What makes cyanobacteria a very good source of biofertilisers?

Explanation

### Step-by-Step Solution:

1. **Definition of Biofertilizers**:
- Biofertilizers are defined as organisms that enhance the nutrient quality of the soil. They contribute to soil fertility by adding essential nutrients, particularly nitrogen, which is crucial for plant growth.

2. **Introduction to Cyanobacteria**:
- Cyanobacteria, also known as blue-green algae, are a group of photosynthetic bacteria. Examples include Nostoc and Anabaena. They are recognized for their ability to fix atmospheric nitrogen.

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