By Jim Patrico
Progressive Farmer Senior Editor
Sounds like magic: Attach a set of sensors to your fertilizer applicator, drive it across a cornfield and sit back in the cab as technology "sees" crop health and applies the right amount of nutrients to produce the most profitable crop. That is the promise of technologies such as GreenSeeker by Trimble, OptRx by Ag Leader and CropSpec by TopCon.
The promise has some merit. University of Missouri research shows a significant economic advantage for growers who use crop sensors as key tools for nitrogen application. In some cases, corn farmers can boost yields while decreasing nitrogen use.
"The sensors are able to see things you can't with your own eyes about plant health as you are driving through the field," explained Mark Enninga of Fulda, Minnesota, as he described his experience with GreenSeeker. "We know as farmers and environmentalists that every part of a field has different nitrogen needs, so any tools or technologies that will help us coordinate the timing and amount of nitrogen is moving in the right direction. The GreenSeeker technology is certainly one that will do that."
After three years of crop sensor use, Enninga added this caveat: "It (the technology) is not without its challenges, though."
He bought a used system and said he spent parts of the first two years struggling with technical issues. He also cited the importance of doing some agronomic homework before pulling into the field.
"It is not a system someone can just pick up and go [with] without first understanding how it works," Enninga said. "Every single field you have to think, 'Does this (variable application rate formula) make sense?' You have to use your brain a little bit."
Corn and soybean grower Ryan Britt of Clifton Hill, Missouri, has a similar take on sensors. After seven seasons of using OptRx, he said, "The limiting factor to the system is that it does exactly what you tell it to do. And that can be good or bad. Depending on how you program it, you can over or under-apply nitrogen. You need to know what you want to do going into the season (and into each field)."
Bottom line: crop sensors are not magic, but they do add an important second set of eyes when looking for the right fertilizer formula.
UNIQUE START
Crop sensors have a nearly 20-year history dating back to when they were created -- perhaps ironically -- to kill plants rather than nourish them. A product named the Patchen WeedSeeker came from a joint venture between Oklahoma State University and a private company. The device used light-emitting sensors to detect growing weeds and then spray them with herbicides. The original use was to kill weeds in railroad rights-of-way. The product later evolved into an agricultural product, the descendants of which are now sold by Trimble under the name WeedSeeker.
Branching off that work, OSU researchers developed crop sensors that use both sunlight and emitted light to collect biomass and NDVI readings (Normalized Difference Vegetation Index) in growing crops, particularly wheat. The sensors work by analyzing reflected light to determine -- among other things -- the amount of chlorophyll in crop leaves, which is indicative of nitrogen content and/or need. Those readings, when fed into growth potential and fertilizer rate algorithms, can generate variable rate nitrogen application prescriptions on the go. Researchers used a nitrogen-rich reference strip of crops to set growth and yield goals for the areas they treated using sensors.
The OSU work evolved into a technology — also eventually bought by Trimble, which now markets it as GreenSeeker.
At about the same time the OSU research was getting started, a Nebraska engineer named Kyle Holland was developing a similar technology using sunlight and pulsing light sources to detect crop health. AgLeader eventually bought his system, which became OptRx. (Holland later developed a crop-health sensor and data collector named Crop Circle, which he markets through Holland Scientific.)
Both GreenSeeker and OptRx have been on the market since the mid-2000s.
A third on-the-go sensor/application system -- CropSpec -- came onto the mass market in 2010. It is similar in concept and design to the other systems and uses its own algorithms to determine nitrogen applications.
RESEARCH EXPANDS
Peter Scharf has studied crop sensors from the beginning. As an Extension nutrient management specialist at the University of Missouri, he tested passive sensors (which use sunlight only) in the mid-1990s. Later, the technology evolved into sensors that emitted a secondary source of light so they could function in cloudy conditions and even at night.
While the technology has always had great promise, growers have been slow to adopt it, he said, in part because of its original high cost. Earliest systems, for instance, sold for about $1,000 per foot of spray boom. At a cost of $80,000 to outfit an 80-foot boom, "Lo and behold, they didn't sell many," Scharf said.
But prices have come down. GreenSeeker systems now sell for about $10,000, for a four-sensor setup, to $13,500 for a six-sensor setup which gives the potential for more variable rates. Displays needed to run the systems (FmX or TMX-2050) add $5,000 to $7,000. To outfit an 80-foot boom with OptRx systems sensors, it costs about $12,000 for four sensors, plus about $900 for a master module and about $600 for cables and fittings.
