Yield and Yield Gaps in Central US Corn Production Systems

The magnitude of yield gaps (YGs) (potential yield -farmer yield) provides some indication of the prospects for increasing crop yield. Quantile regression analysis was applied to county corn (Zea mays L.) yields (1972-2011) from Kentucky, Iowa, and Nebraska (irrigated) (total of 115 counties) to estimate the attainable potential yield (APY) (yield in the most favorable environments in the 40-yr record) for each county. The YG for each year was the difference between the APY and the county yield. Potential productivity (40-yr mean county yield) varied substantially within and among states (579-1001 g m(-2)). The mean relative yield gap (RYG) varied from 9 to 24% of APY and decreased linearly (p < 0.0001) as the mean county yield increased for each state. Large YGs were partially related to very low yields that occurred in some years and may reflect the ability of the soil to supply water to the crop; other soil or management factors may also be involved since irrigation did not reduce the RYG in Nebraska to zero. The highest mean county APY was 30% (Kentucky), 22% (Iowa) and 14% (Nebraska) higher than the lowest county APY. This second YG occurred in favorable environments. Reducing the first YG in Kentucky and Iowa will probably require irrigation. Reducing the second YG may be more difficult if it is related to intractable soil characteristics. These results suggest that soil conditions may play an important role in determining the size of YGs in Midwestern corn production systems.