GreenSeeker Proves Worthy For Wheat

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Sensors that can scan a crop and make an instant judgment on what it needs aren’t new, but this “active optical sensor” technology, now available from several different manufacturers, has recently come into its own. GreenSeeker is just one type of active optical sensor and 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.

Chris Holzapfel, researcher with the Indian Head Agricultural Research Foundation (IHARF), explains that recent 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 apply a predetermined amount of N at or before seeding — typically enough to support their farm’s average crop yield. Then they need to develop a benchmark strip by applying 1.5 times that rate to a test strip in the field. This benchmark strip provides an in-field comparison to determine if the crop will respond to added N later in the growing season.

Once it’s time to go in and measure yield potential — at the five and a half leaf stage for cereals (and all the way to flag leaf) and the early six-leaf stage for canola (up to the start of flowering) — farmers drive a high-clearance sprayer equipped with active optical

sensors through the normal part of the field and again through the benchmark strip, telling the computer what it’s measuring. The computer then calculates what an N-rich crop looks like and compares that to the rest of the field.

In short, the six optical sensors mounted on the sprayer’s boom judge biomass on the fly. Measured at specific growth

stages, GreenSeeker’s NDVI value (essentially a biomass measurement) has been shown to correlate very closely to yield potential, Holzapfel says. By comparing NDVI value for the field with NDVI value for the high-N strip, 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 — based on fertilizer price, crop type and crop price.

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 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 frequently recommended more N.

“It’s not an N reduction tool, necessarily,” Holzapfel says. That said, N rates were typically reduced for spring wheat and durum while maintaining yields. Spring wheat plots averaged a 15 per cent reduction in N and durum 24 per cent less N. Although average N rates across all canola plots were reduced by six per cent, in many cases the GreenSeeker called for more pounds. “Canola is a big N user and it is easy to underestimate the requirements of the crop, so it’s not too surprising that we would sometimes end up applying higher N rates with the GreenSeeker,” Holzapfel says.

PROFITABILITY

In years when N fertilizer prices are high, it doesn’t take long for the GreenSeeker to start paying its way. Holzapfel compared profitability at 56¢ per pound of N and $1 per pound of N and used $3.50 per acre for the in-crop application cost. At the $1 price, profits were higher using GreenSeeker with N in all cases. At the 56¢ price, spring wheat and canola both had instances of lower profitability, even with reduced application rates on spring wheat.

In this particular trial, profits on spring wheat averaged 58¢ per acre higher with the GreenSeeker when calculated at the lower N price, but at least two sites had lower returns, largely because of the added cost of application. These profit calculations compare GreenSeeker-based split application versus applying the full rate at seeding.

The trial also compared a standard split rate of 65 per cent at seeding and 35 per cent in crop to a GreenSeeker split rate, which was 65 per cent at seeding and then the GreenSeeker’s suggested rate applied in-crop. In this comparison, profitability on durum plots averaged higher ($2.39 per acre higher to be specific) in all but one trial location using the GreenSeeker’s rates. And that is based on the more realistic 56¢ per pound of N.

Canola showed a wider range of results than spring wheat and durum. Applying N in-crop was money-loser more often in canola than in spring wheat and durum, but in canola the practice did provide “significant” yield increases on two separate instances, Holzapfel says. That said, one trial lost over $10 per acre — even at the lower N price.