Using perennial plant varieties for use as living mulch for winter cereals. A review

Both from the environmental and economical perspective, reducing the use of mineral nitrogen and herbicides is one of the future challenges in cereal production. Growing winter cereals on perennial legume living mulch such as white clover ( Trifolium repens L.) or lucerne ( Medicago sativa L.) is one of several options to reduce the need for mineral nitrogen fertilizer and herbicides in winter cereal production. Given the importance of winter cereals in the world, adopting this technique could greatly improve the sustainability of crop production. Through competition with the crop however, the living mulch can negatively affect cereal yield. Here, we (i) review how living mulch can be introduced in the system, (ii) synthetize potential advantages and disadvantages of that system, and (iii) explore different strategies to control the competition between the crop and living mulch. The major findings are that (i) competition between cereals and mulch can lead to significant yield reductions if not controlled properly and (ii) perennial legume varieties used as living mulch so far are varieties bred for forage production. We hypothesize that a dedicated breeding program might lead to living mulch varieties with a smaller impact on cereal yield compared to forage varieties, allowing to grow cereals with reduced nitrogen and herbicide inputs. We propose the main characteristics of an ideotype for such a perennial legume variety.