Corn yield trends continue to increase in Iowa and across the country. In Iowa, yield is increasing at about 2 bushels per acre per year since the early 1970s. Research conducted at Iowa State University by Don Duvick, adjunct professor of agronomy, focused on comparing "era hybrids" to modern-day hybrids. Analysis of these hybrids has shown that approximately half of the annual yield increase is due to plant breeding efforts and the other half is due to improved crop management practices.