Nitrogen sustainability and soil carbon sequestration in fresh grain legume-based rotations: The vital role of the cover crop mixture

Summary

Building soil carbon (C) while retaining nitrogen (N) is central to sustainable agriculture. Integrating fresh grain legumes (GLs) with cover crops could achieve both, yet documentation of combined C and N benefits is lacking at the rotation scale. In particular, no study has quantified total C inputs, including root fragments and rhizodeposited C, from both main GLs and cover crops within a single crop sequence. We conducted a two-year rotation in Denmark, comparing fresh GLs (faba bean, pea, pea-barley mixture) with a cereal reference (barley), each followed by two cover crop types (pure ryegrass or a mixture of ryegrass, plantain and chicory) and a subsequent cereal. We tracked N recycling (biological N₂ fixation, soil N availability, residual N fertility) and quantified root fragments