CRITICAL ZONE INTERACTIONS BETWEEN GROUNDWATER, SOIL, AND AGRICULTURAL PRODUCTION

To meet increasing global food requirements while sustainably managing water resources, it is imperative to understand the role of saturated and unsaturated critical zone processes play in driving agricultural yield variability. Here, we investigate the interactions between groundwater depth and soil texture heterogeneity in influencing food production. Typically, crops grown in fine-grained soils are more vulnerable to oxygen stress and waterlogging during wet years, a problem which is exacerbated when groundwater is close to the land surface. However, during dry years, these same characteristics (high water retention properties, shallow groundwater supply) can buffer yield losses due to drought. Based on a multi-year field study of two commercial cornfields in south-central Wisconsin and biophysical modeling using AgroIBIS-VSF, we demonstrate that both the saturated zone (groundwater depth) and vadose zone (soil textural properties) interact to impact corn productivity. We find that yield varies spatially, due to differences in soil texture and groundwater availability. The nature of these relationships shifts across years, due to variable growing season weather conditions. In 2013, a year with higher-than-average early season rain leading to shallow water tables and flooding, yield was suppressed in low-lying and fine-grained portions of the study area. In contrast, during a severe drought in 2012, these low-lying/fine-grained regions had the highest yield. The modeled optimum groundwater level for peak yield changes due to both soil texture and growing season weather conditions, but across most years the presence of shallow groundwater can lead to increased yield relative to free drainage conditions, which we define as the groundwater yield subsidy. These results illustrate the complex nature of interactions occurring between water, soil, and vegetation spanning the critical zone, and highlight the need to understand the in situ influence of shallow groundwater and soil texture on crop yield to sustainably increase food production in the 21^st century.