Use of crop sensors "has gone up a lot," Scharf said, but is still "not a high percentage of acres planted."
New thinking on application timing might cause a surge in crop sensor use. Corn growers, especially, are looking to rebalance pre-plant/in-season formulas for nitrogen application.
Currently most corn growers apply the bulk of nitrogen as pre-plant, "70-, 80- even 100% of what they think the crop will need," Scharf said. Many who use a technology like crop sensors to vary sidedressing rates see them merely as a supplement to pre-plant.
That is a mistake, Scharf said: "They (sensors) are not well-suited for that, and I don't think you can get much benefit [out of using sensors that way]."
Instead, corn growers should apply less than half their nitrogen at pre-plant, then most of their nitrogen with in-season applications using crop sensors, he said.
NEW STRATEGY
Variability within fields is one reason for this strategy.
Nitrogen availability is determined by organic matter, soil temperatures, oxygen content and moisture content, which can vary greatly over a farm, Scharf said. "It's a very complex spatial thing. In our research, for instance, we studied eight fields and five of them had places where they didn't need nitrogen at all and others had places that needed the full 250 pounds, which was the highest rate we used. So there is a lot of variability in what the plant needs."
What's important is "what the soil is giving," not how much nitrogen is applied at pre-plant, and that is where sensors shine. "Making the main nitrogen application based on sensors to me is the best way to get real benefit from them," Scharf said.
For proof, he pointed to early 2000s research. It indicated that when crop sensors were used as the main nitrogen application, they produced a gain of 2 bushels per acre while saving 14 pounds of nitrogen per acre.
PREFERRED TIMING
A key question in crop sensor use is: When is it best?
The earliest in the season Scharf has tried crop sensors is at v4 or v5, when corn plants are about 8 inches tall. It didn't work well. "Sensors are looking mostly at soil then," he said. On the other hand, when he used sensors on 1-foot-tall corn plants, the results were "very successful."
It's also important to wait until weeds have been sprayed and are brown. Otherwise their chlorophyll content can throw off readings.
How tall can you go? "I feel comfortable with wide range of times," Scharf said. Yield results are not much different when plants are 1 to 7 feet tall. But profitability goes up slightly when crop sensors are used in taller corn, because there is more plant material to see and analyze.
PLACING BETS
Missouri farmer Britt likes to sidedress at v8 to v10. He has tried both earlier and later applications. "The question is, how much do you put down up front to get you to the sidedress? The earlier you go with sidedress, the more risk you have as far as not putting enough on or having it last until the end of the season. On the other hand, if you apply later, you risk being able to apply at all because of weather." He had that problem this year when a rainy summer kept his Hagie sprayer and Y-drop toolbar out of the field entirely.
About half the highly variable 3,500 acres Britt farms with his father, Randy, and brother-in-law, Ryan Edwards, are in corn each year. When they began beta testing the OptRx system in 2008, they thought it would mainly cut fertilizer costs.
"We thought we would be able to cut back on nitrogen and save some money. But in reality we put on more nitrogen now [with OptRx], in part because Ag Leader's algorithms were more aggressive than what we were on our own. The result is we now use more nitrogen but we also produce more bushels. The important thing is that even with more N, we are putting it where the return on investment is best. We changed our tune."
OTHER APPROACHES
Other farmers are also looking for the best return on their investments.
Andrew Dierks is always looking for efficient ways to fertilize corn. He farms near Mark Enninga in southern Minnesota, and the two men share some technology and equipment including a GreenSeeker system. Dierks also has experimented on his own farm with the Encirca system from DuPont Pioneer. Both Encirca and Climate Corp's FieldView Pro use localized weather records and other agronomic data to help a grower determine timely nitrogen needs based on models.
Having both GreenSeeker and Encirca at his command, Dierks did side-by-side comparisons in 2015. Modeling and sensors, "essentially do the same thing in my eyes," he said. He did not see much difference in results, either in application amounts or yields but will continue to test the systems. "Any time you use a technology you should analyze the results so you know what you are gaining."
Missouri farmer Ryan Britt also has used both OptRx and Encirca. In 2014 he did an Encirca plot in addition to OptRx fields and found that nitrogen recommendations came within a couple of pounds with each either. Yields also were within a bushel or two. Because he already owned an OptRx system, Britt said, it had a better cost per acre than Encirca.
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Editor's note: DTN provides weather data to DuPont Pioneer for use in its Encirca product.
This is the second in DTN/The Progressive Farmer's series on Finesse Field Fertility, helping farmers fine-tune how to feed their crops and get the most value from every input and practice.
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