It is widely accepted that yields decline when corn (Zea mays L.) is grown continuously vs. in rotation with soybean [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 with third‐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 significant 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 with CCYP, 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 DELTADIFF to 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.

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ABSTRACTe need to intensify agricultural production due to a growing human population requires yield gaps to be closed. In 2009 and 2010, ve management factors were assessed for their individual and cumulative contributions to reducing the corn (Zea mays L.) yield gap and yield components in a corn-soybean [Glycine max (L.) Merr.] rotation. Five management factors (plant population, transgenic insect resistance, fungicide containing strobilurin, P-S-Zn fertility, and N fertility) were evaluated. An incomplete factorial design with these factors resulted in 12 treatments, including two controls: high technology (HT) and standard technology (ST), comprising all ve factors applied at the supplemental or the standard level, respectively. e HT control yielded 2.9 Mg ha -1 (2.12-3.50 Mg ha -1 across sites and years) more grain (28%) than the ST control, demonstrating the yield gap between traditional farm practice and attainable yield using available technologies. All management factors except plant population were necessary for reducing the yield gap. Fungicide and Bacillius thuringiensis gene (Bt) traits provided the greatest yield increases compared to the ST system. Averaged over sites and years, if each factor was withheld from the HT system, yield decreased by decreasing kernel number. Increased plant population reduced the yield gap when all other inputs were applied at the supplemental level. Kernel number was more signi cant for increasing yield than kernel weight. e yield contribution of each factor was greater when applied as part of a full complement of supplemental inputs than when added individually to the standard input system. Abbreviations: Bt, Bacillius thuringiensis gene; -Bt, HT control system with non-Bt variety; +Bt, ST control with Bt-containing variety added; CU, Champaign-Urbana study site; DS, Dixon Springs Research Center site; -Fung, HT control treatment without fungicide; +Fung, ST control treatment with added fungicide; HT, high technology level; +N, additional side-dress N to ST control; -N, HT control without side-dress application; +Pop, high population treatment added to ST control; -Pop, decreased population treatment within HT control; +P-S-Zn, P, S, and Zn combination fertilizer added to ST control; -P-S-Zn, HT control treatment without P-S-Zn combination fertilizer; ST, standard technology level; VT, tasseling.Numerous recent papers have established that agricultural production must increase substantially to meet the increasing per capita demand for food, feed, fuel, and fi ber of a burgeoning human population (Keyzer et al., 2005, Food and Agriculture Organization, 2009. From a global perspective, it is generally agreed that agricultural intensifi cation (increasing agricultural production per unit area) is preferable to extensifi cation (expanding agriculture onto new areas) as a means of increasing crop production Burney et al., 2010;McLaughlin, 2011;Tilman et al., 2011;Foley et al., 2011). In contrast to the question of whether yield increases are needed, the more practical i...

Corn (Zea mays L.) production systems can benefit from introducing a leguminous winter cover crop into the rotation, especially with regard to increased N availability (i.e., legume N credit); however, it is not known if the full agronomic benefit is realized in the first year of cover crop introduction or if the benefit is cumulative with time. The objective of this study was to determine the apparent red clover (Trifolium pratense L.) N credit to corn in a conventional system where red clover was introduced for the first time compared with three agricultural systems that had a 14‐yr history of using cover crops. The apparent red clover N credit was calculated by the difference in unfertilized corn N accumulation between cover and no‐cover split‐split plots. These data suggest that corn growers can realize the full benefits of a red clover cover crop in the first year of introduction.

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