Decomposers' role in the nitrogen cycle is to recycle nitrogen by turning it into ammonia. The ammonia is returned to the soil, allowing the nitrogen cycle to start over again. A small amount of the nitrogen is returned to the atmosphere in this step.
The nitrogen cycle is a five-step process that produces a fixed form of nitrogen. Organisms use this form of nitrogen to produce amino acids. During the first step, nitrogen-fixing bacteria take in nitrogen from the atmosphere and use it to produce ammonia. Other bacterial organisms use the ammonia to produce compounds called nitrates and nitrites. These compounds contain oxygen and nitrogen.
Plants use the nitrates and nitrites to produce amino acids. When herbivores and omnivores eat plants, they use the amino acids in the plants to make their own amino acids. These compounds are the building blocks of proteins. Decomposers then convert the nitrogen in dead or decaying organisms into ammonia. Denitrifying bacteria participate in an opposing process called denitrification. These bacterial organisms reduce nitrate to nitrogen gas, releasing the gas back into the atmosphere.
The nitrogen cycle is essential for life because most organisms cannot use atmospheric nitrogen. This cycle makes nitrogen available to plants in the form of ammonium ions, nitrate ions and urea. Then animals get the nitrogen they need by eating plants or feeding on organisms that eat plants.