SPECIES IDENTITY IMPORTANT TO ACHIEVE BENEFITS OF DIVERSE GRASSLAND MIXTURES

Summary

In semi-natural grasslands, plant diversity has shown to correlate with increased primary production and reduced weed invasion. If such positive effects also apply to low input agricultural grasslands, the resource-use efficiency could be improved.
To investigate whether other grassland species and diverse grassland mixtures could be more productive, a grassland on a shallow sandy soil in the south of the Netherlands was sown in April 2009 with seven non-leguminous grassland mixtures. Though some sown species vanished quickly, diverse mixtures proved less susceptible for invading species three years after sowing (p<0.05). Yields in 2010 and 2011 were 11% higher for mixtures with two functional groups of grassland species compared with mixtures with only one functional group (p<0.05). A further increase in species diversity did not further increase production though overyielding was significant, transgressive overyielding was not apparent, mainly due to the strong effect of one specific functional group: mixtures containing tussock grass had a 14% higher production than mixtures without tussock grass. Tussock grass (mainly Dactylis glomerata) also had a major effect on botanical composition: Trifolium repens did invade into mixtures without tussock grass to a much higher extent (19% of the ground cover) than into mixtures with tussock grass (6%; p<0.01). However, total ground cover by invading species was mainly influenced by the number of functional groups present in the sown mixture.
The results suggest that diverse grassland mixtures can improve agricultural production and reduce the susceptibility of grass sods for invading species, but that the specific composition of the mixtures has a strong influence.