Reseeding is one of the most cost-effective on-farm investments and is costing in the region of €750/ha. With increased profitability due to dry matter production and nitrogen use efficiency, Teagasc estimates that within two years, the new sward will cover the cost of reseeding. It takes up to 11 months for the new sward to fully establish, which is why it is so important to manage your reseed correctly.
When it comes to timing, there are positives and negatives for both spring and autumn reseeding. The positives of a spring reseed are the more favourable ground conditions, soil temperature to promote seed germination and good weather conditions for post-emergence spraying and grazing.
The negatives of spring reseeding are mainly around timing – if done to early, low spring temperatures slow germination, while if done too late in the spring, dry conditions can also disrupt germination.
This year, all of these issues had a part to play. Slow spring growth followed by a wet May and a dry June meant some spring reseeds were slow to germinate and resulted in a much longer turnaround time than normal. For others, the poor spring growth meant they could not afford to take ground out of the rotation, as this could result in a grass shortage.
Giving your reseed the best start
Whether you reseed in the spring or autumn is a personal choice, but the fundamental principles behind a successful reseed are the same for both.
Start by selecting an underperforming paddock – do not just select a paddock for reseeding based on how long it has been since it was last reseeded. If you are recording grass measurements on PastureBase Ireland, your annual tonnage will show up the worst-performing paddocks.
Reseeding will not solve soil fertility issues, so having an up-to-date soil sample result will show the paddock’s suitability for reseeding. Ideally, the paddock should be in index three for both phosphorous (P) and potassium (K). The pH should be 6.3 in order to give the seed the best environment for germination.
The next step is to burn off the old pasture. Once you have the paddock sprayed off, cultivation can begin seven to 10 days later. If there is a large weed infestation, delaying will ensure the herbicide gets to the roots and there is a good kill.
There is very little difference between the success of different methods of reseeding, once they are done correctly. The aim is to create a fine, firm and level seedbed, whatever your preferred option is. This must then be followed by rolling to ensure there is good seed-to-soil contact in order to promote germination.
When setting the seed, it is also important to apply fertiliser to ensure the nutrients are available for the seed to germinate. The most common fertiliser used at reseeding is 10:10:20 at a rate of three bags per acre. Nitrogen is not required in high amounts at sowing, but is required at the post-emergence stage and should be spread at a rate of 30 units per acre.
Post-emergence spraying is one of the most important stages in establishing a new sward. This is your best chance at killing off any weeds present in the sward. Spraying weeds at the rosette stage will ensure a better kill. If you have clover included in your grass seed mix, it is vital to use a clover-safe spray.
Finally, at what stage do you graze the new sward? A pull test is the easiest way to assess if a reseed is suitable for grazing. Simply pull the grass and if the roots come up, it is not ready. As most grass varieties used in Ireland are perennial rye grasses, they produce tillers, which in turn grow and support the high DMD leaf we target to graze with cows and cattle. Tillering will also mean a denser sward.
For this reason, target grazing the new reseed at a cover of 800kg DM/ha on the first grazing and no higher than 1,100kg DM/ha for the next three grazings at least. Grazing at lighter covers ensures that light is getting to the base of the sward and any seedlings that germinated later are given a chance to establish.
Spring reseeding 2021
Grass growth in 2021 has been very variable across the country. The success of a spring/summer reseed this year was very much dependant on timing which has resulted in some reseeds coming back into the rotation within six weeks and others taking almost double that.
In cases where poor germination took place due to a lack of moisture, weeds have had a chance to establish.
Controlling weeds in a reseed is your best chance of having a clean sward going forward. Target spraying at five to six weeks when the weeds are young and target spraying docks when they are the size of a two euro coin. Spraying early will stop weeds shading out the grass seedlings and allow them to grow.
Reseeded ground that has germinated poorly due to conditions at sowing needs to be treated with care. You must first establish if the seeds germinated and then died, and if so you may need to stich in more seed.
If conditions were too dry, it is likely that the seed did not germinate and once it gets moisture, it will start to grow. At the five to six week stage, spread 30 units of Nitrogen per acre. Walk your reseed often and once it is at a cover of 800kg DM/ha, graze it.
Grazing at a light cover below 1,100kg DM/ha for the following three to four grazings will encourage it to tiller and fill out. Grazing is very dependent on weather conditions, given the openness of the sward. Avoid poaching at all costs.
Autumn reseeding 2021
The number one pitfall with autumn reseeding is not doing it early enough.
When it is left too late, ground conditions begin to deteriorate and this in turn results in delaying or missing the opportunity to post-emergence-spray and a reduced opportunity to get it grazed before winter.
Late July or early August is the ideal time to get the reseeding process started. Having the seed in by mid-August will greatly increase the chances of getting it sprayed with a post-emergence spray for weeds five to six weeks after sowing, as soil conditions should still be good.
Ground conditions will also be better for grazing the earlier you begin. Grazing once, if not twice, before closing will promote tillering. A well established sward will be better set up to grow more grass the following spring.