Which of the following is widely used as a successful biofertiliser in Indian rice fields ?

Options

A. Rhizobium
B. Acacia arabica
C. Acalypha indica
D. Azolla pinnata

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a biofertilizer that is widely used in Indian rice fields. Biofertilizers are substances that contain living microorganisms which promote plant growth by increasing the supply or availability of primary nutrients to the host plant.

2. **Analyzing the Options**: The options provided are:
- A) Rhizobium
- B) Cassia arabica
- C) Acacia indica
- D) Azolla pinnata

3. **Evaluating Each Option**:
- **Rhizobium**: This is a genus of bacteria that forms symbiotic relationships with legumes, fixing nitrogen in the soil. However, it is not primarily used in rice fields.
- **Cassia arabica**: This is a plant species and not known as a biofertilizer.
- **Acacia indica**: This is also a plant species and does not serve as a biofertilizer for rice.
- **Azolla pinnata**: This is a free-floating aquatic fern that is known for its symbiotic relationship with the cyanobacterium Anabaena. This association allows Azolla to fix atmospheric nitrogen, making it an effective biofertilizer for rice cultivation.

4. **Identifying the Correct Answer**: Based on the evaluation, Azolla pinnata is widely recognized for its role in increasing rice yields in Indian rice fields due to its nitrogen-fixing capability through its symbiotic relationship with Anabaena.

5. **Conclusion**: The correct answer to the question is **D) Azolla pinnata**.

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