Europe scale simulation of reduced fertilization scenarios

Soil organic carbon is an effective measure to remove and store CO2 and is one of the few available large-scale CO2 sinks that could help mitigate climate change. The amount of soil organic carbon (SOC) is a balance of the carbon input from plants and organic amendments and the carbon output due to mineralisation. A reduction in N fertilisation, as proposed by the F2F strategy, decreases the plant growth which leads to lower C input in form of above- and belowground harvest residues. Based on estimated yield reductions from WP3 from -20% mineral N fertilisation, we derived the corresponding loss in carbon input and its impact on soil organic carbon after 30 years. European scale simulations were performed for the six major crops wheat, barley, maize, rapeseed, potatoes and sugar beet. Given the lack of data on how/if plant carbon allocation changes under nitrogen reduction, two common allocation functions were applied, each of them coupled to a version of the widely applied soil organic carbon model RothC that has been calibrated with the respective allocation function. The 20% reduction of mineral nitrogen results in mean European SOC losses of 0.9 t per hectare of agricultural land, mainly caused by wheat and rapeseed cultivation due to the big share in agricultural area and high yield reductions, respectively. Czechia (-2.2 t SOC/ha), United Kingdom (-1.7 t SOC/ha) and Slovakia (-1.6 t SOC/ha) suffer the major losses, due to large shares of high-yielding crop in their agricultural areas. The SOC simulations reveal an overall moderate impact of Farm-to-Fork nitrogen reductions on European SOC due to the six major crops. However, in some countries, these crops cover less than 20% of total agricultural land and, therefore, the real impact in these regions will be -much- higher than our results show.