Breaking the pathway of phosphorus and sediment entering waterways
By Peter Comer, Teagasc Adviser, Ballina
THIS week is Water Quality Week and Teagasc, in collaboration with the dairy processing co-ops and the Local Authority Waters Programme (LAWPRO), are running a series of events in the media and online.
The purpose of the week is to provide focused water quality information and advice to farmers to help minimise losses of nutrients, sediment and pesticides to water from their farming practices. A broad range of topics will be available to farmers and the public, primarily through short videos posted on digital media platforms and local print media.
This article looks at breaking the pathway of phosphorus and sediment entering waterways.
When farmers are applying fertilisers, cultivating or grazing their land or draining land close to watercourses, careful site specific land management practices can minimise the risk of phosphorus and sediment loss to nearby waterbodies.
Nutrient application followed by significant rainfall on poorly drained soils leads to overland flow transporting nutrients to waterbodies. Targeted fertiliser application at optimum times throughout the main growing season, particularly on low permeability soils, along with suitable land management practices can help mitigate against this.
Farmers should have a nutrient management plan and follow the recommendations closely to ensure that nutrients from slurry, FYM and chemical fertiliser are directed to where they are most needed.
Slurry should only be applied when soil temperatures are above 6 degrees and ground conditions and weather forecast is suitable. Having 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 soils this period should be extended further.
Spreading slurry with Low Emission Slurry Spreading (LESS) equipment can dramatically reduce losses and improve nutrient efficiency. LESS can lead to reduced sward contamination which allows more flexibility to spread on heavier grass covers as the weather and ground conditions improve.
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.
Phosphorus does not bind well to peat soil particles, so unlike mineral soils, peat soils do not have the capacity to build up a store of phosphorous. On these soil types only apply the phosphorus that the plant needs and can use for growth immediately – do not apply excess amounts of P as it risks being lost to waterbodies.
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, cattle access drinking points to streams and poor management of farm roadways can lead to loss of sediment and phosphorus.
Mitigation options to reduce sediment loss include:
Prevent access by livestock to drains and streams.
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 of July to September.
Only one side of a drain to be cleaned at a time.
Don’t over-clean - retain as much vegetation as possible.
Ensure the bank is sufficiently sloped afterwards to prevent collapse.
Silt/sediment traps should be in place prior to installing new open drains leading to streams.
Stone should not be filled to the surface of new field drains.
Further information is available Water Quality Week is availble on https://www.teagasc.ie/environment/water-quality/water-quality-week/