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United States Department of Agriculture

Agricultural Research Service

Research Project: Cropping Systems for Enhanced Sustainability and Environmental Quality in the Upper Midwest Title: Nitrous oxide emissions from intensively managed agroecosystems: The role of carbon inputs

Authors
item Castellano, Michael -
item Basche, Andrea -
item Iqball, Javed -
item Kaspar, Thomas
item Miguez, Fernando -
item Mitchell, David -
item Parkin, Timothy

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 13, 2013
Publication Date: December 13, 2013
Citation: Castellano, M.J., Basche, A., Iqball, J., Kaspar, T.C., Miguez, F., Mitchell, D.C., Parkin, T.B. 2013. Nitrous oxide emissions from intensively managed agroecosystems: The role of carbon inputs. American Geophysical Union Meeting Abstract Database. Available at: http://abstractsearch.agu.org/meetings/2013/FM/sections/B/sessions/B14C/abstracts/B14C-01.html.

Technical Abstract: In agroecosystems, many reports demonstrate a positive relationship between N2O emissions and N fertilizer inputs. This relationship has been incorporated into IPCC model estimates of N2O emissions and implies that inorganic N limits N2O emissions. However, evidence indicates that denitrification accounts for most N2O emissions from agroecosystems and N2O production from denitrification requires reduced C in addition to oxidized N. Using two experiments and meta-analysis we highlight the potential importance of reduced carbon availability for N2O emissions from agroecosystems. Experiments were conducted in maize-based cropping systems, restored prairies and perennial vegetation buffers in Iowa, USA. These systems have high soil organic C (SOC) concentrations. In the first experiment, a cover crop preceding maize increased N2O emissions despite immobilizing large amounts of NO3. Laboratory incubations of these soils demonstrated that glucose, but not NO3, increased N2O emissions. Because the cover crop had no detectable effect on total or potentially mineralizable SOC, these results indicate that the relatively small cover crop C input increased N2O emissions from this system. In a second experiment that compared land uses (maize, restored prairies, and perennial vegetation buffers) with significant differences in total SOC (2.3, 2.8 and 3.0% C, respectively), 15N tracer demonstrated the increase in SOC across land uses was associated with more complete denitrification to N2 rather than an increase in N immobilization or N2O emissions. Results from these experiments suggest a complex interaction between the relative availabilities NO3 and potentially mineralizable C affects denitrification emissions of N2O and particularly the N2O/(N2+N2O) ratio; although a small plant-based C input increased N2O emissions in a NO3-rich soil, a larger long-term increase in total SOC reduced N2O emissions by decreasing the N2O/(N2+N2O) ratio. Consistent with our cover crop experiment, a meta-analysis revealed that 60% of published reports find that cover crops increase N2O emissions while 40% of published reports find that cover crops decrease N2O emissions. As a wide variety of options are considered for mitigation of N2O emissions from agroecosystems, both C and N availability must be considered.

Last Modified: 9/21/2014
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