Slurry stores required capacity

Find out why you should have sufficient slurry storage for your farm system. It is a legal requirement under several regulations. These regulations differ between England, Scotland and Wales but their primary purpose is to protect human health and the environment.

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Slurry storage capacity

When calculating your slurry storage requirement, you must account for any additional rainwater or washings that will enter the store, either directly or from other areas of the site, such as the silage clamps. This will require you to know your annual expected rainfall.

You must also allow for the minimum freeboard space. Freeboard is the vertical distance between the top of your tank or lagoon and the slurry surface. For a steel or concrete store, you must include a minimum of 300 mm of freeboard. For earth-banked stores, you will need a minimum of 750 mm. This freeboard must always be maintained.

Having the right amount of slurry storage for your specific farm operation will allow you to make the most of the valuable nitrogen content of your slurry. It will give you the flexibility to spread slurries at times when the nitrogen will be best for the crop, resulting in less need for bagged fertiliser.

AHDB’s Slurry wizard is a helpful tool that can be used to calculate the amount of slurry storage required for a dairy farm system.

Try the Slurry Wizard

Save money and protect the environment

As well as the practical benefits of sufficient slurry storage, it is also a legal requirement under several regulations. These regulations differ between England, Scotland and Wales, but their primary purpose is to protect human health and the environment.

England, Scotland and Wales

The Water Resources Control of Pollution (Silage, Slurry and Agricultural Fuel Oil) Regulations

Commonly known as SSAFO regulations, this legislation requires a minimum of four months of slurry storage and is enforced across the whole of England, Scotland and Wales. However, since this legislation came into force, it has been cancelled out by the regulations listed below. It is, therefore, unlikely that four months will be sufficient.

More information on the SSAFO regulations can be found on Gov.UK.

The Nitrate Pollution Prevention Regulations (NVZ Regulations)

The NVZ regulations are enforced only within designated NVZ areas. To comply, you must have enough slurry storage to do the following:

  • Comply with the minimum storage period for livestock manure
    • 22 weeks for cattle slurry
    • 26 weeks for pig slurry
  • Adhere to the NVZ closed periods for spreading
  • Spread slurry only in the correct conditions
  • Comply with the maximum stocking densities and application rates of nitrogen

More information on the NVZ regulations can be found on Gov.UK.


The Reduction and Prevention of Agricultural Diffuse Pollution (England) Regulations

Commonly known as the ‘Farming Rules for Water’, this regulation was introduced in England in 2018. These rules do not state a minimum capacity for your store. However, it does stipulate that you must plan your applications of manures and fertilisers so that you do not exceed the needs of the crop or soil. You can use AHDB’s nutrient management guide RB209 to create a nutrient management plan which would be required to demonstrate this.

With every slurry application, you must be able to show that the application was made to meet the nutrient needs of the crop and not to empty your slurry store. This means that you would also need to justify the timing of your slurry application.

More information on the Farming Rules for Water can be found on Gov.UK


Water Resources Control of Agricultural Pollution (Wales) Regulations 2021

These regulations were introduced in February 2021, replace the previous NVZ regulations and apply to the whole of Wales. The transitional periods highlighted within the regulations will not generally apply to farms currently within NVZs.

Detailed guidance documents will be published on the Welsh Government website providing a step-by-step approach to the implementation of the regulations. The latest information can be found on the following Welsh Government webpages.


The Water Environment Diffuse Pollution (Scotland) Regulations

These regulations are commonly called the ‘General Binding Rules’. These rules state that slurry stores must be built in line with SSAFO regulations which require a minimum offour months’ slurry storage. This requirement will be superseded by the NVZ regulations when inside an NVZ area.