Impact of grassland diversity and fertilization::yield and weed control in one-to-four-year-old leys

Increasing species richness in grassland leys has recently gained attention. However, especially in intensively managed systems, the yield potential, persistence, and impact of management are yet to be explored. This study evaluated the effect of grassland mixtures and slurry application rates on herbage yield, species composition, and weed suppression in one- to four-year-old leys in an organic field experiment in Denmark. Two grassland mixtures; 3-sp (Lolium perenne L., Trifolium repens L., Trifolium pratense L.), and 12-sp (3-sp+5 forbs+4 additional legumes) were grown under four N-rates (0, 100, 200 and 300 kg total-N/ha in cattle slurry). The 12-sp had a higher yield than the 3-sp, which increased with increasing N-rates and was affected by the sward age, showing significantly higher yield in the three- and four-year-old swards. The weed proportion decreased significantly (from 20.7 to 11.1%) when increasing species diversity and was higher in the three- and four-year-old swards (1st = 12.0%, 2nd = 8.9%, 3rd = 17.9%, 4th = 24.6%). However, no interaction was observed between grassland mixture and sward age. This study shows that grass mixtures with more species have higher yields and better weed suppression.