Monday, November 13, 2006 - 2:00 PM
91-3

Continuous Measurement of Soil Surface CO2, N2O and CH4 Fluxes to Estimate Global Warming Potentials in Great Plains Agricultural Ecosystems.

Hui Shen, Timothy Arkebauer, and David Scoby. University of Nebraska-Lincoln, 203 KCR Building, East Campus, Lincoln, NE 68583

Recent changes in global climate have been characterized by increasing atmospheric concentrations of CO2, CH4 and N2O. Mitigation strategies include sequestering atmospheric carbon in soil. The maize-based cropping systems that dominate the Great Plains region are considered to have significant carbon sequestration potential. The primary goal of the program is to qualify global warming potential through continuous year-round measurements of soil surface CO2, N2O and CH4 fluxes. We are integrating the three gas fluxes over diurnal, seasonal and annual time scales for comparison among various treatments (e.g., maize versus soybean, irrigated versus dryland). The seasonal pattern showed that CO2 flux in continuous maize cropping system was greater than in maize-soybean rotation system. In irrigated cropping system, there were more CO2 emissions from soil than in dryland cropping system. However, there was no significant difference of soil surface N2O fluxes among these treatments except during period following irrigation and N-fertilizer application. We are analyzing flux readings in terms of supporting measurements (e.g., soil temperature, soil moisture content etc.) to elucidate the effects of relevant controlling factors. Our data indicated there was an exponential relationship between soil surface CO2 flux and soil temperature. N2O and CH4 fluxes didn’t give us such relationship though. Nevertheless, we found that N2O flux exhibited higher peaks in a few days after irrigation/precipitation. We estimate annual global warming potentials for each cropping system, and compare results between the various cropping systems. GWP is expressed as CO2-equivalents. GWP calculations for N2O and CH4, using IPCC(2001) 20-year time horizon factors of 275 for N2O and 62 for CH4, and using 100-year time horizon factors of 296 for N2O and 23 for CH4.

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