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Large variability in N2O emissions from managed grasslands may occurbecause most emissions originate in surface litter or near-surface soil wherevariability in soil water content (θ) and temperature (Ts)is greatest. To determine whether temporal variability in θ andTs of surface litter and near-surface soil could explain this inN2O emissions, a simulation experiment was conducted withecosys, a comprehensive mathematical model of terrestrial ecosystemsin which processes governing N2O emissions were represented at hightemporal and spatial resolution. Model performance was verified by comparingN2O emissions, CO2 and energy exchange, and θ andTs modelled by ecosys with those measured by automatedchambers, eddy covariance (EC) and soil sensors on an hourly timescale duringseveral emission events from 2004 to 2009 in an intensively managed pastureat Oensingen, Switzerland. Both modelled and measured events were induced byprecipitation following harvesting and subsequent fertilizing or manuring.These events were brief (2–5 days) with maximum N2O effluxes thatvaried from  <  1 mg<mspace linebreak="nobreak" width="0.125em"/>N<mspace linebreak="nobreak" width="0.125em"/>m−2<mspace linebreak="nobreak" width="0.125em"/>h−1 in early spring and autumnto  >  3 mg<mspace linebreak="nobreak" width="0.125em"/>N<mspace width="0.125em" linebreak="nobreak"/>m−2<mspace linebreak="nobreak" width="0.125em"/>h−1 in summer. Only very small emissionswere modelled or measured outside these events. In the model, emissions weregenerated almost entirely in surface litter or near-surface (0–2 cm)soil, at rates driven by N availability with fertilization vs. N uptake withgrassland regrowth and by O2 supply controlled by litter and soilwetting relative to O2 demand from microbial respiration. In themodel, NOx availability relative to O2 limitation governed boththe reduction of more oxidized electron acceptors to N2O and thereduction of N2O to N2, so that the magnitude of N2Oemissions was not simply related to surface and near-surface θ andTs. Modelled N2O emissions were found to be sensitive todefoliation intensity and timing which controlled plant N uptake and soilθ and Ts prior to and during emission events. Reducingleaf area index (LAI) remaining after defoliation to half that under currentpractice and delaying harvesting by 5 days raised modelled N2Oemissions by as much as 80 % during subsequent events and by an averageof 43 % annually. Modelled N2O emissions were also found to besensitive to surface soil properties. Increasing near-surface bulk density by10 % raised N2O emissions by as much as 100 % during emissionevents and by an average of 23 % annually. Relatively small spatialvariation in management practices and soil surface properties could thereforecause the large spatial variation in N2O emissions commonly found infield studies. The global warming potential from annual N2O emissionsin this intensively managed grassland largely offset those from net C uptakein both modelled and field experiments. However, model results indicated thatthis offset could be adversely affected by suboptimal land management andsoil properties

biogeosciences

Ecological controls on N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O emission in surface litter and near-surface soil of a managed grassland: modelling and measurements