On farms aiming to harvest silage in the last week of May or first week of June, fields need to be closed up inside the next week.
Assuming silage swards get 100 units/acre of nitrogen by Saturday 8 April, grass will be safe to cut and ensile around 28 May, weather-dependent.
As fertiliser remains expensive and weather conditions are far from ideal, outlined are some tips to closing off silage swards this spring.
1. How much fertiliser to apply?
Grass growth will hit peak levels in May and swards can quickly bulk out provided adequate nitrogen has been applied.
On good-quality ryegrass swards at index 2 for phosphate (P) and potash (K), aim to apply 100 units/acre of nitrogen (N) to drive yields, along with 25 units of P and 120 units of K.
Spreading 3,000 gallons/acre of cattle slurry should provide most of the P and K requirement, but will need topping up with three bags/acre of a product such as 25:2.5:10 with added sulphur.
On older silage swards with less ryegrass, there is little point applying more than 80 units/acre of N between slurry and chemical fertiliser, as the growth response will not be cost effective.
2. Don’t spread slurry and chemical nitrogen on the same day
Do not apply slurry and chemical N to silage swards on the same day. Leave a gap of one week between each application to avoid enzyme reactions that cause N loss.
3. Splitting the fertiliser allocation
Ground conditions are poor and grass growth is struggling at present. Applying 100 units/acre of N in one go is a big dressing and grass will struggle to utilise it, increasing the risk of run-off.
Therefore, to get a more cost-effective return on N, consider splitting the N in two dressings.
Target half the N in early April and the remaining half at the end of the month when growth is rising towards peak.
It is more time consuming and consumes more diesel, but can stop N being wasted in a difficult spring.
4. Spraying weeds
Where grass covers are low, target weeds such as docks and thistles to get maximum kill.
Spraying weeds at an immature rosette stage is much more effective than leaving it until weeds have matured and produced seed heads.
5. Rolling surface-damaged swards
If silage swards have been grazed over winter or at some point this spring and there is some surface damage, lightly roll to level out ground.
Leaving an uneven field presents problems. First off, poached ground can hold surface water. Secondly, there is a risk of soil contaminating grass swards during harvesting and being ensiled.