Angels, there are some quite sophisticated uses of GPS in farming now.
For one example, found after a quick Google , see
FarmerGPS - Welcome! (or .com). Or do a search of your own if that interested.
I am not an expert. But while doing a survey on fertiliser usage with some local farmers, I encountered one who described his system (not the one in the reference above).
He used a company which sent an ATV over every field, taking soil samples at every 10 metre point, showing soil composition and characteristics. The system then plotted a “contour” map of the field, showing which parts were chalky, which not, which low on (e.g.) nitrogen etc. If you know nothing about farming, you would be amazed at how much it varies over a field, let alone from one to the next. Certainly true in East Anglia UK, and probably lots of other UK places, where the geology and microclimate changes a lot from one place to another.
The fertiliser typically comes in 3 parts, N, P and K. Instead of spreading a mixture with averaged proportions, each was spread by different spreaders on a GPS-controlled machine, using the survey data. The farmer told me it was fascinating to see one spreader wheel slowing down and another speeding up as it reached a bit low on P and high in K etc. Overall, it reduced the total usage and net cost of fertilising.
Other uses of GPS include semi-automatic combine harvester operation.
These and other things require reasonably high positional accuracy from the GPS.
If GPS were stopped, going back to old methods would be challenging, I suspect.
Chris N.
PS – At
Precision Farming Tools: Global Positioning System (GPS) - Virginia Cooperative Extension there is what seems an excellent article on GPS, accuracy, etc. – intended for farming but the general descriptions look good to me.