If the dark green is the result of excess overlap, then it shows more N is needed across the board, especially if it shows up on the yield maps.  The interesting part is fertilizer is a lot like feeding cattle; if you limit feed a group of cattle (fertilize) so they clean up the bunk every day, some of the pushier ones get more feed (excess overlap) while others get shorted on feed (low rate) and thus take longer to finish.  The trouble is when you ship the entire pen (harvest) at the same time they they are not uniform, some 1600# and others are 1200#.  You could hold the lighter ones back and feed them more until they get to 1600# and ship them and this will take more feed.  Now the interesting part, is if you feed enough that they never clean up the bunks the group will be more uniform and when you ship them at 1400# you will have fed the pen the same amount of feed and produced the same pounds of beef as the 1200-1600# limit fed group (the pushed 1400# groupl may be slightly more simply because of less days on feed making them more efficeint)   So while the field is streaked, total field yield is likely the same since the amount of fertiziler remained the same and the streaking mere exposed there is a lot more potential for the field.