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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

View larger version (43K): [in a new window]   Fig. 1. Schematic of the 21-ha Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) research site showing four field boundaries, surface topography, first-order stream, and selected instrument locations.

View larger version (13K): [in a new window]   Fig. 2. Omnidirectional semivariogram of the depth to the restricting layer for the entire Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) research site. The dotted line represents population variance for the depth to the subsurface restricting layer.

View larger version (57K): [in a new window]   Fig. 3. Depth to the ground-penetrating radar (GPR)–identified clay lens for the Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) research site. Dotted lines denote boundaries for Fields A, B, C, and D.

View larger version (64K): [in a new window]   Fig. 4. Spatial distribution of standard error associated with depth to the clay lens in Field B. Spatial contours represent the standard error of the depth to the restricting clay layers. Plus signs (+) denote locations where depth to the clay lens was digitally recorded, and dots represent the field boundary. Flow pathways are denoted by the blue lines and the soil moisture probe locations are denoted with an alphanumeric designation.

View larger version (74K): [in a new window]   Fig. 5. Topography of the subsurface restricting clay layer and location of ground-penetrating radar (GPR)–identified flow pathways. Blue lines denote the flow pathways while the moisture probe locations are designated alphanumerically. HAMSL, height above mean sea level.

View larger version (31K): [in a new window]   Fig. 6. Example of preferential funnel or matrix flow processes on subsurface soil moisture as a function of proximity to a ground-penetrating radar (GPR)–identified flow pathway. Soil moisture content was determined at 1.2-, 1.5-, and 1.8-m depths. Arrows indicate precipitation events of >5 mm. The BM3 and BM1 soil moisture probes are 5 and 15 m away from GPR-identified flow pathways, respectively.

View larger version (51K): [in a new window]   Fig. 7. Relationships between yield and organic matter content (left) and yield and surface elevation (right) over a 3-yr period. HAMSL, height above mean sea level.

View larger version (55K): [in a new window]   Fig. 8. Spatial corn grain yield patterns and their corresponding variograms for 1998 through 2000 growing seasons. On the left, darker regions indicate higher-yielding regions within the field while dotted lines on the right denote population variances. Dashed lines represent corn grain yield variance.

View larger version (43K): [in a new window]   Fig. 9. Schematic of regions representing three buffer zones of increasing distance from the ground-penetrating radar (GPR)–identified flow pathways. Shaded blue regions indicate soil areas for each specified buffer zone and black lines denote GPR-identified flow pathways.

View larger version (28K): [in a new window]   Fig. 10. Impact of the ground-penetrating radar (GPR)–identified clay lens depth on the averaged corn grain yield from three zones representing increasing distance from GPR-identified subsurface flow pathways. The gray-scale denotes the percentage of the Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) site covered by this analysis. Yield data from all four fields are presented in this analysis.

View larger version (16K): [in a new window]   Fig. 11. Effect of horizontal distance from flow pathways on averaged corn grain yield. Yield data from regions where the clay lens was >2 m below the soil surface were excluded from this analysis.

View larger version (34K): [in a new window]   Fig. 12. Averaged surface soil water content as a function of distance from ground-penetrating radar (GPR)–identified flow pathways. Surface soil moisture data (0.10 m) were averaged for three buffer zones (0–5, 5–10, and 10–15 m) around the GPR-identified flow pathways. The vertical dotted line of the left identifies the planting date while the vertical dotted line on the right denotes when reproductive stage begins.