Effectiveness of soil management strategies for mitigation of N2O emissions in European arable land: A meta-analysis

Soil management strategies involving the application of organic matter (OM) inputs (crop residues, green and livestock manure, slurry, digestate, compost and biochar) can increase soil carbon storage but simultaneously lead to an increase in non-CO₂ greenhouse gas (GHG) emissions such as N₂O. Although multiple meta-analyses have been conducted on the topic of OM input impacts on GHG, none has focused specifically on European arable soils. This study plugs this gap and can assist policymakers in steering European agriculture in a more sustainable direction. The objective of this meta-analysis was to quantify how OM inputs of different nature and quality, but also the application strategy, can mitigate soil N₂O emissions in different pedoclimatic conditions in Europe. We quantitatively synthesised the results of over 50 field experiments conducted in 15 European countries. Diverse arable crops, mainly cereals, were cultivated in monoculture or in crop rotations on mineral soils. Cumulative N₂O emissions were monitored during periods of 30–1070 days in treatments, which received OM inputs, alone or in combination with mineral N fertiliser; and in controls fertilised with mineral N. The overall effect of OM inputs had a slight tendency to reduce N₂O emissions by 10% (n = 53). With the increasing carbon-to-nitrogen ratio of the OM inputs, this mitigation effect became more pronounced. In particular, compost and biochar significantly reduced N₂O emissions by 25% (n = 6) and 33% (n = 8) respectively. However, their effect strongly depended on pedoclimatic characteristics. Regarding the other types of OM inputs studied, a slight N₂O emission reduction can be achieved by their application alone, without mineral N fertiliser (by 16%, n = 17). In contrast, their co-application with mineral N fertiliser elevated emissions to some extent compared to the control (by 14%, n = 22). We conclude that amongst the seven OM inputs studied, the application of compost and biochar are the most promising soil management practices, clearly demonstrating N₂O emission reduction compared to mineral N fertiliser. In contrast, other OM inputs had a small tendency to mitigate N₂O emissions only when applied without mineral N fertiliser.