There are various methods for the production of nitrates from ammonia. One example is the Ostwald process.
Going the other way is not generally done, because nitric acid (and nitrates) are made industrially from ammonia - so producing ammonia by this method is pointless, you'd use the Haber process instead.
It is probably possible though, and can probably be achieved by catalytic hydrogenation (H2 over Pd, Pt etc.) but I don't have any evidence to back that up - nitroalkanes and related compounds are readily reduced to amines this way - just a hunch.