Nitrogen-Cycle

Nitrogen occurs in numerous oxidation states ranging from —3 (as in ammonia) to +5 (as in nitrate). It 

Discovery of bacterial nitrogen fixation was yet another impressive illustration of the critical dependence of the element s biospheric pathways on microorganisms. Less than a decade before Hellriegel s lecture, a convincing experiment demonstrated the bacterial origins of nitrification, conversion of ammonia to nitrate. This reaction is of great importance for all crops because nitrates are much more soluble than ammonia is, and plant roots can absorb them more readily from solutions in soil. 

Gayon s fundamental discovery literally closed the biospheric nitrogen cycle. Since that time we have not discovered any other major flows in nitrogen s agricultural cycle—but our research has provided enormous amounts of detailed information concerning every important reservoir of the nutrient and its intricate transfers among 

Sergei Nikolaevich Winogradsky (1856-1953). From the author s collection. 

The atmosphere is nitrogen s largest biospheric reservoir, containing some 3.9 x 10 t of the gas. Stable N2 molecules dominate, forming 78% of atmospheric volume. Highly variable concentrations of nitric oxide (NO) and nitrogen dioxide (NO2), often designated jointly as NOx, nitrous oxide (N2O), nitrates (NOa ), 

Nitrifying bacteria present in soils and waters transform NH3 to N03 , a more soluble compound plants prefer to assimilate. Assimilated nitrogen is embedded mostly in amino acids that form plant proteins. Heterotrophs (animals and people) 

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The energy of the sun and stars can be attributed at least in part to the well-known carbon-nitrogen cycle. 

One of the things that environmental scientists do IS to keep track of important elements in the biosphere—in what form do these ele ments normally occur to what are they transformed and how are they returned to their normal state Careful studies have given clear although compli cated pictures of the nitrogen cycle the sulfur cy cle and the phosphorus cycle for example The carbon cycle begins and ends with atmospheric carbon dioxide It can be represented in an abbrevi ated form as... 

Fig. 1. Biological pathways and processes iavolved ia the nitrogen cycle.

The Royal Society, The Nitrogen Cycle of the United Kingdom A Study Group Report, The Royal Society, London, 1983. 

The continuous interchange of nitrogen between the atmosphere and the biosphere is called the nitrogen cycle. Global estimates are difficult to obtain and there are frequently regional and local impacts which vary greatly from the mean. However, some indication of the size of the various reservoirs of nitrogen in the atmosphere, on land, and in the seas is... 

C. C. Delwiche, The nitrogen cycle. Chap. 5 in C. L. Hamilton (ed.), Chemistry in the Environment, Readings from Scientific American, W. H. Freeman, San Francisco, 1973. 

I. M. Campbell, Energy and the Atmosphere, 2nd edn. Wiley, London, 1986, Nitrogen cycles, pp 169-81. 

There is also considerable current environmental interest in hyponitrite oxidation because it is implicated in the oxidation of ammonia to nitrite, an important step in the nitrogen cycle (p. 410). Specifically, it seems likely that the oxidation proceeds from ammonia through hydroxylamine and hyponitrous acid to nitrite (or N2O). 

The natural supply of nitrogen available to plants from the nitrogen cycle is limited. To meet the growing demands for agriculture crops, nitrogen is added to soil in the form of fertilizers. An estimated one-third of the human population is fed as a result of the use of synthetic fertilizers. 

Sandia National Laboratories, Albuquerque, NM Biofuels Nitrogen Cycle... 

Like sulfur, nitrogen has stable compounds in a wide range of oxidation states and many of them are foimd in the atmosphere. Again, both gaseous and particulate forms exist as do a large number of water-soluble compounds. Table 7-5 lists the gaseous forms. The nitrogen cycle is discussed in Chapter 12. 

Christensen J. P., Murray, J. W., Devol, A. H. and Codispoti, L. A. (1987). Denitrification in continental shelf sediments has major impact on oceanic nitrogen cycle. Glob. Biogeochem. Cycles 1,97-116. 

To fully understand some of the major players in the nitrogen cycle, we should also consider some of the industrial and social implications of these compounds. 

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