Sowing more plant species in grassland increases yield, a global experiment has shown. Such species-rich mixtures also thrive under lower nitrogen inputs and in a warming climate.
‘It is not unexpected that species-rich grassland produces more biomass, but it is remarkable that we can now demonstrate in a global experiment that the benefits truly cut both ways. A grassland with six plant species produces more than a monoculture receiving twice as much synthetic nitrogen fertiliser. That is not only good for biodiversity and pleasing to the eye, but also offers farmers an attractive prospect’, says Martijn Bezemer, an ecologist at Leiden University. He is co-author of a paper on the global LegacyNet experiment, conducted at 26 sites, which tracks the effects of adding plant species to grassland (Science, 5 December).
Plots containing two grass species, two legumes and two herbs produce on average 12.3 tonnes of biomass per hectare per growing season – an 11 per cent higher yield than plots with a grass monoculture receiving twice the nitrogen input. Compared with plots containing two grass species and legumes, the six-species plots yield as much as 18 per cent more biomass. The experiment was carried out in a highly systematic manner under the leadership of statisticians from Trinity College Dublin, across fifteen countries spanning a broad range of temperate climates, from North America to China and New Zealand. The Netherlands had two trial sites: one in Wageningen and one run by the Louis Bolk Institute near De Moer in North Brabant.
‘We set up our trial site in Wageningen in 2020, almost as a hobby project, and it comprises seventy plots of five by three metres. Management was partly carried out by the experimental farm Unifarm, because they have access to machinery used in farming practice’, says Bezemer. ‘I subsequently moved to Leiden and did a great deal of vegetation surveying at weekends. The experiment was, incidentally, designed to examine the effects of biodiversity on the soil and on subsequent crops. Publications on that are also in the pipeline.’
At the Wageningen trial site, the grass species sown were perennial ryegrass (Lolium perenne) and timothy (Phleum pratense), with red and white clover (Trifolium pratense and T. repens) as legumes, and chicory (Cichorium intybus) and ribwort plantain (Plantago lanceolata) as herbs. At other sites, different species were chosen to reflect local agricultural practices. A notable ‘bonus finding’ in the current paper is that the yield advantages of more diverse grasslands increase further at higher temperatures. ‘Greater biodiversity makes grasslands more resilient to climate change – that is good news’, says Bezemer.
Follow-up research will still need to establish whether higher biomass yield also translates into greater nutritional value for livestock. Irish agro-ecologist and co-author John Finn, of the agricultural research institute Teagasc in Wexford, highlights the practical implications in a press release. ‘This research gives farmers the knowledge to design grassland more effectively by sowing roughly equal proportions of grasses, legumes and herbs’, says Finn. ‘Ultimately, we show that multi-species mixtures produce higher yields with less nitrogen fertiliser.’