Do you have to verify the additional yield ? I'm a new business and they wouldn't accept historic yields as its a sewers the business@Turra farmer in an NVZ N-max is 180kg for standard yield of 6.5t/ha, then 20kgN per tonne of yield above that. So N-max for a 9t crop is 230kg.
So it's quite legal to push the N and the yield. Just a matter of keeping it standing up!
As you say, lower straw yields on spring barley. Between 4 and 8 x 200kg bales per acre here, 6.5 bales would be about the norm for a 2.9t crop. All goes to pot if we get either drought or waterlogging.