Seasonal Distribution of Nitrous Oxide Emissions from Soils in the Parkland Region

Abstract

The temporal variability of soil‐derived N2O emissions presents a major challenge to the accurate quantification of N2O‐N losses from agroecosystems. We characterized the seasonal distribution of N2O emissions from two agricultural sites in the Parkland region of Alberta during 1993 and 1994. Treatments studied were fallow, and spring wheat (Triticum aestivum L.) with and without urea fertilizer, under conventional till management. Gas samples were collected from vented static soil chambers and were analyzed for N2O with a gas chromatograph equipped with a 63Ni electron capture detector. Soil water content and concentrations of NO‐3‐N, NH+4‐N, and water‐soluble organic C (WSOC) were measured several times during the season. A brief burst of N2O emission was recorded at both sites during and immediately following spring snow melt. A second period of activity occurred between mid‐June and mid‐July. Between 16 and 60% of estimated annual N2O‐N loss occurred during spring thaw, while >80% of cumulative annual N2O‐N loss had occurred by mid‐July. Mean soil NO‐3‐N concentration explained up to 65% of the temporal variability in geometric mean N2O emissions. A multiple regression model that included fall soil concentrations of NO‐3‐N, NH+4‐N, and WSOC explained 94% of the variability in estimated cumulative N2O‐N loss during the following spring thaw. Most N2O‐N losses in the Parkland region appear to occur during spring thaw and early summer; therefore, sampling schedules need to focus on these time periods. Management practices that minimize N availability during spring thaw may be an effective mitigation strategy for this region.

Upscaling chamber-based measurements of N2O emissions at snowmelt

“…The cumulative emissions calculated for the non-manured cropland sites in the Laird study are all below 0.15 kg N 2 O-N ha -1 and 8 of 12 sites are below 0.1 kg N 2 O-N ha -1 ; even the manured site only has cumulative emissions of 0.33 kg N 2 O-N ha -1 . These are comparable to the cumulative emissions from pasture and forested sites in Corre et al (1996) St. Louis sites, to the two lowest cumulative values from Lemke et al (1998a) work and are well below the values of Nyborg et al (1997). Moreover the values for these two studies are calculated using medians and geometric means, which are likely to give lower values relative to the UMVU estimators used in this paper.…”

“…The UMVU means used for the daily summaries in our study give values that are considerably higher than those from median or geometric means; for example, the areaweighted cumulative emissions from the Laird township is only 58.7 g N 2 O-N ha -1 if median values are used for the daily summaries, rather than the 93.5 g N 2 O-N ha -1 calculated using daily UMVU means. Nonetheless the range of maximum daily N 2 O flux for non-manured cropped sites at Laird is comparable to the lower end of Corre et al (1999) and Lemke et al (1998aLemke et al ( , b, 1999 emissions and are well below the higher maximum emissions of these two studies and all of the Nyborg et al (1997) calculated rates. Pennock and Corre's (2001) results from Hepburn, Saskatchewan are for a spring thaw following a year with above-average precipitation.…”

“…Cumulative emissions at snowmelt for each site were calculated by interpolating the flux observed during the measurement period to the total time period between measurements. For Corre et al (1996) and Lemke et al (1998a) for temporal scaling in the snowmelt and early spring period.…”

Wavelet analysis of wintertime and spring thaw CO2 and N2O fluxes from agricultural fields

“…Spatial and temporal variation of N 2 O fluxes is large as N 2 O production is often episodic, occurring at times of soil wetting and thawing, and is dependent on the spatial distribution of soil characteristics which control N 2 O production through denitrification (Christensen and Tiedje, 1990;Christensen and Christensen, 1991;Nyborg et al, 1997;Lemke et al, 1998;Lark et al, 2004;Pennock et al, 2005;Yates et al, 2006). Van Bochove et al, 2000;Dö rsch et al, 2004).…”

“…Van Bochove et al, 2000;Dö rsch et al, 2004). Spring thaw emissions can represent up to 70% of annual N 2 O emissions (Lemke et al, 1998;Wagner-Riddle and Thurtell, 1998;Dö rsch et al, 2004;Teepe et al, 2004;Wagner-Riddle et al, 2007). Spring thaw emissions of CO 2 can represent 10-30% of annual C budget, but most research has examined boreal and arctic wetlands (Brooks et al, 1997;Alm et al, 1999;Grogan et al, 2001).…”