Question

Which of the following biofertilizer is used to fix Nitrogen from the atmosphere nonsymbiotically

• A. Rhizobium
• B. Azolla
• C. Azotobacter
• D. Azospirillum

Hint:

Rhizobium = Symbiotic (Legumes).
Azotobacter = Free-living (Non-legumes).
Azospirillum = Associative (Cereals).
Azolla = Water-fern symbiosis (Paddy).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify a biofertilizer (nitrogen-fixing organism) that functions independently in the soil without forming a structured symbiotic relationship with a plant host.
Detailed Explanation:

• Free-living (Non-symbiotic) Fixers:
These organisms fix nitrogen while living freely in the soil, utilizing organic matter as energy.
{Azotobacter is a classic example of an aerobic, free-living nitrogen fixer. It is used as a biofertilizer for non-leguminous crops like wheat, rice, and vegetables.

• Symbiotic Fixers:
Rhizobium: Must form nodules on the roots of legumes to fix nitrogen. It is a true symbiont.
Azolla: An aquatic fern that has a symbiotic relationship with the cyanobacterium Anabaena azollae inside its leaves.

• Associative Symbiotic Fixers:
Azospirillum: This bacterium lives in close association with the roots (rhizosphere) of cereal crops (like maize and jowar) but does not form specialized structures like nodules. It is often termed "associative" rather than purely non-symbiotic.

• Conclusion:
Among the options, Azotobacter is the definitive choice for a non-symbiotic biofertilizer.

Step 2: Final Answer:
The biofertilizer used for non-symbiotic nitrogen fixation is Azotobacter.