Technical Abstract: Understanding hydrologic processes is fundamental for characterizing agricultural chemical behavior and crop production at the field and watershed scales. Unfortunately, crop production patterns and hydrologic processes exhibit significant spatial and temporal variability. The concept of soil moisture response zones has been proposed and found to be an effective means for identifying areas within a field that are hydrologically similar. Soil moisture response zones were determined using normalized spatial yield patterns from divergent climatic conditions on a small watershed at the USDA-ARS Agricultural Research Center, Beltsville, Maryland USA. Subsurface hydrology was determined by identifying subsurface convergent flow pathway locations using ground-penetrating radar (GPR), digital elevation maps (DEM) and a GIS. Frequent volumetric soil moisture measurements confirmed the existence of discrete preferential funnel flow processes occurring near the GPR-identified preferential flow pathways. Although the spatial variability of corn (Zea mays L.) grain yield generated coefficients of variation > 114% during a drought, yield were strongly effected by their proximity to GPR-identified subsurface flow pathways. Corn grain yields and the soil moisture response index decreased as the horizontal distance from the GPR-identified subsurface flow pathways increased during a drought. During a growing season where precipitation was abundant, this quantitative relationship was reversed. This research suggests that GPR is an effective tool for quantifying the impact hydrology on crop production.