What does the future hold for grazing swards in Ireland?

Professor Trevor Gilliland is a researcher who knows a thing or two about grass varieties and pasture performance. The former head of agriculture at AFBI in Northern Ireland has spent his career researching the best grass and clover varieties, with over 180 published papers on the subject.

At last week’s seminar on swards for the future, which was organised by Teagasc, Trevor was asked to give his views on where the industry goes next in terms of the role of additional species in grass and white clover swards.

His conclusion was that the majority of Irish farmers on good organic soils, with good grass growth potential, should continue to optimise perennial ryegrass and clover as their main sward type.

He did say that where there was specific issue causing a sward performance problem, then including a herb or a resilient grass is worth trying out.

However, Trevor did dismiss what he called the blunderbuss approach to multispecies swards where they are “expected to do everything because they contain a little bit of everything”.

Instead, he suggested that farmers should be including species for specific reasons, albeit the science in this area is only catching up.

He said that in many of the research studies on multispecies swards, they are compared to monoculture perennial ryegrass swards and not perennial ryegrass and clover swards.

He also said that while many studies have shown improved performance with multispecies swards, this wasn’t linear as the number of species in the mixtures increased.

Trevor acknowledged the gains with multispecies, particularly in relation to overyielding whereby the sum of the multispecies yields were greater than the individual species yields sown in isolation.

Other benefits include reduced greenhouse gas emissions and better drought tolerance.

He said that many of these gains have been demonstrated on early adapter farms such as the ArcZero project. Read more here.

He said his concerns about multispecies centre on the instability of the swards, with several experiments showing herb content falling to less than 10% after two to four years.

He said that using multispecies as a short-term crop is not the answer as ploughing loses carbon, so a minimum term of 10 years for any sward is essential.

As our knowledge of multispecies increases, the complexity of some mixtures today will be replaced by simpler mixtures in the future

He said that minimum tillage can reinstate a single herb but this is not really possible for a complex multispecies sward.

In terms of management, he said that longer rotations such as three-week rotations during high growth rates in spring and then longer rotations of five weeks or more in summer are required.

He also said that leaving a slightly higher post-grazing residual is important for sward persistency and to avoid grazing in heavy wet soils to protect the tap roots.

In terms of the future, Trevor predicted that as our knowledge of multispecies increases, the complexity of some mixtures today will be replaced by simpler mixtures in the future. He said that only the minimum number of species will need to be included at a rate sufficient to get a productive response.

He also said that the other benefits of multispecies such as increased carbon sequestration, reduced methane and nitrous oxide emissions and improved biodiversity/ecosystem services are all factors, which may lead to greater use of multispecies swards in the future.

There were also two French researchers speaking at the seminar. Katja Klumpp is a researcher based at Clermont Auvergne, and she presented a paper on grazing’s impact on carbon sequestration.

She suggested that grazing systems will sequester more carbon than mowing systems but said that carbon storage was increased in all systems through better grassland management as greater production meant more carbon was captured and stored in the soil.

In answer to a question from the floor, French researcher Luc DeLaby suggested that Ireland has been too slow off the mark when it comes to getting clover established.

“We had this debate [on chemical nitrogen use] in France 20 years ago and now all grazing farmers there are using perennial ryegrass and clover and have made huge reductions in chemical nitrogen usage. Irish farmers need to do the same.”