Soil carbon balance at various landscape positions in Dedelow, Northeastern Germany

The influence of soil erosion on the development of soil organic carbon (SOC) stocks in agricultural lands is up to now uncertain. Eroding landscapes are thought to contribute to the 'missing terrestrial carbon sink' as explained by the assumption that carbon (C) sequestration happens at the eroded sites due to dynamic replacement. Furthermore, this offsets the potential soil C losses from other landscape positions like the depression and hilltops. CO2 measurements were carried out at a hummocky ground moraine site grown with winter wheat in 2015 using automatic chambers. CO2 fluxes were calculated using the empirical gap-filling model of Hoffman et al. (2015), which uses temperature and radiation to simultae ecosystem respiration (Rcco) and gross primary production (GPP) and to calculate net ecosystem exchange (NEE). NPP sub shoot, derived from the C content and the aboveground biomass, is then added to NEE to evaluate SOC. Returning crop residues in the field (NEE sub residual) should also be considered in SOC calculation. Results showed that four measurement (hilltops, backslope and depression) acts as a C source. More CO2 is emitted from the depression releasing 314 g C/m/yr of CO2. Emissions from the hilltop and midslope does not vary significantly and is twice lower compared to the depression. Lastly, the midslopes showed the lowest emission by four times with respect to the emissions from the depression. Crop residue addition and its effects in SOC are difficult to isolate with erosion effects. Addition of crop residue sequestered C from -123 in the backslopes to 139 g C/m/yr of CO2 in the depression. Eroding landscapes showed a higher potential of C storage compared to the depression and hilltops. But in the event of returning crop residues to the field, that erosion effect is negated. Regardless of the landscape position which is shaped by the erosion events, agricultural lands become C sink to the same degree when this particular farming practice is imposed.