When a farmer changes the crops each year in same field that is called?

That's called crop rotation.

Here's why it's important:

* Nutrient replenishment: Different crops use different nutrients from the soil. By rotating crops, you can help replenish the nutrients that were depleted by the previous crop.

* Pest and disease control: Rotating crops can help break the life cycles of pests and diseases that are specific to certain crops.

* Soil health: Crop rotation helps improve soil structure, aeration, and water infiltration.

Let me know if you have any other questions!