Azolla is used as a biofertilizer because it

Options

A. multiplies very fast to produce massive biomass.
B. has an association of nitrogen - fixing Rhizobium
C. has an association of nitrogen - fixing cyanobacteria
D. has an association of mycorrhiza

Answer

To solve the question "Azolla is used as a biofertilizer because it," we need to analyze the options provided and understand the role of Azolla in agriculture.

### Step-by-Step Solution:

1. **Understanding Azolla**:
- Azolla is a type of water fern that grows in aquatic environments. It is known for its ability to fix nitrogen in the soil.

**Hint**: Remember that Azolla is a water fern and has a unique relationship with certain microorganisms.

2. **Evaluating the Options**:
- **Option 1**: "Azolla multiplies very fast to produce massive biomass."
- While Azolla does multiply quickly, this characteristic alone does not explain its role as a biofertilizer.

**Hint**: Think about how biomass alone contributes to soil fertility.

- **Option 2**: "An association of the nitrogen-fixing Rhizobium."
- This option is incorrect because Rhizobium is typically associated with legumes, not Azolla.

**Hint**: Consider which organisms are known for nitrogen fixation in aquatic environments.

- **Option 3**: "An association of nitrogen-fixing Cyanobacteria."
- This is the correct answer. Azolla has a symbiotic relationship with cyanobacteria (specifically Anabaena), which helps in fixing atmospheric nitrogen, enriching the soil.

**Hint**: Identify the specific type of bacteria that works with Azolla to enhance nitrogen levels.

- **Option 4**: "An association of mycorrhizae."
- Mycorrhizae are beneficial fungi associated with plant roots, not directly with Azolla.

**Hint**: Recall the role of mycorrhizae and how they differ from cyanobacteria.

3. **Conclusion**:
- The correct answer is **Option 3**: Azolla is used as a biofertilizer because it has a symbiotic association with nitrogen-fixing cyanobacteria, which increases the fertility of the soil.

### Summary:
Azolla is utilized as a biofertilizer due to its symbiotic relationship with nitrogen-fixing cyanobacteria, which enhances soil fertility and promotes better crop yields.