With fertilizer prices these days, an investment in GreenSeeker technology for applying nitrogen at variable rates could pay for itself in short order, according to new research at Agriculture Canada’s research centre in Indian Head, Sask.
Guy Lafond, a production systems agronomist with Agriculture Canada, has studied the effectiveness of variable rate application technology for more than a decade.
While initial progress in precision farming has proven slower than first predicted, that may soon change, said Lafond, who presented his latest results at Ag Days in Brandon last week.
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Similar to the explosion in direct seeding during the 1970s – which faltered due to problems caused by cool, wet soil until dependable technology and equipment was developed – variable rate nitrogen application may be following a similar development curve, he said.
But the goal of matching inputs with agronomic practices based on soil and crop requirements, and how they vary within a field, is the wave of the future, he added.
Lafond noted that in the 1990s, precision farming research was carried out by soil scientists, who looked mainly at soil test results. Now, researchers are looking at above-ground indicators in the plants.
Testing of optical sensors began at the research centre in 2004 with the goal of more precisely managing nitrogen in canola and spring wheat.
Now, the question is: can measuring crop characteristics provide more information about productivity and variability in the field than soil characteristics?
Beginning in 1997, a 308 acre site was split into eight roughly 40-acre plots, and field scale equipment was used on a spring wheat-canola-spring wheat-field pea rotation.
Using Landsat satellite imagery, Lafond said researchers were able to determine areas of high and low production on the site, which were later verified in the course of two growing seasons.
With GPS tracking and variable rate application, the field has taken on a checkerboard appearance of varying shades of green revealed by aerial photography, which indicates the accuracy of the system.
Normalized Difference Vegetative Index, or NDVI, which uses visual satellite imagery based on light spectrum analysis to measure the variability in shades of chlorophyll and determine plant health and nutrient requirements, was found to be useful in determining varying productivity on the field scale to create management zones, Lafond said.
However, that research indicated shortcomings in the data and further unanswered questions.
“The follow-up question was: can the crop tell us its nutrient requirements early enough in the growing season and can optical sensors provide us with the fine-tuning of N management that we are looking for?” said Lafond.
“And more importantly, can we operate in real-time and do something this year to take advantage of whatever growing conditions we have?”
The GreenSeeker system, which costs roughly $18,000 to outfit a typical ground sprayer, consists of a series of optical sensors mounted on the boom that meter out rates of liquid UAN based on real-time measurements of the yield potential in the vegetation directly below the nozzle. A hand held device is also available for about $4,000.
“It’s robust equipment that is going to last a long time. If you’re buying a $300,000 sprayer, you could be collecting a lot of information even if you’re not using it just for nitrogen application,” he said.
Nitrogen management depends on source, placement and timing, he said.
“Our feeling is that the aspect of nitrogen management that is the most difficult is deciding on a nitrogen rate. I think the optical sensor has the capability to help us refine our understanding of our nitrogen needs.”
A complex algorithm for operating the application controller in canola was developed using 1,800 samples accumulated with a hand-held GreenSeeker in test plots in the mid-bolting to early flowering stage. Those were later incorporated into a yield curve that could predict final grain yield within a 15 percent range. In predicting yield for spring wheat, the device is most effective at the flag leaf stage, he added.
The key to successfully calibrating the sensors is the creation of a nitrogen-rich strip in the field to provide a baseline for maximum yield potential. In it, nitrogen is applied at 1.5 to two times the target rate to make sure that plant nutrient availability is not a limiting factor.
Then, the NDVI of the rich strips is fed into the GreenSeeker. The device is then able to compare the maximum potential benchmark with the real-time data coming from the optical sensor as it moves over the field. The device regulates the application rate to top up the nitrogen where needed.
“In the algorithm that we have for spring wheat, for example, the N-rich strip is telling us that there is a yield potential of 53 bushels per acre. Then, if we look at the rest of the field, we see that there is a yield potential of 45 bu. So that’s a difference of eight bu.,” he said.
“So if the potential is 53, can I do something early in the growing season to bump it up to the limit of 53?”
Given that nitrogen use efficiency is typically only 50 percent, the GreenSeeker would have to apply an additional 22 pounds of nitrogen to realize peak crop performance in all areas.
“As you’re going down the field, it is comparing the readings to the maximum and making a decision instantaneously as to whether it should add more nitrogen,” he said. “Of course, it is done electronically, so it’s super fast.”
Field test results using an RT200 unit mounted on a high clearance sprayer showed nitrogen savings benefits over typical farmer practice, which was defined as the amount of fertilizer that would have been applied by a farmer at seeding time that particular cropping year based on his own instincts and soil test results.
In comparison, the split-fixed application method put 66 percent of the fertilizer on during seeding, then top dressed the remaining 44 percent using the optical sensor technology.
In four trials of spring wheat, using the farmer practice guideline, 50-110 lb. of nitrogen were applied per acre. Using the GreenSeeker delivery method, the applied rate was found to be about 13 percent less, ranging from 42-90 lb. per acre.
“In grain yields, farmer practice and the GreenSeeker were the same in three out of four years. But in one year, the farmer practice was greater.”
In the split-fixed plots, farmer practice and GreenSeeker were the same in two years, with farmer practice higher in one year and less in another.
Tests conducted on durum wheat showed 21 percent less fertilizer used with the GreenSeeker than regular farmer practice, while at the same time producing similar yields in all four years.
“If we’re using 21 percent less nitrogen with the GreenSeeker, with the price of fertilizer these days, I think it will cover the cost of the extra application,” he said.
For canola, farmer practice nitrogen use ranged from 75-128 lb. per acre, compared to 71-108 for the high-tech gadget, resulting in a 7.5 percent average reduction.
“But in some cases, we actually used more. So in every year and in every field, the crop is going to be different,” Lafond said.
In terms of grain yield, farmer practice was the same as GreenSeeker in seven of nine years, but farmer practice was less in two.
Farmer practice was the same in the fixed-split plots in seven of nine years, but less in two.
“So, again, I think we’re on the right track, even though in the canola in some situations a little bit more was used.”
He added that the technology could also have advantages for fungicide application. By programming the economic threshold into the device, it could shut itself off when passing over crop areas that aren’t worth spraying.
