1. C.6 The nitrogen and phosphorous cycle
Applications:
The impact of waterlogging on the nitrogen cycle
Insectivorous plants as an adaptation for low nitrogen availability in waterlogged soils
Understanding:
Nitrogen-fixing bacteria convert atmospheric nitrogen to ammonia
Rhizobium associates with roots in a mutualistic relationship
In the absence of oxygen denitrifying bacteria reduce nitrate in the soil
Phosphorous can be added to the phosphorous cycle by application of fertilizer or removed by the harvesting of agricultural crops
The rate of turnover in the phosphorous cycle is much lower than the nitrogen cycle
Availability of phosphate may become limiting to agriculture in the future
Leaching of mineral nutrients from agricultural land into rivers causes eutrophication and leads to increased biochemical oxygen demand
Skills:
Drawing and labeling a diagram of the nitrogen cycle
Assess the nutrient content of a soil sample
Nature of science:
Assessing risks and benefits of scientific research: agricultural practices can disrupt the phosphorous cycle

2. Nitrogen Fixation
78% of atmosphere is nitrogen gas: N2 Plants cannot take up this form of nitrogen Bacteria ‘fix’ nitrogen gas and turn it into ammonia NH3 Plants can absorb this form.

3. Rhizobium
Convert atmospheric nitrogen into a usable organic form. Live in close symbiotic association in the roots of plants Example of a mutualistic relationship

4. Rhizobium
Create root nodules Convert atmospheric nitrogen in the soil into ammonia. Host plant cannot do this itself Plant provides the bacteria with carbohydrates produced during photosynthesis for energy

5. Ammonia  nitrites
Ammonia produced by nitrogen fixation is converted to nitrite NO2 By bacteria: Nitrosomonas Use electrons gained from oxidation of ammonia to produce energy (chemoautotrophs)

6. Nitrites  nitrates
Nitrites are then converted to nitrates By bacteria Nitrobacter Also chemoautotrophs as they gain energy from inorganic compounds Nitrate is a form that is available to plants

7. Water logging
Soil saturated with water through flooding or irrigation with poor drainage
Short supply of oxygen
Favours denitrification
Leads to
Eutrophication
Loss of nitrogen available to plants

8. Denitrification
Denitrification is the reduction of nitrate NO-3 to nitrogen N2 By bacteria Pseudomonas denitrificans Use oxygen as an electron acceptor usually, however in oxygen short environments they use nitrates This releases N2 back into the atmosphere Reduces nitrogen available for plants

9. Nitrogen cycle Draw your own, including the following: Pools
Fluxes/processes
Nitrogen gas in atmosphere
Nitrates
Nitrites
Ammonia
Plant protein
Animal protein
Nitrogen fixation by living organisms
Mutualistic nitrogen fixing bacteria in root nodules
Free living nitrogen fixing bacteria in soil
Nitrification by Nitrosomonas
Nitrification by Nitrobacter
Uptake and assimilation by plants
Nitrogen fixation by non-living processes
Transfer of nitrogen in the food chain death and decomposition
Ammonification by decomposers
Denitrification

10. Carnivorous plants
Permanently water logged soils (bogs or swamps) Nitrogen deficient soils Become carnivorous to obtain nitrogen through digestion of animals

11. Phosphorous cycle
Draw your own, include the following: Phosphate in soil Weathering Phosphate rocks Mining Geologic uplift Plant and animal waste Decomposers Run off and leaching Dissolved in waterways Shallow ocean sediments Deep ocean sediments

12. Phosphorous cycle
Rate of turnover much lower than nitrogen cycle All living things require phosphorous to produce molecules: DNA, RNA, ATP Also for maintaining skeletons and cell membranes

13. Phosphorous cycle
Phosphorite is a sedimentary rock containing high levels of phosphate-bearing minerals Weathering and erosion = release of phosphates into soil Phosphates readily taken up by plants = enters food chains

14. Human activity
Affects phosphorous cycle. Phosphates mined and converted to phosphate based fertilisers Fertilisers transported elsewhere and applied to crops. Crops then harvested and transported elsewhere, taking phosphorous with it each time

15. Human activity
Mining of phosphates is increasing due to intensive farming and demand for fertilisers Peak phosphorous = point in time at which the maximum global phosphate production rate is reached and then begins to fall due to depletion of reserves

17. Human activity
No phosphate to mine = no fertilisers created No fertilisers = yields plummet No alternative sources of phosphates and no synthetic way to create it Global famine

19. Eutrophication
Create a summary using the video:

20. Solutions to disruptions in phosphorous cycle
Agriculture = removal of nutrients from an area Nutrients have to be re added using fertilisers Intensive farming = higher inputs needed to supply a growing population Searching for a solution for depleting phosphorous

21. Solutions to disruptions in phosphorous cycle
Recover phosphorous from sewage Humans excrete between 200 – 1000 grams of phosphorous annually in urine Use bacteria that selectively accumulate phosphorous – removed and used as fertilisers Chemical precipitation with iron chloride (more expensive)

22. Solutions to disruptions in phosphorous cycle
Genetic modification – Enviropig Produces phytase in its saliva. Able to digest normally insoluble phytate in pig feed. More phosphate absorbed, less released in manure
Benefits
Harmful effects
Less release of phosphorus to the environment in pig manure
Less risk of phosphorus deficiency in growing pigs
Less need to deplete world mineral phosphate reserves by use as a dietary supplement in pig feed
Traces of phytase in pork might cause allergies in humans
Phytase gene might transfer to wild species by cross breeding
GM might cause suffering to pigs in some way

23. Soil quality testing kits
Soil testing
Soil quality testing kits
Add a chemical to a sample of soil that reacts with the nutrient in question if present
Colour produced that can be visually compared to a key

24. Soil testing
Leaf quality