The holy grail from a farmer’s perspective is growing high-yielding swards of high-quality grass that can be easily and efficiently converted to meat, milk or winter feed, with minimal inputs and loss to the environment.

Achieving this is difficult. Perennial ryegrass swards, which have dominated grass-based dairy advice for the last 100 years, are high-yielding and digestible, but they have a relatively high nitrogen requirement and their growth pattern is not very uniform, ranging from zero to 100kg DM/day from winter to summer.

Multi-species swards at Curtin's Farm, Moorepark.

Some farmers and researchers are looking for alternatives to perennial ryegrass monocultures.

The most well known of these is the perennial ryegrass and clover combination. The significance of clover is that it is a legume that fixes nitrogen from the atmosphere and puts it into the soil. This biologically-fixed nitrogen is available to the clover plant, but also to companion plants such as perennial ryegrass. It is also available for leaching.

Another advantage of clover is that it is highly digestible, even at high covers, and animal performance is usually very good in grass/clover swards. Studies at Teagasc have shown increased animal performance when clover is included in the sward.

The significance of clover is that it is a legume that fixes nitrogen from the atmosphere and puts it into the soil

One of the main downsides to clover is that it has a more uneven growth pattern than perennial ryegrass, being slower to grow in spring and slowing down earlier in autumn. It is also a more complex plant to manage than perennial ryegrass and can easily be out-competed by the ryegrass, leading to a reduction in clover content in the sward and persistency issues.

How to establish white clover

There are two ways of establishing clover into a sward. The first and probably the most successful method is to sow clover while undertaking a full reseed. This involves sowing 1kg to 1.5kg of clover seed per acre in addition to grass seed. Apart from making sure only a clover-safe post-emergence spray is used, management of the clover seedling is similar to that of the grass seedling. Regular grazings at light covers will facilitate the grass to tiller and it will also help prevent the clover seedling from being shaded out. Oversowing clover into existing swards is another way of establishing it, but this is a bit more risky, as long-term success can be hit and miss. There are two methods of oversowing – broadcasting using a fertiliser spreader or similar, or precision sowing using a tine harrow cultivator with pneumatic seed drill.

Teagasc's multi-species swards field trial in Johnstown Castle, Co Wexford. \ Thomas Hubert

These scratch the surface and place the seed on the ground. Rolling or spreading soiled water after sowing is recommended if using either method, to increase seed to soil contact.

Regular grazings at light covers will prevent the existing grass sward from shading out the new clover seedlings. These paddocks should be grazed at covers of no more than 1,000kg/ha for the first few months after sowing. The phosphorus and potassium status of the soil should be good. Nitrogen should be reduced after oversowing to reduce the dominance of the existing ryegrass swards. Oversowing is most successful when carried out in late spring, in swards that have a high proportion of perennial ryegrass, are not too dense and are clean at the base.

Typical multi-species mixtures contain six different species made up of grass, legumes and herbs

It’s relatively easy to get clover established, but keeping it in the sward long-term is a much greater challenge. Teagasc research looking into why clover doesn’t last has not had clear results. It seems cutting the field for silage helps clover, as clover stolons recover faster after cutting compared to ryegrass. However, routinely cutting the field for silage is bad for clover persistency. Closing fields with a high clover content for the winter at a high cover appears to be bad for clover content in the following grazing season.

Multi-species

‘Multi-species swards’ is the new buzz phraze in grazing mixtures. Typical multi-species mixtures contain six different species made up of grass, legumes and herbs. Some multi-species mixtures can contain up to 12 different species. While the terminology around multi-species is new, multi-species swards themselves are nothing new and are probably a lot more reflective of the swards Irish farmers grazed 100 years ago than the predominant swards we have today.

Multi-species sward on Martin Heaney's farm in Meath.

The thinking behind these swards is that they provide a more diverse pasture than just monoculture perennial ryegrass or perennial ryegrass and clover. This diversity is reflected in a number of different ways:

  • Different species have different growth patterns depending on the time of year, so the overall pasture growth rate should be more consistent.
  • Different species have different rooting depths, which increases drought tolerance in dry weather and increases drainage ability in wet weather.
  • Some species grow slower than others and have a higher mineral and vitamin profile.
  • Legumes fix nitrogen, which can be used by other species.
  • Over winter, growth rate can be higher than with perennial ryegrass, so nitrogen uptake should be higher.
  • There is evidence that plantain can reduce the nitrate concentration in urine patches.
  • However, there are also perceived downsides to multi-species swards. I say perceived, as the Irish research on them is really only in its infancy. Where multi-species have been sown on commercial farms, there appear to be issues around persistency of certain species, particularly chicory, plantain and red and white clover. Docks can also be an issue, as there is no spray that can kill docks, but is safe for all of the species in a multi-species sward.

    Where multi-species have been sown on commercial farms, there appear to be issues around persistency of certain species

    The best way to establish a multi-species sward is through a full reseed. If persistency is an issue for multi-species swards, that means they could need to be reseeded more regularly than perennial ryegrass swards in order to maintain the desired number of species in the sward. There are four implications to more regular reseeding:

  • Reseeding costs money in terms of cultivation and seed costs. Multi-species seed mixtures are more expensive than perennial ryegrass. Typically, it costs €65 for seed to reseed an acre with grass/clover, while it costs €110 for seed to reseed an acre with multi-species.
  • If land is out for reseeding, then it is not growing feed.
  • Reseeding releases large amounts of nitrates to the environment.
  • Reseeding permanent pastures releases large amounts of carbon to the atmosphere.
  • Low input

    Both multi-species swards and grass/clover swards are both considered low-input swards as the amount of nitrogen required to grow the same amount of pasture is less than with perennial ryegrass only swards. The driver of this is the legumes, as these fix atmospheric nitrogen.

    There are ongoing Teagasc trials looking at different nitrogen inputs with clover and multi-species swards. Generally, chemical nitrogen applications are front-loaded to the spring when clover content is low.

    Comment

    The way I see it, there are four or five certainties when it comes to establishing a low-input permanent pasture. The first is that it can be done – these pastures can deliver high quantities of good-quality feed with low levels of nitrogen. The second is that policymakers are looking to restrict the use of nitrogen as a result of this. The third is that these lower-input systems are complex to manage, even in a research setting, and just because something is possible doesn’t mean it is easy to achieve. In my opinion, the researchers are still learning, so farmers shouldn’t be asked to adopt this practice until the researchers are confident that they can manage it.

    Finally, there could be some unintended consequences from some of these low-input pastures. If they are less persistent, then they will need to be reseeded more often, which releases soil carbon and background nitrogen. If production is reduced on low-input pastures, then more supplement will have to be imported on to the farm, or stocking rates reduced.

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