12 August 2024

Getting it right with autumn reseeding

Are you planning an autumn reseed? Stephen O’Callaghan, Drystock Advisor, Teagasc Mullingar, looks at the important factors affecting the success of autumn reseeds.

As silage ground comes back into the grazing platform and grass becomes more plentiful, many farmers will consider reseeding some of their poorer-performing paddocks. Reseeding has many benefits. It enables the farm to grow more grass, carry more stock, increase live-weight gain and silage quality, and use nitrogen fertiliser more efficiently. Autumn reseeding has traditionally been the preferred time for reseeding on farms, but it presents its own set of challenges. There is significant cost involved in reseeding grassland so it is important that we get it right, below are some of the key factors affecting its success.

Timing

Timing of the reseed has a significant effect on its success. You should aim to have the crop sown before the first week in September at the latest. As autumn progresses, soil conditions can deteriorate quickly given the wrong spell of weather. This will reduce your ability to apply a post emergence spray and graze the new sward. Shorter daylight hours and lower soil temperatures also reduce seed germination rates.

Soil fertility

Getting soil fertility correct is crucial if perennial ryegrass and clover is to establish well and persist after reseeding. Soil test for phosphorus (P), potassium (K) and pH (lime requirement) before reseeding to assess your soil fertility. It is important to plan ahead as it can take several weeks to receive results.

When you receive your soil results, consult your advisor about a liming/fertiliser programme for the field that will bring the pH up to 6.3 (mineral soils) and the P & K indices up to soil index 3 and keep them there.

If the soil is not being ploughed and a min-till method is being used, i.e. discing or power harrowing, lime will need to be applied to counteract the acidity that will be produced as the old sward decays.

Weeds

If there is a weed burden in the field, you may consider spraying off with glyphosate before reseeding. It is important that this herbicide is given time to kill weeds down to the root before tilling. If ploughing, leave at least 10 days after spraying; in this situation spraying should be carried out before August 20. If using a min-till method, such as discing or power harrowing, you should leave three weeks from spraying off until tilling the ground. A lot of surface thrash makes it difficult to create a good seedbed and can create an ideal environment for pests. If removing thrash through grazing, avoid spraying off covers above 1100kg DM/ha, as getting livestock to graze covers above this will be difficult when sprayed.

Post-emergence spray

It is widely acknowledged that the most effective time to control weeds in grassland is after reseeding through the use of a post-emergence spray. Apply a post emergence weed spray when the grass is at the 2-3 leaf stage. The timing of this spray can vary between farms depending on the growth rate but is typically 5-6 weeks post sowing. The advice is to target the seedling dock when it is the size of a €2 coin. If including clover in your reseed, ensure that you use a clover-safe spray.

Clover

The use of white clover in grass mixtures has the potential to fix up to 150kg of nitrogen per hectare, as well as increasing animal performance. To establish a grass clover sward, 2kg/acre of white clover should be included in the seed mix.

Sowing in the autumn can reduce the chances of successful clover establishment, as soil temperatures are on the decline. If you are planning on incorporating clover in the autumn, the earlier you can sow the better.

Post-sowing management

After sowing, the field should be rolled to ensure good soil to seed contact and preserve the moisture in the soil. If clover is being incorporated, it is important make sure the seed is on the surface and not harrowed in.

As a general rule of thumb, three bags of 10:10:20 per acre are required after a reseed to help the grass to establish, but this will depend on the soil test results and if the farm is allowed to buy any phosphorous (P) fertiliser. FYM or slurry can both be used to reduce or replace chemical fertiliser.

It takes around eleven months for the sward to fully establish, so good grazing management is very important during this period. It is important that autumn reseeds are grazed before the first winter to encourage tillering and thicken the sward. New reseeds are ready to be grazed as soon as the plants do not pull out of the ground, at approximately 700-1,000kg DM/ha. Calves or young stock are a good option for the first grazing, particularly during poor grazing conditions. Graze the reseed at lower covers (1,000 kg DM/Ha) for the subsequent grazings to allow light into the base of the sward and aid clover establishment.