Modelling soil carbon measures on dairy farms

Soil carbon sequestration is one of the pathways for the dairy sector to mitigate climate change. Soil carbon measures have been reviewed extensively, including estimates of their impacts on regional or national scales. Eventually, these measures are to be implemented by farmers themselves, justifying an assessment at farm and field level. Here, we simulated the soil carbon changes of 96 fields on 9 dairy farms under current management and after implementation of six carbon measures. The fields were in use as permanent grassland or as a grass-arable rotation with forage maize or other crops. Under current management, the annual changes of simulated soil carbon were +0.68 and +0.39 t ha-1 year-1 for permanent grasslands and crop rotations, respectively. The simulation of carbon measures showed that converting crop rotations with temporary grassland to permanent grassland had a large effect on additional soil carbon storage (0.5 t ha-1 year-1). Other measures like catch crops, applying more manure or compost, and increasing the sward age of permanent grassland had moderate effects (up to 0.1 t ha -1 year-1).