[Stampeder]

Where I come originally up in Canada, it's always wet in the spring on the hay fields. The big problem isn't flotation of your tires it's the suction caused by the R4 tires in the mud. Ag. tires are better than R4's in the application you're talking about for this very reason. Because they are thinner they tend to get stuck due to the suction effect and they have deaper lugs to promote better traction in the mud.
You might want to consult an Ag. tire dealer and check this out.
Good luck with your haying. Incidently, I'm doing the same thing right now here in East Texas.....and got my tractor stuck up to the door bottom the other day. It took a big backhoe to get me out.

Cheers.
Glenn.