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Title: NET GLOBAL WARMING POTENTIAL AND GREENHOUSE GAS INTENSITY IN IRRIGATED CROPPING SYSTEMS IN NORTHEASTERN COLORADO

Author
item MOSIER, A - U OF FL/GAINESVILLE
item Halvorson, Ardell
item Reule, Curtis
item LIU, XUEJUN - AG UNIV/BEIJING, CHINA

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2005
Publication Date: 7/6/2006
Citation: Mosier, A.R., Halvorson, A.D., Reule, C.A., Liu, X. 2006. Net global warming potential and greenhouse gas intensity in irrigated cropping systems in northeastern Colorado. Journal of Environmental Quality. 35:1584-1598.

Interpretive Summary: The impact of crop management practices on global warming potential (GWP), crop productivity, and greenhouse gas intensity (GHGI) in irrigated agriculture are not well documented. In this study, we evaluated the effects of nitrogen (N) fertility level and tillage practices under irrigated crop rotations on soil organic C (SOC) sequestration and trace gas fluxes for 3 years to facilitate a complete greenhouse gas accounting of GWP and GHGI. Fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were measured one to three times per week, year round, from April 2002 through October, 2004 within conventional till (CT) continuous corn (CT-CC) and no-till (NT) continuous corn (NT-CC) plots and in NT corn-soybean rotation (NT-CB) plots. Methane fluxes were small and did not differ between tillage systems. N2O fluxes increased linearly with increasing N-fertilizer rate each year, but emission rates varied with years. CO2 efflux was higher in CT compared to NT in 2002 but was not different by tillage in 2003 or 2004. Based on soil respiration and residue C inputs, NT soils were net sinks of GWP when adequate fertilizer was added to maintain crop production. CT soils were smaller net sinks for GWP than NT soils. Based on soil C sequestration, only NT soils were net sinks for GWP. Both estimates of GWP and GHGI indicate that when optimum crop production levels are achieved, net CO2 emissions are reduced. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of N fertilizer.

Technical Abstract: The impact of management on global warming potential (GWP), crop production, and greenhouse gas intensity (GHGI) in irrigated agriculture is not well documented. A no-till (NT) cropping systems study initiated in 1999 to evaluate soil organic C (SOC) sequestration potential in irrigated agriculture was used in this study to make trace gas flux measurements for 3 yr to facilitate a complete greenhouse gas accounting of GWP and GHGI. Nitrogen fertilizer rates ranged from 0 to 224 kg N ha-1. Methane fluxes were small and did not differ between tillage systems. N2O fluxes increased linearly with increasing N-fertilizer rate each year, but emission rates varied with years. CO2 efflux was higher in CT compared to NT in 2002 but was not different by tillage in 2003 or 2004. Based on soil respiration and residue C inputs, NT soils were net sinks of GWP when adequate fertilizer was added to maintain crop production. CT soils were smaller net sinks for GWP than NT soils. The determinant for the net GWP relationship was a balance between soil respiration and N2O emissions. Based on soil C sequestration, only NT soils were net sinks for GWP. Both estimates of GWP and GHGI indicate that when appropriate crop production levels are achieved, net CO2 emissions are reduced. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of fertilizer.