The characteristics of the nitrogen cycle are as follows:
- Nitrogen Fixation: Nitrogen fixation is the process by which atmospheric nitrogen gas (N2) is converted into a form that can be utilized by living organisms. This conversion is carried out by nitrogen-fixing bacteria, which convert N2 into ammonia (NH3) or nitrate (NO3-), which can then be used by plants.
- Nitrification: Nitrification is the process by which ammonia (NH3) or ammonium (NH4+) is converted into nitrite (NO2-) and then further into nitrate (NO3-). This process is carried out by nitrifying bacteria. Nitrate is the primary form of nitrogen that plants can uptake and use for growth.
- Assimilation: Assimilation is the process by which plants and other organisms take up nitrate (NO3-) or ammonium (NH4+) from the soil and incorporate it into their own organic molecules, such as amino acids and proteins. This allows the nitrogen to be transferred through the food chain to other organisms.
- Ammonification: Ammonification is the process by which organic nitrogen compounds, such as dead plant and animal matter, are decomposed by bacteria and fungi, resulting in the release of ammonia (NH3) or ammonium (NH4+). This process recycles the nitrogen from organic matter back into the soil.
- Denitrification: Denitrification is the process by which nitrate (NO3-) is converted back into atmospheric nitrogen gas (N2). This occurs in oxygen-depleted environments, such as waterlogged soil or sediments, and is carried out by denitrifying bacteria. Denitrification completes the nitrogen cycle by returning nitrogen to the atmosphere.
The nitrogen cycle is essential for the cycling and availability of nitrogen in ecosystems. It ensures that nitrogen, an essential nutrient for life, can be utilized by plants and other organisms. Understanding the nitrogen cycle is crucial for sustainable agriculture, as it helps optimize fertilizer use, reduce pollution from nitrogen runoff, and maintain soil fertility.
The nitrogen cycle is the way that nitrogen in nature is changed into many different forms that are used by living organism[s].
Air is about 78% nitrogen. Nitrogen chemicals are needed for life. Nitrogen is a necessary part of proteins, DNA, and RNA. In plants, nitrogen is needed for photosynthesis and growth.  However, living things cannot use the elemental nitrogen in the air for these things. Nitrogen fixation is needed to change the nitrogen in air (N2) into forms that can be used by life. Most nitrogen fixation is done by microorganisms called bacteria. These bacteria have an enzyme that combines N2 with hydrogen gas (H2) to make ammonia (NH3).
Some of these bacteria live in the roots of plants (mostly legumes). In these roots, they make ammonia for the plant and the plant gives them carbohydrates. Other plants take nitrogen compounds out of the soil through their roots. All nitrogen in animals comes from eating plants.
Ammonium (NH4) in soil is made by nitrogen-fixing bacteria and decomposers, bacteria and fungi that break down dead life into its parts. This process is called ammonification. Ammonium has a positive charge. It easily joins to clay and humus in the soil. Ammonia and ammonium are poisonous to fish and other animals. Sewage and other waste-water is regularly measured because of this. If ammonia levels are too high, nitrification must happen.
Nitrification is the oxidation of ammonia and ammonium to nitrite (NO2−) and then to nitrate (NO3−) by bacteria. Because nitrite and nitrate have a negative charge they do not easily join to soil and will wash out of the soil during rain and irrigation. High nitrate levels in drinking water are harmful for babies and can cause blue-baby syndrome.  High nitrate levels can also cause too much algae growth in lakes and pools. This eutrophication can be harmful to fish and other water animals. The use of fertilizers is controlled because of this.
Where there is no oxygen, some bacteria will make nitrate into nitrogen gas (N2) to extract energy. This starts the nitrogen cycle over again. This process is called denitrification.