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Nitrogen cycle (Sustainable management: (Management of biological wastes:
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Nitrogen cycle
Sustainable management:
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
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Human impacts
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
Main processes
With living organisms
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
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Fixation - some micro-organisms can chemically reduce nitrogen to ammonia, can be bacteria in soil or in root nodules of legumes
Without living organisms
Ionisation - processes such as lightning and meteor trails provide energy for atmospheric nitrogen and oxygen to react and produce oxides of nitogen
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
Nitrogen fixation:
- nitr i tes -> nitr a tes
- N2 converted into NH4 (Ammonium)
- can happen by lightning ~ ionising
- only way organisms cab attain N2 is directly from atmosphere ~ called nitrogen fixating organisms
- bacteria e.g rhizobium convert it to ammonium through metabolic process