Azolla pinnata has been found to be an important biofertiliser for paddy crops. This quality is due to the presence of

Options

A. `N_(2)` fixing bacteria
B. `N_(2)` fixing cyanobacteria
C. mycorrhizae
D. all of these

Answer

**Step-by-Step Solution:**

1. **Identify the Organism**: The organism in question is Azolla pinnata, which is a species of fern.

2. **Common Names**: Azolla pinnata is commonly known as water velvet and mosquito fern.

3. **Role in Agriculture**: Azolla pinnata is recognized as an important biofertilizer for paddy (rice) crops.

4. **Reason for Biofertilizer Quality**: The biofertilizer quality of Azolla pinnata is primarily due to its ability to fix nitrogen in the soil.

5. **Symbiotic Relationship**: This nitrogen-fixing ability is a result of a symbiotic relationship with cyanobacteria (also known as blue-green algae).

6. **Process of Nitrogen Fixation**: In this symbiotic relationship, cyanobacteria convert atmospheric nitrogen into a form that is usable by plants, which is then incorporated into the soil.

7. **Importance of Nitrogen for Paddy Crops**: Nitrogen is essential for the growth of rice plants, as it is a crucial nutrient that promotes healthy growth and high yield.

8. **Cultivation Method**: Farmers cultivate Azolla in wet soil, and after a certain period, they plough it under the soil. This process enriches the soil with nitrogen, enhancing its fertility.

9. **Outcome**: The incorporation of Azolla into the soil leads to improved nitrogen content, which supports the growth of paddy crops, resulting in higher yields.

**Final Answer**: The quality of Azolla pinnata as an important biofertilizer for paddy crops is due to the presence of cyanobacteria, which facilitate nitrogen fixation.

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