Rill density prediction and flow velocity distributions on agricultural areas in the Pacific Northwest

This research focused on rill formation, rill density, and associated flow velocity distribution in rills at the field level and with different tillage treatments in the inland Pacific Northwest. The study was conducted by applying flow at three different rates under winter conditions, which provides the greatest potential for rill formation. The following tillage treatments were tested: chisel plow, moldboard plow, conventional seedbed tillage, and untilled stubble from no-till seeded peas. Twelve plots of 7.3 m were established for each tillage treatment and flow applied on them. The conventional seedbed tillage plots were the most susceptible to rill formation, with one or two resultant rills per meter. On the opposite, the untilled stubble plots did not form rills in most of the cases. Increase in applied flow, soil moisture content, and slope appeared to favor rill formation, while the effect of random roughness and residue was the opposite. By including these variables, an equation for predicting rill density was developed. Rill flow velocity distributions were clearly different for each tillage treatment. Higher flow velocities implied the formation of more rills. At least 0.35 m/m of residue cover was necessary to reduce in a half the average flow velocity in the unfilled stubble plots respect to the conventional seedbed plots. Therefore, the use of untilled stubble tillage system is recommended to minimize soil erosion. These results provide information for advancing the understanding of the rill erosion process. # 2004 Elsevier B.V. All rights reserved.