Early nitrogen applications – when and what rate?

In order to boost spring grass growth, farmers need to carefully consider the time and rate at which nitrogen (N) fertiliser and slurry is applied.

While the appropriate application of early N is beneficial from a grass growth perspective, the incorrect application of early N is wasteful, costly, pollutes water and increases greenhouse gas emissions.

In order to avoid this and to allow for the efficient use of nutrients, researchers in the Teagasc Grassland Science Department, Moorepark have developed chemical N fertiliser and slurry application guidelines for well drained and heavier farms, along with a nitrogen strategy for clover swards. All three guidelines are available to view in the tables below.

Spreading dates

Before committing to spread chemical fertiliser, however, you firstly need to be aware of the permitted spreading dates for your region. These are as follows:

• The prohibited period for chemical fertiliser applications (nitrogen or phosphorus applications) for farmers in Zone A, encompassing the counties of Carlow, Cork, Dublin, Kildare, Kilkenny, Laois, Offaly, Tipperary, Waterford, Wexford and Wicklow, ended on January 26^th, 2025.
• The prohibited period for chemical fertiliser applications in Zone B, which consists of counties Clare, Galway, Kerry, Limerick, Longford, Louth, Mayo, Meath, Roscommon, Sligo and Westmeath, ended on January 29^th.
• The earliest date farmers in Zone C counties - Cavan, Donegal, Leitrim and Monaghan – can spread chemical fertilisers containing N or P is February 15^th, as the prohibited period for applications ends of February 14^th in this zone.

Other important considerations

Along with adhering to the permitted spreading dates, farmers also need to pay heed to ground conditions, weather, grass availability and the product chosen.

Key points to note:

• Checking the weather forecast in advance of spreading fertiliser is critical to minimise runoff and leaching of nutrients.
• Never spread chemical fertilisers, livestock manures, soiled water or other organic fertilisers when:
  • The land is waterlogged.
  • The land is flooded, or it is likely to flood.
  • The land is frozen or covered with snow.
  • Heavy rain, i.e., a Met Eireann ‘yellow’, ‘orange’ or ‘red’ rainfall warning, is forecast within 48 hours.
• To maximise nutrient uptake, chemical fertiliser should be applied when the crop is growing (soil temp > 6^o C) and no heavy rainfall forecast for at least 48 hours. On poorer draining soils, this period should be longer.
• Do not spread chemical fertilisers on land within 3 meters of any surface waters
• Chemical fertilisers should not be spread on ground with a steep slope (>10%) and if there is a significant risk of causing pollution.
• Where early fertiliser applications are required, they should be applied to productive fields in good fertility to maximise nutrient use and to prevent losses. Target areas most likely to respond to early application of N - fields with a high perennial ryegrass content or recently reseeded, drier areas, fields with a grass cover > 400kg DM/ha (6 cm), fields with optimum soil fertility (index 3 for P and K, pH > 6.2).
• Check the soil trafficability before spreading to avoid damage to soil;
• Measure farm cover and use the grass growth predictions (available in the Grass10 newsletter, on the PastureBase Ireland website, on the Farming Forecast on Sunday on RTÉ 1) to inform decision making around slurry and N fertiliser application

Chemical N fertiliser and slurry application guidelines 2025

The guidelines for chemical N fertiliser and slurry applications for well drained and heavy farms are available to view in tables 1 and 2 below. The nitrogen strategy based on clover content is available to view in table 3 below.

Table 1: Chemical N fertiliser and slurry application guidelines 2025 (well-drained farm)

Notes: ¹Application of N for February/March grazing; ²Assumes slurry at 6% DM, adjust application rates based on slurry DM%; ³Some of this area will be silage ground; ⁴Combination of Protected Urea and cattle slurry.

Table 2: Chemical N fertiliser and slurry application guidelines 2025 (heavy farms)

Notes: ¹Assumes slurry at 6% DM, adjust application rates based on slurry DM%; ²Some of this area will be silage ground ³Combination of Protected Urea and cattle slurry.

Table 3: Nitrogen strategy for clover swards based on April paddock clover contents

Notes: Apply spring slurry N as per Spring N fertiliser and slurry guidelines; Soiled water used whenever zero chemical N application; +25kg of organic N applied.

Also read: Why protected urea? 

Also read: Key points for spreading protected urea

Also read: Fertiliser planning: How did protected urea perform in 2024?