Trade-offs between carbon sequestration by cover crops and off-season nitrous oxide emissions in hemiboreal cereal production

The use of cover crops in cereal production as a climate smart agricultural practice is generally used to increase carbon sequestration in soils. However, increased plant biomass in wintertime can trigger N₂O emissions due to decay during freeze-thaw cycles. So far little is known about N₂O winter emissions from cover crops which, in the worst case, could cancel out the carbon gain by cover crops. Here we report N₂O emissions from a two-year field experiment in SE Norway with barley and various cover crops (perennial and Italian ryegrass, oilseed radish, summer and winter vetch, phacelia and a mixture of different herbs) measured against controls without cover crops. A field robot was used for measuring N₂O emissions at high temporal resolution during off-season, i.e., the period from cereal crop harvest to cereal crop sowing. During the first winter, the snow cover was poor and the significantly higher N₂O emissions were measured from oilseed radish during spring thaw whereas perennial ryegrass reduced emissions. A second winter is measured and N₂O emissions from both years will be presented. In addition, continuous measurements are needed to assess the effect of diurnal freeze-thaw cycles on N₂O emissions before scaling up to annual N₂O emission fluxes and comparing with C sequestration.