**5. Conclusions**

This study illustrated the impact of the pedoclimatic condition on cover crop biomass produced using CCBRT systems, which subsequently impacted weed species and biomass dynamics throughout the soybean growing season. Despite location and year effect, choice of cover crop species remains a

fundamental decision for adequate weed suppression and sustainable soybean yields. Specifically, the results show that cereal rye remains the best candidate for successful organic CCBRT soybean production. The allelopathic e ffect of cereal rye likely suppresses weed seed germination to a greater degree than what is achieved by other annual cereal grain species. In addition, cereal rye is more winter hardy and reaches anthesis earlier than triticale, benefiting both biomass accumulation and timely planting with the roller-crimper. Our results provide further confirmation that su fficient cover crop biomass is crucial to suppress weeds throughout the cash crop production season. However, depending on location and year (e.g., dry, wet, degree and length of time below freezing), failures in cover crop establishment and/or poor development may be encountered with cereal rye and can lead to significant yield losses. On a farm-scale level, moving beyond evaluating cover crop decisions solely on agronomic performance, economic and practical considerations may impact farmer's choice. For example, cereal rye seed can be more expensive and di fficult to access in some regions, such as southern France, as compared to other cereal grain species. With the high seeding rates needed in CCBRT systems, seed cost is a critical factor in the net profitability of the system. Mixing cereal rye with another high biomass cereal species such as triticale may allow for beneficial aspects of both species, including maximizing soil coverage among a variety of soil and climate conditions while reducing seed costs. In addition to the multi-tactic strategies previously highlighted to optimize cover crop biomass production (e.g., planting date, fertilization, irrigation, etc.), additional cover crop varieties and species mixes should be considered for further research (e.g., forage rye, forest rye, etc.). More broadly, in a changing climate, future CCBRT research should focus on flexible decision-support tools based on multi-tactic cover crop managemen<sup>t</sup> to assist farmers in making the best decisions to ensure cover crop performance and weed managemen<sup>t</sup> throughout the cash crop growing season.

**Author Contributions:** L.V.-C. reviewed the literature and wrote the initial draft of the paper with the assistance from L.V. Then L.V-C, L.V, E.S. and J.P., contributed to revising the manuscript.

**Funding:** The financial support for this project provided by transnational funding bodies, including partners of the FP7 ERA-net project, CORE Organic Plus, and cofunds from the European Commission, the TERRA ISARA foundation, the French Water Agency 'Rhône Méditerranée Corse'. The USA portion of the work was partially funded by the Ceres Trust and by a USDA ARS Cooperative Agreement (58-5090-7-072). The text in this paper is the sole responsibility of the authors and does not necessarily reflect the views of the national and European funding bodies that financed this project.

**Acknowledgments:** We acknowledge V. Payet for his assistance on the statistical analysis. We would like to thank the technical teams from the University of Wisconsin-Madison and ISARA. We would like to give a special thanks to the organic farmers who carried out the French trials.

**Conflicts of Interest:** The authors declare no conflict of interest.
