Abstract
Agricultural soils in Canada have been observed to emit a large pulse of nitrous oxide (N2O) gas during the spring thaw, representing a large percentage of the annual emissions. We report on three years of spring thaw N2O flux measurements taken at three Alberta agricultural sites: a crop production site (Crop), cattle winter-feeding site (WF), and a cattle winter-grazing site (WG). Soil fluxes were calculated with a micrometeorological technique based on the vertical gradient in N2O concentration above each site measured with an open-path (line-averaging) FTIR gas detector. The Crop and WG sites showed a clear N2O emission pulse lasting 10 to 25 days after thawing began. During this pulse there was a strong diurnal cycle in emissions that paralleled the cycle in near-surface soil temperature. The emission pulse was less pronounced at the WF site. The average spring thaw losses (over 25 to 31 days) were 5.3 (Crop), 7.0 (WF), and 8.0 (WG) kg N2O-N ha−1, representing 1 to 3.5% of the annual nitrogen input to the sites. These large losses are higher than found in most previous western Canadian studies, and generally higher than the annual losses estimated from the Intergovernmental Panel on Climate Change and Canadian National Inventory Report calculations. The high N2O losses may be explained by high soil nitrate levels which promoted rapid denitrification during thawing. The application of a high resolution (temporal) micrometeorological technique was critical to revealing these losses.
Highlights
Agricultural soils are the primary anthropogenic source of nitrous oxide (N2 O) to the atmosphere [1], and quantifying N2 O emission rates is important for greenhouse gas (GHG) inventory assessments and for developing GHG mitigation strategies
This paper describes N2 O fluxes measured during spring thaw using a rather new micrometeorological application
The objective of this paper is to highlight the surprisingly large spring N2 O-N losses measured from the three study sites, to compare those losses to estimates made using the Intergovernmental Panel on Climate Change (IPCC, [21]) emission factor methodology used in the Canadian National Inventory Report (NIR, [14]), and to examine reasons for the large losses
Summary
Agricultural soils are the primary anthropogenic source of nitrous oxide (N2 O) to the atmosphere [1], and quantifying N2 O emission rates is important for greenhouse gas (GHG) inventory assessments and for developing GHG mitigation strategies. In temperate regions the spring thaw is well-known as a high N2 O emission period [2,3,4] during which a large percentage of the annual N2 O losses can occur [5,6]. Wagner-Riddle et al [7] estimated that neglecting emissions during thawing leads to an underestimation of global agricultural N2 O emissions by 17 to 28%. An accurate accounting of emissions during the spring thaw is important to understanding agricultural GHG emissions. The focus of this paper is N2 O emitted during spring thaw from agricultural landscapes in the western Canadian province of Alberta. Previous studies from the region have reported a wide range of spring thaw emission losses. At cropping sites in central Alberta, Nyborg et al [8] found
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