More than 90 percent of all nitrogen are fixed as ammonia, nitrites, and nitrates by soil microorganisms. Symbiotic bacteria associated with leguminous plants fix nitrogen by the formation of root nodules. In which of the following plant nitrogen fixation does not occur?

The Correct answer is Option 4. 

Key Points

• Common Beans (1):  Common beans (Phaseolus vulgaris) are leguminous plants and form symbiotic relationships with nitrogen-fixing bacteria (Rhizobium), leading to nitrogen fixation.  Nitrogen fixation occurs.
• Soybeans (2):  Soybeans (Glycine max) are also legumes that establish symbiotic relationships with nitrogen-fixing bacteria, enabling them to fix nitrogen.  Nitrogen fixation occurs.
• Peanuts (3):  Peanuts (Arachis hypogaea) are leguminous plants that form root nodules with nitrogen-fixing bacteria, facilitating nitrogen fixation.  Nitrogen fixation occurs.
• Oats (4): Oats (Avena sativa) are not legumes and do not form symbiotic relationships with nitrogen-fixing bacteria. Therefore, they do not fix nitrogen in the same way that legumes do.  Nitrogen fixation does not occur.
• Nitrogen fixation does not occur in Option 4: Oats. Hence Correct answer is Option 4.