Your local fuel distributor knows best.
Let's see. Somewhere in the owners manual for the tractor it has a blurb about acceptable fuel. The most common being #2 diesel fuel oil (on or off-road) Your home heating oil is usually #2 (diesel) fuel oil. Colder climates get #1 fuel oils. LSD is Low Sulphur Diesel, ULSD is Ultra Low Sulphur Diesel.
#2 diesel does not get red-dye added, and is now getting more sulphur (lubricant) removed. #2 diesel also has more additives to make it burn "cleaner" and a lower ash content. Supposedly, by removing more of the sulphur, it is making it more environmentally safe (and produce less smoke)
#2 fuel oil can have a higher ash count, more sulphur and burn "dirtier". Part of this helps explain why your "oil burner" needs to have the flue and firebox cleaned on a regular basis.
Your tractor will happily use any of the above mentioned fuel oils and would accept JP-4, JP-5 or JP-8. If using a ULSD in an older tractor, it would be wise to use a lubricant additive. If not using the tractor regularly, keeping the tank topped off (less area for condensation to form) and adding Sta-bil doesn't hurt either.
Of course, you could just run it on peanut oil (with a couple additives). Or you could go the french fry route, WVO, waste vegetable oil but you gotta strain and triple filter it and then add stuff to it.
Bottom line - use whatever you feel comfortable with and fits your pocketbook best. None of it will make your tractor "blow up".
Did you have someone determine the lowest nozzle size useable or have you been replacing it with the same size the oil co. put in?
Typically, the oil co. service guys use the largest size so you'll burn more oil