Pictured left: A heap of maize in India
Maize (corn) is a grain and the most widely grown crop in the Americas with 332 million metric tons grown annually in the United States. Approximately 40% of the crop - 130 million tons - is used for corn ethanol. Transgenic maize (Genetically Modified Corn) made up 85% of the maize planted in the United States in 2009. While some maize varieties grow to 12 metres (39 ft) tall, most commercially grown maize has been bred for a standardized height of 2.5 metres (8.2 ft).
Maize is widely cultivated throughout the world, and a greater weight of maize is produced each year than any other grain. The United States produces 40% of the world's harvest; other top producing countries include China, Brazil, Mexico, Indonesia, India, France and Argentina. Worldwide production was 817 million tonnes in 2009—more than rice (678 million tonnes) or wheat (682 million tonnes). In 2009, over 159 million hectares of maize were planted worldwide, with a yield of over 5 tonnes/hectare. Production can be significantly higher in certain regions of the world; 2009 forecasts for production in Iowa were 11614 kg/ha.
Maize was domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable or starch. The Olmec and Mayans cultivated it in numerous varieties throughout central and southern Mexico, cooked, ground or processed through nixtamalization. Between 1700 and 1250 BCE, the crop spread through much of the Americas. The region developed a trade network based on surplus and varieties of maize crops. After European contact with the Americas in the late 15th and early 16th centuries, explorers and traders carried maize back to Europe and introduced it to other countries. Maize spread to the rest of the world due to its ability to grow in diverse climates. Sugar-rich varieties called sweet corn are usually grown for human consumption, and are usually shorter in length than field corn varieties, which are used for animal feed and as chemical feedstocks.