Most nitrogen fixation occurs naturally, in the soil, by bacteria. In Figure 3 above , you can see nitrogen fixation and exchange of form occurring in the soil. Some bacteria attach to plant roots and have a symbiotic beneficial for both the plant and the bacteria relationship with the plant [ 6 ]. The bacteria get energy through photosynthesis and, in return, they fix nitrogen into a form the plant needs. The fixed nitrogen is then carried to other parts of the plant and is used to form plant tissues, so the plant can grow.
Other bacteria live freely in soils or water and can fix nitrogen without this symbiotic relationship. These bacteria can also create forms of nitrogen that can be used by organisms.
This stage takes place in the soil. Nitrogen moves from organic materials, such as manure or plant materials to an inorganic form of nitrogen that plants can use.
This becomes important in the second stage of the nitrogen cycle. Mineralization happens when microbes act on organic material, such as animal manure or decomposing plant or animal material and begin to convert it to a form of nitrogen that can be used by plants. All plants under cultivation, except legumes plants with seed pods that split in half, such as lentils, beans, peas or peanuts get the nitrogen they require through the soil.
Legumes get nitrogen through fixation that occurs in their root nodules, as described above. The first form of nitrogen produced by the process of mineralization is ammonia, NH 3. The NH 3 in the soil then reacts with water to form ammonium, NH 4. This ammonium is held in the soils and is available for use by plants that do not get nitrogen through the symbiotic nitrogen fixing relationship described above.
The third stage, nitrification, also occurs in soils. Nitrates can be used by plants and animals that consume the plants. Some bacteria in the soil can turn ammonia into nitrites. Although nitrite is not usable by plants and animals directly, other bacteria can change nitrites into nitrates—a form that is usable by plants and animals.
This reaction provides energy for the bacteria engaged in this process. The bacteria that we are talking about are called nitrosomonas and nitrobacter. Nitrobacter turns nitrites into nitrates; nitrosomonas transform ammonia to nitrites. Both kinds of bacteria can act only in the presence of oxygen, O 2 [ 7 ]. The process of nitrification is important to plants, as it produces an extra stash of available nitrogen that can be absorbed by the plants through their root systems.
The fourth stage of the nitrogen cycle is immobilization, sometimes described as the reverse of mineralization. These two processes together control the amount of nitrogen in soils. Under ordinary conditions, nitrogen is a highly inactive element.
It neither burns nor supports combustion. However, high temperature, high pressure and catalysts are effective in forcing nitrogen into chemical combinations with other elements.
For example, under high heat conditions nitrogen can be made to combine with oxygen to form nitric oxide. Lightning often creates nitric oxide by heating the air to extreme temperatures. Automobile engines also create nitric oxide, which is a major compound in smog:. Nitrogen can also be forced to combine with some of the active metals to form nitrides. For example, combining nitrogen with aluminum under the right conditions results in aluminum nitride:.
There are several methods to prepare nitrogen from air, both in the laboratory and commercially. Nitrogen can also be prepared from nitrogen compounds. One method of creating nitrogen from air is oxidize some material to rid the air of the oxygen in it. To appreciate the intricacies of nitrogen loading to coastal waters , some understanding of how nitrogen reacts chemically in the environment may be useful.
Nitrogen is an element that can combine with itself or with other elements to make different compounds. For instance nitrogen gas, N 2 , is a compound made when two nitrogen atoms form a chemical bond. So nitrogen gas is very common and plentiful. However, only a specialized group of bacteria, and industrial fertilizer manufacture, can "fix" this largely inert compound into biologically useful nitrogen compounds.
Fertilizer production now exceeds natural nitrogen fixation in making N 2 available to the biosphere. Nitrogen is a component of amino acids and urea. Amino acids are the building blocks of all proteins. Nitrogen compounds are present in organic materials, foods, fertilizers, explosives and poisons. Nitrogen is crucial to life, but in excess it can also be harmful to the environment. Named after the Greek word nitron , for "native soda," and genes for "forming," nitrogen is the fifth most abundant element in the universe.
On the other hand, the atmosphere of Mars is only 2. In its gas form, nitrogen is colorless, odorless and generally considered as inert. In its liquid form, nitrogen is also colorless and odorless, and looks similar to water, according to Los Alamos. Nitrogen was discovered in by chemist and physician Daniel Rutherford, when he removed oxygen and carbon dioxide from air, demonstrating that the residual gas would not support living organisms or combustion, according to the Los Alamos National Laboratory.
Other scientists, including Carl Wilhelm Scheele and Joseph Priestly, were working on the same problem, and called nitrogen "burnt" air, or air without oxygen. In , Antoine Laurent de Lavoisier, called nitrogen "azote," which means "lifeless.
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