I would give UTILIZE a try if you're trying to increase yields.  It's less than applying all that N (unless of course you're that deficient in N... whole 'nother story there) and it is a foliar nutirent applied in the R1 - R5 range. It's a Helena product and it is specifically formulated to increase yields and plant health.

Cost is minimal (check w/ rep.) compared to 25# of N, rate is 8oz to the acre, and the average yields have been around 4 bu/ac.

Just a thought...

http://magissues.farmprogress.com/STF/SF05May11/stf007.pdf

http://www.cdms.net/LDat/ld9ML002.pdf