J. H. Prueger1, W. P. Kustas2, L. E. Hipps3, J.L. Hatfield1, A. Cahill4, C. Williams5, J. Albertson6, W. E. Eichinger7, D. I. Cooper8, N. Brunsell9 and R. Gillies9

1 U.S. Dept. of Agriculture, National Soil Tilth Laboratory, Ames, IA 2 U.S. Dept. of Agriculture, Hydrology and Remote Sensing Laboratory, Beltsville, MD 3 Dept. of Biological and Irrigation Engineering, Utah State University, Logan, UT 4 Civil Engineering Department, Texas A&M University, College Station, TX 5 Arts and Sciences, University of Virginia, Charlottesville, VA 6 Dept. of Civil Engineering, Duke University, Duke, NC 7 Dept. of Civil and Environmental Engineering, University of Iowa, Iowa City, IA 8 Experimental Atmospheric and Climate Physics, Los Alamos National Lab, Los Alamos, NM 9 Dept. of Geography and Earth Resources, Utah State University, Logan, UT

The Walnut Creek Watershed near Ames, Iowa is a typical corn/soybean production region of the Upper Midwest Corn Belt of the United States. This region comprises an area of over 40 million hectares of corn/soybean farming rotation mostly dependent on summer convective precipitation events for production water supply. Intuitively, intensively managed cropping systems bring to mind homogeneous surfaces and thus relatively uniform exchanges of heat, water and carbon dioxide. However a number of factors can induce significant differences in exchange rates of turbulent fluxes across a corn/soybean production landscape. These can include soil variability, surface topography, seed variety, different planting dates, soil water contents, variability in precipitation amounts and local microclimate conditions. As part of the Soil Moisture-Atmosphere Coupling Experiment (SMACEX) conducted in the Walnut Creek Watershed over the period from June 15-July 13, 2002 an intensive network of eddy covariance stations were installed across the watershed to measure sensible and latent heat fluxes as well as carbon dioxide fluxes over corn and soybean production fields. Approximately an equal number of stations were deployed over corn and soybeans and in fields representing a diversity of soil types, topography and planting densities. In addition to each site, ancillary measurements of net radiation, soil heat flux and soil temperatures, air temperature and humidity as well as radiometric temperatures of soil and plant canopies were made. Results will show considerable variation in energy exchange rates across the watershed as a function soil variability, landscape position, management practice and precipitation distribution.

For submission to the 17th Conference on Hydrology, Long Beach, February 9-13, 2003