U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska
Date of this Version
2007
Citation
Published in Agron. J. (2007) 99:285–296. DOI:10.2134/agronj2005.0116S
Abstract
Energy balance and CO2 exchange of agricultural crops has been investigated through limited field studies because of the expense of the monitoring equipment and availability of fields to place equipment. Quantifying the spatial and temporal variation in the energy balance and CO2 dynamics over crop canopies will improve regional-scale estimates of water and C fluxes. A study was conducted in central Iowa during 2002 as part of the Soil Moisture Experiment to evaluate soil moisture energy exchange across an intensive corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production area near Ames, IA (lat. 41.98380985, long. -93.75497316). Surface energy balance and CO2 flux stations were placed in 12 corn and soybean fields across different soils and landscapes in and around the Walnut Creek watershed. Variability among fields was induced by three factors. Within a day, variations among fields were due to the presence of cumulus cloud formation in the afternoon. Short-term differences across days among the fields were due to variation in the spatial pattern of rainfall events causing differential drying. Throughout the season, differences among fields were due to soil water availability, which affected crop growth and ground cover. Differences in early season ground cover were correlated with energy balance (r = 0.80). During the growing season, latent heat and CO2 uptake were closely related (r = 0.85). Characterization of the spatial distribution of energy balance and CO2 uptake in an intensive cropping region provides guidance on the confidence that can be placed in interpreting single-site measurements.