nitrogen cycle

ionisation

processes such as lightning and meteor trails provide the energy for atmospheric nitrogen and oxygen to react and produce oxides of nitrogen

fixation

some micro organisms can chemically reduce nitrogen to ammonia

they can be free living in soil bacteria or live symbiotically in root nodules of legumes

food chains

nitrogen passes between organisms as amino acids and proteins in food

nitrification

involves the oxidation of ammonium ions to nitrites then to nitrates by nitrifying bacteria in the soil

denitrification

the chemical reduction of nitrates in soil to nitrogen and nitrogen oxide gases by denitrifying bacteria in the soil reducing soil fertility

occurs under anaerobic conditions

leaching

high solubility of nitrates means they are easily leaches out of soils into water bodies where they act as nutrients of aquatic plants and algae

root absorption

plants absorb nitrogen as soluble ions mainly as nitrates but also as ammonium ions

ammonification.

the amino groups in proteins are released as ammonium ions by the action of bacteria, fungi and detritivores as they decompose dead organic matter