Impact of growing-season weather on corn and soybean yield in Illinois

This study aims to (a) investigate growing-season weather conditions with the yield of soybean and corn commercially grown in alternate rotation on a farm in Champaign, Illinois, (b) identify anomalies in this relationship, and (c) evaluate changes in microclimate variables during crop growing stages and associated changes in annual yield. To achieve these aims, we evaluated 21 years (1997–2017) of annual yield data alongside hourly microclimate measurements from a 10-m flux tower at the crop site. While the annual yield for the study period varied about the mean of 350 ± 63 g m^-2 for soybean and about 1200 ± 185 g m^-2 for corn, our evaluations using linear regression best-fit equations showed generally low correlations between microclimate variables and the annual yield. The growing season daily soil water within the top 1-m soil depth showed consistent values above 300 mm that were close to the field capacity (330 mm) of the dominant field soil of silty clay loam. Fitted regression lines between yield and microclimate variables averaged over June, July and August showed modest correlations for corn yield versus growing degree days (R² = 0.52), precipitation (R² = 0.43) and evapotranspiration (R² = 0.41), as well as a modest correlation between soybean yield and precipitation (R² = 0.31). Regressions between yield and vapor pressure deficit, solar radiation, soil water content and carbon dioxide flux showed poor correlations that were less than R² of 0.21. This study offers a useful evaluation of the yield in rainfed corn and soybean conditions and demonstrates that simple regression analysis may be insufficient in representing complex crop-microclimate interactions. However, the microclimate evaluation presented in this study could serve as a valuable contribution to the application of dynamic crop models.