Active optical sensor technology can help fine-tune nitrogen application rates to better match yield potential in wheat, durum and canola, but that's only one use of the technology.

GreenSeeker isn't the only setup of its kind, but it was the focus of recent farm-scale trials at Indian Head, Sask., looking at ways to match nitrogen (N) rates with yield potential once the crop is off and running.

Optical sensor technology could be used to better match N application rates with some crops' yield potential, IHARF researcher Chris Holzapfel says. -- Lyndsey Smith photo

Chris Holzapfel, a researcher with the Indian Head Agricultural Research Foundation (IHARF), explains that software advances have made determining yield potential and the potential for the crop to respond to N fairly straightforward.

“It's now possible to make real-time decisions on N rates in a single pass,” he says, eliminating the need to come up with subscription maps ahead of time.

To make the most of the technology, Holzapfel says, growers should determine a planned N application rate -- something western Canadian growers are very good at -- then apply a 1.5x rate to a test strip in the field.

This sets the grower up with an in-field comparison of if the crop will respond to added N. Once it's time to go in and measure yield potential, farmers simply set themselves up with the sprayer down the middle of the normal vs. high rate of N, tell the computer what it's measuring, and the computer does all the calculating.

In short, the optical sensors judge biomass on-the-fly. Biomass, measured at specific growth stages, has been shown to correlate very closely to yield potential, Holzapfel says.

By comparing the average and high rate the software determines if the crop will respond to added N. From there, it's up to the farmer to decide if an in-crop top-up is worthwhile.

The economics certainly favour the use of an in-crop application for durum, most of the time for spring wheat and some of the time for canola. What's interesting is that the GreenSeeker typically recommended less overall N per acre than what the farmer would apply and achieved the same yield, except in canola where GreenSeeker ratings actually recommended more N.

“It's not an N reduction tool, necessarily,” Holzapfel says.

Profitability

What's more, profitability on durum was improved with in-crop N, whether at a fixed rate or at a rate determined by the GreenSeeker. On average, durum growers could save $8 per acre, assuming $1 per pound of N fertilizer. For spring wheat, profitability varied but GreenSeeker plots still came out ahead over $5 per acre more profitably, largely due to a reduced fertilizer bill.

Canola's profitability was most varied. N application in-crop actually lost money more years than compared to wheat and durum; however, there were two separate instances of significant yield increases, Holzapfel says.

At the same price for N, canola plots did still average over $7 more profit per acre, even with additional N.

Holzapfel is impressed with GreenSeeker's ability to prescribe N rates in-crop, but he sees other applications for the setup as well. If you pay money for aerial or satellite images, you can get the same kind of data but use it for several different applications, he says.

It would be interesting, he says, to see how much could be saved on fungicides and desiccant applications based on biomass in the field.

“If there's very little crop (in an area), you might not want to spray at all, or at a half rate (of fungicide),” he says. The same concept could work with desiccants.

GreenSeeker technology is available through Pattison Liquid Systems and is now owned by Trimble.

-- Lyndsey Smith is an associate editor with Grainews in southern Saskatchewan.