If you get a chance to do some testing (frost depth, soil temps ect) if you can, report back with what you find out.
 I did some tests this AM and this what i found out.
 I went out in some ground that was soybeans last year, it was worked last fall so it was pretty bare. I found the frost  layer at 18.75 inches.  The soil temp at 10:30 AM was 48.6 F and 61 F at 2:40 PM. That situation reminds me of a previous post about planting corn when there is frost in the ground.  http://talk.newagtalk.com/forums/thread-view.asp?tid=469093&posts=10&highlight=frost&highlightmode=1#M3812380

 I also tested some spring wheat stubble that was still standing, it caught some snow this winter. I got the rod pushed down to 42"  so i am thinking the frost is gone in this field. I got the temp probe down to 27" and temp at that level was 37.4 degrees F. I will try to get the temp probe down further tomorrow to see what the temp is down lower.