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Index >> Soil / Agriculture Microbiology >> Nitrogen Fixation

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Soil Microbiology Nature of Soil Soil Habitats (Lithosphere) Microorganisms in Soil Decomposition of Organic Matter in Soil Bacteria in Soil Physiological Types of Bacteria in Different Soils Fungi in Soil Protozoa in Soil Algae in Soil Viruses in Soil Functions of Microorganisms in Soil Humus Functions of Humus Cycles of Elements Carbon Cycle Nitrogen Cycle

Nitrogen Fixation

	Nitrogen Fixation - The nitrogen cycle shows obvious loss of fixed nitrogen, particularly through denitrification. Secondly there is a loss into the sea which is not recovered. Thirdly there is a Joss by explosives while this may seem minor except in war, it is actually reasonably large, because of blasting of rock, earth, etc.
These are relatively large losses and eventually the fixed nitrogen would be used up. On the other hand animals and plants are unable to utilize in any way vast stores of nitrogen in the air. A small amount of non-biological nitrogen fixation occurs in the atmosphere through lightning discharges. Nitric oxide which is formed reacts with water to produce nitric acid.
This combines with ammonia and some ammonium nitrate is brought to the soil. There are a few man-made processes (Haber, Berkland-Eyde, Cynamide) where nitrogen is fixed, but they require rather drastic conditions of temperature and pressure. In contrast to this microorganisms fix atmospheric nitrogen very smoothly at atmospheric pressure and at a temperature of 20°C.
There are two main groups of nitrogen -fixing organisms according to their mode of fixation. (1) Symbiotic nitrogen fixer : those capable of fixing molecular nitrogen by living in the roots of leguminous plants; and (2) non symbiotic nitrogen fixers: those capable of fixing molecular nitrogen to cellular nitrogen independently of other living organisms

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Sulphur Cycle Ammonification in Soil Nitrification in Soil Nitrate Reduction in Soil Denitrification in Soil Nitrogen Fixation Symbiotic Nitrogen Fixation Rhizobium Specificity of Bacteria and Legumes Non-Symbiotic Nitrogen Fixation Non-symbiotic Nitrogen Fixing Microorganisms Mechanism of Nitrogen Fixation Oxidation of Sulphur and Sulphur Compounds by Bacteria

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