Untangling the Influences of Shallow Groundwater and Soil Texture on Corn Yield Variability.

To meet growing global food requirements in the face of climate change, understanding interactions between drivers of subfield-scale yield variability and growing season weather conditions is critical. We ask (1) can the presence of shallow groundwater increase/decrease corn yield?; and (2) how do soil texture and growing season weather conditions lead to variability in the relationship between groundwater and productivity? Using multiple years of yield measurements from two cornfields in south-central Wisconsin, we identify sections of the fields most vulnerable to either wet or dry growing season weather conditions. We find that areas most vulnerable to wet growing seasons tend to have the shallowest water tables (< 1 m), while areas that perform the worst tend to have the deepest groundwater (> 3 m) and areas with intermediate groundwater depths are relatively consistent from year-to-year. A modeling experiment shows that, at our field site, benefits of shallow groundwater in creating drought resilience outweigh potential yield losses. Based on a factorial suite of simulations, we demonstrate that groundwater yield subsidies are both more frequent and larger in coarse-grained soils, though the optimum water table depth changes at a relatively constant rate across soil types. Overall, this study finds that soil texture sets a relatively static baseline upon which slow (groundwater) and fast (weather) hydrological variables interact to determine year-end yield.