Soils play a central role in the global carbon (C) and nitrogen (N) cycles and constitute a large carbon reservoir. In addition, nitrogen is an essential nutrient for plants and microorganisms, which is released by organic matter mineralization or biologically fixed by plant-microbial symbioses. Mineralization of organic matter is needed for N cycling, but excessive mineralization could lead to increased greenhouse gas emissions and C losses. Consequently, there is an urgent need to increase our common understanding about sources, mechanisms and processes that regulate organic matter mineralization and stabilization, and to identify those management practices and processes which mitigate greenhouse gas emissions, helping increase organic matter stabilization with suitable supplies of available N.

With regards to these C and N dynamics, important uncertainties remain among our understanding of the effect of heterogeneities at various scales. Similar issues with uncertainty also persist with the balance and interaction between production and uptake in the soil profile, and/or the effect of changing conditions on organic matter mineralization, N supplies and greenhouse gas production. Adsorption to clay and silt particles, formation of micro- and macroaggregates, humification processes, charcoal formation, etc., can stabilize organic matter for long periods. These processes are complex and to date no techniques are available to accurately describe the continuum of soil organic and inorganic matter.

The purpose of this session is to get a state of the art overview of recent findings and future research challenges about physical, chemical and biological processes controlling soil carbon and nitrogen dynamic and greenhouse gas emissions from soils. In this session, we welcome 1) studies on soil organic matter dynamics, organo-mineral interactions and biological activities, 2) new techniques to assess soil greenhouse emissions and organic matter quality and stability, and 3) modelling of processes at all scales ranging from controlled lab experiments and field studies to large-scale assessments.