please define:-  1. Nitrogen fixation 2. Nitrification 3. Denitrification 4. Nitrogen assimilation 5. Ammonification

Also, Explain the difference b/w Biological Nitrogen fixation and Atmospheric Nitrogen fixation...

 

Nitrogen fixation is the process of conversion of atmospheric nitrogen (N2) into ammonia (NH3) by the help of certain bacteria or lightening.

Nitrification is a processes in which ammonia is converted into nitrite and then into nitrates by action of bacteria Nitrosomomas and Nitrobacter respectively.

Denitrification is the process of reduction of nitrates into nitrogen by bacteria like Pseudomonas and Thiobaccilus.

Ammonification is the decomposition of organic nitrogen of dead plants and animals into ammonia by the help of microorganisms. 

Biological nitrogen fixation by some plants and microbes. Atmospheric nitrogen fixation by lightning. It is also done artificially by fertilizers.

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Nitrification is the biological oxidation of ammonia with oxygen intonitrite followed by the oxidation of these nitrites into nitrates. Degradation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle insoil. This process was discovered by the Russian microbiologist,Sergei Winogradsky.

Denitrification is a microbially facilitated process of nitrate reduction that may ultimately produce molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products.

Nitrogen fixation is a process by which nitrogen (N2) in the atmosphere is converted into ammonia (NH3).[1] Atmospheric nitrogen or molecular nitrogen (N2) is relatively inert: it does not easily react with other chemicals to form new compounds. Fixation processes free up the nitrogen atoms from their diatomic form (N2) to be used in other ways.

Nitrogen assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants, fungi and certain bacteria that cannot cannot fix nitrogen gas (N2) depend on the ability to assimilate nitrate or ammonia for their needs. Other organisms, like animals, depend solely on organic nitrogen from their food.

When a plant or animal dies, or an animal expels waste, the initial form of nitrogen is organic. Bacteria, or fungi in some cases, convert the organic nitrogen within the remains back into ammonium (NH4+), a process called ammonification or mineralization.

Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase.[1] The reaction for BNF is:

N2 + 8 H+ + 8 e → 2 NH3 + H2

The process is coupled to the hydrolysis of 16 equivalents of ATP and is accompanied by the co-formation of one molecule of H2. In free-living diazotrophs, the nitrogenase-generated ammonium is assimilated intoglutamate through the glutamine synthetase/glutamate synthase pathway.

Enzymes responsible for nitrogenase action are very susceptible to destruction by oxygen. Many bacteria cease production of the enzyme in the presence of oxygen.[1] Many nitrogen-fixing organisms exist only in anaerobic conditions, respiring to draw down oxygen levels, or binding the oxygen with a protein such as leghemoglobin whereas 

Atmospheric Nitrogen Fixation means

Leguminous cover crops fix atmospheric nitrogen. To ensure that nitrogen fixation takes place, it is important to use seed inoculated with the appropriate Rhizobium strain (Table 1.10-3). The amount of nitrogen fixed is directly related to the amount of biomass produced by the cover crop.

For cover crops established in the fall, the most popular leguminous cover crop currently available is hairy vetch. A second, less winter-hardy choice is crimson clover. In a study conducted in Maryland, hairy vetch fixed approximately 2 lbs/A of nitrogen per day from early March onward, totaling 150 lbs/A of nitrogen when it was killed in early May.

If the cover crop can be established in the spring or summer, growers have more choices for leguminous cover crops, such as red clover, white clover, field peas, and sweet clover. Research suggests that the leguminous cover crops do not need to be incorporated to obtain their maximum nitrogen benefit for the following crop. If incorporated, the leguminous cover crop will decompose more rapidly, and release greater amounts of nitrogen early in the season and lower amounts later in the season. In fact, incorporating large quantities of a leguminous cover crop such as hairy vetch in the soil may lead to nitrate losses in water draining from the soil profile in a wet spring. Research with hairy vetch and rye/vetch mix has shown that much of the nitrogen requirement of the following corn crop can be provided by hairy vetch without incorporation. If the vetch is mixed with rye, the nitrogen will be released more slowly. Perennial leguminous cover crops that are used for conservation plantings or living mulches are crownvetch, birdsfoot trefoil, and flatpea.

By-Komal 
IXth
 

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