The oxygen is of interest if you want to run a nearby gasifier. The other choices are building in an industrial area where you will find existing air separation plants and thusly no need for more capacity. If you build in a rural area you'll end up with an air separation plant and no customers.

  Ammonia is made first and urea is evolved from it, as are ammonium nitrate and other, less common compounds used for fertilization.

  A national recycling/composting effort would help but this is really a mass balance problem - something like two thirds of all humans alive are here because we learned to synthesize ammonia so if we stop that process not long after we have a disaster.