Stability of Corn Yield Response to Crop Rotation: A 40-Year Retrospective.

Numerous studies have confirmed that continuous corn (CC) exhibits reduced grain yields in comparison to a corn-soybean rotation (CS). However it is unclear what factors drive this yield lag. Using grain yield and weather data from an on-going, 40-year long term tillage and crop rotation experiment near West Lafayette, IN, the objective of this study was to discern what critical environmental factors lead to the reduced yields observed in CC cropping systems. Treatments include both tillage (no-till, fall chisel plow, fall moldboard plow) and crop rotation (CC, CS). The overall average yield reduction in CC compared to CS was 1074 kg ha^-1. Previous research suggests that the gap between CC and CS yields increases with added years of CC. Our analysis of the change in grain yield over time, however, shows that CC and CS yields have increased at the same rate over the past 40 years. There has also been speculation that CC yield depression is partially explained by increased corn residue in the spring causing wetter and colder soils at the time of planting. Although no individual weather factor was a strong predictor of grain yield, our analysis found that either season-long cumulative growing degree days or precipitation had a greater influence on final yield than either factor alone in the 30 days before, or in the 0-30 or 31-60 days after planting, thus disproving this theory. The weather factor that was most sensitive to final grain yield in both CC and CS was the Shannon diversity index, used to quantify the distribution of rainfall over a given period. Heavy rainfalls in short time frames within the first 60 days were particularly detrimental to final yield. Although this analysis was unable to determine which environmental factors are responsible for the depression of CC yields, we have established that CC yields have increased at the same rate as CS over time and CC yields are not affected differently by climatic factors such as growing degree day accumulation, cumulative precipitation, or rainfall distribution.