The main advantage of reseeding grassland is that it will increase both the quantity and quality of grass grown, writes Michael Donoghue, B&T Dairy Adviser, Teagasc Galway/Clare.
Estimates vary but new reseeds should grow in the region of 20-40% more grass and importantly a lot of this extra growth will occur in the spring and autumn.
Increased animal performance, improved responsiveness to Nitrogen and a great opportunity to tackle weeds are all important additional benefits.
However, at roughly €300/acre, it represents a significant investment, while also being without the field for between 5-8 weeks. Thus the importance of a successful reseed is vital.
Before spending money on reseeding; any drainage issues need to be addressed first. Drains should be cleaned and if shores are required they should be installed.
Ploughing can help with drainage and levelling badly damaged fields but be aware that the “good soil” with the high fertility is being buried and this make take some years to be built back up again.
In general, the rule is, the earlier in the growing season reseeding is done the better. The reason for this is that post-seeding management, grazing off the sward and post spraying can be difficult once we get later into the year.
A young grass plant is not very strong and will struggle badly with competition from weeds. Thus it is essential to spray off the old sward. Any of the glyphosate products are effective but rates need to be carefully checked as they can differ a lot.
Most of the products need 7 plus days to fully absorb the chemical. After the plant is dead, the sward can be cut for silage or grazed.
Ensuring adequate Phosphorus (P), Potassium (K) and Lime are essential for successful reseeding. The most accurate way to judge a soils requirement for these is to do a soil test, but this can take 2 weeks to get results back, so plan in advance.
If the soil is not being ploughed and a min-till method is been used, i.e. discing or power harrowing, lime will need to be applied, 2t/ac, to counteract the acid that will be produced as the old sward decays.
As a general rule of thumb 3 bags of 10:10:20 per acre are required for reseeding but this will depend on the soil test results and if a farm is allowed to buy in Ps. FYM or slurry can both be used to reduce or replace bag fertiliser.
Fine, firm seedbed
There is sometimes a lot of debate about ploughing or using min-till. The decision will depend on a number of factors including cost, stoniness of ground, equipment available etc.
All the methods can give excellent results but the basic requirement does not change which is a fine firm seedbed. After sowing, the field should be rolled to ensure good soil to seed contact and preserve the moisture in the soil. If clover is important, make sure this is on the surface.
Chickweed, redshank and docks commonly emerge after sowing. These should be sprayed, preferably with a clover safe spray, 4-5 weeks after sowing. Pests like fruit flies and leather jackets can attack reseeds and should be sprayed early if present.
These tend to be more of a problem when there is a lot of trash left on the surface.
Reseeding is an expensive investment which can deliver excellent returns. However for the investment to succeed, attention to detail and giving the young delicate grass plant every chance to establish is vital.
By Michael Donoghue, B&T Dairy Adviser, Teagasc Galway/Clare