SS18000 - SL16 Biological Nitrogen Fixation 1 D.H. Hubbell...

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SL16 Biological Nitrogen Fixation 1 D.H. Hubbell and Gerald Kidder 2 1. This document is SL-16, one of a series of fact sheets of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First printed: July 1978. Revised February 1992. Reviewed April 1998, September 2003. Please visit the EDIS Web site at http://edis.ifas.ufl.edu. 2. D.H. Hubbell, professor emeritus (deceased) and Gerald Kidder, professor emeritus, Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611-0290. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean. The Importance of Nitrogen Molecular nitrogen (N 2 ) is the major component (approximately 80%) of the earth's atmosphere. The element nitrogen is an essential part of many of the chemical compounds, such as proteins and nucleic acids, which are the basis of all life forms. However, N 2 cannot be used directly by biological systems to build the chemicals required for growth and reproduction. Before its incorporation into a living system, N 2 must first be combined with the element hydrogen. This process of reduction of N 2 , commonly referred to as "nitrogen fixation" (N-fixation) may be accomplished chemically or biologically. Nitrogen (N) is the nutrient element most frequently found limiting to the growth of green plants. This results from the continual loss of nitrogen from the reserve of combined or fixed nitrogen, which is present in soil and available for use by plants. It is continually depleted by such processes as microbial denitrification, soil erosion, leaching, chemical volatilization, and perhaps most important, removal of nitrogen-containing crop residues from the land. The nitrogen reserve of agricultural soils must therefore be replenished periodically in order to maintain an adequate (non-growth limiting) level for crop production. This replacement of soil nitrogen is generally accomplished by the addition of chemically fixed nitrogen in the form of commercial inorganic fertilizers or by the activity of biological nitrogen fixation (BNF) systems. The significance of BNF as the major mechanism of recycling of nitrogen from the unavailable atmospheric form to available forms in the biosphere cannot be overemphasized. The Mechanism of Nitrogen Fixation
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This note was uploaded on 03/10/2008 for the course MCDB 120L taught by Professor Hirsch during the Winter '07 term at UCLA.

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SS18000 - SL16 Biological Nitrogen Fixation 1 D.H. Hubbell...

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