Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online.Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. Degradation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil. This process was discovered by the Russian microbiologist, Sergei Winogradsky.The oxidation of ammonium into nitrite is performed by two groups of organisms, ammonia oxidizing bacteria and ammonia oxidizing archaea. Ammonia oxidizing bacteria can be found among the Î²- and Î³-proteobacteria. In soils the most studied ammonia oxidizing bacteria belong to the genera Nitrosomonas and Nitrosococcus.