When animals and plants die the nitrogenous biochemicals or nitrogen compounds are decomposed into the soil on land or into ocean water.
The nitrogen compounds are decomposed by fungi and bacteria, depositing ammonium ions in the soil, which are then absorbed by plants and incorporated into the nitrogen cycle back through the ecosystem. After the decaying and decomposing process, the bacteria and fungi convert nitrogen into form that plants are able to use, other types change nitrogen dissolved in water environment into a form that allows it to return it to the atmosphere.
