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Silage Storage & Water Quality


Silage effluent is a highly polluting liquid and can cause fish kills in watercourses/rivers and contaminate wells if not collected, stored and land spread properly. It is important to examine and repair silage pits and collection channels when pits are empty to ensure safe storage.

Silage pits – slabs and walls - need to be structurally sound to ensure ensiling is completed safely and effluent is not lost to the environment. Silage effluent is a highly polluting liquid and can cause fish kills in watercourses/rivers and contaminate wells if not collected, stored and land spread properly. Silage effluent collection channels and tank storage must be capable of managing the volume of effluent generated. Slab and channels must be leak proof and all silage effluent must be collected and safely stored.  If the pit is not fit for purpose, cease using until all repairs are completed. 

When silage pits are empty is the time to examine the slab and channels to see what maintenance and repairs are needed before the pit is used again.

Inspect / Repair slab -Clean slab thoroughly (power wash) to identify any problems.    Defects or problems should be remedied before silage making commences.

Making silage

It is important that you know how much silage your slab is capable of storing. If your pit is designed to store 50 acres of silage at normal yield then that is all that should be stored in the pit. A lot of the problems with effluent arise from over filling the slab. Where capacity is insufficient additional silage should be stored on another slab or made into round bales.

When cutting silage aim to wilt for 24 hours before ensiling. This will reduce the volume of silage effluent produced. All effluent should enter the channels under the cover of the silage polythene and the edge of the ensiled grass should not extend onto or over any channel. The open space should be maintained by placing a plastic drainage pipe in the channel. Ensure effluent is diverted to an effluent tank. Depending on how wet the grass is at ensiling the volume of effluent generated can range from 0 – 350 litres of effluent per tonne of grass.

Where a suitable wilt is not possible due to wet weather it is advisable to provide additional drainage pipes to help get the liquid away. For example, additional pipes could be laid at the butt of clamp walls or for long clamps additional pipes could be laid across the pit. These will help relieve the pressure build up from the effluent and reduce the possibility of the pit slipping. To prevent effluent from flowing out over silage walls in the first few days it is important not to pile the grass too high over the walls and to slope the grass back at 45˚ from the top of the walls

Land spreading of silage effluent. When land spreading silage effluent dilute the effluent with one part water/slurry to one part effluent. Do not spread if rain is forecast in the next 24 hours. Do not spread within 5m of any watercourse, 10m where field slope exceeds 10%, 20m from lake/main river or 25 – 200m well/public water supply.  

Round Bale Storage

Where round bales are made in wet conditions then these bales can generate silage effluent. The effluent from round bales is treated the same as from silage pits and must be collected and stored in same way. It is recommended not to store bales greater than 3 bales high as this will lead to more effluent being generated due to weight pressure and also for farm safety reasons.

David Webster, Teagasc ASSAP Advisor has more information in the below video

Get more information on Water Quality Week here