The nitrogen cycle is important due to its role as a basis for the production of nitrogen that is essential to all forms of life. The atmosphere contains a vast majority of the natural nitrogen found on Earth.
The nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. Nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and DNA, the building blocks of all life. Plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. Animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter. Nitrogen is commonly converted back into inorganic material when it joins the biogeochemical cycle through decomposition. The nitrogen is then typically changed into ammonium ion by bacteria and fungi through a process called mineralization.
When ammonium enters the soil, it is bound to certain clay particles. The ammonium is then released from these particles by cation exchange. When the ammonium is released, its chemical properties are altered by special bacteria and allowed to be dispersed from the soil. The new form of nitrogen can then be transferred to oceans by the hydrologic system, where it is released back into the atmosphere after being converted into gas through the denitrification process.