Silage being stacked
Introduction
Chopped or forage-harvested silage is handled and stored in bulk. It can be harvested using forage wagons, flail, single and double chop, and precision (metered) chop forage harvesters. The silage is chopped to various lengths, depending on the machine setting.
Silage buns or stacks
Silage buns, also called stacks, are usually a short-term method of storing chopped silage. They are often sited in or near the paddock being harvested, but can be near an intended feedout point.
Buns should be sited:
- On a reasonably level area of ground, ideally with a slight slope to allow rain water to drain away freely, particularly during feedout;
- Away from depressions where water may pond or areas where water may run during heavy rain; and
- Away from trees (tearing of the plastic sheeting by falling limbs and bird damage is more significant if buns are sited near trees).
Silage buns are very simple to construct. The harvested forage is dumped on top of the ground, then compacted by rollingwith a tractor.
During rolling, the shape of the bun is formed by pushing the uncompacted forage with a blade or bucket. The forage should be covered with a plastic sheet as soon as harvesting and rolling are completed.
An airtight seal is achieved by burying the edges of the plastic sheet. If compacted and sealed effectively, the silage is preserved with little visible waste. Buns are produced either by filling from one end or by topping up over the length of the stack.
The latter method is primarily used for buns formed using forage wagons, where the harvested material is offloaded as the wagon is driven across the bun. As there are no walls, the height to which the bun can be safely constructed is limited.
The amount of surface area to volume (the surface area to volume ratio) is high and, as a result, the risk of in-silo spoilage is also high. Circular buns are popular in some areas. They are round stacks of forage, which may be as high as 2-3 m at the centre.
Being round, their surface area to volume ratio – and therefore plastic costs – are higher than that of long, narrow buns. Because there are no walls to provide physical support, silage buns can be unstable, and tractors may tip or bog during rolling.
Care must be taken when rolling or delivering and dumping on the stack. Drivers should be experienced or closely supervised by someone who is.
Vacuum silage
Vacuum silage is no longer common, although it has been used in Queensland and found to be economically and practically feasible for short-term storage. Forage is sealed in an airtight plastic cover, which is then evacuated (air removed) with a pump.
However, a well-preserved silage can be produced without the added expense of evacuating if the stack is well compacted and sealed quickly. Vacuum silage requires some compaction by rolling to provide a firm base for machinery to pass over the stack.
Additional compaction also occurs when spreading the chopped forage around the stack. However, most of the compaction is achieved in the evacuation process. The system only works well with young, leafy material that is easily compacted.
Forage with woody stems may puncture the plastic cover during evacuation of the air. This risk increases as chop length increases.
Vacuum packed silage
Portable clamps or walls
Portable clamps or walls can be removed (or left in place) after the stack is completed. They suit stacks where the tractor and cart can travel over the stack’s length when delivering the harvested forage.
They can be very dangerous if the walls are not strong and stable enough for the size and weight of machinery used to fill and compact the stack. They are usually built from metal pipe or tube and sheets of tin or strong plywood.
The walls – usually 1.5-2.0 m high – must have sturdy guide rails to prevent the wheels of the rolling tractor slipping over the edge. Anyone intending to build or use portable walls should seek expert advice to ensure adequate strength, stability and safety.
Although some producers have used large round or square bales of hay as ‘side walls’, they are not recommended as it is difficult to create an airtight seal
- The edges are usually poorly compacted;
- A lot of air can be trapped between the forage and the bales; and
- Bales can easily puncture or tear the plastic during rolling and sealing.
The use of portable clamps or walls is not recommended because of the risks involved in filling and compacting the stack.
