Dead organic matter ~ proteins, they release ammonium compounds as they decompose

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

Denitrification - chemical reduction of nitrates in soil to nitrogen gas and nitrogen oxide gases by dentrifying bacteria in soil, reduces soil fertility, occurs in anaerobic conditions

Root absorption - plants absorb nitrogen as soluble ions, mainly as nitrates but also ammonium ions

Nitrification - oxidation of ammonium ions to nitrites then to nitrates by nitrifying bacteria in soil

Leaching - high solubility of nitrates means they're easily leached out of soils into water bodies where they act as nutrients for aquatic plants and algae

Food chains - nitrogen passes between organisms as amino acids and proteins in food

Fixation - some micro-organisms can chemically reduce nitrogen to ammonia, can be bacteria in soil or in root nodules of legumes

Agriculture:

• use of nitrate fertilisers may increase leaching problems including eutrophication, espc if there's heavy rain or its close to a river
• drainage of fields makes soil more aerobic which increases nitrifying bacteria and decreases dentrifying bacteria
• ploughing disturbs soil which increases rate of decomposition of DOM releasing more nitrogen oxides into atmosphere
• leguminous plants e.g peas, beans and clover are grown to increase nitrogen levels in soil which crops then absorb

Pollution:

• oxides of nitrogen released into atmosphere by combustion so subsequently increase amount washed into soil by rain

Haber process:

• industrial process to form ammonia from nitrogen and hydrogen
• uses iron catalyst at high pressure and temperature
• uses lots of energy
• ammonia may be converted to nitrates
• main purpose is manufacture of agricultural fertilisers

Management of biological wastes:

• enzymes produced by bacteria remove amino groups which dissolves ammonium ions, can be useful or cause issues

Organic fertilisers:

• wastes such as manure, sewage and food production waste used as organic fertilisers to increase nutrient and humus levels
• may be ploughed into soil , applied to surface, composted aerobically, digested anaerobically or before fertilisers
• reduce bulk of material making application easier
• produces fertiliser with better carbon, nitrogen ratio
• composting and digestion reduce carbon content as CO2 or CH4 gases are lost leaving more nitrogen rich fertiliser

Control of NOx releases:

• use post-combustion processes e.g catalytic converters and urea sprays

Eutrophication:

• biological wastes may be washed into water or deliberately put there
• ammonium compounds converted to nitrites then nitrates, causing eutrophication

Control of combustion process:

• reduction in use of fossil fuels
• principles of circular economy
  
  • more low temp manufacturing processes e.g polymers produced by living organisms rather than using fossil fuels

Management of soil processes:

• farming practises can be changed to increase soil nitrate levels
  
  • cultivation of legume crops
  • crop rotation
  • minimal use of pesticides that harm soil biota
  • control of nitrate leaching
  • not applying fertilisers during rain or when it's likely
  • use of low solubility fertilisers e.g urea
  • use of low tillage techniques to reduce soil disturbance
  • uncultivated 'buffer strips' left along rivers
  • minimal use of nitrate fertiliser where leaching into aquifers is likely