See more from this Session: Resource Management and Monitoring: Impact On Soils, Air and Water Quality and General Environmental Quality (Graduate Student Poster Competition)
Monday, October 17, 2011
Henry Gonzalez Convention Center, Hall C, Street Level
In the semi-arid Texas High Plains, agricultural systems which integrate cattle with perennial-based systems have been shown to conserve water, maintain productivity and increase soil organic matter. Offsets to enhanced C sequestration however can occur via nitrous oxide (N2O) and carbon dioxide (CO2) emissions. The purpose of this study is to examine the magnitude and seasonal patterns of CO2 and N2O fluxes associated with two long-term (>5 years) ICLs supporting five vegetation types. ICL_1, a dryland system, was comprised of three vegetation types: cotton and millet (planted in rotation) and perennial native grasses (PNG). ICL_2, a deficit-irrigated system, was comprised of bermudagrass and W.W.B.Dahl-Old World Bluestem (OWB). Fluxes (CO2 via Li-COR LI-8100 system; N2O via static chambers) were measured weekly from July-September 2010 and monthly from October-June 2011. Fluxes of CO2 and N2O averaged 113 mg CO2-C m-2h-1 and 0.006 mg N2O-N m-2h-1, respectively and most responsive following precipitation events. Greatest fluxes were measured under bermudagrass, followed by PNG and OWB, with the lowest fluxes produced in cotton-millet rotations. Peak bermudagrass CO2 flux (508 mg CO2-C m-2h-1) occurred on 1-July-2010. N2O fluxes produced only two significant spikes occurring within 48-hours of precipitation events (0.059 mg N2O-N m-2h-1 on 30-June-2010 and 0.113 mg N2O-N m-2h-1 6-August-2010). From December to April 2011 CO2 fluxes averaged 37 mg CO2-C m-2h-1 during the dormant period for all vegetation types. Increased N2O fluxes were observed in ICL_1 following the largest precipitation event (128.5 mm) of the active phase compared to ICL_2 in which flux rates decreased. As of mid-August 2010 N2O fluxes in both ICLs had decreased to an average 0.005 mg N2O-N m-2h-1 with no significant variations detected. Although bermudagrass produced the greatest CO2 and N2O fluxes, they are low compared to most cropland emissions, and are partially offset by higher total C contents.