玉米与小麦、水稻、马铃薯和大豆合称世界5大主要作物,也是美国最重要的作物。在美围每年约播种玉米7500万英亩(4.6亿亩),产值200亿美元。杂种玉米以其优异的茎秆强度和整齐度而适合于机械收获和贮藏。玉米杂交种技术改进经40年之后出现了单交种。优良的自交系和先进的栽培技术使单交种得以推广。廉价的氮肥、更高的密度和更有效的除莠剂是实现杂交种增产的主要因素。遗传改良也有长足的 Together with wheat, rice, potatoes and soybeans, maize is the fifth largest crop in the world and the most important crop in the United States. Approximately 75 million acres (460 million mu) of corn are sown every year in Miwei, with a production value of 20 billion U.S. dollars. Hybrid maize is suitable for mechanical harvesting and storage for its excellent stalk strength and uniformity. Improvements in maize hybrids occur 40 years after the single cross breed. Excellent inbred lines and advanced cultivation techniques have allowed the promotion of single crosses. Cheap nitrogen fertilizers, higher densities and more effective herbicides are major contributors to increased yields of hybrids. Genetic improvement is also substantial