When it comes to navigating through your crop, how accurate is accurate enough? It wasn’t so long ago that farmers scoffed at autosteer, saying “straight-ish” was straight enough. Now, as some producers are realizing the benefits of inter-row seeding and as soil compaction is becoming a more mainstream concern, controlled traffic farming and accurate-to-the-inch navigation are gaining attention.
Why it matters: As soil compaction moves into the spotlight, controlled traffic farming and accurate-to-the-inch navigation continue to garner attention, however, costs for RTK technology remain high — about $9,000 to install a base station or $1,500 per year for a subscription service.
The technology in typical GPS receivers has improved to the point that it can accurately identify positioning to within two to three feet — perfect if you’re looking for a coffee shop in an unfamiliar town, but not so good if you’re trying to lay seed alongside last year’s stalks.
To improve positioning accuracy, a GPS signal needs to compute corrections based on a known position. WAAS, a free, publicly available, U.S.-based system, bounces signals off other satellites to triangulate rough corrections, improving GPS accuracy to inches.
That said, both GPS and WAAS offer limited repeatability due to satellite drift.
“Without RTK (real-time kinematic technology), the line you set in spring is going to drift over time,” says Jesse Larson, manager at Prairie Precision Network. “A free service’s repeatability is only pass to pass. This means you can only go back to your previous location, plus or minus the range of accuracy your service is capable of, within a time frame of 15 minutes — there are no guarantees made beyond that.”
To solve the repeatability issue, different providers now offer various, subscription-based positioning services that achieve “limited repeatability.”
“Trimble has Centrepoint RTX. John Deere has SF3. That level of limited repeatability might offer controlled traffic through one season, but if you come back the next season it probably won’t work,” says Larson. “If you’re trying to do true controlled traffic farming, where you’re driving on the same wheel tracks each year, you need a service like RTK to put you in exactly the same spot in a field year after year.”
RTK technology, which uses a series of fixed base stations to compute corrections, is the only technology currently available that offers farmers ultra-precise, multi-year positioning guidance.
Cost and requirements
While RTK technology is incredibly accurate, it is not cheap.
RTK first requires building or accessing a base station. Manitoba producer and president and researcher at Agritruth Research, Adam Gurr, estimates he spent between $8,000 and $9,000 to install a basic base station.
“The station itself isn’t fancy — we just stuck it on a bin. And then antennas and wiring were cheap, maybe another $100,” he says. “We didn’t need it to look impressive; it just needs to work.”
Farmers who would prefer not to install their own base stations can instead purchase subscription-based access to a corporate-owned base station. Costs for subscription vary depending on the service offered. Prairie Precision Network’s RTK subscription, for example, costs $1,500 per year.
RTK next requires the on-board technology to send and receive and then act on positioning signals. Typically, this is cellular modem-based hardware that requires a one-time activation fee.
“We paid a one-time fee of $2,000 per receiver to unlock the RTK capacity, so a total of $8,000 for four receivers,” says Gurr.
With the exception of certain proprietary signals (specifically John Deere’s), activations follow the hardware and can be shared between multiple pieces of equipment. As such, a producer can generally transfer the hardware from seeder to sprayer to combine as the season progresses, for example.
In addition to activation, RTK also requires a cellular plan for the modem.
While most of today’s equipment is RTK-ready, retrofitting older equipment typically costs in the range of $10,000 per machine.
Gurr has been pleased with the technology’s functionality. Though early RTK base stations had frustrating limitations, especially in hilly landscapes, the technology he is using has proven very reliable.
“RTK used to need line-of-sight, but they’ve made it better recently, so if you lose your RTK signal, it’ll switch to a subscription signal just briefly. It allows you 20 minutes or so to reacquire your signal,” says Gurr. “We’re probably within about 10 miles of our tower at all times. We’ve had no issues with signal in any of our fields.”
While RTK’s functionality is impressive, its price remains a significant deterrent for many Prairie producers.
“If you’re in British Columbia or Ontario, where you depend on repeatability in high-value crops, controlled traffic farming is huge. RTK has much slower uptake on the Prairies,” says Larson.
“RTK used to be sold as a way to reduce overlap and save inputs. But now, instead of setting your machine for three feet of overlap, an intermediate service lets you set your overlap to an inch. That’s good enough for most Prairie producers.”
That said, if you truly want to minimize soil compaction, says Larson, “that’s when you need RTK.”