Alberta ag did a study on Nitrogen from feeding on fields, they came in about 50 pounds of actual N per acre.
I use manure on the field that I got 42 bushels on, but I have been learning more about the effects of raw or merely aged manure on land vs true compost.
I used to think my manure was composted, but I don't turn it enough and I am thinking it might be anerobic instead of aerobic.
Manure, even if aged, can be hard on microbes necessary to convert it to plant available form.
The seed treat I use is a mixture of seaweed and fish fertilizer. It won't burn the seed and is available all season. It seems to generate a beneficial area around the plant root that allows microbes to thrive. The science says bacteria and fungus in the right amounts will generate all the nutrients a crop needs. That is a 10 second overview of pages of biology. I am still experimenting, but I like the reduced risk.
Some systems use a 3 year strategy reducing fertilizer each year until no chemical fertilizer is applied, but I was dried out in 2003 with fertilizer and went cold turkey after that. I am looking at plow downs as an alternative if this doesn't sustain a reasonable yield, but at $8 inputs and $3.50 barley.... you do the math.