The most effective methods for reseeding grassland

In Ireland, the average grass yield produced nationally is 9.1t DM/ha, with the top farms producing over 15t DM/ha after reseeding grassland with highly rated perennial ryegrasses from the Pasture Profit Index (PPI).

With older swards producing lower-yielding and lower-quality grass and forage over time, reseeding is fundamental to driving climate smart performance. By maximising sward production, you can get more from fewer inputs.

Reseeding can increase livestock production

As a plant breeder, Germinal Horizon has developed the award-winning Aber High Sugar Grass (HSG) range, featuring varieties that rank consistently high on the PPI. These have included the likes of AberGain, AberSpey, and AberClyde, with new varieties continuously being developed.

Aber HSG varieties are bred to help livestock more efficiently capture the protein in grass. This drives meat and milk production in profitable livestock systems while reducing ammonia and nitrous oxide emissions by minimising protein wastage.

Reseeding with Germinal mixtures can grow higher-yielding, higher-quality grass that lowers bought-in feed costs, drives production and reduces emissions.

The benefits of reseeding grassland

• Increased total DM production
• Produce better quality feed and digestibility meaning increased animal performance
• Improved spring and autumn grass supply
• Increased farm productivity and profitability
• Better response to fertiliser, increasing efficiency
• Access to new breeding genetics

When reseeding, remember that your success depends on several factors:

• Soil fertility
• Paddock characteristics
• Cultivation techniques
• Timing of seeding
• Mixture or seed selection
• Grazing and cutting management

Ultimately, healthy pasture produces more high-quality grass and forage to drive animal performance and reduce feed costs.

Tips for reseeding grassland: 12-point plan

Identify fields for reseeding: Keep grassland productive by aiming to reseed 10-15% of your farm annually:

1. Identify fields for reseeding: Keep grassland productive by aiming to reseed 10-15% of your farm annually.
2. Soil test: Target pH is 6.2-6.5 while P and K index is 3. If ploughing, wait until after before soil sampling.
3. Spray off the old sward: Use adequate water to achieve good coverage.
4. Choose the best reseeding method: Prepare a fine, firm seedbed. Choose a reseeding method that makes sense for your needs.
5. Liming fields: Apply to counteract any acidity from the old sward.
6. Fertiliser: Apply NPK based on the specific requirements identified in your soil test.
7. Select the best grass and forage seed: Pick a mixture with varieties suited to the paddock’s purpose – for example, grazing or silage.
8. Germinal’s Aber High Sugar Grasses are consistently top performers on the PPI.
9. Sow the seed: Sow 14 kg seed/acre in good conditions (warm with rain forecast), no deeper than 10-15 mm. Farms in derogation must include 0.6 kg clover seed/acre or 1 kg/acre pelleted clover in their mixtures.
10. Rolling: Ensure good seed-to-soil contact and encourage germination.
11. Pest control: Monitor your reseed for pest attacks (e.g. slugs, frit fly, leatherjacket, rabbits etc). Act quickly where needed.
12. Weed control: Post-emergence weed spray is essential. Apply roughly five to six weeks after establishment; before first grazing. Where clover seed was sown, use a clover-safe spray.
13. Grazing management: Graze a new reseed frequently and at light covers to assist in tillering and help create a dense sward.

The best time to reseed grassland?

Reseeding in spring or early summer is ideal due to improving soil and air temperatures and ground conditions versus autumn. Rising spring temperatures and longer days can help achieve good germination and establishment of the new seed.

Better ground conditions will allow more frequent grazing of your new reseed. This is vital for the tillering process while allowing more time to use a post-emergence spray than you would have with an autumn reseed.

Alternatively, autumn reseeding suits from a feed budget perspective and in arable rotations. The ideal sowing time is August, whereas clover swards should be sown before the middle of July.

When reseeding is delayed into September, this can mean lower temperatures and will potentially impact germination. Having more rainfall can also make ground conditions worse and inhibit grazing. Even delaying a sowing date from September to October can impact results.

Effect of sowing date on sward establishment

Source: (Culleton et al 1992)

Soil test before reseeding

When you start with soil testing, you can confirm the pH level and nutrient makeup of your soil. You can then correct any deficiencies, giving the reseed the best chance of success. You can also save money by targeting your fertiliser applications, which also benefits the environment.

Soil pH target

Germinal typically recommends reseeding in healthy soil with a 6.2-6.5 pH range, where macronutrients are in much greater supply. You can target 5.5 pH for peaty soils.

Take a soil sample

Divide your farm into 2-4 ha areas that can be managed individually for a specific fertiliser application program. Select soil samples from different areas based on:

• Soil type
• Slope
• Drainage
• Crop history
• Poor yields
• Avoid areas that won’t be used for reseeding
• Having a wide range of samples will help you improve soil fertility across your farm.
• Follow a ‘W’ soil sampling pattern to ensure that the sample is representative of the entire field.
• Take approximately 20 cores. Ensure that all soil cores are taken to the full 100mm depth.
• Place the 20 cores in the soil box to make up the soil sample.
• Write the field number and sample number on the soil box.

Make sure to wait three to six months after your last fertiliser application before sampling a field for P and K. With lime, allow two years before sampling.

Soil damage

When soil testing, it also helps to determine the soil structure. This can highlight whether there are any concerns in terms of compaction or if a solid pan has formed at the bottom. If so, mechanical intervention might be required to remedy the issue before reseeding grassland.

