http://www.precisiontillage.com/assets/uploads/Root%20growth_temp_important2007.pdf
When strip-tillage has occurred in the late-fall or early winter
exposing the soil surface to radiant heat from the sun and moving residue off to the side between the row,
soil temperatures climb 4 to 9°F compared to what is under the residues and sometimes 1 to 5°F warmer
than conventional tilled ground.
Here is my spin. In the conventionally tilled the suns radiation is spread across the whole soil surface but in the strip-till most of it is reflected by the surface residue. Is it possible that the bare strip is getting a little more radiation besides what is directly hitting it, by some refected by the residue heating the strip even more?