The chart tells a nice, short story of U.S. agriculture — particularly corn, one of its most important crops. For most of the 19th century, American farmers were able to produce more and more food by planting on ever more acreage.* By the late 1800s, however, yields had stagnated. Policymakers got nervous, and the federal government undertook a series of initiatives to boost U.S. food production — irrigation and dam projects to bring farming to desert areas, railroads to transport food to cities.
The major gains, however, began in the 1920s and 1930s, when scientists began breeding hybrid strains of corn with bigger ears that could bunch more closely together in the field. New industrial fertilizers that could satisfy corn's voracious appetite for nitrogen were also developed. Tractors and other mechanized tools appeared. As the chart shows, yields began skyrocketing. Corn could now be grown in areas that were once unthinkable, like parts of the Great Plains. As Paul Roberts explains in The End of Food, "between 1930 and 1940, the number of bushels of corn per acre doubled, and then continued to rise each year."