Lecture 15 - Nitrogen cycle and use of fertilisers Flashcards
What is the flow of nutrients in an ecosystem?
Cyclic
How do plants uptake nitrate ions (No3-)
Active transport through their root hairs
Are Nitrate ions soluble or insoluble?
Soluble and leach easily from the soil
How does the nitrogen cycle restore nitrate levels?
Decomposition Agricultural systems (which draws a lot of nitrogen from soils) levels are increased by addition of fertilisers
What are the four stages of the nitrogen cycle?
- Ammonification
- Nitrification
- Nitrogen Fixation
- Denitrification`
What happens during ammonification of the nitrogen cycle
- Ammonia (NH4) produced from organic ammonium
1a. Contains compounds e.g.: urea, proteins, nucleic acids, vitamins - Saprobiotic microorganisms, fungi and bacteria, feed on these materials and release Ammonium ions (NH3-)
- Releases nitrogen to the non-living component of the ecosystem
What happens during Nitrification of the nitrogen cycle
- Nitrifying bacteria in soil converts ammonium ions to
nitrate ions - Oxidation reaction = energy released for bacteria (chemotrophs)
- Two stages for process
a. NH3- –> NO2-
(oxidation of ammonium ions to nitrite ions)
b. NO2- —> NO3-
(oxidation of nitrite ions to nitrate ions) - Nitrifying bacteria require oxygen for this process, farmers must ensure soil is well aerated via plouging
- Good drainage also important as it prevents waterlogging with airspaces being filled with water
What happens during Nitrogen Fixation of the nitrogen cycle
- Process of converting gas to nitrogen containing compounds
- Haber process (lightning and industrial process) converts nitrogen compounds performed by bacteria
- Free-living nitrogen-fixing bacteria; reduce N2 to ammonia and then use to make amino acids.
Compounds released to soil when bacteria die - Mutalistic nitrogen-fixing bactier
- live in root nodules of legumes
- Bacteria recieve carbs from plant and plant acquires amino acids from bacteria
What happens during denitrification of the nitrogen cycle
- When soil is short of o2 nitrogen-fixing bacteria can no longer function
- Anaerobic denitrifying bacteria increase in numbers and convert soil nitrates to nitrogen gas
- Reduces the level of nitrates in soil for plants reducing productivity
How to prevent denitrification?
- Ploughing and drainage
Why are natural or artificial fertilisers needed to be used?
- Intensive farming depletes nitrate levels of soil
- Harvested crops means nitrates are not returned
- Animals that eat plant mater are no longer returned to same area
- Low nitrate levels in soil often limiting factor in productivity
Where are natural organic fertilisers from?
- Dead and decaying remains of plants and animals as well as animal waste such as manure or bone meal
Where are artificial inorganic fertilisers from?
- Mined from rocks and converted. Most minerals contain nitrogen phosphorous and potassium
What are the environmental consequences of using nitrogen fertilisers?
- Reduces species diversity
- nitrogen-rich soils favour growth of grasses, nettles and other rapidly growing species.
- Species rich hay meadows only survive when nitrate levels are low enough to allow other species to compete with grass - Leaching
- process by which nutrients are removed from soil
- rain water dissolves soluble nutrients such as nitrates and carry them deep into soil away from plant roots
- leached nitrates drain into streams and rivers entering fresh water
- harmful effect on drinking water
- Leached nitrates cause eutorphication
What is eutrophication?
(consequence of nitrogen fertilisers)
process by which nutrients build up in bodies of water, a natural process that occurs mostly in freshwater lakes and lower reaches of rivers
