The quantity of fertiliser N applied to grassland will now depend on the quantity of herbage production required, and the background release of nitrogen from the soil.
The quantity of herbage production required will depend on the grass sward type (grazed or cut), stocking rate and animal type. The supply of background Nitrogen from the soil will depend on the soil, the clover content of the sward and whether the sward is old pasture or newly sown.
Nitrogen fertiliser advice is based on the following 6 steps:
- Determine available N rates for grazed swards
- Determine available N rates for cut swards
- Take account of available N in slurry and farmyard manure.
- Calculate chemical fertiliser N.
- Determine maximum N allowance, and confirm that N advice for the holding is compliant with Irish NAP – SI 605 of 2017
- Determine timing of N application throughout year.
Step 1: Determine available N rates for grazed swards
|Annual maximum fertilisation rates of available nitrogen on grassland|
|Grassland stocking rate (kg/ha/year)¹||Available nitrogen (kg/ha)²|
|Grassland stocking rate greater than 170kg/ha/year|
- Total annual nitrogen (kg) excreted by grazing livestock averaged over the net grassland area (ha) (grazing
and silage area). Stocking rate refers to grassland area only.
- The maximum nitrogen fertilisation of grassland shall not exceed that specified for stocking rates less than
or equal to 170 kg/ha/year unless a minimum of 5% of the net area of the holding is used to grow crops
other than grass or a derogation applies in respect of the holding.
- This table does not imply any departure from Article 20(1) which prohibits the application to land on a
holding of livestock manure in amounts which exceed 170kg Nitrogen per hectare per year, including that
deposited by the animals themselves (or 250kg in the case of a derogated holding).
- The application of Nitrogen from livestock manure (including that deposited b
Step 2: Available N fertiliser for cut swards
The amount of fertiliser N to apply to cut swards is influenced by many factors, especially by whether it is a new ley and by the number of cuts taken each year and by the grazing history. N advice for cut swards is given in the silage section of this website.
Step 3: take account of available N in slurry and farmyard manure
To calculate the available N contained in slurry and farmyard manure, multiply the quantity of each material that is applied to grassland by the content of available N that is contained in the material. The N fertiliser replacement value of organic fertilisers, particularly slurry, will depend to a large extent on minimising the potential for gaseous losses of N as ammonia gas at the time of application.
Typical N levels in organic fertilisers¹´²
|Organic fertiliser type||Total N contained in 1 tonne³ (kg/t)|
|Dungstead manure (cattle)||3.5|
|Slurry (layers 30% dry matter)||13.7|
|Layers (55%) dry matter||23.0|
- Values for N are those that must be used for compliance with SI 31 of 2014
- Dry matter and nutrient contents can vary widely between farms
- 1 tonne of slurry=1m³. 1000 gallons=4.5tonnes. 1000gallons/acre=11tonnes/ha
Nutrient availability in organic fertilisers according to SI 31 of 2014
|Organic fertiliser type||Nitrogen Availability %|
|Pig and Poultry Manure||50|
|Cattle and other livestock manure (included that produced on the holding)||40|
Step 4: Calculate chemical fertiliser N
The application rate of chemical fertiliser N can be calculated as follows:
Chemical fertiliser N (kg/ha) = Available N – Available N applied in organic fertilisers