Cover crop´s carbon inputs to soils via aboveground and root biomass as affected by species, mixtures and sowing date

An increased use and optimised management of cover crops is a promising way to promote soil organic carbon accrual in agricultural soils. However, data is lacking on aboveground and especially root biomass of important cover crop species depending on the length of their cultivation window and on climatic conditions. We sampled aboveground and root biomass in a German field trial covering twelve common cover crop species and eight commercially available seed mixtures in 2021, a year with a rather wet summer, and 2022, a year with a rather dry summer. Each species and mixture were sown at three different dates and were sampled in early November, after having grown for 8 to 14 weeks.

Root and shoot biomass differed significantly between species, years and sowing dates. Oil radish, Phacelia, Bristle oat and Italian rye-grass had the highest root biomass. Cover crop mixtures did not have significantly higher aboveground or root biomass than single species. Aboveground biomass was 60% lower in 2022 compared to 2021 and root biomass on average 52% lower. Biomass generally decreased substantially with later sowing dates, by up to 80%. In 2021, the root to shoot ratio decreased by on average 41% from the earliest to the latest sowing date.

Based on the results of our study, management recommendations can be given regarding the selection and management of cover crop species for soil carbon accrual. Our data is also useful for more accurate mechanistic modelling of the soil carbon dynamics under different agricultural management scenarios. We conclude that there is a large optimisation potential for cover crop cultivation in Europa that could reveal a significant soil carbon sequestration potential.