Statistical Technologies Used to Analyse Plant Diversity in Grasslands Aimed at Combating the Climate Crisis

01 September 2021

Six-species swards outperformed perennial ryegrass monocultures and were considerably more resistant to drought, research has found.  The research from Teagasc, Johnstown Castle and the ADAPT Centre at Trinity College Dublin shows that multi-species mixtures receiving 150 kg per hectare  per year of nitrogen fertiliser, out-yielded perennial ryegrass monocultures receiving double that amount of fertiliser (300 kg per hectare per hear). 

Speaking about the research, Dr Caroline Brophy, Associate Professor of Statistics at Trinity College Dublin and Funded Investigator at the ADAPT Centre, said: “We are using innovative statistical technologies to address questions of critical importance in the face of the climate crisis. It is urgent that greenhouse gas emissions from agriculture are reduced – with this research, we show that multi-species grassland mixtures can provide a farm-scale solution to reduce fertiliser usage and hence emissions, without compromising on grassland production. We combine computational statistical methodologies with state-of-the-art experimental design in this collaboration with Teagasc, where the experiment was implemented.”

Increases in plant diversity up to six species in intensively managed grasslands reduced the impact of drought, and produced more yield with less fertiliser.

Higher-diversity lower-input mixtures produced higher yields than low-diversity high-input monoculture. Averaged across the two years of the trial, mixtures with all six species produced the highest yields, and yielded more than the best of the six monocultures. Under rainfed conditions, the mixture with equal proportions of all six species at sowing (produced 11.8 tonnes/ha/year) outperformed the best-performing monoculture (produced 10.5 tonnes/ha/year).

Higher diversity mixtures produced similar yields under drought as other comparisons under rainfed conditions. As expected, total annual yields were generally reduced by the experimental drought. Nevertheless, the higher-diversity lower-input mixtures under unfavourable drought conditions achieved similar yields to those from the low-diversity, high-input comparison under favourable rainfed conditions. This indicates the potential for multi-species mixtures to mitigate the effect of more variable weather conditions on grassland yields across the whole year.

Dr John Finn, a senior researcher at Teagasc’s Environment Research Centre at Johnstown Castle said; “The need for research on drought in Irish grasslands has become all too obvious in recent years, and that need will only increase in the coming decades. The use of multi-species is one strategy to improve the resilience of grassland production.”

What proportions of grasses, legumes and herbs are the best? The most productive swards were a combination of species from the three functional groups of grasses, legumes and herbs. With legume proportion between 30 and 70%, yields were better than the best monoculture.