The correct answer is option 4, "For increasing fertility of the soil."

Rotation of crops is an important agricultural practice that involves growing different crops in the same area over a period of time. This practice helps to improve the fertility of the soil.

When the same crop is grown in the same area year after year, it depletes the soil of specific nutrients and can lead to the build-up of pests and diseases. By rotating crops, different plant species are introduced to the soil, which helps to break the cycle of nutrient depletion and reduce the threat of pests and diseases.

Additionally, different crops have different nutrient requirements, so by rotating crops, the soil is given an opportunity to naturally replenish and regain its fertility. This ultimately leads to healthier crops, improved yields, and sustainable agriculture practices.