Farm Ireland

Thursday 22 March 2018

5 benefits of grass reseeding

Tommy Boland

Tommy Boland

We are eight weeks from the start of the ewe breeding season here in Lyons, and just two weeks away from the return of our students to Belfield and Lyons.

Where has the summer disappeared to? Attention is now focussed on finishing lambs and preparing ewes for mating. As the year progresses, the energy content in grass declines, and this is even more pronounced where grassland management has been less than ideal in the early part of the grazing season.

In my last article I mentioned how we welcomed the rainfall that had just arrived. We would now welcome a stop.

The main hill grazing ground stands up very well to high levels of rain, but the lower ground is getting wet at this stage.

Another issue with the high levels of rainfall is the negative effect it has on grass intake. Dry matter content in the grass drops during rainfall events which in turn reduces grass dry matter intake.

This wet grass is also not used as efficiently by the sheep's digestive system, meaning less of the available nutrients are captured by the animal to be converted into meat.

As 2017 is 'The Year of Sustainable Grassland' some discussion of pasture reseeding is merited.

I have written a lot in these pages over the last couple of years about our work using 'alternative' grazing swards.

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My colleague Dr Helen Sheridan expands further on these swards elsewhere in this week's edition, but perennial ryegrass continues to dominate grass seed sales in this country.

There are many very good reasons for this, not least the potential of ryegrass to produce high quantities of high quality feed. It is also highly tolerant to grazing but it must be managed appropriately.

Ireland's geo-climatic conditions make it ideally suited to growing grass.

For some, reseeding is a central part of their grassland management protocols.

For others, reseeding is seen as the beginning of a journey to improve grassland management. Unfortunately, this is where some lose the value of reseeding.

Reseeding is an expensive procedure, costing up to €300 per acre (€750 per ha) depending on the method employed. So we must ensure we get value for this investment.

The main objective with a perennial ryegrass reseed should be to grow and utilise more grass, but many factors need to come together to achieve this.

Soil fertility and lime

Soil fertility particularly soil pH and phosphorus and potassium status must be correct, or corrected at reseeding.

This gives the newly established sward the optimum chance of performing. Soil pH is lower than optimum on the majority of Irish farms, and can be corrected through lime application. Lime application has declined dramatically since the 1980s though there has been an increase in recent years. Lime is often referred to as the cheapest fertiliser available. Perhaps this is part of the problem - do we confuse low cost with low value?

Applying lime will raise soil pH which will increase the availability of many of the key nutrients in the soil to support plant growth.

As with any biological system, and the soil is not different, things are not black and white. There are different lime types and different soil types and these must be matched to achieve the desired outcome.


Perennial ryegrass has a high nitrogen requirement, and this nitrogen must be supplied through bag fertiliser or nitrogen fixation from associated clover inclusion in the sward. If the reseeded sward is not fertilised appropriately then non-sown species can enter the sward and take over under certain circumstances. Once again this means we lose the value of the reseeding.

Sward type

We need to consider what type of sward we want. Is it a grazing only sward? One cut of silage and grazing? Or a more intensive silage sward? The correct varieties must be selected to meet these objectives. Recently monoculture swards have gained some traction, but more commonly three or four varieties will be included in the reseeding mixture. The pasture for profit index (PPI) ranks ryegrass varieties on their potential to influence farm profitability, and should be consulted in deciding what varieties are to be used.

Weed spray

Post emergence weed spray is a must in my opinion. The one area where I've seen farmers 'get away' without using one, but even here it is questionable, is following three or more years of tillage, where much of the weed control has taken place.

When reseeding permanent pasture the existing seed back contains plenty of weed seeds, and the newly reseeded ground is designed to support seed germination.

A surprising number of reseeds do not receive a post emergence spray and the results are obvious to see. Any decisions on herbicide product used must be cognisant of whether or not clover is present and what the weed challenge is.

Grazing infrastructure

Now that we have established the new grass, the farm must be set up to utilise it. Grazing infrastructure is critical here. Paddock fencing is one of the best investments that can be made on a livestock farm. Costs of establishing paddocks are very different on a dairy compared to a sheep farm, with each metre of fencing being significantly more expensive on a sheep farm.

Even a relatively simple five-paddock rotation system as practiced at Lyons and Teagasc Athenry will greatly enhance the capacity to utilise the grass. Additional actions like grass measuring and budgeting will further increase the potential to utilise grass.

The comments above relate to reseeding in general, not just sheep farms. There are many other points to consider like when to reseed, the method of reseeding to use, seeding rates etc.

Benefits of reseeding include: swards which are more responsive to fertiliser, higher annual DM yield especially in spring and autumn, higher sward quality, increased grass utilisation and increased stock carrying capacity.

Assoc Prof Tommy Boland is a lecturer in Sheep Production at Lyons Farm, University College Dublin @Pallastb

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