What would put the nitrogen cycle out of balance?

Question

how could the nitrogen cylce be put out of balance, n dnt say it already is lets just assume is isnt n give me n answer

Answer 1

As Dalton's law would say, every gas for itself.  If N2 were in deficiency then it would just be replaced by other gases such as O2 and CO2.  If there is too much N2, then there could be a problem, at least for us,  

Answer 2

kill all plants.

but that has undesirable side effects.

Answer 3

nitrogen fixing bacterias