For what purposes the chemical fertilizers are used in crop fields ?

Explanation

### Step-by-Step Solution:

1. **Understanding Chemical Fertilizers**: Chemical fertilizers are substances that contain essential nutrients required for plant growth. These nutrients typically include nitrogen (N), phosphorus (P), and potassium (K), among others.

2. **Nutrient Depletion in Soil**: Over time, continuous agricultural practices can lead to the depletion of essential nutrients in the soil. This depletion occurs because crops absorb these nutrients for their growth, and if they are not replenished, the soil becomes less fertile.

3. **Purpose of Chemical Fertilizers**: Farmers use chemical fertilizers to replenish the nutrients in the soil. By adding these fertilizers, they aim to restore the nutrient levels, which helps in promoting healthy plant growth.

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