Assessing Spring Thaw Nitrous Oxide Fluxes Simulated by the DNDC Model for Agricultural Soils

Abstract

Large N2O emissions from agricultural soils have been reported during winter and spring thaw. The objective of this study was to assess the ability of the DNDC model to simulate N2O emissions resulting from freeze–thaw cycles, particularly the timing of flux events. The DNDC model was tested against micrometeorological fluxes measured during 5 yr in Ontario, Canada. There was a very large discrepancy between simulated and observed fluxes in terms of magnitude and timing. The simulated event occurred, on average, 38 d later than observed, and N2O fluxes were up to 3.5 times larger than the highest measured flux. Examination of simulated soil conditions indicated that the mechanism underlying freeze–thaw‐induced N2O flux in the DNDC model, release of ice‐trapped N2O, was not correct. This misconception had not been identified before, possibly because cold conditions in previous studies were not as extreme as observed in our data set or because continuously measured N2O fluxes were not available for model assessment. As a result of this analysis, DNDC 9.1 was revised by removing the release of ice‐trapped N2O and adding N2O newly produced by denitrification in the surface layer as the main mechanism for N2O production (DNDC 9.3). Comparison between simulated N2O fluxes using DNDC 9.3 and our data indicated improved timing to within 1 d of observed events. The magnitude of simulated flux differed from measurements by more than a factor of two, however, suggesting that an improved algorithm for N2O production and diffusion under soil freezing and thawing is needed.

Assessing the effects of agricultural management on nitrous oxide emissions using flux measurements and the DNDC model

“…(Table 6). Studies in Canada indicate that more N 2 O emissions usually occur under conventional tillage than reduced tillage in dryer semi-arid and sub-humid soils due to higher rates of nitrification under a more aerated soil, and in eastern humid soils more emissions usually occur under reduced tillage due to wetter soil conditions resulting in higher rates of denitrification (Helgason et al, 2005;Kariyapperuma et al, 2011;Rochette et al, 2008b;Smith et al, 2010). The emissions at our TGAS-Man site were similar between tillage treatments, which might be expected since precipitation levels were moderate.…”

“…This is an indicator that a freeze period followed by a thaw does promote N 2 O emissions. The spring thaw component of DNDC93 was reformulated by Kariyapperuma et al (2011) to increase emissions during thaw events from newly produced denitrification in the surface layer due to availability of microbial populations and substrates that remained dormant during the freeze period. This routine, which is also utilized by DNDCv.CAN1 performed well for the TGAS-Man site.…”

“…As an alternative to direct measurements, process-based models enable the integration of the contributing biogeochemical processes and are increasingly used internationally to simulate N 2 O emissions in agroecosystems (Jarecki et al, 2008;Kariyapperuma et al, 2011;Parton et al, 1988;Smith et al, 2002;Wolf et al, 2012). Dynamic process based models are mathematical models which describe the growth and development of a crop interacting with a soil-carbon system (Wallach et al, 2006).…”

Effects of soil rewetting and thawing on soil gas fluxes: a review of current literature and suggestions for future research

“…DAYCENT, Parton et al, 2001;DNDC, Li et al, 1992;ecosys, Grant and Pattey, 2003). Most existing process-based models require additional work to improve simulating rewetting and thawing effect on soil gas fluxes (Jarecki et al, 2009;Norman et al, 2008;Kariyapperuma et al, 2011;Wolf et al, 2012). Groffman et al (2009) suggested that modelling peak fluxes associated with drying and rewetting events requires: (1) accurate simulation of moisture changes in different soil layers and complex shifts in utilisation of fast-and slow-cycling soil organic matter pools by microbes that take place during these events (Miller et al, 2005), and (2) daily or sub-daily simulations of both physical and biological processes (Kiese et al, 2005).…”

Modeling impacts of climate change and grazing effects on plant biomass and soil organic carbon in the Qinghai–Tibetan grasslands

“…The model has been used widely in more than 20 countries to obtain accurate calibration and verification results in various ecosystems (Abdalla et al, 2009;Chen et al, 2015;Li et al, 1996Li et al, , 2017Xu et al, 2003;Kariyapperuma et al, 2011;Zhao et al, 2016;Liu et al, 2006;Zhang and Niu, 2016).…”