Carbon storage in agricultural topsoils and subsoils is promoted by including temporary grasslands into the crop rotation

•The role of temporary grasslands as negative emission technology was assessed.•A new approach to account for bias in bulk density is developed.•C-deficit in croplands decreases linearly with the increase of temporary grasslands.•SOC storage potential in top and subsoil are equivalent.•SOC storage potential corresponds to 1 year of GHG emissions from the same region.