Increasing plant diversity in agricultural grasslands boosts yields, reducing reliance on fertiliser

Higher plant diversity in agricultural grasslands increases yields with lower inputs of nitrogen fertiliser. Under warmer temperatures, the yield benefits of more diverse grasslands further increase. There are headline results from a landmark study across 26 international sites as part of LegacyNet, and published in Science. 

Sown productive grasslands (used to supply forage for livestock or as a ley in a crop rotation) typically comprise low species diversity. Two widely used grassland practices comprise 1) a single grass species (monoculture) managed with high inputs of synthetic nitrogen fertiliser, and 2) a two-species grass-legume combination that receives lower inputs of nitrogen fertiliser.

The research, published in Science, outlines the findings of a common experiment conducted across 26 international sites that spanned a wide gradient of temperate climates and local conditions. The LegacyNet sites include some in Ireland, as well as others in Europe – from Denmark to Italy, and the Netherlands to the Czech Republic – and further afield, from China to the US, Canada and New Zealand.

In this study, we considered whether adding more species (up to two grasses, two legumes, and two herbs) to these grasslands and creating ‘multispecies mixtures’ could maintain or improve yields while reducing the reliance of nitrogen fertilisers that have negative environmental impacts.

The results showed that:

• Multispecies mixtures achieved high yields due to strong grass-legume and legume-herb synergistic interactions – the yield of the mixtures was much greater than the sum of the parts.

• Sowing two grasses, two legumes and two herbs each in approximately equal proportions can optimise yield and nitrogen-saving benefits
• The six-species multispecies mixture produced on average 12.3 tonnes per hectare per growing season, representing an 11% increase in yield compared to the grass monoculture that had more than double the nitrogen fertiliser, and an 18% increase in yield compared to the two-species grass-legume combination.

This confirms that multispecies mixtures outperform two widely used conventional practices in agricultural grasslands. The journal article is available here: https://doi.org/10.1126/science.ady0764

Caroline Brophy, Professor in Statistics in Trinity College Dublin’s School of Computer Science and Statistics, is senior author of the research. She said: “We urgently need to make agricultural grasslands more sustainable, but at the same time it is crucial that these systems maintain or improve agronomic performance and can adapt to changing climates. This is an internationally relevant issue as agricultural grasslands are globally distributed, economically important and threatened by the climate crisis.

“The big-picture message from this work is that transitioning to multispecies mixtures in agricultural grasslands can drive more environmentally sustainable forage production, improve yields, and enhance adaptation to a warming climate. That’s a win-win-win.”

 

James O’Malley, PhD Candidate in Trinity’s School of Computer Science and Statistics, is the first author of the research. He added: “A major strength of our study lies in the broad geographic and climatic spread of sites in our experimental design, which spanned 26 different locations across Europe, North America, China and New Zealand.”

“Having a common experiment at many sites enhances our statistical power and greatly improves the generality of our results. Statistical models applied to our multi-site data showed that sowing two grasses, two legumes and two herbs in equal proportions was a reliable strategy for delivering high yields across sites, and the yield benefits of multispecies mixtures compared to less diverse grasslands were even stronger under warmer climates.”

 

Dr John Finn, Senior Researcher at Teagasc, is a leading co-author of the research and said: “Across a variety of sites and environmental conditions, our study shows conclusively that six-species multispecies mixtures are not only better yielding than grass monocultures with higher inputs of nitrogen fertiliser, but they also outyield combinations of perennial ryegrass and white clover.”

 “This research provides farmers with the knowledge to better design grassland leys (2-3 year duration) by sowing approximately equal proportions of grasses, legumes and herbs. For longer term grasslands, it shows the high potential benefit of grassland management strategies to maintain those proportions over time. Ultimately, we show that multispecies mixtures deliver more yield from less nitrogen fertiliser."

Dr Carsten Malisch, Assistant Professor at Aarhus University, is a co-founder of LegacyNet and said, "This research shows conclusively that adding diversity doesn't reduce yields - it increases them. And these benefits will only become larger with climate change. Beyond the science, this publication marks the culmination of a seven-year journey that began with the founding of LegacyNet during my PostDoc."

The international scale of the LegacyNet experiment

 A major strength and novelty of the LegacyNet experiment is its scale – the same experiment was conducted at 26 different locations across Europe, North America, China and New Zealand. It is highly unusual to have a common experiment coordinated across so many locations. The team tested the research questions across this wide gradient of climatic conditions, varying management practices and local soil conditions. The ability to generalise the key results on account of this scale is part of why the research is published in the prestigious journal Science.

 

Why, where and how did it all begin?

The LegacyNet Founders and Directors are Professor Caroline Brophy (Trinity College Dublin, Ireland), Dr John Finn (Teagasc, Ireland) and Dr Carsten Malisch (Aarhus University, Denmark). This trio – a statistician, an ecologist and an agronomist – shared a vision over several years. They believed that multispecies mixtures could potentially provide a key solution to improving the performance and sustainability of agricultural grasslands. By then, there had been no wide-scale testing of their hypothesis, and it was crucial that a large-scale study be set up to provide farmers with the knowledge that they would need to sow multispecies mixtures with confidence. The first LegacyNet experiment got underway at Teagasc, Johnstown Castle in Co. Wexford, Ireland and the LegacyNet Directors set about recruiting members to share their vision by implementing the same experiment. And so LegacyNet was born! Today, the membership of LegacyNet boasts researchers from many leading agricultural and ecological institutions from across multiple continents.  

Click on this link to the journal article: https://doi.org/10.1126/science.ady0764

Acknowledgements

This research is part of the “LegacyNet” network of researchers which was founded and is co-Directed by Professor Caroline Brophy, Dr John Finn and Dr Carsten Malisch a tenure-track Assistant Professor at Aarhus University, Denmark; support for LegacyNet was provided by the institutions of all participating member sites. This research was also supported by several funding agencies, including Research Ireland (via the Frontiers for the Future programme); the Department of Agriculture, Food & the Marine, and the Department of Agriculture, Environment and Rural Affairs; the European Union’s Horizon 2021 doctoral network programme under a Marie Skłodowska-Curie grant; and a Trinity College Dublin Postgraduate Research Studentship. 

Click on this link to the journal article: https://doi.org/10.1126/science.ady0764