When choosing to store silage in bags, be sure to keep in mind the following advantages and disadvantages:
Pros
- Cost competitive when compared to silage stored in bunkers
- A good option when expanding an operation
- Offers a lower initial investment cost
- Low annual storage costs
- Lower loss of dry matter (DM) during storage
- Flexibility to store different qualities, forage types and different cuttings and feed according to quality for different production classes of livestock
- Avoids the need for packing tractors
- Avoids overhangs experienced in high bunkers
- Offers a rapid rate of feedout
Cons
- Correct bag size must be used
- Can result in significant losses of DM if bags are not routinely monitored for holes and tears
- Occasionally bags split open, usually due to inadequate venting of fermentation gases
- Plastic from silage bags needs to be disposed of properly
- Ensiling forage with large variations in DM from load to load can result in variability in silage DM at feedout
Filling and Packing
The process of packing forage in a bag, particularly corn silage, can result in significant additional mechanical treatment to the forage. This additional mechanical action of the packing mechanism has been shown to benefit silage by reducing particle size, lowering the number of whole cobs and lessening the number of whole kernels in the final silage. Take this into consideration when settling the theoretical length of cut (TLC) at the chopper.
| SILAGE | Mean particle size before bagging (mm) | Mean particle size after bagging (mm) | Coarse fiber action before bagging % | Coarse fiber action after bagging % |
|---|---|---|---|---|
| Unprocessed 9.5 mm TLC | 11.3 | 7.3 | 17.4 | 4.6 |
| Processed 9.5 mm TLC | 8.9 | 5.6 | 5.1 | 1.2 |
| Processed 14 mm TLC | 10.5 | 7.4 | 24.7 | 6.5 |
| Processed 19 mm TLC | 14.1 | 7.6 | 44.5 | 13.5 |
Site preparation is critical for bagged silage. Be sure to select a clean, hard surface for the bag and locate bags away from heavily trafficked areas, trees and livestock. Ensure the site is free of sharp rocks and sticks to reduce potential damage to the bag. Concrete, asphalt or packed gravel makes for a base with good drainage properties and minimizes hygienic issues during feedout. The bag should be positioned so the face is not in the direction of the prevailing wind.
Leave about 4 feet, or 1 meter, of space between bags. Do not overfill bags.
| Bag Diameter | Bag Diameter Ground-to-Ground Measurement |
|---|---|
| 8 ft. or 2.44 m | 19.5 ft or 5.94 m |
| 9 ft. or 2.74 m | 20.5 ft. or 6.25 m |
| 10 ft. or 3.05 m | 21.5 ft. or 6.55 m |
| 12 ft. or 3.66 m | 27 ft. or 8.23 m |
The target density for bagged silos is:
- At least 13 lbs. DM/ft3 or 200 kg DM/m3
- 36 lb FM/ft3 or 600 kg FM/m3
In general, a pressure of 400 to 450 psi should be used and then adjusted as appropriate, based on the stretch indicators when initially setting the cable drum brake. Stretch indicators must not be exceeded. If insufficient pressure is applied, then an uneven fill of the bag occurs. This can be compounded with forage harvested at a high DM level or at too-long of a chop length.
Efficient filling of the silage bag is achieved by ensuring appropriate drum-break pressure and tension against the cables. Physical conditions of bagging directly impact the brake pressures required to effectively fill the bag:
| Reduced Brake Pressure | Increased Brake Pressure |
|---|---|
| Bagging uphill | Bagging downhill |
| Bagging with a heavier tractor | Bagging with a lighter tractor |
| Bagging in muddy/sandy surface | Bagging on a hard surface (concrete, etc.) |
| Bagging very wet forage | |
| Bagging dry grains |
Once bagging has commenced if the bag does not have a smooth appearance then the bagging pressure may need to be improved. If the bag overstretches, the pressure needs to be reduced.
The easiest and most effective point of inoculant application is always on the forage harvester. If this is not possible, then inoculant can be applied at the bagger. It is advisable to raise the liquid application rate of the inoculant — dilute and apply a greater liquid volume of inoculant so that the desired microbial application rate is achieved — if it is being applied at the bagger due to the reduced amount of turbulence of the forage.
Covering and Sealing
Use a quality bag for ensiling. For example, the brand Ag-Bag™ is one commonly used type of bag.
All fermentations produce gas (carbon dioxide) with the efficiency of the fermentation directly impacting the amount of gas that is produced. If the forage has been ensiled with residual nitrate in the plant then toxic gas can be produced as the pH of the forage falls.
Be sure to use bag vents to release the gases produced during fermentation to avoid the bag becoming pressurized and ripping or blowing open. Vents can be placed in the bags once completed to allow the produced gas to be released from the bag and the bag to be resealed airtight.
To insert the vent valve:
- Remove the cover from the vent cutter tool. Turn the cutting portion around so the cutter is away from the cover, line up the notches and insert the cutter into the cover.
- Take the threaded side of the valve, line up the notches and slide it over the cutter end of the tool. Slide the threaded portion all the way onto the cutter.
- Locate where you want to insert the valve, press the cutter into the cover to create a hole, push the tool with the threaded portion of the vent through the hole and pull the cutting tool out, leaving the threaded end of the vent sticking through the bag.
- Assemble the valve lid onto the threaded portion and turn the lid to the left to tightly secure.
- Slide the lid of the vent open sufficiently to allow the gas to escape. Close the lid within 2 days and leave the vent within the bag until that end of the bag is fed out. If excessive gassing occurs leave the vent open an additional day. If the bag ‘puffs up’ again after closing the vent open the vent again and close after the gas recedes.
Storing forage in bags can result in significant losses in DM if bags are not routinely monitored for holes and tears. It may be necessary to limit the access of birds and wildlife to the storage area with fences, bird netting and other pest control measures.
Feedout
Ensiling forage with large variations in DM from load to load can result in variability in silage DM at feedout. Collect samples of forage periodically to determine the variability in DM content.
Feed silage at a rate that prevents heating. Loose plastic should be cut off tight to the face. The bag should not be resealed as this encourages a greenhouse environment and fosters daily losses. Recommended feedout rates are 6 to 12 inches (15.24 cm.) of silage per day. Reach the higher end of the range during warmer temperatures or with lower density ranges.
When removing silage for feeding, the silage face should remain tight and smooth. Avoid methods that result in dislodging the face. Creating gouges, cracks and potholes result in air penetration deep into the silage mass and lead to added spoilage.
Storage Life
The typical life of silage stored in bags is around 12 months due to plastic integrity issues. If bags are to be stored for longer, the farm should consider the use of shade cloths to protect plastic from ultraviolet (UV) light degradation.
Additional Reading
- Download the “Silage Bag Capacity Calculator” from the University of Wisconsin Extension to help estimate the quantity of forage in a bag silo.
