2008 Annual Report 1a.Objectives (from AD-416) Project objectives are. 1)develop infrastructure for long-term monitoring of spatial and temporal variation of CO2/H2O vapor exchange and C storage in corn/soybean systems,. 2)evaluate the effects of alternative agricultural practices on net greenhouse gas exchange, . 3)investigate biophysical interactions that regulate greenhouse gas exchange, water use, and energy transfer to enhance predictive capabilities of emission and soil C sequestration, and. 4)develop infrastructure to conduct year-round measurements of nitrous oxide emissions as a function of agronomic and nitrogen management practices. 1b.Approach (from AD-416) A long-term measurement site will be located and maintained in central Iowa, near the center of the Upper Midwest Corn Belt. The area is intensively cultivated in corn and soybeans. Three instrument towers will be installed in two adjacent fields with crops alternating every season. Each tower will be instrumented to measure energy balance parameters, evaporation, and CO2 fluxes. Another field site will be used to evaluate tillage, rotation, cover crop, crop residue, and N fertilization management on CO2, nitrous oxide, and methane fluxes. Chamber techniques will be utilized on replicated plots for the various treatments. These studies are part of the ARS multi-location Greenhouse Gas Reduction through Agricultural Carbon Enhancement Network (GRACEnet). Observed greenhouse gas fluxes and soil C sequestration will be coupled with supporting biophysical data to allow testing of simulation models for the prediction of climate changes. 3.Progress Report A QA-QC algorithm is now used to screen all eddy covariance flux data collected since the site was developed. Annual datasets have been standardized and archived. Gap-filling procedures have also been established to fill in the missing data. These data have been analyzed and a manuscript on energy balance parameters is in preparation. An intercomparison of the fluxes from four locations, Illinois, Iowa, Minnesota, and Nebraska is being conducted to determine the differences among CO2 and H2O vapor fluxes for both corn and soybeans. Eddy covariance CO2 flux data is being compared with chamber flux measurements during non-growing season periods with no plants present. This method comparison will be used to determine whether additional corrections are necessary for the eddy covariance data. A flux system consisting of 8 automated, long-term chambers have been installed along a transect to measure patterns of soil CO2 flux with landscape position. The chambers collect measurements hourly and are operated throughout the growing season. The flux data is supported by detailed soil temperature and water content measurements at the same location. These data supplement an evaluation of the spatial variation in CO2 fluxes conducted in 2007 in a corn field that demonstrated a large variation in fluxes along different landscape positions. (NP204, Component 2) 4.Accomplishments 1. Evaluation of a Nitrous Oxide Emission Model Models that predict soil emissions of the greenhouse gas, N2O, need improvement. A paper was published that compares daily N2O emissions predicted with a computer model (DAYCENT) to N2O emissions measured in a Central Iowa corn field. Simulated and measured emissions were significantly correlated; however, time series analyses indicate that the simulated fluxes were out of phase with the measured fluxes. Discrepancies between measured and simulated fluxes may be due to inaccurate simulations of soil water content and soil N dynamics. Improved models of N2O emissions will assist scientists in predicting how management changes may influence N2O emissions. (NP204, Component II) 2. Novel Method to Measure Carbon Dioxide Fluxes Alternatives to micrometeorological and chamber methods are needed for measuring trace gas fluxes. A method was tested that involved continuous measurement of CO2 concentrations in the soil using porous tubing and infrared gas analyzers. These concentrations were used with soil diffusion coefficients to estimate CO2 flux from the soil. This technique is less disruptive than chamber techniques and also provides data on soil CO2 concentrations. This method provides another choice for trace gas measurements needed to quantify greenhouse gas production and transport from soils. (NP204, Component II) 5.Significant Activities that Support Special Target Populations Project scientists are continuing experiments as part of the GRACEnet project, a multi-location ARS project that seeks to quantify relationships among agricultural management practices, net greenhouse gas emissions, C sequestration, other benefits to soil, water, and air quality, and agricultural productivity. Research has also progressed to interface with other national efforts on global change research including the U.S. Environmental Protection Agency's State and Local Climate Change Program and the National Science Foundation's North American Carbon Program (NACP) and the AmeriFlux network. 6.Technology Transfer Review Publications Akinyemi, O.D., Sauer, T.J., Olowofela, J.A. 2008. Reducing contact resistance errors in measuring thermal conductivity of porous media. Journal of Applied Science and Technology. 12:58-64. Parkin, T.B. 2008. Effect of Sampling Frequency on Estimates of Cumulative N20 Emissions. Journal of Environmental Quality. 37:1390-1395. De Sutter, T.M., Sauer, T.J., Parkin, T.B., Heitman, J.L. 2008. A subsurface, closed-loop system for soil carbon dioxide and its application to the gradient efflux approach. Soil Science Society of America Journal. 72:126-134. Heitman, J., Horton, R., Sauer, T.J., Desutter, T. 2008. Sensible heat observations reveal soil-water evaporation dynamics. Journal of Hydrometeorology. 9:165-171. Akinyemi, O.D., Sauer, T.J. 2007. Effects of heat sink compounds on contact resistance of porous media. Thermal Science. 11:113-124. Hatfield, J.L., Prueger, J.H., Kustas, W.P. 2007. Spatial and temporal variation of energy and carbon fluxes in corn and soybean fields in central Iowa. Agronomy Journal. 99:285-296.