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Title: Friction velocity and aerodynamic roughness of conventional and undercutter tillage within the Columbia Plateau, USA

Author
item Sharratt, Brenton
item FENG, GUANGLONG - WASHINGTON STATE UNIV

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2009
Publication Date: 10/15/2009
Citation: Sharratt, B.S., Feng, G. 2009. Friction velocity and aerodynamic roughness of conventional and undercutter tillage within the Columbia Plateau, USA. Soil & Tillage Research 105:236-241.

Interpretive Summary: Windblown dust originating from agricultural fields has contributed to poor air quality within the Columbia Plateau region of the Pacific Northwest. Undercutter tillage has been promoted as a conservation tillage practice to reduce windblown dust emissions, but there is a lack of understanding for this reduction in dust emissions as compared with conventional tillage. We examined differences in soil surface characteristics of undercutter and conventional tillage and found that undercutter tillage resulted in a rougher and trashier soil surface, which then required a higher wind velocity to initiate movement of particles on the soil surface as compared with conventional tillage. Undercutter tillage appears to be an effective conservation tillage tool that can be used by growers and the USDA-NRCS for protecting the soil surface against the forces of wind and improving air quality.

Technical Abstract: Friction velocity and aerodynamic roughness are characteristics of the soil-plant-atmosphere interface which affect wind erosion. Although exchange of momentum at the interface can be altered by land management practices, no attempts have been made to quantify the effect of tillage on friction velocity and aerodynamic roughness within the Columbia Plateau region of the Pacific Northwest United States. Wind velocity profiles above adjacent field plots (>2 ha) subject to conventional or undercutter tillage during the summer fallow phase of a winter wheat – summer fallow rotation were measured to determine friction velocity and aerodynamic roughness of tillage treatments during high wind events in 2005 and 2006. Wheat stubble plots were either disked (conventional) or undercut with wide sweeps (undercutter) in spring and then periodically rodweeded prior to sowing winter wheat in late summer. Friction velocity ranged from 0.31 to 0.56 m/s for conventional tillage and from 0.33 to 0.58 m/s for undercutter tillage while aerodynamic roughness ranged from 0.001 to 0.012 m for conventional tillage and from 0.001 to 0.021 m for undercutter tillage across 50 high wind events observed over two years. Friction velocity and aerodynamic roughness during high wind events were respectively 10 and 75% greater for undercutter tillage than for conventional tillage. Vertical dust flux estimated from friction velocity and threshold friction velocity for high wind events prior to sowing was null for undercutter tillage and was 0.5 and 4.5 µg/m2/s for conventional tillage in subsequent years. Undercutter tillage, therefore, appears to be an effective management practice to roughen the surface and suppress dust emissions from agricultural land subject to summer fallow within the Columbia Plateau.