Several ways.....
but none as easy as having stem at 6 o'clock and giving it a little push.
Not trying to be smart ass - but you did ask, you can take the tire off the tractor, you will know quickly.
Another way is wait for a very humid morning after a cool night - the tire will actually sweat a bit, the water will condensate on the rubber skin.
Curious - why would you not just give a little push on the valve?