As part of a study to see if corn yield trends have accelerated since the mid-1990s, agricultural economists at the University of Illinois looked at the impact of weather and technology on corn yields in Illinois, Iowa and Indiana from 1960 to 2007.
"There has been considerable discussion in the agricultural community that improved technology has caused corn trend yields to increase at an increasing rate in recent years," says Scott Irwin, who prepared the study with former graduate student Mike Tannura and Department of Agricultural and Consumer Economics colleague Darrel Good. "There has been a fairly widespread acceptance that a new and higher trend began in the mid-1990s, and it should be used as a starting point for estimating future yields."
However, they found that most of the increase since 1996 is the result of more favorable weather than the area had over the past 20 years. There is some evidence from other university trials and producers that increased yields may be a result of stacked trait corn hybrids, but the researchers say large-scale yield data needs to be examined before assuming an increase in corn trend yields is the result of biotechnology.
The full report "Are Corn Trend Yields Increasing at a Faster Rate?" can be viewed online at the
"This is important not only to individual producers," Irwin says, "But also to current policy debates about the amount of additional acreage that will be needed for corn production in the future to meet ethanol-driven demand growth."
The authors say research by Louis Thompson in 1969 and 1975 about weather and technology's affect on corn yields suggests that a historical weather cycle may be at work. Thompson concluded that cooler weather between warmer than normal temperatures had led to higher production.
"More unfavorable weather for the development of corn followed in 1980, 1983, and 1988," Irwin says. "This further identified the 1960s through the early 1970s - the period that Thompson first studied - as a favorable weather period."
Whether or not you draw a parallel between weather patterns from 1960-1972 and 1973-1995, Irwin says history suggests being cautious about trying to project recent and favorable weather patterns into the future.