various bacteria called nitrification and de-nitrification bacteria

One method to stop nitrification is to use nitrification inhibitors, such as dicyandiamide (DCD) or nitrapyrin, which can help to slow down the conversion of ammonium to nitrate by inhibiting the activity of nitrifying bacteria. Another approach is to minimize the application of nitrogen-containing fertilizers to reduce the amount of ammonium available for nitrification. Improving soil drainage and aeration can also help reduce nitrification rates in waterlogged conditions.

The first step in nitrification is the conversion of ammonia (NH3) to nitrite (NO2-) by ammonia-oxidizing bacteria (AOB).

nitrification

nitrification