nitrogen fixation

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ni·tro·gen fix·a·tion

process in which atmospheric nitrogen is converted to ammonia.

nitrogen fixation

1. The conversion of atmospheric nitrogen into compounds, such as ammonia, by natural agencies or various industrial processes.
2. The conversion by certain soil microorganisms, such as rhizobia, of atmospheric nitrogen into compounds that plants and other organisms can assimilate.

ni′tro·gen-fix′er (-fĭk′sər) n.
ni′tro·gen-fix′ing adj.

nitrogen fixation

the process by which free nitrogen in the atmosphere is converted by biological or chemical means to ammonia and to other forms usable by plants and animals. Biological nitrogen fixation is the more important process and is accomplished by microorganisms in the soil, either free living or in close association with root nodules of certain plants. In contrast, chemical nitrogen fixation, as is used in industry, requires extremely high temperatures and pressures.

nitrogen fixation

the utilization of atmospheric nitrogen in the synthesis of AMINO ACIDS by some bacteria. Such bacteria can be free-living (e.g. Azotobacter, an aerobe; Clostridium, an obligate anaerobe) while others (e.g. Rhizobium) live in association with plants, occupying swellings in the root called root nodules. The latter relationship is one of SYMBIOSIS, in that the plant gains nutrients and thus can live in nitrogen-poor soils, while the nitrogen-fixer obtains a supply of carbohydrates from the plant. The nitrogen is reduced to ammonia in the microbes by action of the enzyme nitrogenase: N2 + 3 H22 NH3, the ammonia then reacting with keto acids to form amino acids.


a chemical element, atomic number 7, atomic weight 14.007, symbol N. See Table 6. It is a gas constituting about four-fifths of common air; chemically it is almost inert. It is not poisonous but is fatal if breathed alone because of oxygen deprivation. Nitrogen occurs in proteins and amino acids and is thus present in all living cells.

nitrogen balance
the state of the body in regard to the rate of protein intake and protein utilization. When protein is metabolized, about 90% of the protein nitrogen is excreted in the urine in the form of urea, uric acid, creatinine and other nitrogen end products. The remaining 10% of the nitrogen is eliminated in the feces.
A negative nitrogen balance occurs when more protein is utilized by the body than is taken in. A positive nitrogen balance implies a net gain of protein in the body. Negative nitrogen balance can be caused by such factors as malnutrition, debilitating diseases, blood loss and glucocorticoids. A positive balance can be caused by exercise, growth hormone and testosterone.
blood urea nitrogen (BUN)
see urea nitrogen.
nitrogen dioxide
see nitric oxide.
nitrogen fixation
conversion of atmospheric nitrogen into organic nitrogenous compounds by bacteria which may be symbiotic, e.g. Rhizopus spp., which grow on the roots of legumes and put those plants in an advantageous position with respect to nonlegumes.
nitrogen-free extract (NFE)
consists of carbohydrates, sugars, starches, and a major portion of the hemicellulose in feeds. Calculated when crude protein, fat, water, ash, and the fiber are added and the sum is subtracted from 100.
nitrogen mustards
a group of toxic, blistering alkylating agents homologous to dichlorodiethyl sulfide (mustard gas), some of which have been used as antineoplastics. The group includes mustine hydrochloride, cyclophosphamide, thiotepa, chlorambucil and melphalan.
nonprotein nitrogen (NPN)
1. the nitrogenous constituents of the blood exclusive of the protein bodies, consisting of the nitrogen of urea, uric acid, creatine, creatinine, amino acids, polypeptides, and an undetermined part known as rest nitrogen.
Measurement of nonprotein nitrogen is used as a test of renal function, but has been largely replaced by measurement of specific substances, e.g. urea and creatinine.
2. also used in relation to feeds and refers to those nitrogen-containing constituents which are not proteins, e.g. nucleic acids, amino sugars, urea, etc.
nitrogen trichloride
nitrogen washout test
measures the rate at which the nitrogen concentration in the expired air is reduced when the horse is made to breathe pure oxygen. The rate is less in incompetent lungs, e.g. those affected by emphysema.
References in periodicals archive ?
PLANTING nitrogen fixing crops such as peas and beans will count towards farmers' greening measures under the new Common Agriculture Policy rules, it has been revealed.
Phosphorous is an essential nutrient for plants, but most Australian soils are old and, in their native state, don t have enough phosphorus or nitrogen to support modern agriculture, so phosphorus fertilisers and nitrogen fixing legumes helps rectify these deficiencies.
The nitrogen fixing bacteria such as Azotobacter and Azosperillium reduce the nitrogen gas to ammonia using intensive energy to break the nitrogen bonds so that it can combine with hydrogen to form ammonia.
Houlton and Ying-Ping Wang of the Commonwealth Scientific and Industrial Research Organization in Australia ran the same models with added information on nitrogen fixing and the global use of artificial fertilizer.
Coastal waters contain other bacteria that have the genes to perform this vital trick--an energy-consuming set of chemical reactions known as nitrogen fixing.
One announcement that has emerged from the European Commission is that if Nitrogen Fixing crops are to be used as a possible EFA option, they will have a weighting element applied to them of 0.
In order to respond to these threats the Liberian NAPA has identified, as urgent priority interventions, to enhance resilience to increasing rainfall variability through the diversification of crop cultivation and small ruminants rearing; modifying the timing of crop cultivation in response to changing rainfall patterns; intercropping, irrigation and optimization of lowland/swamp farming practices; pest control, including fencing of farms against rodents, bird scare scrolls, regular weeding, and the use of echoing bells; and, maintaining fast growing nitrogen fixing tree species to improve soil fertility and using multiple-purpose tree species on farmlands to maintain forest cover.
Biofertilizers can be classified as nitrogen fixing, phosphate solubilizing, and others that include potash mobilizing and zinc mobilizing, based on product type.
A number of member states argued to include features such as hedges, ditches and trees as well as areas of nitrogen fixing crops.
Nitrogen fixing biofertilizers - Phosphate solubilizing biofertilizers - Potash mobilizing biofertilizers - Others
Major Biofertilizers are nitrogen fixing biofertilizers, phosphate solubilizing biofertilizers and potash mobilizing biofertilizers.