Prior to sowing rice, why was a legume crop cultivated and ploughed back into the field?

Explanation

### Step-by-Step Solution:

1. **Understanding the Crop Rotation**: Prior to sowing rice, farmers often practice crop rotation, which involves growing a different crop before the main crop. In this case, a legume crop is cultivated.

2. **Selecting Legumes**: Legumes, such as beans, peas, and lentils, are chosen because they have a unique ability to fix atmospheric nitrogen into the soil.

3. **Role of Nitrogen-Fixing Bacteria**: Legumes host nitrogen-fixing bacteria, primarily Rhizobium, in their root nodules. These bacteria convert atmospheric nitrogen (N2) into a form that plants can use, such as ammonia.

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