Please note that soil compaction can be caused by using heavy machinery. With soil compaction potentially causing a 20% drop in yield, according to Harper Adams University, it helps to plan different entrances and exits into fields and to provide multiple water points for livestock.

Preparation: Spray off the old sward

With grasses becoming less productive and weeds starting to take over, yield and profitability decline significantly in ageing pastures that are seven years or older.

Prepare for reseeding by spraying off the old sward. Seven to 10 days after, cut the sward tightly to ensure a clean seedbed when sowing. Then wait 10 days before ploughing or 16 days for min-till.

Methods for reseeding grassland

Regardless of the reseeding method, prepare a fine, firm seedbed before sowing grass and forage seed. This is to achieve:

• Good seed-to-soil contact for germination.
• Firmness to avoid seed getting buried too deep.
• Moisture retention in the soil, which is critical for the new plant.
• A level even seedbed to help the sward establish.

Use a seed rate of 14 kg seed/acre in good conditions (warm with rain forecast) and no deeper than 10-15 mm.

Ploughing

Ploughing is the first of three well-known grassland reseeding methods. It provides an opportunity to level a field or break a pan if there is a soil compaction issue. The plough inverts the top layer of soil, burying the old sward.

Ploughing gives very reliable results, but it can release carbon and disturb microorganisms. If desired, there are sustainable alternatives that can also be effective under the right circumstances.

If reseeding without ploughing, it is crucial to use lime or granulated lime to neutralise surface acidity. This applies to the following reseeding methods.

Minimum tillage

Min till can be viable if you are considering reseeding grassland without ploughing. Typically, this involves a tine or disc harrow to cultivate the soil. Spray off the old sward and wait up to three weeks before min-till to ensure adequate kill of old grasses and weeds.

Disc and one pass

Aim for two to three passes of the disc harrow. The second run should be at an angle different to the first run to ensure the breakup of the sod and sufficient soil is turned up. Avoid excessive forward speeds as this can result in uneven seedbed.

Direct drilling/no-till

This allows the establishment of the crop without disturbing the soil beyond what is necessary to place the seed at the correct depth. Start by spraying off your sward and cutting down tightly after the spray withhold period.

You can then check for thatch and see if it needs to be tine harrowed. This enables good seed-to-soil contact and lets sunlight in around the base. In these conditions, grass and forage seed can be drilled into the soil with minimal disturbance.

Overseeding grassland

Grassland can be overseeded to rejuvenate an old sward where full reseeding is not desirable. Results can vary and depend on multiple factors. Good seed-to-soil contact is essential, so this is unlikely to work if the existing sward has excessive thatch.

Slot seeding via direct drilling is recommended, but first graze the old sward hard or ideally use this method after taking a heavy cut of silage.

Use a seed rate of 20-25kg/ha (8-10kg/acre) and graze the sward frequently at light covers to avoid the existing sward shading out the new seeds.

Liming fields

Applying lime is important to counteract any acidity resulting from the old sward decaying. Even if a field was limed in the last two years, applying 1-2 tonnes of lime when sowing will help your new sward establish well.

Where soil pH is adequate, some gran-lime will be of benefit. Especially in min-till or direct drill situations to counteract surface acidity and increase the rate of decay of the old sward.

Apply fertiliser

Apply nitrogen (N), Phosphorous (P) and Potassium (K) when sowing. N provides seedlings with energy for growth while P and K support root and tiller development. Apply fertiliser according to your soil requirements from testing and follow the national guidelines.

Rolling

Post-sowing rolling is essential as it compresses the soil, keeping more moisture in the seedbed. Rolling also aids seed-to-soil contact and supports successful germination.

Pest control

Pest attacks are more prevalent with an autumn reseed. The following points all help reduce the risk of an attack:

• Killing off an old sward effectively and removing dead trash.
• Allowing sufficient time between spraying and cultivation.
• Preparing a good seedbed in the best growing conditions for a new reseed.
• Post-sowing rolling.

Common pests include:

• Slugs: More common in wet weather or damp sections of a paddock, particularly with high levels of surface trash or inadequate/no rolling. Slugs are indicated by shredded leaves. Direct-drilled reseeds are at the greatest risk as slits in the ground provide shelter for slugs. Use slug pellets if direct drilling or if a problem is identified. Reduce the risk with a fine, firm seedbed and adequate rolling.
• Leatherjackets: Found in bare patches. Leatherjackets are the larvae of the crane fly (Daddy-long-legs). They cut off the plant just below the surface, destroying the seedling. Large crow populations feeding can indicate a leatherjacket problem.
• Frit-fly: Can result in patchy, poorly established reseeds. Frit-fly larvae burrow into the base of newly emerging grasses, cutting off the plant at the growing point. Autumn reseeds and min-till are at the greatest risk.

Weed control

Post-emergence weed spray can help weed control in new swards. Weeds are easier and cheaper to control when seedlings as they are more susceptible to herbicides.

Apply a spray targeting the weed types present five to six weeks after sowing seed. If it’s a grass-clover sward, use a clover-safe spray during the three-leaf stage.

For more advice, check out our grassland weed control guide.

Grazing management after reseeding

Grazing is critical for grass tillering and the first grazing should occur at a low herbage mass. You can proceed if the sward passes the pull test.

Pull the grass leaves by hand as if to mimic a grazing animal. If the leaves break off, it is ready for grazing. If pulling causes the plants and roots to come out, the sward needs more time to anchor. Ideally, avoid cutting for silage in the first year if possible.

Ask the grass experts

Are you thinking of reseeding? Contact us today to discuss best practices and mixture options.