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.

Multi-species swards: more forage with less fertiliser, and more resilient to drought

Based on a Teagasc press release from August 2021

Six-species swards outperformed perennial ryegrass monocultures and were considerably more resistant to drought. New research from Teagasc, Johnstown Castle and Trinity College Dublin shows that multi-species mixtures receiving 150 kg/ha/year of nitrogen fertiliser, out-yielded perennial ryegrass monocultures receiving double that amount of fertiliser (300 kg/ha/year). Increases in plant diversity up to six species in intensively managed grasslands reduced the impact of drought, and produced more yield with less fertiliser.

6-species swards from dairy grazing system at Teagasc, Johnstown Castle. 

Report: Independent evaluation of environmental effects of GLAS

The Green Low-Carbon Agri-Environment Scheme (GLAS) has been the Agri-Environment Scheme in Ireland over the RDP period 2014-2020. GLAS. A report from summer 2020 provides an evaluation of GLAS by an independent environmental consultancy. The report is available on the DAFM website here: Evaluation of the Green Low-Carbon Agri-Environment Scheme (GLAS): Synthesis of evidence, and includes an Executive Summary and list of recommendations in addition to the main report. 

Methodology to include farmland habitats in sustainability assessments

A new Teagasc publication to be published in the Irish Journal of Agricultural and Food Research outlines the development of scalable methods to include farmland habitats in sustainability assessments. Here, I give a brief 'taster' of the content of that paper, and an overview of the approach that is based on categorising farmland habitats using satellite imagery. 

Multi-species mixtures: our publications

I regularly get asked for references to our work on multi-species mixtures. Here’s an overview of the research that we have published over the last 15 years or so.

Four-species mixtures increased weed suppression in intensively managed grasslands

Diversity robustly suppresses weeds in intensive grassland systems

How can we get more from less use of natural resources in agricultural systems? The use of multi-species mixtures (plant diversity) in intensively managed systems has been proposed as one strategy to improve agricultural sustainability. We show that four-species forage mixtures greatly increased weed suppression in intensively managed grasslands.

Uncontrolled weed growth can represent a major source of inefficiency, diverting nutrients, water, light and labour to an undesirable form of biomass, while herbicides incur significant environmental and economic costs. In pastures, weeds can impair forage quantity and quality resulting in reduced animal production, and increase the need for reseeding with its consequent costs. If diversity helps in maintaining a low level of weeds in pastures (and increases yield) it can increase the sustainable production of higher quality forage compared to systems relying on monocultures.