The tool used for sowing seeds by a tractor is called a seed drill. 

A seed drill is a modern seed-sowing tool which is attached to the back of the tractor and has multiple pores on it. The tool is dragged along the soil and the seeds fall on the soil at equal distances.

The seed drill ensures that each seedling has enough space to grow and access the resources it requires, such as sunlight, water, and nutrients, by sowing seeds at equal distances and at a consistent depth. This can result in a more even plant stand, which can help to maximize yields and reduce crop losses caused by overcrowding or disease.