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The clover effect

In 2011 Teagasc researchers began studying the important role white clover plays in sustainable Irish pasture-based dairy and beef farms. 

Here, we speak to Head of Grassland Research Michael O’Donovan and his team to find out more about this work and the benefits it will have for Irish farmers. Joining him are Senior Research Officer Deirdre Hennessy, Grassland Technologist Fergal Coughlan and Grassland PhD student Aine Murray. 

TResearch Autumn Winter 2021Clover research is central to Teagasc’s grassland programme, which looks at ways to utilise grass to improve the profitability and sustainability of Ireland’s milk and meat production.

One of the key areas of focus is the use of white clover on pastures, as agriculture in Ireland is facing increasing pressure to reduce the use of nitrogen fertiliser and greenhouse gas emissions.

What is the link between white clover and nitrogen fertiliser?

Michael O’Donovan: Nitrogen fertiliser helps crops to grow faster and attain higher dry matter yields. But with the new Farm to Fork Strategy (designed to accelerate our transition to a sustainable food system approach), nitrogen fertiliser use will have to reduce on farms. White clover is a plant that, with the help of bacteria living on it, stores extra nitrogen from the atmosphere and then releases it into the soil once it dies. This process is known as nitrogen fixing, and it’s important because it makes nitrogen digestible for other plants.

Where is white clover found?

Aine Murray: It’s found in grassland that is grazed by livestock. Its stolons grow along and above the ground surface, establishing plant roots formed from any non-root tissue and producing leaves at different points. This special growth pattern is what enables it to survive when grazed.

Why should farmers consider introducing white clover onto farms? 

Fergal Coughlan: As Michael already mentioned, white clover can “fix” nitrogen – and a lot of it – which means the use of nitrogen fertiliser can be reduced in swards where clover is present. The less chemical fertiliser used, the more work clover does, helping the ecosystem.

Aine: White clover can also benefit animal and sward performance. It has higher nutritional value for livestock – including high quality protein and other nutrients. Herbage production and quality can also be greater on grass-clover swards compared to grass-only swards, especially where the use of nitrogen is lower.

Fergal: That’s a good point – clover actually thrives in soil with lower nitrogen levels, so extra chemical fertiliser isn’t needed for clover to grow.

What experiments have you been doing to test the effects of white clover use?

Deirdre Hennessy: We’ve been using grazing plot experiments to assess issues like the comparison of cultivars and nitrogen fertiliser application rate and strategy. We’re also undertaking studies to increase our knowledge in areas such as the nutritional value of white clover and the effects of nitrogen fertiliser on growth and persistence. 

Michael: We’ve also expanded our research to include farm systems experiments – an approach that is similar to how commercial farms are run, which allows us to make closer commercial farm comparisons.

What have the results of your experiments shown so far?

Deirdre: They’ve been encouraging. We’ve seen first-hand some of the benefits that Aine and Fergal mentioned earlier, like increases to the productivity and profitability of Irish grazing systems thanks to higher herbage quantities and quality.

Michael: It’s also shown that white clover is more compatible with intensive grazing regimes (eight to 10 grazings each year). This helps reduce the amount of chemical fertiliser required, and increase the efficiency of nitrogen use, milk solids produced per cow and farm profit.

Deirdre: In March 2021 we launched a national farm study across 30 farms to give us a launchpad to see how clover can work on commercial farms.

What does this national study involve?

Fergal: Farms have been set the target of establishing grass-white clover swards with 20-25% clover content in the next three years. White clover is being established on those farms using both reseeding and over-sowing methods. The establishment and persistence of clover and the factors influencing it will also be examined over the next 10 years.

Why is white clover not already being used more widely on farms?

Aine: Something that is generally taken for granted and remains a big challenge is that good grazing management is required at farm level in order to maintain white clover. Improved methods and management of sowing are required to establish sufficient amounts.  

Outside of the benefits white clover has, why should farmers be interested in this research?

Michael: EU policy initiatives have targets to reduce fertiliser use by up to 20%, so farmers will need to find ways to cut back. Furthermore, clover is pivotal to our grassland system, so we need it working on all grassland farms.  

In good company

Combined, you have over three decades of experience in clover research. What is it about this area of study that you find so interesting?

Michael: I like that clover provides a challenge in that we have to shift the previously held view that it doesn’t last on farms. Our paddocks in Teagasc Moorepark are nine years in production and still have 20% clover content – being able to prove clover’s durability is great.

Deirdre: For me, it’s increasing our understanding of the role of white clover, which goes with what Michael said about misconceptions. By providing farms with information on the performance of white clover in grassland over time, we can give them the confidence to utilise clover in their pasture-based systems.

Fergal: I also like experimenting with previously set boundaries when it comes to farm systems and then sharing our findings with the industry. We get to explain the do’s and don’ts with first-hand experience to support our guidance.

Aine: I chose to carry out my PhD in clover research as it is one of the main ways Irish farmers can reduce greenhouse gas emissions. Clover is very topical, and I’m constantly questioned by farmers and advisors on how they can improve their knowledge in the area, which is promising.