Wednesday, August 7, 2013

Nitrogen

Nitrogen (N) is one of the essential building blocks of nucleotides for DNA and RNA and of amino acids for proteins. Nitrogen is necessary for all of life on earth. For plants, nitrogen is the limiting factor for growth and the primary ingredient in fertilizer. Plant’s can only absorb nitrogen as ammonia (NH3) or as nitrate (NO3). These molecules are relatively scarce compared to atmospheric nitrogen (N2) that makes up 78.09% of earth’s atmosphere. 

Before 1913, all of the nitrogen in plants and animals was produced by organic bacteria with special enzymes that convert atmospheric nitrogen to absorbable forms. Today more than half of the nitrogen in our bodies was produced industrially from fossil fuels using a synthetic process of Nitrogen fixation. Industrial nitrogen fertilizers are a major source of environmental pollution.

The nitrifying reactions of bacteria
Atmospheric nitrogen to ammonia:
N2 + 8H+ + 8e- => 2NH3 + H2
Ammonia to nitrite by Nitrosomonas bacteria:
2NH3 + 3O2 => 2NO2 + 2H+ + 2H2O
Nitrite to nitrate by Nitrobacter bacteria:
2NO2- + O2 => 2NO3-
Ammonia is the first product of nitrogen fixation by bacteria called diazotrophs using the enzyme nitrogenase. These bacteria are abundant in low-oxygen environments like soil, mud and decomposing organic materials. Urea, a component of animal urine is also metabolized by bacteria with the enzyme urease to produce ammonia. Ammonia is a weak base and reacts with acids to form ammonium (NH4+) salts. The ammonium ion in water is readily available for absorption by plants.

Nitrosomonas bacteria convert ammonia to nitrite, which is not a form of nitrogen available to plants. Nitrobacter bacteria convert nitrite to nitrate which is available to plants.
Plant Nutrition Facts
Nitrogen (N)
Absorbable Forms Nitrate (NO3-) and Ammonium (NH4+)
Fertilizers ammonium nitrate, sodium nitrate, potassium nitrate, calcium nitrate, urea
Symptoms of Deficiency Oldest leaves turn yellow and die prematurely; plant is stunted
Action
Necessary for the synthesis of proteins and nucleic acids. Nitrogen is the limiting factor of vegatation and growth.
Plant Nutrition
Plants need nitrogen throughout the grow cycle. Plants use more nitrogen during the vegetative stage to grow and produce leaves. Plants use less nitrogen when flowering and fruiting.
Origin
Synthetic: The major source of industrial nitrogen fertilizer is anhydrous ammonia: a chemical gas most abundantly derived from non-renewable fossil fuels.

Organic: Nitrogen is made available organically through decomposition by nitrogen-fixing bacteria in soil. Organic fertilizers use natural sources for nitrogen like animal waste or composted materials.

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