Silage effluent, storing silage & water quality
Silage effluent is highly pollutant to waterbodies and must be stored and collected according to best practice. An accidental discharge can have serious effects on a rivers ecology including fish kills for long distances downstream. Kieran Kenny, Teagasc ASSAP advisor, Roscommon has practical advice
Silage effluent risks
The effluent provides microorganisms in the waterbody with a food source of sugars and other plant material to decompose. During this process dissolved oxygen levels in the water become depleted, eventually causing fish to die. There is a higher risk during a summer drought, with warm and dry periods, leading to lower flows and reduced oxygen carrying capacity in our rivers.
Farmers need to be vigilant in their preparations for silage making and to continually monitor for an extended period post harvesting as pollution incidents can occur for several weeks.
Silage pits
The concrete slab and walls need to be structurally sound and leak proof to allow ensiling and ensure no effluent is lost. The effluent collection channels should be cleaned out and sufficient storage available in the tank to manage the volume of effluent generated. Most importantly, do not forget the diversion system. It should be checked, engaged and ready to direct effluent to the tank.
When cutting the crop aim to have the grass dry and wilt for 24 hours. This will reduce the volume of silage effluent produced. Volumes of effluent can range from 0 - 350 litres per tonne of grass. For example grass >25% DM will produce little or no effluent. In difficult conditions where the grass is wet, with a risk of the pit moving or slipping, use drainage pipes to improve effluent flow. Ensure the pit is not over filled with grass as this will increase the risk of effluent loss.
It is important to extend the silage cover beyond the channels to ensure that no rainwater is collected with the effluent. This practice will also enable the farmer to extend the period for diverting seepage to the tank. Regularly inspect the effluent channels to free any obstructions and check the storage tank to avoid overflow.
When land spreading silage effluent dilute in equal proportions with water or slurry. Do not apply within 2 days of heavy rainfall and adhere to similar buffer zones for organic manures (minimum of 5m for waterbodies).
Baled silage
In general there is less pollution risks involved with silage bales. Typically the grass is wilted for approximately 48 hours (30% DM) and does not normally produce effluent. Wilted bales with no risk of effluent discharge can be stored on gravel or concrete without the requirement for a collection facility. However, where effluent does arise a collection facility must be in place.
Stacking the bales will inrease the risk of effluent seepage. Ensure they are sufficiently wilted before deciding to store them 2 or 3 high. According to best practice and DAFM regulation silage bales stored outside the farmyard must not be located within 20m of a waterbody. This buffer is required to reduce the risk of runoff.
In the unlikely event of an effluent discharge on your farm, seek immediate advice from your agricultural advisor and notify both the Local Authority and Inland Fisheries Ireland.
ASSAP – Agricultural Sustainability Support and Advisory Programme
Kieran Kenny is a Teagasc ASSAP Advisor based in Co. Roscommon. ASSAP – Agricultural Sustainability Support and Advisory Programme working with farmers to help improve water quality. As a country we are required to have all our waters achieving “good status” by 2027 which is a goal we must all work towards. The Agricultural Sustainability Support and Advisory Programme (ASSAP) is an advisory service available to all farmers situated in Priority Areas for Action to support with farming and water quality issues. Read more about the ASSAP programme here
You might also be interested in reading Best Practice use of pesticides also by Kieran Kenny