An interactive showing the main components of the terrestrial1 nitrogen cycle2. Select one of the buttons to find out more.
Go here to view the full transcript and copyright information.
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This interactive shows the main components of the terrestrial nitrogen3 cycle. Select one of the buttons to find out more.
Transcript
Nitrogen in the atmosphere
Lightning
Fossil fuel emissions
Volatilisation
Rain
Legumes
Produce
Fertilisers
Dung and urine
Run-off
Soil organic matter
Decomposition and mineralisation
Plant and microbial uptake
Nitrification
Nitrogen fixation
Leaching to groundwater
Denitrification
Soil nitrogen gas
Nitrogen in the atmosphere (N2)
About 80% of the atmosphere4 is dinitrogen gas, which is more or less unavailable to most plants. Nitrogen gas in the atmosphere is basically unusable by most of biology5 – plants and animals – but there are a few species6 of microbes in conjunction with plants that can convert the dinitrogen gas into usable forms of nitrogen like ammonium7, and then that will turn into organic8 nitrogen or nitrate9, and that can then enter the biological system.
The conversion of nitrogen gas into biologically available forms of nitrogen is critical for the functioning of the ecosystem10.
ACKNOWLEDGEMENTS
Dr Kristine A Nichols
Professor Louis Schipper, University of Waikato
Lightning
Lightning11 storms are important for converting nitrogen gas in the atmosphere through to forms that are biologically available.
ACKNOWLEDGEMENTS
Image licenced through 123rf.com.
Fossil fuel emissions (NOx)
Fossil fuels12 are deposits of essentially animals or plants that have died in the past and become buried and then converted through to highly concentrated forms of energy like oil or coal.
If you think about plants and animals, both of them contain quite a lot of nitrogen, so when they get converted through to energy forms such as fossil13 fuels, that nitrogen is still contained in that fossil fuel14. When you burn the fossil fuel, either say coal or oil, you are essentially releasing that nitrogen back up into the atmosphere – not necessarily as dinitrogen gas but maybe other forms of nitrogen that are more available to plants and animals.
So if that material goes up into the atmosphere, it can be rained out again and deposited on the land as a form of biologically available nitrogen.
Fossil fuels release nitrous oxide15, which is one of the greenhouse gases16 that is released into the atmosphere, so fossil fuel17 burning does contribute to greenhouse gases18, not only through the production of CO2 but also nitrous oxide19.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Volatilisation (NH3)
Volatilisation20 is the conversion of dissolved ammonia21 – found in urine patches – into ammonia gas that can go into the atmosphere. This can happen if it’s hot, dry and windy. It is loss of nitrogen from the paddock to be avoided if possible. The rain may wash it back down but not necessarily to your farm. It could end up in a forest or out in the ocean.
ACKNOWLEDGEMENTS
The University of Waikato Te Whare Wānanga o Waikato
Rain (NOx, NH4+)
There are different nitrogen gases that come out of the soil. Ammonium, for example, will volatilise up into the atmosphere, fossil fuel burning will release nitrogen into the atmosphere and lightning will convert dinitrogen gas in the atmosphere to water-soluble forms of nitrogen. And when it rains, the rain will strip that nitrogen out of the atmosphere and deposit it onto the surface of the land.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Legumes
Legumes22 such as clover are incredibly important for nitrogen cycling, particularly in New Zealand. In the early days, when we didn’t have nitrogen fertilisers23, they encouraged the growth of nitrogen fixers by adding phosphorous fertilisers. And the neat thing about clover is that it harbours a bacteria24 called rhizobia and houses them and encourages them to grow, and they will take dinitrogen gas out of the atmosphere and convert it through to ammonia and ammonium that the plant can then use. That nitrogen ultimately ends up getting into the soil and taken up by other plants. So clover growth has hugely increased the production of New Zealand pastures.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Damon Taylor
Professor Frank Dazzo
Produce
To make sure that you get good crop yields or grass yields, you need to make sure that you’ve got enough nitrogen for them to be able to build their proteins and the enzymes25 that they need. So without a good supply of nitrogen, it is hard to get large yields or grow the amount of food that you need. It is estimated that about 40% of the world’s population26 is fed by food that is grown using nitrogen that has been brought in either as fertiliser27 or through the deliberate cultivation28 of plant crops that are able to fix nitrogen out of the atmosphere.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
David Higgitt http://creativecommons.org/licenses/by-sa/2.0/deed.en
Deeporaj http://creativecommons.org/licenses/by-sa/3.0/deed.en
Jan Ulrich http://creativecommons.org/licenses/by-sa/3.0/deed.en
Mark Silcock, McDonald’s Lime
Certain photos in this video are the copyrighted property of 123RF Limited, their contributors or licensed partners and are being used with permission under licence. These images and/or photos may not be copied or downloaded without permission from 123RF Limited.
