Wet Silage - How to Manage Your Pit
Tom Ryan, Teagasc, Kildalton
Pits will be fuller than ever this year. Dry matters are low. This type of grass has the potential to release up to 350 litres of effluent. Although, as grass gets more stemmy the volume released per tonne will reduce, especially as weather conditions improve, but the increased yield will still mean that large volumes of effluent will have to be collected, contained and disposed of safely.
In many situations, with the bulk of material being ensiled this year pits will take up more space in the farmyard. There will also be a tendency to pile the grass higher. This will cause greater problems for effluent collection than usual.
With silage bases every effort should be made to confine the width of the clamp to the space between the channels. If material is placed out over the channels or slips out past the channels effluent will escape unless some sort of temporary kerb (e.g. mud, ground limestone, etc.) is used to trap it and divert it to storage. In order to pack more material into the pits many farmers will be forced to extend them out past the front channel. A temporary kerb should be used to contain the spread of effluent over the concrete at the front of the pit and divert it to the storage tank. If rain falling on the yard in front of the pit is allowed to mix with the effluent it will boost the volume of effluent that has to be handled. It will also do more damage to the yard surface and create smells. The rainwater from the silage pit cover should be, if at all possible, diverted away from the effluent storage tank. Otherwise, a sudden downpour may overflow the tank. This can be achieved keeping the kerb close to the pit and by bringing the silage cover out over the temporary kerb.
Where pits have channels these channels should be used in the normal way by placing a plastic drainage pipe in the channel to form an open space for effluent to get away quickly. These should take the most of the effluent and reduce the volume of flow at other temporary kerbs, etc., used to control the effluent.
In walled pits, as well as providing front and rear channels, it is necessary to use drainage pipes at the walls to allow effluent to drain away quickly and relieve effluent pressure on the floor and walls. If no drainage is used there is a chance that the silage will split and shift forward under the pressure of trapped effluent.
Drainage pipes can either be placed at the butt of the wall or in channels near the wall, if they are provided. This year, to improve effluent flow it would be worthwhile to place pipes both in the channels near the wall and at the butt of the wall. We did this here in Kildalton this year and there is effluent flowing in both, with a stronger flow from the one at the butt of the wall. Throwing a shake of straw over the drainage pipes should help to improve drainage still further. 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 450 from the top of the walls. Another reason for not piling the grass too high is that a slope greater than this surcharges the walls with extra weight, over the pressure they were designed to resist, with the obvious safety risk.
In long pits there is the option of placing a pipe across the pit in one or two locations to aid drainage. Tap it into the pipes or channels at the side of the pit and cover it with straw and layer of grass. It shouldn't disrupt the filling of the pit too much.