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TECHNICAL REPORTS

Landscape and Watershed Processes

Using Soil Moisture and Spatial Yield Patterns to Identify Subsurface Flow Pathways

^a USDA-ARS Hydrology Laboratory, Natural Resources Institute, Beltsville, MD 20705
^b USDA-ARS Hydrology and Remote Sensing Laboratory, Beltsville, MD 20705
^c Soil Science Department, University of Wisconsin, Madison, WI 53706

^* Corresponding author (tgish{at}hydrolab.arsusda.gov)

Received for publication December 12, 2002. Subsurface soil water dynamics can influence crop growth and the fate of surface-applied fertilizers and pesticides. Recently, a method was proposed using only ground-penetrating radar (GPR) and digital elevation maps (DEMs) to identify locations where subsurface water converged into discrete pathways. For this study, the GPR protocol for identifying horizontal subsurface flow pathways was extended to a 3.2-ha field, uncertainty is discussed, and soil moisture and yield patterns are presented as confirming evidence of the extent of the subsurface flow pathways. Observed soil water contents supported the existence of discrete preferential funnel flow processes occurring near the GPR-identified preferential flow pathways. Soil moisture also played a critical role in the formation of corn (Zea mays L.) grain yield patterns with yield spatial patterns being similar for mild and severe drought conditions. A buffer zone protocol was introduced that allowed the impact of subsurface flow pathways on corn grain yield to be quantified. Results indicate that when a GPR-identified subsurface clay layer was within 2 m of the soil surface, there was a beneficial impact on yield during a drought year. Furthermore, the buffer zone analysis demonstrated that corn grain yields decreased as the horizontal distance from the GPR-identified subsurface flow pathways increased during a drought year. Averaged real-time soil moisture contents at 0.1 m also decreased with increasing distance from the GPR-identified flow pathways. This research suggests that subsurface flow pathways exist and influence soil moisture and corn grain yield patterns.

Abbreviations: DEM, digital elevation map • GPR, ground-penetrating radar • OPE3, Optimizing Production Inputs for Economic and Environmental Enhancement program

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