Fertilisers
Fertilisers give farmers a tool to be able to boost production when they need to. If too much fertiliser is used or fertiliser is used at the wrong time of year, then it’s possible for farms to lose that nitrogen fertiliser either leaching29 down through the soil profile, or it can be converted through to nitrogen gas – as one of them being a greenhouse gas30 – which is what nobody really wants because it represents a loss of productivity. You are losing nitrogen off your farm, but you are exporting that nitrogen somewhere else where it can also act as a fertiliser, like in streams or in waterways, and that’s where you’ll get unwanted growth.
ACKNOWLEDGEMENTS
Mark Silcock, McDonald’s Lime
Juliet Milne, Otago Regional Council
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Dung and urine
Urine in particular is very important for the cycling of nitrogen in pastoral systems. A cow grazes a large area and essentially concentrates all of that nitrogen that was in that grass into its body, and then when it has a urination event, it is depositing all of that nitrogen onto quite a small area.
The amount of nitrogen then in that little patch is way in excess of what the plants can handle, and you get nitrogen moving away from that site, because the plants basically can’t handle it. And you can see these urine patches when you drive past pastures. You’ll see these little tufts of green grass growing, and there are all these little patches out over the pasture. So if you ever go out for a drive and you go past a pasture and you see all of these little lumps – that’s old urine patches.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Run-off
Run-off31 is water that runs off over the surface of the land. If there’s too much rain and it’s greater than the rate that the soil can accept, it can pool on the surface, and if you have a slope, water will sheet over the surface of the land and go into waterways. Nitrate can be lost from soils through run-off.
ACKNOWLEDGEMENT
Public Domain
Soil organic matter
All of the nitrogen that is fixed out of the atmosphere goes into plants and then possibly into animals and then as those animals and plants die, they start to be decomposed, and that then enters into soil organic matter32. So soil is a suite of different types of particles – sands, silts and clays – and some of the clays in particular are able to protect that organic matter33 from further decay.
So you get large build-ups of organic matter in soil, and that contains mainly nitrogen and carbon34. There is more carbon in soils than in all the plants above the soil, and if you also add in the amount of carbon that’s in the atmosphere.
So there’s a tremendous amount of carbon in every hectare of land. For example, in New Zealand, it wouldn’t be unusual for a pasture to have something like 150 tonnes of carbon per hectare down to about a metre’s depth. Now along with that carbon is a lot of nitrogen, usually in a ratio about 10:1, so for every 10 tonnes of carbon, you’ll have about a tonne35 of nitrogen stored in the organic matter.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Barnowl
http://creativecommons.org/licenses/by-sa/2.0/deed.en
Certain photos in this video are the copyrighted property of 123RF Limited, their contributors or licensed partners and are being used with permission under licence. These images and/or photos may not be copied or downloaded without permission from 123RF Limited.
Decomposition and mineralisation
When nitrogen is fixed by plants and then is incorporated into their roots and leaves, that material will eventually die and will form part of the organic matter in soil, and that will start to degrade. It will be degraded by microorganisms36 in soil, and as that degradation occurs, nitrogen is released as nitrate or as ammonium, which then can be used by other forms of bacteria or plants. So mineralisation is the decomposition of litter in soil and the release of nitrogen into forms that plants can take up.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Certain photos in this video are the copyrighted property of 123RF Limited, their contributors or licensed partners and are being used with permission under licence. These images and/or photos may not be copied or downloaded without permission from 123RF Limited.
Plant and microbial uptake (NH4+, NH3-)
Plants and microorganisms can take up different types of nitrogen. The main ones are ammonium or nitrate. This is vital because nitrogen is critical for all life. It forms the backbone of most proteins or enzymes, and it’s also important part of DNA37.
