The Nitrogen Cycle An essential part of proteins, DNA and other compounds needed for life…

Nitrogen: N is needed for life’s DNA, protein, amino and nucleic acids Plants use nitrogen (N), phosphorus (P) and potassium (K) for growth. Earth’s atmosphere is 70% nitrogen gas (N 2 ). Nitrogen gas is a form that very few organisms can use (they can’t absorb it directly). In order to be used by organisms, nitrogen gas must be “fixed”

Nitrogen: Nitrogen gas in the atmosphere is composed of two nitrogen atoms bound to each other. Nitrogen is a fairly non- reactive gas. It takes a lot of energy to get nitrogen gas to break up and combine with other elements, such as carbon or oxygen.

Usable Nitrogen : There are 2 ways atmospheric nitrogen can be converted into a usable form for plants and animals 1. Lightening 2.Nitrogen Fixation

Lightening: Lightning provides enough energy to "burn" the nitrogen and fix it in the form of nitrate, NO 3 - This process is duplicated in fertilizer factories to produce nitrogen fertilizers.

Nitrogen Fixation: N 2 gas is converted (fixed) to NO 3 or NH 4 by bacteria living in the soil or the roots (nodules) of some plants These bacteria use special enzymes to fix nitrogen

Nitrogen Fixation: This is done when nitrogen gas is bound to other elements to make it usable by living organisms. add to oxygen to form: NO 3 nitrate add to hydrogen to form: NH 4 ammonium The most important of these bacteria is Rhizobium, a bacterium that lives in nodules on the roots of plants like legumes (peas, beans, alfalfa and clover). Plants can absorb the fixed nitrogen through their roots. Animals must get nitrogen by eating plants or other animals.

The Cycle Begins 1. Most plants can take up nitrates and convert it to amino acids and then possibly proteins. 2. Animals acquire all of their amino acids when they eat plants (or other animals). 3. When plants or animals die (or release waste) the nitrogen is returned to the soil. 4. The nitrogen that is usually returned to the soil in animal wastes or in the output of the decomposers, is ammonia. Ammonia is rather toxic. 5. Nitrifying bacteria in soil or water convert ammonia to nitrates, which are taken up by plants to continue the cycle.

Cycle Completed Soil also contains bacteria the uses NO 3 - as a fuel source. These Denitrifying Bacteria release N 2 back to the atmosphere.

Human Impact: Agricultural/industrial fertilzer Fossil fuel burning Increase the production of N fixing crops (soya beans, peas) ***Human activities add approximately 140 million tonnes of extra N in the environment