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10:23 dl © BW - QR lll 138%8, A wo ww 6, , The nitrogen cycle is the biogeochemical cycle by, which nitrogen is converted into multiple chemical, forms as it circulates among 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 atmospheric nitrogen,!"4, 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., , Reactive Nitrogen, , , , Global cycling of reactive nitrogen! including industrial fertilizer, production,! nitrogen fixed by natural ecosystems,!! nitrogen, fixed by oceans,! nitrogen fixed by agricultural crops,!5] Nox, emitted by biomass burning, Nox emitted from soil,!7] nitrogen, fixed by lightning,8] NH3 emitted by terrestrial ecosystems,!9!, deposition of nitrogen to terrestrial surfaces and oceans,!1ll11], NH3 emitted from oceans,!"2II31[11] ocean NO2 emissions from, the atmosphere,!4! denitrification in oceans, 4ll"5II"l and reactive, nitrogen burial in oceans.!l, , II O <