A mixture of grass–legume cover crop species may ameliorate water stress in a changing climate

Abstract Climate change models predict increasing precipitation variability in the mid-latitude regions of Earth, generating a need to reduce the negative impacts of these changes on crop production. Despite considerable research on how cover crops support agriculture in a changing climate, understanding is limited of how climate change influences the growth of cover crops. We investigated the early development of two common cover crop species—crimson clover (Trifolium incarnatum) and rye (Secale cereale)—and hypothesized that growing them in the mixture would ameliorate stress from drought or waterlogging. This hypothesis was tested in a 25-day greenhouse experiment, where the two factors (species number and water stress) were fully crossed in randomized blocks, and plant responses were quantified through survival, growth rate, biomass production and root morphology. Water stress negatively influenced the early growth of these two species in contrasting ways: crimson clover was susceptible to drought while rye performed poorly under waterlogging. Per-plant biomass in rye was always greater in mixture than in monoculture, while per-plant biomass of crimson clover was greater in mixture under drought. Both species grew longer roots in mixture than in monoculture under drought, and total biomass of mixtures did not differ significantly from the more-productive monoculture (rye) in any water condition. In the face of increasingly variable precipitation, growing crimson clover and rye together has potential to ameliorate water stress, a possibility that should be further investigated in field experiments. Crop production is being impacted significantly by climate change. Cover crops are a promising mitigation and adaptation strategy, but little is known about how their establishment and early growth are affected by climate-related stresses. We conducted a greenhouse experiment to understand responses of rye, crimson clover and their mixture to water stress—an important consequence of climate change in mid-latitude regions. The two species were affected in contrasting ways: waterlogging limited rye's development whereas drought reduced survival and growth of crimson clover. When grown together, the two species demonstrated better performance under drought compared to their monocultures, specifically, longer total root length and comparable or greater total biomass. These results suggest that a rye and crimson clover mixture may increase the likelihood of stable