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This work began with a meta-analysis of experimental results extracted from 34 scientific articles covering 17 countries, and showed that companion plants associated with different annual crops lead to a 56% reduction in weed biomass compared to a not weeded crop, and 42% compared to a weeded crop. Then, experiments in agricultural plots and under controlled sowing conditions were set up. For oilseed rape, frost-susceptible service plants, most often chosen from the legume family, were sown at the same time as the oilseed rape to compete with weeds and disturb insects during the autumn. As the service plant does not survive the winter, the oilseed rape completes its cycle without competition and benefits from the nitrogen returned by the plant residues. The results of 79 trials conducted in France between 2009 and 2016 have validated this technique and assessed the multi-criteria interests of several management options. Frost-susceptible leguminous plants associated with rapeseed can both reduce fertilisation by 30 kg N/ha without losing yield. In organic farming, compared to sowing after the wheat harvest, sowing under cover in the spring allows the legumes to develop more quickly once the wheat is harvested.  The effects on the wheat are negligible, while weed control is directly linked to the biomass produced before the end of the summer and will only be effective after the wheat harvest, during the intercrop period. A tool to help choose the species to be combined according to agronomic objectives was designed using a participatory approach in order to integrate and share existing knowledge on oilseed rape - service plant associations.  The model developed is based on a functional approach linking the traits of the candidate species to the processes and potential services.

Valantin-Morison M., Verret V., Médiène S., Lorin M., Pelzer E., Celette F., Naudin C., 2019.
ALLIANCE: Amélioration des performances écologiques et économiques par association de plantes de services légumineuses dans des systèmes de grandes cultures.
Innovations Agronomiques 71, 349-365