Top Crop Manager

Precision Ag
Rising fertilizer costs raising interest in newer technology for Canada

November 30, 1999  By Blair Andrews

The need to manage rising fertilizer costs is sparking renewed interest in technologies and methods aimed at maximizing farmers’ investments in nitrogen. Those bills are climbing again, thanks to the lure of higher crop prices and farmers’ willingness to pay the higher fertilizer prices to increase crop yields.

One innovation that may attract more inquiries from farmers in Eastern Canada is the GreenSeeker system from Trimble Agriculture. The variable rate application and mapping system has been around for about 20 years in the United States and has been in use on farms in Western Canada since 2008.

Billed as a piece of technology that can boost yields while using less fertilizer, GreenSeeker uses optical sensors with an integrated application system to measure crop status and variably apply the crop’s nitrogen requirements. Whereas current precision agricultural methods rely on historical information or mapping to make the nitrogen (N) recommendation, the technology operates in real time, allowing the operators to make variable rate applications on the go.


The sensor uses light-emitting diodes to generate red and near-infrared (NIR) light. The top-end system includes six sensors placed across a 90-foot boom. The light generated is reflected off of the crop and measured by a photodiode located at the front of the sensor head. Red light is absorbed by plant chlorophyll and healthy plants absorb more red light and reflect larger amounts of NIR than those that are unhealthy. The reflectance values are used to calculate the Normalized Difference Vegetation Index (NDVI), which is an indirect measurement of the crop’s aboveground growth. By comparing the NDVI of the crop being evaluated to that of an N-rich strip in the field, the technology can be used to respond to field variability. “If we can predict yield when the wheat is three or four inches high, then we can do a lot with that value in terms of working backwards to determine what the optimum fertilizer rate is going to be,” says agronomist Bill Raun, a regents professor at Oklahoma State University, where the GreenSeeker technology was developed. “Because producers, whether in Canada, the US or Mexico, are applying way too much N fertilizer for the most part, we just need to say, ‘Okay, here’s the yield we think you can produce if you don’t fertilize and here’s the yield we think you can produce if you do fertilize.’ That’s what our method does using the GreenSeeker sensor,” says Raun.

As the applicator moves across the field, a built-in microprocessor analyzes the NDVI readings and determines the N requirements that are needed to meet full yield potential. Predetermined algorithms calculate the amount of N required. The information is relayed to the rate controller to provide variable rate N application in real time as the applicator moves across the field.

Raun says the key to determining the right amount of fertilizer in a given year is to apply an N-rich strip in the field. The concept is to plant one strip of a field with a very high N rate to simulate an N-rich environment where the crop’s N requirements are being satisfied. The farmer would then drive the GreenSeeker sprayer over the N-rich strip to set the upper NDVI limit. If the crop is capable of using additional N, the sensor will determine the magnitude and generate an N recommendation based on the predicted yield.

Using the N-rich strip and sensor calculations increases the chance of using the correct rate each year, and only applying N when it is needed. “If I can predict yield, and I can put out an N-rich strip and determine what the end responsiveness is going to be, then I can get a really good N rate that will optimize yield and minimize inputs,” says Raun, noting that nitrogen demand varies significantly each year because of soil and weather conditions. “Five years ago, we put out 2000 N-rich strips with farmers all over Oklahoma to get them accustomed to the fact that there’s a radical difference in the N demand from one year to the next, and they’re not going to know what the demand is until they put out the N-rich strip,” says Raun.

Ontario results
Paul Raymer, a precision agriculture specialist at The Farm Office in Tavistock, Ontario, which is also a Trimble dealer, has seen the GreenSeeker technology at work in Ontario. The RT200 application system was put to the test on a 126-acre parcel near Arthur, Ontario. “It’s really amazing when you are going through the field and you can see the low vigour areas and you see the (N) target rate go up. You can hear the pump wind up and send out a higher rate. Then, it gets to a spot where it doesn’t need (an application) and shuts right off,” says Raymer.

Besides its role in variable rate nitrogen applications, Raymer says the technology offers other advantages. For one, there is the environmental benefit of using nitrogen more efficiently.

In addition, he says the system can map crop vigour during fungicide or herbicide applications. “The grower is actually seeing an overview of the health of his crop,” notes Raymer. “He can see that variability and see the opportunity to address that crop and vary the proportions. Or, he can go take a look at a specific area of the field and see that there is a certain emerging issue to diagnose such as spider mite infestations.”

As for the payback of the GreenSeeker, Raymer conservatively estimates the savings at $15 per acre for corn and $20 for wheat, depending on the price of fertilizer. Late in 2010, Raymer states that the technology “would have paid for itself” after being used on 1500 acres, “with 2000 acres at most.”

The top-end system with six sensors costs approximately $22,000.

As N prices rise, farmers are showing more interest in splitting the N applications to boost their profits. Tim Danberry, an agronomist with the Crystal Valley Co-op in Janesville, Minnesota, says farmers can earn an extra $20 per acre by using the GreenSeeker systems for variable-rate sidedress N applications on corn. “The growers we’ve got currently using the program will put on a reduced amount of N in the fall, knowing that we’re coming back with the GreenSeeker program,” says Danberry. “We’ll put down 130 pounds and follow up with a GreenSeeker application of anywhere between from two gallons to 15 gallons at 28-0-0 per acre.”

Danberry adds that yield response was particularly good this past year. It was another wet year in parts of Minnesota, where Danberry says some areas received 11 inches of rain in August. “So, N loss was pretty drastic. But on a few trials we had this year, we saw a 15 to 20 bu/ac advantage (on corn) with the Green-Seeker program.”

And the technology appears to be catching on with members of the Crystal Valley Co-op. After starting with just one system in 2008, Danberry says 10 systems will be available in 2011 to meet a growing demand by farmers to get the most from their N applications


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