I am wondering the same thing about why the strip is warmer than the coventional tilled ground. As you can see in the following charts the low temperatures between the two treatments are not that much different. One possible reason  is the way i had the loggers set up. Back then i had them set up to record every hour so there could have been higher temperatures in between that were higher.

 The other possibility was the the crop rotation on the field that was strip tilled. Up to 2002 it had been in alfalfa for a few years. Then in the fall of 2002 the alfalfa was terminated, then was planted to winter rye. We harvested the rye in 2003 for grain.
 I can`t remember the moisture conditions for the winter of 2003-2004, but i am thinking that since there was alfalfa in the rotation that the soil profile was short of moisture thus the reason for the higher soil temperatures.
 The conventional tilled field i think had soybeans or spring wheat as the previous crop. The reason i said "i think" because it was farmed by another party. 
 Thats all that i can think of for now, but will do more research and try to come up with some more spin.

(strip till 2004 3.jpg)

(strip till 2004 4.jpg)

strip till 2004 3.jpg (30KB - 54 downloads)

strip till 2004 4.jpg (30KB - 52 downloads)