Capture of plateau runoff by global positioning system-guided seed drill operation

Abstract

Contour seeding has long been recommended as a means of detaining water on hillslopes, increasing infiltration, and reducing runoff and soil erosion. Highly undulated land- scapes 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 using digital elevation models (DEMs) and global positioning system-based guidance systems to efficiently and effectively conduct terrain contouring seeding on a small portion of a field to intercept concentrated runoff. 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) to 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, super- active, mesic Calcidic Haploxerolls) with 0% to 20% slopes. Planting was performed with a deep-furrow drill, creating furrows 20 cm (7.9 in) deep. Measurements of the amount of precisely contoured area needed to capture water introduced through furrows perpendicular to the contour furrows show this technique has the potential to increase detention stor- age, infiltration, and consequently, to influence overland flow and erosion processes. A DEM was developed from data representing global positioning system collection at three different implement widths: 3, 6, and 9 m (9.8, 20, and 29.5 ft). Digital elevation data were collected with a real-time kinematic global positioning system and were 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 y, 24 h storm if the contour strip area was approxi- mately 2% of the runoff collection area. Using DEM-derived contour lines, precisely tracked by farm equipment and applied to areas above steep slopes, contour planting of small, select areas of a field will improve soil and water conservation in tillage systems. The method can be implemented using commercially available mapping software and autosteering equipment designed for tractors and drills.