Notes

https://www.bbc.co.uk/news/business-38305504
Population growth
We are in the middle of a global experiment.
One result is already clear: plenty of food for lots more people.
If you look at a graph of global population, you will see it shoot upwards just as Haber-Bosch fertilisers start being widely applied.
Again, Haber-Bosch was not the only reason for the spike in food yields.
New varieties of crops like wheat and rice also played their part.
Still, if we farmed with the best techniques available in Fritz Haber's time, the earth would support about four billion people.
Our current population is around seven and a half billion, and growing.
Back in 1909, as Haber triumphantly demonstrated his ammonia process, he could hardly have imagined how transformative his work would be.
On one side of the ledger, food to feed billions more human souls; on the other, a sustainability crisis that will need more genius to solve.
For Haber himself, the consequences of his work were not what he expected.
As a young man, he converted from Judaism to Christianity, aching to be accepted as a German patriot.
Beyond his work on weaponising chlorine, the Haber-Bosch process also helped Germany in World War One.
Ammonia can make explosives, as well as fertiliser.
Not just bread from air, but bombs too.
When the Nazis took power in the 1930s, however, none of this outweighed his Jewish roots.
Stripped of his job and kicked out of the country, Haber died, in a Swiss hotel, a broken man.

https://www.bbc.co.uk/bitesize/guides/z637hyc/revision/1#:~:text=The%20chemical%20element%20nitrogen%20is%20essential%20to%20living,the%20soil%20and%20use%20them%20to%20produce%20proteins.
Nitrogen in ecosystems
The chemical element nitrogen is essential to living organisms because it is needed to make proteins, which are essential for growth and repair and as enzymes and hormones.
The nitrogen cycle
Most nitrogen is found in the air as a gas. Most plants obtain nitrogen in the form of nitrates from the soil and use them to produce proteins. Animals obtain nitrogen as part of the proteins they consume. The movement of nitrogen between the air, soil compounds and compounds in the bodies of living organisms is called the nitrogen cycle. Different groups of bacteria are very important for keeping the cycle going so that nitrogen is always available in a form that living organisms can use.

The stages of the nitrogen cycle
1. Nitrogen-fixation
Legume plants such as peas, beans and clover contain nitrogen-fixing bacteria. These bacteria live in swellings in the plant roots called nodules. Nitrogen-fixing bacteria convert nitrogen gas from air into a form that plants can use to make proteins.

Free-living nitrogen-fixing bacteria are also found in the soil. When they die the nitrogen they have fixed into their biomass is converted into ammonium.

2. Feeding
Animals consume plant protein, digest it using specific enzymes and absorb the free amino acids.

3. Production of nitrogenous waste products
Animals cannot store excess protein in their bodies. They break it down and turn it into waste products and excrete them from their bodies.

4. Decomposition
Decomposers (some free-living bacteria and fungi) break down animal and plant proteins (from dead organisms) and nitrogenous waste products to release energy. As a result of decomposition nitrogen is released into the soil in the form of ammonium.

5. Nitrification
A group of free-living soil bacteria called nitrifying bacteria convert ammonium into nitrates in order to obtain energy.

6. Uptake of nitrates
Non-legume plants absorb nitrates from the soil into their roots and use the nitrates to produce their proteins.

7. Denitrification
This is when bacteria in the soil convert the nitrate back into nitrogen gas which then gets released back into the atmosphere.