nitrification
(noun)
 the conversion of ammonium into nitrites (NO2−) by nitrifying bacteria
Examples of nitrification in the following topics:
- 
The Nitrogen Cycle- This process occurs in three steps in terrestrial systems: ammonification, nitrification, and denitrification.
- Second, the ammonium is converted to nitrites (NO2−) by nitrifying bacteria, such as Nitrosomonas, through nitrification.
- A similar process occurs in the marine nitrogen cycle, where the ammonification, nitrification, and denitrification processes are performed by marine bacteria.
 
- 
The Role of Prokaryotes in Ecosystems- Nitrification is the conversion of ammonium to nitrite and nitrate.
- Nitrification in soils is carried out by bacteria belonging to the genera Nitrosomas, Nitrobacter, and Nitrospira.