Corn originated in the tropical and subtropical highlands of Central and South America centered on Mexico and Guatemala, and American Indians began to grow corn about 7000 years ago. After Columbus discovered the New World, he took corn to Spain. With the development of world navigation, corn has gradually spread all over the world and become one of the most important food crops. About the middle of16th century, China began to introduce corn, which was introduced to India in18th century. At present, China has become the second largest corn producing area in the world.
Among the cereal crops in the world, the planting area and total output of corn are second only to wheat and rice, ranking third and the average yield is the first. It can be planted from 58 north latitude to 42 south latitude, from Turpan Basin in Xinjiang, China, which is below sea level, to high altitude areas above 3600 meters above sea level. The planting area of corn is the largest in North America, followed by Asia, Latin America and Europe. China's corn planting area and total output rank second in the world, and it is concentrated in the oblique belt from northeast to southwest through north China, accounting for about 85% of the national corn planting area.
Corn can be classified in different ways. In the usual trade, there are only two kinds of corn: powder and gel. According to the color, there are two common types: yellow corn and white corn. Common classification methods are divided into nine types according to the grain morphological structure: hard grain type, horse tooth type, powdery type, sweet type, sweet powder type, burst type, waxy type, barnyard grass type and semi-horse tooth type. According to the classification of growth period, it can be divided into three varieties: early maturity, middle maturity and late maturity. According to the grain composition and use, it can be divided into two varieties: special corn and ordinary corn, among which special corn can be divided into high lysine corn, waxy corn, sweet corn, popcorn and high oil corn.
Corn seeds contain 70-75% starch, 10% protein, 4-5% fat and 2% multivitamins. The contents of protein, fat, vitamin A, vitamin B 1 and vitamin B2 in cereals are higher than those in rice. There are more than 500 kinds of processed products made from corn. At present, corn has become the most important feed crop. Corn accounts for more than 65% of the world's coarse grain output and 90% of China's coarse grain output. Corn is the most important raw material for making compound feed, generally accounting for 65-70%.