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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #175667
Title: RILL DENSITY PREDICTION AND FLOW VELOCITY DISTRIBUTIONS ON AGRICULTURAL AREAS IN THE PACIFIC NORTHWEST

Author
item Mancilla, GABRIEL - WASHINGTON ST. UNIVERSITY
item CHEN, SHULIN - WASHINGTON ST.UNIVERSITY
item McCool, Donald

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2004
Publication Date: 11/30/2004
Citation: Mancilla, G.A., Chen, S., McCool, D.K. 2005. Rill Density Prediction and Flow Velocity Distributions on Agricultural Areas in the Pacific Northwest. Soil and Tillage Research. 84(1):54-66. Available: http://dx.doi.org/10.1016/j.still.2004.10.002

Interpretive Summary: Rill erosion is the most visible and serious form of soil erosion on conventionally tilled non-irrigated cropland of the Northwestern Wheat and Range Region (NWRR) of the USA. Because soil erosion often causes economic loss, negatively affects soil conditions, and creates environmental problems, it is important to understand the factors that contribute to the erosion process and subsequent formation of rills. Rill formation, rill density, and associated flow velocity distributions in rills were studied at the field level with different tillage treatments. The study was conducted by applying flow at three different rates under winter conditions, which provides the greatest potential for rill formation in the NWRR. Tillage treatments tested were chisel plow, moldboard plow, conventional seedbed tillage, and untilled stubble from spring peas. The following variables were found to have an effect on rill formation and density: applied flow, antecedent soil moisture content, slope, random roughness, percentage of residue cover, and bulk density. Depending on the tillage treatment, these variables were found to impact rill formation in various ways. Specifically, higher applied flow, soil moisture content, and slope appeared to favor rill formation, while the effect of random roughness varied. Equations for predicting rill densities were developed. Under similar applied runoff rates, the resultant number of rills per meter was close to one except in the conventional seedbed tillage area, where two rills per meter was more representative. Rill flow velocity distributions were clearly different for each tillage treatment. Higher flow velocities implied the formation of more rills. These results advance the understanding of the rill erosion process and its inclusion in field-scale erosion models.

Technical Abstract: This research focused on rill formation, rill density, and associated flow velocity in rills at the field level and different tillage treatments in the Northwestern Wheat and Range Region (NWRR) of the USA. 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 spring peas. Twelve plots of 7.3 sq m were established for each tillage treatment and flow applied to them. The conventional seedbed tillage plots were the most susceptible to rill formation, with one or two resultant rills per meter. 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 35 percent residue cover was necessary to reduce in half, the average flow velocity in the untilled stubble plots with respect to the conventional-tilled 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.