The SOMMIT Project: SUstainable Management of soil Organic Matter to MItigate Trade-offs between C sequestration and nitrous oxide, methane and nitrate losses

Within the context of climate change there is increasing focus on the implementation of agricultural practices which contribute to soil C sequestration (Cseq) to mitigate rising atmospheric CO₂ levels. The agricultural sector is, however, also the largest global contributor to anthropogenic non-CO₂ GHGs. N₂O and CH₄ emissions contribute substantially to the Earth’s radiative forcing and even small impacts on their fluxes could hamper climate change mitigation efforts. While it is known that Soil Management Strategies (SMS) aimed at increasing Cseq in agricultural soils also affect soil N₂O and CH₄ fluxes and N losses through leaching, data and knowledge are still fragmented. Thus, a Europe-wide policy approach to the resulting trade-offs is urgently needed, given the high global warming potential of N₂O. Mitigation effects of agricultural practices enhancing Cseq can largely be offset if N₂O emissions increase but SMS enhancing Cseq and reducing non-CO₂ GHG emissions imply a “double-win” situation for climate change mitigation. Integrated, coupled investigations are still scarce, with only a few studies addressing trade-offs comprehensively.

Overall, the ∑OMMIT project evaluates trade-offs and synergies between soil C sequestration, nitrous oxide, methane and nitrate losses as affected by soil management options aimed at increasing soil C storage. The integrated and interdisciplinary approach will address the main pedo-climatic conditions and farming systems in Europe, through 1) synthesis and meta-analysis of available literature and data; 2) targeted, novel measurements on key long-term experiments; and 3) simulation of long-term agro-ecological system responses to contrasting management options. Moreover, obtained data will be synthesized through a fuzzy-expert system which will allow for 4) evidence-based identification of optimal strategies for mitigation of trade-offs, and 5) effective stakeholders’ involvement. Overall, we aim at increasing our understanding on the mechanisms and driving forces affecting N₂O and CH₄ fluxes. Our approach works from different perspectives, allowing a cross-validation on the observed interactions and feedbacks. Here, the current status of the ∑OMMIT project will be presented. We will show the most important results obtained so far and will discuss the implications for soil management strategies in the agricultural European context.