In 1999, the United States produced a substantial share of the world's agricultural commodities. Agricultural exports reached $56.7 billion in 2001. The United States had an agricultural trade surplus of $11.7 billion in 2001, third after Australia and Brazil.
Between 1930 and 1998, the number of farms in the United States declined from 6,546,000 to an estimated 2,190,000. The total amount of farmland increased from 399 million hectares (986 million acres) in 1930 to 479 million hectares (1.18 billion acres) in 1959 but declined to 386 million hectares (954 million acres) in 1998. From 1930 to 1998, the size of the average farm tripled from 61 to 136 hectares (from 151 to 435 acres), a result of the consolidation effected by large-scale mechanized production. The farm population, which comprised 35% of the total US population in 1910, declined to 25% during the Great Depression of the 1930s, and dwindled to less than 2% by 1998.
A remarkable increase in the application of machinery to farms took place during and after World War II (1939–45). Tractors, trucks, milking machines, grain combines, corn pickers, and pickup bailers became virtual necessities in farming. In 1920 there was less than one tractor in use for every 400 hectares (1,000 acres) of cropland harvested; by 1997 there were five tractors per 400 hectares. Two other elements essential to US farm productivity are chemical fertilizers and irrigation. Fertilizers and lime represent more than 6% of farm operating expenses. Arable land under irrigation amounted to 12% of the total in 1998.
Substantial quantities of corn, the most valuable crop produced in the United States, are grown in almost every state; its yield and price are important factors in the economies of the regions where it is grown. Production of selected US crops in 1999 (in 1,000 metric tons), and their percent of world production were wheat, 62,662 (10.7%); corn, 239,719 (39.9%); rice, 9,546 (1.6%); soybeans, 71,928 (46.6%); cotton, 3,691 (20.2%); and tobacco, 576 (8.1%).