There are a lot of questions and arguments floating about which signal level you should be on for your operations. In general, there are 3 signal levels. Free(WAAS, SF1) +/- 8″ Pass to Pass, Paid Subscription Via Satellite(SF2, OmniStar, Excludes Trimble RTx) +/-2″ or 4″ Pass to Pass, and RTK <1″ all the time. Now, there are multiple different ways to get RTK corrections but it should all represent close to the same accuracy. Everyone is the same, I want the most bang for my buck. But, can you really save money by staying with the Free service when you should really have the Paid Subscription?
Lets breakdown what the operations should be for each system.
- Broad application
Subscription Via Satellite
- Application Control (Shut Offs, Prescriptions)
- Repeatable Operations (Strip tilling, Planting, Sideressing for example)
Most people realize when they are in need of RTK. It is enough of a jump that there isn’t much gray area between Subscription and RTK. If you need to repeatedly run the same lines year in and out, multiple times a year you NEED RTK. What some people don’t realize though is there are other ways of justifying the cost of going to RTK. Take for example the planter in my picture at the top of the page. Notice that there aren’t any markers? We bought that planter in 2006. How many people do you know that would buy a planter without markers in 2006? I’m guessing you are calling us crazy at this moment. We weighed our options. It was $16000 option for markers on that planter or we could go to RTK and get section control for the planter for $23000 and not have the added stress of the markers on the planter frame. It was a no brainer. We just swapped one guidance system for the other, that will get used in multiple applications through the year and provide us with very reliable service. Its options like that one that makes getting to RTK easier.
Now for the meat of this discussion. Free Vs. Subscription. I have many people a year in my office asking if they can get buy with just the free signal. Each time its a loaded question and I end up asking them more questions than they had for me. I’ll break this out in guidance vs. application control.
The guidance aspect is an easy one. Both of those services will drive you in a straight line. The question is will you play close attention to the guess row? I tell them if they are willing to drop the marker each time and doesn’t mind constantly hitting the shift line button you can get by with the Free signal. But they have to be paying very close attention to it. The Subscription service relieves this but still needs to be paid attention to. You might not have to drop your markers because it is going to be hard to notice the small shifts the line makes. Overnight there is still a chance for a large line shift, so you have to be prepared for that.
Application control is the deciding factor in what signal level you should be, and it is NOT the Free service. The Free signal drifts way too much to allow application control to work the way it should. I’m not just talking shutoffs, I’m also talking about your prescriptions that you worked hard to get just right. If the signal has the ability to drift 6″ – 8″ every 15 mins (the definition of Pass to Pass Accuracy) and it takes you 2 hours to plant a field you could be off 4 ft in either direction. That could be 4ft of skip, or 4ft of Overlap. And if you don’t finish the field in the same day, you might as well just shut it off and go back to manual.
For any application control, you HAVE to be on the Subscription service at minimum to get your money out of what you paid to have application control put on. At this point you have made the commitment to save and make money with application control, don’t jeopardize it by not using the accuracy level you should be.
Lets put some numbers to this. Lets say you have 160 acre square field (hypothetical of course) Which is 2640 ft x 2640 ft. Your end rows get offset by 4 ft. Which means you will overlap 4ft one way, skip 4ft the other. You have a 40′ planter. 2640 / 40 = 66 passes. Half of those are skip, half are overlap, but because you have 2 ends to the field you can figure you have 66 skips, and 66 overlaps. You are planting corn at $300/bag, 34,000 Pop. averaging 175 Bu/Ac.
The skips account for lost yield. So you have:
- 66 passes x 40 ft = 2640 ft * 4ft skip = 10,560 sq. ft of skip.
- 10,560 sq. ft./43560 sq. ft/ac = .24 ac.
- .24 ac * 175 bu = 42.4 bu.
- 42.4 bu. x $6/bu = $254 in lost yield revenue, or $1.5/ ac.
Using the same .24 acre for overlap, you have extra seed cost, and yield loss due to over plant.
- .24 ac x 34000 pop = 8160 seeds / 80000 sds/bag = .102 bags extra.
- .102 x $300 = $30.6.
Yield loss is arguable. I use 30% yeild loss due to overplant, although I really think it can be much higher by looking at my yield maps.
- 175 bu/ac x 30% loss = 52.5 bu/ac loss.
- 52.5 * .24 = 12.6 bu loss
- 12.6 * $6 = $60 loss revenue
So for the overlap you are looking at a total of $90.5 loss, or $.56/ acre. Bringing our total loss/ac to $2.06. Say you had 1600 acres of corn, that could mean a loss of $3296. I hear you saying well that doesn’t cover the cost of going up a level in accuracy, and you are right, for the first year. But the second year you could have the upgrade cost saved, and then all you are working against is an $800/yr subscription.
Would you spend $800 to save $3200? And this was only figuring one operation. Would be more by the time you add spraying and fertilizing in. Land prices are expensive. We are all looking for that little bit that helps. By all means, this number could be more than it really is, or it could be less than what could happen if we have a really wacky GPS year. Just remember every time you have to shift your line, your previous coverage has moved as well.