Nitrous oxide emissions from digestate as influenced by soil compaction and water dynamics

This study evaluated the impact of soil compaction on nitrous oxide (N2O) emissions following fertilisation with a digestate and examined relationships with soil physical properties, soil water dynamics, and climatic drivers. Nitrous oxide emissions were monitored during a maize growing season using a closed dynamic chamber system. Soil water content, soil temperature, and weather variables were measured concurrently, and topsoil samples were collected for soil characterisation and gas diffusion measurements. Nitrous oxide emissions increased (0.091–0.557 kg N2O-N ha−1 d-1) following digestate input, with elevated fluxes persisting for 7 days. Smaller secondary emission peaks occurred after 28 days following a drying-rewetting cycle. Smooth function predictions indicated higher nitrous oxide emissions from uncompacted soil 10 days after digestate application, whereas higher emissions from compacted topsoil were predicted to occur around day 30. Topsoil compaction altered soil physical properties, resulting in reduced air permeability and gas diffusivity and increased water-filled pore space, indicating changes in pore functionality. Despite these differences, early N2O emissions were higher from uncompacted soils, suggesting that soil physical structure alone did not explain the short-term emission patterns following fertilisation. In contrast, later emission peaks following rainfall events were more pronounced under compacted conditions, suggesting that the importance of interactions between soil structure and soil water dynamics for N2O emissions increased over time. Cross-correlation analysis identified significant associations between N2O emissions and soil temperature and evapotranspiration on multiple days, whereas individual parameters reflecting pore functionality showed weaker relationships. Overall, digestate input and soil water dynamics exerted a stronger control on N2O emissions than topsoil compaction alone, and the effects of compaction were time- and site-specific. These findings emphasise the need to know the dynamic interacting effects of fertilisation, soil physical conditions and climate when evaluating management strategies to mitigate N2O emissions from agricultural soils.