Lucas, thanks for the information.
 I have a template made up to figure gdd`s on lotus 123, but i am going to try your formula to see if works better than what i got.
 As to the amount of residue in each treatment i didn`t think of measuring it, it is something i will have to for future projects. What is a good way to measure it, by depth or take a representative sample and weigh it?
 As to the ET, the site that i use wants you to start when the crop emerges, what i am wondering at the early stages what part of the ET is evaporation?
http://ndawn.ndsu.nodak.edu/crop-water-use-table-form.html
 I use the site at Britton,SD.
 I am going to try to figure the evaporation for the two treatments.

Mike