|Robertson, David - Dave|
Submitted to: American Geophysical Union
Publication Type: Proceedings
Publication Acceptance Date: 9/9/2004
Publication Date: 4/5/2005
Citation: Williams, J.D., Robertson, D.S., Oviatt, H.S. 2005. Changes in storm flow responses as a result of direct seed farming practices on the Columbia Plateau croplands. American Geophysical Union.
Technical Abstract: Mass cultivation of the prairie and shrubland-steppe on the Columbia Plateau began in the 1880's. This region is characterized by very fertile, highly erodible silt-loam soils, developed on steep slopes over Miocene basalts. Early farming practices led to excessive soil loss; lower cropland productivity, fouled in-stream habitat for andronomous and non-andronomous salmonids and eels, and deposition of sediment in first, second, and third order channels that continues to migrate down stream during storm runoff events. Sixty years of soil and water conservation efforts have slowed soil loss from fields. Presently much of the sediment moved during stormflow originates from stream bank erosion, although the annual development of rills in many fields is still observed. To quantify the continuing contribution of sediment to streams, and to evaluate the effectiveness of direct seed farming practices to soil and water conservation, four first order drainages, and one hillslope were instrumented with flumes, weirs, and storm sediment samplers. The area of instrumented drainages and hillslope were, respectfully, 25.0, 18.1, 10.0, and 6.1 ha, and a 25 percent hillslope of 1.6 ha. The 6.1 ha drainage was managed using fallow and inversion tillage practices. In October 2002, the crop stubble was fall burned and the soil was inverted using a moldboard plow; the following spring and summer the drainage was field cultivated and rod-weeded three times to control weeds and prepare the seed bed for winter wheat in October 2003. All other drainages, and the hillslope site, were farmed using direct seed technology consisting of one pass using a direct seed drill to seed and fertilize the crop, one pass to harvest the crop, one pass to break-up crop stubble, and multiple passes to spray herbicides for weed control. Total crop year precipitation for 2002-03 and 2003-04 was 10 percent lower and 15 percent higher, respectively, than the long-term average, representing typical winter-time precipitation patterns for the Columbia Plateau. Four runoff events were recorded from October 2002 through September 2003; the stage recorder failed in the conventionally tilled drainage during two of the events. During the events in which the runoff was recorded, the conventionally tilled drainage yielded 19.39 m^3 and 20.83 m3; for those same events the 10.0 ha direct seed drainage yielded 0 m^3 and 7.24 m^3. Total recorded runoff for the year from the conventionally tilled drainage was 40.21 m^3, and 40.96 m^3 from the 10.0 ha direct seeded drainage. Total annual erosion from the conventionally tilled drainage was 127.05 kg/ha and 8.18 kg/ha from the direct seeded drainage. No runoff or erosion were recorded from the direct seeded 25.0, 18.1 drainages, or the 1.6 ha hillslope. From October 2003 through September 2004, one runoff event was missed and eight events were recorded from the conventionally tilled drainage, yielding 149.89-m^3 runoff, and 286.71-kg/ha soil loss. The direct seeded drainages and hillslope produced no runoff or erosion. Under the climatic conditions during these two winters, the direct seed practices used in this study effectively controlled, runoff and erosion compared to a conventionally farmed drainage, at scales both larger than and smaller than the conventionally drained area. These results demonstrate the immediate soil and water conservation effectiveness of the direct seed technology. They also portend changes in the downstream processes as channels adjust to reduced stormflow volume and energy, and a reduced sediment supply.