Continuous Corn and Soybean Yield Penalties across Hundreds of Thousands of Fields

CORE IDEAS: Analysis of 748,374 yield records showed a 4.3% yield penalty for continuous corn. Corn yield penalties were more severe in areas with low moisture and low yields. Continuous soybean showed a 10.3% yield penalty, worse in low‐yielding years. Corn yield penalties grew with up to 3 yr of continuous cropping, but not more. Soybean penalties increased monotonically with number of years continuously cropped. The effects of crop rotations on yields have historically been assessed with field trials, but new datasets offer an opportunity to evaluate these effects using data from commercial farmers’ fields. Here we develop a unique dataset of 748,374 joint observations of field‐level yields, crop histories, and soil and weather conditions across the U.S. Midwest to empirically evaluate crop rotations. For rainfed fields, we found an average continuous corn (Zea mays L.) yield penalty (CCYP) of 4.3% and continuous soybean [Glycine max (L.) Merr.] yield penalty (CSYP) of 10.3% during the 2007 to 2012 growing seasons. The CCYP is greater in locations with low moisture, while the CSYP shows the opposite pattern. Relatedly, irrigation decreases the CCYP but not the CSYP. Both penalties increased with the number of years a field had been continuously cropped, and while the CCYP leveled off after 3 yr in corn, the CSYP showed significant increases out to the (very rare) 5‐yr continuous soybean sequence. An analysis of weather, soil, and planting date interactions with the CCYP and CSYP suggests that timely planting, favorable soil‐climate, and warm early and late‐season minimum temperatures correlate with reductions in the CCYP, while dry conditions and less favorable soil‐climate correlate with reductions in the CSYP. The results of this study not only help refine estimates of rotation effects in commercial fields, but also shed light on the relationships between rotation effects and other factors, thereby offering insight into potential causal mechanisms.