Feasibility of the 4 per 1000 initiative in Bavaria: A reality check of agricultural soil management and carbon sequestration scenarios

An increase of soil organic carbon (SOC) stocks in agricultural soils does not only have positive effects on soil quality and soil resilience but may also contribute to climate change mitigation. The ‘4 per 1000′ (4p1000) initiative launched at the 2015 United Nations Climate Change Conference in Paris aims at increasing global SOC stocks in 0–40 cm depth by annually 4‰ in order to compensate the increase of anthropogenic CO₂ emissions. In this study we analysed the feasibility of this target for agricultural soils in Bavaria, Southeast Germany. Assuming a total organic carbon (OC) amount of 276 Tg currently stored in the upper 40 cm of agricultural soils in Bavaria (cropland and grassland), the 4p1000 goal corresponds to an annual carbon (C) sequestration of 1.1 Tg. Based on a site-specific analysis of present soil management, we developed spatially explicit C sequestration scenarios including five promising management practices (cover cropping, improved crop rotation, organic farming, agroforestry and conversion of arable land to grassland). The results revealed that the 4p1000 target is not feasible for Bavaria. The total potential of the five practices to sequester C resulted in increases in 0.3 to 0.4 Tg OC per year corresponding to around 1‰ of the present SOC stocks. Expansion of cover crops and agroforestry were identified as most promising options to increase SOC in agricultural soils. Although only around 1.5% of Bavaria's yearly GHG emissions would be compensated, this represents an essential contribution to climate change mitigation. Besides the need to develop new incentive systems (particularly for agroforestry), implementation of networks including farms and/or field trials that demonstrate improved soil management practices would be required to inform farmers and other stakeholders about the benefits of such practices. To maintain a resilient agriculture that withstands more extreme weather conditions in the future, healthy soils are needed. We therefore conclude that expected positive effects of a SOC stock increase on nutrient and water storage, soil erosion, biodiversity and food security are crucial for climate change adaptation.