Aerodynamic Characteristics of Standing Corn Stubble

Maintenance of crop residues on the soil surface is promoted as a management practice for reducing soil erosion by wind and water. Crop residue on the soil surface, however, also influences turbulent exchange processes that affect surface water and energy balances. At present, there are very limited data on the aerodynamic properties of residue-covered surfaces. The objective of this research was to derive estimates of the aerodynamic properties (momentum roughness length zo, zero-plane displacement d, and drag coefficient Cd) of fields with standing corn (Zea mays L.) stubble. Wind speed and air temperature measurements were made at six heights above two no-tillage fields near Ames, LA, in the spring and fall of 1994 and in the spring of 1995. Both sites had standing corn stubble approximately 0.3 m tall at a density of greater than 60 000 stalks ha ⁻¹ and nearly 95% residue cover. An iterative, least-squares linear regression technique was applied to wind profiles obtained under neutral atmospheric conditions to determine Zₒ, d, and the friction velocity (u.). Mean values of Zₒ and for each of the three measurement periods varied from 11.8 to 24.3 and 119 to 169 mm, respectively. The ratios Zₒ/hₛ/is and d/hₛ, where hs is the mean stubble height, averaged 0.058 and 0.53, respectively, for all profiles. The magnitude of zo and d and their weak dependence on wind speed are consistent with turbulent flow over a surface with sparse, rigid roughness elements. The Zₒ and Cₐ were higher for the fall measurement period, suggesting that the loose, fresh residue presented a comparatively rough surface that was then smoothed by weathering and compaction beneath snow. Contribution of the USDA-ARS Natl. Soil Tilth Lab. Research supported in part by BARD Research Grant Agreement no. IS-2102-92.