I did a plot this year in combination with a PHI C-Pro plot.  We planted four different varieties at two populations.  34,000 & 38,000 per acre.  There was 150-0-0 preplant NH3 spring applied.  The rows were planted north south, 1/2 mile plus long.  We then tilled paths across the rows to give us four equal sized portions of the field. On the first and third blocks I applied an additional 50-0-0 of 32% at normal sidedress time.  On the second and fourth blocks we did a Y- drop pass with 50-0-0 pre tassel.  This field has been corn on corn for nearly ten years.  The plot area has been in C-Pro plots for the last three or four years, usually with four hybrids at four populations.  No fertility differences.  The plot usually does between 180-260 bpa depending on the variable.  Unfortunately the whole farm doesn't always do that well, but the plot area is very consistent.  

This year there was no statistical difference between any of the hybrids in regard to either nitrogen treatment regardless of population.  We just didn't have enough big rains to cause nitrogen loss this year and this ground holds nitrogen pretty well.  Normally I apply fall NH3, but didn't get it done last fall due to time constraints.  Fall application is still my favorite on a lot of the ground I farm.  I still think the best nitrogen application timing  is determined by the weather during the season.  It's not possible to guarantee that a late application will pay.  Some years it will pay huge dividends, but not this year, on this farm.