Influence of tillage intensity and soil compaction on N2O emissions under field conditions

Nitrous oxide (N 2 O) emissions from agricultural soils are strongly influenced by soil management. However, the effects of tillage intensity and traffic-induced soil compaction in regulating N 2 O emissions under field conditions remain unclear. This study quantified the effects of ploughing (PL), reduced tillage (RT) and direct seeding (DS) on N 2 O emissions in a two-year field experiment (2023–2025) at two Danish sites (Holstebro and Slagelse) and evaluated the additional effect of wheel-track compaction at the Holstebro site. Nitrous oxide fluxes were measured for two 8-month periods using static chambers, and soil physical properties and mineral nitrogen were assessed concurrently. Nitrous oxide fluxes were event-driven and closely associated with fertilization. During the first period at Holstebro, cumulative emissions were higher under PL than DS (2886 vs. 751 g N 2 O–N ha −1 ; P < 0.05), with RT showing intermediate values. However, no significant effects of tillage treatments were detected during the second period at Holstebro or at Slagelse in either period. Tillage effects on soil physical properties varied between sites, sampling periods and soil depths. At Holstebro, DS consistently had higher bulk density and lower total porosity than PL and RT, while differences in water-filled pore space, air-filled porosity, air permeability and gas diffusivity depended on sampling period, soil depth and matric potential. These results suggest that the N 2 O response to tillage depended on interactions between tillage-induced changes in soil structure, gas transport and transient environmental conditions, particularly soil moisture and N availability. In the wheel-track experiment, compaction increased six-week cumulative emissions by 6- to 34-fold (1572–1865 vs. 39–260 g N 2 O–N ha −1 ; P < 0.001), independent of tillage treatments. Wheel-track compaction increased bulk density and reduced air-filled porosity, air permeability and gas diffusivity ( P < 0.05), indicating restricted gas transport and soil aeration, thereby favoring N 2 O production from denitrification. Overall, tillage effects on N 2 O emissions were variable and dependent on site and environmental conditions, whereas traffic-induced soil compaction consistently increased N 2 O emissions. This highlights the importance of minimizing traffic-induced soil compaction as part of strategies for mitigating N 2 O emissions in arable systems.