There are legal requirements for the design (capacity), construction and maintenance of storage facilities for silage, and slurry. Silage effluent and slurry have been the source of serious pollution, often due to inadequate storage capacity or poor construction.
The SSAFO (Silage, Slurry and Agricultural Fuel Oil) Wales Regulations set standards for storing silage, slurries and agricultural fuel oil so as to minimise the risk of pollution.
The SSAFO Wales Regulations 2010 replace Regulations first made in 1991. Installations that were in use, or built before March 1991, or where a contract for construction was entered into before March 1991 and completed before September 1991 are ‘exempt structures’.
The guidance note can be downloaded on the from the Welsh Government website.
This is described in two ways:
© Ffermio / Telesgop / S4C
Adequate storage is needed in order for the slurry to be applied at the correct time of the year. This timing is essential to ensure the nutrients are present in the soil when the plants require them. It also ensures that pollution is minimized.
Court Farm is a 101 hectare specialist dairy farm with 220 dairy cows and up to 30 dairy heifers of various ages. The farm lies within an existing NVZ area. The farm has expanded over recent years and there has been a moderate level of reinvestment. The business intends remaining in milk production for the foreseeable future and is prepared to invest in additional slurry storage if required.
Current storage capacity
The current slurry storage comprises a slurry tower with a small reception pit. The tower is three rings high and 22m in diameter. It has a capacity of 1730m3 with an additional 45m3 of storage in the reception pit.
Farm business profile
Farmer: Mr a Mrs John Evans
Farm: Tafarn yr Oen, Sir Gâr
Cows: 220 dairy cows plus followers
Yields: 9100 litres
Youngstock: 15 per annum
Crops: Grass & maize
NVZ: The farm lies within an existing NVZ area
Work out if the farm has enough storage capacity for 5 months over the winter period.
In addition to actual slurry produced by the cows there are additional water sources that would dilute in with the slurry.
This is due to surface run off of dirty collecting yard water, rain that falls in to an uncovered slurry store and parlour washings.
These are added to the equation as follows:
Slurry + The average rainfall for the full 5 months in meters + water for washing down which + 3 cubic meters per cow /5 months.
Slurry + rainfall + parlour/yard washings
To see if the farm has enough storage:
Storage capacity - slurry production = ?
If both figures match you are just right, but a plus or a minus indicates too much capacity or not enough.
How do you work it out?
Multiply its length (m) by its width (m) by its height (m)
The height should be reduced by 0.3m to allow for freeboard as a safety margin against increased risks of pollution from storm events.
Measure the circumference.
Calculate the radius by dividing the circumference by 3.142, then dividing by 2
Calculate the floor area by multiplying the radius by the radius, then multiply by 3.142
Multiply the floor area (m2) by the height (m) (reduce the height by 0.3m to allow for freeboard) to give the capacity of the slurry store (m3)
Estimate the length (m) and width (m) and average depth (m), from the top of the bank to the base of the lagoon.
Reduce the average depth by 0.75m to allow for freeboard and to give the watering depth.
Reduce the measured length and width of the lagoon by enough to allow for the sloping sides.
Multiply the adjusted length by the adjusted width by the watering depth to obtain the storage capacity (m3).
Work out the storage capacity of the following facilities.
Your answer should be in m³.
Cow slurry is known to have a very harmful effect on the environment if it pollutes rivers, ponds. Cows produce a large amount of slurry, and this mixed with rain water and dirty water off the farm yards create fertilizer, which enable the nutrients to be applied at the right time of the year.
Calculations can be made to help farmers work out their storage needs and their storage capacity.
It is important that there is enough storage for the amount of slurry.