in the last article we discuss about the nutrient cycle so, now let’s see the nitrogen cycle Nitrogen is a very important and essential element for plants. We know that nitrogen is the most abundant gas in the air. Air contains 78% nitrogen. However it can not be used by plants directly similar to oxygen and carbon dioxide. This is because.
The nitrogen is inert for biological systems in atmospheric molecular form Leaves of the plants do not contain any enzyme to capture and reduce nitrogen. Plants can take up nitrogen in the form of ammonium ions or nitrate ions. Nitrogen therefore needs to be fixed before it can be utilised by the plants.
Nitrogen fixation is the process of converting atmospheric molecular nitrogen into ammonia (or ammonium 1ons) and into nitrate ions.
Nitrogen fixation may be brought about with help of certain symbiotic bacteria (like Rizobia).
They convert atmospheric nitrogen into ammonium ions. Such a fixtion is called biological nitrogen fixation. In addition some, cyanobactera (like Nostoc,Anabaena), etc. can also fix the atmospheric nitrogen.
Ammonia can also be formed by soil decomposers from the organic organic matter present in detritus. This is called ammonification.
The ammonia in the soil can be directly used by the plants (as ammonium) or it may be converted into nitrite and nitrate ions with the help of certain re living bacteria such as Azotobacter, Clostridum, etc. This 1s called nitrification Some of the nitrate contents are released to atmosphere as molecular nitrogen and some are used by the plants.
In this way nitrogen maintains a cycle in the nature, known as nitrogen cycle.