Slurry Spreading - Advice for Farmers and Slurry Contractors

As the slurry spreading season comes to a close across the country over the coming days, Noel Meehan and Sinead Devaney of the Teagasc ASSAP Programme explain why it is very important that farmers and agricultural contractors apply slurry very carefully so as to prevent nutrient losses to water.

The loss of nutrients, phosphorus (P) and nitrogen (N), to water from fertiliser application is a key factor impacting water quality in Ireland.

Regulatory requirements when spreading slurry

The last day to spread slurry is September 30^th. Over this weekend, farmers are asked to make slurry contractors aware of any water features that may be present in the fields that slurry is being applied and to ensure that slurry is kept back the correct distance – that is 10m from watercourses now for the last two weeks in September, see table 1 for more information.

Table 1: Buffer margin for spreading organic fertilisers from waters

* Distance is 10m for two weeks before and two weeks after the closed period for spreading organic manures

When spreading slurry, it is also important to remember that weather and ground conditions can have a significant impact on nutrient being lost to water. Spreading slurry on fields that are waterlogged, flooded or likely to flood is prohibited by the regulations. The reason why it is prohibited is because adding slurry to fields under these conditions greatly increases the likelihood that the nutrients from slurry will be lost to water either by over land flow in the case of saturated soils or by leaching to ground water. When ground conditions are suitable, it is important to check the weather forecast as slurry should not be spread when heavy rainfall is forecast as this can also lead to soil saturation and nutrient losses.

Figure 1: 10m buffer zone being adhered to in the final two weeks of the spreading period

Best practice advice when spreading slurry

It is important to ensure that all slurry in the tanks is spread before the closed period, provided the correct conditions are present. 2024 has been a good year for slurry spreading conditions in the main. Farmers leaving slurry in the tanks going into the closed period will be reducing the storage availability over the winter period. Farmers that find themselves under pressure to spread slurry should examine if they have enough slurry storage in place or if there is clean rain water entering tanks and impacting storage. Ask your advisor for help with this and take action if there is a shortage.

Farmers should also consider the following:

Timing:

When organic fertilisers are applied has a large influence on the uptake of nutrients by plants and the potential for losses to waters, and farmers need to be aware of weather conditions when applying organic fertilisers. A consistent soil temperature of 6˚C and preferably rising will mean that grass is growing and has the potential to take up the nutrients applied. This is one reason why we have closed periods, due to the fact that we have shorter days in winter, colder temperatures and higher rainfall in general. These conditions reduce grass growth rates and therefore uptake of nutrients by the grass crop. In this situation, there is a higher chance of nutrient losses to water.

Soil moisture content:

Another essential factor is the soil moisture content. Is the soil saturated or can tractor work occur without causing structural damage to the soil? Soil that is close to or at saturation point will lead to surface water runoff if there is additional rainfall. Checking the soil moisture content of the field and the weather forecast is important prior to applying organic fertilisers. This is especially important when using the umbilical slurry spreading system.

This system is particularly high risk to water quality if used incorrectly, as it allows slurry to be spread when a slurry tanker wouldn’t be able to travel on land due to ground conditions. While this system does reduce soil compaction, it should not be used on saturated soils as it would pose a risk of nutrient loss to waters.

Location

The fields that slurry is applied to should be chosen carefully. These should be the fields that have a requirement for phosphorus (P) and potassium (K) and with a good pH. They should also be the drier fields on the farm, ideally with no drainage system in place and away from streams and rivers. Fields that have high connectivity to the drainage network or fields with critical source areas (CSAs) should be avoided until later in the spring to lower the risk of nutrient loss to water.

Rates

It is important to match the rates of application of organic fertilisers to the growth rates of the grass/crop. Applying slurry at rates greater than crop demand means that nutrient is available to be washed away into the drainage network or leached to groundwater.

Summary points

• Slurry at 6% DM applied by LESS is worth €29/1,000 gallons (equivalent to a 50kg bag of 9-5-32
• Farmers should assess their slurry storage facilities to ensure that they meet the minimum storage requirements for their county
• The last day for slurry spreading is September 30^th
• For two weeks leading up to the closed period for spreading, slurry must be kept at least 10 meters away from rivers, streams, watercourses and drains
• Slurry cannot be spread on fields that are:
  • frozen or snow covered
  • waterlogged
  • flooded or likely to flood
  • heavy rain is forecast within 48 hours
• Maximise the nutrient content of slurry by spreading when:
  • Soil temperatures are at 6˚C and rising
  • Soils are trafficable and are not saturated
  • Slurry is targeted to drier fields with a requirement for P and K and have a good pH
  • Avoid applying to fields that are highly connected to the drainage network of the farm, critical source areas (CSAs), until weather conditions are favourable
  • Application rates of slurry must match growth rates of the crop

Find out more about Teagasc ASSAP (Agricultural Sustainability and Advisory Programme) here. 

Teagasc recently launched the Better Farming for Water Campaign. Learn more about the campaign and what it entails here.