Before reseeding grassland with agricultural grass seed, you can prepare by reading this guide. This grassland management guide covers a variety of topics, including soil health, reseeding methods, timings and more.
The average level of grass produced nationally is 9.1 t DM/ha, with the top farms producing over 15 t DM/ha. Therefore, there is huge scope on most farms to increase the total grass grown, and hence increase grass in the diet, while reducing feed costs in livestock production systems.
Reseeding: 10-point plan
- Soil test – target pH is 6.2-6.5, target P and K index is 3. If ploughing, wait until after ploughing to soil sample
- Spray off the old sward with glyphosate
- Cultivate to ensure a fine, firm seedbed is achieved. Ploughing will help level any rough fields. Apply lime as per soil test results
- Select Irish Recommended List varieties suited to intended field use (e.g. grazing or silage)
- 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
- Roll well to ensure good soil/seed contact
- Apply N, P and K as per guidelines and soil test results
- Monitor your grassland reseed for pest attacks (e.g. slugs, frit fly, leatherjacket, rabbits etc). Take immediate action where necessary
- Post-emergence weed spray is essential, apply approx. (5-6 weeks after establishment, prior to first grazing). Where clover seed was sown, use a clover-safe spray
- Graze the new reseeds, frequently and at light covers to assist in tillering and to help create a dense sward
Soil health is another crucial factor that will play an important role when reseeding grassland. Unfortunately, environmental factors can accelerate the damage caused by everyday usage.
Before reseeding grassland, it is important to perform a soil test and determine the health of your soil. By doing this, you can attempt to correct the pH level and ensure that you will be reseeding in healthy soil within the pH range of 6.2 to 6.5 (potentially 5.5 for peaty soil). In the 6.2 to 6.5 range, macronutrients are in much greater supply.
Correcting soil pH
To correct an imbalance, nitrogen, phosphorus or potassium can be applied, accordingly. If fertiliser is in short supply, then it can help to apply slurry. However, this should not be considered a quick fix, as you should use a hydrometer to ascertain the exact N, P and K levels of your slurry.
You can learn more about soil fertility here.
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 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.
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 compaction issue. The plough inverts the top layer of soil, burying the old sward. Generally, gives very reliable results.
Minimum tillage can be a viable alternative for farmers who are thinking about reseeding grassland without ploughing. Typically, this involves a tine or disc harrow to cultivate the soil. It is important to spray off the old sward and wait up to three weeks before min-till to ensure adequate kill of old grasses and weeds.
Direct drill allows the establishment of the crop without disturbing the soil beyond what is necessary to place the seed at the correct depth. Begin by spraying off your sward and cutting down tightly after the spray withhold period.
You can then check for thatch and determine if it needs to be tine harrowed to allow for good seed-to-soil contact and to let sunlight in around the base.
In these conditions, agricultural grass seed can be drilled into the soil with minimum disturbance. Ensure seed is placed at the correct depth and avoid deep sowing – 10 mm is ideal for agricultural grass seed.
Timing: When to sow agricultural grass seed in Ireland?
- Improving temperatures aid germination and establishment of new sward
- Opportunity to take several grazings to help tiller the new sward
- Improved soil conditions will make it easier to apply a post-emergence spray
- The sward will be well “settled” in the following spring
- Easier to establish clover seed
Autumn reseeding may suit from a feed budget perspective in grassland management, but there are some risks:
- Lower soil temperature can decrease seed germination – aim to sow agri grass seed by early September
- Poor weather may make it more difficult to graze a new reseed or apply a herbicide for weed control – grazing helps tiller the grass plants and creates a dense sward
- Ideally, agricultural grass seed should be in the ground by the first week of September avoid later sowings as it may compromise the result depending on the weather
Effect of sowing date on sward establishment
|3 September||4 October|
|Seedlings six weeks later/m²||760||570|
|kg DM/ha in March||913||478|
Source: (Culleton et al. 1992)
Reseeding: Grassland management advice
The method used to reseed usually makes little difference to yield in the first full year. More important is making sure whichever method you use is done properly and your grassland management strategy is undertaken effectively.
Liming is important to help counteract any acidity resulting from the old sward decaying. Even if a field was limed within two years, applying 1-2 tonnes lime at sowing helps the new sward establish well.
The ideal soil pH is 6.2-6.5. In situations 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.
Ground preparation is critical, aiming to produce a fine, firm and level seedbed – one you can ride a bike across. If direct drilling, check for rain before drilling as it’s less successful in dry conditions.
Post-sowing rolling is essential. It helps compress the soil, keeping more moisture in the seedbed. Rolling also helps seed-to-soil contact and the best chance of successful germination.
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:
- 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.
- Leatherjacket: 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.
- Slugs: Most prevalent in wet weather or damp sections of a field, particularly in areas 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. Risk is reduced by creating a fine, firm seedbed with adequate rolling.
Post-emergence weed spray provides the best opportunity for weed control in the new grass sward. Weeds are easier and cheaper to control when they are seedlings and most susceptible to herbicides.
Apply a spray targeting the weed types present five to six weeks after sowing agri grass seed. If it’s a grass and clover sward, take care to use a clover-safe spray at the three-leaf stage.
Trust a grass expert
If you have any questions about reseeding grassland or when to sow agricultural grass seed in Ireland, then talk to our grass and forage experts.