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Net Global Warming Potential and Greenhouse Gas Intensity in Irrigated Cropping Systems in Northeastern Colorado

^a Agricultural and Biological Engineering Department, University of Florida, 281 Frazier Rogers Building, Museum Road, P.O. Box 110570, Gainesville, FL 32611
^b USDA-ARS, 2150 Centre Avenue, Building D, Suite 100, Fort Collins, CO 80526-8119
^c College of Resources and Environmental Sciences, China Agricultural University, Beijing, China

View larger version (37K): [in a new window]   Fig. 1. (A) Daily minimum and maximum air temperature at the field site, April 2002–October 2004; and (B) soil temperature at a 5-cm depth, measured at the time of each gas flux measurement. Note the different temperature scales.

View larger version (30K): [in a new window]   Fig. 2. (A) Precipitation and (B) irrigation at the field site, and (C) volumetric soil water content measured at the time of each gas flux measurement.

View larger version (34K): [in a new window]   Fig. 3. Soil–atmosphere CH4 exchange observations from 28 Apr. 2002 until 28 Oct. 2004 in (A) plots to which no fertilizer N was applied, (B) plots to which 134 kg N ha–1 fertilizer N was applied, and (C) plots fertilized with 202 kg N ha–1 in 2002 and 224 kg N ha–1 in 2003 and 2004. Note the different scales for CH4 flux.

View larger version (40K): [in a new window]   Fig. 4. Average soil–atmosphere exchange rates of CH4 during (A) the 2002, 2003, and 2004 growing seasons; and (B) during the fallow seasons, November–April of 2002–2004. Note the different scales for CH4 flux.

View larger version (38K): [in a new window]   Fig. 5. Soil–atmosphere exchange of CO2 from (A) unfertilized conventional-till continuous corn (CT-CC), no-till continuous corn (NT-CC), and no-till corn–soybean rotation (NT-CB) plots; (B) CT-CC and NT-CC plots fertilized with 134 kg N ha–1; and (C) CT-CC and NT-CC plots fertilized with 202 kg N ha–1 in 2002 and 224 kg N ha–1 in 2003 and 2004, and NT-CB plots fertilized with 202, 56, and 224 kg N ha–1 in 2002 (corn year), 2003 (soybean year), and 2004 (corn year), respectively.

View larger version (55K): [in a new window]   Fig. 6. Soil–atmosphere exchange of CO2 during (A) the 2002, 2003, and 2004 growing seasons (May–October); and (B) during the fallow seasons (November–April) 2002–2003 and 2003–2004. Note the different scales for seasonal CO2 flux.

View larger version (35K): [in a new window]   Fig. 7. Nitrous oxide flux rate observations made during 28 Apr. 2002 through 28 Oct. 2004 from (A) unfertilized conventional-till continuous corn (CT-CC), no-till continuous corn (NT-CC), and no-till corn–soybean rotation (NT-CB) plots; (B) CT-CC and NT-CC plots fertilized with 134 kg N ha–1 yr–1; and (C) CT-CC and NT-CC plots fertilized with 202, 224, and 224 kg N ha–1 in 2002, 2003, and 2004, respectively, and NT-CB plots fertilized with 202, 56, and 224 kg N ha–1 in 2002 (corn year), 2003 (soybean year), and 2004 (corn year), respectively. Note the different scales.

View larger version (42K): [in a new window]   Fig. 8. Seasonal averaged N2O fluxes during (A) the 2002, 2003, and 2004 growing seasons from plots fertilized at the rates of 0, 134, and 202 or 224 kg N ha–1 in conventional-till continuous corn (CT-CC) and no-till continuous corn (NT-CC) plots and 0 and 202, 0 and 56, and 0 and 224 kg N ha–1 in no-till corn–soybean rotation (NT-CB) plots in 2002 (corn year), 2003 (soybean year), and 2004 (corn year), respectively; and (B) the November through April 2002–2003 and 2003–2004 fallow seasons. Note the different scales.

View larger version (40K): [in a new window]   Fig. 9. Effect of N fertilizer rate on growing season N2O emissions in (A) 2002, (B) 2003, (C) 2004, (D) three-year average, and (E) all three years of data. Note the different scales.

View larger version (40K): [in a new window]   Fig. 10. Net global warming potential calculated (A) from changes in soil organic carbon (SOC) from 1999 to 2004; and (B) from soil respiration and crop residue input data for the conventional-till continuous corn (CT-CC) and no-till continuous corn (NT-CC) 0, 134, and high N (HN) kg N ha–1 N rate treatments. Note the different scales.