ACKNOWLEDGEMENT
The University of Waikato Te Whare Wānanga o Waikato
Nitrification
Nitrification38 is one of the steps in the nitrogen cycle where ammonium is converted to nitrate. First, ammonium is converted to nitrite by specialised bacteria. Other bacterial species are responsible for the conversion of nitrite to nitrate. Nitrate is easily taken up by plants, but it is also susceptible to loss because it doesn’t stick to soil and is quite mobile. It is easily leached39 from the soil through rain.
ACKNOWLEDGEMENT
The University of Waikato Te Whare Wānanga o Waikato
Nitrogen fixation (NO2 → NH4+)
Nitrogen fixation40 is the conversion of nitrogen gas from a mostly unusable form to a form that can be used by plants. The conversion of dinitrogen gas through to ammonium is carried out in the nodules of clover plants by bacteria called rhizobia. There are other forms of nitrogen fixers, such as kōwhai trees – they also have bacteria in root nodules that can convert dinitrogen into nitrogen that can be used by plants.
Inage shows rhizobia nodules attached to roots of Vigna unguiculata.
ACKNOWLEDGEMENT
Dave Whitinger, CC BY-SA 3.0
Leaching to groundwater
Water can leave the land through a process called leaching, and this is where the water moves directly down through the soil profile and into groundwater41.
And that’s probably the largest way that nitrogen will leave a farm is when you have got water in excess of what is a called the field capacity of the soil at that site, which is the amount of water that a soil can normally hold without leaching – basically, water starting to move down through it.
As that water moves, it can carry different chemicals42 with it as well and in particular carries negatively charged chemicals with it. Positively charged chemicals are held by the soil because soil is slightly negatively charged. One of the important forms of nitrogen is called nitrate, and that is negatively charged and so is repelled by soil, and you get that moving down with the water to groundwater and then onto surface waters43 like streams.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Denitrification (NO3- → N2O, N2)
Denitrification44 is a microbial45 process where microorganisms use nitrate, which is a form of nitrogen that is biologically available, and they convert it through back to nitrogen gas. So it is essentially the completion of the nitrogen cycle. In some ways, it’s the opposite to nitrogen fixation. So nitrogen fixation takes nitrogen gas out of the atmosphere and makes it biologically available, whereas denitrification converts that nitrogen back out of the soil back to nitrogen gas, completing the nitrogen cycle.
ACKNOWLEDGEMENTS
Professor Louis Schipper, The University of Waikato Te Whare Wānanga o Waikato
Soil nitrogen (N2) gas
Nitrogen gas makes up about 80% of the gases in the atmosphere and in the soil and can be fixed by specific microbes in conjunction with plants such as clover. Those plants can be eaten by cows or other animals and then excreted, which allows the fixed nitrogen to enter the rest of the ecosystem and start a cycle through other plants and animals.
ACKNOWLEDGEMENT
The University of Waikato Te Whare Wānanga o Waikato
- terrestrial: Belonging or from the land. This term is often used to describe plants and animals, meaning they live on the land.
- nitrogen cycle: The process by which nitrogen passes through the ecosystem.
- nitrogen: A non-metal – symbol N, atomic number 7. Nitrogen is essential for life. It is a component of many molecules that make up cells, including DNA and proteins.
- atmosphere: 1. The layer of gas around the Earth. 2. (atm) A non-SI unit of pressure equivalent to 101.325 kPa.
- biology: The science of living things.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- ammonium: NH4+. Derived from ammonia by combination with a hydrogen ion. A nitrogen compound taken up by plants from soils.
- organic: 1. Molecules that contain carbon and that have a biological origin. 2. Grown using natural processes with nutrients from natural sources.
- nitrate: A chemical composed of three oxygen atoms for every nitrogen atom.
- ecosystem: An interacting system including the biological, physical, and chemical relationships between a community of organisms and the environment they live in.
- lightning: A large-scale natural spark discharge, visible as a flash of blue-white light, that occurs within the atmosphere or between the atmosphere and the Earth’s surface. The lightning channel consists of extremely high-temperature plasma.
- fossil fuel: Materials such as coal, oil and natural gas formed from the fossilised remains of plants that lived many millions of years ago. Often burned as fuel – although this releases large amounts of CO2, which contributes to global warming. Fossil fuels are also not renewable – there is a limited amount.
- fossil: The remains or imprint of an organism preserved in some manner. Typically fossils are found in sedimentary rock as a result of mineral replacement or imprinting in once soft silt or sand layers. Normally, rock fossils only include the hard parts of an organism such as the skeleton or shell. Fossils can also include the original remains (including soft tissue) preserved in amber, pitch or ice, or preserved in ‘fossil layers’ in special sheltered cave environments.
