The nitrogen cycle
Nitrogen A substance formed by the chemical union of two or more elements. found in cells include proteins. Nitrogen from the air is converted into soluble Electrically charged particle, formed when an atom or molecule gains or loses electrons. that plant roots can absorb. It forms part of nitrogen compounds in the plants, and is then passed from one Living entity, eg animals, plants or microorganisms. to the next. It is returned to the atmosphere as nitrogen gas. This is the nitrogen cycle.
Image caption, Stage one of the nitrogen cycle
Fixation
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Stage one - fixation
About 78 per cent of the air is nitrogen gas. However, nitrogen is too unreactive to be used directly by plants to make protein. It must be converted into soluble ions, such as The chemical absorbed from the soil by plants to produce their protein.. The bacteria found free-living in the soil or in the root nodules of some plants such as peas and clover that convert nitrogen gas into nitrate. found in A small swelling on the roots of plants such as peas, beans and clover that contains nitrogen-fixing bacteria and free living in the soil are able to do this. Lightning can also convert nitrogen gas into nitrates.
Stage two - absorption into roots and incorporation into plants
Plants absorb nitrates from the soil and use these to make proteins.
Stage three - moving along food chains and excretion
The excretion of A nitrogenous waste product resulting from the breakdown of proteins. It is excreted in urine. (in animal urine) releases nitrogenous compounds into the soil. Bacteria in the soil make an enzyme called An enzyme made by bacteria which converts urea in the soil into ammonia. which converts this urea into Ammonia is a gas at room temperature but readily dissolves in water to form an alkaline solution.. The bacteria that produce nitrate which is released into soil. convert the ammonia into nitrates which plants can now absorb.
Stage four - death of animals
An organism which eats dead organisms, fallen leaves, animal droppings, etc, and breaks them down into simpler materials. break down the protein in the dead bodies of animals and plants, converting it into ammonia. Nitrifying bacteria then convert the ammonia into nitrite, and then nitrates.
Stage five - release into atmosphere
The bacteria that convert nitrates in the soil into nitrogen gas which is released into the atmosphere. in the soil break down nitrates and return nitrogen gas to the air. This occurs in Without oxygen. conditions. Farmers try to prevent The stage in the nitrogen cycle that involves denitrifying bacteria converting nitrates in the soil into nitrogen gas which is released into the atmosphere. as plants grow best when there are plenty of nitrates in the soil for them to use to make the proteins they need for growth.
There are steps that farmers can take to prevent denitrification.
- Plough the soil regularly to encourage aerobic conditions (get oxygen in).
- Drain any waterlogged areas.
- Rotate crops by planting Peas, beans or clover which have root nodules containing nitrogen-fixing bacteria and so can live in low nitrate (infertile) soil. every few years. These have root nodules filled with nitrogen-fixing bacteria that can convert nitrogen gas directly from the air into nitrogenous compounds the plants can use, increasing soil fertility.
This video highlights a method of keeping soil fertile: