Fertiliser: Start planning now for best silage results

The prohibited period for applying chemical and organic fertilisers – nitrogen, phosphorus and potassium (N, P and K) – is coming to an end later this month.

Getting out with fertiliser as early as possible on the grazing platform and the area earmarked for silage should be a priority on dairy farms.

Speaking at Teagasc’s National Dairy Conference, Michael O’Donovan of Teagasc highlighted that the fertiliser and economic input required to grow a high-yielding, high-quality crop of grass for silage production is substantial.


Explaining some recent research findings Michael noted that these calculations are based on high-fertility soils with adequate pH, P and K.

“These are just the nutrient requirements to grow a 5-6tDM/ha crop of first-cut silage,” he stressed.

“Slurry at a rate of 3,500 gallons/ac should be applied in late January or early February,” Michael noted.

On farms where slurry is not available then 150kg/ha of an 0:7:30 compound fertiliser type product should be applied.

Turing to N, Micheal recommended that 80-100kg of N/ha should be applied in addition to slurry. Again, if no slurry is available for use then 125kg of N/ha should be applied.

Strategy for silage harvesting. Source: Teagasc

“Nitrogen should be applied by March 25 and the silage area closed,” he explained.

Michael recommended closing the area for 60 days. Farmers should then target to harvest the grass by May 25.


Speaking about fertiliser costs, Michael said that “€110/ac – almost €270/ha – is the cost to grow a 5-6tDM/ha crop of first-cut silage”.

Fertilising a silage crop. Source: Teagasc


According to Teagasc research, if the area earmarked for silage was grazed tight to a residual of 5cm during late autumn, then not grazing this area in early spring will not affect silage quality.

Grass digestibility (DMD%) for a first-cut harvest on May 18, depending on previous management (average of two years results). Source: Teagasc

However, if the area was not grazed off tight during late autumn, then silage quality will be reduced. Therefore, in order to achieve high-quality first cut silage, grazing the area to a residual of 5cm before closing is advisable.