I have been tracking two fields of corn this year using data loggers to collect air and soil temperatures. One field was soybeans last year that was tilled last fall and again this spring, the other field was soybeans last year also, but a rye cover crop was no-tilled into the soybean stubble last fall. This field has been continious no-till for over twenty years, and is under irrigation.
 I just got done making a model for each field using the soil temperatures up to 6 collars, then air temperatures thereafter to calculate the gdd's. From the time of one day after planting to 8/1 the tilled field acumulated 1618 gdd's, and the field that was no-tilled into green rye has acumulated 1586 gdd's. Since the no-till was planted about 1.5 days earlier, i would say its about 2 - 3 days behind in maturity.
 I will post some more updates on what i observed during the growing season, and try to explain the possable reasons for what i saw.