It might be limited slip or open. It should be in your tractor specs. Its almost surely not a posi-locker cuz that would really hamper turning.
The worst case for motive force would be the open diff because its limit is 2x the force delivered by the wheel with least traction. If one wheels on ice its almost like both are.
A limited slip is better, sending more torque to the wheel with more traction.
A locker is like a solid axle. It forces both wheels to turn equally.
How Differentials Work | HowStuffWorks
My 7520 front is a Carraro limited slip. If one wheel has no traction it just spins like its an open diff. ... But if one has ~ 20 or 30% of what the other has they both will spin.
I'm quite sure my tractor has open front end, when ever one wheel comes off the ground that one spins and usually have to lock the rears in, it's really a 3 wheel drive.