Millar, N., I. Gelfand, K. Kahmark, S. Bohm and G. P. Robertson
Presented at the GLBRC Sustainability Retreat (2010-02-10 to 2010-02-12 )
Nitrous oxide (N2O) and methane (CH4) are potent agricultural greenhouse gases (GHGs), with global warming potentials (GWPs) of 298 and 25, respectively, compared with 1 for carbon dioxide (CO2). Nitrous oxide is the predominant GHG emitted by US agricultural activities. Typically cropping systems are not a direct source of CH4, however agricultural conversion can significantly reduce natural rates of CH4 consumption in soils.
A full GHG cost accounting of the effects of establishing and maintaining bio–energy cropping systems, is vital to determine the impact of these systems on the agricultural contribution to atmospheric radiative forcing, and to evaluate options for emission mitigation through management practice and policy intervention.
Emissions of N2O and CH4 from recently established bio–energy systems at the GLBRC intensive experiment site at the Kellogg Biological Station (KBS) are presented. These include bi–weekly flux measurements from static chambers in 2008 and 2009 (1st and 2nd establishment years (E1 and E2), respectively), and near continuous flux measurements from automated chambers during spring 2009 at each of the 10 existing treatments.
Initial results show a reduction in cumulative N2O emissions in E2 when compared to E1 in all treatments. Nitrous oxide emissions ranged between 0.6±0.2 and 3.9±1.0 kg N-N2O ha-1 over the growing seasons, with the lowest emissions from the old-field and grass mix treatments, and the highest emissions from Miscanthus and intensive agricultural treatments. Trends in CH4 fluxes were less discernible, with no significant emission differences between E1 and E2 in any treatment, and average fluxes varying between 0.4±1.0 and -3.8±0.6 g ha-1 d-1.
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