1) The more I think about it,  the more I see the value in having that check plot with no poultry manure.  It would really have shown how much "available" N (or should I say "utilizable N?)  you were getting.

2) Why mix red clover with crimson clover?  The only reason I could see is if seed supply is limited.  If you take your numbers at face value - and that is questionable at this point - you got a 38 bu/ac yield response from using crimson clover versus using red clover.  Even if the red clover was free - and the drilling was free- I could still afford to buy the crimson clover.   (of course,  I really don't think there is that much difference between the red clover and the crimson, but that is what your plot shows.)