- fossil fuel: Materials such as coal, oil and natural gas formed from the fossilised remains of plants that lived many millions of years ago. Often burned as fuel – although this releases large amounts of CO2, which contributes to global warming. Fossil fuels are also not renewable – there is a limited amount.
- nitrous oxide: N2O. A naturally occurring atmospheric gas. It is used as a mild anaesthetic and as a fuel. It is also a greenhouse gas.
- greenhouse gases: A natural or manmade gas that traps heat in the Earth's atmosphere and contributes to the greenhouse effect. The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone and industrial gases such as chlorofluorocarbons (CFCs). These gases in the Earth's atmosphere trap warmth from the Sun and make life possible. An overabundance of greenhouse gases leads to a rise in global temperatures – known as the greenhouse effect.
- fuel: 1. A combustible substance that provides energy. 2. A body fuel such as fat, carbohydrates and protein that supplies energy for animals’ activities.
- gases: The state of matter distinguished from the solid and liquid states. Gases have the ability to diffuse readily and to become distributed uniformly throughout any container.
- nitrous oxide: N2O. A naturally occurring atmospheric gas. It is used as a mild anaesthetic and as a fuel. It is also a greenhouse gas.
- volatilisation: The conversion of liquid into gas.
- ammonia: A compound of nitrogen and hydrogen with the formula NH3. It is a colourless gas with a characteristic pungent smell.
- legume: A plant having fruits that are developed from a simple superior ovary and usually dehiscing into two valves. Legumes bear nodules on the roots, which contain nitrogen-fixing bacteria. Examples are peas, beans and clovers.
- fertiliser: Compounds that are given to plants to promote growth.
- bacteria: (Singular: bacterium) Single-celled microorganisms that have no nucleus.
- enzyme: A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.
- population: In biology, a population is a group of organisms of a species that live in the same place at a same time and that can interbreed.
- fertiliser: Compounds that are given to plants to promote growth.
- cultivation: Working land in order to grow crops. Promoting or improving the growth of plants through labour or attention. Propagating organisms by providing the proper environmental conditions.
- leaching: When a compound becomes dissolved in water and moves from one place to another, for example, a fertiliser in the soil dissolves in rain water and ends up in a stream.
- greenhouse gases: A natural or manmade gas that traps heat in the Earth's atmosphere and contributes to the greenhouse effect. The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone and industrial gases such as chlorofluorocarbons (CFCs). These gases in the Earth's atmosphere trap warmth from the Sun and make life possible. An overabundance of greenhouse gases leads to a rise in global temperatures – known as the greenhouse effect.
- run-off: Water carried away from land to streams and rivers.
- organic matter: The decomposed remains of living organisms and their waste products.
- matter: The basic structural component of all things that have mass and volume.
- carbon: A non-metal element (C). It is a key component of living things.
- tonne: A non-SI unit of mass – 1 tonne = 1000 kg.
- microorganism: A living organism which is too small to be seen with the naked eye and can only be observed using a microscope. Includes bacteria and most protists.
- DNA: Deoxyribonucleic acid (DNA) is a molecule that contains the instructions needed for an organism to develop and function. These instructions are stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C) and thymine (T).
- nitrification: Part of the nitrogen cycle. A process that takes place in the soil where bacteria convert ammonium into nitrites and then nitrites into nitrates.
- leaching: When a compound becomes dissolved in water and moves from one place to another, for example, a fertiliser in the soil dissolves in rain water and ends up in a stream.
- fixation: The process of converting atmospheric nitrogen (dinitrogen gas, N2) to forms that can be used by plants and animals to carry out many of the functions of life.
- groundwater: Water located beneath the Earth’s surface in soil spaces and in fractures of rocks.
- chemicals: Everything is made up of chemicals. All matter (anything made of atoms) can be called chemicals. They can be in any form – liquid, solid or gas. Chemicals can be a pure substance or a mixture.
- surface water: A body of water above the substrate or soil surface – for example, streams, rivers, lakes and oceans.
- denitrification: Part of the nitrogen cycle. A process where bacteria in soil breaks down nitrates into atmospheric nitrogen gas.
- microbial: Anything of, or related to microorganisms.