Rhizosheath formation and persistence in winter cover crop mixtures in the field

Background and Aims: While much research has focused on the benefits of cover crop diversity for crop productivity, there is limited evidence on how root diversity and species selection stabilise soil. Although cover crops can potentially improve on-farm soil and water management, how they bind soil (through rhizosheath development) and whether multi-species cover crops offer additional benefits has attracted little attention. This study aimed to assess rhizosheath persistence in field-grown cover crops and their mixtures to understand the impact of species diversity on soil binding capacity. Methods: Brassica juncea, Secale cereale and Vicia faba were sown as monocultures and mixtures in a winter cover crop field trial near Dundee, Scotland. Soil cores were collected three times during January-March 2023. Measurements included rhizosheath mass, root length, and root hair length and density. Results: While overall rhizosheath mass decreased by 27% with plant age, Secale cereale maintained the largest rhizosheath mass per unit root length (1.75 and 5.60 times greater than Vicia faba and Brassica juncea, respectively) regardless of time, diversity or species combination. The fibrous rooting system and long, dense root hairs of Secale cereale made this cover crop exceptionally effective at binding soil. Root hair length and density partially explained (42%) the variation in rhizosheath mass. Conclusion: This field trial highlights that species selection is more important than diversity per se and indicates that Secale cereale is particularly effective at binding soil to the roots, suggesting it might be a particularly valuable cover crop over winter months.