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Title: Nitrogen fertility rates and landscape positions impacts on CO2 and CH4 fluxes from a landscape seeded to switchgrass

item MBONIMPA, ERIC - South Dakota State University
item HONG, CHANG OH - South Dakota State University
item OWENS, VANCE - South Dakota State University
item Lehman, R - Michael
item Osborne, Shannon
item SCHUMACHER, THOMAS - South Dakota State University
item CLAY, DAVID - South Dakota State University
item KUMAR, SANDEEP - South Dakota State University

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2014
Publication Date: 4/29/2014
Citation: Mbonimpa, E.G., Hong, C., Owens, V., Lehman, R.M., Osborne, S.L., Schumacher, T., Clay, D., Kumar, S. 2014. Nitrogen fertility rates and landscape positions impacts on CO2 and CH4 fluxes from a landscape seeded to switchgrass. Global Change Biology Bioenergy. doi:10.1111/gcbb.12187.

Interpretive Summary: Switchgrass is being considered as a feedstock for cellulosic ethanol production. Therefore, switchgrass production systems are being evaluated for their economic feasibility and their potential environmental impacts. We examined the effects of nitrogen fertilization (none, low, and high) and landscape position (crest and toe) on the production of carbon-containing greenhouse gases (carbon dioxide, methane) over three years from switchgrass plots located in the north central U.S. (Bristol, SD). We found that carbon dioxide fluxes were significantly influenced by landscape position with high fluxes recorded in the toe compared to the crest landscape position. No effect of landscape position was observed on methane fluxes. No effect of nitrogen fertilization was observed on either carbon dioxide or methane fluxes. Carbon dioxide emissions were correlated with annual temperature patterns while methane fluxes were highest in the late winter and early spring. Methane fluxes were generally negative (methane uptake) in the summer and fall. Considerable annual variation in gas fluxes was observed among the three years of the study that could be explained by annual variations in temperature and precipitation. Management factors (e.g., fertilization) and landscape topography of switchgrass production systems may influence the production of carbon-containing greenhouse gases and should be accounted for in comprehensive life cycle analyses of these systems.

Technical Abstract: This study was conducted in north central US (Bristol, SD) to evaluate the impacts of nitrogen (N) fertility management and landscape positions on carbon dioxide (CO2) and methane (CH4) fluxes from switchgrass (Panicum virgatum L.). The experimental layout was a factorial design of three N levels (low, 0 kg N ha-1; medium, 56 kg N ha-1; and high, 112 kg N ha-1), and two landscape (crest and toe) positions. Soil CO2 and CH4 fluxes were monitored bi-weekly from May 2010 through October 2012. Soil CO2 fluxes (but not CH4 fluxes) were influenced by landscape positions. Well structured, aerated and wetter soils at the toe increased CO2 fluxes compared to the crest position. Soil CO2 and CH4 fluxes were not impacted by N rates. Seasonal variations showed highest CO2 releases and CH4 uptake in summer and fall, likely due to warmer and moist soil conditions. Higher CH4 releases were observed in winter at crest, especially at high N rate, possibly due to increased anaerobic conditions. However, year to year (2010-2012) variations in soil CO2 and CH4 fluxes were more pronounced than variations due to the impact of landscape positions and N rates. Annual average temperatures and low soil moisture indicated drought conditions at the study site in 2012. These drought conditions result in higher summer and fall CO2 fluxes (between 1.3 to 3 times) than in 2011 and 2010. These conditions also promoted a net CH4 uptake in 2012 in comparison to 2010 when there was net CH4 emission. Results from this study conclude that landscape positions, air temperature, and soil moisture content strongly influenced soil CO2 fluxes, whereas, soil moisture impacted the direction of CH4 fluxes (Uptake or release). However, a comprehensive life cycle analysis would be appropriate to evaluate environmental impacts associated with switchgrass production under local environmental conditions. [GRACEnet publication]