Diversity promotes production of ryegrass-clover leys through inclusion of competitive forb species

Highly productive temporary grasslands in Europe are usually composed of only a few plant species, and are typically dominated by perennial ryegrass-clover mixtures. Including additional competitive forb species holds potential for enhancing productivity in temporary grasslands, but requires further demonstration. In a grassland biodiversity experiment, one or all of the three forb species: chicory (Cichorium intybus L.), caraway (Carum carvi L.) and plantain (Plantago lanceolata L.), were grown in different proportions with the perennial ryegrass (Lolium perenne L.)-red clover (Trifolium pratense L.)mixture under two slurry application levels (0 and 250 kg total N ha-1 year-1). Dry matter (DM) yield and botanical composition were determined in 2014 and 2015. Results showed that plantain-containing mixtures significantly increased DM yield by on average 9.5% (20% plantain in seed mixture) to 13.6% (60% plantain) compared to the ryegrass-clover mixture, while other mixtures with forb species produced yields similar to that of the ryegrass-clover mixture. These effects were independent of slurry application and consistent over two years. Moreover, plantain-containing mixtures produced higher yield than chicory- and caraway-containing mixtures, through greater biomass of plantain and/or complementary effects on red clover. These findings firstly demonstrate that increasing species diversity through including certain competitive forbs promotes production of ryegrass-clover mixtures