Nitrogen cycle
Nitrification is the oxidation of ammonia and ammonium to nitrite (NO2−) and then to nitrate (NO3−) by bacteria. Because nitrite and nitrate have a negative charge they do not easily join to soil and will wash out of the soil during rain and irrigation.  High nitrate levels in drinking water are harmful for babies and can cause blue-baby syndrome.   High nitrate levels can also cause too much algae growth in lakes and pools.  This eutrophication can be harmful to fish and other water animals.  The use of fertilizers is controlled because of this.