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Approach field, prescription in hand

As Jeff, a hypothetical farmer, starts planning for spring seeding, he is considering variable rate applications, and would like to plug a “field prescription” into the tractor’s rate controller, sit back and see what happens.

May 1, 2009  By John Dietz

As Jeff, a hypothetical farmer, starts planning for spring seeding, he is considering variable rate applications, and would like to plug a “field prescription” into the tractor’s rate controller, sit back and see what happens. But getting all the components and prescription working takes a lot of planning, and consideration.

Ground-truthing data helps ensure prescriptions are required.
Photo by Bruce Barker.

Terry Aberhart, of Langenberg, Saskatchewan, writes his own field nutrient prescriptions for about 10,000 acres of current crop production on the family farm. He also is an agri-coach for Agri-Trend Agrology Ltd. Aberhart, together with senior geo-coach, Warren Bills, developed the Precision Management Process employed by Agri-Trend for developing field prescriptions.

Aberhart says that Jeff should probably have an agronomist-consultant to help set up his first field prescription, if he needs one and if he is ready for it, then, he will need to choose the approach.


Minimum ‘hardware’ requirements for producing a variable rate prescription map include a digital map of targeted fields and a controller that is capable of changing application rates on the fly. Of course, the air seeder, air drill, planter or sprayer also has to be plumbed for it. And, all the components need to talk in digital or electronic signals they understand. “The most important thing to look at is service support,” Aberhart says. “If you buy from somebody who doesn’t have the ability to come out and help you get going, it’s not worth much. It doesn’t matter who made it. You need good support all the way through.”

Whether Jeff needs a field prescription is another matter, Aberhart says. “The concept behind precision farming with variable rate is great, to put things where they’re needed, but it still has to make agronomic and economic sense,” he says.
It is not always or only nitrogen that will make the most sense. Drainage, soil type, pH, micro-nutrients, even weed or disease pressure need to be considered. In the end, carefully working through all these factors will give a sustainable precision management solution.
Fields that have big problems usually give a quick payback. But, a big problem may not be a nutrient problem or something to solve with a prescription map. “There’s no point in putting $20,000 into variable rate capacity if you don’t need it, so I prefer to first figure out the driving agronomic variables that are most limiting to yield,” Aberhart says. “Working through each field prescription is a process. One can be short, another can be longer. You can invest a lot of money in variable rate and find out you didn’t get the result you wanted. It’s no different than trying out new seed or a new chemical.”

Aberhart has gradually brought his own fields into prescription farming, but not all of them. It has been a gradual process, with benchmarks for later reference. He also varies the approaches, for instance, he has a large field with 10 years of yield maps, plus aerial and satellite images. He has done soil tests with a plan to divide it into management zones, and been forced to take a second look. “We came back with soil tests that were all the same. So, then we needed to go to a sector approach on that field,” he says. “If Jeff wanted to do the whole farm for this spring, I’d suggest he take a bit more time to develop a solid strategy to put behind the prescriptions. He should leave out some fields, just to quantify the results later. I prefer to get one prescription working well, then apply the strategy to more of the farm with some confidence.”

Aberhart developed his own approach, thanks to a background in soil science, plant science and computer technology, but Jeff will need help. It is open territory here; there is no standardized federal or provincial licensing or associations.

Common to any field prescription, is some analysis of the history, the present condition and desired outcome. The analysis can come from using digital records of crop yields, from soil maps, from topographical maps, from aerial photos and from satellite photos. Soil testing is an absolute requirement, and ground-truth visits may be required, as well. Jeff or his advisor needs software to ‘crunch’ the information and a plan for the 2009 crop along with crop inputs. Jeff can do a little shopping at this point, for the advisor and approach he prefers. He may want the ‘ultimate’ package, something like six zones to each field, with three depths in each zone, varying four nutrients and utilizing satellite imagery along with his own maps. He could take it one step further, if money is not an issue, and go to soil testing on a five-acre sector basis or even a grid if he grows potatoes.

Alternatively, he could take a less intensive approach, perhaps offered through a local farm supply centre.

For instance, Echelon is an agronomic consulting company based in southeast Saskatchewan. Echelon integrates satellite photos, soil testing and InSite VRN (Variable Rate Nutrient) software to produce prescriptions, along with services such as crop planning and integrated pest management.

InSite VRN is supplied by Mosaic, representing fertilizer industry leaders IMC Global and Cargill Crop Nutrition. InSite VRN develops a detailed prescription for each field that incorporates variable yield goals, pre-plant fertility levels and measures for organic-nitrogen, manure nitrogen, legume nitrogen, and for nitrates in irrigation water.

Rather than zones or grids, Echelon uses a minimum set of ‘constant’ soil test sites in each field for determining nutrient levels. It avoids the extreme areas, finding instead the middle-ground or average sites for testing. Samples are collected from the identical sites each year.

Echelon links the soil test results with data on an infrared satellite image taken at close to the peak biomass, usually the first week in July. The variability in that digital image, along with the farmer’s own field knowledge, enables an Echelon agronomist to tailor fertilizer rates across the field. “It’s a much less labour-intensive way to manage low yielding areas,” says Regan Miller, Echelon consultant in Carlyle, Saskatchewan. “Two low yielding areas can have totally different soil properties, but we still give them the nutrients they need to grow a 15 bushel crop.”

A third approach is represented by Farmers Edge Precision Consulting. Wade Barnes, president and CEO, started Farmers Edge at Pilot Mound, Manitoba, in 2005 at age 30 and has built it into an international business with a staff of 18 in offices across the Prairies. His consultants handled about 700,000 acres in 2008. Farmers Edge also uses a range of possible data sources. The mix includes satellite images, soil tests and ground-truthing visits, plus yield maps and field history along with software analysis to produce prescription maps that are ready to plug into a rate controller.
Ultimately, it takes a lot of diagnostic work to understand field problems and write the prescription that really improves field performance. Aberhart concludes, “The most important thing is to verify your data and results.”


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