Thanks to positive interactions between species, growing mixtures of cover crops allows improving the ecosystem
services provided by cover crop cultivation. In this study, the influence of species diversity but also of
species identity and mixture composition on cover crop biomass production and its stability in diverse growing
conditions was studied. Several field experiments (varying soil type, preceding crop, soil tillage, sowing density,
nitrogen fertilization and spatial replication) were set up in Switzerland during the period 2013−2016. In these
experiments, the performance of cover crop species grown as sole crops was compared to that of multispecific
mixtures. Part of these experiments followed a simplex design in which four cover crop species were combined
together with different proportions, producing a total of 25 mixtures of varied diversity. The other experiments
compared sole crop and mixture biomass production in standard randomised block or split plot experiments.
Globally, mixtures tended to produce slightly more biomass than the sole crops, with an average between 2 t/
ha and 3.2 t/ha for sole crops and of about 3.5 t/ha for mixtures. Overyielding as well as transgressive overyielding
were observed, in 81% and 37% of the cases on average, respectively. However no effect of the level of
species diversity within mixtures could be found. Biomass production of cover crops was highly influenced by
their growing conditions and by the identity of the species involved, especially for sole crops and bispecific
mixtures. The analyses of the simplex experiments allowed to show that species interactions played an important
role in biomass production in 7 out of 15 growing conditions, even for a short growing period of about three
months. Most of the cover crop mixtures with the highest biomass production had a rather low diversity, i.e.
about two species on average, but the identity of the species involved in these mixtures depended on the growing
conditions. Our results do not show a strong diversity effect on the biomass production of cover crop mixtures
cultivated for a short growing period, but a stronger effect of species identity and of the growing conditions.
Mixtures with low diversity generally outcompete more diverse mixtures, but more diverse mixtures offer an
insurance effect given the unpredictability of growing conditions during cover crop cultivation.