For farmers aiming to harvest first-cut silage around the start of June, silage fields need to be closed up inside the next week.

Assuming a combined nitrogen application of 100 units/acre between slurry and chemical fertiliser on 15 April, target cutting date will be around 5 June, weather depending.

Given the cost of fertiliser this spring, it is important to make best use of chemical nitrogen. Therefore, outlined are five tips to closing up fields for first-cut silage.

1. How much nitrogen to apply

Grass growth will hit peak levels in May and early June, giving the most cost-effective response to fertiliser at any stage in the year.

Spreading around 100 units/acre of nitrogen is recommended to maximise first-cut yield. The more grass grown in the first cut, the better.

This will take the pressure off the second cut and potentially free up some silage ground for grazing in summer.

There is no point applying higher fertiliser applications on older, less-productive swards. Limit these swards to between 60 and 70 units/acre of nitrogen.

Slurry applied at 3,000 gallons/acre will supply around 15 to 20 units of nitrogen, which means two bags/acre of CAN or one bag/acre of urea will suffice.

For more-productive swards, applying 3,000 gallons/acre of slurry and three bags/acre of CAN will supply adequate nitrogen for first cut.

2. When to close off fields

As a rule of thumb, grass will utilise two units of nitrogen per day. Therefore, if applying 100 units for first cut, then grass will be safe to cut after 50 days.

Cutting can be pulled forward a few days if conditions are good and grass can be wilted for 24 to 48 hours before lifting.

If the target cutting date is 1 June, fields should be closed up around 10 April at the outlined application rate.

3. Leave short interval between slurry and chemical

Avoid spreading slurry and chemical fertiliser to silage swards on the same day.

Leave an interval of around one week between each application. This avoids enzyme reactions that cause nitrogen loss.

4. Consider a split nitrogen application

Applying three bags/acre of fertiliser in one go is a big nitrogen dressing and will not be utilised by soils in one go.

This means there is a risk of surplus nitrogen being lost to the atmosphere or by leaching out of soils in wet conditions.

Therefore, to lower the risk of nitrogen loss, consider splitting fertiliser across two applications.

Yes, this is more time consuming and consumes more diesel. But if it increases the availability of nitrogen for silage, yields will be higher and offset this.

5. Spraying weeds early

Get on top of weeds early. Target any sprays for docks after closing up field as grass covers will be low.

Ideally, spray weeds when they are at the rosette stage, as herbicides are more effective. Don’t wait until weeds mature and start producing seeds, as spraying is too late at this stage.

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