The Continuous Corn Penalty: Seven Years of Rotation and Nitrogen Fertilization Impacts On Corn Yield.

Although corn can be cropped continuously, it is widely accepted that there is a yield reduction compared to corn rotated with soybean.  The objectives of this study were to elucidate the source of the continuous corn penalty and to identify circumstances under which increased nitrogen (N) fertilizer rate can alleviate the penalty.  The experiment was conducted from 2005-2010, beginning with 3^rd year corn or soybean as the previous crop.  There was a strong year effect, revealing that the continuous corn penalty may be overcome during a favorable growing season when N fertilizer rate is increased.  During 2006, the 3^rd year of continuous corn production and a favorable growing season, corn yields in both continuous corn and corn-soybean attained an average of 12 Mg ha^-1; however, an additional approximately 50 kg N ha^-1 was required to reach the same yield plateau in continuous corn as in corn-soybean.  During a poor growing season, additional N fertilizer will not overcome the continuous corn yield penalty, as seen in 2005.  The penalty became greater as the continuous corn rotation was extended.  By the 7^th year of continuous corn, an unacceptably high N fertilizer rate (greater than 224 kg N ha^-1) would be required to overcome the continuous corn yield penalty, regardless of growing season conditions.    Although the specific source(s) of continuous corn yield penalty was not definitively proven, we showed that it was not entirely due to N immobilization, as is commonly asserted.  It was also not due to poorer corn emergence or stand establishment in continuous corn since corn was thinned in all plots to a specific population.  It appears likely that the corn penalty is primarily the result of soil property changes resulting from the presence of the previous season’s corn stover although an autotoxic response of corn has not been disproven.