The years from 1945 to 1970 saw a second agricultural revolution in the United States. In 1954, tractors outnumbered mules and horses on farms for the first time. In 1940, one farmer could feed 10.7 people. By 1970, that ratio was 1 to 75.8. This advertisement shows how one person could plant several rows of corn by barely lifting a finger. International Harvester Company.