Much soil erosion in the inland Pacific Northwest dryland farming region occurs with low intensity rainfall onto frozen soil, often accompanied by snowmelt. The erosion is most acute in fields with steep slopes and minimal green or residue cover, a condition common to wheat - summer fallow cropping practices. Rough surfaces, green cover, crop residues, contour tillage and seeding, and terracing are established and typically employed erosion control methods. These methods often are inadequate, however, when erosion is associated with frozen soil, rain, and possible snow melt. The creation of contour tillage channels in frozen soil provides an opportunity to increase field infiltrability by providing flow pathways to unfrozen subsoil, and decrease soil loss form the field. Frozen soil tillage was evaluated in field tests conducted between 1990 and 1995, in north-central Oregon near Pendleton in fields both annual cropped and summer-fallowed, and planted to winter wheat. Contour tillage was conducted after seeding, rill initiation and with 3 cm to 10 cm of frozen soil. The tillage channels were 25 cm to 35 cm deep. Erosion or deposition was determined using a rill meter and dependent on natural rainfall events. Grain yield was determined from 1 m2 plots centered on the tillage channel. No measurable frozen soil -erosion events occurred from 1990 through 1994. In 1995, a 2 cm, four day event occurred after frozen soil tilalge. As a result, soil accumulated in the tillage channel and rills that had been ripped, whereas the rills unchecked by ripping continued to serve as channels for soil and water loss. Grain yield immediately adjacent to tillage channels was not significantly reduced despite a reduction in the wheat stand. We hypothesis that the grain yield was maintained by additional water captured by the tillage channels. These results support the results reported for natural-rainfall field-studies conducted in southeastern Washington and ponded infiltration studies conducted in north-central Oregon.
John D. Williams USDA-ARS-PWA Columbia Plateau Conservation Research Center P.O. Box 370 Pendleton OR 97801 Telephone: 541.278.3292 Facimile: 541.278.3795 Email: williajo@ccmail.orst.edu