Silage balers

Variable chamber round baler

What are the different types of silage balers?

Variable versus fixed chamber round balers.

Variable-chamber balers compress the bale from the initial filling of the chamber and make a bale with a ‘hard’ centre.

Fixed chamber balers do not begin compressing the bale until the whole chamber is full; as a result the bales are not packed as densely in the middle as at the outsides – they have ‘soft’ centres.

The soft-centred bales produced by the early model fixed-chamber balers were not ideal for silage production. Air trapped in the centre of the bales increased the risk of poor fermentation and mould growth.

The problems increased with drier or more heavily wilted forages. New models produce higher-density bales, with firmer centres and less risk of fermentation problems. No research data are available on the quality of silage produced from these bales at higher DM contents (>50%).

Square balers

The bales made by square balers are called ‘large squares’ to differentiate them from the traditional small square hay bales. Bale sizes (width x height) vary, depending on which of the many commercially available square balers are used.

Most produce bales with a maximum length of about 2.4 m, but this is often adjusted to 1.5 m when making silage for wrapping and ease of handling.

Most large square bales produced by current-model balers have the advantage of being denser than round bales, but do require more power to produce. The shape of the square bales is more suited to a range of storage systems, with better utilisation of space and ease of sealing effectively.

Square baler

Chopping balers

Round and square balers are available with a series of knives that chop the forage just after pick-up and before entering the baling chamber.

Most have a nominal chop length (Theoretical Length of Chop) of about 75 mm; the actual chop length will depend on whether the forage has passed lengthways (unchopped) through the chopping mechanism or across the knives (chopped).

The length of the chopped material will usually vary between about 40 and 110 mm. The baler can be operated with or without engaging the knives. The Orkel® is another version of the chopping baler, incorporating flails to chop the forage.

An advantage of this type of baler is claimed to be in the flail action, which chops the forage more than knives (used by most other balers); the forage stems are split, releasing more Water Soluble Carbohydrates (WSCs) for fermentation.

Potential benefits in chopping the forage at the time of baling include:

  • Less air is trapped in the bale – reduced respiration and risk of mould growth
  • Greater release of water soluble carbohydrates (WSC) resulting in a more rapid fermentation and reduced fermentation losses.
  • Increased bale density (and weight) – reduced storage (plastic, wrapping) and transport costs for each tonne of silage;
  • Increased intake by animals, less selection and reduced wastage
  • Possibly more thorough mixing of silage additives sprayed onto the material before chopping (although there is no hard evidence to support this); and
  • Chopped, baled forage is easier to process in mixer wagons.

In a Danish study, whole crop barley was ensiled with a variable-chamber baler either with or without chopping knives. Chopping the bales increased silage density, reduced losses, and there was a slight improvement in fermentation quality (lower pH).

Combined baler and wrapper

Combined round baler and wrapping machines

In an attempt to reduce labour costs, several manufacturers have developed machines that bale the forage and then wrap the bale. The wrapper can be built within or behind the baling chamber, or trailed behind as a separate unit.

A disadvantage of these machines is that the bale has to be moved after wrapping, increasing the risk of damage to the plastic wrap.

Net wrap versus twine

Round silage bales can be tied using twine or net wrap. Net wrap, although more expensive than twine, is a more convenient and faster method of tying round bales.

Net wrap is recommended for use in very stemmy crops such as lucerne, cereal crops and summer forages, or over-mature pastures, to help avoid stems poking holes in the plastic seal.

Sisal twine that has been treated with oil should not be used as it can chemically react with the plastic, with holes forming along the string line.

Heavy-duty twine must be used on squarebaled silage.