Modelling soil organic carbon in Danish agricultural soils suggests low potential for future carbon sequestration

- The simulated management effects using simple carbon model (C-TOOL) agree well with results of long-term experimental trials, and Danish national monitoring network.
- The estimates from C-TOOL model show rather small potential for increasing soil organic carbon in Danish cropping systems.
- Use of cover crops and conversion to grassland would enhance soil carbon sequestration corresponding to offsetting emissions by 0.50 million ton CO2 per year.

Soil organic carbon (SOC) is in active exchange with the atmosphere. The amount of organic carbon (OC) input into the soil and SOC turnover rate are important for predicting the carbon (C) sequestration potential of soils subject to changes in land-use and climate. The C-TOOL model was developed to simulate the dynamics of SOC storage on medium- to long-term trends in the whole soil profile (0-100 cm), and was used to compare SOC changes under typical Danish farming conditions for two sites in Denmark having the greatest possible temperature differences for the period 1986 and 2012. For this purpose, various agricultural management scenarios were considered including characteristic crop rotations with and without the presence of cover crops, and the application of organic amendments. We compared these simulated management effects with management effects estimated from Danish SOC monitoring network over the same period of time. The results of the C-TOOL simulations demonstrated that application of organic manure, use of cover crop, and converting the croplands to grassland had the potential to increase SOC in Danish mineral soils. The simulated data also suggested that C-TOOL gave a reasonably good account of SOC changes when compared with measured SOC values from a Danish national monitoring network, and the simulated management effects agree well with results of long-term experimental trials. The estimates show rather small potential for increasing SOC in Danish cropping systems, even when there is conversion to rotations with more grasslands or the use of cover crops is increased.