Performance of lucerne genotypes for biomass production and nitrogen content differs in monoculture and in mixture with grasses and is partly predicted from traits recorded on isolated plants
Résumé
Grass–legume mixtures are key crops to improve agricultural sustainability. Despite their significant use in
mixture, lucerne (Medicago sativa L.) varieties are mostly tested and bred for monocultures. This study was performed to
evaluate whether the ranking of lucerne genotypes for biomass components and quality was similar in monoculture and
mixture, and whether traits recorded on isolated plants could help to predict performance in monoculture and mixture. For
46 genotypes planted in the three competition conditions, plant biomass, shoot height, shoot number and protein content
were recorded. In addition, maximum leaf size, internode length, stem diameter, growth habit, specific leaf area and leaf
dry-matter content were measured on isolated plants. A general positive correlation was observed between the performance
of genotypes in monoculture and in mixture. However, significant changes in genotype ranking indicated that the species
of its neighbours could modify the relative performance of a genotype. The traits that minimised competition intensity
also changed according to the neighbour species. In mixture, competition intensity was highest for plants with long
internodes, a high shoot number and a non-erect growth habit. In monoculture, plants with long internodes and larges
leaves suffered less from competition. The agronomic performance of lucerne varieties differing in their architecture
should be compared in monoculture and mixture to finally identify the traits to be phenotyped to improve lucerne variety
performance in both cultivation modes.