<P> The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among the atmosphere , terrestrial , and marine ecosystems . The conversion of nitrogen can be carried out through both biological and physical processes . Important processes in the nitrogen cycle include fixation , ammonification , nitrification , and denitrification . The majority of Earth 's atmosphere ( 78 % ) is nitrogen , making it the largest source of nitrogen . However , atmospheric nitrogen has limited availability for biological use , leading to a scarcity of usable nitrogen in many types of ecosystems . The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes , including primary production and decomposition . Human activities such as fossil fuel combustion , use of artificial nitrogen fertilizers , and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle . </P>
<P> The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among the atmosphere , terrestrial , and marine ecosystems . The conversion of nitrogen can be carried out through both biological and physical processes . Important processes in the nitrogen cycle include fixation , ammonification , nitrification , and denitrification . The majority of Earth 's atmosphere ( 78 % ) is nitrogen , making it the largest source of nitrogen . However , atmospheric nitrogen has limited availability for biological use , leading to a scarcity of usable nitrogen in many types of ecosystems . The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes , including primary production and decomposition . Human activities such as fossil fuel combustion , use of artificial nitrogen fertilizers , and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle . </P>
what is the largest source of nitrogen on earth
what is the largest source of nitrogen on earth
Earth 's atmosphere
Earth 's atmosphere