Identifying factors controlling the continuous corn yield penalty

It is widely accepted that yields decline when corn (Zea mays L.) is grown continuously vs. in rotation wiThsoybean [Glycine max (L.) Merr.], although causes for the yield reduction are unclear. The primary objective of this study was to elucidate the source(s) of the continuous corn yield penalty (CCYP). The experiment was conducted from 2005 to 2010 in east-central Illinois beginning wiThthird-year continuous corn (CC) or a soybean-corn (SC) rotation at six N fertilizer rates. Averaged across all years, yield at the agronomic optimum N rate for CC was 8.84 Mg ha^-1 and for SC was 10.20 Mg ha^-1, resulting in a CCYP of 1.36 Mg ha^-1; values ranged yearly from 0.47 to 2.23 Mg ha^-1. Using a regression model, three signifi cant and independent predictors explained >99% of the variability in the CCYP: unfertilized CC yield (0NCCYD), years in CC (CCYRS), and the difference between CC and SC delta yields (maximum yield - Unfertilized yield) (DELTADIFF). The strongest predictor, 0NCCYD, reflects net soil N mineralization and demonstrates that it decreases in CC systems. The CCYRS was strongly and positively correlated wiThCCYP, indicating that the CCYP increased through Year 7. We believe that CCYRS measures the effects of accumulated corn residue in CC systems. Finally, we consider DELTADIFFto be a measure of the interaction between yearly weather patterns and crop rotation, which results in more negative yield responses for CC than SC under hot or dry conditions. This study concluded that the primary causative agents of the CCYP are N availability, corn residue accumulation, and weather.