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. Microbiology and ecology The oxidation of ammonium into nitrite is performed by two groups of organisms, ammonia oxidizing bacteria… (More on Nitrification)