Modern Agriculture
In the N and W United States the era of mechanized agriculture began with the invention of such farm machines as the reaper, the cultivator, the thresher, and the combine. Other revolutionary innovations, e.g., the tractor, continued to appear over the years, leading to a new type of large-scale agriculture. Modern science has also revolutionized food processing; refrigeration, for example, has made possible the large meatpacking plants and shipment and packaging of perishable foods. Urbanization has fostered the specialties of market gardening and truck farming. Harvesting operations (see harvester) have been mechanized for almost every plant product grown. Breeding programs have developed highly specialized animal, plant, and poultry varieties, thus increasing production efficiency. The development of genetic engineering has given rise to genetically modified transgenic crops and, to a lesser degree, livestock that possess a gene from an unrelated species that confers a desired quali