The mood music coming out of clover research over the last few years has all been positive.

Over the four years of the clover study in Clonakilty, the grass and clover swards grew an extra 1.2t DM/ha and the cows produced an extra 48kg MS/cow.

The grass and clover swards at Moorepark grew similar amounts of pasture, but with 100kgN/ha less nitrogen, and the cows still produced an extra 35kg MS/cow. These results cannot be ignored.

Nitrogen fertiliser, while effective at growing grass, is a dirty product. If spread in too high quantities, it leaches and pollutes water.

If Ireland is to retain its nitrates derogation, both groundwater and water quality in rivers must improve. That is not to suggest that it is bad to begin with, but it needs to improve all the same.

A consultation process is under way on future conditions in the nitrates derogation.

If Ireland is to retain its nitrates derogation, both groundwater and water quality in rivers must improve

The other thing about nitrogen is that it has a big carbon footprint. For every kilo of nitrogen applied, around 10kg of carbon dioxide is emitted.

This is the total carbon footprint, including the carbon dioxide emitted in making the fertiliser and the carbon dioxide emitted in the soil while the fertiliser is doing its work.

As we know, carbon dioxide is a potent greenhouse gas. To put this in context, the carbon footprint of nitrogen is around 25 times higher than that of muriate of potash.

Clover-rich swards increase milk yield and allow for similar, or increased, pasture growth with less chemical nitrogen required. It is a win for the farmer and it is a win for the environment.

However, clover is not without its issues. There are three major drawbacks:

  • Slower growth at the shoulders of the year.
  • It can take over the sward leading to bloat and other issues.
  • Its persistency is poor.
  • Growth pattern

    The trial results from Clonakilty show that the grass clover swards actually grew similar to the grass-only swards in spring. This is despite the fact that clover has a higher soil temperature threshold for growth at 8°C as opposed to 6°C for grass. However, in the early part of the study, when clover content was highest, growth rate over the winter (December and January) was less. While the growth was similar in spring, the opening farm cover was much lower in the clover swards, meaning around 150kgDM of silage had to be fed while cows on the grass and clover treatment were on grass.

    Clover emerging on fields farmed by Lawrence Sexton in Cork..

    In the latter half of the study, when clover content reduced, the difference in growth rate between grass-only and grass-clover swards over the winter was less. But so too was the gain from clover, with less of a difference in milk solids and grass growth over the last two years of the study compared with the first two years. This tells us that a stable level of clover at 20% to 30% of the sward is preferred to very high, or low clover contents.

    Bloat

    The main cause of bloat is clover dominating the sward, so preventing this from happening is the best control method for bloat. Cutting fields for silage is an issue as clover tends to dominate the subsequent sward as it has reduced competition from the grass while it is recovering from being cut. Where there are high levels of clover in the sward, preventing cows from gorging on clover (by making sure they don’t go into high clover fields very hungry) or using bloat oil are preventative measures.

    Persistency

    The persistency of clover in the sward is poor. Unlike perennial ryegrass, which under the right management will persist for decades, clover has a shorter lifespan. In the first two years of the experiment at Clonakilty, clover content averaged around 30%, but this fell to 17% for the following two years and the clover content in 2018 was only 10%.

    However, 2018 was also a bad year for grass growth after the cold spring and very dry summer. Fergal Coughlan, the farm manager in Clonakilty, is now over-sowing clover back into the swards. Another reason for lack of persistency is poor soil fertility.

    Clover is particularly sensitive to imbalances in pH, phosphorus and potash. That said, persistency of clover in Moorepark has been much better where reduced levels of nitrogen were spread.

    Oversowing results

    Nine commercial dairy farms took part in a project looking at over-sowing clover led by Teagasc researcher Mike Egan in 2016 and 2017. The farmers over-sowed between 1.5kg and 2kg of non-pelleted clover per acre into existing grass swards between April and August using an Einboch tine harrow and air seeder.

    “Of the nine farms that took part, three have substantial quantities of clover on the farm with sward clover content averaging between 17% and 19% in 2018. Of the remaining six farms, all had good levels of clover at establishment, but over the next two years clover did not persist as well. Four farms had between 6% and 11% clover content in 2018, while the remaining two farms have no clover,” Mike says.

    For Mike, good establishment is when there is an average clover content of around 20% in the sward. He says that best results are achieved when the clover is sown after a tight grazing (less than 4cm post-grazing height) and the field is grazed for the rest of the year at a light cover of around 1,200kg/ha pre-grazing yield.

    Clover can be good for the farmer and good for the environment.

    The farms where clover didn’t take tended to have heavier soils, were hilly, north-facing or had dense, butty-type swards. Mike says that old swards should get a full reseed as opposed to over-sowing.

    Fergal Coughlan is spreading the seeds with fertiliser. He mixes the seed with the fertiliser in the field to prevent the seed from settling when driving to the field.

    He is spreading 2kg/acre of Chieftan and Crusader seed along with one bag/acre of 0-10-20 to fields that have just been grazed.

    About 2,000 gallons/acre of watery slurry is spread after the seed goes out.

    Key to all methods is to not do too much at once, as the fields need to be grazed when they have light covers and not cut for silage for the rest of the year.

    If too much of the farm is done at once, then it won’t be possible to give the field special treatment. Clover seed costs around €8/kg.

    Farmer focus: Lawrence Sexton, Kilbrittain, Co Cork

    Lawrence took part in Mike Egan’s trial on over-sowing clover. Lawrence reseeds about 10% of the milking platform every year but he thinks it’s better not to sow clover with the grass and instead sow the clover after the new grass has got its post-emergence spray. He started over-sowing clover on the rest of the farm in May 2017 and average clover content across most of the farm is around 20% across the grazing season.

    “Clover likes heat and light. While we have a south-facing farm, we have some paddocks near the yard with a lot of trees in them and the clover didn’t take there at all. I prefer smaller leafed clovers as they are hardier and more robust. I try to make sure that the cows aren’t too hungry when they go into fields which have a lot of clover to avoid any potential issues with bloat,” Lawrence says.

    Read more

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    Dairy management: breeding cows, fertiliser and calmag