EJP-Soil First call: Understanding tradeoffs and interactions between SOC stocks and GHG emissions for climate-smart agri-soil management

Globally, soils store more carbon than vegetation. However, soil organic carbon (SOC) stocks are declining world-wide due to intensive agriculture, with detrimental effects for soil quality and fertility. Implementation of soil management methods targeted to increase SOC stocks can counteract this trend and, at the same time, absorb greenhouse gases (GHG). Management strategies commonly used to increase SOC stocks include the use of externally or internally recycled organic amendments (e.g., plant litter, residues, animal manures, digestates, biochar), alternative cropping practises (e.g., continuous green cover, cover crops) or measures that reduce SOC losses (e.g., reduced tillage, adapted grazing). However, these management strategies also have the potential to increase greenhouse gas (GHG) emissions by stimulating decomposition of previously sequestered C and N thus increasing the emission of carbon dioxide (CO2) and nitrous oxide (N2O) and/or reducing methane (CH4) uptake. In the worst case, climate savings by increased SOC sequestration can be cancelled out by increased N2O and CH4 emissions. TRUESOIL will quantify the ‘true’ climate effect of management practices aimed at increasing SOC stocks by measuring CO2 exchange and CH4/N2O emissions simultaneously. Emissions will be monitored in ongoing field experiments in 11 partner countries inside (Germany, France, Spain, Portugal, Irland, Norway, Finland) and outside the EU (Chile, Argentina, Indonesia and Ethiopia). Soils will be sent to partner laboratories to study abiotic and biotic factors controlling soil carbon sequestration and interactions with GHG emissions in more detail. A highly prioritized question to be addressed is why certain soils show ‘carbon-saturation’, while others do not. Together, TRUESOIL will create a basis for developing scientifically sound and locally adapted management strategies which increase soil carbon sequestration while reducing GHG emissions.

Agricultural soils are depleted in soil organic carbon (SOC) and have the potential to sequester substantial amounts of C, which could be used in climate change mitigation. Common management practices for increasing SOC include the use of external or internally recycled OC inputs (organic amendments/fertilizers, biochar, plant residues), alternative cropping options (continuous green cover, cover crops) or measures that reduce OC losses (reduced tillage, adapted grazing). These practices have a potential to increase greenhouse gas (GHG) emissions by stimulating decomposition of previously sequestered C and N in soil. TRUESOIL assesses mechanisms and drivers behind increased GHG emissions in SOC-augmenting management practices and studies their interactions with increased SOC sequestration under different soil and climatic conditions (boreal, temperate, Mediterranean and semi-oceanic). Many C-augmenting management interventions are known, or have the potential, to modify soil N cycling, resulting in enhanced N2O emissions. To understand potential trade-offs between OC storage and GHG emissions, we combine intensive measurements of GHG fluxes in various cropping systems with carbon-nitrogen cycling studies and microbiological analyses. Comparison of soils that are SOC saturated with those that continue to accumulate SOC will aid to identify major drivers. Using rainfall exclusion experiments, we will also examine the future impact of reductions in precipitation on interactions between SOC accumulation and GHG emissions. TRUESOIL works towards an increased understanding of how environmental factors and management control OC sequestration, SOC persistence and stabilization and how this is linked to GHG emissions, opening for designing soil- and climate specific management strategies for climate smart crop production.