Submitted to: Journal of Hydrometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 5, 2005
Publication Date: December 28, 2005
Citation: Prueger, J.H., Hatfield, J.L., Kustas, W.P., Hipps, L.E., Macpherson, J.I., Neale, C., Eichinger, W.E., Cooper, D.I., Parkin, T.B. 2005. Tower and aircraft eddy covariance measurements of water vapor, energy and carbon dioxide fluxes during SMACEX. Journal of Hydrometeorology. 6:954-960.
Interpretive Summary: Agriculture has the potential of being a contributor to solutions to reduce carbon dioxide levels in the atmosphere. The uptake of carbon dioxide by growing plants and the storage of this carbon into the soil may provide a long-term storage that will reduce the greenhouse impact of agriculture. One of the primary limitations to the current knowledge base is our understanding of the variation of carbon dioxide exchanges in agricultural crops with enough certainty to begin the evaluation of potential management scenarios. A study was conducted in central Iowa during 2002 in which twelve different energy balance systems were placed in corn and soybean fields in central Iowa. The variation among these sites was largest during the early growing season. There was good agreement between the average of all of the sites and measurements obtained with a low-flying aircraft equipped with carbon dioxide sensors. It may be possible to collect data over large areas with aircraft to obtain a regional estimate of carbon dioxide exchanges. These results are being used to help policy-makers and scientists design better studies for more detailed analysis of agricultural impacts on carbon dioxide exchanges.
The water and carbon balance of agricultural lands has been evaluated in limited studies; however, there is a lack of information about the spatial variation in water and carbon fluxes over large areas. To address this problem a study was conducted in central Iowa during the summer of 2002 to compare the energy and carbon balance over corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) canopies. A network of micrometeorological flux stations and aircraft based water and carbon dioxide (CO2) sensors were established as part of the Soil Moisture Coupling experiment (SMACEX) to measure the fluxes during growing season. Sensible heat, water vapor, and CO2 fluxes showed the greatest spatial and temporal variability during the early crop growth stage. Differences were detectable between corn and soybean throughout the season in all energy balance components; however, within a crop there was large variability evident in the fluxes. Network average fluxes were in good agreement with area-average aircraft flux measurements.