Barley intercropped with undersown species in northern Europe: a modest yet positive impact on carbon dioxide uptake during the shoulder seasons

Agriculture is an important source of greenhouse gases (GHG) globally. Unlike conventional practices which have contributed to declines in biodiversity, soil health and soil organic carbon, regenerative agriculture has the potential to mitigate and enhance resilience to climate change, support the restoration of soil health and biodiversity, among other advantages. Increasing plant diversity in grasslands has shown multiple environmental benefits, but similar studies in cereal crops are lacking. To study the impact of increased plant diversity on GHG and other agronomical parameters, zero to eight undersown species were intercropped with barley in southern Finland. GHG fluxes were measured with the chamber technique over two years alongside environmental parameters. Results showed higher CO 2 uptake in barley with undersown species compared to barley monoculture during the shoulder seasons. In 2020–2021, based on gap-filled CO 2 data and aboveground biomass, treatments with undersown species lost 42% less carbon than barley monoculture. Overall, CH 4 and N 2 O fluxes were small, and no differences were observed between treatments except in fall 2020. Soil temperature was modestly but significantly lower in barley with undersown species by 0.36 °C in summer 2020 while no differences were observed in soil moisture. There were no clear trends between one, four or eight undersown species, which suggest that adding one undersown species can already have an impact on CO 2 fluxes, vegetation and soil parameters. Further studies are needed to more specifically assess how the different functional traits of the undersown species, such as rooting depth and nitrogen-fixing properties, impact GHG emissions.