Abstract
Nitrous oxide (N2O) is an important greenhouse gas with an
atmospheric lifetime of ~ 120 years and a global warming potential ~300
times that of CO2. Atmospheric N2O concentrations
have increased from ~270 ppbv during pre-industrial times to ~330 ppbv
today. Anthropic emissions are a major source of atmospheric
N2O and about half of global anthropic emissions are from the
agricultural sector. N2Oemissions from soils exhibit high
spatial and temporal variability. Estimation of N2O emissions
from agricultural soils is particularly challenging because
N2O fluxes are affected by fertilizer type and application
rates, land-use history and management, as well as soil biological
activity. We studied ecosystem level N2O emissions from
agricultural lands using a combination of static chamber methods and
continuous N2O exchange measured by a quantum cascade
laser-based, open-path analyzer coupled with an eddy-covariance system.
We also compared N2O emissions between different static
chamber methods, using both laboratory-based gas chromatography (GC) and
an in situ quantum cascade (QC) laser for N2O analyses.
Finally, we compared emissions estimated by the two static chamber
methods to those estimated by eddy-covariance. We examined pre- and
post- fertilization N2O fluxes from soils in two no-till
continuous corn fields with distinct land-use histories: one field
converted from permanent grassland (CRP-C) and the other from
conventional corn-soybean rotation (AGR-C). Both fields were fertilized
with ~160 kg urea-N ha-1. We compared N2O
emissions from these fields to those from an unmanaged grassland (REF).
In addition, we examined the potential effect of post-fertilization
precipitation on N2O emissions by applying 50 mm of
artificial rainfall to the static chambers at all three locations.
Measurements of N2O emissions using both GC and QC laser
methods with static chambers were in good agreement (R2 =
0.96). Even though average soil N2O fluxes before
fertilization were low, they still exhibited high temporal and spatial
variability. Fluxes from the CRP-C site were higher than fluxes from the
AGR-C site, and fluxes from the REF site were lowest, ranging from 2 -
22, 1 - 3, and ~1 g N2O-N ha-1 day-1,
respectively. Post-fertilization fluxes were minor as well due to very
dry soil conditions in 2012. However, after applying artificial rain,
soil N2O fluxes were distinctly higher in all systems,
increasing to 106 - 208 g N2O-N ha-1
day-1 at the CRP-C site, to 36 g N2O-N
ha-1 day-1 at Ag-C, and to 5 g N2O-N
ha-1 day-1 at the REF site. Fluxes decreased to
pre-rain levels 1-2 days after wetting. This single rain event resulted
in total emissions of 5, 43, and 251 g N2O-N ha-1
from REF, Ag-C, and CRP-C systems, respectively. A comparison between
static chambers and the open-path method at CRP-C system revealed
similar diurnal trends in N2O fluxes and similar cumulative
N2O-N emissions. Overall, we found a strong relationship
between land-use history and soil N2O emissions: soils with
higher organic carbon content (CRP-C) exhibited greater fluxes. In
addition, we found that N2O emissions increased significantly
after a post-fertilization rain event, accounting for a significant
proportion of typical total annual emission from these no-till corn
fields. We also present the first measurements of ecosystem level
N2O fluxes using an open-path N2O analyzer and
show the potential of this novel system to study ecosystem level
N2O fluxes.
Original language | English |
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Title of host publication | American Geophysical Union, Fall Meeting 2012 |
Volume | 52 |
State | Published - 1 Dec 2012 |
Externally published | Yes |
Keywords
- 0402 BIOGEOSCIENCES / Agricultural systems
- 0426 BIOGEOSCIENCES / Biosphere/atmosphere interactions
- 0439 BIOGEOSCIENCES / Ecosystems
- structure and dynamics
- 0469 BIOGEOSCIENCES / Nitrogen cycling