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Title: Quantifying nitrous oxide fluxes on multiple spatial scales in the Upper Midwest, USA

item ZHANG, XIN - Yale University
item LEE, XUHUI - Yale University
item GRIFFIS, TIMOTHY - University Of Minnesota
item ANDREWS, ARLYN - National Oceanic & Atmospheric Administration (NOAA)
item Baker, John
item ERICKSON, MATT - University Of Minnesota
item HU, NING - Yale University
item XIAO, WEI - Yale University

Submitted to: International Journal of Biometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2014
Publication Date: 5/31/2014
Publication URL:
Citation: Zhang, X., Lee, X., Griffis, T.J., Andrews, A.E., Baker, J.M., Erickson, M.D., Hu, N., Xiao, W. 2014. Quantifying nitrous oxide fluxes on multiple spatial scales in the Upper Midwest, USA. International Journal of Biometeorology. DOI: 10.1007/s00484-014-0842-4.

Interpretive Summary: Nitrous oxide is a key greenhouse gas, with 300 times the warming potential, on a molecular basis, as CO2, and the largest source of it is fertilized agricultural fields. While it is generally assumed that all of it is produced by soil microbes, there have been some reports suggesting that some of it is produced by plants. Our objective was to separately measure nitrous oxide emissions at three scales: direct emission from corn and soybean plants, whole field emission (ncluding both plant and soil component), and regional scale. Plant emissions were measured with chambers, whole field emissions were measured by a micrometeorological technique (eddy covariance), and regional emissions were measured with a boundary layer budget approach, using concentration profiles measured on a 200 m radio tower. We found that direct emission from plants, while measurable, was much smaller than the whole-field measurements, indicating that soil microbes are the dominant source within a field. We also found that the whole field measurements accounted for less than 20% of the regional flux, suggesting that other sources, beyond edge-of -field, are major contributors to the nitrous oxide budget. These results provide guidance for mitigation strategies to reduce the impact of agriculture on global climate change.

Technical Abstract: This study seeks to quantify the roles of soybean and corn plants and the cropland ecosystem in the regional N2O budget of the Upper Midwest, USA. The N2O flux was measured at three scales (plant, the soil-plant ecosystem, and region) using newly designed steady-state flow-through plant chambers, a flux-gradient micrometeorological tower, and continuous tall tower observatories. Results indicate that: 1) N2O fluxes from unfertilized soybean (0.03 ± 0.05 nmol m-2 s-1) and fertilized corn plants (-0.01 ± 0.04 nmol m-2 s-1) were about one magnitude lower than N2O emissions from the soil-plant ecosystem (0.26 nmol m-2 s-1 for soybean and 0.95 nmol m-2 s-1 for corn), confirming that cropland N2O emissions were mainly from the soil; 2) Fertilization increased the corn plant flux for a short period (about 20 days), and late-season fertilization dramatically increased the soybean plant emissions; 3) The direct N2O emission from cropland accounted for less than 20% of the regional flux, suggesting the large role of other sources in the regional N2O budget, including nitrogen leaching and runoff.