What is the principle underlying the use of cyanobacteria in agricultural fields for crop improvement ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Cyanobacteria**: Begin by recognizing what cyanobacteria are. They are photosynthetic microorganisms, often referred to as blue-green algae, that can perform photosynthesis and are capable of fixing atmospheric nitrogen.

2. **Principle of Nitrogen Fixation**: The key principle behind the use of cyanobacteria in agriculture is their ability to fix atmospheric nitrogen. This means they can convert nitrogen gas (N₂) from the atmosphere into ammonia (NH₃), which can then be utilized by plants.

3. **Benefits to Crop Improvement**: The nitrogen fixed by cyanobacteria enriches the soil, making nitrogen available to crops. This leads to improved growth and yield of the crops, as nitrogen is an essential nutrient for plant development.

...