Grassland contribution to soil organic carbon stock under climate change scenarios in Basque Country (Spain)

In this study, we estimated the contribution of managed grasslands to the “4 per 1000” initiative in Basque Country under two climate scenarios (RCP4.5 and RCP8.5) adopted by the IPCC in its Fifth Assessment Report. For this purpose, the RothC model was calibrated and validated with a historic database of grassland soil organic carbon (SOC) (1983 to 2019). The results at field-scale show a rate of increase of 1.26 t C ha −1 year −1 at a depth of 0–30 cm over a 36-year simulation. The model was run at the regional scale in short- (2020–2040), medium- (2041–2070), and long-term (2071–2090) future climate scenarios. For all the simulations, agricultural practices and available data for grassland systems were considered. RothC model projections showed how SOC stock responses varied depending on initial SOC and climate subregions, with higher values for a lower initial SOC stock under the highest precipitation regime subregion. A 4 per 1000 storage rate could be achieved in grassland soils with an initial SOC < 80 t C ha −1 . The overall trends showed that future climate change will lead to a decrease in the SOC stock in grasslands with a higher initial SOC if appropriate practices are not implemented to maintain the SOC stock.