed to accomplish the same thing, but which works differently. And Topcon is bringing a third sensor, apparently one they developed themselves, to the market.

For Nielsen, it's not a question of if sensor technology can be used to detect nitrogen differences and be useful in applying more N during the growing season. Neilsen and Jim Camberato, also a Purdue Extension agronomist, have been experimenting with sensors, primarily the type now offered by Ag Leader, for several years. "We're very comfortable that in waist-high corn, we can do a good job of selecting differences in nitrogen and determining which areas ought to receive extra N at that point," he says.

The Purdue pair has proven this to themselves by checking sensor readings on known N rate strips within a field or plot. A high-rate plot where lots of N was applied serves as a reference strip for running the device over the rest of the field. What the sensors are reading is light reflectance, and translating that into an estimate of nitrogen content in corn plants. How they do it differs, but the concept is the same.

The problem is whether of not the same concept works at sidedressing time. While it's not yet totally clear if all three companies with these new products intend to market them for use at sidedressing, it remains a possibility.

"We haven't been successful at picking up differences in nitrogen on younger corn," Nielsen told the audience. "We even tried it on V8 corn, which is at the top edge of what you would want to sidedress. But so far we can't say that we've picked up differences in N that would let us make recommendations at that stage. Later on, at waist high, yes, definitely. But then you're talking coming in and applying that last 50 pounds or so with either high-clearance sprayers or with drops."

Nielsen still sees value for the concept, and will continue studying it. In fact, a graduate student will being a new project next spring, trying to determine at exactly what stage of growth of corn it is possible to detect differences in nitrogen within plants, based on known or applied nitrogen levels.

Stay tuned!