Water, Soil and Air Code 2009: Protecting our Water, Soil and Air. A Code of Good Agricultural Practice for farmers, growers and land managers

4.2 Silage stores and effluent handling

  • Even small amounts of silage effluent from crops in an enclosed pit or silo, or from baled silage, will kill fish and other water life for a long way downstream if it gets into surface waters.

Silage effluent should be contained and stored safely until it can be applied to land to make use of its nutrient content, or it can be used for animal feed.

If possible, recycle clean silage wraps, bags and sheets.

© Environment Agency

The construction of facilities for making and storing silage and storing effluent are controlled by law (Reference 51).

Seek advice from the Environment Agency if:

  • you intend to construct a new silo or substantially enlarge or reconstruct an existing silo.
  • you want to make field silage (field heaps or non-baled bagged silage). Sites must be notified to the Environment Agency.

You must notify the Environment Agency before you use new or substantially altered facilities for the first time.

See 'Regulations' below.

Good practice

179. Every year before using silos, you should inspect effluent tanks from the outside (as much as you can see) for leaks and corrosion - do not go into them. Also check channels, drains, silo floors, walls and wall/floor joints. Carry out repairs well before the silage making season.

180. During silage making:

  • check around the silo and effluent tank for leaks and blockages daily. Put right any problems immediately;
  • check effluent tank levels frequently and empty as necessary; and
  • check ditches, surface waters and clean water drains for signs of pollution. If any are found, put your accident and emergency plan into action.

181. You can minimise the amount of effluent produced by wilting grass to at least 25% dry matter before it is ensiled. Harvest other crops (such as whole crop cereals and maize) at the correct stage of maturity.

182. Apply effluent to land in accordance with your manure management plan (see Section 3.2). To avoid scorch when applying to a growing crop - dilute the effluent in a slurry tanker with the same amount of water, dirty water or slurry, and do not apply more than 50 m³/ha. Note: adding effluent to slurry or dirty water will increase the risk of causing an odour nuisance.

183. For baled silage:

  • you must store bales at least 10 metres away from field drains, ditches and surface waters. Do not remove plastic wrap within this 10-metre zone as effluent may be released. If bales are stored directly on the ground (i.e. not on a specially constructed base), you must ensure they do not leak effluent. Bales should be located well away from any ruts or tracks that could provide a pathway for effluent to get into ditches, surface waters or damage habitats; and 
  • when crop dry matter is below 25%, using a 750 mm wide bale wrap (rather than 500 mm) will reduce the quantity of effluent released during storage. This applies for both 4 and 6 wrap systems.

184. For field silage - field heaps or large bags (non-baled):

  • choose a level site and make a careful assessment of pollution risk to groundwater and surface water. Discuss your proposals with the Environment Agency well in advance of silage making;
  • sites must be at least 10 metres away from field drains, ditches and surface waters; and at least 50 metres away from springs, wells and boreholes where water is used for human consumption or in farm dairies; and
  • make sure bags are closed and sealed at each end. If there is any effluent inside the bag you must use it or dispose of it safely.

185. There are legal obligations that control how you make and store silage in a silo; or in wrapped and sealed or bagged bales; or in a tower silo; or as field silage (field heaps or non-baled bagged silage). The requirements (reference 52) for silos include having impermeable floor and walls (they must not leak), being corrosion resistant, the base must extend beyond the walls and have channels on all sides to collect effluent, it must have an effluent tank of appropriate size, and no part may be within 10 metres of any field drains or surface waters. Effluent tanks must have a design life of 20 years without maintenance.

186. If you intend to remove silage from where it was originally made and put it into another store - either that store must comply with the regulations, or you must get prior approval from the Environment Agency.

Designing new silos

187. The base and wall of the silo should be professionally designed to suit the conditions of the site. There are a number of British Standards or other equivalent standards involved. Building work should be supervised to make sure the silo is structurally sound and effluent cannot escape. Further guidance is available (reference 67, 68). The use of hot-rolled asphalt (HRA) surfacing is an activity that should be carried out by a specialist (Reference 69).

Feeding effluent to livestock

188. Silage effluent contains only a small quantity of dry matter but it does have some feed value. You may be able to use some of the effluent in this way - but take advice particularly on how to feed it to dairy cows. Any new storage facilities for feeding purposes must meet the regulations (reference 51).

Silage additives

189. Most additives are extremely polluting. They should be stored safely and handled at least 10 metres from a field drain or surface water. Do not leave undiluted product out on site or allow additives or used containers to get into surface waters (see Section 7).

Disposal of silage plastics and tyres

190. Silage wraps, bags and sheets will require disposal. Ideally they should be recycled off-farm using specialist collectors but make sure such wastes are as clean and free from soil as possible. Tyres used for holding down silage sheeting will eventually require disposal. Do not burn plastics or tyres in the open. For disposal options - see Section 7.

Safety Note

Effluent tanks can contain lethal gases. Do NOT go into them at any time. Lock tank covers. Display a clear warning notice.

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