Plants use nitrogen in fertilizers for growth. However, much of the nitrogen goes unused. What is one direct outcome of this excess nitrogen?

There are many environmental negative direct outcomes of unused excess nitrogen from nitrogenous fertilizers. One of these is eutrophication. Eutrophication is the excessive richness of nutrients in a water body as a result of fertilizer run offs from the land, which causes a dense growth of plants in the water. Other negative outcomes are: green house effects, acid rain and contamination of underground water which has negative effects on human health.