Progress 10/01/01 to 09/30/05
Outputs
4d Progress report. This report serves to document research conducted under Specific Cooperative Agreement #02-5402-2-0200 between ARS and NRI-CGP National Research Initiative Competitive Grants Program Department of Agriculture. Additional details of research can be found in the report for the parent project 5402-12130-007-00D Improving Soil and Nitrogen Management Systems for Sustaining Land and Water Quality. 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. Fluxes of CO2, CH4 and N2O were measured, using static, vented chambers, one to three times per week, year round, from April 2002
through October, 2004 within conventional till continuous corn (CT-CC) and NT continuous corn (NT-CC) plots and in NT corn-soybean rotation (NT-CB) plots. 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. This project was completed in FY05 and manuscripts submitted for publication.
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Progress 10/01/03 to 09/30/04
Outputs
4. What were the most significant accomplishments this past year? This documents research conducted under a Trust agreement with USDA- CSREES in the form of a National Research Initiative (NRI) grant that was received in FY2002 entitled "Irrigated Crop Rotation, Tillage, and Nitrogen Impacts on Net Greenhouse Gas Storage". Lead scientists are Drs. Ardell Halvorson, Arvin Mosier, and William Parton (Colorado State University). Managing agricultural systems to optimize soil organic carbon (SOC) storage and minimize nitrous oxide (N2O) emissions can impact future concentrations of greenhouse gases, CO2 and N2O, in the atmosphere as well as the sustainability of irrigated cropping systems. Nitrogen fertilization is essential to maintaining economical crop yields, but excessive N application increases N2O emissions which can offset gains in SOC storage. Information is critically needed for developing irrigated crop management systems that will increase SOC storage and
decrease N2O emissions, thus, decreasing the net global warming potential (GWP) in the future. The effects of crop rotation, tillage system, and N fertilization on the net GWP are being measured under irrigated conditions with data collected being used to verify the DAYCENT ecosystem C, N and trace gas model output so that the model can be used in regional net GWP studies for irrigated agriculture. Measurement of methane (CH4) and N2O fluxes from conventionally tilled (CT) and no-till (NT) systems that were continuously cropped with corn, CT-CC and NT-CC, respectively, continued through 2003. Methane fluxes were small and did not differ between tillage systems. Methane fluxes were slightly positive in 2002 and slightly negative in 2003, with the difference between years likely due to weather and irrigation intensity. Soils were dry at planting in 2002 and irrigation intensity early in the growing season was high while soils were much wetter at planting in 2003. N20 fluxes
increased linearly with N-fertilizer rate in both years although emission rates were much higher in 2003 than in 2002. In 2002 and 2003, the increase in N2O-N emitted per kg ha-1 of fertilizer N added was 4.42 and 14.6 g ha-1 for CT-CC and 3.14 and 11.4 g ha-1 for NT-CC, respectively. In both years N2O flux was significantly higher in CT compared to NT. The SOC is increasing in the NT system but not the CT system.
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