Citric acid and ammonium nitrate
Ammonium nitrate is very soluble in water, so watering the soil will remove it, though, depending on the amount and dilution, it could then pollute streams, lakes and other bodies of water, possibly causing an algae bloom. 

Your best choice might be to experiment with nitrate-tolerant plants, such as lettuce, ornamental cabbage and rhubarb, or perhaps bell peppers.

Citric acid will not help in any way, and would make the soil less likely to support life.

In nature, denitrifying bacteria will slowly reduce the $\ce{NH4NO3}$. In an anaerobic environment, it might be converted to $\ce{NH4+}$.