Aerodynamic Characteristics of Standing Corn Stubble Thomas J. Sauer,* Jerry L. Hatfield, and John H. Prueger ABSTRACT 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 C d ) of fields with standing corn (Zea mays L.) stubble. Wind speed and air tempera- ture 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"' and nearly 95% residue cover. An iterative, least-squares linear regression technique was ap- plied to wind profiles obtained under neutral atmospheric conditions to determine zo, d, and the friction velocity («•). Mean values of zo and d for each of the three measurement periods varied from 11.8 to 24.3 and 119 to 169 mm, respectively. The ratios zo//i s  and dlh s , where h s  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 C d  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. T.J. Sauer, USDA-ARS, Biomass Res. Ctr., Univ. of Arkansas, Fayette- ville, AR 72701; J.L. Hatfield and J.H. Prueger, USDA-ARS, Natl. Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011^420. Contribution of the USDA-ARS Natl. Soil Tilth Lab. Research supported in part by BARD Research Grant Agreement no. IS-2102-92. Received 19 Sept. 1995. *Corresponding author (Email: tsauer@comp.uark.edu). Published in Agron. J. 88:733-739 (1996). T HE PROFILE OF WIND speed above an aerodynamically rough surface under adiabatic conditions is generally assumed to be logarithmic with height above the surface. Considerable effort has been devoted to measuring wind profiles above plant canopies to determine the momentum roughness length (zo) and zero-plane displacement (d) parameters of the log profile equation (Seginer, 1974; Businger, 1975; Maki, 1975; Azevedo and Verma, 1986; Jacobs and van Boxel, 1988; Kustas et al., 1989; Rau- pach, 1994). The surface drag coefficient (C d ) has also been the subject of study at both canopy and individual leaf scales (Udagawa, 1966; Thorn, 1971,1975; Azevedo and Verma, 1986). Information on these parameters not only improves our understanding of momentum transport processes at the surface but, through similarity argu- ments, provides insight into the turbulent transport of sensible and latent heat. Knowledge of the aerodynamic properties allows the calculation of surface resistances to momentum, heat, and mass (vapor) transport (Szeicz and Long, 1969; Verma and Barfield, 1979; Verma, 1989). These resistances are widely used in modeling turbulent transfer processes above crop canopies. In contrast to the wealth of aerodynamic property data for full crop canopies, mere is very limited information available for crop residue-covered surfaces. Businger et al. (1971) reported values of z 0 and d of approximately 24 and 100 mm, respectively, for a field in Kansas with wheat (Triticum aestivum L.) stubble 0.18 m tall. Aase and Siddoway (1980) made wind profile measurements over wheat fields in Montana with stubble 0.19 and 0.35 Abbreviations: d, zero-plane displacement; Cd, drag coefficient; /i s , mean stubble height; r,, aerodynamic resistance; SSE, sum of squares error; u*, friction velocity; zo, momentum roughness length. Published September, 1996