What is your baled silage telling you after months of storage
Frank Mickan, Pasture and Fodder Conservation Specialist, DEPI Ellinbank
Baled silage is expensive enough without pulling the wrapping off to find mouldy and/or unpleasant smelling silage inside when feeding it out 6 – 12 months later. However, just like a carcass competition, farmers and contractors can learn a lot when the plastic 'skin' comes off.
Whenever the ensiling process has been compromised (e.g. punctured plastic seal, baled too wet or too dry), Dry Matter (DM) and nutrient losses will occur, as well as animal health issues occasionally. These losses may appear to be small but are usually far greater than first thought. The extra effort to prevent, avoid or repair problems is well worthwhile financially.
Understanding a simple 'act of nature' equation can be very useful in determining problems in baled (and forage harvested) silage.
Silage + Oxygen = Carbon Dioxide + Water + Heat produced
Freshly mown grass, sealed silage with damaged plastic film and silage at opening/feeding out also have the same result when exposed to air (oxygen); carbon dioxide, water and heat are produced.
When determining a problem, if mould is present, air is usually, or has been, present also. If the bales themselves or the plastic film is obviously wetter than expected, or wetter than when wrapped, then the silage is probably breaking down inside and producing this excess water which you can see. Carbon dioxide will have been produced but not seen. Heat is sometimes, but often not felt because generally it has escaped before being detected.
Failed baled silage can be due to:
- incorrect dry matter content at baling;
- wrapping/sealing problems;
- damage to the plastic seal;
- quality of the plastic film (continued in February issue); and/or
- pests (continued in February issue).
1. Incorrect DM content at baling
If DM content is too high, mould growth can occur in the bale.
With round bales, material that is baled too dry (over 50 – 55 per cent DM) cannot be compacted enough to expel excess air. This entrapped air will allow plant respiration and aerobic (requiring oxygen) microbial activity to continue, leading to DM and quality losses. A certain amount of mould (and yeast) growth may also occur depending on the quantity of trapped air. The problem is dramatically compounded in over-dry bales if the plastic wrap is holed, because the air can enter more quickly and further into the bale (see Figure 1).
If DM is too low, bales will be sunken and misshaped, and will usually have undergone very poor fermentation (see Figure 2).
Bales under about 38 per cent DM may undergo clostridial or enterobacterial fermentation. This is due to the high moisture content and slower rate of fermentation because the material is not chopped as in a forage-harvested crop. The wetter the silage becomes towards the base of the bale, the wetter it was at baling, or the more it has broken down due to incoming air.
Solution: Round bales should be 40 – 50 per cent DM. Large square bales should be 40 – 60 per cent DM. Use a chopper baler for over dry bales with all knives in place. Use a fermentation enhancing silage additive for over wet bales.
Figure 1: Mould due to the presence of air
Figure 2: Baled too wet without silage additive
2. Wrapping/Sealing problems
Unevenly shaped bales
Despite bales being correctly wrapped with four layers at 50 per cent overlap and 55 percent stretch air will still very slowly enter the bale over time. These losses are minimal over twelve months, sometimes longer. However odd-shaped bales will not have the minimum of four layers of plastic over the entire surface of the bale. Underlapping of the film will occur (Figure 3), which will allow air to enter the bale at a much higher rate where the film is three layers instead of four.
To expose or verify underlapping for the lighter coloured films, cut out a square section (roughly 30 cm square) of the suspect area, and hold it up to the light. Carefully pry apart the film and count the number of layers in the lighter zone.
Solution: Ensure bales are square or slightly convex in shape. Apply extra wrap over underlapped sections.
Figure 3. Bale wrap underlapped
Figure 4. Poor application if black tape on light green film.
The film passes through a pre-stretcher to ensure the film forms an airtight seal on the bale. Poorly serviced pre-stretchers may over- or under-stretch the film. If the film is not stretched enough, is over-stretched, or the film runs through the pre-stretcher the wrong way, then the seal will be inadequate.
With the advent of pre-stretched films onto the market, separate gear sets were required for these new films. In the event of a machine being on-sold, or the correct gears being lost or forgotten to be exchanged etc, sealing problems are the result. Dust and rain will settle between the film layers and will prevent a good seal forming. Unused plastic rolls stored in the sun's heat during the day's harvesting will not 'neck down' or stretch as far as they were designed to.
Solution: Service the pre-stretcher regularly. Use the correct gearing for the specific plastic wrap used. Store unused rolls away from direct heat and avoid dust and moisture getting between the film layers at wrapping.
3. Plastic wrap is damaged
Holes in plastic film
The drier the forage is, the larger the hole and the higher the ambient temperature will be. The longer a hole is left unpatched, the greater the losses in quality will be. Make no mistake, even a very small hole will quickly lead to large DM and quality losses if left unsealed for too long.
Sometimes pin-sized holes will occur in plastic rolls which have been removed from their protective box/wrap and are moving freely in the back of a ute, more so if there is sand or gravel on the ute floor. Where lucerne or cereal stalks protrude from the bale holes and which seemingly act as a plug against air entry, will soon rot off and allow air in.
Often patching is unsuccessful, even when carried out immediately. Ordinary duct tape will not last very long and some tapes will break down quickly in sunlight. Repair tape that is applied to dirty, wet or hot plastic will also fail. Applying a dark coloured tape to a light coloured plastic will often fail due to differences in plastic shrinkage and expansion in hot/cold conditions (see Figure 4). Tape not applied correctly can allow air entry (Figure 4).
Solution: Regularly inspect bales and patch holes as quickly as possible using repair tape specifically designed for plastic wrap. Before applying the patch, clean and dry the holed area, cut the tape to length before applying and apply a similar coloured tape to that of the bale wrap. Avoid doing this in hot weather.
Transportation of bales
Spiking wrapped bales for transportation leaves large holes in the plastic film, as well as in the centre of the bale itself. If the bale is moved roughly, the whole bale will lose its shape, leaving a larger hole around the spiked area and also breaking the tack (stickiness) on the plastic film, which aids in the sealing process. Research has shown that silage grabs or grips are much gentler on the wrap, as long as they are used carefully.
Many bale wraps are also bruised or grazed when transporting, loading, unloading and when standing bales on their ends by all types of silage transportation equipment. Even though the film is not broken, there may now only be 3.0 to 3.5 layers covering that area, sometimes less.
Solution: Ideally wrap bales at the storage site. If wrapping in the paddock, gently move the bales with equipment that does not puncture the film.
TO BE CONTINUED
Issues of quality of the plastic film and pests will be covered in the February edition.