Early application of N is beneficial…but should I spread?

With the closed period coming to an end on farms in Zone A, and with the remaining Zones due to open later in the month, this doesn’t necessarily mean that this is the best time to spread nitrogen (N) fertiliser.

It is well known that the lack of N in the soil can be a limiting factor in spring-grass growth, but the timing and rate of fertiliser N application are key decisions that need to be taken into consideration by every livestock farmer.

Research has shown a large range in grass response to early N application – between 5kg to 18kg DM/kg N applied.

The appropriate application of early N is beneficial; while the incorrect application of early N is wasteful, costly, pollutes water and increases greenhouse gas emissions, according to Teagasc.

Teagasc has released some key ‘do’s’ and ‘don’ts’ to guide you in your decisions around early fertiliser application, to help prevent incorrect application of N.

Teagasc has outlined the following ‘do’s’:

  • Check Teagasc guidelines on application of early N;
  • Check the weather forecast prior to making fertiliser N application decisions;
    • Check the soil moisture deficits (SMDs) for your area and only spread if SMD is greater than zero (check this on the Met Éireann website);
    • Only apply fertiliser N when soil temperature is greater than 5° and rising;
  • Target fields for early N that are most likely to respond to an early N application, such as:
    • Perennial ryegrass / recently reseeded paddocks;
    • Drier, free draining paddocks;
    • Paddocks with a cover of greater than 400kg of DM/ha or 5cm;
    • Paddocks with optimum soil fertility;
  • Replace chemical N fertiliser on approximately one-third of the farm with cattle slurry. Target these applications to paddocks with low phosphorus (P), low potassium (K) levels and low grass covers;
  • Use protected urea (NBPT) for early N applications;
  • Apply up to 30kg of N/ha (24 units of N/ac) in first split in late January or early February and avoid fields that have received an application of cattle slurry;
  • Link your early N application strategy with spring feed budget for the farm;
  • Calibrate and maintain your fertiliser spreader in good condition.

Teagasc has also outlined the following ‘don’ts’:

  • Don’t apply fertiliser N before the end of the prohibited spreading period;
  • Never apply fertiliser on waterlogged or frozen soils;
  • Don’t apply fertiliser if a yellow rainfall warning is in place or is forecast within the next 48 hours;
  • Never apply fertiliser into buffer margins and know your buffer margins;
  • Delay N on bare fields (<400kg of DM/ha); instead spread on fields with 5cm (cover of 400kg DM/ha) grass cover or greater;
  • Don’t apply N fertiliser on fields that received slurry in the first round;
  • Don’t apply more than 30kg of N/ha (24 units of N/ac) in first split in late January / early February;
  • Don’t apply more than 90kg of N/ha (slurry N plus chemical N) in total up to April.