If you read the take home messages section it states clearly there that the soil already had quote " very high nitrogen reserve [ 359 kg N / Ha to 60cm ] " so they were not unfertilised as you put it....they had no added fertiliser...... a big difference.
79 days I believe is based on the Zadoks scale which represents the growth stages of a wheat plant....at~79 days any heads that are going to appear are there. IMO the reason for the cut off.
25% seem to be the mortality rate for Qld at least. 90% germination with 75% survival. See below.
DB
