Video: Reseeding under the microscope in Mayo

Reseeding is a costly exercise and it can result in an outlay of approximately €250-350/ac to complete.

However, when done correctly, the added benefits of the rejuvenated swards – including increased growth, nitrogen efficiency and quality – can cover the costs associated with reseeding in just two years.

At a recent reseeding demonstration, organised by Aurivo in Claremorris in Co Mayo, farmers were presented with a number of key factors they need to consider when reseeding this autumn.

Germinal’s Dr. Mary McEvoy discussed spraying off and the important steps farmers need to take to ensure that their investment is a success.

McEvoy advised farmers to allow for adequate time when it comes to spraying off an old sward – especially if min-till sowing techniques are going to be used.

“Allowing the spray long enough to work is absolutely critical and that’s really important if you are talking about power harrowing or discing.

“When sowing, an old rule of thumb is that you should be able to cycle a bike across the seedbed; that’s how firm the ground needs to be before you can sow the seed.

“Often, especially after power harrowing, you will have quite a loose and puffy seedbed. In that scenario, seed can get buried too deep and it’s much more difficult for seed to get up and going.

The importance of the Recommended List

McEvoy stressed that farmers should only select varieties present on the Department of Agriculture’s Recommended List.

“The Recommended List is published by the Department of Agriculture each year and it’s based on trial results from five sites across the country.

“Every variety that gets onto that list has been on at least four years of trials; so we know that those varieties are the most suited to Irish conditions.

They have been tried and tested under our climate and we know that they are going to grow well.

“If you are buying a bag of grass seed, you want to make sure that every variety in that bag is on the list – if it’s not on the list you have to ask yourself a few questions on why it’s not there.”

Grazing varieties

“For grazing ground, seasonal yield is going to be important; we want grass that can grow more in the spring and longer into the autumn – that’s going to reduce feed costs on the farm.

“Good seasonal yield is also important as it reduces concentrate and silage requirements and leaves more money in your back pocket.

“Quality is going to drive the palatability of your sward. We know that higher dry matter digestibility (DMD) grasses are more palatable to animals and we see higher intakes and utilisation off these swards.

“And, when animals eat more high-quality grass, it’s going to have a positive impact on animal performance – whether that’s increased milk yield or sheep or beef growth rates.

“When you are reseeding grazing ground, you need to make sure that you are picking mixtures that are excelling in terms of the quality sub-indices within both the Recommended List and the Pasture Profit Index (PPI),” she said.

The importance of heading date

Another area that the Germinal representative touched on was heading date and it’s importance when it comes to selecting varieties for silage swards.

“Ideally, the mean heading date of the mixture should occur 5-7 days after your first silage cutting date. If you are aiming to take the first cut around May 25, a mixture with a mean heading date of June 2 is ideal to optimise the quality and yield of that sward,” she said.

Image source: Shane Casey

Diploid or tetraploid grasses?

The proportion of diploid or tetraploid grasses will depend on the soil type, McEvoy said.

“Diploids bring the density to the sward and they act like a carpet to help minimise the risk of poaching.

“Tetraploid varieties, on the other hand, are more upright in terms of their growth habit and they have a larger leaf. Generally speaking, they are also of higher quality.

“They are also higher yielding and we do see higher animal intakes with tetraploids and higher animal performance.”

AFBI grass utilisation

Soil type is the most important factor to consider when selecting varieties on ploidy, McEvoy said, and different mixtures are required on either heavy or dry ground.

“On better ground, you are talking about 40-45% tetraploid and 55-60% diploid varieties. As the ground gets heavier, you should increase the diploid proportion to reduce the risk of poaching.

“On heavier soils, you will probably be targeting 15-20% tetraploid varieties and 80-85% diploid varieties because sward density is going to be much more important on heavier ground.”

When should I graze?

Ideally, McEvoy said swards should be grazed at lower covers – once the sward is able to withstand the ‘pull test’.

“At the first grazing you want to be going in at a cover of approximately 800kg/ha; the next couple of grazings can increase to 1,100-1,200kg/ha.

“Don’t leave it until the cover gets too heavy. Heavy covers creates shading of the lower aspects of the sward and that can cause tiller death.

On reseeding date, she said: “Aim to have ground reseeded by the end of the first week of September. After that, weather and ground conditions can start to deteriorate and this can hamper seed establishment.”

Soil fertility

Gouldings’ Ciaran Kenny also discussed the importance of adequate soil fertility when it comes to reseeding.

“Permanent grassland has a high requirement for phosphorous (P) and it’s held in the top few centimeters of the soil.

“It’s very important if you are ploughing not to plough down too deep.

“Ploughing too deep can have a big effect on fertility and performance and it can cause a lot of phosphorous displacement,” he said.

Kenny also advised farmers to soil test their ground prior to reseeding and nutrient management decisions should be based around these results.

“Reseeding is the best time to apply lime and correct pH. For ryegrass, you should have a pH of 6.3-6.5; that increases to 6.5-6.7 for clover swards.


“60% of grasslands have soils below target pH so there’s serious deficiencies out there that have to be corrected if you want to grow more grass.

“Phosphorous is required for rooting and tillering and potassium (K) is for crop yield and nitrogen uptake.

“If you are on index three soils, you will need to apply 30kg/ha of P and 50kg/ha of K. There’s a couple of different ways that you can meet that requirement; you can use 18:6:12, 10:10:20, 0:7:30 or 0:10:20,” he said.

Post-emergent sprays – are they needed?

TP Whelehan’s John Boylan also gave a talk on the importance of post-emergent sprays.

Boylan said: “In recent trials, it was found that the most beneficial weed control in grassland is through the use of a post-emergent spray. That spray should be applied approximately six weeks after sowing.”

He said that applying a post-emergent spray is important to control weeds such as docks and chickweed. The latter is the most commonly found weed in new reseeds.

“A mature dock can produce 60,000 seeds each year and these seeds can remain dormant in the soil for up to 80 years.

“At reseeding you have created a perfect seedbed for your new grasses, but you have also created the perfect environment for weeds to germinate.

“Those weeds will win the race unless you control them and the best time to do so is about six weeks after you have sown your new grasses, when the grasses are at the four-to-five leaf stage,” he said.

Cost of machinery work

The reseeding demonstration was held on Liam Trenche’s farm. The Trench family have been involved in the contracting game for three generations and their primarily focus is on grassland reseeding and silage harvesting.

Liam Trench explained that they work approximately 500-600ac each year with a fleet of mainly Valtra and Fendt tractors.

On the contracting cost of reseeding, he said: “An operation involving disc harrowing and seeding costs between €90-120/ac and plough, harrow, level, sow and roll methods work out at about €150/ac.”