Grassland management and clover
Why is this research important?
In Ireland, dairy production systems are based on the conversion of grazed pasture to milk. Ireland has a competitive advantage in ruminant production, compared to other European countries, due to its temperate maritime climate that promotes the efficient growth and utilisation of relatively high levels of pasture. Grazed grass continues to be the lowest cost feed for dairy systems, and is reliant on chemical nitrogen (N) fertiliser for production. Traditionally, swards sown in Ireland consisted mainly of perennial ryegrass (Lolium perenne L.) which requires relatively high levels of chemical N fertiliser to maximise its productivity. However, recent European Union and Irish Government policy changes have placed significant emphasis on reducing N fertiliser use at farm level, with the aim of improving the environmental sustainability of agriculture. To facilitate this reduction in N fertiliser use, pasture-based ruminant production systems require the introduction of white clover (Trifolium repens L.). In this scenario the reduction in N use would be offset by utilising the N fixing capacity of clover plants to supply N to the sward and thus maintain pasture production. In this manner, white clover can improve milk production and improve farm gate N use efficiency.
What the research tells us
White clover grazing systems research
The research at Teagasc Moorepark and Clonakilty Research Farm commenced in 2012, with both having a similar primary objective of reducing chemical N fertiliser input to temperate grass-based milk production systems by incorporating white clover into grassland swards, and in turn reduce farm gate N surplus. The systems trial at Moorepark has changed slightly over the years, but currently there are three grazing treatments; grass-only swards receiving 200 kg N/ha (Gr200) and grass-white clover swards receiving 100 (Cl100) or 150 kg N/ha (Cl150) annually. Animals grazing the grass-white clover swards produced an additional 41 kg milk solids/cow and a nitrogen use efficiency (NUE) of +23% compared with the grass treatment, with similar levels of herbage grown (14.9 kg DM/ha), despite the 50 and 100 kg reduction in chemical N. Similarly at the Clonakilty Research Farm, there have been some modifications to the trial work since 2012, but currently there are four grazing treatments; a grass only sward receiving either 225 or 150 kg N/ha (GO-225 and GO-150) and grass-white clover swards receiving either 150 or 75 kg N/ha (GC-150 and GC-75). When fertiliser was reduced in the absence of clover (GO-150), herbage production and milk production were reduced by 600 kg DM/ha and 29 kg MS/cow, respectively, compared to the GC-150 treatment, which had a similar DM production to the GO-225 treatment (14.3 T DM/ha) and an additional 15 kg MS/cow. Both studies highlighted the role clover can play in reducing chemical N fertiliser while maintaining DM production and increasing animal production.
On farm Clover150 Programme
The uptake of white clover in grass swards on commercial farms has been low, however there has been a rapid increase in the past 2 years, mainly driven by increased fertiliser prices. Establishing clover on-farm can take a number of years, thus reseeding an entire farm to introduce white clover into pastures is impractical and costly, and as such, there needs be a two-pronged approach (reseeding and over-sowing). In 2021, a group of 30 farmers from across the country enrolled in the Clover150 programme; these farms had a range of land types, geographic spread and farming enterprises, with an overall objective to establish clover, reduce chemical N fertiliser and farm gate N surplus while maintaining herbage production. White clover was established on farms by a combination of reseeding and oversowing.
The area of the farms under clover has increased substantially over the course of the 4 years, from <10% in 2020 to 65% in 2023, and a similar trend has been observed in yearly average sward clover content (from 10% to 23%). There was a significant reduction in the level of total N applied on farms from 2020 to 2023 (232 to 156 kg N/ha, respectively). Although a reduction in the level of chemical fertiliser being applied is undoubtedly a significant move forward, there was a slight reduction in cumulative herbage production from 2020 to 2023 (900 kg DM/ha). The average N surplus for the group of farms was 194 kg N/ha/yr in 2020 when the programme commenced; however there has been a steady decline in 2021 and 2022, with the most recent recording at 140 kg N/ha in 2023, a 54 kg reduction.
As part of the Clover150 programme, there has been a national campaign on clover in 2022, 2023 and 2024 as evidenced by 13 on-farm clover walks across the country each year and publication of a clover pocket manual on the establishment and management of white clover.
Clover Agronomy
Understanding how plants grow and reproduce is vital for correct sward management, which in turn is necessary for increased production and long term persistence. Previous grassland agronomy work has primarily focused on perennial ryegrass; however as clover is now a vital plant in our grazed swards, a research programme on legume agronomy (both white and red clover) is underway in Teagasc. The primary objective of the programme is to improve plant establishment and gain an understanding of nutrient requirements during the establishment phase so that long term production and persistence may be improved. Additionally biological N fixation of legumes is of critical importance, and gaining a deeper knowledge of fixation in relation to timings and quantities and the strategic use of fertiliser to promote greater fixation from legumes is key.
Outputs
Links to papers
More information
Contacts
Moorepark clover farm systems trial: Aine Murray (Aine.Murray@teagasc.ie)
Clonakilty Clover System: Brian McCarthy (Brian.McCarthy@teagasc.ie)
Clover150 on farm programme: Michael Egan (Michael.Egan@teagasc.ie) and Caitlin Looney (Caitlin.Looney@teagasc.ie)
Clover agronomy: Michael Egan (Michael.Egan@teagasc.ie)