Here is an interesting question. What fraction of the organic nitrogen in your body is ultimately from the Haber-Bosch Process? Any guesses? This question arose during dinner discussion following a rousing seminar on frustrated Lewis pairs. There is no connection to frustrated Lewis pairs, but the speaker raised the question.
Oh, I don’t have an answer. This happens in science. I’m guessing ~50 %, depending on the extent of protein containing corn products consumed. Any meat science people out there?
Lamentations on Chemistry 
What fraction of ingested organic nitrogen traces back to fertilized agriculture? Nearly 100% of grain (no soy, easy on the beans), maybe 80% of meat (corn-fed; is hay fertiliized?). Fish are farmed with rejected grain and meat. Wild fish trace back to plankton loving farm run-off. 70% of my organic nitrogen may qualify, plus NOx air pollution fertilization.
What percentage of nitrogen in the plants is taken in from Haber-Bosch processed nitrogen vs. other sources?
I also thought shortly about it from a different perspective: the existence of a nitrogen cycle proposes that eventually all nitogen will find itself being rended inside a reactor, but the numbers quickly became huge:
Wikipedia states that 100 x 10^6 tons of fertilizer are produced each year as NH3, NH4NO3 and N2CCOCN2. Not having a specific breakdown, assume 33.3% of each. Nitrogen then makes up 54.7% of that total. The mass of the earth’s atmosphere is 5 * 10^15 tonnes, of which 78% is nitrogen. There’s about 8-9 orders of magnitude difference, and that is not even including what is sequestered in existing vegitation. So it will be a while until we have reacted them all. In hind sight, it should have been obvious as no one is concerned about the process significanly modifying the make up of the atmosphere.