Aug 21, 2023
Most grassland reseeding traditionally takes place in the autumn (August/September), with about one-third of reseeding occurring in late spring (April/May).
Autumn reseeding is the preferred option on many farms. This is due to reduced pressure on grass availability, increased availability of grazing ground after second-cut silage and the threat of drought has subsided.
However, as autumn progresses, the weather can change quickly so timing is critical. The aim for autumn reseeds is to have the ground reseeded before the first week in September. Delaying it until later on in September risks poor germination due to falling soil temperatures, deteriorating soil conditions - making it more difficult to establish a firm seed bed - as well as less opportunity to use a post-emergence spray and get a grazing in before the winter.
The target turnaround time for an autumn reseed should be 50-60 days. Therefore, farmers need to be picking the paddocks for reseeding and putting a grazing and spraying plan in place now. If the grass seed is to be sown by the first week of September, you can work back from this date.
If discing or power harrowing, leave three weeks from spraying off until tilling the ground. If ploughing, it’s okay to sow 10 days after spraying; in this situation, you would need to be spaying off before the 21st of August. A lot of surface thrash makes it more difficult to create a good seedbed. Farmers need to be able to remove as much trash as possible through either grazing or cutting at least five days after spraying. 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.
Getting soil fertility correct is crucial if perennial ryegrass and clover is to establish well and persist after reseeding. Soil test for phosphorous (P), potassium (K) and pH (lime requirement) before reseeding. If ploughing, take another soil sample six months later to check that soil fertility hasn’t changed significantly since ploughing. Consult your advisor about a liming/fertiliser programme for the field to be reseeded that will bring the pH up to at least 6.3 (mineral soils) and the P and K indices up to soil index 3 and keep them there.
Use the Pasture Profit Index (PPI) to identify a suitable seed mix for your farm. The PPI is a variety selection tool used to identify the best varieties to sow when reseeding. The PPI expresses the relative differences between varieties for agronomic traits such as spring, summer and autumn herbage yield; herbage quality; silage yield; and grazing utilisation.
Seed mixtures that have varieties that are not on the PPI should not be used, as these varieties failed to reach the minimum standard of performance. For silage reseed mixes, choose varieties that score highly on the silage sub index. Be mindful, however, to keep the heading date range to about 6-7 days. Reseeds that are destined for grazing should score highly on traits such as grazing utilisation, quality and spring and autumn herbage production.
The number of varieties sown in a mix should be limited to a maximum of four. Mixtures that contain many varieties can dilute the performance of the better varieties in a mix. Combining diploids and tetraploids in a mixture will create a dense, high-quality sward, but ensure you select cultivars which express high performance in the key traits on the PPI.
When selecting white clover cultivars to sow, use the Department of Agriculture, Food and the Marine Recommended List. Small and medium-leaved cultivars are best suited to intensive grazing systems, with large leaf clovers more suited to silage-based systems.
Sowing in the autumn can reduce the chances of a successful establishment, as soil temperatures are on the decline. At this time of the year, it is more difficult for clover to compete with the grass. If yiu are planning on incorporating clover in the autumn, the earlier the better.
The use of white clover in grass mixtures has the potential to offset up to 150-200kg N/ha per hectare, as well as improving weight gains when cattle are at grass. In general, to establish a sward with >25% white clover, which is the level required for an animal production benefit, 1.5-2kg/ac of white clover should be included in the seed mix.
How paddocks are prepared for reseeding depends on soil type, amount of underlying stone and machine/contractor availability. There are four main different cultivation and sowing methods available. All methods, when completed correctly, are equally effective.
Table 1: Cultivation methods
Apply a post emergence weed spray when the grass is at the 2-3 leaf stage, this is usually 5-6 weeks after sowing. In the autumn, docks and chickweed are the two most critical weeds to control so make sure you use a spray that is effective against both these weeds. If clover is sown, make sure to use a clover-safe spray. It is important that autumn reseeds are grazed before the first winter. Graze the new reseed as soon as the plants do not pull out of the ground, approximately 700-1,000kg DM/ha. Calves or young stock are a good option for the first grazing, particularly during poor grazing conditions.
This article first appeared on Agriland as part of the Teagasc DairyBeef 500 Summer Beef Series. For more information on the DairyBeef 500 Campaign, click here.
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