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Nitrogen is an essential element because it is a part of nucleic acids (DNA and RNA). So the nitrogen in the organisms is converted into atmospheric nitrogen (highly unreactive) while decomposition. For that instance, nitrogen-fixing bacteria like Rhizobium, Azotobacter, Anabaena convert atmospheric N2 into unstable ammonia. So,

'Nitrogen fixation refers to the process of converting atmospheric nitrogen into ammonia.

Nitrogen-fixing bacteria use the enzyme nitrogenase for fixing nitrogen in soil. As nitrogenase contains molybdenum; it ensures effective nitrogen fixation.

Nitrogen fixation play important role in agro- systems by substituting biofertilizers and techniques.

(1.) Biofertilizers - These fertilizers are produced by utilizing nitrogen fixing bacteria. Bacteria like anabaena, helps in stimulating the fertility of soil and enhances plant growth.

(2.) Crop- rotation - In this technique , farmers grow leguminous plants in one season for increasing the fertility of soil and grow the other crop in next season for enhancing it's productivity.

So these are eco-friendly techniques by which means farmers enhances the fertility of soil and plant growth for better yield.