Heat and momentum transfer characteristics of adjacent fields of soybeans and maize

Measurements made as part of studies of the evolution of the planetary boundary layer (the Sangamon experiments of 1975 and 1976) are used to compare the surface eddy fluxes of heat and momentum over adjacent fields of soybeans and maize. Although the maize canopy was much taller and rougher than that of the soybeans, daytime eddy fluxes of momentum over the maize exceeded those over the soybeans by only about 35%, in good agreement with predictions based on PBL similarity theory. Heat flux was about 10% greater over the maize, probably as a consequence of greater evaporation over the soybeans. Infrared surface temperatures generally differed by less than 0.4 °C and net radiation by less than 10%. For the soybean canopy, the momentum displacement height was found to be located at approximately 90% of the crop height, and the roughness length was about 5%. The roughness length for sensible heat transfer was found to be 2–3% of the soybean canopy height. For the maize canopy, the momentum displacement height was about 60% of the crop height, and the roughness length about 7%.Work supported under the auspices of the U.S. Department of Energy.