1)  You are looking at one set of numbers from one plot with no replication.  How much does field variability factor in?  Lots I'd say.  It would be interesting to have a statitician look at the standard deviation to show where the real significant differences are.  (Maybe Greg Roth or his assistane Mark Antle could help with that?)

2) You seem to be using 100% of the poultry nitrogen being available.  Is that a realistic number? 

3) Looking at the N numbers, if you use 75 lb N from poultry litter, then 80 lb N coming from Crimson Clover.  That seems in line with what we expect. 

4) How much growth was on the oats?  Would that have an effect of the amount of N tie-up (as someone else suggested could be a cause) ?

5) How much growth did you have on that hairy vetch?  In light of the yield of the "no cover", I would have expect more from the hairy vetch.  How did it over-winter?  What was the size when you killed it?

6) I have to wonder what your numbers would look like if you had no-tilled those cover crops into fields harvested as corn silage.  I think I always see a yield response to planting corn into wheat stubble versus planting into corn stubble. In a year like this one, hopefully you would not have a lot of excess N in the soil after harvest, so your numbers would give a true(er) indication of what you would be getting from the manure and cover crops.

7) If you do this again, you should have a strip of "no manure, no cover", just for comparison. Enough for a yield check.  

I've read about Berseem clover years ago, and I remember that winter-kill could be a problem with it.  So we never got on that band-wagon. I've been impressed with the crimson clover we used so far.  I had some farmers plant some hairy vetch this fall for the first time.  We'll see how it works.  we'll evaluate next summer and then decide whether to push more clover, or vetch, or ????