Which Tuskegee Institute scientist encouraged southern farmers to stop planting cotton and tobacco (which wore out the soil) and focus on peanuts and sweet potatoes?

That would be George Washington Carver. Carver is a very famous person. He was a slave, who worked hard to gain his education. He succeeded and became a scientist and a lecturer at the Tuskegee Institute. Carver was instrumental in introducing new ways for Southern farmers to utilize the peanut. He devised many uses for this crop including dyes and gasoline.