Plants use nitrogen (N), phosphorus (P) and potassium (K) for growth. Earth’s atmosphere is 80% 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 Cycle Explained Nitrogen is critically important to life, as it is a basic building block for amino acids and proteins. 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.
Nitrogen gas can be taken from the atmosphere (fixed - reacted) in two basic ways. 1. 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. 2. Nitrogen fixing bacteria use special enzymes to fix nitrogen (react the nitrogen with oxygen or hydrogen). Nitrogen Fixation
Nitrogen Fixation continued: 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 job of “fixing” nitrogen is up to certain bacteria that are found in the soil and water. The most important of these 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.