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Organic Fertiliser Nutrients – Maximum use, minimum loss

Good management when applying organic fertiliser to grassland is recommended to maximise grass growth, while at the same time minimising nutrient and gaseous losses to water and to the atmosphere. This is particularly important as we approach the 15th of October and the closed period for the application of organic manures. Slurry, Soiled Water, Farmyard Manure (FYM), Spent Mushroom Compost (SMC) and Poultry Litter are sources of organic nutrients that can impact our environment if not managed correctly.

The diffuse loss of nutrients (N & P) to waters from organic fertiliser can occur at any time of the year. However as we enter the last few weeks of the open period for spreading organic fertilisers, typical autumn weather of increased rainfall leading to wetter soils and lowering grass growth rates  increases the risk of diffuse nutrient losses and careful management of organic fertilisers is required where these are applied in the run up to the 15th of October.

Farmers can play a significant role in preventing nutrient losses from organic fertilisers to waters in autumn by:

  • When applying organic fertilisers adhere to the 5m buffer zone from drains and watercourses. Remember that this increases to 10m between October 1st and October 15th. See table below for other buffer zones.
  • Apply slurry where ground conditions are suitable, i.e. apply to soils that are trafficable.
  • Umbilical slurry spreading systems should only be used where ground conditions are suitable. Using this system where soils are saturated to avoid soil damage from tankers poses a risk to water quality. When using umbilical spreading systems ensure slurry is not over applied.
  • Slurry should not be spread if heavy rainfall is forecast. The high rainfall levels can lead to soils becoming saturated and water flowing over the surface of the fields bringing with it the nutrients applied.
  • Make use of the new EPA PIP maps, ask your advisor for assistance. These maps will help identify Critical Source Areas (CSA’s) on your farm that are high risk of diffuse N or P losses. Avoid spreading organic fertilisers in these locations as they have high connectivity to waters.
  • They can also identify surface flow pathways and delivery points into the drainage network. Avoid spreading organic fertilisers in these locations as they have high connectivity to waters.
  • While soils temperatures are generally good in autumn, growth rates for grass declines the later into autumn we go so it is very important to match applications to grass growth rates to maximise nutrient uptake.
  • Where a contractor is spreading organic fertiliser for you take the time to show the tractor driver the locations of any drains, streams, wells, etc. and that they observe the relevant buffers.
  • Farmers are reminded to have all slurry tanks, FYM stores etc., empty prior to the housing of cattle over the winter so as to avoid shortages of storage capacity later in the winter or early spring.
  • Apply slurry with Low Emission Slurry Spreading (LESS) equipment. This allows slurry to be spread on heavier grass covers which improves nutrient uptake and helps reduce the risk of diffuse nutrient and ammonia losses.

It also makes financial sense to maximise organic fertiliser use as chemical fertiliser prices have risen considerably in the past 12 months and are up to €100/ton more expensive. They are a valuable source of nutrient for the farmer and can help reduce the overall farm fertiliser bill. For example the guide fertiliser value of 1,000gls of cattle slurry is €25, equivalent to 1 Bag of 6.5.30 NPK (this value is dependent on Dry Matter content of slurry and timing of application).

In order to maximise the efficiency of organic fertilisers spread on your farm, it is recommended to apply them in accordance with a Nutrient Management Plan. This will ensure that organic manures are targeted to fields that have sub-optimal fertility.


Organic fertilisers can be a valuable asset on a farm, but only if managed correctly. When spread, organic fertiliser is either absorbed by soil and plants or lost to air and water. By minimising losses through careful application, farmers can retain more nutrients, reduce sward contamination and reduce the fertiliser bill on the farm. This will increase farm profit while helping to protect our air, atmosphere and water quality.

Buffer Zones for Organic Manure Spreading
Water body / Feature Slurry or FYM
Water Supply > 100m³ or > 500 people 200m
Water Supply > 10m³ or > 50 people 100m
Water Supply < 10m³ or < 50 people 25m
Lake shoreline 20m
Exposed cavernous or karstified limestone features (e.g. swallow holes) 15m
Any surface watercourse where the slope towards watercourse is >10% 10m
All other surface waters


 * The 5 meter buffer zone is increased to 10 meters for a period of two weeks preceding and two weeks following the periods when application of fertilisers to land is prohibited.