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Improving water quality ‘Breaking the pathway of Phosphorus and sediment entering waterways’

By Kieran Kenny,

Teagasc Soils and Environment Adviser, Castlerea.


When farmers are applying fertilisers, cultivating, grazing or draining land close to watercourses, careful  land management can minimise the risk of Phosphorus and sediment loss and help improve water quality.

Nutrient application followed by significant rainfall on poorly draining and low permeability soils leads to overland flow transporting nutrients to waterbodies. Targeted fertiliser application at optimum times, particularly on low permeability soils, along with suitable land management can help mitigate against the risk of phosphorus & sediment making their way to our rivers and streams. Farmers should have a Nutrient Management Plan for the farm prepared and implemented to ensure the nutrients in slurry, FYM and chemical fertiliser are directed to where most needed.

Spreading Slurry

Slurry should only be applied when soil temperatures are above 6 degrees and ground conditions and weather forecast are suitable. On very heavy land it may be necessary to delay spreading until after the first cut silage. Extra slurry storage allows more flexibility on spreading times, particularly in a very wet spring. Under the nitrates directive, slurry must not be spread if heavy rain is forecast within 48 hours, but on poorly drained soil this period should be extended further to 3 or 4 days. Spreading slurry with Low Emission Slurry Spreading (LESS) equipment such as a trailing shoe, dribble bar or the injector system can reduce losses and improve nutrient efficiency. LESS results in reduced sward contamination which allows more flexibility to spread on heavier covers in improved weather and ground conditions.

Riparian buffer zone

A riparian buffer zone is an area adjacent to a water body where no chemical and organic fertilisers, cultivation or spraying can be carried out. These zones vary in width and are required to protect waters from diffuse losses of nutrients, sediment and chemicals. The introduction of trees or rough dense vegetation in these areas can act as a barrier, shade streams and stabilise river banks while the roots can absorb soil nutrients. To be effective, riparian buffer zones must be located at the points on the farm most likely to allow nutrient, sediment or pesticides enter a waterbody. These are often low-lying parts of farms where surface runoff accumulates in high concentration. Phosphorus does not bind to peat soil particles, so unlike mineral soils, peat soils do not have the capacity to build up a store of phosphorous. A little and often approach is recommended on peat soils, to ensure the applied P fertiliser is taken up by the grass crop.

Sediment loss

Sediment loss to water has been identified as a major concern in recent years. If sediment finds its way to the stream, it can settle on the river-bed in slow flow areas, resulting in the loss of macroinvertebrate habitat and spawning ground. Phosphorus binds to sediment and when washed into the watercourse, can cause excess nutrient load and promotes algal blooms which reduce oxygen levels in the stream. Agricultural practices such as land drainage and reclaimation, cattle access drinking points to streams, outwintering and poor management of farm roadways can lead to loss of sediment & phosphorus.

Mitigation options to reduce sediment loss include:

  • Prevent access by livestock into drains and streams and providing alternative drinking water sources.
  • Minimise soil damage through poaching and rutting.
  • Divert all surface runoff from farm roadways to a field or soak pit.
  • Establish targeted riparian buffer zones.
  • Employ proper drain maintenance practices including the following:
  • Only carry out drain maintenance during the months July to September.
  • Only one side of a drain should be cleaned and retain as much vegetation as possible.
  • Drains should not be over-cleaned or widened (V shape channel is best).
  • To reduce sediments entering the main waterbody a 10 to 20m length of uncleaned drain should be left at the end of the  of the channel to act as a sediment trap.
  • Field drains should not have stone filled to the surface.


The loss of phosphorus and sediment to our waters from agriculture is causing a decline in water quality. As a country we are required to have all our waters achieving “good status” by 2027 which is a goal we must all work towards. The Agricultural Sustainability Support and Advisory Programme (ASSAP) is an advisory service available to all farmers situated in Priority Areas for Action to support with farming and water quality issues. For further detail visit: www.teagasc.ie/assap

Teagasc provides a Local Advisory and Education service to farmers. They have offices based in Roscommon Town  (Tel: 090 6626166), Castlerea (Tel: 094 9620160) and Longford Town (Tel: 043 3341021), You can find us on Facebook @Teagascroscommonlongford and twitter @teagascRNLD. Email; RoscommonLongfordAdvisory@teagasc.ie