Teagasc researcher Deirdre Hennessy summed it up well at the recent Teagasc national dairy conference when she said that clover “will help to reduce the amount of chemical nitrogen to be applied, but it has bigger benefits also such as increasing milk production, it’s going to increase farm profitability because it’s going to reduce costs due to less fertiliser use but also, importantly it’s going to reduce greenhouse gas emissions”.

While all of the above is undoubtedly true, there is no magic wand to get clover established or to maintain it in the sward.

I recently had the pleasure of being a judge on the Grassland Farmer of the Year competition, but one disappointing aspect of the farms the judges visited was the relatively poor uptake of clover across the farms.

Platform

Most had less than 20% of the milking platform in clover, so across the whole farm, including outfarms, the amount of clover is much less.

If these top farmers are struggling to get clover established, it says a lot about the difficulties in doing so.

It’s generally accepted that there are two ways to get clover established - through oversowing and through a full reseed.

The Teagasc advice is for farmers to reseed 10% of their farm per year and to oversow 15% of the farm per year, thereby getting 25% of the farm established per year.

However, this is very difficult to achieve, as it means that 25% of the farm is either out of production or at lower production than the rest of the farm because of having to graze at lower covers and use reduced nitrogen on the oversown parts of the farm.

Highly stocked farms trying this can and do run into problems, so it’s not for the fainthearted. Not having enough grass for cows in June is very costly.

Failure

Personally, I feel oversowing to be very antagonising for the majority of farmers. Failure, even after doing everything correctly, is as common as success.

For me, oversowing should be used to improve clover content of fields that already have clover and use full reseeding to get clover established where no clover currently exists.

Then there is the debate about fertiliser use. Some say that nitrogen should be applied at half rate from May on, while others say that good clover swards don’t need nitrogen at all.

Analysis

New on-farm analysis released by Teagasc’s James Humphreys and William Burchill shows that farms that cut back significantly on chemical nitrogen on high-clover fields did not suffer from reduced grass growth on these fields.

Farmers assigned paddocks on their farm to one of four treatments based on their interpretation of clover content.

The treatments were high nitrogen on grass-only swards and these got an average of 182kg N/ha and grew an average of 12.3t DM/ha in 2022.

The next treatment was zero chemical nitrogen on very high-clover swards and these grew 12.5t DM/ha in 2022.

The next treatment was chemical nitrogen in spring only and these paddocks received an average of 58kg N/ha and grew 12.4t DM/ha in 2022.

The final treatment was spring nitrogen and half-rate chemical nitrogen, with a total of 140kg N/ha applied and a cumulative growth of 12.3t DM/ha.

Where clover is present in sufficient quantities, applying additional chemical nitrogen from June or July onwards is probably wastefu

The amount of slurry applied varied across the treatments and some high clover fields were bound to have been reseeded recently and, as such, have better soil fertility and so on, but, either way, the results are remarkable.

They give comfort to those thinking of reducing fertiliser use on high clover swards. Where clover is present in sufficient quantities, applying additional chemical nitrogen from June or July onwards is probably wasteful.

The reverse is also true, in that I do come across farmers cutting back on chemical N on fields that just don’t have enough clover present to contribute enough to the soil and so grass growth is bound to suffer.

Some reduction in growth is inevitable when trying to oversow fields or encourage clover, but it needs to be looked at in the round - developing a summer or winter feed deficit is not a good outcome.