Currently we are in the middle of the closed period for organic manure applications. This is an important measure to protect water quality. While the weather this autumn was good, we all recall how wet conditions were last year.

Research from the Agricultural Catchments Programme shows that for the typical year, 43% of phosphorus and 45% of nitrogen lost to water occurs during the closed period. The addition of slurry during the closed period to grassland will likely result in this percentage increasing.

Farmers should plan ahead for the spring and consider how best to maximise the use of slurry for growing crops, and minimise its impact on the environment.

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 frozen or snow covered, waterlogged, flooded or likely to flood is prohibited by the regulations.

The reason being, 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 – this can also lead to soil saturation and nutrient losses.

While many farmers will be able to hold off on spreading slurry until later in the spring when conditions are more suitable, others will need to spread slurry due to tanks being full.

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 adviser for help with this and take action if there is a shortage.

Contractors

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, see Table 1 for more information.

When to apply

When organic fertilisers are applied, this has a large influence on the uptake of nutrients by plants and the potential for losses to waters. 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.

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 P and 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. This is especially important in the early spring period, where growth rates are at their lowest. 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. Lower application rates of organic fertilisers are recommended in early spring.