Question:
...... is used as green manure
...... is used as green manure
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Azolla + Anabaena symbiosis = natural nitrogen fertilizer.
Updated On: Jul 18, 2026
- Crotalaria juncea
- Azolla
- Azadirachta indica
- Hevea brasiliensis
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The Correct Option is B
Solution and Explanation
Step 1: Understanding green manure.
Green manure refers to plants that are grown specifically to be ploughed back into the soil. These plants enrich the soil with organic matter and nutrients, especially nitrogen. It improves soil fertility naturally without chemical fertilizers.
Step 2: Role of nitrogen fixation.
Green manure plants often have the ability to fix atmospheric nitrogen. This increases nitrogen content in the soil and improves crop productivity. Such plants are especially useful in sustainable agriculture systems.
Step 3: Understanding Azolla.
Azolla is a water fern that lives in symbiosis with nitrogen-fixing cyanobacteria (Anabaena). It is widely used in paddy fields as a biofertilizer and green manure. It decomposes quickly and enriches soil nitrogen content.
Step 4: Evaluation of other options.
Crotalaria is also used as green manure but Azolla is more efficient in aquatic systems. Azadirachta indica is used for medicinal purposes and Hevea brasiliensis is a rubber-producing plant.
Step 5: Agricultural significance.
Azolla improves soil structure, increases nitrogen availability, and reduces dependence on chemical fertilizers. It is widely used in sustainable rice cultivation systems.
Step 6: Final conclusion.
Thus, Azolla is correctly identified as green manure.
Green manure refers to plants that are grown specifically to be ploughed back into the soil. These plants enrich the soil with organic matter and nutrients, especially nitrogen. It improves soil fertility naturally without chemical fertilizers.
Step 2: Role of nitrogen fixation.
Green manure plants often have the ability to fix atmospheric nitrogen. This increases nitrogen content in the soil and improves crop productivity. Such plants are especially useful in sustainable agriculture systems.
Step 3: Understanding Azolla.
Azolla is a water fern that lives in symbiosis with nitrogen-fixing cyanobacteria (Anabaena). It is widely used in paddy fields as a biofertilizer and green manure. It decomposes quickly and enriches soil nitrogen content.
Step 4: Evaluation of other options.
Crotalaria is also used as green manure but Azolla is more efficient in aquatic systems. Azadirachta indica is used for medicinal purposes and Hevea brasiliensis is a rubber-producing plant.
Step 5: Agricultural significance.
Azolla improves soil structure, increases nitrogen availability, and reduces dependence on chemical fertilizers. It is widely used in sustainable rice cultivation systems.
Step 6: Final conclusion.
Thus, Azolla is correctly identified as green manure.
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