1.) Internal soil C cycling and C input to the soil (crop rotations, Roots and crop residues)
Roots and crop residues are the key sources for the development of soil organic matter in agricultural soils comprising the majority of the carbon input to the soils. However, little is known how modern crop species and recent changes in crop rotations affect this C-input. Crops and grassland species with intensive and deep rooting systems may disproportional contribute to maintain and buildup soil carbon.
2.) External C input to the soil (organic amendments)
In Germany, only 60% of all croplands receive organic fertilisers even though organic amendments are important for nutrient supply and build-up of soil organic carbon. New types of organic amendments were developed during the last years, including biochar and carbonized composts, and their effects of soil carbon stocks and biogeochemical cycling are still unclear. However, organic amendments are external inputs to the soil and their fluxes need to be assessed at farm or regional scale for the net C sequestration effect.
3.) Carbon monitoring, modelling and farmer´s tools
Soil carbon management relies on methods to detect and monitor soil carbon contents and stocks changes. Thus, farmers need practicable tools that predict the current soil carbon content and possible changes under different management scenarios. These tools need to be based on soil carbon models in order to capture the complexity of soil carbon fluxes. New monitoring options rose with in situ measurements and remote sensing that allow a new dimension in monitoring and modelling soil carbon dynamics in agricultural systems.