@MB
I would grab a multi-meter and after about a week or so of not using the tractor (if it stays parked up that long) and when the panel is in full sun just check the battery terminal voltage.
If it is between 12.6 to 13.4 max (ideally 12.7 to 13.1) and around 12.9 is perfect.
The aim of what you are doing is to stop the battery sulphating which means the voltage has to be held above 12.4 ish
The by product of that aim is that it also means at least an almost full capacity battery.