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HomeBeef‘Don’t skimp on the fertiliser for silage’
Catherina Cunnane
Catherina Cunnanehttps://www.thatsfarming.com/
Catherina Cunnane hails from a sixth-generation drystock and specialised pedigree suckler enterprise in Co. Mayo. She currently holds the positions of editor and general manager at That's Farming, having joined the firm during its start-up phase in 2015.
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‘Don’t skimp on the fertiliser for silage’

In this article, a Teagasc advisor covers how to make good quality silage.

According to Austin Callaghan, drystock advisor, Teagasc Claremorris, silage fields should be closed by April 10th each year.

On wetter farms, he noted, this may be a week later. Where there is a butt of old grass, farmers should ideally graze this before closing.

“This can be difficult on cattle only farms, especially in wet weather conditions, but every opportunity should be taken to graze from mid-February each year, up to the first week of April.”

“On many farms, producing average to poor quality silage is somewhat the norm. Cattle or sheep fed this silage will have reduced growth rates, and breeding females’ reproductive performance will be below optimal levels. It is surprising then there is not a greater effort made to improve the quality of silage made.”

“Well managed grazed grass has a similar feeding value to barley, and the aim in making silage is to maximise the energy value of this grass ensiled in a silage bale or a pit,” Callaghan commented.

Fertilising the crop 

To do this, the Teagasc advisor stressed, the silage crop needs to grow quickly in a 6-7-week period.

For this to happen, you need to adequately fertilise the crop with nitrogen, phosphorus, potassium, and sulphur.

It will take the following per acre unit applications to grow a crop of quality silage in 7 weeks:

  • Nitrogen (N) 80-100;
  • Phosphorus (P) 16;
  • Potassium (K) 100;
  • Sulphur (S) 16.

“Many crops are not receiving this level. What happens in this scenario, after 6-7 weeks when the crop is inspected, and the silage yield is low? The silage crop is allowed to grow for another 1 – 2 weeks.”

“In doing this, the crop will bulk up, but the unit energy value will be diluted. The grass will now have more stem and more seed heads.”


“Is your silage crop receiving adequate fertiliser applications? Slurry will per 1000 gallons supplies 5-11 units of N, five units of P and 30 units of K. A slurry application before closing is vital in supplying a substantial portion of the P and K requirements.”

If you apply 2,500 gallons per acre, this should supply 12 units of P and 75 units of K per acre. Watery, diluted slurry will have lower P & K content. Depending on the weather and the application method, this 2,500 gallons of slurry could supply 10 – 25 units of N per acre.

The chemical fertiliser will then need to supply 70 – 80 units of N, four units of P and 25 units of K.

A suitable application, in this case, would be three bags of Cut Sward (24. 2 ½. 10) per acre. To supply the required sulphur, use a similar compound that also includes sulphur.

“The message is don’t skimp on the fertiliser for silage. This is false economy because if you have to let the crop grow well past the seven weeks, then you will produce a silage crop lower in energy. This silage will have a lower feeding and monetary value and will result in reduced animal performance.”

“Having the silage grown and cut allows for a quicker return of the field for grazing or closing for second-cuts.  Quality Silage is money in the bank. It gives you options. Making poor silage is a very expensive feed.”

Making good quality silage 

  • SOIL TEST: You need to soil test your silage fields every three years. Many of these fields have below the required pH (lime), P & K levels. Acidic soils will give a poorer response to all slurry and chemical fertilisers. Where soil P & K levels are low, additional applications of P & K to those recommended above will be required to build these levels.
  • NO slurry spread: Where no slurry applied before closing, you may need to apply one bag of 0.7.30 per acre to supply adequate P & K. The Teagasc advisor stressed that farmers should care not to spread slurry at more than 3,000 gallons per acre.
  • Silage analysis: Have a silage analysis done every year and use it to improve your understanding of making better silage.
  • Reseeding: According to Callaghan, to produce real top-quality silage, you probably need to reseed silage fields.
  • Cutting date:He advises farmers to aim to cut silage from May 20th onwards. Be ready and avail of suitable weather conditions when they arrive. This silage will be good feed for all growing cattle, autumn-calving suckler cows and cows that calf over the period December to February and are calved for many weeks prior to going to grass.

Further reading

Read more farming tips and advice.


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