PS 68-144 - The effect of landscape and cropping system on greenhouse gas emissions in an agro-ecosystem

Thursday, August 11, 2011
Exhibit Hall 3, Austin Convention Center
Ryan J. Williams, Agricultural and Biosystems Engineering, Iowa State University, Ames, IA, Sarah K. Hargreaves, Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA, Thomas M. Isenhart, Natural Resource Ecology and Management, Iowa State University, Lisa A. Schulte, Natural Resource Ecology and Management, Iowa State University, Ames, IA and Kirsten S. Hofmockel, Pacific Northwest National Laboratory, Richland, WA

Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are greenhouse gases (GHG) that contribute substantially to anthropogenic radiative forcing. The use of biofuel crop-derived ethanol as an alternative to fossil fuels reduces GHG emissions from combustion by 40 to 110%. However, GHG emissions from agricultural production are not taken into consideration when assessing the value of biofuel crops. As more land is converted to biofuel cropping systems, it is important to evaluate their relative contribution to greenhouse gases across a landscape. The purpose of this study was to observe in situ gas flux from different cropping systems (continuous corn, switchgrass, and sorghum-triticale) in different landscape positions (from a hill summit to a floodplain) throughout the growing season at the Landscape Biomass Experiment in Ames, Iowa. Along with gas flux, we measured other related soil physiochemical properties including microbial biomass, total carbon, inorganic nitrogen, soil texture, and water content.


Sampling in August had the most pronounced landscape position effect on GHG emissions. At this date, landscape position had a significant effect on CO2 and N2O flux (P=0.03 and P=0.03 respectively) with the largest CO2 flux at the shoulder position and largest N2O flux at the backslope position. Averaged across all sampling dates N2O flux was highest at the backslope as well (P=0.01). We did not detect a significant difference between cropping systems, which may be due to sampling in only the second growing season of the experiment.  Changes between cropping system could become more pronounced over time, especially in treatments including perennial crops. In August, the potential for soil physiochemical gradients driving differences between peak CO2 and N2O flux was the most apparent. This study highlights the importance of seasonality and landscape position in quantifying greenhouse gas emissions from agro-ecosystems.

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