A farmer divided his piece of land into 4 equivalent groups. The quality of the soil is the same across the 4 groups of land. He planted the same crop in all 4 groups of land and recorded the yield of the crop in all 4 groups for a 4 week period. Is the study observational or experimental? If it is an experiment, what is the controlled factor?

The study is an observational study.
The study is an experiment. The controlled factor is the 4 week observation period. The study is an experiment. The controlled factor is the land.
The study is an experiment. The controlled factor is the growth of the crops.