The U.S. has led developments in seed improvement, such as hybridization, and in expanding uses for crops from the work of George Washington Carver to bioplastics and biofuels. The mechanization of farming and intensive farming have been major themes in U.S. history, including John Deere's steel plow, Cyrus McCormick's mechanical reaper, Eli Whitney's cotton gin, and the widespread success of the Fordson tractor and the combine harvester. Modern agriculture in the U.S. ranges from hobby farms and small-scale producers to large commercial farms covering thousands of acres of cropland or rangeland.