“You start thinking, jeez, I wonder if we should be spraying this field?”
– TERRY ABERHART
A thick, even stand of canola makes it easy to justify investing in a fungicide application to ward off sclerotinia.
But what if it suddenly thins out because of frost, too wet, too dry, uneven germination or too much straw?
“You start thinking, jeez, I wonder if we should be spraying this field?” asked Agri-Trend coach Terry Aberhart, during an infield presentation during the company’s summer training session in July.
“I know that happens a lot on our farm. It’s a hard thing to know what you should be doing because of variability. Maybe only certain portions of the field would need an application.”
The answer, said Aberhart, is in-season satellite imagery to pinpoint areas of good canola growth and use variable-rate fungicide application to spray where the crop is worth protecting.
Then, when rolling over the weak patches, a computerized control system that interprets the mapping data in real time will shut off the nozzles and keep that expensive chemical in the sprayer tank.
Up-to-date information is critical for applying variable-rate fungicide because last year’s maps often aren’t worth the paper they are printed on, mainly because weather is such an important factor for canola.
“In most cases, running an application based off a previous year’s yield map just doesn’t make any sense at all,” he said.
New tools such as high-resolution mapping imagery of up to one metre per pixel makes variable-rate fungicide application very effective.
To illustrate, Aberhart held up a piece of paper comparing various levels of accuracy. On it were pictures showing different views of the same half-moon-shaped irrigated field.
The Real Shot map, produced at 1m resolution was so clearly defined that even the pivot tracks through the crop were clearly visible.
Another, from RapidEye, a new company with five privately owned satellites used for agricultural applications, showed up to 5m per pixel imagery, and a reasonable image of the crop’s variability was evident.
The third, from Landsat, had a blurry picture at 30m-per-pixel resolution. That means each square or pixel on the map represents a 90×90-foot parcel. It’s available for free off the Internet, but it’s far too imprecise for variable rate, he said.
“The bottom line is that resolution is very important and you get what you pay for.”
To get Real Shot maps, a plane is ordered well in advance to fly over the field and get an image, ideally at least 10 days before the
crop is to be sprayed and when the plants are beginning to bolt.
Then, with aerial map in hand, the farmer or crop coach walks through the field to “ground truth” the variability and make sure that the green patches aren’t just thistles or wild oats. Next, the image data is fed into the computer on the sprayer and the fungicide can be applied.
On a 160-acre application map, Aberhart showed 22 acres representing the “blue” zone where full rates were applied, 89 acres of “green” at a lower rate, and 50 acres of “red” where the booms were shut off because there was nothing worth spraying underneath.
“It cost us about $3.50/acre to get the imagery, $1.50 to do the ground truthing, and make the prescription and put it in the sprayer,” he said. “At the end of the day, we had a net savings of about $3.80 an acre.”
There is also a time saving aspect. With jumbo-size farms, Aberhart added, less wasted chemical means that more acres can be covered without having to refill the tank.
“With the accuracy of the 1-metre resolution, and controllers in the sprayer, they can shut separate boom sections off within five feet of the line. If part of the boom is in the red area, it’ll shut that part off while the other booms are still spraying. That is just super cool,” he said.
“If we were using 30-metre satellite, it could be 50 feet either way before it knows what it should be doing.” [email protected]