Author
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Williams, John |
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Long, Daniel |
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Wuest, Stewart |
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Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/20/2011 Publication Date: 5/1/2012 Citation: Williams, J.D., Long, D.S., Wuest, S.B. 2012. Capture of Plateau Runoff by GPS Guided Seed Drill Operation. Journal of Soil and Water Conservation. 66(6):355-361. Interpretive Summary: Contour seeding has long been recommended as a means of detaining water on hillslopes, increasing infiltration, and reducing runoff and soil erosion. Highly undulated landscapes with complex slopes such as those found in the inland Pacific Northwest have stymied application of this practice. New technology consisting of digital elevation models (DEMs) and GPS-based guidance or autosteer systems could be used to help farmers use contour seeding under in this region. To evaluate the feasibility of combining this new technology with proven practices, we assessed (1) the potential for contour planting to capture water that collects on plateaus that otherwise would run off and form severe rills, and (2) determine the resolution and accuracy of terrain representation by DEMs for deriving routing information for planting on elevation contours. We tested the capacity of 8 inch deep furrows to capture and infiltrate runoff in a cultivated Ritzville silt loam. We determined 2% of the contributing area is needed to capture runoff, increase infiltration, and consequently influence overland flow and erosion processes. A GPS unit mounted on an implement with a 30 ft swath was able to capture data with sufficient accuracy to model the terrain and create contour paths to be followed while seeding. Using DEM-derived contour lines, precisely tracked by farm equipment and applied to areas above steep slopes, contour planting will improve soil and water conservation in mechanical tillage systems. The method can be implemented using commercially available mapping software and autosteering equipment designed for tractors and drills. Technical Abstract: Contour tillage has long been recommended as a means of detaining water on hillslopes, increasing infiltration, and reducing runoff and soil erosion. Highly undulated landscapes with complex slopes such as those found in the inland Pacific Northwest have stymied application of this practice. This study investigated the potential usefulness of creating tillage paths using digital elevation models (DEMs) and GPS-based guidance systems to efficiently and effectively conduct terrain contouring seeding. The objectives were to (1) assess the potential for contour planting to capture water that collects on plateaus that otherwise would run off and form severe rills, and (2) determine the resolution and accuracy of terrain representation by DEMs for deriving routing information for planting on elevation contours. A preliminary infiltration and runoff study was conducted in a cultivated field, in a Ritzville silt loam (coarse-silty, mixed, superactive, mesic Calcidic Haploxerolls) and 0% to 20% slopes. Planting was performed with a deep furrow drill on the contour creating furrows 20 cm deep. Measurements of the area needed to capture water introduced through furrows perpendicular to the contour furrows show this technique has the potential to increase detention storage, infiltration, and consequently influence overland flow and erosion processes. A DEM was developed from data representing global positioning system (GPS) collection at three different implement widths: 3 m (9.8 ft), 6 m (20 ft), and 9 m (29.5 ft). Digital elevation data were collected with a real time kinematic global positioning system (GPS) and processed using four software interpolation methods to develop surface models. The ability of each interpolation method to accurately create contour paths for equipment to follow was compared to points established on the ground with a laser-level. Our results demonstrated that a strip of deep-furrow seeding precisely contoured on the upper shoulder slope should provide sufficient detention storage to capture and hold the runoff from a 100 yr 24 h storm if the contour strip area was approximately 2% of the runoff collection area. The maximum difference in horizontal and vertical distances between the reference and modeled contour lines increased with decreasing DEM resolution from 3 to 6 and 9 m (9.8, to 20, to 29.5 ft). Despite this, interpolation using the regularized spline method produced contour lines at ±0.85 m (33.5 in) horizontal and ±0.07 m (2.8 in) vertical from reference elevation points in the 9 m (29.5 ft) DEM cell size. Using DEM-derived contour lines, precisely tracked by farm equipment and applied to areas above steep slopes, contour planting will improve soil and water conservation in mechanical tillage systems. The method can be implemented using commercially available mapping software and autosteering equipment designed for tractors and drills |
