. In humid, crop-producing areas the adoption of tractors during the 1930s and 1940s freed up land that had been used to feed horses. Increased use of fertilizer and improved seed varieties raised total production without adding more acres to the farm. These options, largely unavailable to livestock producers who dominated the drier sections of the Plains, resulted in only modest changes in farm numbers and size in the eastern third of the Dakotas and Nebraska, and northeastern Kansas. Average farm size increased less than 20 percent in many eastern counties before 1950.
