Annual Energy Balance of a Midwestern No-Till Corn and Soybean Field

As part of the National Oceanic and Atmospheric Administration's (NOAA) contribution to the Global Energy and Water Cycle Experiment (GEWEX) a long term energy/carbon flux tower system was established on a no-till corn and soybean field in central Illinois. Flux measurements have been collected continuously since August of 1996. One year of data has been collected over a soybean crop, and two years over a corn crop. These measurements are unique in the provision of continuous energy balance, carbon dioxide and water vapor, and weather measurements throughout all seasons of the year. This paper will discuss the differences in the energy balance of the four seasons of the year. The energy balance partitioning during the transition periods of crop establishment and canopy development, and crop maturity and harvest will be described. The period of the year from harvest through early crop establishment, which includes the late fall, winter and early spring seasons, show large swings in the Bowen Ratio depending upon the wetness of the soil surface. As the crop canopy begins to develop, the Bowen Ratio becomes less variable and the heat stored in the soil (G) begins to decline. As the crop begins to mature and leaves die the Bowen Ratio becomes large. The differences between the corn and soybean crop will also be described.