Spring 2024 has been one to forget as ground conditions remain saturated on the vast majority of farms across the island.

Wet conditions have also limited opportunities for slurry and chemical fertiliser, although plenty of farmers have yet to purchase nitrogen.

The lack of fertiliser, and plant stress caused by waterlogged soils, have left grass swards and crops turning yellow.

But until ground conditions improve, that scenario is unlikely to change as the weather is ultimately out of farmers’ control.

Late spring

The wet spring is creating a backlog of problems for farmers as April gets under way.

On cattle and sheep farms, delayed turnout to grass is the obvious downside to the wet weather.

However, the lack of spring fertiliser will impact on harvesting dates and grass yields in first-cut silage.

Farmers planning to harvest first cut around the end of May to early June, weather depending, need to be closing off fields by mid-April, which is just one week away.

Even if the weather takes a turn for the better, it will take another week or more for land to dry out and carry machinery.

That means farmers need to take a more flexible approach to fertiliser use in April with a few considerations to closing off silage ground outlined.

Silage fertiliser: know your options

When it comes to closing off fields for first-cut silage, there are some options to give consideration depending on the farm, time and type of livestock wintered on farm.

1 Go for a lower fertiliser rate: on farms with autumn-calving cows and finishing cattle, producing good-quality silage is important to limit concentrate feeding.

If the aim is to target a cutting date around late May, there is no point going with the traditional 100 units/acre of nitrogen if closing off ground around mid-April.

Taking the rule of thumb that grass uses two units of nitrogen daily, 100 units would mean a growing period of around 50 days. That would push harvesting date into early June.

However, if the weather was good during the last week of May, mowing date could be pulled forward a few days, provided wilting grass for 24 to 48 hours is possible.

Wilting will increase dry matter, reducing the risk of a high nitrate residue in grass inhibiting fermentation in the clamp.

It is a big gamble to take. So if the aim is a late May cut, the best compromise is to reduce nitrogen levels to 80 units/acre, which is three bags of CAN and no slurry when closing off fields.

2 Splitting silage fertiliser application: on farms with drier land, a couple of dry days in succession can see fields carrying machinery for fertiliser applications. However, until soil temperatures increase, plant uptake of nitrogen will be on the low side.

If 100 units of nitrogen is applied in one go, there is a risk of nutrient loss via surface runoff in rain or atmospheric loss until soils warm up and growth rates improve.

One option to get around this is splitting silage fertiliser in two applications, starting with 30 to 40 units/acre.

Swards can be topped with 60 to 70 units at the end of the month when grass growth should be on the rise.

The downside to this option is the doubling of fieldwork. A long, dry spell is possible in late April, so getting fertiliser washed in could be an issue on some farms.

3 Go for bulk and focus on quality in second cut: another option is to aim for bulk by cutting silage in early to mid-June, then target high-quality forage in second cut or by taking out surpluses on grazing paddocks. This may be the preferred option on heavier land, where ground is unlikely to travel for a few weeks yet and housing in early autumn is common, along with a seven-month winter.

An upside to this option is that with plenty of fibre in the first cut, there is no need to mix straw into winter diets for certain cattle groups on higher concentrate levels.

This could also be a cost-saver on farms using straw bedding, as high fibre forage will keep dung firm, reducing the rate that bedding is soiled.

4 Avoid slurry on fields with strong grass covers: use slurry with caution when closing off silage fields for first cut from mid-April onwards as the time period until harvesting grass is getting closer.

If a dry spell does materialise after spreading, there is a risk of slurry contamination coming back into the clamp which creates a host of problems.

On swards with medium to good grass covers, which is above ankle height, the best option may be to use 100% chemical fertiliser when closing off fields in mid-April.

Slurry can be targeted to silage aftermath after first cut, and again later in summer when second cuts have been harvested.

Just be mindful of mowing at a higher residual to avoid picking up slurry residue

On bare swards, slurry is an option. But consider application rates of 1,500 to 2,000 gallons per acre to reduce the risk of contamination. Diluting slurry as much as possible is also recommended.

Using low emission slurry spreading equipment can reduce sward contamination compared to splash plate tankers.

Just be mindful of mowing at a higher residual to avoid picking up slurry residue.

Comparing costs on nitrogen fertiliser

Fertiliser remains an expensive commodity with CAN costing €390 to €400/t and urea trading close to €500/t.

Grassland compounds like 18-6-12 are on par to urea prices.

When it comes to buying fertiliser, don’t just go by the price per tonne. The nitrogen content varies between fertiliser products.

Therefore, the cheapest product per tonne is not necessarily the cheapest when pricing nitrogen on a unit or kilogram basis.

Cost per unit

For example, take a farmer looking to apply 80 units/acre of chemical nitrogen for first-cut silage.

The farmer prices around and gets quotes of €490/t for urea and €390/t for CAN. The initial reaction is that CAN is €100/t cheaper and that is the product to choose.

However, one tonne of CAN contains 275kg of nitrogen or 550 units. At €390/t, that works out at €1.41/kg or €0.71/unit of nitrogen. So, 80 units/acre of CAN would cost €57.


Urea contains 460kg of nitrogen, or 920 units which at a purchase price of €490/t, works out at €1.06/kg of nitrogen or €0.53/unit.

Again, at an application rate of 80 units/acre, urea works out at €42, which in this case works out cheaper than CAN at the same fertiliser rate.


However, while it is important to work out fertiliser costs on a per-unit basis, there are other factors to keep in mind.

Straight urea is most efficient when applied in changeable weather conditions and availability with merchants is less common in late spring to early summer.

It is prone to atmospheric losses when used in dry weather. Also, it should not be applied shortly after liming soils.

CAN is a more stable product and can be used when moisture is more limited in late spring and summer, although protected urea is also an option in such conditions.

Sprayer testing clarification

Last week’s sustainability article listed that trailed sprayers require retesting every year. This is not the case and trailed sprayers require retesting every three years.

Read more

ACRES soil sampling extension a welcome move

Dairy management: dealing with a silage shortage